Thermomechanical properties of monodomain nematic main-chain liquid crystal elastomers

Abstract

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.

Molecularly‐Engineered, 4D‐Printed Liquid Crystal Elastomer Actuators

“…Control of LCE properties, such as transition temperatures and actuation strain, can be achieved by varying the thiol chain extender, crosslinker, and/or mesogen concentration . We first varied the crosslinker concentration within the inks (0.1, 0.2, 0.4, and 0.6 molar ratio) (Table S1, Supporting Information) while maintaining EDDT as the chain extender and RM82 as the mesogen.…”

Body‐temperature shape‐shifting liquid crystal elastomers

“…A two-stage Michael Addition and Photopolymerization scheme was applied to fabricate the LCE (Figure 1), as described in previous studies. 3,27 The constituent F I G U R E 1 (a) Schematic of the chemicals used in the fabrication of LCE. A two-stage fabrication scheme was employed -first Michael Addition reaction, followed by a radical Photopolymerization reaction.…”

“…Unfortunately, for potential biomedically-related applications, the nematic-isotropic transition temperature is typically upwards from 70 C. 27,28 Recently, only a few researchers have reported LCEs that undergo nematicisotropic transition at a lower temperature. 16,28 Inoue et al fabricated a novel LCE system that shifts diffusivity, rather than shape, at body temperature.…”

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

“…These results are in good agreement with the DSC results. Furthermore, the tan δ peak values were approximately 1.6 times greater than those of the LCEs with a high crosslink density, which implies that these samples have higher damping capabilities compared with the LCEs having a higher crosslink density [ 25 ].…”

“…More recently, extensive studies on LCE synthesis have been reported based on diacrylate-, divinyl-, or diglycidyl-functionalized LC monomers (so-called reactive mesogens). These monomers can first be chain-extended using alkyl dithiols [19][20][21][22][23][24][25][26][27][28], alkyl amines [29][30][31], or alkyl dicarboxylic acids [32,33], and then they can be crosslinked in the presence or absence of multifunctional crosslinkers to obtain main-chain LCEs. One of the major advantages of the above-mentioned method is that various LC alignment methods can be integrated during LCE synthesis.…”