Synthesis of Elastomeric Liquid Crystalline Polymer Networks via Chain Transfer

Godman, Nicholas P.; Kowalski, Benjamin A.; Auguste, Anesia D.; Koerner, Hilmar; White, Timothy J.

doi:10.1021/acsmacrolett.7b00822

Cited by 72 publications

(100 citation statements)

References 40 publications

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“…Finally, we show that an additional degree of design freedom is available: deformation can occur either on heating or on cooling, with the reference (flat) temperature readily tuned by adjusting the composition as reported in [20]. This freedom can be exploited to create deforming membranes that keep the same shape at their rim so that they can be anchored to rigid substrates with no stress penalty.…”

mentioning

confidence: 92%

“…As the bath is slowly heated, the dimensional changes in the sample are visually apparent ( Figure 1). Here, we use a recently reported approach [20] to prepare LCEs that exhibit large deformations upon relatively modest temperature changes. The synthesis of these materials is largely based on commercially available liquid crystalline monomers (diacrylates) that homopolymerize to form glassy liquid crystalline films with good uniformity [21].…”

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confidence: 99%

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Curvature by design and on demand in liquid crystal elastomers

et al. 2018

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The shape of liquid crystalline elastomers (LCEs) with spatial variation in the director orientation can be transformed by exposure to a stimulus. Here, informed by previously reported analytical treatments, we prepare complex spiral patterns imprinted into LCEs and quantify the resulting shape transformation. Quantification of the stimuli-induced shapes reveals good agreement between predicted and experimentally observed curvatures. We conclude this communication by reporting a design strategy to allow LCE films to be anchored at their external boundaries onto rigid substrates without incurring internal, mechanical-mismatch stresses upon actuation, a critical advance to the realization of shape transformation of LCEs in practical device applications.Liquid crystal elastomers (LCEs) are exciting materials that show promise for enabling multifunctional character in flexible devices. The mechanical response of these materials is inherently and programmably anisotropic, governed by the molecular-level liquid crystalline orientation. This generates a rich variety of reversible, shape-morphing behaviors [1] with large strains

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confidence: 92%

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confidence: 99%

Curvature by design and on demand in liquid crystal elastomers

et al. 2018

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“…Accordingly, these LCNs exhibit comparatively larger mechanical response (20–30% strain) relative to LCNs prepared from the homopolymerization of the diacrylate LCM . Previously, we reported alternative methods to prepare main‐chain and elastomeric LCNs (LCEs) to further amplify strain and enable spatial variation in the director profile . Two approaches have been explored: 1) aza‐Michael addition of diacrylate LCM to prepare main‐chain LCEs with comparatively larger molecular weight between crosslinks and 2) the use of chain transfer agents (CTAs) to prepare hyperbranched LCEs from the polymerization of diacrylate LCM.…”

Section: Introductionmentioning

confidence: 99%

“…Two approaches have been explored: 1) aza‐Michael addition of diacrylate LCM to prepare main‐chain LCEs with comparatively larger molecular weight between crosslinks and 2) the use of chain transfer agents (CTAs) to prepare hyperbranched LCEs from the polymerization of diacrylate LCM. Both approaches are facile methods to prepare robust, locally organized LCE material actuators from 2D films …”

Section: Introductionmentioning

confidence: 99%

Microstructured Photopolymerization of Liquid Crystalline Elastomers in Oxygen‐Rich Environments

McCracken

Tondiglia

Auguste

et al. 2019

Adv Funct Materials

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Liquid crystal elastomers (LCEs) are soft materials that undergo large anisotropic shape change in response to stimuli. Rational organization of the local director field can impart spatial control of the strain profile, enabling stretch-based deformation capable of nearly 20 J kg −1 of output force. LCEs are increasingly being considered in end-use applications in robotics, therapeutics, and optics. Here, a new synthetic approach is introduced to prepare LCEs composed of main chain mesogens via the cationic photopolymerization of the epoxy liquid crystal monomer (LCM). This examination details the optical, mechanical, and thermal properties of epoxide-based LCEs as a function of spacer length (3, 6, or 11 carbons). The oxygen insensitivity of the cationic photopolymerization of these monomers makes this approach particularly attractive for implementation with emerging additive manufacturing techniques. This contribution focuses on microstructuring LCEs via 2-photon direct laser writing (2P-DLW). A custom heated cell facilitated 2P-DLW of the aligned LCE epoxy resin melts to fabricate diverse geometric arrays. Enabled by the orthogonality of the reaction chemistry, hybrid and microstructured material compositions are prepared via the encapsulation of LCE epoxy micropatterns with free-radical polymerization of acrylate-based LCEs. The distinct thermomechanical response of the hybridized and microstructured LCE composites enables local and spatially controlled actuation.

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“…For the fabrication of shape memory CLC coatings, we designed a reactive liquid crystal mixture that is composed of a difunctional crosslinker 1 , monofunctional acrylates 2 and 3 , chiral dopant 4 , photoinitiator 5 , and a difunctional thiol 6 ( Figure a). The thiol acts as an oxygen inhibitor thereby allowing photopolymerization in air, and as a chain extender via radical thiol‐acrylate polymerization, thereby reducing the crosslinking density and lowering the T g to room temperature (vide infra) . The composition of the mixture was chosen such that a red reflective, deformable coating was obtained, but in principle any color is possible by varying the chiral dopant concentration .…”

Section: Resultsmentioning

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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Synthesis of Elastomeric Liquid Crystalline Polymer Networks via Chain Transfer

Cited by 72 publications

References 40 publications

Curvature by design and on demand in liquid crystal elastomers

Curvature by design and on demand in liquid crystal elastomers

Microstructured Photopolymerization of Liquid Crystalline Elastomers in Oxygen‐Rich Environments

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

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