The Experts below are selected from a list of 9090 Experts worldwide ranked by ideXlab platform
John A Hart - One of the best experts on this subject based on the ideXlab platform.
-
high fidelity replica molding of glassy Liquid Crystalline Polymer microstructures
ACS Applied Materials & Interfaces, 2016Co-Authors: Hangbo Zhao, Davor Copic, Ryan C Oliver, Alvin Orbaek White, John A HartAbstract:Liquid Crystalline Polymers have recently been engineered to exhibit complex macroscopic shape adaptivity, including optically- and thermally driven bending, self-sustaining oscillation, torsional motion, and three-dimensional folding. Miniaturization of these novel materials is of great interest for both fundamental study of processing conditions and for the development of shape-changing microdevices. Here, we present a scalable method for high-fidelity replica molding of glassy Liquid Crystalline Polymer networks (LCNs), by vacuum-assisted replica molding, along with magnetic field-induced control of the molecular alignment. We find that an oxygen-free environment is essential to establish high-fidelity molding with low surface roughness. Identical arrays of homeotropic and polydomain LCN microstructures are fabricated to assess the influence of molecular alignment on the elastic modulus (E = 1.48 GPa compared to E = 0.54 GPa), and side-view imaging is used to quantify the reversible thermal actuation o...
-
high fidelity replica molding of glassy Liquid Crystalline Polymer microstructures
ACS Applied Materials & Interfaces, 2016Co-Authors: Hangbo Zhao, Davor Copic, Ryan C Oliver, Alvin Orbaek White, John A Hart, Jeong Jae Wie, Sanha KimAbstract:Liquid Crystalline Polymers have recently been engineered to exhibit complex macroscopic shape adaptivity, including optically- and thermally driven bending, self-sustaining oscillation, torsional motion, and three-dimensional folding. Miniaturization of these novel materials is of great interest for both fundamental study of processing conditions and for the development of shape-changing microdevices. Here, we present a scalable method for high-fidelity replica molding of glassy Liquid Crystalline Polymer networks (LCNs), by vacuum-assisted replica molding, along with magnetic field-induced control of the molecular alignment. We find that an oxygen-free environment is essential to establish high-fidelity molding with low surface roughness. Identical arrays of homeotropic and polydomain LCN microstructures are fabricated to assess the influence of molecular alignment on the elastic modulus (E = 1.48 GPa compared to E = 0.54 GPa), and side-view imaging is used to quantify the reversible thermal actuation of individual LCN micropillars by high-resolution tracking of edge motion. The methods and results from this study will be synergistic with future advances in Liquid Crystalline Polymer chemistry, and could enable the scalable manufacturing of stimuli-responsive surfaces for applications including microfluidics, tunable optics, and surfaces with switchable wetting and adhesion.
Timothy J White - One of the best experts on this subject based on the ideXlab platform.
-
photomechanical effects in Liquid Crystalline Polymer networks and elastomers
Journal of Polymer Science Part B, 2018Co-Authors: Timothy J WhiteAbstract:Liquid crystals are widely employed as stimuli-responsive materials. Liquid crystallinity can be retained in Polymeric form. Photoinduced mechanical effects in Liquid Crystalline Polymer networks and elastomers have been a topic of considerable recent research. This review details the historical underpinnings and recent advances in the synthesis and the corresponding photomechanical response of these materials. In nearly all cases, the conversion of light into mechanical work has employed azobenzene as either a guest additive or covalently attached to the network. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018.
