Liquid Crystal Elastomer Based Novel Functional Materials
Doctor of Philosophy
Liquid crystal elastomers (LCEs) are fascinating materials in which the elasticity of polymer network is coupled to liquid crystalline (LC) order and exhibits rich behavior under various stimuli such as heat, light, electric and magnetic fields. Previous studies were helpful in understanding isolated properties of bulk LCEs under static conditions and large-strain deformation. In this thesis we focused on the development of new functional materials based on LCEs and gaining new insight into their mechanical properties under dynamic deformations. In chapter-2&3, LCE based buckling instability in thin films is discovered and found to be useful for nanoscale thin film metrology (down to 30nm). This overcomes the limitations of earlier known techniques that require clamping and mechanically straining of films and present challenges with small samples. For thick PS films (over 500nm), well-defined self-folding 3D dynamic structures (like lotus or helix) are achieved just by engineering film patterning on LCEs. The phenomena are quantitatively captured through FEM simulations and could be used to predict the film patterning on LCE to achieve desired 3D deformed structure. In chapter-4 a LCE based dynamic wrinkling instability is demonstrated by synthesizing an electrically conductive LCE nanocomposites (LCE-NCs) using a new two-step approach. LCE-NCs exhibit rapid (response times as fast as 0.6 s), large-amplitude (up to 30 %), and fully reversible shape changes (stable to over 5000 cycles) under externally applied voltages (5 – 40V) via joule heating. Neonatal rat ventricular myocytes were cultured on LCE-NCs substrates, and good cell attachment and viability is observed. LCE-NCs provide a straightforward and scalable route to investigate cell response to a dynamically changing surface pattern. In chapter-5 a novel self-stiffening behavior in LCEs is discovered, a dramatic 90% increase in stiffness is observed under low-amplitude, repetitive (dynamic) compression. Such stiffening behavior is common in biological tissues but rare in synthetic elastomers. Combination of rheological measurements, optical microscopy, 2D- WAXD and FEM simulations, demonstrates dynamic stiffening is due to rotation of the nematic director under repetitive compression. The use of low-strain, repetitive compression represents a facile method to prepare uniformly aligned LCEs and finds applications in biocompatible, adaptive materials for tissue replacement.
Liquid crystal elastomers; functional materials