Responsive Polymer Surfaces E-Book
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- Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
- Kategorie: Fachliteratur
- Sprache: Englisch
Adopting an integrated approach, this book covers experiments, theory, and emerging applications.
In the first part surfaces are described that change from flat to either a random corrugated or to a well-structured structure, while the second part deals with those surface structures integrated in the coating surface where the structures change their shape or dimension when addressed by an external trigger. A variety of materials are addressed, including liquid crystal polymers, hydrogels, hard acrylates, and soft silicones. The whole is rounded off by a discussion of various applications, including surface controlled flows in microfluidic systems.
Of interest to chemists and engineers, researchers in industry and academia, as well as those working in the paint industry and hydrodynamics.
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Veröffentlichungsjahr: 2017
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Table of Contents
Cover
Title Page
Copyright
List of Contributors
Preface
Chapter 1: Light-responsive Surface: Photodeformable Cross-linked Liquid-Crystalline Polymers Based on Photochemical Phase Transition
1.1 Introduction
1.2 Photochemical Phase Transition
1.3 Photodeformation
1.4 Effect Factors of Photodeformation
1.5 Deformation Induced by Visible and NIR Light
1.6 Soft Actuators Based on CLCPs
1.7 Summary
References
Chapter 2: Inkjet Printed Liquid Crystal Cilia
2.1 Introduction
2.2 Thermal Actuation Based on Anisotropic Thermal Expansion
2.3 Light Stimulated Deformation
2.4 Inkjet Printing Actuators: Toward Polymer Cilia
2.5 Conclusion
Acknowledgment
References
Chapter 3: Liquid Crystal Coatings Switched between Flat and Corrugated Surface Texture
3.1 Introduction
3.2 Liquid Crystal Networks
3.3 Thermal-Responsiveness
3.4 Photo-Responsive Liquid Crystal Networks
3.5 Photo-Induced Surface Deformation
3.6 Photo-Induced Surface Deformation Preset by Patterned Director Orientation
3.7 Mechanism of Surface Deformation
3.8 Conclusions
References
Chapter 4: Computational Modeling of Light-triggered Topography Changes of Azobenzene-modified Liquid Crystal Polymer Coatings
4.1 Introduction
4.2 Photo-mechanical Model
4.3 Results and Discussion
4.4 Conclusions and Outlook
Acknowledgment
References
Chapter 5: Dynamic Tribology in Liquid Crystal Coatings
5.1 Introduction
5.2 Dynamic Friction Analysis
5.3 Static Friction Coefficients
5.4 Conclusions
References
Chapter 6: Actuating Hydrogel Thin Films
6.1 Introduction
6.2 Hydrogel Bilayer
6.3 Patterned Hydrogel Film
6.4 Bending of Complex Structures
6.5 Intrinsic Anisotropy
6.6 Applications of Hydrogel Actuators
6.7 Conclusions and Outlook
References
Chapter 7: Photoresponsive Polymer Hydrogel Coatings that Change Topography
7.1 Introduction
7.2 Photoresponsive Polymer Hydrogel Coatings
7.3 Photoresponsive Mixing and Flow Control in Microfluidic Devices
7.4 Photoresponsive Wettability
7.5 Photoresponsive Cell Adhesion
7.6 Conclusions and Perspectives
References
Chapter 8: Electrically Responsive Fluoropolymer Surfaces and Devices
8.1 Electrically Responsive Surfaces
8.2 Electrowetting Materials
8.3 Historical Development and Devices
8.4 Electrofluidic Arrays
8.5 Industrialization
8.6 Challenges and Conclusions
References
Chapter 9: Functional Polymer Surfaces via Post-polymerization Modification
9.1 Introduction
9.2 Polymer Brushes
9.3 Reactive Polymer Layers
9.4 Concluding Remarks
References
Chapter 10: Haptic Perception of Material Properties
10.1 Introduction
10.2 Experimental Methods
10.3 Roughness
10.4 Compliance
10.5 Temperature
References
Index
End User License Agreement
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Guide
Cover
Table of Contents
Preface
Begin Reading
List of Illustrations
Chapter 1: Light-responsive Surface: Photodeformable Cross-linked Liquid-Crystalline Polymers Based on Photochemical Phase Transition
Figure 1.1 Phase diagrams of the photochemical phase transition of azobenzene/LC systems (N, nematic; I, isotropic).
Figure 1.2 Schematic illustration of reversible LC-isotropic photochemical phase transition.
Figure 1.3 Photo-induced contraction of CLCP prepared from
1a–f
. □ = 313 K, Δ = 308 K, ○ = 303 K, * = 298 K. (Inset) Recovery of the contracted CLCP at 298 K after irradiation was switched off.
Figure 1.4 Photographs of photodeformation of azobenzene side-on CLCP (a) before irradiation and (b) under irradiation with UV light.
Figure 1.5 Plausible mechanism of the photoinduced bending of CLCP film.
Figure 1.6 (a) Precise control of the bending direction of a film by linearly polarized light: photographs of the polydomain film in different directions in response to irradiation by linearly polarized light at different angles of polarization (white arrows) at λ = 366 nm; the bent films are flattened by irradiation with visible light at λ > 540 nm. (b) Schematic illustration of the plausible bending mechanism.
Figure 1.7 Photoresponsive behavior of the hydrogen-bonded CLCP films of (a)
4a
+
4c
and (b)
4b
+
4c
.
Figure 1.8 Photoresponsive behavior of EB-cross-linked Components
5
/PE bilayer films upon irradiation with UV (220 mW cm
−2
) and visible (50 mW cm
−2
) light at room temperature. (a) Schematic illustration of the experimental setup; (b) photoresponsive behavior of bilayer film prepared by EB irradiation at a dose of 0.5 MGy; (c) photoinduced bending behavior of the film prepared by EB irradiation at a dose of 10 MGy. Film size: 5 mm × 4 mm; thickness of the bilayer film: 25 µm (PE) and 2.5 µm (Components
5
).
Figure 1.9 (a) Schematic illustration of experimental setup. (b) Photographs of the CLCP fiber that exhibits photoinduced bending and unbending behavior upon irradiation with UV light (100 mW cm
−2
) and visible light (120 mW cm
−2
). The inset of each photograph is a schematic illustration of the state of the fiber. The size of the fiber is 30 mm × 20 µm.
Figure 1.10 Photographs of the main-chain CLCP fiber that exhibit photoinduced bending and unbending behaviors upon irradiation with 365 nm UV light (150 mW cm
−2
) and visible light (λ > 430 nm, 120 mW cm
−2
) at 60 °C. The size of the fiber is 11 mm × 21 µm.
Figure 1.11 Chemical structure of two monomers
7a
and
7b
, and cross-linker
7c
. (a) Preparation of an oriented CLCP/CNT nanocomposite film. (b) Photographs of a CLCP/CNT composite film during one bending and unbending cycle after alternate irradiation by UV light at 365 nm (100 mW cm
−2
) and visible light at 530 nm (35 mW cm
−2
), respectively.