-
synthesis of elastomeric Liquid Crystalline Polymer networks via chain transfer
ACS Macro Letters, 2017Co-Authors: Nicholas P Godman, Benjamin A Kowalski, Hilmar Koerner, Anesia D Auguste, Timothy J WhiteAbstract:Materials capable of complex shape changes have broad reaching applications spanning biomimetic devices, componentless actuators, artificial muscles, and haptic displays. Liquid crystal elastomers (LCE) are a class of shape programmable materials which display anisotropic mechanical deformations in response external stimuli. This work details a synthetic strategy to quickly and efficiently prepare LCEs through the usage of chain transfer agents (CTA). The polyacrylate materials described herein exhibit large, reversible shape changes with strains greater 475%, rivalling properties observed in polysiloxane-based networks. The approach reported here is distinguished in that the materials chemistry is readily amenable to surface alignment techniques. The facile nature of the materials chemistry and the compatibility of these materials with directed self-assembly methods could further enable paradigm shifting end uses as designer substrates for flexible electronics or as actuating surfaces.
-
pixelated Polymers directed self assembly of Liquid Crystalline Polymer networks
ACS Macro Letters, 2017Co-Authors: Benjamin A Kowalski, Tyler Guin, Anesia D Auguste, Nicholas P Godman, Timothy J WhiteAbstract:Polymeric materials are pervasive in modern society, in part attributable to the diverse range of properties that are accessible in these materials. Polymers can be stiff or soft, dissipative or elastic, adhesive or nonstick. Localizing the properties of Polymeric materials can be achieved by a number of methods, including self-assembly, lithography, or 3-d printing. Here, we detail recent advances in the preparation of “pixelated” Polymers prepared by the directed self-assembly of Liquid Crystalline monomers to yield cross-linked Polymer networks (Liquid Crystalline Polymer networks, LCN, or Liquid Crystalline elastomers, LCE). Through the local and arbitrary control of the orientation of the Liquid Crystalline units, monolithic elements can be realized with spatial variation in mechanical, thermal, electrical, optical, or acoustic properties. Stimuli-induced variation of these properties may enable paradigm-shifting end uses in a diverse set of applications.
-
twists and turns in glassy Liquid Crystalline Polymer networks
Macromolecules, 2015Co-Authors: Taylor H Ware, Timothy J WhiteAbstract:Three-dimensional shape control is an enabler of dexterous motion in nature. Herein, we report on the thermally initiated out-of-plane (torsional) responses observed in a series of glassy, Liquid Crystalline Polymer networks prepared with a range of cross-link densities. The three-dimensional shape of these materials is strongly dictated by both cross-link density as well as the preparation conditions (Polymerization temperature). All of the materials examined herein undergo torsional inversion of the handedness with increasing temperature. The temperature at which the material flattens (crossover between handedness inversion) can be positioned by the Polymerization temperature. Monoliths prepared with either multimaterial composition or multidirector orientations are shown to exhibit spatial variation in shape adaptivity.
-
thermally and optically fixable shape memory in azobenzene functionalized glassy Liquid Crystalline Polymer networks
Molecular Crystals and Liquid Crystals, 2014Co-Authors: Timothy J WhiteAbstract:Thermally and optically fixed shape memory is examined in glassy, azobenzene- functionalized Liquid Crystalline Polymer networks (azo-LCN) in the twisted nematic (TN) geometry. The thermal and optical responses of two materials with a large difference in crosslink density are contrasted. The crosslink density was reduced through the inclusion of a monoacrylate Liquid crystal monomer RM23. Reducing the crosslink density decreases the threshold temperature of the thermally-induced shape change and increases the magnitude of the deflection. Surprisingly, samples containing RM23 also allows for retention of a complex permanent shape, potentially due to differentiated thermal response of the pendant and main chain mesogenic units of the azo-LCN material.
Erqiang Chen - One of the best experts on this subject based on the ideXlab platform.
