Membrane technology has become an important separation technology over the past few decades and is a promising way to cope with problems such as environmental protection, water shortage and energy consumption. Poly(vinylidene fluoride) (PVDF) has received great attention as a membrane material with regard to its outstanding properties such as high mechanical strength, thermal stability, chemical resistance, and high hydrophobicity, compared to other commercialized polymeric materials. PVDF membranes have been extensively applied in ultrafiltration and microfiltration for general separation purposes, and are currently being explored as potential candidates in the applications of membrane contactor and membrane distillation [1]. However, there are still challenging issues, such as, the relationship between polymorph and mechanical strength and permeability of PVDF membranes. In this study, we focused our attention on the relation between PVDF chains and solvent molecules used in the NIPS and TIPS processes. We refer to the most common PVDF crystalline forms, which differ in chain conformations through trans (T) or gauche (G) linkages: (a) the non-polar ? phase (TGTG') forms upon rather rapid cooling from the molten state; (b) the polar piezoelectric ? phase (TTTT) forms by mechanical orientation and/or poling during cooling from melt at temperatures below 50°C. We performed molecular dynamics (MD) simulation to probe self-organization and structure of PVDF molecular chains and the relationship between chains and solvents. The theoretical results are used to better understand the relationship between PVDF crystalline forms and membrane preparation conditions.
Investigating Membrane Polymorph: a Molecular Point of View
TOCCI Elena;
2015
Abstract
Membrane technology has become an important separation technology over the past few decades and is a promising way to cope with problems such as environmental protection, water shortage and energy consumption. Poly(vinylidene fluoride) (PVDF) has received great attention as a membrane material with regard to its outstanding properties such as high mechanical strength, thermal stability, chemical resistance, and high hydrophobicity, compared to other commercialized polymeric materials. PVDF membranes have been extensively applied in ultrafiltration and microfiltration for general separation purposes, and are currently being explored as potential candidates in the applications of membrane contactor and membrane distillation [1]. However, there are still challenging issues, such as, the relationship between polymorph and mechanical strength and permeability of PVDF membranes. In this study, we focused our attention on the relation between PVDF chains and solvent molecules used in the NIPS and TIPS processes. We refer to the most common PVDF crystalline forms, which differ in chain conformations through trans (T) or gauche (G) linkages: (a) the non-polar ? phase (TGTG') forms upon rather rapid cooling from the molten state; (b) the polar piezoelectric ? phase (TTTT) forms by mechanical orientation and/or poling during cooling from melt at temperatures below 50°C. We performed molecular dynamics (MD) simulation to probe self-organization and structure of PVDF molecular chains and the relationship between chains and solvents. The theoretical results are used to better understand the relationship between PVDF crystalline forms and membrane preparation conditions.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
