Novel Zwitterionic Copolymers to Enhance Hydrophilicity of PVDF Membranes: A Comprehensive Computational Study
Date
2019-09-27
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0003-2826-7762
Type
Thesis
Degree Level
Masters
Abstract
Membrane technology covers all the engineering approaches with a key growth for large-scale industrial applications, including biotechnology, biomedical applications, food industry, and water and wastewater treatment. Poly (vinylidene fluoride) (PVDF) membrane has been gained remarkable attentions in recent years due to its excellent advantages in terms of thermal stability, chemical resistance, and high mechanical strength for water treatment. Despite its outstanding advantages, the performances of PVDF membranes are substantially limited by fouling problems. In this research study, we designed novel zwitterionic (ZW)-PVDF membranes with high hydrophilicity by employing a set of comprehensive computational methods. To achieve our goal, we first investigated the interactions occurring between water molecules and the fragments of hydrophobic and hydrophilic membrane models at the molecular level using the pair interaction energy decomposition analysis (PIEDA) as part of the fragment molecular orbital (FMO) method’s framework. This research direction is critical, since a research study of the reasons behind the interactions between water molecules and membrane materials would help design ground-breaking membranes with superior hydrophilicity.
The computational studies and experimental analyses of PVDF and Polyacrylonitrile (PAN) membranes were considered as the models for hydrophobic and hydrophilic membranes, respectively. Density-functional theory (DFT), based on B3LYP functional and split-valance 6-311+G (d, p) basis sets, was used in order to optimize the geometry of PAN, PVDF, and their complexes with different numbers of water molecules. Furthermore, the functional groups of membrane surfaces were experimentally evaluated through Fourier-transform infrared spectroscopy (FTIR- ATR), 13C cross polarization magic angle spinning (13C CP MAS) Solid State Nuclear magnetic resonance SSNMR, and Fourier transform Raman (FT-Raman) spectroscopies. The confocal microscopic was also employed to interrogate water transport and the interactions between fluorescence particles through the membrane matrices.
The non-covalent interactions in terms of electrostatic, exchange-repulsion, and charge-transfer parameters were comprehensively investigated for the designed ZW-PVDF copolymers. The performance of ZW moieties was derived from three different anionic groups in the ZW head, specifically, carboxylate, sulfonate, and phosphate. This approach was used in addition to the inclusion of a linker between the ZW head and the PVDF backbone, such as trimethyl ammonium groups and hydroxyl group, for an improvement of PVDF hydrophilicity. The quantum chemical calculations were conducted to examine the hydration structure of moieties. The interactions between the ZW moieties, with water molecules confirmed that it depended on the charged groups in addition to the chemical functional groups between charged groups. Furthermore, the types of anionic groups, the polar functional groups between charged groups, and the hydrophilic group, as a linker between charged groups of the ZW to the PVDF polymer backbone are the key reason for membrane hydrophilicity and the membrane water uptake. The double Zwitterionic PMAL®-C8-CB-OH-SB-PVDF was designed through the addition of protonated carboxyl group on a backbone of copolymer PMAL®-C8, and the protonated nitrogen atom of the amide group. This double zwitterion showed strong electrostatic interactions between individual water molecules and the secondary ammonium and the Oxygen of carboxybetaine, compared to PMAL®-C8-OH-SB-PVDF model. Our designed hydrophilic ZW-PVDF membranes, and especially the double zwitterion membrane, are an exciting development that can be applied in a broad range of water applications.
Description
Keywords
hydrophilicity, interactions, hydrophobicity, Pair Interaction, fragment, DFT, hydrogen bond, electrostatic, spectroscopy, Zwitterions, PVDF, Hydrophilicity, Hydrophobicity, FMO, PIEDA, charged groups, double zwitterion, hydration
Citation
Degree
Master of Engineering (M.Eng.)
Department
Chemical and Biological Engineering
Program
Chemical Engineering