M. A. Moskvina

Study of phase transitions in highly dispersed systems of tridecanoic acid-oriented polymer matrix*

Polarization IR spectroscopy and differential scanning calorimetry were used to study the effect of temperature upon the orientation and state of tridecanoic acid, crystallized in oriented polymer matrices of PE and PTFE; these were obtained by elongation of polymers in n-propanol—an adsorption-active medium. In polymer micropores tridecanoic acid in the temperature range studied (between 15° and T melt =38–39°) is in the C −-form, which is thermodynamically stable in the conventional state above 34°. In the range below T melt the structure of tridecanoic acid is less ordered, compared with the structure in volumetric crystals. Above T melt the state of tridecanoic acid in PE and PTFE matrices, on the other hand, is of higher order than in a free melt at the same temperature. Melting of tridecanoic acid in micropores of polymer matrices studied takes place in a much wider temperature range than for its macrocrystals.

Preparation method for noble metal-polymer matrix nanocomposites

A method is described for the preparation of new nanocomposites based on poly(ethylene terephthalate), poly(vinyl chloride), and polypropylene on the one hand and on noble metals (Ag and Pt) on the other. The method comprises the formation of nanoporous polymer matrices by crazing the polymers with simultaneous incorporation of noble metal precursors (AgNO3 or H2PtCl6) into the matrices. Subsequent in situ reduction of the precursors yields the metal-polymer nanocomposites. Prospects for the practical application of the developed method for the production of metal-polymer nanocomposites are discussed.

Structure and optical characteristics of the polymer-dye composites prepared via solvent crazing

Optical characteristics of the composites based on an amorphous polymer and a luminescent dye [poly(vinyl chloride)-Rhodamine 6G] prepared via solvent crazing are studied. After annealing at temperatures above glass transition temperature T g, the samples show a dramatic increase in the intensity of absorption and luminescence bands of Rhodamine Y and a marked decrease in light scattering. The observed changes are due to the diffusion of dye molecules in the polymer matrix and healing of the porous structure of crazes. The above processes are independent and proceed simultaneously. As a result, transparent composites with a low level of light scattering and with a uniform distribution of dye molecules in the polymer matrix are formed. When the PVC-Rhodamine 6G samples are annealed at temperatures above T g, dramatic changes in their spectral luminescent characteristics and color allow the above composites to be considered specific photochromic materials.

Phase state of cetyl alcohol in micropores of oriented polymer matrices

Abstract The results of the DSC investigations show that the phase composition of cetyl alcohol (CA) in the highly dispersed state in micropores of HDPE and PTFE polymer matrices differs markedly from that in the free state. Crystallization of CA from melts and solutions in the free state results in the formation of different low temperature modifications (the β- or γ-form), whereas crystallization in the studied polymer matrices under like conditions invariably takes place and results in a blend of the high-temperature α-form plus one of the two possible low-temperature β-forms. The ratio of the forms changes as filling of the micropores decreases (as the degree of dispersity of CA particles increases) in the direction of a higher content of the α-form.

Features of the development of amorphous-polymer-dye composites prepared via solvent crazing

The migration of dye molecules and healing of structural heterogeneities (internal interfaces) in an amorphous-polymer-dye system during thermal treatment are studied for the PVC-Rhodamine 6G composite prepared via the method of solvent crazing. The kinetic data on the above processes are collected through spectroscopic measurements in the visible spectral region and parallel measurements of the linear dimensions of the samples. During thermal treatment at temperatures above T g, dye molecules in the monomer modification migrate from the surface of the fibrillar craze material into the volume of the bulk polymer matrix; as a result, uniformly colored transparent samples form. In the general case, healing of the polymerdye composites includes two stages: a fast stage and a slow stage (∼1 and ∼2000 min at 85°C, respectively). The molecular mechanism of the first stage is related to the growth of the conformational entropy during shrinkage of the sample; as a result of this process, porosity decreases. The slow stage involves the disappearance of interfibrillar boundaries and occurs owing to the reptational mobility of macromolecules. The phenomenon of healing (in the broad meaning of this term) should be treated as a process that decreases the free surface energy of the polymer system.