Figure 1.12
8a
acts as the host mesogen, while the UV-active component is
8b
. (a) Schematic illustration of twisted and uniaxial arrangements. (b) Photoinduced coiling of a film in the twisted configuration.
Figure 1.13 (a) Molecular organization in the twist cell (top view) and the angular offset ϕ, which characterizes the angle at which the ribbon is cut. The orientation of the molecules at mid-plane is shown with a double-headed arrow. The cutting direction, which is also the long axis of the ribbon, is represented by a dotted line. The elongated rods represent molecules (left) and the twist-nematic molecular orientation through the thickness of the film (side view) (right). (b) Schematic illustration showing the direction in which the ribbons are cut. (c) Spiral ribbons irradiated for 2 min with UV light (λ = 365 nm) display isochoric winding, unwinding, and helix inversion (ϕ was defined as the angle between the orientation of the molecules at mid-plane and the cutting direction; R: right-handed; L: left-handed).
Figure 1.14 (a) Experimental setup and (b) photographs of the homeotropic film that exhibits photoinduced bending and unbending behavior. The white dash lines show the edges of the films, and the inset of each photograph is a schematic illustration of the film state. (c) Schematic illustration of the bending mechanism in the homeotropic film.
Figure 1.15 Photographs of the ferroelectric CLCP film that exhibits bending and unbending behavior upon alternative irradiation with UV and visible light at room temperature: the film bent toward the actinic light source along the alignment direction of mesogens in response to irradiation at λ = 366 nm, and were flattened again by irradiation with visible light at λ > 540 nm. (b) Change of the load on ferroelectric CLCP film when exposed to UV light at 366 nm with different intensities at 50 °C. The cross-section area of the film is 5 mm × 20 µm. An external force of 20 mN was loaded initially on the film to keep the length of the film unchanged.
Figure 1.16 Photographs of CLCP film exhibiting different bending and unbending behavior at 70 °C (a) and 90 °C (b) upon irradiation of UV (366 nm, 18 mW cm
−2
) and visible (>540 nm) light. The size of the film was 4 mm × 4 mm × 20 µm. A schematic illustration of (c) the mesogens alignment and the backbone conformation in the smectic and nematic phase and (d) a plausible mechanism of the different bending modes of the CLCP films at different temperatures.
Figure 1.17 Chemical structures of the monomer
12a
and cross-linker
12b
. (a) Experimental setup. (b) Photoinduced bending and unbending behavior of azotolane CLCP film in sunlight through a lens and glass filters. The sunlight at >430 nm and at >570 nm was acquired by using different filters.
Figure 1.18 Schematic illustration of the mechanism of CW NIR-light-induced deformation of the azotolane CLCP/UCNP composite film, and photographic frames of the composite film bending in response to the NIR light at CW 980 nm and being flattened after removing the light source. (b) UCL emission spectrum (blue line) of a colloidal CHCl
3
solution of UCNPs (1 mg ml
−1
) excited with a 980 nm CW laser (power = 600 mW, power density = 15 W cm
−2
) and the UV–vis absorption spectrum (black line) of azotolane CLCP film. The inset shows a photograph of UCL from the UCNPs in CHCl
3
.
Figure 1.19 Chemical structures of the sensitizer PtTPBP (
13a
) and the annihilator BDPPA (
13b
). (a) UCL emission spectrum (blue line) of toluene solution of PtTPBP&BDPPA (λ
ex
= 635 nm, power density = 200 mW cm
−2
) and the UV–vis absorption spectrum (red line) of the azotolane CLCP film. (b) Schematic illustration of the preparation of the assembly film composed of azotolane CLCP film and PtTPBP&BDPPA-containing polyurethane film. (c) Photographs of the as-prepared assembly film bending toward the light source along the alignment direction of the mesogens in response to the 635 nm laser with the power density of 200 mW cm
−2
(thickness of each layer in the assembly film: 15 µm of upconverting film and 27 µm of CLCP film). (d) Schematic illustration demonstrating plausible mechanism for the photoinduced deformation of the as-prepared assembly film.
Figure 1.20 (a) Schematic illustration of a light-driven plastic motor system used, showing the relationship between light irradiation positions and a rotation direction. (b) Photographs showing time profiles of the rotation of the light-driven plastic motor with the CLCP-laminated film induced by simultaneous irradiation with UV and visible light at room temperature.
Figure 1.21 (a) Artificial, light-driven cilia produce an asymmetric motion controlled by the spectral composition of the light. (b) Schematic representation of the macroscopic setup, showing the orientation of the molecules. (c) Steady-state responses of a 10-µm-thick, 3-mm-wide, and 10-mm-long modular liquid-crystal network actuator to different colors of light (scale bar 5 mm). (d) Side view of the actuation of polymer cilia with ultraviolet light (1 W cm
−2
) in water.
Figure 1.22 Schematic illustration of the microrobot and photographs showing microrobot picking, lifting, moving, and placing the object to a nearby container by turning on and off the light (470 nm, 30 mW cm
−2
). The thickness of both PE and films was 20 µm. They were connected with each other by the adhensive. White arrows denote the parts irradiated with visible light.
Figure 1.23 (a) The section of assembled prototype. (b) Photo of experimental prototype (1, inlet; 2, press plate; 3, photodeformable material; 4, outlet; 5, pump membrane; 6, pump chamber).
Figure 1.24 (a) Schematic illustration of the PDMS-soft-template-based secondary replication process. (b) Optical photo of microarrayed CLCP film with two patterned areas named as D15 and D5. Large-area optical microscopic image and local amplified image (inset). The patterns of D15 and D5 are all square-arrayed square posts with the post width of 10 mm. The spacings between two nearest posts for D15 and D5 are 15 and 5 mm, respectively. (c) Light-controlled quick and reversible switching of superhydrophobic adhesion between rolling and pinning on microarray CLCP with a 2 µl water droplet.
Figure 1.25 (a) Schematic illustration showing the change in the geometry of the pillars of the azobenzene CLCP microarray. (b) Reflection spectra of the azobenzene CLCP microarray under the UV light irradiation (365 nm, 20 mW cm
−2
, 15 min) and the following visible light irradiation (530 nm, 20 mW cm
−2
, 5 min) with the angle of incidence of 60°.
Figure 1.26 SEM surface images of (a) the SiO
2
opal film and (b) the CLCP inverse opal film, and SEM cross-section images of (c) the SiO
2
opal film and (d) the CLCP inverse opal film. The inset is the locally amplified image. Thickness of the inverse opal film is about 17 mm. SEM images of the inverse opal film (e) before and (f) after UV light irradiation. The red regular hexagon and straight lines represent the arrangement of the holes before UV light irradiation; the green hexagon and lines represent the arrangement of the holes after irradiation with UV light. After UV light irradiation, the shape of the hexagon becomes irregular, and the straight lines have become curves. (g) Reflection spectra of the azobenzene CLCP inverse opal film under UV light irradiation (365 nm, 50 mW cm
−2
, 5 min) and subsequent visible light irradiation (530 nm, 20 mW cm
−2
, 15 min). (h) Reflection spectra of the inverse opal film as a function of temperature.
