Light controlled friction at a liquid crystal polymer coating with switchable patterning

Liu, Danqing; Broer, Dirk J.

doi:10.1039/c4sm01249f

Cited by 63 publications

(57 citation statements)

References 36 publications

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“…The fingerprint texture is of particular interest as it contains multiple alignment regions (homeotropic and planar) directly upon application, and does not require additional electric fields or other processing states to achieve this condition. By containing both planar and homeotropic alignment regions in the same coating, the film will both expand and compress, respectively, leading to larger deformations [94,101]. For these types of azo-LCN coatings, it was found that the actuation and relaxation time were both close to 10 s [103].…”

Section: Light-induced Reversible Surface Topographies In Azo Cross-lmentioning

confidence: 93%

“…This makes the coating more attractive for applications such as generation of variable friction surfaces that can respond in the order of seconds (see Figure 11d,e). fields creates azo-LCN coatings with alternating domains of planar (director parallel to the substrate) cholesteric and homeotropic (director perpendicular to the substrate) nematic alignment within the same film (see Figure 11a-c) [94,101]. With this alignment setup, the coating will contain areas that expand and contract in thickness adjacent to one another, resulting in larger differential topographical features.…”

Section: Light-induced Reversible Surface Topographies In Azo Cross-lmentioning

confidence: 99%

“…The researchers used the pillar-structured coatings to study the interactions of living cells in contact with structured surfaces. Stable topographies can also be prepared by locally controlling the alignment of the liquid crystal coating prior to polymerization and then generating the stable topographies in the film with uniform UV exposure after polymerization (that is, not using a mask as in the previous example) [13,100,101,104]. Stable topographies require the presence of radical scavengers during polymerization of the LC coating.…”

Section: Light-induced Permanent Surface Topographies In Azo Cross-limentioning

confidence: 99%

“…LCs allow for a high degree of control over molecular alignment, which is important in forming topographies. LCNs are created from reactive LC monomeric mixtures that can be aligned by a variety of techniques (among them are various interfacial techniques, mechanical [14,94,95], optical [96][97][98][99][100] and electrical [101]). These mixtures typically contain an azobenzene moiety (molecule 4 in Figure 9c) acting both as a cross-linker and deformation trigger molecule.…”

Section: Light-induced Permanent Surface Topographies In Azo Cross-limentioning

confidence: 99%

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Light-Triggered Formation of Surface Topographies in Azo Polymers

et al. 2017

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Properties such as friction, wettability and visual impact of polymer coatings are influenced by the surface topography. Therefore, control of the surface structure is of eminent importance to tuning its function. Photochromic azobenzene-containing polymers are an appealing class of coatings of which the surface topography is controllable by light. The topographies form without the use of a solvent, and can be designed to remain static or have dynamic properties, that is, be capable of reversibly switching between different states. The topographical changes can be induced by using linear azo polymers to produce surface-relief gratings. With the ability to address specific regions, interference patterns can imprint a variety of structures. These topographies can be used for nanopatterning, lithography or diffractive optics. For cross-linked polymer networks containing azobenzene moieties, the coatings can form topographies that disappear as soon as the light trigger is switched off. This allows the use of topography-forming coatings in a wide range of applications, ranging from optics to self-cleaning, robotics or haptics.

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Section: Light-induced Reversible Surface Topographies In Azo Cross-lmentioning

confidence: 93%

Section: Light-induced Reversible Surface Topographies In Azo Cross-lmentioning

confidence: 99%

Section: Light-induced Permanent Surface Topographies In Azo Cross-limentioning

confidence: 99%

Section: Light-induced Permanent Surface Topographies In Azo Cross-limentioning

confidence: 99%

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Light-Triggered Formation of Surface Topographies in Azo Polymers

et al. 2017

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“…SMP coatings that change both topography and color are appealing for a range of reconfigurable nanophotonic devices for optical data storage, photovoltaics, and optical sensors, as well as smart adhesives, biosurfaces, and battery‐free optical time‐analyte indicators . Regular surface topographies exhibiting structural colors have been fabricated in SMPs by top‐down methods including locally induced surface wrinkling, nanoimprint lithography, compression molding, or templating via microspheres .…”

Section: Introductionmentioning

confidence: 99%

Photonic Shape Memory Chiral Nematic Polymer Coatings with Changing Surface Topography and Color

Nickmans

Heijden

Schenning

2019

Advanced Optical Materials

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optical time-analyte indicators. [21,22] Regular surface topographies exhibiting structural colors have been fabricated in SMPs by top-down methods including locally induced surface wrinkling, [23] nanoimprint lithography, [24,25] compression molding, [26] or templating via microspheres. [27] In these examples, hot pressing of the surface features results in a temporary flattened and colorless state, which is reversible upon heating. [24][25][26][27] To circumvent the cumbersome topdown nanoforming steps to generate the structural color, photonic SMP coatings generated by bottom-up self-assembly have also been employed. [17,28,29] For example, shape memory photonic films have been produced from core-interlayer-shell polymer microspheres that form opal structures. [30][31][32] Alternatively porous inverse-opal SMPs have been templated by silica colloids. [33] Capillary pressure-induced "cold" programming of these materials results in a disordered temporary state consisting of collapsed pores and an arbitrarily roughened surface, which can be recovered by pressure, heat, organic vapors, solvents, and microwave radiation. [34][35][36][37][38][39] Unfortunately, the fabrication of such SMP coatings is still hampered by the lack of facile methods and materials. [40] Reactive liquid crystalline materials are exciting from this perspective since they form nanostructured phases via selfassembly, and can be easily processed via photopolymerization [41][42][43][44] to fabricate polymeric coatings. [45][46][47][48][49] Chiral nematic liquid crystalline (a.k.a. cholesteric liquid crystalline (CLC)) phases are of particular interest for their periodic helical structures which lead to the selective and incident-angledependent reflection of light, resulting in iridescent structural colors. [50] CLC coatings have been reported that respond to stimuli including heat, light, and humidity. [17,[51][52][53][54][55][56][57] In addition, CLC coatings have been reported that simultaneously change surface topography and color in a reversible manner. [41,55] Recently, our group reported that irreversible thermoresponsive photonic coatings can be fabricated based on CLC polymer networks using a shape memory approach. [58,59] Indentation of a small area (≈1 mm 2 ) of the CLC film, at a temperature above the T g of the polymer network, resulted in a blue-shift of the reflection band through a reduction of the pitch of the cholesteric helix, which was fully recovered upon heating.We now report a new approach for the fabrication of shape memory photonic coatings that irreversibly change both topography and color. Polymeric CLC films with a red structural The fabrication of shape memory coatings that change both reflectivity and topography is hampered by the lack of facile methods and materials. Now, shape memory photonic coatings are fabricated by high-speed flexographic printing and UV-curing in air of a chiral nematic liquid crystal ink. Deformable polymeric films with a red reflection band and a smooth surface topography are obtained which...

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Photomechanical Effects in Materials, Composites, and Systems: Outlook and Future Challenges

White

2017

Photomechanical Materials, Composites, and Systems

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Light controlled friction at a liquid crystal polymer coating with switchable patterning

Cited by 63 publications

References 36 publications

Light-Triggered Formation of Surface Topographies in Azo Polymers

Light-Triggered Formation of Surface Topographies in Azo Polymers

Photonic Shape Memory Chiral Nematic Polymer Coatings with Changing Surface Topography and Color

Photomechanical Effects in Materials, Composites, and Systems: Outlook and Future Challenges

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