No abstract

The isothermal rise in supermolecular order (SMO) in aqueous solutions of poly (vinyl alcohol) (PVA) over a wide range of temperature and concentration and also under shear has been studied. SMO was characterized by the equivalent average radius of super‐molecular particles (SMP) rΛ, estimated by the turbidity spectrum τ = τ(Λ). The methods of gradient dependence of viscosity electron and polarize‐optical microscopy, and light scattering according to Debye‐Zimm have also been used. It is shown that the process of isothermal rising of SMP over a wide range of temperature and solution concentration consists of two distinct stages: a relatively rapid rise and then a slow rise of SMP. In aqueous PVA solutions SMO represents, generally, the hierarchy of some its levels. The first level is considered to be the supermolecular particles, which form after the dissolution of the whole polymer mass. The character of this level is determined by the microstructure of the sample in the condensed state and dissolution conditions. The particles of the first level are the heterogeneous formation nuclei of the second level–particles of the fibril type. Fibrils, which have risen from the solution at high temperature (T ≥ 80°C) have shown the ability to aggregate into anisodiametric structures as the solution cools. These aggregates, determined to be the third level, are very sensitive to temperature. In turbulent shear the rising rate of SMO increases greatly as the characteristic concentration is made smaller. The results obtained give us reason to conclude that the rise in SMO in aqueous PVA solutions is due to the crystallization of macromolecules when the low molecular weight component is available.

The process of formation of the supermolecular order (SMO) in aqueous solutions of poly(vinyl alcohol) (PVA) has been studied by the method of turbidity spectrum in a turbulent flow produced by a blade stirrer rotating at a rate of 1,500 rpm. The kinetics of SMO formation has been investigated depending upon the polymer molecular weight (Mw) and concentration (C) and temperature (T) of the solution. The rate of formation of SMO was characterized in the first stage of the process by a relative increment in τ at 540 nm per hr. The concentration dependence, K = K(C), is extremal in character having its maximum at C = 0.5–1 g/dl. When T was increased from 20 to 50°CC, K decreased, whereas average equivalent size of supermolecular particles, rλ, remained unchanged. The colloid disperse phase of supermolecular particles (SMP) appears to be in a quasi‐equilibrium with the molecular‐disperse solution, since, after removal of SMP, the process of formation of SMO is resumed at the same rate. To a greater extent the character of SMO formation depends on the chemical structure of PVA (K drops off to zero with increasing content of the acetate groups up to 7.6%) and physical prehistory of the PVA sample (an increase in K after thermal treatment of the polymer in the condensed state). PVA films cast from stirred solutions revealed (by IR spectra) a greater degree of crystallinity then those cast from unstirred solutions. All other conditions being equal, K in a turbulent flow is higher by one to two orders of magnitude than K under static conditions. The data obtained have been explained from the point of view of crystallization of PVA when intensified by the turbulent regime of solution stirring.

No abstract