Formation of supermolecular order in aqueous solutions of poly(vinyl alcohol) in a turbulent flow

Abstract

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.

Structure of Crystallizable Polymer Solutions

“…Second-level SMP are formed during thermostating of crystallizable polymer solutions within wide ranges of temperature and concentration. The kinetics of this process shows each and every indication of polymer crystallization in the presence of a solvent [1][2][3][4][5][6][7][8][9][14][15][16][17]. The temperature dependence of the second-level SMP formation rate goes through a maximum.…”

“…Our previous series of experiments [1,2] has revealed no liquid-liquid phase separation range in the poly (vinyl alcohol) (PVA) + water system at least below 150°C. Therefore, those SMP which are present in solution on visual dissolution (the first level of supramolecular order (SMO)) or formed with in wide temperature and concentration ranges are of crystal nature [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Hence, the structure of PVA solutions is generally the same as in any solution of a crystallizable polymer.…”

Structure of Crystallizable Polymer Solutions

“…В предыдущей серии экспериментов было установлено отсутствие области фазового разделения типа жидкость-жидкость для системы поливиниловый спирт (ПВС) ПВС+вода, по крайней мере, при температурах Т<150 ○ С [1][2][3]. Таким образом, НМЧ, остающиеся в растворе после визуального растворения (первый уровень надмолекулярного порядка (НМП)) и формирующиеся затем в широкой области температур и концентраций, имеют кристаллическую природу [1][2][3][4][5][6][7][8][9]. Из этого следует общность структуры растворов ПВС со структурой растворов кристаллизующихся полимеров.…”