Structural levels of supermolecular organization in aqueous solutions of poly (vinyl alcohol)

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.

Poly(vinyl alcohol) Grafting in Miniemulsion Polymerization

“…In the case of the miniemulsion, most of the PVOH was adsorbed on the monomer droplets, whereas in the case of conventional emulsion polymerization, most of the PVOH was in the aqueous phase (either dissolved or forming aggregates through hydrogen bonding due to its polyhydroxy group). In addition, the PVOH aggregated presents a supermolecular organization with a paracrystalline structure . The formation and presumably the dissolution of these aggregates is a kinetic process that may take relatively long times.…”

Aged layered double hydroxide nanosheet–polyvinyl alcohol dispersions for enhanced gas barrier coating performance

“…These are due to the formation of supramolecular particles of crystalline features that have been recognised as the ageing effect. 35,36 Thus, LDH particles are easier to align as ageing time increases under shear stress, which is probably related to the increased effective volume fraction. 37…”

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.…”