N. L. Levshin

Structural phase transitions in langmuir liquid crystal films

The isotherms of water molecule absorption on hyperfine Langmuir films made based on liquid crystals are investigated. A sharp increase in the adsorption capacity of the films at temperatures of 75°C (for a film with a thickness of ten monolayers) and 102°C (for a film with a thickness of five monolayers) has been revealed. This behavior is explained by structural phase transitions that take place at these temperatures.

A study of the influence of methanol and iodine molecule adsorption on the conductivity of Langmuir films of TDOB AM BCC liquid crystals

This paper studies the influence of adsorption of methanol and iodine molecules on the conductivity of para-tetradecyloxybenzyliden-amino-2-methylbutyl-cyanocinnamate that was obtained using the Langmuir-Blodgett method. The growth of conductivity of the studied films at methanol absorption and the reduction of conductivity upon iodine absorption was discovered. An explanation of the observed conductivity variation at adsorption is proposed.

Study of the conductance of ultrathin tin diphthalocyanine films

The frequency dependences of the conductance and capacitance of Langmuir-Blodgett tin diphthalocyanine films in vacuum and in the case of adsorption of water molecules were studied. An increase in the film conductance due to adsorption was detected. Possible conduction mechanisms of tin diphthalocyanine in vacuum and water vapor are discussed. The permittivity of tin diphthalocyanine films was estimated from an analysis of the frequency dependence of the capacitance.

Structural phase transition in Langmuir films of vanadyl phthalocyanine

The Langmuir-Blodgett films based on vanadyl phthalocyanine (NHSO2C18H37)4 were studied. By the method of piezoresonance quartz balance, the isotherms of adsorption of water, pyridine, and hexane on film surfaces were obtained. A structural phase transition in the Langmuir films of vanadyl phthalocyanine at about 313 K was revealed. The phase transition was observed in ultrathin films and disappeared as the number of layers increased.

Changes in Optical Properties of TDO BAM BCC Langmuir Films during a Phase Transition

The isotherms of water molecule adsorption and the spectra of absorption, diffusion reflection, and polarization of reflected light for hyperfine Langmuir films that were fabricated based on liquid crystals are investigated. Singularities in the reflection spectra at the temperature of the structural phase transition (∼70°C) are revealed. Some reasonable assumptions on the nature of the phase transition are made.

Changes in adsorption and optical properties near the phase transition of super thin vanadyl phthalocyanine Langmuir films

Structural transition in thin vanadyl-phtalocyanine films deposited by Langmuir technology was studied in detail with the help of the vacuum adsorption and optical spectroscopy techniques. The reversible structural transition observed only in super-thin Langmuir films is accompanied by nonreversible changes during heating. This transformation of the film having defects and amorphous regions occurs during the film transition from a metastable state to a more stable one that is characterized by a lower free energy.

Effect of gas phase adsorption on the conductivity of Langmuir-Blodgett films of vanadyl phthalocyanine

Frequency dependences are obtained of the conductivity in Langmuir films of modified vanadyl phthalocyanine in vacuum and under the conditions of adsorption of donor and acceptor molecules. It is found that, upon the adsorption of NO2 and CH4O molecules, the film conductivity at f < 10 kHz increases by several orders of magnitude. It is shown that, in vacuum and upon adsorption of acceptor molecules, the dominant charge transfer mechanism is the hopping of holes via localized states. In the case of adsorption of donor molecules, the ionic conductivity mechanism appears to prevail.

Effect of reversible adsorption of water molecules on the magnetic susceptibility of iron borate

A change in the quasistatic magnetic susceptibility in thin plates of iron borate (FeBO3), which is a weak ferromagnet, has been revealed at adsorption of water molecules. The measurements have been performed at room temperature with the use of the magneto-optical Faraday effect. The change of the susceptibility in saturated water vapors is about 30%. The observed effect is reversible. The time of establishing the susceptibility after the introduction of water vapors is 1.5 min, which is twice as large as the time of establishing the susceptibility after the evacuation. The effect is explained by the appearance of uniaxial surface magnetic anisotropy in the basal plane because of the adsorption of water molecules.

Effect of the Texture of Langmuir Copolymer Films on Structural Phase Transitions

An atomic-force microscopy study has surprisingly revealed that ultrathin copolymer films fabricated according to Langmuir technology constitute a network of tangled filaments. A long-range order is absent in the samples. The observed filaments consist of several parallel-packed copolymer chains. The shape of ferroelectric domains in a film is independent of the direction of copolymer chains. Each domain includes a large number of filaments. The nature of high-temperature (ferroelectric) and low-temperature phase transitions has been discussed in terms of structural data.

Effect of the synthetic procedure on the properties of thin films of liquid crystals

Liquid-crystal films prepared by different procedures and having different thicknesses were studied. A structural phase transition was found in these films at ∼75°C. The nature of this transition was examined by investigating the temperature dependences of the electric capacity and conductivity of the films; the optical absorption and reflection spectra were also studied. It was concluded that the samples contained a ferroelectric phase. The structure of the films was studied by atomic force microscopy. As a result of the structural studies, the peculiarities of the temperature dependences of conductivity and capacity, in particular, the temperature range in which the phase transition was observed were explained.