Figure 1.27 (a) SEM image of a microwalker lying upside down. Scale bar: 10 µm. (b) Side view of the microwalker with 500 nm leg tip shown in the inset. Scale bar: 10 µm. (c) Top row shows the initial state of microwalkers on different surfaces. Bottom row shows the microwalker randomly walking on the polyimide coated glass surface, rotating with one leg stuck onto the polyimide coated surface, walking with self-reorientation on the clean glass surface, walking in the direction determined by the grating groove pattern (vertical). Insets of the top row show the schematics of the surface.
Chapter 2: Inkjet Printed Liquid Crystal Cilia
Figure 2.1 Principle of photopolymerization of a liquid crystal monomer in its oriented state (a). By controlling the boundary of the liquid crystal or by chirality different alignment patterns can be established (b). Some examples of liquid crystal diacrylates (c) and monoacrylates (d) and their liquid crystal transition temperatures.
Figure 2.2 Anisotropic linear thermal expansion α
i
of cross-linked liquid crystal networks (LCNs) measured by determining changes in length parallel (‖) and perpendicular (⊥) to the director as a function of temperature. A relatively small decrease in order upon heating causes a negative thermal expansion parallel to the director and an increasing positive thermal expansion perpendicular to it. The various data points correspond to the chemical structures given in Figure 2.1c (top and bottom structure) polymerized at different temperatures. The monomer with the methyl substituent in the central ring and polymerized at the lowest temperature shows the most pronounced effect.
Figure 2.3 Cross-section of an LCN with a splayed director gradient. The cross-sectional texture of a 60-µm-thick LCN film, as shown by scanning electron microscopy image, resembles the director gradient. During heating the homeotropically aligned surface is anticipated to expand whereas the planarly aligned surface will shrink. The result is that the initially close to flat film at RT rolls up when the temperature is increased.
Figure 2.4 Deformation Figure upon thermal actuation of a clamped 60 µm LCN film with twisted and splayed alignment respectively. In both cases the alignment is parallel to the film axis at the top of the film and perpendicular at the bottom.
Figure 2.5 Azobenzene modified liquid crystal monomer and its change in absorption spectrum undergoing the change from the trans to the cis state.
Figure 2.6 Cycled response of aligned azobenzene-based films parallel and perpendicular to the alignment direction to alternating UV (1 W cm
−2
UVA) and visible (broadband incandescent lamp) illumination. The film is based of C6M monomer (Figure 2.1c, bottom structure) modified with 8 wt% A6MA (Figure 2.5). Positive values indicate elongation, and negative values indicate contraction. These plots have been corrected to account for the contribution of temperature variations.
Figure 2.7 An example of an electric-driven micro-actuator. The thin film composite of acrylate and chromium bends under stress and rolls out when a voltage is applied across the electrodes. In the actuated position the actuator is “stealthed” by lying flat at the surface of the substrate. The stills of a movie taking while switching shows a switching from flat to bend to flat within 0.2 s.
Figure 2.8 Monomers used to form the inkjet printed actuators. The two photoactive monomers are A3MA and DR1A. The host polymer matrix is built from C6M, C6BP, and C6BPN. The surfactant PS16 is used to obtain the desired alignment at the air interface prior to polymerization.
Figure 2.9 The splay-bend molecular organization through the thickness of the film. The molecular alignment is visible in a cross-section of a fractured film. The scale bar indicates 5 µm (a). Schematic representation of a splay-bend molecular orientation through the thickness of the film. (b) The arrows indicate the direction of the material response upon actuation.
Figure 2.10 Device design and an overview of the four basic processing steps to produce the modular cilia. (a) Structured deposition of the polyvinyl alcohol release layer (1). (b) Spincoating, curing, and buffing of polyimide alignment layer (2). (c) Patterned inkjet deposition of the monomer mixtures (3) and subsequent curing by light. (d) Dissolving the polyvinyl alcohol release layer leaving non-contact area for the cilia.
Figure 2.11 Microscope images of micro-structured cilia obtained by inkjet printing following the procedure given in Figure 2.10. (a) An optical microscope image before removal of the poly(vinyl alcohol) sacrificial layer and a scanning electron microscope image after removal of the sacrificial layer. (b) The cilia observed through a polarizing microscope with crossed polarizers with their axis at 45° and parallel to the lower polarizer.
Figure 2.12 Deformation of inkjet printed cilia under exposure with light. Exposure of the A3MA polymer cilia while immersed in water at room temperature (a). Strain response of printed cilia (b,c). Calculated strains from A3MA polymer (filled diamonds) and DR1A polymer (squares), in response to ultraviolet light (250–390 nm) (a), randomly polarized, and to visible light (488 nm) (b), with the polarization state parallel to the molecular director. The inset (b) shows how the bending radius was measured by fitting a circle to the bending part of the flap.
Figure 2.13 Bimorphing structures based on composites of differently responding azobenzene dyes. (a) Schematic representation of the macroscopic setup with two attached films based on DR1A (red) and A3MA (yellow), and photographs of their steady-state responses of a 10 µm thick, 3 mm wide, and 10 mm long modular LCN actuator to different colors of light (scale bar 5 mm). (b) An inkjet printed bimorph structure on glass. (c) A schematic representation of light-driven cilia to produce an asymmetric motion controlled by the spectral composition of the light. (d) Frontal view of actuation of multicolor cilia in water addressed with VIS (4 mW cm
−2
) and UV (9 mW cm
−2
) light. All scale bars indicate 0.5 mm.
Chapter 3: Liquid Crystal Coatings Switched between Flat and Corrugated Surface Texture
Figure 3.1 Schematic representation of the formation of a liquid crystal network (a). Besides uniaxial alignment, the LCs can be ordered in twisted, splayed, or chiral-nematic configurations, for example, by using surface techniques or chiral additives (b). Some examples of LC di-acrylates (c) and mono-acrylates (d) often used in polymerizable LC formulations.
Figure 3.2 Examples of thermal-induced deformations. (a,b) Temperature triggered deformation in LC network films with molecule in a splayed configuration. (a) Splay alignment and its deformation upon decreasing in the degree of alignment and (b) bending of the film with splay alignment. (c–e) Polarizing optical microscope images and interference microscope images of polymer cylinders with isotropic order surrounded by areas with cholesteric order. The inset in (c) shows the photomask used for polymerization of the cholesteric area during the first UV exposure. Images (d,e) are white-light interferometer images taken at RT and at 200 °C respectively.
