Liquid crystalline elastomers (LCEs) are soft, anisotropic materials that exhibit large shape transformations when subjected to various stimuli. Here we demonstrate a facile approach to enhance the out-of-plane work capacity of these materials by an order of magnitude, to nearly 20 J/kg. The enhancement in force output is enabled by the development of a room temperature polymerizable composition used both to prepare individual films, organized via directed self-assembly to retain arrays of topological defect profiles, as well as act as an adhesive to combine the LCE layers. The material actuator is shown to displace a load >2500× heavier than its own weight nearly 0.5 mm.

Layer-by-layer (LbL) assembly has emerged as the leading non-vacuum technology for the fabrication of transparent, super gas barrier films. The super gas barrier performance of LbL deposited films has been demonstrated in numerous studies, with a variety of polyelectrolytes, to rival that of metal and metal oxide-based barrier films. This Feature Article is a mini-review of LbL-based multilayer thin films with a 'nanobrick wall' microstructure comprising polymeric mortar and nano-platelet bricks that impart high gas barrier to otherwise permeable polymer substrates. These transparent, water-based thin films exhibit oxygen transmission rates below 5 × 10(-3) cm(3) m(-2) day(-1) atm(-1) and lower permeability than any other barrier material reported. In an effort to put this technology in the proper context, incumbent technologies such as metallized plastics, metal oxides, and flake-filled polymers are briefly reviewed.

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.

Layer-by-layer (LbL) assembly of nanocoatings on fabric substrates has been very successful in terms of reduction of flammability. In particular, an LbL system comprised ammonium polyphosphate as the polyanion and chitosan as the polycation, applied to cotton fabric, dramatically reduced cotton flammability. At this point, the fire-retardant (FR) mechanism of action of this system has never been fully elucidated. Sonicated and nonsonicated coated cotton fabrics were evaluated using a vertical flame test and mass loss calorimeter. Coating morphology was investigated before and after burning. Thermal analyses and chemical analyses in the condensed phase (and in the gas phase) were conducted to reveal the FR mechanism of action. At the cotton surface, a combination of both condensed (formation of aromatic char) and gas phase (release of water and highly flammable gases) mechanisms impart the FR behavior, promoting a kind of "microintumescence" phenomenon.

distinctive due to the salient features of light that can allow remote and wireless activation, spatial and temporal control, and regulation via wavelength, intensity, and polarization. To date, photomechanical effects in photochromic polymeric materials have been predominately examined in azobenzene-functionalized compositions typified by a short-lived deformation (<24 h). [8] In end use implementations, the short-lived deformation will limit utility or require constant energy expenditure to maintain the desired shape reconfiguration. As such, there is an unmet need to develop photoresponsive polymeric materials capable of long-lived energy efficient deformations.The azobenzene moiety can be functionalized to exhibit liquid crystalline phases that undergo order-decreasing phototropic phase transitions with light irradiation. [9] By functionalizing azobenzene molecules with polymerizable groups such as acrylates, azobenzene-functionalized liquid crystalline polymer networks (LCNs; T g above room temperature) and elastomers have been synthesized and examined. For azobenzenefunctionalized LCNs and LCEs, light irradiation can induce isothermal disorganization. Specifically, the photoinduced trans→cis isomerization of azobenzene alters the geometric configuration of the chromophore in the macromolecular network. The result is photoinduced directional strain wherein the network contracts parallel to the nematic director and expands in the orthogonal directions. [9,10] Azobenzene-functionalized LCNs and LCEs have been demonstrated to exhibit photoresponsive shape reconfiguration, [11] responsive surfaces, [12] and motility. [13] Azobenzene-functionalized LCNs and LCEs have primarily been based on the copolymerization of acrylate monomers consisting of 2-30 wt% of the classical azobenzene chromophore. The short-lived photomechanical deformations of these materials are governed by the thermal relaxation of the azobenzene cis-isomer. Substitution of the azobenzene chromophore in the para-or ortho-positions of the molecule has been long known to influence the kinetics of the cis→trans isomerization. [10a,14] Of particular relevance to our interest in realizing long-lived and all-optical control of shape are prior examinations detailing substitutions that increase the lifetime of the cis-isomer. [15] Recently, ortho-fluorination of azobenzene has been presented as a method to produce stable cis-isomers with a dramatic half-life of approximately 700 days. [16] The small size of the fluorine substituents leads to minimal distortion of the planar azobenzene structure, making this an ideal approach for the preparation of azobenzene-functionalized LCNs and LCEs with long-lived macroscopic shape changes. Photoresponsive liquid crystal elastomers (LCEs) are a unique class of anisotropic materials capable of undergoing large-scale, macroscopic deformations when exposed to light. Here, surface-aligned, azobenzene-functionalized LCEs are prepared via a radical-mediated, thiol-acrylate chain transfer reaction. A long-lived, macrosc...