In this study, we want to realize the influence of temperature on the ferroelectric liquid crystal flow and rubbing strength on the surface free energy of the polyimide thin film. The rubbing strength is determined by pile impress and the number of rubbing. The surface energy of the samples is measured. On the other hand the ferroelectric liquid crystal flow on the polyimide thin film was observed using a polarizing microscope. We found that the polyimide film treated by rubbing the surface properties will become non-uniformity. When the number of rubbing increased to a certain extent, polar energy is not changed, white disperse energy is continued to show fluctuations. In liquid crystal flow observation, we found that when the polyimide thin film temperature is low, the flow of ferroelectric liquid crystal is relatively slow, and its flow direction is in rubbing direction. When the polyimide thin film temperature is high, ferroelectric liquid crystal has two-dimensional flow. In addition to the direction of the original rubbing direction, but also increased the flow in the direction of the vertical rubbing.

Ces travaux de thèse ont porté sur des matériaux constitués de dispersions de particules colloïdales nanométriques, issues d'un matériau ferroélectrique, dans un cristal liquide chiral à phase smectique ferroélectrique. Ils ont pour but d'étudier les effets occasionnés par ces dispersions sur les propriétés du nanocolloïde, notamment celles liées à leur ferroélectricité. Cette étude a montré que les comportements mésomorphes et ferroélectriques de ces matériaux sont conservés. Une baisse de polarisation spontanée ainsi qu'un recul des températures des transitions ont été mis en évidence pour des faibles concentrations en NPs. Une "transition" de ces comportements a été observée pour une concentration critique au-delà de laquelle les particules s'agrègent pour former des amas au sein du milieu cristal liquide. Nous nous sommes intéressés ensuite à deux modes de relaxation diélectriques. Le premier lié aux mouvements de distorsions de l'hélice dans la phase ferroélectrique, le second aux mouvements de compression des couches smectiques de part et d'autre de la transition ferroélectrique-paraélectrique. Les comportements observés semblent être gouvernés par les modifications des propriétés visco-élastiques des nanocolloïdes, occasionnés par l'intercalation des nanoparticules entre les couches smectiques. / The present thesis work concerns materials made of dispersions of nanometric colloidal particles, from a bulk ferroelectric material, dispersed within a chiral smectic phase of a ferroelectric liquid crystal. The goal of this work is to study the effect of the dispersed nanoparticles over the nanocolloïd properties, specially the ones related to ferroelectricity. This study showed no change over mesomorphic and ferroelectric behavior of the materials. A decrease in spontaneous polarization and phase transition temperatures was found for low nanoparticle concentrations. A "transition" of these behaviors was observed for a critical concentration, beyond which, nanoparticles aggregate and form clusters inside the liquid crystal matrix. Afterwards, we have studied two dielectric relaxation modes. The first one related to distorsions of the helix in the ferroelectric phase and the second one to the compression movements of the smectic layers around the ferroelectric-paralectric transition. The observed behaviors seem to be due to modifications of the visco-elastic properties of nanocolloids, produced by intercalation of nanoparticles between the smectic layers.

The generation and application of human stem-cell-derived functional neural circuits promises novel insights into neurodegenerative diseases. These networks are often studied using stem-cell derived random neural networks in vitro, with electrical stimulation and recording using multielectrode arrays. However, the impulse response function of networks is best obtained with spatiotemporally well-defined stimuli, which electrical stimulation does not provide. Optogenetics allows for the functional control of genetically altered cells with light stimuli at high spatiotemporal resolution. Current optogenetic investigations of neural networks are often conducted using full field illumination, potentially masking important functional information. This can be avoided using holographically shaped illumination. In this article, we present a digital holographic illumination setup with a spatial resolution of about 8 µm, which suffices for the stimulation of single neurons, and offers a temporal resolution of less than 0.6 ms. With this setup, we present preliminary single-cell stimulation recording of stem-cell derived induced human neurons in a random neural network. This will offer the opportunity for further studies on connectivity in such networks.