Figure 3.3 Photo-induced shape changes. (a) A bi-functional azobenzene monomer and its absorption spectra in solution after exposure with visible light corresponding to a preferentially trans state of the monomer, and after exposure with UV light corresponding to a preferentially cis state of the monomer. (b) When embedded in a splayed LC network it gives contraction at one side of the film and expansion at the opposite side, regardless of the position of the light source.
Figure 3.4 Actuation principle. An initially highly ordered state in a free standing film leads to expansion perpendicular and contraction parallel to the director (a). When the film is adhered to a solid substrate in-plane dimensional changes are prohibited and one might find an expansion perpendicular to the surface (b).
Figure 3.5 Chiral-nematic polymer network. (a) Schematic view of a cholesteric polymer film and the expansion related to a loss of order upon actuation. (b) Transmission spectrum for circularly polarized light of a chiral-nematic film modified with azobenzene. (c) Materials used for photosensitive chiral-nematic compositions.
Figure 3.6 Mask exposure of a chiral-nematic coating results in local deformation of the film. Interferometer microscopic measurements show 3D images and surface profiles of (a) azobenzene-modified cholesteric film. (b) Cholesteric film containing an inert dye. (c) Isotropic film containing azobenzene.
Figure 3.7 Line patterned coatings with locally different director profiles. (a) Schematic view of a coating with alternating stripes of chiral-nematic order next to isotropic order that deforms from a flat to a deformed state under exposure with UV light. (b) Polarization microscope image taken between crossed polarizers showing black isotropic lines and bright chiral-nematic areas; the inset is the photomask used. (c)A cross-section of the film before (blue) and during (red) exposure measured by interference microscopy. (d) 3D images obtained from the same technology. (e) Coating with alternating stripes of planar chiral-nematic order next to homeotropic order. (f) Coating measured by interference microscope measure prior to UV exposure. Inset is the POM image taken under the crossed polarizers. (g) The same film under exposure with UV light.
Figure 3.8 Responsive coating with a chiral-nematic fingerprint pattern (a) schematic representation of the planar helix axis with local expansion along the normal where the molecules are aligned planar and shrinkage where they are aligned homeotropic. (b) Microscopic picture of the sample as observed between crossed polarizers. (c,d) 3D interference microscope images before and during actuation by UV light. (e,f) Cross-sections of the deformation obtained by the same measurements.
Figure 3.9 Analysis of the fingerprints. (a) Pitch a function of chiral dopant concentration for different surface anchoring conditions. (b) Effect of pitch on the strain of fingerprints for an azobenzene concentration of 2 wt%. (c) Effect of azobenzene concentration on the strain of fingerprints. (d) Deformation of fingerprints increases with increasing UV intensity. (e) Polarization optical microscope image of a regular texture and (f) surface profile of the same at the initial non-actuated state (red) and during actuation (black).
Figure 3.10 Liquid crystal polymer network coating with a polydomain pattern. (a) Schematic representation of the dynamics of the polydomain liquid crystal. From 1 to 3, molecules are aligned in a uniaxial (1), homeotropic (2), and tilted (3) manner. The arrows illustrate the direction of expansion propensities upon actuation and the blue insert illustrates the anticipated formation of surface structures. (b) Polarized optical microscopy images of a polydomain texture as observed between crossed polarizers. Bright regions correspond to planar or tilted regions and the black and whitish areas to regions where the orientation is (close to) homeotropic. In some black regions the orientation is tilted or planar with the
x–y
projection of the director parallel to one of the polarizer axes. (c) 3D interference microscope image measured in dark, and (d) during UV actuation. (e,f)f The corresponding cross-sections obtained from the same measurements.
Figure 3.11 Density change in a chiral-nematic film containing azobenzene and Tinuvin (a) before UV exposure, both the Tinuvin and azobenzene film are at the bottom of flask, (b) snapshot of films during exposure showing the azobenzene film to float and the Tinuvin film to remain at the bottom, and (c–e) after removing of UV light, the azobenzene film sinks to reach its initial position at the bottom. The Tinuvin-modified film remained at the bottom during the whole experiment.
Figure 3.12 Deformation by mask-wise UV exposure of a homeotropically aligned LC network coating. (a) Representation of homeotropically aligned network and the deformation based on a reduction in molecular order, predicting lateral shrinkage. (b) 3D view of protrusions and (c) surface profiles in cross-section made by exposing the azobenzene modified homeotropic film through a line mask with a periodic pitch of 400 µm and an opening of 200 µm showing lateral expansion.
Figure 3.13 Kinetic mismatch between photo-chemistry and mechanical response. (a) Mechanical response measured as a height change of a 4 µm thin film versus time upon actuation by 365 nm light of intensity 78 mW cm
−2
and a subsequent relaxation in dark. (b) Change in absorbance during thermal relaxation in dark from the cis to the trans state of azobenzene integrated in a chiral-nematic polymer network measured at room temperature.
Figure 3.14 Modulation depth (a) and surface profile (b) measured at a mask exposed chiral-nematic polymer film under various illumination conditions. The 365 nm LED light intensity was chosen to be 300 mW cm
−2
. The 455 nm LED light was added in different intensities in ratio varying between 0 (455 nm LED switched off) and 1 (equal intensities of 455 and 365 nm light). The surface profile of the two wavelength exposure corresponds to the maximum in the left figure.
Figure 3.15 Comparison of the actuation of an azobenzene-modified chiral-nematic network with and without fluorescent dye. (a) The fluorescent dye and its excitation/emission spectra. (b) Free-volume formation as a function of the dye concentration when exposed to 100 mW cm
−2
365 nm light. (c) Interference microscopy measurement of the surface deformation of a 10 µm coating when exposed through a line mask with dye and without dye, and (d,e) the corresponding 3D surface profiles.
Chapter 4: Computational Modeling of Light-triggered Topography Changes of Azobenzene-modified Liquid Crystal Polymer Coatings
Figure 4.1 A 3D schematic illustrating the mechanism of photo-induced conformational changes of azobenzene-modified liquid crystal networks. Illumination of UV light can trigger isomerization of the cross-linked azobenzene molecules (blue) from the rod-like trans-state to the bent-like cis-state, disturbing the alignment order of the neighboring LC molecules (green). This disturbance results in a contraction along the average direction of the LC molecules, denoted by the director , together with expansions in the plane perpendicular to the director. The reverse reaction can be activated under visible light exposure or heating.
Figure 4.2 Definition of the director orientation and its local reference frame (, , and ) under the global Cartesian coordinate system (, , and ) by the tilt angle and the azimuthal angle . The arrows indicate the positive directions of the two angles. Due to symmetry, both and range from 0° to 180°.
Figure 4.3 A schematic overview illustrating the three LC coating systems studied in this chapter: (a) polydomain film, (b) linearly patterned film (unit-cell in the gray region), where denotes periodic boundary conditions, and (c) fingerprint film. The polydomain coating consists of piece-wise square-shaped domains having directors that are randomly distributed throughout all domains, but inside each domain the director is uniformly distributed. The patterned coating is made of two distinct director alignments. The fingerprint film features planar chiral nematic director distributions that are uniform through the thickness. The incident UV light is exposed from the top (normal to the surface) and propagates in the negative direction from toward the substrate at .
