Determination of the crystalline phases of poly(vinylidene fluoride) under different preparation conditions using differential scanning calorimetry and infrared spectroscopy

Abstract

A method with good precision has been developed to quantitatively measure the degree of ␣-, ␤-, and ␥ crystallinity in poly(vinylidene fluoride) (PVDF) by means of infrared spectroscopy. The phase composition of solutiondeposited PVDF films was 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 ␣-phase PVDF, but when a layer of polar solvent (acetone or methanol) remained on the surface, the films produced were predominantly ␥ phase. Higher humidity promoted a higher fraction of ␥ crystallinity in the solution-deposited PVDF films. Solution-cast films had highly variable composition across the substrate, whereas spin-cast films were uniform. High-temperature annealing of PVDF films normally converts the polymer to the ␥ 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 premelting 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.

High Ionic Liquid Content Polymeric Gel Membranes: Preparation and Performance

“…26 Also the melting enthalpy of our copolymer (42 J/g) is quite close to that of PVDF (ca. 50 J/g in the second heating run 27 ), justifying the hypothesis of a PVDF-like crystal phase.…”

Caracterização físico-química do enxerto de osso bovino liofilizado

“…The samples were heated from -23°C to 250°C, at a heating rate of 5°C/min, and the heating was done twice. The experiments were carried out under a dynamic nitrogen atmosphere (N2), at a flow rate of 30 ml/min, using a Mettler Toledo 822 e (14) .…”

“…The spectra were obtained with 32 repetitions, readings from 4000 to 400 cm -1 and resolution of 4 cm -1 . A tablet of potassium bromide (KBr) was incorporated with the sample for this analysis (14) .…”

Spin cast ferroelectric beta poly(vinylidene fluoride) thin films via rapid thermal annealing

“…4 Furthermore, PVDF has the higher Curie temperature of ϳ170°C than that of the copolymers with TrFE which always give rise to ferroelectric ␤ structure.…”