External stimulus driven variable-step grating in a nematic elastomer

Abstract

We report on the creation of micro-patterns in an oriented nematic elastomer (an artificial muscle material) by photopolymerization of surface aligned nematic liquid crystal monomers. We demonstrate that microscopic techniques are able to create accurate patterns in rubber-like liquid crystal materials. Two approaches, based on one and two-photon excitations respectively, are implemented using a microscope-based setup. Due to its high spatial selectivity, the two-photon excitation mode yields finer patterns. Benefitting from the intrinsic, thermally-induced, contractile properties of the material, gratings with variable steps in response to temperature changes were fabricated.

Conventional elastomers doped with benzophenone derivatives as effective media for all-optical fabrication of tunable diffraction elements

“…It is noteworthy that the VDGs presented here are sufficiently simpler in terms of materials comparing with elastic HPDLCs 19 and azobenzenecontaining liquid crystalline elastomers. 20a, 32,33 In the terms of the gratings performances we can sign out the following advantages of our elastic VDGs: higher efficiency (up to $100% in one order); higher spatial resolution (of about 140 nm for the reection gratings, as will be demonstrated below); higher fully reversible tunability (more than 100%, depending on the used elastomer); no degradation of the grating performances at elevated temperatures and non-sensitivity to light polarization. Comparing with alternative methods for the production of elastic gratings, e.g.…”

Mechanical Manipulation of Diffractive Properties of Optical Holographic Gratings from Liquid Crystalline Elastomers

“…This corresponds to the increase of the critical exponent ζ= 1/(γ − 1) and the decrease of the parameter A in Equation (4). To illustrate the associated effects, the dependences of n e (T,T 0 ,ε ⊥ ) and n e (T,T 0 ',ε ⊥ ) corresponding to γ' = γ/2 = 2.4 and A' = A/10 = 0.008 for the unilluminated and for the UV-illuminated strained material are shown as dashed lines in Figure 8b.…”

“…Straining in the direction perpendicular to n0 in its initial stage (before reaching the plateau region in the σ(ε⊥) curve) causes a decrease of the internal strain, and consequently also a decrease of the order parameter S [39]. This corresponds to the increase of the critical exponent ζ= 1/(γ − 1) and the decrease of the parameter A in Equation (4). To illustrate the associated effects, the dependences of ne(T,T0,ε⊥) and ne(T,T0',ε⊥) corresponding to γ' = γ/2 = 2.4 and A' = A/10 = 0.008 for the unilluminated and for the UV-illuminated strained material are shown as dashed lines in Figure 8b.…”

“…As optical holographic materials, they show many intriguing properties. For instance, they exhibit recording sensitivity that is several orders of magnitude larger than conventional (non-liquid crystalline) elastomers containing similar photoisomerizable moieties [4][5][6][7][8][9]. The recording process takes place in a very nonlinear manner that allows an intricate control over the spatial structuring of the refractive index modulation.…”

“…In LS-LCEs, illumination with ultraviolet (UV) light affects the stress-strain relationship in a similar manner as heating, i.e., it causes a decrease of the liquid crystalline order that is governed by the illumination intensity [2,[18][19][20]. The experiments exploring this effect are usually performed either with homogeneous or with macropatterned UV illumination generated with the use of photolithographic masks [4,13,[21][22][23], while in our study, we used micropatterned UV illumination generated by holographic lithography.…”