Figure 4.4 Fraction of the cis-state azobenzene (a) and the reduced light intensity (b) against the propagating depth normalized by the attenuation length of the trans-state azobenzene for a coating of thickness with various tilt angles for diffuse light illumination, for and . It is good to note that and for the planar director () and the cholesteric phase are identical, since for diffuse light the results are independent of the azimuthal angle.
Figure 4.5 Fraction of the cis-state azobenzene (a) and the reduced light intensity (b) against propagating depth normalized by the attenuation length of the trans-state azobenzene for increasing with . A tilted director with is chosen for illustration purposes.
Figure 4.6 Predicted 3D surface topographies with a superimposed contour plot for the displacement along the thickness direction (in micrometers) and the corresponding surface profiles. The surface profiles are relative to the averaged surface height after light illumination. The aspect ratio, , of the domains in (a)–(c) is equal to 1 and equal to 3 for (d) and (e). Input parameters , , m, and m are used in the simulations. (
Figure 4.7 Variations of the average height and the Wenzel roughness as a function of the aspect ratio of polydomain films. The error bars indicates the standard deviations for four tested samples. (
Figure 4.8 A schematic showing the top view of a polydomain coating with (a) square-shaped domains (side length ) and (b) a nonuniform polydomain film with rectangular domains, in which the side lengths, and , are different for each domain.
Figure 4.9 Dependencies of the predicted roughness parameters, the average height normalized by the thickness (, a) and the Wenzel roughness (, b), against the aspect ratio for the polydomain films with nonuniform domain sizes and shapes. The horizontal error bars indicate the range of the aspect ratio, and the vertical error bars are the standard deviations of four tested samples. The default input parameters are used in this simulations (Table 4.1).
Figure 4.10 (a,b) Schematic representing the unit cells of the two patterned films modeled here, namely, the cholesteric/homeotropic coating under flood exposure and the uniform cholesteric coating under localized illumination. The structures are uniform along the -axis, is the thickness, denotes the length along the axis for the phase (,2), and is the length of the unit cell, . The bottom surface is bonded to the substrate, the lateral surfaces are subjected to periodic boundary conditions, and the top surface is traction-free. (c,d) Normalized surface profiles for the two patterned coatings after illumination with increasing . The horizontal axes are normalized by the length of the unit cell and the height is normalized by the thickness. Here we take . We assume four pitches of the chiral nematic helices along the thickness and the director at the bottom has an azimuth angle of .
Figure 4.11 Variations of the roughness parameters, normalized by the thickness and , for the surface transformations of the patterned films shown in Figure 4.10. (a) Results for the cholesteric/homeotropic film under flood exposure and the uniform cholesteric film under localized exposure with increasing . As in Figure 4.10, we take . (b) Results for the cholesteric/homeotropic film with various and different relative length configurations for the two phases, characterized by .
Figure 4.12 Variation of the roughness parameters against for the cholesteric/homeotropic coating with and . (a) Wenzel roughness for the starting angles of 0 and 90. The inset shows the fluctuations for small . (b) Roughness results and for various and starting angles, ranging from 0 to 180.
Figure 4.13 (a) Schematic of the asymmetric transition scheme in a planar/homeotropic patterned coating (cw-p-ccw-h), where is the length of the transition regions, is the thickness of the coating, is the length of the unit cell with and denoting the individual length of each domain. (b) The predicted surface profiles for various ratios of with , , and . (c) The variations of the normalized average height and the Wenzel roughness against with various for the asymmetric transition scheme (cw-p-ccw-h). (d) The variations of for the symmetric clockwise (cw-p-cw-h) and the symmetric counterclockwise (ccw-p-ccw-h) transition.
Figure 4.14 (a) A schematic of the regular fingerprint film where the helix pitch axes are all parallel to the substrate and along the -axis. is the distance needed for a full 360 rotation of the directors. (b) The predicted surface profiles for a full pitch with their in-plane dimensions normalized by the corresponding pitch lengths with increasing using , , and . (c,d) The variations of the normalized average height and the Wenzel roughness against with various . The default input parameters of Table 4.1 are used here.
Figure 4.16 Experimentally 3D confocal microscopic measurement of a random fingerprint sample. 3D image before the illumination (a) and its surface profile (c). 3D image after UV light illumination (b) and its surface profile (d). (
Figure 4.15 (a) Polarization optical microscope image of a regular fingerprint film and the experimentally measured surface profiles after illumination. Volcano-shape protrusions were found. (
Figure 4.17 (a) 3D topography images superimposed by contour plots of the out-of-plane displacement for an irregular fingerprint film with a fixed thickness and increasing lateral dimensions, , with , 8, 16, and 32. (b) Evolutions of the normalized surface profiles along a certain cross-section in the – plane for various . (c) Variations of the normalized average heights as well as the Wenzel roughnesses of the random fingerprint films against . The horizontal error bars are the variation range for the pitch length and the vertical error bars indicate the standard deviation of the roughness parameters. The results for the regular fingerprint structures are added for comparison, showing a close resemblance.
Figure 4.18 Comparisons of the roughness parameters (a) , (b) modulation, and (c) Wenzel roughness for the patterned films (the cholesteric/homeotropic and the uniform cholesteric film under localized exposure) and the regular fingerprint films, assuming that a half pitch periodicity is equivalent to one unit cell in Figure 4.10. The patterned film results use the bottom horizontal axis and the fingerprint films use the top axis. The results indicate that, for a fixed in-plane length, or , the alternating cholesteric/homeotropic patterned film produces the highest roughness parameters. However, if the modulation is the main goal, the fingerprint structure is also interesting because of the possibility of downsizing. For all the results here, the default input parameters (Table 4.1) are used.
Figure 4.19 Comparison of the roughness parameters and the Wenzel roughness for two random liquid crystal films, that is, the polydomain and irregular fingerprint films, assuming a half pitch periodicity is equivalent to two domains in the polydomain film. The polydomain film results use the bottom horizontal axis and the random fingerprint films use the top axis. The comparison results show that the polydomain film yields slightly higher and than the random fingerprint film. The default input parameters (Table 4.1) are used here.
Figure 4.20 Comparison of the roughness parameters and for the alternating patterned cholesteric/homeotropic film, the fingerprint and the polydomain film as a function of with a fixed . The dimensions for the films are chosen in a way that their undulation sizes are the same: for the patterned films; (aspect ratio) for the polydomain film; and for the regular fingerprint film. The default input parameters (Table 4.1) are used here.
Figure 4.21 Variations of the average height normalized by the attenuation length of trans and the Wenzel roughness as a function of with various ratios for the linearly alternating cholesteric/homeotropic patterned film. All other default input parameters from Table 4.1 are used here.
