Bula Dutta

Correlation between nucleation, phase transition and dynamic melt-crystallization kinetics in PAni/PVDF blends

In this study, polyaniline (PAni)/poly(vinylidene fluoride) (PVDF) blends of different compositions were prepared by in situ chemical polymerization of aniline in a mixture of PVDF and dimethylformamide (DMF). Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetry (TG) and differential scanning calorimetry (DSC) were utilized to understand the effect of different amounts of in situ PAni loading on the crystalline structure, phase transition and dynamic melt-crystallization kinetics of PVDF. The images for morphology obtained using scanning electron microscopy and polarizing optical microscopy also provided the confirming evidences. FT-IR studies revealed that the transition of the crystalline structure (from β- to α-phase) of pure PVDF during recrystallization is hindered by the incorporation of PAni within the matrix. The dynamic crystallization kinetics data were analysed with different macroscopic models to describe the polymer crystallization, and the parameters obtained from the analyses were correlated with the structural evidence to verify their applicability for the systems under investigation. Values for the effective activation energy (EX) of the crystallization process of PVDF and its blends were calculated by the differential isoconversional methods of Friedman. It was observed that, although PAni acted as an effective nucleating agent to induce a great number of heterogeneous nuclei within the blends, it actually delayed the overall crystallization process. The increased values of the crystal growth parameters obtained from the analysis of the temperature-dependent EX by the modified Hoffman–Lauritzen theory also support the above mentioned interpretations.

Electroactive phase nucleation and non-isothermal crystallization kinetics study in [DEMM][TFSI] ionic liquid incorporated P(VDF-HFP) co-polymer membranes

The electroactive phase nucleation and subsequent non-isothermal crystallization kinetics of different extents of aliphatic quaternary ammonium-based ionic liquid (IL) N,N-diethyl-N-(2-methacryloylethyl)-N-methylammonium bis(trifluoromethylsulfonyl) imide ([DEMM][TFSI]) incorporated poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP) co-polymer membranes have been explored using Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). Different macroscopic models are used to assess the overall non-isothermal crystallization parameters of the membranes. The effective activation energy (EX) of the crystallization process of the membranes is estimated by the differential isoconversional methods of Friedman. The analysis of DSC responses, infrared spectra, and X-ray diffractograms of the different IL incorporated polymer membranes reveal that a possible interaction between the ions of the IL and disordered dipoles of the co-polymer in the melt state, essentially delays the overall crystallization process and preferentially yield different electroactive (all trans or trans-gauche) chain conformations at different cooling rates of crystallization. The proportional variation of effective activation energy and the value of the Hoffman–Lauritzen crystal growth parameters, adopting the method proposed by Vyazovkin, with the IL content also support the same.

Dependence of the carrier mobility and trapped charge limited conduction on silver nanoparticles embedment in doped polypyrrole nanostructures

The present article demonstrates an intensive study upon the temperature dependent current density (J)-voltage (V) characteristics of moderately doped polypyrrole nanostructure and its silver nanoparticles incorporated nanocomposites. Analysis of the measured J–V characteristics of different synthesized nano-structured samples within a wide temperature range revealed that the electrical conduction behavior followed a trapped charge-limited conduction and a transition of charge transport mechanism from deep exponential trap limited conduction to shallow traps limited conduction had been occurred due to the incorporation of silver nanoparticles within the polypyrrole matrix. A direct evaluation of carrier mobility as a function of electric field and temperature from the measured J–V characteristics illustrates that the incorporation of silver nanoparticles within the polypyrrole matrix enhances the carrier mobility at a large extent by reducing the concentration of traps within the polypyrrole matrix. The c...

Correlation of the average hopping length to the ion conductivity and ion diffusivity obtained from the space charge polarization in solid polymer electrolytes

Herein, a physical model, based on impedance spectroscopy and space charge polarization with the consideration of low frequency capacitance dispersion is presented to evaluate the parameters describing the electrical transport properties of some previously studied polymer electrolytes. Implementing the model, the complete frequency response of complex conductivity within the measured frequency range can be imitated, which enables us to appropriately evaluate the macroscopic DC conductivity, hopping frequency and double layer frequency within the measured temperature range. The temperature dependent mobile ion concentration, free-ion diffusivity and average ion hopping length have also been estimated from the analysis of the frequency dependent real and imaginary parts of the complex permittivity spectra, using the same model. Reasonable agreement of the ion diffusivity obtained from the present analysis to that obtained previously from the pulsed-field gradient (PFG) NMR measurements strongly justifies the applicability of the model to a wide variety of ion conducting systems.

Ion dynamics in NaBF4 salt-complexed PVC–PEO blend polymer electrolytes: correlation between average ion hopping length and network structure

Electrical transport properties of a series of NaBF4 salt-doped PVC–polyethylene oxide blend polymer electrolytes are studied using impedance spectroscopy. X-ray diffraction, Fourier transform infrared spectroscopy, and differential scanning calorimetry are implemented to characterize the structural properties of the electrolytes. The characterization data clearly indicate that the interaction between the dopant salt and the polymer host substantially influences the overall crystallinity of the electrolytes. Experimental frequency-dependent complex conductivity and loss tangent data are analyzed using a physical model to extract separately the mobile ion concentration and ion mobility of the charge carriers and the type of their thermal activation. The average hopping length of free ions, which essentially controls the macroscopic ion transport within the electrolytes, is found to be strongly correlated to the network structure of the electrolytes. Both the dc conductivity and free ion mobility are observed to be strongly coupled with the segmental dynamics of blend polymer host over the entire range of ion content studied.

Correlation of carrier localization with relaxation time distribution and electrical conductivity relaxation in silver-nanoparticle-embedded moderately doped polypyrrole nanostructures

The electrical conductivity relaxation in moderately doped polypyrrole and its nanocomposites reinforced with different proportion of silver nanoparticles was investigated in both frequency and time domain. An analytical distribution function of relaxation times is constructed from the results obtained in the frequency domain formalism and is used to evaluate the Kohlrausch-Williams-Watts (KWW) type decay function in the time domain. The thermal evolution of different relaxation parameters was analyzed. The temperature-dependent dc electrical conductivity, estimated from the average conductivity relaxation time is observed to depend strongly on the nanoparticle loading and follows Mott three-dimensional variable range hopping (VRH) conduction mechanism. The extent of charge carrier localization calculated from the VRH mechanism is well correlated to the evidences obtained from the structural characterizations of different nanostructured samples.

Electroactive phase nucleation and isothermal crystallization kinetics in ionic liquid-functionalized ZnS nanoparticle-ingrained P(VDF-HFP) copolymer nanocomposites

Poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP))-based copolymer nanocomposites are prepared by blending with hydrophobic ionic liquid-functionalized ZnS nanoparticles. Different characterization techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and differential scanning calorimetry (DSC) are employed to investigate the effect of the nano-additives to the conformational changes of copolymer chain segments before and after the melt crystallization. Isothermal crystallization kinetics of the nanocomposites are studied using DSC at different crystallization temperatures. Analysis of the experimental data reveals that the functionalized nanoparticles in nanocomposites gradually retard the crystallization rate through strong dipole–dipole interaction, but accelerates the nucleation rate, providing a large number of heterogeneous nucleation sites. However, at higher loading, they substantially restrict the crystal growth rate, leading to the formation of a large number of imperfect crystallites and a consecutive reduction in overall crystallinity. Different nucleation parameters such as initial laminar thickness, fold surface free energy and the work of chain folding during isothermal crystallization were evaluated from the analysis of the crystallization kinetics data using Avrami, Hoffman–Week and Lauritzen–Hoffman theories, also supports the same.