Volume generation towards dynamic surface morphing in liquid crystal polymer networks

Liu, Danqing

doi:10.1080/02678292.2016.1195898

Cited by 20 publications

(17 citation statements)

References 47 publications

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“…This result becomes most clear in the local exposure of a homeotropic film. Based on arguments of the scalar order parameter, the film would shrink; however, because of the free volume formation, the film expands in the perpendicular direction forming a small hill rather than a valley . Further information on this experiment is described in section .…”

Section: Light‐responsive Liquid Crystal Networkmentioning

confidence: 99%

“…A good example demonstrating the existence of free volume in LCNs, next to the direct measurement of the density (vide supra), is the local exposure of a uniform homeotropic coating where the mesogenic units are aligned perpendicularly to the substrate surface . According to the classical anisotropic expansion arguments, the coating should contract at the exposed places, thus forming indentations, as illustrated in Figure a.…”

Section: Light‐responsive Liquid Crystal Networkmentioning

confidence: 99%

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Surface Dynamics at Photoactive Liquid Crystal Polymer Networks

Liu

2019

Advanced Optical Materials

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creating insulation under cold conditions and emitting evaporable liquid when it is warm. [1][2][3] Peacock feathers, wings of certain butterflies, and plants exhibit color by means of structural color to communicate attraction or, inversely, repulsion. Often, the colors originate from periodic structures on or under a surface, thus benefiting from the interplay of light and diffractive effects.A surface is the outermost layer of matter and therefore is primarily perceived by humans upon touch or vision. Surfaces provide perceptible information by not only shape, color, and/or reflective properties but also how the matter feels upon touch, e.g., smooth or rough. Welldocumented static structures have been reported for haptic applications. [4] Studies have suggested that humans can distinguish changes in topographical dimensions down to nanometers. [5] Additionally, a surface is the first contact between objects of matter, either of the same object or that of another origin. Surfaces facilitate man-machine interactions, [6] either by touch (smooth, rough, heat conductive, etc.) or by vision (scattering, specular reflection, printed information, etc.). [7][8][9] In relation to this function, tribological properties such as friction, stick, and adhesion coefficients also find application in the field of haptics, where robotic manipulation is of importance. In contrast to nature, the surface structures in modern man-made technology are often still static. Mimicking the lotus flower, surfaces with artificially formed micrometer-sized structures that are produced by lithography or micromachining have been made, and they indeed show improved cleaning under rainy conditions. However, one expands the surface function when these structures are made dynamic, rather than static, for example, the surface would be able to remove dirt under dry conditions, as well. In the case of topographies for haptic use, man's sensitivity could be enhanced when the corrugations are moving with a frequency tuned to the maximum sensitivity of humans. However, only a few publications have described dynamic structures to enhance human-surface interactions, which could even help visually disabled people. Moreover, in an advanced technology such as microfluidics, the low Reynolds number prohibits turbulent mixing of fluid components. Mixing can be induced by surface topographical structures in the microchannels to increase the contact area and the contact time between the reagents. The microfluidic functionality would be enhanced if the topography of its inner walls could be switched in a dynamic way, e.g., to decide on the exact location and time that switching The field of advanced and responsive soft materials is at the edge of a new era. After several decades during which liquid crystals generated new functions for information displays and could solve many problems in emerging fields such as (tele)communications, this material system is being utilized to reach out to completely new application fields with functions that can take over biologica...

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Section: Light‐responsive Liquid Crystal Networkmentioning

confidence: 99%

Section: Light‐responsive Liquid Crystal Networkmentioning

confidence: 99%

Surface Dynamics at Photoactive Liquid Crystal Polymer Networks

Liu

2019

Advanced Optical Materials

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“…Realignment of the LCN is prohibited by the high crosslink density of the polymer network. Subsequently, it creates microscopic molecular voids and related geometrical deformations in the polymer film as shown in Figure c. To enhance the interaction with the field, we designed a mixture that consists of mono‐ and diacrylates exhibiting a net positive dielectric anisotropy (Figure d).…”