Chapter 5: Dynamic Tribology in Liquid Crystal Coatings
Figure 5.1 Home-built friction measurement tool. Typically, the samples are UV exposed by a mercury lamp (EXPR Omnicure S2000).
Figure 5.2 Fingerprints sample and friction coefficient. An interference microscopy measurement of the film surface in dark (a) and under illumination (b). Panel (c) shows the friction force as the function of normal loading when coating is flat (solid circle) and corrugated (hollow circle) under dark and illuminated conditions respectively. (d) Dynamic force traces when coating transfers from flat to 3D the elevated fingerprint texture and vice versa.
Figure 5.3 Snapshots of a gripper that releases an object upon UV illumination.
Figure 5.4 Comparison of the flat liquid crystal coating in terms of contact angle of a water droplet and the kinetic friction coefficient () between (a) non-modified surface and (b) coating surface modified with fluorine group.
Figure 5.5 Polydomain liquid crystal network coatings and friction measurements. Poly-domain coating switched from (a) flat in dark to (b) jagged surfaces during UV illumination. (c) Corresponding friction forces versus loading of a flat coating (solid circle) and activated coating (hollow circle). (d) Dynamic force trace when the coating surface is switched from the flat (“off”) state to the corrugated (“on”) state. The normal loading exerted on the two coatings is 0.5 N.
Figure 5.7 Friction dynamics when linear protrusions are formed and erased. (a) Friction forces measured under illumination as a function of normal loading for the various cases shown in Figure 5.6. (b) Time resolved friction force traces when the UV light source is switched from off to on during the sliding experiment.
Figure 5.6 Direction-dependent kinetic friction of the coatings with switchable linear protrusions. The 3D interference microscopic images showing the coatings in the off (a) and the on (b) state. The actuated sides are facing each other during sliding. The three orientations of the coatings with respect to each other, with the protrusions parallel (c) and (d), and perpendicular (e). The arrows indicate the sliding directions.
Figure 5.8 Angular dependence of the friction force. Schematic view of (a) two coatings placed on top of each other with angle θ, (b) interlocking when θ = 0°, (c) the linear protrusions of the coatings align orthogonally at θ = 90°. (d) Friction coefficient as function of angle between the two coating structures. Results of both inactive and activated coatings are presented.
Figure 5.9 Schematic illustration of the measurement of the static friction coefficient.
Figure 5.10 Sliding top glass plates by changing the static friction coefficient. (a) From an interlocking to a flat state and (b) from a flat to a state with orthogonal alignment. (c) The direction of the changes in static friction coefficients are indicated for the cases (a) and (b).
Chapter 6: Actuating Hydrogel Thin Films
Figure 6.1 Bending of a homogenous hydrogel due to local increase in concentration of ions – ionoprinting. Stresses induced by the lines ionoprinted with a (slightly tilted) copper wire anode are used to fold a 3D gel coil. This 3D shape is conserved when the gel is dehydrated. Scale bar, 5 mm.
Figure 6.2 Different scenarios of folding of poly(
N
-isopropylacrylamide)–poly(methyl methacrylate) bilayers (a) depending on the presence of substrate and (b) shape of the film (c). Scale bar is 200 µm.
Figure 6.3 Temperature-responsive swelling of bistrips based on poly(
N
-isopropylacrylamide)-based hydrogel: (a) scheme; (b) folding of a simple shape; (c) folding of a complex shape with radial gradient of swelling properties. When the temperature of the aqueous medium is increased, the bistrip shrinks, unrolls, and finally recovers a flat shape. Scale bar is 200 µm.
Figure 6.4 Schematic of a sheet composed of stripes of poly(acrylamide-
co
-butyl methacrylate) gel (H1), poly(
N
-vinyl imidazole)/poly(acrylamide-
co
-butyl methacrylate) (H2) and poly(acrylamide-
co
-butyl methacrylate)/poly(methacrylic acid) (H3) at pH = 6.8. The regions of H1, H2, and H3 are shown with dark-blue, light-blue, and purple colors, respectively. (a′) A planar gel sheet patterned as shown in
a
at pH = 6.8. (b) Schematic of the gel sheet patterned as shown in (a) and exposed to acidic solution at pH = 2.3. (b′) An arc-shape gel sheet as in (b) at pH = 2.3. (c) Schematic of the gel patterned as shown in (a) and exposed to basic solution at pH = 9.5. (c′) A helix formed by the gel sheet shown in (c) at pH = 9.5. 1 mm,
t
0
= 0.44 mm. The stripes of H2 and H3 are running at θ = 0 and θ = 45°, respectively, to the long axis of the gel sheet.
Figure 6.5 Schematic illustrations of deformation of inhomogeneous hydrogels (hydrogels where “blue” and “red” parts have different swelling properties): (a) bending, (b) polypeptide -type twisting, (c) DNA-type twisting actuators based on poly(2-hydroxyethyl methacrylate)-based gels.
Figure 6.6 Fabrication of self-folding polymer origami. (a) A thin layer of a photo-cross-linkable glassy polymer (PpMS) on a substrate pre-coated with a sacrificial layer is (b) photolithographically patterned with open stripes of width
W
v
to define the positions and angles of the valley folds. (c) Next, a thicker layer of a photo-cross-linkable temperature-responsive polymer (PNIPAM) is coated on top and uniformly cross-linked over the entire area of the bottom PpMS sheet. (d) Finally, a third layer of PpMS is coated and patterned with open stripes of width
W
m
to define the positions and angles of the mountain folds. (e) A magnified schematic of the resulting trilayer film (dimensions not to scale), with hN and hP as the respective thicknesses of PNIPAM and PpMS layers. (f) An optical image of a trilayer film patterned to fold into Randlett's flapping bird (scale bar: 400 µm), along with a schematic indicating the locations and widths of mountain (solid lines) and valley (dotted lines) folds. (g) A photograph of Randlett's flapping bird folded using paper, (h) alongside a fluorescence image of the self-folded trilayer film.
Figure 6.7 Deformation of natural actuators and synthetic actuators based on poly(
N
-isopropylacrylamide)-based hydrogel with structural inhomogeneity. (a,b) – A conifer pinecone (a) dried out and (b) fully hydrated. (c) Cartoon schematic indicating the predominant orientation of cellulose fibers within a pinecone scale. (d,e) – Synthetic pinecone scales constructed by orienting magnetic platelets in a similar bilayer structure within gelatin shown (d) as-prepared and (e) fully hydrated. (f,g) – A wheat awn system (f) dried out and (g) fully hydrated. (h) – Cartoon schematic indicating the predominant orientation of cellulose fibers within a wheat awn. (i,j) – Synthetic wheat awn systems constructed by orienting magnetized alumina platelets in a similar bilayer structure within gelatin shown (i) as-prepared and (j) fully hydrated. (k,l) – An orchid tree seedpod (k) hydrated and (l) dried out. (m) Cartoon schematic indicating the predominant orientation of CMFs (cellulose microfibrils) within the orchid tree seedpod. (n,o) – Synthetic chiral seedpods constructed by orienting magnetic platelets in a similar bilayer structure within gelatin shown (n) as-prepared and (o) fully hydrated. All scale bars are 1 cm.
