Kaufman, Jack and Gortz, Verena (2022) Confinement of Nematic and Chiral Nematic Systems and Their Response to External Stimuli. PhD thesis, Lancaster University.
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Abstract
In this thesis, several examples of responsive liquid crystal elastomer microparticles are reported, as well as chiral nematic films. Bipolar nematic liquid crystal elastomer particles were of significant interest due their reversible shape change at the liquid crystal to isotropic phase transition. Furthermore, a spontaneous deformation of spherical droplets into spindle shaped particles upon irradiation with UV light was investigated. The spontaneous deformation and resulting particle surface morphology was studied to elucidate the phenomenon. Droplets and particles were subjected to external stimuli such as temperature and magnetic fields to produce samples with polar alignment not seen before in the literature. In addition, a microfluidic method is reported for the introduction of nanoparticles into bipolar nematic droplets with greater control of both droplet diameter as well as the number of nanoparticles within droplets compared to methods previously reported. To achieve this, polymer nanoparticles were dyed with fluorescent dye and suspended in organic solvent so that they were compatible with the microfluidic inner phase containing nematic monomer, photoinitiator and crosslinker in chloroform, to which they were added. After photopolymerisation, yielding nanoparticle infiltrated elastomer microparticles, we demonstrated, for the first time, a reversible shape change response to temperature of nematic elastomer microparticles with localised nanoparticles, an initial step for applications of these materials within areas such as micromechanics and soft robotics. Finally, doped chiral nematic systems were produced in the form of elastomer film and microparticle optical reflectors, and in some cases the dopant was extracted to produce chiral imprinted elastomers. Chiral doped monomer systems with tuneable selective reflection colours across the whole visible spectrum at room temperature are reported along with their responsiveness to temperature and pressure. Elastomer microparticles exhibited high quality optical properties after polymerisation, due to preserved internal mesogen alignment stemming from the particle size, monodispersity and overall quality of the droplets produced using our microfluidic method.