We report the light beam action on the nematic liquid crystal film with a free surface. It was found that a weak light absorption by the liquid crystal substrate dramatically changes the orienting properties of the light beam; in particular, a thermal gradient field induces an umbilical defect formation.

Wormlike micelles (WLMs) of surfactants with rheological properties highly responsive to pH are of growing interest for various applications. The present paper proposes an approach to enhance their rheological properties and make the pH-response more pronounced. It consists of the incorporation of a percolated network of cellulose nanocrystals (CNCs) into the solution of entangled WLMs. To provide pH-responsiveness, potassium oleate was used as a surfactant. Rheological studies demonstrated that CNCs increase the viscosity and storage modulus by one order of magnitude. This effect was attributed to the interaction of WLMs with nanocrystals and the formation of entanglements of WLMs with percolated CNCs. Moreover, added CNCs make the pH-response stronger. The lowering of pH from 10.1 to 9.7 leads to a sharp drop in viscosity by ca. 2000 Pa·s, which is much higher than the decrease in viscosity of the WLM solution without CNCs. According to SANS data, the drop in viscosity is due to the transformation of WLMs into vesicles. It occurs as a result of the protonation of surfactant carboxylic groups decreasing surface charge on the micelles. In the presence of CNCs, the transition pH shifts to an alkaline medium, indicating that CNCs promote vesicle formation. Also, CNCs cause some of the vesicles to aggregate with each other, as follows from dynamic light scattering and optical microscopy data. Both observations suggest an interaction between CNCs and vesicles, which is supported by ITC data. These findings are valuable for the research and development of high-performing surfactant-based products.

Wormlike micelles (WLMs) of surfactants are widely used as smart thickeners in various applications, including enhanced oil recovery. However, their thickening ability needs to be improved both at ambient and elevated temperatures. In the present paper, we propose to enhance the viscoelastic properties of surfactant solutions by incorporating carboxymethylated cellulose nanocrystals (CNCs). Upon addition of CNCs, dilute solutions of short WLMs acquire viscoelasticity and then transition into a viscoelastic solid state. This process is accompanied by an increase in the viscosity and storage modulus by up to five and four orders of magnitude, respectively. The observed effect of CNCs on the storage modulus and viscosity is greater than that of any of the previously studied WLM-CNC systems. It is attributed to the formation of a network of fibrillar-like aggregates composed of WLMs and CNCs, which was confirmed by cryo-TEM data. To our knowledge, such kind of aggregates have not been observed before. When CNCs are added to a transient network of long entangled WLMs, the viscoelastic solution transitions into a viscoelastic solid state, which results in an increase in the viscosity and storage modulus by up to two orders of magnitude. CNCs provide the WLM solution with greater resistance to heating, such that the storage modulus remains almost unchanged when the temperature increases from 20 to 70 °C. Moreover, a heat-induced gelation was observed. It was shown that higher concentrations of nanocrystals lower the critical gel temperature, indicating that they promote the gelation of the mixture. SANS data revealed that the local structures of both micelles and nanocrystals are preserved in the mixed system upon heating. According to ITC data, at room temperature, the interaction between surfactant ions and similarly charged nanocrystals is governed by both enthalpy and entropy, which suggests that hydrogen bonding plays a major role in this process, although hydrophobic interactions may also be involved. When the temperature increases to 60 °C, the aggregation becomes entropy-driven, indicating that hydrophobic interactions begin to dominate. The results obtained can expand the range of practical applications of WLMs as thickening agents, in particular, to higher-temperature conditions in deeper oil wells.