Figure 6.8 Cantilever sensor based on polyacrylamide hydrogel, which bends when the environmental conditions are changed.
Figure 6.9 Imaging devices based on hydrogel actuators: (a) smart optical lenses with tunable focal length based on poly(
N
-isopropylacrylamide)-based hydrogel (Dong
et al
. 2006 [54]. Reproduced with permission of Nature Publishing Group.); (b) “artificial skin” with tunable topography – device, which contains 4–225 actuators within an area of 37.7 mm × 37.7 mm.
Figure 6.10 Porous periodic hydrogel with switchable coloration based on poly(
N
-isopropylacrylamide).
Figure 6.11 Smart biomimetic hydrogel valve based on hydrogel bistrip. When exposed to pH = 8 phosphate buffer, the bistrip hydrogel changes its size and shape to form a normally closed check valve; when exposed to pH = 3 buffer, the valve is deactivated due to shrinking. The activated valve allows forward fluid flow when forward pressure reaches a threshold value while resisting backward flow. Scale bars are 500 µm.
Figure 6.12 Walking device based on a polyelectrolyte multilayer film that can drive a walking device carrying a load 120 times heavier than the actuator and can walk steadily on a ratchet substrate under periodic alternation of the relative humidity (RH) between 11% and 40 % (see picture). NOA63: Norland Optical Adhesive 63, PAA: poly(acrylic acid), PAH: poly(allylamine hydrochloride).
Figure 6.13 (a) Locomotion of octopus aquabot under an electric field. Initially, tentacles 1 and 2 are each in the clockwise direction relative to the “Ref Line,” while tentacles 3 and 4 are bent in the counter-clockwise direction. During the receding phase, all four tentacles were slowly bent upward, ready to propel; during the propelling phase, the aquabot rapidly moved upward by the propulsion of all four tentacles (scale bar = 1 mm). (b) Velocity and distance profile for two periods with corresponding control signal (+7 V and −15 V were applied alternatively for different periods of time). (c) Behavior of sperm aquabot with changing voltage (scale bar = 1 mm). (d) Trajectory of sperm aquabot and corresponding control signal. (e) Walking motion of myriapod aquabot with a mean translational speed of 0.125 mm s
−1
(scale bar = 500 µm).
Figure 6.14 Examples of 2D and 3D microfabricaiton using polyethylene glycol and poly(
N
-isopropylacrylamide)-based actuators.
Figure 6.15 Switchable surfaces based on polymeric actuators: (a) self-regulating oscillating surfaces based on stimuli-responsive hydrogel pillars (see explanation in the text); (b) surfaces with switchable adhesion based on arrays of shape memory pillars.
Chapter 7: Photoresponsive Polymer Hydrogel Coatings that Change Topography
Figure 7.1 Images of light-responsive surfaces consisting of patterned CrO
2
in (a) striped and (b) square configurations. The dark lines represent CrO
2
. Before actuation, both surfaces were coated with polyNIPAAM films, of which the thickness upon immersion in water was 4 and 16 µm, respectively. The corresponding 3D surface topographic images during the photoactuation of these films are shown in (c) and (d), respectively.
Figure 7.2 Relationship between the isomerization of spiropyran into protonated merocyanine, the hydration behavior of a poly(Sp-NIPAAM) chain, and the volumetric change in a poly(Sp-NIPAAM) gel in acidic aqueous solution.
Figure 7.3 (a) Chemical structure of the polymer used for the preparation of the photoresponsive hydrogel structures, where bR represents bacteriorhodopsin. Images of hydrogel arrays of (b) PAA conjugated with and (c) PAA without bacteriorhodopsin before (dark) and after (light) illumination, as measured by contact-mode AFM at room temperature in water at pH 9.0.
Figure 7.4 (a) A sensor platform currently in use, all fluidic handling components (pumps, valves) are located off-chip. (b, c) Fluidic chips used in autonomous instruments showing fluidic inputs, optical cuvette and waste output. Having the fluidic handling components on-chip cuts the costs and reduces dead volume.
Figure 7.5 (a) A schematic illustration showing the mechanism of light-controllable micro-conveying system composed of a sheet-like poly(Sp-NIPAAM)-based hydrogel. (i) Light-irradiation forms a pit into which a glass bead is trapped. (ii) The region partly overlapped with the first pit is irradiated to form a next pit. Disappearance of the first pit by reswelling of the gel results in transportation of the bead to the second pit. (b) A composite image from overhead views of conveying a glass bead on the sheet-like hydrogel film.
Figure 7.6 (a) The monomers that are used for a poly(Sp-NIPAAM)-based ratchet: spiropyran-based acrylate (
1
),
N
-isopropylacrylamide (
2
), acrylic acid (
3
), and
N
,
N
′-methylenebis(acrylamide) crosslinker (
4
). 3D height profiles (left) and corresponding cross-sections (right) of the ratchet before (b) and after (c) light exposure (dimensions of the surface are 505 × 946 µm
2
).
Figure 7.7 (a) Isomerization of a protonated merocyanine (McH+) and the spiropyran (Sp) form with (b) the corresponding effect on the size of a hydrogel by irradiation with light, (c) implemented as light-responsive valve in microfluidics. (d) Photographs of a microvalve before (channel at the top, valve is closed) and after exposure (microchannel at the bottom, valve is open).
Figure 7.8 Microscopic images of a photoresponsive culture surface (a) before and (b) after regional UV irradiation and (c) after a second regional UV irradiation. Yellow rectangles indicate UV-irradiated regions.
Figure 7.9 (a) Molecular structure of poly(AAm-
co
-VDT-
co
-SPAA) hydrogels and (b) microscopy images of mouse fibroblast L929 cells on the PAVSP hydrogel surface after regional cell detachment.
Chapter 8: Electrically Responsive Fluoropolymer Surfaces and Devices
Figure 8.1 Electrowetting principle, material configuration, and basic electrical circuit.
Figure 8.2 Comparison of droplet electrowetting data with theory.
Figure 8.3 Effect of surface properties on reversibility of electrowetting.
Figure 8.4 The four electrowetting regimes that accompany electrowetting at increasing electric field strength.
Figure 8.5 The dependence of voltage and electric field on insulator thickness.
Figure 8.6 Structure of commercial amorphous fluoropolymers. For Cytop carbon atoms in white, fluorine in green, and oxygen in red. Repeating monomer unit is CF
2
−CF
2
−CF (−CF
2
−CF
2
−O−)−CF.
Figure 8.7 The effect of oil on the switching lifetime of electrowetting.
Figure 8.8 Activation/reflow cycle for amorphous fluoropolymer.
Figure 8.9 Effect of RIE treatment on the fluoropolymer surface.
Figure 8.11 The effect of thermal reflow on the water contact angles on the fluoropolymer (AF1600) surface.
