Bending Dynamics and Directionality Reversal in Liquid Crystal Network Photoactuators

Abstract

Liquid crystalline photoactuators typically bend toward the light source, driven by the isomerization of azobenzene. In samples with a relatively large thickness and high azobenzene loading such as LC photoactuators, intense optical beams are seen to be absorbed in spatially nonexponential ways. Here we show that the dynamics of the related mechanical behavior is also strongly nonlinear, where the actuator reaches a maximum bend before unbending again to its equilibrium deformed state. The effect is amplified when combined with actuators with an internal composition gradient, leading to a reversal of the bending direction away from the light source.

Reverse switching of surface roughness in a self-organized polydomain liquid crystal coating

“…To study these effects for polydomain liquid crystal coatings, we have developed a finite element model to predict the changes in 3D surface topography as a result of the director-dependent attenuation of UV light. It is assumed that the magnitude of the optomechanical effect is linearly proportional to the fraction of cis, n c (36). The coefficients of the photoinduced strain tensor with respect to the local coordinate system read « ph ij = P ij n c , with the local x 1 axis aligned with the directorñ.…”

Liquid-crystal photonic applications

“…Of course, as in every review article, it is impossible to list all the fascinating new scientific results or breakthroughs. Therefore, the authors apologize for not including some novel exciting phenomena or applications such as light-induced switching of LC polymers [1][2][3] or novel retardation structures such as broadband cholesteric filters. 4,5 0091-3286/2011/$25.00 C 2011 SPIE Numerous books and articles exist that deal with physical properties of LCs [6][7][8] and with display applications.…”

Photomechanical Response of Composite Structures Built from Azobenzene Liquid Crystal Polymer Networks

“…Since this work, considerable effort has pursued a variety of aspects of this unique means of transducing energy in primarily liquid crystalline materials. Notably, this research has expanded into looking at glassy, azobenzene-functionalized liquid crystal polymers [7][8][9][10][11][12][13][14][15][16]. To capture both elastomeric and glassy liquid crystalline systems, we refer to the broader area as azobenzene-functionalized liquid crystal polymer networks (azo-LCN) and emphasize the glassy or elastomeric nature of the given chemistry.…”

“…Photomechanical responses in azo-LCN materials have been most often observed as uniaxial contraction of a film (typically elastomers-large strain) [6,[17][18][19] or bending of a cantilever (typically glasses-lower strain) [7][8][9][10][11][12][13][14][15][16]. The magnitude or directionality of the photomechanical response of azo-LCN materials has repeatedly been controlled by the alignment of the linear polarization of the actinic source and the sample geometry [8,9,11,12,[14][15][16].…”

“…The magnitude or directionality of the photomechanical response of azo-LCN materials has repeatedly been controlled by the alignment of the linear polarization of the actinic source and the sample geometry [8,9,11,12,[14][15][16]. Theoreticians have found the unique blend of polymer physics, photochemistry, and mechanics a rich challenge [18,[20][21][22].…”