Determination of the Crystalline Phases of Poly(vinylidene fluoride) Under Different Preparation Conditions Using Differential Scanning Calorimetry and Infrared Spectroscopy
Marcel Benz, William B. Euler, Journal of Applied Polymer Science, 2003, 89, 1093 – 1100
Abstract
A method with good precision has been developed to quantitatively measure the degree of α-, β-, and γ-crystallinity in poly(vinylidene fluoride) (PVDF) by means of infrared spectroscopy. The phase composition of solution deposited PVDF films were found to be strongly influenced by the presence of hydrophilic residues on the silicon substrate, the relative humidity present at film deposition, the spatial position on the substrate, and the thermal treatment of the deposited film. Films produced on pristine surfaces gave predominantly α-phase PVDF but when a layer of polar solvent (acetone or methanol) remained on the surface the films produced were predominantly γ-phase. Higher humidity promoted a higher fraction of γ-crystallinity in the solution deposited PVDF films. Solution cast films had highly variable composition across the substrate while spin-cast films were uniform. High temperature annealing of PVDF films normally converts the polymer to the γ-phase, but annealing the film while still attached to the silicon substrate inhibited this phase transformation. Low temperature annealing of freestanding films led to a previously unreported thermal event in the DSC, a pre-melting process that is a kinetic event, assigned to a crystalline relaxation. Higher temperature annealing gave a double endotherm, assigned to melting of different sized crystalline domains.