Quantitative characterization of the formation of an interpenetrating phase composite in polystyrene from the percolation of multiwalled carbon nanotubes

Abstract

For the first time, an interpenetrating phase polymer nanocomposite formed by the percolation of multiwalled carbon nanotubes (MWCNTs) in polystyrene (PS) has been quantitatively characterized through electrical conductivity measurements and melt rheology. Both sets of measurements, in conjunction with scanning electron microscopy (SEM) images, indicate the presence of a continuous phase of percolated MWCNTs appearing at particle concentrations exceeding 2 vol% MWCNTs in PS. To quantify the amount of this continuous phase present in the PS/MWCNT composite, electrical conductivity data at various MWCNT concentrations, β, are correlated with a proposed degree of percolation,C(β), developed using a conventional power-law formula with and without a percolation threshold. To quantify the properties of the interpenetrating phase polymer nanocomposite, the PS/MWCNT composite is treated as a combination of two phases: a continuous phase consisting of a pseudo-solid-like network of percolated MWCNTs, and a continuous PS phase reinforced by non-interacting MWCNTs. The proposed degree of percolation is used to quantify the distribution of MWCNTs among the phases, and is then used in a rule-of-mixtures formulation for the storage modulus, G (β,C(β), ω), and the loss modulus, G (β,C(β), ω), to quantify the properties of the continuous phase consisting of percolated MWCNTs and the continuous PS phase reinforced by non-interacting MWCNTs from the experimental melt rheology data. The properties of the continuous phase of percolated MWCNTs are indicative of a scaffold-like microstructure exhibiting an elastic behavior with a complex modulus of 360 kPa at lower frequencies and viscoplastic behavior with a complex viscosity of 6 kPa s rad −1 at higher frequencies, most likely due to a stick-slip friction mechanism at the interface of the percolated MWCNTs. Additional evidence of this microstructure was obtained via scanning electron microscopy. This research has important implications in providing a new methodology based on the electrical and rheological properties of the polymer nanocomposite for quantifying the continuous phase formed by the percolation of new functionalized nanostructures being developed for: (a) controlling the percolation of the nanostructures through self-assembly, (b) enhancing their interaction with the continuous reinforced polymer phase, (c) enhancing the cohesion between nanostructures.

Thermal degradation kinetics of PET/SWCNTs nanocomposites prepared by the in situ polymerization

“…The intense dispersion process by ultrasonication and high speed stirring of CNTs in liquid monomer (1,4-butanediol) and subsequent in situ polycondensation enabled to receive PBT/SWCNT (single-walled CNT) nanocomposites in which the percolation threshold for conductivity was around 0.2 mass% of SWCNT [19]. Furthermore, significant enhancement in rheological properties and electrical conductivity (20 orders of magnitude to 1 S m -1 at 12 vol.%) for the PS/MWCNTs due to the formation of the interpenetrating phases was observed [20]. It is already known that PET/clay nanocomposites show onset decomposition temperature of 3-19°C higher than that of pure PET [21].…”

“…During second stage, when temperature is higher, the remaining nanotubes along with the residues of the first stage are burned. 10,20, ) methods were applied to TG data to obtain kinetic parameters (activation energy, Arrhenius constant at 600 K and A factor) and Criado method to kinetics model analysis. In this kinetic model, energy activation is increasing with the increase of nanotubes concentration.…”

Superposition approach for description of electrical conductivity in sheared MWNT/polycarbonate melts

“…of nanotubes not belonging to the percolating phase, and, correspondingly, 1 -#f describes the fraction of nanotubes in the percolating phase. A quite similar superposition approach to the electrical conductivity of CNT/polymer composites has been proposed in the studies of Bruck and co-workers [43,44]. The total electrical conductivity of MWNT/polystyrene composites in these studies was represented as a sum of two terms: the temperature-independent polystyrene conductivity and the conductivity of percolating phase described by a conventional power-law relationship.…”

“…To model the conductivity increase due to thermal annealing [44], the authors assumed that the effective volume fraction of percolated particles increases with annealing time according to a stretched exponential law, in which the characteristic relaxation time is assumed to obey the Arrhenius temperature dependence. The main difference between the approach of Bruck and co-workers [43,44] and our approach is that the first approach neglects the contribution of non-percolating particles to the total composite conductivity, while we take this contribution explicitly into account by considering a reinforced matrix conductivity described by the first term on the right side of Equation (1). Besides, there is no shear dependence of the effective volume fraction of percolated particles in the first superposition approach, as the authors have only considered the effect of thermal annealing on the composite conductivity [44].…”

Low electrical percolation threshold and PL quenching in solution-blended MWNT–MEH PPV nanocomposites

“…Recently, t value of 0.97 [27] has been reported for pristine MWNTs (synthesised by CVD approach) and poly(bisphenol A carbonate) (PC) composites prepared by solution blending approach. Percolation corresponds to the formation of a CNT network that allows electron transport by tunnelling or electron hopping along CNT interconnects [28][29][30]. The low value of percolation threshold (0.5 wt%) obtained is a useful characteristic with regard to the nanocomposite system.…”