-
microphase separation facilitating and stabilizing hierarchical segment self assembly of combined main chain side chain Liquid Crystalline Polymer in diblock coPolymer
Macromolecules, 2013Co-Authors: Guohui Wen, Ben Zhang, Helou Xie, Xin Liu, Guanqun Zhong, Hailiang Zhang, Erqiang ChenAbstract:A series of diblock coPolymers (PS-b-PBBHCSs) composed of polystyrene (PS) and poly(2,5-bis{[6-(4-butoxy-4′-oxybiphenyl)hexyl]oxycarbonyl}styrene) (PBBHCS) were successfully synthesized via atom transfer radical Polymerization, with their chemical structures confirmed by various characterization techniques. While PS is a conventional coil Polymer, PBBHCS is a novel combined main-chain/side-chain Liquid Crystalline Polymer (MCSCLCP) which can exhibit hierarchically ordered structures. Small-angle X-ray scattering results show that the diblock coPolymers with different compositions could present lamellar and rectangular cylinder morphologies before the order–disorder transition. Combining the differential scanning calorimetry and X-ray scattering results, we find that the PBBHCS block in the confined space of microphase separation is still able to exhibit its Liquid Crystalline (LC) structures with the rectangular main-chain scaffold on the nanometer scale and the side-chain ordering on the subnanometer sca...
-
hemiphasmidic side chain Liquid Crystalline Polymer from smectic c phase to columnar phase with a bundle of chains as its building block
ACS Macro Letters, 2012Co-Authors: Junfeng Zheng, Xin Liu, Xiaofang Chen, Xiangkui Ren, Shuang Yang, Erqiang ChenAbstract:We synthesized a new hemiphasmidic side-chain Liquid Crystalline Polymer (P-n, n is the number of carbons in alky tail of the side chain, n = 4–12) using free radical Polymerization. The side chain of P-n has a biphenyl in the middle, linked to the polystyrene backbone and to the terminal phenyl group with three alkyl tails via only methyleneoxy units. Upon increasing n, the mesophase of P-n changes from bilayer smectic C to hexagonal columnar (Φh) phase with the a-dimension of ∼6 nm. Both of the mesophases are long-range ordered, which can be well aligned by simple shearing. The oriented Φh shows a quite low rotational disorder around the shear direction. Most likely, the Φh phase takes a bundle of chains (e.g., ∼five chains) rather than a single chain as its building block. This “multi-chain model” of the Φh phase may represent a new type of self-assembly in side-chain Polymers.
-
design synthesis and characterization of a combined main chain side chain Liquid Crystalline Polymer based on mesogen jacketed Liquid crystal Polymer via atom transfer radical Polymerization
Journal of Polymer Science Part A, 2008Co-Authors: Helou Xie, Erqiang Chen, Xuefei Zhang, Hailaing Zhang, Qifeng ZhouAbstract:A novel combined main-chain/side-chain Liquid Crystalline Polymer based on mesogen-jacketed Liquid crystal Polymers (MJLCPs) containing two biphenyls per mesogenic core of MJLCPs main chain, poly(2,5-bis{[6-(4-butoxy-4'-oxy-biphenyl)hexyl]oxycarbonyl)styrene) (P1-P8) was successfully synthesized via atom transfer radical Polymerization (ATRP). The chemical structure of the monomer was confirmed by elemental analysis, 1 H NMR, and 13 C NMR. The molecular characterizations of the Polymer with different molecular weights (P1-P8) were performed with 1 H NMR, gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). Their phase transitions and Liquid-Crystalline behaviors of the Polymers were investigated by differential scanning calorimetry (DSC) and polarized optical microscope (POM). We found that the Polymers P1-P8 exhibited similar behavior with three different Liquid Crystalline phases upon heating to or cooling in addition to isotropic state, which should be related to the complex Liquid crystal property of the side-chain and the main-chain. Moreover, the transition temperatures of Liquid Crystalline phases of P1-P8 are found to be dependent on the molecular weight.
Albertus P H J Schenning - One of the best experts on this subject based on the ideXlab platform.
