E. V. Rusinova

Phase transitions of hydroxypropylcellulose liquid-crystalline solutions in magnetic field

The phase transitions and the phase state of hydroxypropylcellulose-DMAc and hydroxypropylcellulose-ethanol solutions both under an applied magnetic field and in its absence have been studied via the cloud-point method, polarization microscopy, and polarization-photoelectric measurements. The magnetic field changes the structure of solutions and increases the phase transition temperature. The higher the field strength, the more pronounced this effect. As the molecular mass of the polymer grows, the ability of its macromolecules to orient in the magnetic field tends to increase. Hydroxypropylcellulose solutions fall into the family of memory systems. When the magnetic field is switched off, the orientation of macromolecules and the increased phase transition temperature are preserved for many hours.

Thermodynamics of liquid-crystalline solutions of hydroxypropyl cellulose in water and ethanol

Phase diagrams were constructed and comprehensive thermodynamic analysis was performed for hydroxypropyl cellulose-water and hydroxypropyl cellulose-ethanol systems with the use of the static sorption, calorimetry, cloud-point, polarization microscopy, and X-ray diffraction analysis techniques and the measurement of transmitted polarized light intensity. The concentration dependences of the enthalpy, entropy, and Gibbs energy of the formation of liquid-crystalline phases in the systems were determined. It was found that the formation of liquid-crystalline solutions of hydroxypropyl cellulose in water is associated with the energy term of interaction between the components and that in ethanol solutions is due to changes in combinatorial entropy.

Effect of Magnetic Field on Phase Transitions in Solutions of Cellulose Derivatives

LC transitions occurring in mixtures of cyanoethyl cellulose with DMAA or DMF and hydroxypropyl cellulose with ethanol, DMAA, or water in the presence and absence of magnetic field have been studied. With an increase in the polarity of solvent molecules and a decrease in the molecular mass of the polymer, the LC phase develops at higher concentrations and lower temperatures. Under application of magnetic field, the domain structure is formed in solutions and the temperature-concentration region of the LC phase widens. Cyanoethyl cellulose and hydroxypropyl cellulose solutions are found to possess memory: after the magnetic field is switched off, the orientation of macromolecules and the increased temperature of phase transitions are preserved for many hours. As the molecular mass of the polymer is increased, the ability of macromolecules to orient themselves in the magnetic field declines. The threshold mechanism governing the effect of magnetic field on LC transitions in polymer solutions has been discovered. The critical value of magnetic intensity that brings about a shift in boundary curves is consistent with the value of H cr necessary for the cholesteric liquid crystal-nematic liquid crystal phase transition.

Phase transitions in liquid-crystalline cyanoethyl cellulose solutions in magnetic field

The cloud-point method and polarization microscopy have been used to investigate the phase transitions and the phase state of cyanoethyl cellulose-dimethylacetamide and cyanoethyl cellulose-dimethylformamide systems in the presence and absence of magnetic field with the help of polarization photoelectric and magnetic setups. The temperature-concentration region of the existence of the liquid-crystalline phase in solutions widens in the magnetic field; the higher the field strength and polymer concentration, the more pronounced this widening. Cyanoethyl cellulose solutions are found to possess “memory”: after the magnetic field is switched-off, the orientation of macromolecules and the increased phase transition temperature are preserved for many hours.

Phase liquid-crystalline transitions in hydroxypropylcellulose-ethanol and hydroxypropylcellulose-acetic acid systems under deformation

The phase transitions and phase state of hydroxypropylcellulose mixtures with ethanol and acetic acid under static conditions and in the shear field have been studied by the turbidity-point method and polarization microscopy with the use of a polarization-photoelectric setup and a modified plastoviscometer. The deformation of solutions leads to a decrease in the temperature of mesomorphic phase formation and to a change in the type of liquid crystals from cholesteric to nematic.

Phase transitions in solutions of hydroxypropoyl cellulose and cyanoethyl cellulose

LC phase transitions in mixtures of cyanoethyl cellulose and hydroxypropyl cellulose with different solvents have been studied by the cloud point and polarization microscopy methods and polarization photoelectric measurements. It has been found that, as the solvent polarity is decreased and the molecular mass of a polymer is increased, boundary curves delimiting the regions of isotropic and anisotropic solutions shift to the region of lower concentrations.

Phase transitions in liquid crystalline solutions of hydroxypropyl cellulose under deformation

Phase transitions and the physical state of the hydroxypropyl cellulose-dimethylacetamide system under static conditions and in a shear field were studied by the cloud-point and polarized optical microscopy techniques with a polarization-photoelectric setup and a modified plasticorder. The deformation of solutions leads to a change in their structure and elevation of liquid-crystalline phase formation temperatures, a result that is due to the additional orientation of macromolecules in the flow direction. The ability of macromolecules to be oriented in a shear field decreases with an increase in the molecular mass of the polymer. The influence of deformation on phase transitions in hydroxypropyl cellulose solutions is nonmonotonic in character.

Phase transitions in solutions of polystyrene with poly(methyl methacrylate) and polybutadiene under deformation

By the cloud point and static sorption methods, phase diagrams are constructed and the concentra- tion and temperature dependences of the Gibbs free energy of mixing and the interaction parameter are deter- mined under static conditions and in a shear field for the poly(methyl methacrylate)-polystyrene-ethyl acetate, polystyrene-polybutadiene-toluene, polystyrene-polybutadiene, poly(methyl methacrylate)-polystyrene, poly(methyl methacrylate)-ethyl acetate, and polystyrene-ethyl acetate systems. Phase separation in the sys- tems both under heating and cooling, as well as coexistence of three phases, is observed in the polystyrene- poly(methyl methacrylate)-ethyl acetate system. Deformation changes the phase separation temperature by 30-40 K.