Membrane assisted crystallization is a well-known technology where microporous hydrophobic membranes are used not as selective barriers but to promote the water vapor transfer between phases inducing supersaturation in solution [1]. This has been successfully tested in the crystallization of ionic salts, low molecular organic acids, and proteins [2]. Although some experimental studies probed the early stage of crystals formation, thanks to advanced techniques such as cryo-TEM [3], atomic force microscopy [4], molecular modelling helped to investigate the mechanism of nucleation and crystals growth [5,6]. In this paper we will present a detailed computational analysis of the crystal nucleation and growth of sodium chloride in contact with hydrophobic polymer surfaces at a supersaturated concentration of salt. The amorphous polyvinylidene fluoride (PVDF) surface together with the alpha and beta phases analysed in this work will provide new insight into peculiarities of their influence in crystal formation mechanism. The salt nucleation is faster with amorphous PVDF model then ? and ? PVDF and can be attributed to difference in the ability of amorphous membrane to induce supersaturation in less time. Molecular models confirm the highly efficient packing of the alfa nd beta polymer chains, in comparison to the amorphous one resulting in greater diffusion of water molecules. Furthermore, the rate of aggregation for Na+ Cl- ions was higher for the amorphous PVDF leading to a much more massive nucleation and crystallization.
Influence of polymorphisms in NaCl crystals nucleation and growth
ML Perrotta;F Macedonio;E Drioli;E Tocci
2020
Abstract
Membrane assisted crystallization is a well-known technology where microporous hydrophobic membranes are used not as selective barriers but to promote the water vapor transfer between phases inducing supersaturation in solution [1]. This has been successfully tested in the crystallization of ionic salts, low molecular organic acids, and proteins [2]. Although some experimental studies probed the early stage of crystals formation, thanks to advanced techniques such as cryo-TEM [3], atomic force microscopy [4], molecular modelling helped to investigate the mechanism of nucleation and crystals growth [5,6]. In this paper we will present a detailed computational analysis of the crystal nucleation and growth of sodium chloride in contact with hydrophobic polymer surfaces at a supersaturated concentration of salt. The amorphous polyvinylidene fluoride (PVDF) surface together with the alpha and beta phases analysed in this work will provide new insight into peculiarities of their influence in crystal formation mechanism. The salt nucleation is faster with amorphous PVDF model then ? and ? PVDF and can be attributed to difference in the ability of amorphous membrane to induce supersaturation in less time. Molecular models confirm the highly efficient packing of the alfa nd beta polymer chains, in comparison to the amorphous one resulting in greater diffusion of water molecules. Furthermore, the rate of aggregation for Na+ Cl- ions was higher for the amorphous PVDF leading to a much more massive nucleation and crystallization.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
