Hydrogen bond interactions of hydrated aluminum nitrate with PVDF, PVDF‐TrFE, and PVDF‐HFP: A density functional theory‐based illustration

Abstract

AbstractHydrogen bond (HB) interaction is the main driving factor for the nucleation of electroactive β phase within the nonpolar pristine polyvinylidene fluoride (PVDF) and its copolymers when the hydrated nitrate salts act as additives. The current work elaborates a density functional theory‐based analysis on the HB interactions within aluminum nitrate nonahydrate‐added polyvinylidene fluoride [PVDF/Al(NO3)3∙9H2O], polyvinylidene fluoride‐trifluoro ethylene [PVDF‐TrFE/Al(NO3)3∙9H2O], and polyvinylidene fluoride‐hexafluoro propylene [PVDF‐HFP/Al(NO3)3∙9H2O] composite systems. Polar properties of α (TGTG′) and β (TTTT) phases of the homopolymer and copolymer chains have been compared. Coordination chemistry and formation energies of two stable isomers of Al(NO3)3∙9H2O have been described. Interactions within the polymer/salt complexes have been simulated considering both the salt isomers added to α‐ and β‐tetramer chains of PVDF, PVDF‐TrFE, and PVDF‐HFP. An integral equation formalism polarizable continuum model has been used to replicate the effects of n,n‐dimethyl formamide solvent. HB interaction phenomenon has been described on the basis of electron density difference, interaction energy calculations, symmetry‐adapted perturbation theory, natural bond orbital, Bader's quantum theory of atoms in molecules, delocalization indices, and reduced density gradient analyses. Simulated infra red (IR) and Raman spectra identified the simultaneous presence of CH⋯O (mostly improper) and OH⋯F (mostly proper) HBs between the salt molecule and polymer chains. Correlations among different HB descriptors have been demonstrated to compare the proper and improper nature of the bonds. This research explored some ambiguities in the conventional HB properties, which may be attributed to very low hyperconjugation energies associated with the bonds.