Programmable Liquid Crystal Elastomers Prepared by Thiol–Ene Photopolymerization

Ware, Taylor H.; Perry, Zachary P.; Middleton, Claire M.; Iacono, Scott T.; White, Timothy J.

doi:10.1021/acsmacrolett.5b00511

Cited by 124 publications

(116 citation statements)

References 23 publications

(37 reference statements)

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“…[38][39][40] Recently, main-chain LCEs amenable to photoalignment have been prepared, allowing for arbitrary spatial alignment of the nematic director over area as small as 0.01 mm 2 . [ 43 ] Unfortunately, these LCEs can require heating to as much as 175 °C to generate such large strain that is undesirable for many applications. This reaction proceeds in one pot (in this case an alignment cell) and the resulting LCEs exhibit complex topographical changes with strain up to 55%.…”

Section: Introductionmentioning

confidence: 99%

Photoinduced Topographical Feature Development in Blueprinted Azobenzene‐Functionalized Liquid Crystalline Elastomers

Ahn

Ware

Lee

et al. 2016

Adv Funct Materials

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148

137

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5819wileyonlinelibrary.com or shape (topography). Light is potentially a "smart" stimulus that can uniquely allow for wireless (remote) spatio-temporal control of the force or shape change.A considerable volume of recent research has focused on photomechanical effects in azobenzene-functionalized liquid crystalline polymer networks (azo-LCNs) and elastomers (azo-LCEs) both experimetnally and theoretically. [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] In these numerous efforts, azobenzene has been used as a molecular switch to convert input light energy into conformational change which subsequently generates strain in the polymeric materials. Two related but distinguished photochemical processes have been employed including (i) transcis photoisomerization of azobenzene typically initiated with UV irradiation [ 28 ] and (ii) trans-cis-trans reorientation of azobenzene initiated with blue-green irradiation. [ 12,14,29,30 ] These photoinduced conformational changes convert input photonic energy into a mechanical output by distorting the local polymer network. Trans-cis-trans reorientation has recently been subject to intense fundamental studies focused on the athermal softening of the material at the molecular and macromolecular level. [ 30,31 ] The photogenerated strain has correspondingly been demonstrated to induce motion including bending, oscillation, and torsion. [ 19,32,33 ] For aligned azo-LCNs and azo-LCEs, the strain is anisotropic and oriented parallel to the nematic director. For example, the photogenerated strain in a monodomain (nematic) LCN results in in-plane deformation [ 29,34 ] while offsetting the orientation of the director profi le to the sample geometry results in out-of-plane deformation yielding twisting. [ 15,16,32,35,36 ] Spatial variation in the orientation (programming) of liquid crystalline monomers using surface alignment techniques such as photoalignment has many potential benefi ts. [ 32,37,38 ] In the work presented here, we employ a commercial photoalignment material also based on azobenzene. This material is formulated in solution and applied to glass substrates by spin coating, subsequently evaporating solvent, and then subjecting the surface layer to patterned linearly polarized light. The azobenzene molecules on the surface layer orient orthogonal to the electric fi eld vector of the incident linearly polarized light. Upon fi lling the cell after photoalignment, the LC monomer orients to the local surface and retains this alignment during polymerization. ). The azo-LCEs are synthesized via an orthogonal, two-step reaction between commercially available LC monomers and n -butylamine. By employing surface alignment, the local orientation of the nematic director is spatially complex ("blueprinted"). Exposing the blueprinted LCE fi lms to light as an actinic stimulus generates a photomechanical response which yields reversible shape changes between 2D and 3D shapes. The deformation of azo-LCEs strongly depends on the azobenzene concentration as well as the networ...

