Poly(vinylidene fluoride)/poly(3-methylthiophene) core–shell nanocomposites with improved structural and electronic properties of the conducting polymer component

Abstract

We report significant improvements in the structure and electronic properties of a poly(3-alkylthiophene) representative, namely poly(3-methylthiophene) (P3MT), when it is synthesized in the presence of submicron electroactive poly(vinylidene fluoride) (PVDF) particles. The applied template oxidative synthesis leads to the formation of the PVDF/P3MT composite consisting of core-shell particles. The shells are constituted with a monolayer of 20-40 nm nanoparticles of the doped P3MT (P3MT-Cl) precipitated at the surface of the spherical PVDF cores. This morphology differs strongly from the hierarchical one of the neat P3MT synthesized without PVDF particles. In the latter case, 20-60 nm P3MT nanoparticles form ∼200 nm aggregates, which, in turn, are arranged in a few micrometer agglomerates. Furthermore, we demonstrate that compared to the neat polymer, doped P3MT in the shells of the composite is characterized with higher effective conjugation length, regioregularity of the molecular structure, improved intrachain packing order and lower bipolaron/polaron ratio. These features of the PVDF/P3MT composite strongly suggest applicability of this material in various electronic devices. As a proof of concept, we report on an improved sensing performance of the PVDF/P3MT-Cl composite compared with the neat P3MT-Cl in detection of several volatile organic compounds known as markers for some diseases and toxic substances. We have discovered that the maximal improvement in the sensor response magnitude corresponds to the case when the values of the analyte electronegativity and polythiophene work function are close. We associate this behavior with a higher surface dipole component of the work function of the PVDF/P3MT-Cl composite compared to that of the neat conducting polymer.

On the importance of interface interactions in core-shell nanocomposites of intrinsically conducting polymers

“…Furthermore, after sedimentation of the dispersion for the following 48 hours, the P3MTr emission above 600 nm strongly dropped, while the 525 nm peak remained at practically the same level and was similar to the nanocomposite one (Fig. 5, curve 4) [31].…”

“…In particular, in the case of concentrated dispersion (0.5 mg/ml) in acetonitrile of the pure P3MTr (0.5 mg/ml, Fig. 5, curve 1) the observed emission peak revealed a vibronic structure with two maxima and several shoulders on the both sides [31].…”

“…Based on the TEM and SEM images of the samples (Fig. 4), these changes in the emission due to dilution and sedimentation were interpreted as a manifestation of the influence of the size of the hierarchically arranged P3MT nanoparticles on their emission properties [31]. These results suggest that the low-energy maximum at 685 nm can be assigned, at least partially, to the largest agglomerates of the P3MTr particles.…”

“…Molecular level changes in the polymer shell of the nanocomposite particles are inevitably accompanied by changes in the structure, morphology, charge states, conductivity, sensing activity and other properties of both the shell itself and nanocomposites as a whole. For example, it was found that P3MT-Cl synthesized in the absence and presence of PVDF submicron (200 nm) particles revealed strong morphological, structural and spectral differences [31]. Specifically, one can distinguish three levels hierarchical morphology of pure P3MT-Cl in the TEM and SEM images (Fig.…”

“…It should be emphasized here that the vibronic structure of the PL peak both of the pure and composite P3MTr confirms the above discussed ordering of the P3MTr fractions. The observed ordered phases appeared probably due to π-π-stacking interactions between P3MT's backbones and formation of molecular aggregates typical for P3ATs [31].…”