Effects of photo-isomerizable side groups on the phase and mechanical properties of main-chain nematic elastomers

Abstract

A series of main-chain nematic liquid crystal elastomers containing various photo-isomerizable side groups branching from the main chain were synthesized. The effects of the side groups on the thermal phase and mechanical properties were explored.

Optimal Conditions for Efficient Photomechanical Response in Nematic Elastomers

“…The presently synthesized dithiol azobenzene monomer, OC6, (Scheme and Methods) was chosen to explore the wide range of T NI (from room temperature to ∼100 °C). In the case of the diacrylate azobenzene monomers used in previous studies, ,, the RM257 content must be reduced to maintain the total amount of acrylate, which commonly lowers T NI . As a result, T NI decreased from that of the reference LCE without azobenzene units, which corresponds to the present RLCE with T NI ∼ 70 °C.…”

“…As T increased further, the cis isomers thermally relaxed to the trans state, which appeared as a broad exothermic peak around 80 °C with the present T scanning rate. 8,44,45 Unfortunately, as a result, T NI-cis , which is T NI for the cis-rich state, were not clearly identified by the DSC chart because the inherently weak endothermic peaks may have overlapped with the above thermal cis-to-trans isomerization signal, in addition to noise. After the first heating up to 120− 130 °C, azobenzene units fully isomerized to the thermally stable trans state.…”

“…Indeed, such a relationship has been found in a series of analogue polydomain LCEs. 44 Similar results were observed for the present LCEs by plotting e r at T op with respect to T NI (Figure 7d). The resultant curve crudely expressed as From the mathematical viewpoint, the maximum point originates from the nonlinear shape of Q(T) close to the transition with 0 < ξ < 1; if ξ was 1 in an extreme case, ΔQ(T) would become constant at T > T NI-cis .…”

Photo‐Rewritable Glaring Patterns Composed of Stripe Domains in Nematic Elastomers

“…Diacrylate azobenzene monomer (MC2 in Figure 1a) was synthesized according to a previously reported method. [ 29 ] Thiol monomers, 2,2′‐(ethylenedioxy)diethanethiol (EDDET) and pentaerythritol tetrakis(3‐mercaptopropionate) (PETMP), were purchased from Sigma–Aldrich. Triethylamine (TEA, Sigma–Aldrich) was used as the Michael addition catalyst.…”

“…Thus, if the nematic order is reduced locally by other methods, the location of the stripe domain formation can be specified; that is, arbitrary patterns composed of regions with anisotropic diffusion (glaring) and transparency can be created. This may be possible on azobenzene-containing LCEs, [27][28][29] in which the nematic order is locally photo-controllable via the isomer contents of the azobenzene units. [30][31][32][33][34][35][36][37][38][39][40] By utilizing the reversibility between the trans and cis states, the patterns may become erasable and rewritable.…”