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Section: Introductionmentioning

confidence: 99%

Photoinduced Topographical Feature Development in Blueprinted Azobenzene‐Functionalized Liquid Crystalline Elastomers

Ahn

Ware

Lee

et al. 2016

Adv Funct Materials

Self Cite

148

137

View full text Add to dashboard Cite

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“…When macroscopically aligned, such materials also exhibit large dimensional changes, making them interesting as actuating polymers. Both stimulus‐responsive free standing films as well as LCEs confined to a solid substrate have been reported with programmable shapes and topographies . For CLC elastomers, dimensional changes along the helical pitch direction even resulted in changes in reflective color .…”

Section: Introductionmentioning

confidence: 99%

Easily Processable and Programmable Responsive Semi‐Interpenetrating Liquid Crystalline Polymer Network Coatings with Changing Reflectivities and Surface Topographies

Kragt

Broer

Schenning

2017

Adv Funct Materials

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The fabrication of stimulus-responsive coatings that change both reflectivity and topography is hampered by the lack of easy processable, patternable, and programmable elastomers. Here, an easily applied reflective coating based on a semi-interpenetrating polymer network composed of a liquid crystal elastomer and a liquid crystal network (>15 wt%) is reported. The reflective wavelength of these polysiloxane elastomer photonic coatings can be readily programed by the concentration of chiral reactive mesogen dopant that forms the network. The coatings show a fast and reversible decrease in reflection band intensity with increasing temperature, which can be tuned by the polymer network density. In addition, hierarchical surface relief structures are prepared, which can be reversibly changed with temperature.

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“…Recently, this method has been directed to the synthesis of elastomers. [26][27][28][29] For example, Ma et al prepared acrylate-rich elastomers with pentaerythritol tetrakis (3mercaptopropionate) and tetra(ethylene glycol) diacrylate using Irgacure 184 as a photoinitiator under UV irradiation. 27 Although the reported procedure was simple and very efficient, the obtained elastomers are chemically cross-linked and cannot be redissolved in organic solvents or be melt, known as thermosetting elastomers.…”

Section: Introductionmentioning

confidence: 99%

Multiblock thermoplastic elastomers via one-pot thiol–ene reaction

Thanneeru

Liu

et al. 2016

Polym. Chem.

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We report a facile approach to designing multiblock thermoplastic elastomers using a two-step thiol-ene polyaddition reaction. It is based on the utilization of intermolecular hydrogen bonding of widely available and cost-effective monomer of N, N'-methylenebis(acrylamide) (MBAm) as physical cross-links. Thiol-terminated "soft" prepolymers were first prepared using ethylene glycol dimethacrylate (EGDMA) and an excess of 1,6-hexanedithiol (HDT); subsequently, the thiolterminated prepolymers were further reacted with MBAm as a chain-extension reaction to yield the multiblock thermoplastic elastomers. The prepolymers with oligo(ethylene glycol) segments had a low glass-transition temperature, acting as elastic "soft" blocks; while MBAm units could form up to 4 hydrogen bonds that serve as physical networks to endow the elasticity to multiblock polymers. Proton nuclear magnetic resonance spectroscopy and gel permeation chromatography indicated the occurrence of the two-step thiol-ene reactions. The reaction kinetics of thiol-ene reactions was found to be highly dependent on the molecular weights of monomers. The first thiol-ene reaction of EGDMA and HDT could reach >90% conversion of both monomers within 5 min; while the kinetics of the second chain extension reaction was relatively slow and it took approximately 7 hr to reach 90% conversion. The formation of the intermolecular hydrogen bonding between amide groups of MBAm units was confirmed by variable-temperature Fourier transform infrared spectroscopy and differential scanning calorimetry. The viscoelasticity and elasticity of the thermoplastic elastomers were found to be largely determined by the content of MBAm. With a molar ratio of 15% MBAm relative to EGDMA, the maximum elongation at break of elastomers reached >400%. Our synthetic method has the advantages of mild reaction conditions, high conversion and adjustable mechanical properties of elastomers; additionally, it does not involve heavy syntheses and expensive monomers/catalysts. Our findings conceivably stand out as a new tool to synthesize and engineer thermoplastic elastomers using the combination of thiol-ene chemistry and supramolecular interaction.

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Programmable Liquid Crystal Elastomers Prepared by Thiol–Ene Photopolymerization

Cited by 124 publications

References 23 publications

Photoinduced Topographical Feature Development in Blueprinted Azobenzene‐Functionalized Liquid Crystalline Elastomers

Photoinduced Topographical Feature Development in Blueprinted Azobenzene‐Functionalized Liquid Crystalline Elastomers

Easily Processable and Programmable Responsive Semi‐Interpenetrating Liquid Crystalline Polymer Network Coatings with Changing Reflectivities and Surface Topographies

Multiblock thermoplastic elastomers via one-pot thiol–ene reaction

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