-
photoresponsive nanoporous smectic Liquid Crystalline Polymer networks changing the number of binding sites and pore dimensions in Polymer adsorbents by light
Macromolecules, 2015Co-Authors: Huub P C Van Kuringen, Dirk J. Broer, Giuseppe Portale, Z J W A Leijten, Anne Helene Gelebart, Dirk J Mulder, Albertus P H J SchenningAbstract:Photoresponsive nanoporous Polymer films have been fabricated by adding a photoresponsive azobenzene cross-linker to a hydrogen-bonded smectic Liquid Crystalline Polymer network. A base treatment resulted in the nanoporous material which has been fully characterized. Upon exposure to UV light a decrease in the smectic layer spacing is observed, suggesting a decrease in pore size. In addition, the binding sites in the material could be changed with light, leading to light-induced adsorption of cations and cationic dyes. Finally, light could also be used to create nanoporous channels in the Polymer film.
-
patterned silver nanoparticles embedded in a nanoporous smectic Liquid Crystalline Polymer network
Journal of the American Chemical Society, 2013Co-Authors: Debarshi Dasgupta, Dirk J. Broer, Ivelina K Shishmanova, Amparo Ruizcarretero, Martinus Verhoeven, Huub P C Van Kuringen, Giuseppe Portale, Philippe Leclere, Cees W M Bastiaansen, Albertus P H J SchenningAbstract:A nanoporous smectic Liquid Crystalline Polymer network has been exploited to fabricate photo patternable organic–inorganic hybrid materials, wherein, the nanoporous channels control the diameter and orientational order of the silver nanoparticles.
Jeong Jae Wie - One of the best experts on this subject based on the ideXlab platform.
-
high fidelity replica molding of glassy Liquid Crystalline Polymer microstructures
ACS Applied Materials & Interfaces, 2016Co-Authors: Hangbo Zhao, Davor Copic, Ryan C Oliver, Alvin Orbaek White, John A Hart, Jeong Jae Wie, Sanha KimAbstract:Liquid Crystalline Polymers have recently been engineered to exhibit complex macroscopic shape adaptivity, including optically- and thermally driven bending, self-sustaining oscillation, torsional motion, and three-dimensional folding. Miniaturization of these novel materials is of great interest for both fundamental study of processing conditions and for the development of shape-changing microdevices. Here, we present a scalable method for high-fidelity replica molding of glassy Liquid Crystalline Polymer networks (LCNs), by vacuum-assisted replica molding, along with magnetic field-induced control of the molecular alignment. We find that an oxygen-free environment is essential to establish high-fidelity molding with low surface roughness. Identical arrays of homeotropic and polydomain LCN microstructures are fabricated to assess the influence of molecular alignment on the elastic modulus (E = 1.48 GPa compared to E = 0.54 GPa), and side-view imaging is used to quantify the reversible thermal actuation of individual LCN micropillars by high-resolution tracking of edge motion. The methods and results from this study will be synergistic with future advances in Liquid Crystalline Polymer chemistry, and could enable the scalable manufacturing of stimuli-responsive surfaces for applications including microfluidics, tunable optics, and surfaces with switchable wetting and adhesion.
-
torsional mechanical responses in azobenzene functionalized Liquid Crystalline Polymer networks
Soft Matter, 2013Co-Authors: Jeong Jae Wie, Kyung-min Lee, Richard A Vaia, Matthew L Smith, Timothy J WhiteAbstract:Soft materials capable of both planar and flexural–torsional responses could enable the development of soft robotic elements that emulate the dexterity and functionality of a multitude of creatures in the animal kingdom. Here, we examine the response of azobenzene-functionalized Liquid crystal Polymer networks (azo-LCNs) specifically focusing on realizing large magnitude flexural–torsional responses observed as out-of-plane twisting or coiling. Towards this end, azo-LCNs were prepared in either the twisted nematic (TN) or hybrid orientations. The characterization of the flexural–torsional photomechanical responses is complimented with examination of thermomechanical properties. The diverse range of tailorable photomechanical responses is shown to be strongly dependent on the alignment of the nematic director to the film geometry and the actinic light intensity.