Figure 8.10 The effect of thermal reflow on the fluoropolymer surface.
Figure 8.12 Effect of thermal reflow temperature for various fluoropolymer materials.
Figure 8.13 Recent publications and patents in the electrowetting field.
Figure 8.14 An electrofluidic display pixel – principle and components (Note: Oil thickness and droplet size not to scale).
Figure 8.16 Electrofluidic display materials and architecture.
Figure 8.15 Images of actual electrofluidic pixels (160 µm size) in both the OFF (a) and ON (b) states.
Figure 8.17 Droplet electrowetting test of screen printed films. (a) Applied voltage dependence of the apparent contact angle for 727 ± 16 nm screen printed film and 720 ± 20 nm spin coated films. The symbols correspond to the experimental data from repetitive electrowetting scans and the solid lines to electrowetting theory. Inset: optical image showing droplet profiles at 0 and 100 V. (b) Droplet capacitance as a function of number of switches on screen printed and spin coated films at OFF state (0 V) and ON state (40 V).
Figure 8.18 (a) Photograph of electrofluidic display device whose fluoropolymer was deposited using the screen printing technique with four independent 3″ devices on the same plate. (b) White area fraction versus applied voltage for spin-coated and screen-printed devices. Inset: optical microscope images of pixels with no voltage applied and optical microscope images of pixels in the on state (40 V). (c) The response time of the pixels during the ON and OFF switches at 40 V, 5 Hz (open 100 ms, close 100 ms). (d) Capacitance as a function of switching time (hours at 5 Hz) for a typical device segment area of ∼2 cm
2
(>6500 independent microfluidic elements). Screen printed and spin coated films at OFF state (0 V) and ON state (40 V).
Figure 8.19 Fully automated screen printing of amorphous fluoropolymers on 500 × 400 mm
2
glass substrates.
Chapter 9: Functional Polymer Surfaces via Post-polymerization Modification
Scheme 9.1 Synthesis and post-polymerization modification of MAC2AE brushes.
Scheme 9.2 Synthesis and post-polymerization modification of PPFMA brushes.
Scheme 9.3 Surface-analogous reaction to create different photo-switchable surface coatings, starting from one reactive precursor coating.
Scheme 9.4 Schematic of the procedures used to create polymer brush-functionalized silicon surfaces.
Scheme 9.5 (a) Synthesis of reactive brushes for thiolisocyanate click. (b) Schematic procedure for patterning NCO-containing polymer brush surfaces with sequential X-isocyanate reactions.
Scheme 9.6 The process of conjugate RGD peptide to the PVDF-
g
-PGMA surface via CuAAC reaction.
Scheme 9.7 Procedure for the functionalization of zwitterionic polymers with biotin via a strain-promoted azide–alkyne cycloaddition.
Scheme 9.8 Fabrication process for Mg/Pt-PNIPAM Janus micromotors.
Scheme 9.9 Schematic illustration for the fabrication of PPy/Al
2
O
3
hybrid nanochannels and photographs corresponding to each stage. Au nanoparticles are sputtered onto one side of porous Al
2
O
3
membrane. Polypyrrole is introduced into Al
2
O
3
nanochannels from the Au side by electrochemical polymerization.
Scheme 9.10 Methodology developed to prepare redox responsive copolymer layers onto gold surfaces.
Chapter 10: Haptic Perception of Material Properties
Figure 10.1 Schematic illustration of a typical search task in vision. In the left display, it can be seen that the vertical bar “pops-out” among the more or less horizontal bars. Response time for the decision whether or not this vertical bar is present is independent of the number of distractors (right graph: parallel search). In the middle display, a “T” has to be detected among “L”s. This is a much harder task, even though in this example there are a lot fewer distractors than in the left display. Response times increase with number of items (right graph: serial search).
Figure 10.2 Ordering experiment. (a) Start of the experiment. All 96 samples are presented in piles in front of the participant. (b) Blindfolded participant in the process of haptically ordering all 96 samples based on perceived roughness.
Figure 10.3 Two series of images of a participant performing a haptic search experiment. (a) Example of a “parallel” search. The light patch (in the lower right corner) is rougher than the other ones. A single hand sweep is sufficient to determine whether a rough patch is present among smoother patches. (b) Example of a “serial” search. The dark patch (in the upper left corner) is less rough than the other ones. The participant moves several times over the display, checking the patches one by one.
Figure 10.4 Bunches of stimuli used in a three-dimensional search task. (a) Rough sphere among smooth spheres. (b) Smooth cube among rough cubes. (c) Bunch of smooth spheres without a target (in half of the trials, a target was not present).
Figure 10.5 Series of images of a participant performing a haptic discrimination experiment. The participant has the task to compare the roughness of this stimulus with that of the next stimulus that has the same shape but either or not a different roughness. It can be seen that the participant holds the stimulus with his right hand and makes lateral movements with his left hand. Electromagnetic sensors are connected to his thumbs, his index fingers, and to the stimulus.
Figure 10.6 Examples of stimuli with different compliance, length, and consistency. From left to right: large hard stimulus, large compliant stimulus, large compliant stimulus with steel discs, large mixed stimulus with compliant outer layers and a very stiff inner layer, small compliant stimulus.
Figure 10.7 Stimuli used in a haptic search task. The red stimulus is quite hard, while the white one is very compliant, as can be seen in the left pictures. On the right a participant is ready to grasp a bunch of spheres and has the task of determining whether a hard one is present or not among the soft ones.
Figure 10.8 Examples of temperature profiles that were used as stimuli in the thermal diffusivity discrimination experiment. The dots indicate the actual displayed temperatures, while the solid curves show the nominal curves. Blue: difference between start and end temperature 5 C, time constant 2 s; Yellow: temperature difference 10 C, time constant 4 s; Green: temperature difference 10 C, time constant 12 s.
Figure 10.9 Movement patterns when participants explore nine () different textured samples to answer different question. (a) Schematic illustration of a possible stimulus set. (b) Question “Which sample is the warmest?” Exploration consists of a series of static touches. (c) Question “Describe the relief”. Repeatedly small back and forth movements are made.
List of Tables
Chapter 4: Computational Modeling of Light-triggered Topography Changes of Azobenzene-modified Liquid Crystal Polymer Coatings
Table 4.1 A summary of the default input parameters valid for all simulations of liquid crystal coatings (Sections 4.3.2–4.3.4) unless stated otherwise
Chapter 5: Dynamic Tribology in Liquid Crystal Coatings
Table 5.1 The effect of the orientation of grating on the static friction coefficient
Chapter 8: Electrically Responsive Fluoropolymer Surfaces and Devices
Table 8.1 Structure and properties of some perfluorinated solvents used in formulating Teflon AF
Chapter 10: Haptic Perception of Material Properties
Table 10.1 Overview of our roughness results
Table 10.2 Overview of our compliance results
Table 10.3 Overview of our temperature results
