Conducting nano-channels in an induced piezoelectric polymeric matrix using swift heavy ions and subsequent functionalization

Abstract

Nanohybrids of poly(vinylidene fluoride) with layered silicates have been synthesized by melt extrusion and nano-channels have been fabricated by swift heavy ion (SHI) irradiation followed by chemical etching of the selective amorphous zones in the latent tracks. The channel diameter was reduced to 30 nm in the presence of nanoclay in the nanohybrid, making it suitable for membrane applications. Grafting with styrene was carried out inside the nano-channels using the free radicals created by the SHI exposure. Sulphonation on the grafted polystyrene was carried out to increase the conductivity of the membrane to the semiconducting range through ion channel conduction. The grafting and sulphonation inside the nano-channels were confirmed through spectroscopic techniques viz. NMR, FTIR, UV and molecular weight measurements. The dimensions of the channels are controlled by the SHI fluence and thereby dictates the properties including 10 orders of magnitude higher conductivity by creating a greater number of channels and hence increasing the surface area required for enhanced grafting and sulphonation. The hetero-junction and nano-channel conduction was demonstrated through STM measurements showing that the superior conduction depends on the relative extent of grafting and sulphonation in pure PVDF and the nanohybrid. The matrix PVDF crystallizes in the piezoelectric b-phase in the presence of nanoclay and promotes the formation of smart membranes.

New Generation Fuel Cell Membrane Using Swift Heavy Ions

“…The absorption bands at 1640 and 1542 cm −1 are attributed to –C=C – stretching vibrations of aromatic ring, additionally substantiate the grafting of polystyrene against no peak observed in pristine PVDF in the above range (Figure C ). It should be mentioned that polystyrene, prepared using benzoyl peroxide as initiator, shows the –C=C– stretching frequencies at 1601 and 1494 cm −1 (inset figure) and the significant shifting from 1494→1542 cm −1 and 1601→1640 cm −1 after grafting is due to the restricted conformation of polystyrene graft as they are confined within the nanochannels ,. The feature assimilation band in the wavenumber range of 3411 cm −1 corresponds to the O–H stretching vibration from sulphonic acid group also validates the sulfonation to occur mostly on benzene ring of polystyrene.…”

“…Hence, the extra new peaks at δ =7.9 and 8.1 ppm after sulfonation suggests the predominant sulfonation at para position of benzene ring . Unirradiated PVDF illustrates two distinguished peaks at δ =2.23 and 2.8 ppm attributed to tail‐to‐tail (T−T) and head‐to‐tail (H−T) arrangements in polymer chain, respectively (inset figure of Figure A ) ,,. Figure B shows UV‐Vis absorption spectra of unirradiated, functionalized and sulfonated PVDF and its nanohybrid.…”

“…Scheme shows the creation of nanochannel by chemical etching of the latent track. The associated chemistry evolved within the nanochannels due to free radicals caused by SHI bombardment …”

“… Schematic illustration of creating nanochannel after SHI bombardment followed by its selective etching. Chemical modification after SHI irradiation compares the extent of functionalization in PVDF and nanohybrids …”

“…Auxiliary, the integrated peak area at δ=8.1 ppm, assigned for sulfonated proton in polystyrene grafted nanohybrid (4.08) is appreciably higher as compared to that of sulfonated proton of PVDF (3.38) signifying greater degree of sulfonation in nanohybrid (NH). This is to be noted that grafted specimen of PVDF exhibits peaks at δ =6.9, 7.0 and 7.2 ppm . Hence, the extra new peaks at δ =7.9 and 8.1 ppm after sulfonation suggests the predominant sulfonation at para position of benzene ring .…”