Evidence of Long Two-Dimensional Folding Chain Structure Formation of Poly(vinylidene fluoride) in N-Methylpyrrolidone Solution: Total Form Factor Determination by Combining Multiscattering Data.

Abstract

Very recently, we proposed that poly(vinylidene fluoride) (PVDF) dissolves in a long rectangular column conformation induced by the formation of a two-dimensional folding chain structure in an N-methylpyrrolidone (NMP) solution based on the results obtained from static light scattering (SLS), small- to wide-angle X-ray scattering (S-WAXS), and viscometric experiments. Small- to wide-angle neutron scattering (S-WANS) experiments were able to provide clear decisive evidence for the presence of such a two-dimensional folding chain structure in a deuterated (d)NMP solution of PVDF samples with two different weight average molar masses (Mw) of 100 and 1200 kg mol–1, even under dilute conditions at concentrations less than the overlapping concentrations due to the quite high neutron scattering contrast obtained by using (d)NMP as a solvent. An increase in Mw from 100 to 1200 kg mol–1 substantially increases the particle length and width from L = 80 to 350 nm and w2 = 5.0 to 15 nm, respectively, while the thickness, w1, is maintained at 0.3 nm. Since L is much longer than w2 irrespective of Mw, the particles formed by PVDF molecules in NMP simply behave as long rigid rods in a scattering vector (q) range covered by SLS measurements. A combination study of S-WANS and S-WAXS experiments covering a higher q range with the SLS techniques could clearly reveal increases in both the L and w2 values with increasing Mw.