Proton magnetic relaxation in aromatic polyamides during water vapor sorption

Osmotic phenomena in polymer sorption systems

“…The initial part of (g* > 1) for cellulose and polya mides agrees well with NMR data [12,13]. Here, min imum values of times of the spin spin relaxation of adsorbed water protons are observed, this corresponds to the formation of hydrogen bonds of water molecules as with a single OH group of cellulose or NH groups of polyamides, and bridge bonds with the active groups of neighboring macromolecules as well.…”

“…In the region of inflection on the curves g*(θ), a further sharp fall in the value of g* occurs corresponding to the transition of samples from the glassy to highly elastic state [9,10]. This process is also consistent with the beginning of clustering of water molecules, respectively, with the decrease of the spin lattice relaxation time and approximation of the sorbate structure to the bulk phase [12,13].…”

“…O the marks the calculation using equation (12). and in relaxation time Т 1 [12,13]. In the region of inflection on the curves g*(θ), a further sharp fall in the value of g* occurs corresponding to the transition of samples from the glassy to highly elastic state [9,10].…”

“…However, the states of sor bate and polymer along the sorption isotherms vary considerably. This is evidenced by the bimodal sorp tion theory [8], indicating a state change of the poly mer and sorbate along the sorption isotherm, by NMR data on the state of the polymer and sorbate [8,12,13], by change of the polymer state from glassy to elas tomeric and thick flowing, and by other factors. A theoretic probabilistic model of sorption equation allows one to estimate the value of g; this equation sat isfactorily describes the isotherms of vapor sorption by glassy polymers and elastomers [14][15][16]: (12) where а, а 0 is the value of sorption at the chemical potential of sorbate in the gas phase and , respectively; p/p 0 is the equilibrium pressure of sorbate and the saturated vapor pressure; Е is the characteristic energy of adsorption; n = 0.3-0.33 for densely packed and soluble polymers in the sorbate; n = 0.5 for elastomers; and n = 0.7 for glassy polymers [14].…”

Activity coefficients of the low-molecular-mass components in swelling polymers

“…Depending on the solution concentration, the state of the polymer can transition from the initial glassy state to a rubberlike, viscous flow state. This feature has been shown, for example, in studies of the state of polymer solutions via the NMR method [10][11][12], the bimodal sorption theory [13], the Lindström-Laati kainen model [14], etc. At the same time, the forma tion of the solution is accompanied by ambiguous changes in the volume of the system caused by osmotic effects (swelling pressure) [1].…”