University of Wyoming, Department of Mechanical Engineering, Laramie, WY, USA.
Soft Matter. 2018 Jul 25;14(29):6024-6036. doi: 10.1039/c8sm01178h.
Two-stage thiol-acrylate Michael addition reactions have proven useful in programming main-chain liquid crystal elastomers (LCEs). However, the influence of excess acrylate concentration, which is critical to monodomain programming, has not previously been examined with respect to thermomechanical properties in these two-stage LCEs. Previous studies of thiol-acrylate LCEs have focused on polydomain LCEs and/or variation of thiol crosslinking monomers or linear thiol monomers. This study guides the design of monodomain LCE actuators using the two-stage methodology by varying the concentration of mesogenic acrylate monomers from 2 mol% to 45 mol% in stoichiometric excess of thiol. The findings demonstrate a technique to tailor the isotropic transition temperature by 44 °C using identical starting monomers. In contrast to expectations, low amounts of excess acrylate showed excellent fixity (90.4 ± 2.9%), while high amounts of excess acrylate did not hinder actuation strain (87.3 ± 2.3%). Tensile stress-strain properties were influenced by excess acrylate. Linear elastic behavior was observed parallel to the director with modulus increasing from 1.4 to 6.1 MPa. The soft elastic plateau was observed perpendicular to the director with initial modulus and threshold stresses increasing from 0.6 MPa to 2.6 MPa and 14 kPa to 208 kPa, respectively. Overall, this study examines the influence of excess acrylate on mechanical properties of LCE actuators.
两步巯基-丙烯酸酯迈克尔加成反应已被证明在主链液晶弹性体（LCE）的编程中非常有用。然而，对于单畴编程至关重要的丙烯酸酯过量浓度对这些两步 LCE 的热机械性能的影响之前尚未进行研究。之前对巯基-丙烯酸酯 LCE 的研究主要集中在多畴 LCE 上，或者改变硫醇交联单体或线性硫醇单体。本研究通过在硫醇的化学计量过量中，将介晶性丙烯酸酯单体的浓度从 2mol%变化到 45mol%，使用两步法指导单畴 LCE 致动器的设计。研究结果表明，使用相同的起始单体，通过 44°C 的各向同性转变温度来调整技术。与预期相反，少量过量的丙烯酸酯表现出极好的固定性（90.4±2.9%），而大量过量的丙烯酸酯并不妨碍致动应变（87.3±2.3%）。过量的丙烯酸酯会影响拉伸应力-应变性能。在与指向矢平行的方向上观察到线性弹性行为，其模量从 1.4 MPa 增加到 6.1 MPa。在垂直于指向矢的方向上观察到软弹性平台，初始模量和阈值应力分别从 0.6 MPa 增加到 2.6 MPa，从 14 kPa 增加到 208 kPa。总的来说，本研究考察了过量丙烯酸酯对 LCE 致动器机械性能的影响。
