Evidence of Long Two-Dimensional Folding Chain Structure Formation of Poly(vinylidene fluoride) in...

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 (M _w) 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 M _w from 100 to 1200 kg mol^-1 substantially increases the particle length and width from L = 80 to 350 nm and w ₂ = 5.0 to 15 nm, respectively, while the thickness, w ₁, is maintained at 0.3 nm. Since L is much longer than w ₂ irrespective of M _w, 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 w ₂ values with increasing M _w.