Pair interaction energy decomposition analysis (PIEDA) and experimental approaches for investigating water interactions with hydrophilic and hydrophobic membranes

Abstract

The origins of low and high interactions of polar groups with water molecules are still unknown and need to be further examined for effective future membrane synthesis and modification. The primary aim of this research study is to provide a comprehensive overview of the interactions at the molecular level occurring between water molecules and the fragments of hydrophobic and hydrophilic membranes based on pair interaction energy decomposition analysis (PIEDA) as part of the fragment molecular orbital (FMO) method’s framework. This direction is critical, since a research study of the reasons for water and membrane interactions can help design groundbreaking membranes with superior hydrophilicity characteristics. To accomplish this, the computational studies, the Polyvinylidene fluoride (PVDF [H(–CH2–CF2–)4CH3]) and Polyacrylonitrile (PAN [(H(–CH2–CH(CN)–)4CH3]) membranes were considered as 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, fragment molecular orbit (FMO) and the Pair Interaction Energy Decomposition Analysis (PIEDA) were carefully interrogated. These types of analyses included the inter fragment interaction energy (IFIE), like the electrostatic (ES), exchange repulsion (EX), charge-transfer and mixing term (CT + mix) energies. Furthermore, the hydrophilicity and hydrophobicity of the origins of membrane function groups 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. Confocal microscopic approach was used to interrogate water transport and the interactions between fluorescence particles and membrane layers. Furthermore, the Infrared (IR) spectroscopy was performed to investigate interaction between water molecules and PVDF and PAN. The theoretical results had a good agreement with experimental result.