Effect of Isomeric Amine Chain Extenders and Crosslink Density on the Properties of Liquid Crystal Elastomers

Abstract

<jats:p>Among the various types of shape changing materials, liquid crystal elastomers (LCEs) have received significant attention as they can undergo programmed and reversible shape transformations. The molecular engineering of LCEs is the key to manipulating their phase transition, mechanical properties, and actuation performance. In this work, LCEs containing three different types of butyl groups (n-, iso-, and sec-butyl) in the side chain were synthesized, and the effect of isomeric amine chain extenders on the thermal, mechanical, and actuation properties of the resulting LCEs was investigated. Because of the considerably low reactivity of the sec-butyl group toward the diacrylate in the LC monomer, only a densely crosslinked LCE was synthesized. Most interestingly, the mechanical properties, actuation temperature, and blocking stress of the LCEs comprising isobutyl groups were higher than those of the LCEs comprising n-butyl groups. This difference was attributed to the presence of branches in the LCEs with isobutyl groups, which resulted in a tighter molecular packing and reduced the free volume. Our results suggest a facile and effective method for synthesizing LCEs with tailored mechanical and actuation properties by the choice of chain extenders, which may advance the development of soft actuators for a variety of applications in aerospace, medicine, and optics.</jats:p>

Surface‐Enforced Alignment of Reprogrammable Liquid Crystalline Elastomers

“…For surface aligned LCEs, one of the most commonly studied monomer systems is composed of acrylate‐based liquid crystalline monomers with a primary amine as a comonomer, enabling two‐step processing via aza‐Michael oligomerization and subsequent photopolymerization of acrylate‐terminated oligomers. [ 24 , 25 , 26 ] A similar approach using thiol‐Michael oligomerization and subsequent photopolymerization of acrylate‐terminated oligomers has been previously used to fabricate LCEs by mechanical alignment and additive manufacturing techniques. [ 12 , 27 , 28 , 29 , 30 , 31 ] In this approach, using dithiols as comonomers enables variation of the spacer length and properties when a thiol‐Michael reaction is used to generate linear chains in the polymer before crosslinking.…”

Programmable Shape Change in Semicrystalline Liquid Crystal Elastomers

“…LCE materials generating higher blocking stress have been reported. To our knowledge, there are no reported LCEs capable of generating this high blocking stress at such low temperature values and over such a narrow temperature range. ,,, Actuation strain of an unconstrained semicrystalline LCE sample was also measured using an iso-force test (Figure C). On heating up to 50 °C, LCE films exhibit an actuation strain (contraction) of 0.56 ± 0.07% along the nematic director.…”

Human organ phantoms for catheterization using the radiation crosslinking technique

“…The compressive modulus increased with the increasing radiation dose. Crosslinking density (n) of PVA can be estimated by the following equation 33 :…”

“…The compressive modulus increased with the increasing radiation dose. Crosslinking density (n) of PVA can be estimated by the following equation 33 : where R is the gas constant (8.314 J K −1 mol −1 ) and T is the measurement temperature of 298 K (25°C). It can be seen that as the radiation dose increases, the modulus increases, that is, the crosslinking density increases.…”