Influence of Orientational Genesis on the Actuation of Monodomain Liquid Crystalline Elastomers

Abstract

The macroscopic alignment of the nematic director within liquid crystalline elastomers (LCEs) amplifies the magnitude of the directional strain response. Theory predicts that the stimuli response of LCEs will be affected by the orientational genesis of cross-linking. We examine compositionally identical LCEs aligned by either mechanical or surface techniques. The two-step procedure to prepare LCEs by mechanical alignment first forms cross-links in a disordered state (e.g., isotropic orientational genesis), which thereafter are aligned by deformation during which polymerization (e.g., cross-linking) is completed. Comparatively, cross-linking within surface-aligned LCEs exclusively occurs within the ordered state (e.g., nematic orientational genesis). The orientational genesis of cross-linking in aligned LCEs, in compositionally identical samples, significantly affects the thermotropic and phototropic deformation of these materials. LCEs prepared by mechanical alignment (e.g., isotropic orientational genesis) have actuation temperatures that are as much as 75 °C lower than the analogous LCEs prepared by surface alignment (e.g., nematic orientational genesis). Likewise, the magnitude and rate of photoinduced strain generation in azobenzene-functionalized LCEs prepared by mechanical and surface alignment differ by a factor of 2 or greater.

Cell instructive Liquid Crystalline Networks for myotube formation

“…To be noted that the final properties of the LCNs are strictly dependent on both monomer composition and polymerization conditions, e.g. the temperature set during irradiation can modify the macroscopic properties of the films (Hebner et al, 2021) The materials tested in this study are called LCNx, where x (=10, 20 or 40) represent the % mol/mol of the cross-linker (RM257) present in the formulation. Increasing the amount of RM257 leads to a higher ll OPEN…”

Random Liquid Crystalline Copolymers Consisting of Prolate and Oblate Liquid Crystal Monomers

“…Liquid crystal elastomers (LCEs) capitalize on the interplay between the self-association of LC functional groups and the entropic conformation of polymer backbones, resulting in phase-dependent macroscopic shape deformations. − Past studies have shown that LCEs are capable of exhibiting a rich palette of reversible and well-programed anisotropic shape changes in response to a wide range of external stimuli, including heat, , solvents, light, − and magnetic , and electric fields and have attracted great interest for their potential in the design and synthesis of responsive biomedical devices, − soft actuators, robotics, − and active surface structures. − LC moieties can be incorporated into polymer chains as either part of the polymer backbone (main-chain LCE) or the pendant functional group (side-chain LCE). Previous studies have shown that in LC phases, the conformation of LC polymer chains can deviate from statistically spherical random coils, depending on the configuration of the pendant LC functional groups, as seen in Figure . ,, For prolate LC polymers, polymer backbones align along the orientation of the mesogenic groups (called the director), resulting in a longer radius of gyration parallel to the LC director ( R ∥ ) than that perpendicular to the LC director ( R ⊥ ).…”

Understanding the effect of liquid crystal content on the phase behavior and mechanical properties of liquid crystal elastomers

“…This was attributed to mesogen-mesogen interactions present in the nematic phase during crosslinking. 23,24 While these studies demonstrated that the T NI is dependent on a number of network properties and synthesis conditions, we lack a comprehensive understanding of how T NI varies in LCEs and how to predict changes in T NI for specific changes in network structure and chemistry.…”