The state of Cu2+ ions and highly dispersed CuS immobilized in PVA-PAA polymer matrix

Microheterogeneous water swelling polymer compositions containing highly dispersed semiconductive component CuS have been obtained on the basis of PVA-PAA mixtures. Average CuS particle size range is 8–13 nm. The formation of highly dispersed CuS phase takes place upon attraction of coordinately bonded (immobilized) Cu2+ ions and sulfide ions. The interaction occurs directly in polymer matrix bulk (in situ method). According to IR spectroscopy data, the state of Cu2+ ions in polymer matrix is characterized by formation of coordination centers with donor-acceptor and ionic bonds between Cu2+ and carboxylic groups of PAA. Structure characteristics of highly dispersed polymer-CuS compositions (particle size distribution, crystallite size, specific surface, concentration) and phase boundary intermolecular interactions type in polymer CuS compositions have been studied using X-ray scattering and IR spectroscopy methods. Such compositions possess rather high swelling (∼400 wt%) and under hydrogel state display good mechanical properties (E=0.6 MPa,σb MPa, ɛ=370%) and permeability (∼2 l/m2·h).

Orientation and phase trasitions of cetyl alcohol in micropores of oriented polymeric matrices

Abstract Orientation and phase transitions of cetyl alcohol confined within polymeric matrices of high-density polyethylene and polytetrafluoroethylene deformed in adsorption-active media have been investigated by polarization IR spectroscopy. Phase transitions of cetyl alcohol proceed within broad temperature intervals ∼ 25°C for melting and ∼ 15°C for the polymorphic transition), owing to the existence in the investigated systems of a broad pore size distribution and to a lowering of the transition temperature of highly dispersed cetyl alcohol. Both the entropy and enthalpy of melting of cetyl alcohol and tridecanoic acid entrapped in micropores of polymeric matrices are lowered in comparison with values observed for non-confined compounds.

The structure of polypropylene-TiO2 organoinorganic nanocomposites prepared via solvent crazing

A method is developed for crazing-based production of mechanically strong hybrid polypropylene film composites containing amorphous titanium dioxide nanophase (up to ∼30 wt %). As a whole, the morphology of the composite represents an interpenetrating network in which the inorganic component (TiO2) is distributed in the nanoporous structure of a polypropylene matrix. The structure and composition of amorphous titanium dioxide present an ensemble of TiO2 nanoparticles with a size of ∼1 nm (20 wt %) included in a loose network of titanium oxopolymers (80 wt %) containing ∼30 wt % side OC3H7 and OH groups bonded to titanium atoms.

Structure and properties of hybrid PP/TiO2 nanocomposites and mesoporous TiO2 prepared via solvent crazing

A new method for the preparation of hybrid film polymer PP/amorphous TiO2 nanocomposites and mesoporous crystal TiO2 (anatase) using the crazing phenomenon has been developed. The porous structure and the sorption activity thereof were investigated. The PP/TiO2 nanocomposite has an open-porous structure (Ssp = 5.5 m2/g; Dp = 12, 25, and >300 nm). The hydrophilic-hydrophobic balance of amorphous titanium dioxide in the PP/TiO2 nanocomposite provides significant sorption activity with respect to dye molecules upon sorption from both hydrophobic and aqueous media. The hydrophilic-hydrophobic balance of an inorganic photolytic sorbent, mesoporous crystal TiO2 (Ssp = 140 m2/g, Dp = 24 nm), can be changed by processing in an aqueous medium. The low-temperature nitrogen sorption by the PP/TiO2 nanocomposite was shown to be almost completely irreversible. One possible explanation for this unusual fact is associated with the formation of a thin dense film on the composite surface during the evaporation of nitrogen that prevents the removal of nitrogen from internal areas of the sample.

Specific features of the formation of polymer-dye systems based on nanostructured polymer matrices prepared by solvent crazing

Specific features of the formation of polymer-dye systems based on various nanostructured polymer matrices prepared by the method of solvent crazing are discussed. In the general case, the formation of polymer-dye composites includes four main stages: sorption of dye molecules by the highly disperse fibrillar material of crazes, shrinkage of the polymer composite due to the removal of the solvent, migration of dye molecules from their localized sites on the surface of fibrils, and healing of the structure of crazes (internal interfacial boundaries) under thermal treatment. Analysis of the migration of dye molecules in the polymer matrix includes the following assumptions: first, a metastable (nonequilibrium) state of the system after solvent crazing and introduction of dye molecules into the fibrillar craze material and, second, the statement according to which both the depth and direction of the above migration processes are controlled by the free energy of mixing of components. For amorphous glassy systems (PVC, PS, PC), healing of the fibrillar craze material (after shrinkage and removal of the solvent) is observed. In the case of semicrystalline polymers (PP, vinylidene fluoride-trifluoroethylene copolymer) and amorphous crystallizable polymer matrices (PET), the intensity of healing upon thermal treatment decreases due to the presence of crystalline regions, which slow down the motion of macromolecules.