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confidence: 99%

Oscillating Chiral‐Nematic Fingerprints Wipe Away Dust

2018

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access to water is often limited and waterbased self-cleaning approaches are not applicable. We report here a new concept of a dry self-cleaning method without the aid of water. This will solve a problem for solar farms placed in deserts where accumulated dust and sand at the surfaces of the photovoltaic cells block the sun light, which might cut power production as a result of a sand storm by 40%. [12] For reference, contaminated solar panels in solar farms are still removed from deposited dust by manually brushing. In addition, dust mitigating technologies may be used to protect any mechanical/optical/electric systems that carry out Lunar/Mars missions against dust hazards.[13] The waterfree self-cleaning philosophy we propose here is based on an orchestrated change of the surface topography. The induced vibrations mechanically transport dusts and debris to the edges of the surface, eventually supported by gravity when the surface is tilted. In a previous publication, we reported on homeotropic nematic liquid crystal network (LCN) which we could bring into a volumetric vibration by a high-frequency AC electric field. [14] The dynamic topographies were irregular and rather small, in the order of 100 nm. In order to create larger deformations, we focus here on a chiralnematic LCN that is brought in the so-called fingerprint mode with periodically alternating planar and homeotropic molecular alignment. The electrically induced change of the order parameter, with periodic alternating contraction and expansion, is anticipated to enhance the surface deformation to dimensions capable to transport sand grains. In addition, the topographic periodicity will be determined by the pitch of the molecular helix rather than by electrode spacing.The particle-rejecting coating is made by in situ photopolymerization of a mixture of chiral reactive mesogens that forms a crosslinked LCN on top of interdigitated electrodes (IDE). We chose for the IDE as it provides an in-plane electrical field while the LC coating will form an electrical isolating shield protecting potential users. By controlling the surface conditions of this IDE substrate prior to polymerization as described in Experimental Section the rod-like mesogens in the LCN adapted a helicoidal organization with the helix axes parallel to the surface as schematically shown in Figure 1a. The helix axes take a worm-like configuration (Figure 1b) also known as fingerprint texture. The black area in Figure 1b corresponds to the molecules that are homeotropically aligned while the planar orientation is optically birefringent showing blue color. More fingerprints patterns are shown in Figures S1 and S2 of the Supporting Information.The underlying deformation mechanism is to decrease the LCN order parameter and bringing the LCN into oscillation by a lateral This work presents an approach to create mechanical undulations at a solid organic coating surface under the influence of an electric field. The coating is fabricated through polymerization of chiral reactive mesogens aligned ...

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“…LCNs are polymers that form by polymerizing aligned liquid crystal monomers, thereby maintaining their molecular orientation. 22 Recently, they have been explored for use as actuators and soft robotic applications because they change shape when triggered by light, 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 temperature, 32 , 33 , 34 and electricity. 35 , 36 Here, we form a sponge-like LCN coating by photopolymerizing a smectic mixture of monomers 2 and 3 in the presence of the non-reactive LC 1 and photoinitiator 4 .…”

Section: Resultsmentioning

confidence: 99%

Artificial Organic Skin Wets Its Surface by Field-Induced Liquid Secretion

Zhan

Zhou

Lamers

et al. 2020

Matter

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An artificial organic skin that can secrete liquid and wet its surface is demonstrated. The secretion is triggered by an alternating electric field at radio frequency. The polymer skin is constructed of a porous liquid crystal polymer network with the embedded dielectric liquid. The electric field accumulates the liquid in between the electrodes. By network contraction, the liquid is ejected at the surface of the polymer skin.

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Volume generation towards dynamic surface morphing in liquid crystal polymer networks

Cited by 20 publications

References 47 publications

Surface Dynamics at Photoactive Liquid Crystal Polymer Networks

Surface Dynamics at Photoactive Liquid Crystal Polymer Networks

Oscillating Chiral‐Nematic Fingerprints Wipe Away Dust

Artificial Organic Skin Wets Its Surface by Field-Induced Liquid Secretion

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