In this study, the densities of pyrrole (1) + pyridine (2), pyridine (1) + quinoline (2), pyrrole (1) + quinoline (2), indoline (1) + quinoline (2), indoline (1) + pyridine (2), and indoline (1) + pyrrole (2) were measured over the entire composition range at temperatures T = 298.15-343.15 K and pressure p = 101.305 kPa. The data were used to calculate excess molar volume ( V m E ), partial molar volume (V i ), excess partial molar volume ( V i E ), apparent molar volume (V phi,i ), and the isobaric thermal expansion (alpha p). Excess molar volumes ( V m E ) were fitted to a Redlich-Kister equation to evaluate the deviation from ideal mixing behavior. It was noted that indoline (1) + quinoline (2) has a negative ( V m E ) deviation from ideality. Whereas the pyridine (1) + quinoline (2), pyrrole (1) + quinoline (2), indoline (1) + pyridine (2), and indoline (1) + pyrrole (2) mixtures showed positive excess molar volume deviations from ideality due to dissimilar structures. The FT-IR spectra of all the studied binary mixtures showed the presence of N-H bonding within the molecules. Finally, the sigma profile and the sigma potential of individual compounds were generated and analyzed.

In this contribution, we report the synthesis of a poly(4-vinylpyridine)-reduced graphene oxide-magnetite (P4VP-rGO-Fe₃O₄) organo-magnetogel (OMG), designed for high-performance pollutant adsorption. In the OMG, rGO and Fe₃O₄ nanoparticles are in situ encapsulated during the chemical cross-linking of the 4-vinylpyridine polymer. The adsorption performance of OMG was evaluated using three model water pollutants, viz., organic dyes, heavy metal ions, and waterborne pathogens. The equilibrium adsorption capacity exceeded 400 mg/g for the organic dyes. Beyond dye removal, the OMG also adsorbed heavy metal ions, such as AsO2−, Pb²⁺, Cr2O72−, and Cd²⁺ ions, with removal efficiencies exceeding 60% and adsorption capacities exceeding 200 mg/g. The OMG also exhibited remarkable antibacterial activity against E. coli and S. Typhi, with almost zero viability for S. Typhi. The OMG promises a broad-spectrum applicability in wastewater treatment, offering a sustainable and efficient solution for water decontamination.

One-pot free radical precipitation polymerization was used to synthesize an aqueous suspension of nonionic poly ( ${N}$ -isopropylacrylamide) (PNIPAM) microgel particles. For dielectric measurements in the frequency range of 100 MHz–50 GHz and the temperature range of 288–323 K, 10 wt% of freeze-dried PNIPAM microgels dispersed in heavy water were used. The relaxation process was seen at around 15 GHz, which corresponds to the entire rotational motion of the heavy water, both within and outside the microgel. Furthermore, in the high-frequency relaxation spectrum, heavy water outside the microgel ( ${h}1$ -process with a relaxation time of ${h}1$ , $\tau _{\mathbf {h{1}}}$ , fixed as that of pure heavy water) and confined heavy water within the microgel ( ${h}2$ -process with a relaxation time of ${h}2$ , $\tau _{\mathbf {h{2}}}$ ) were evaluated in view of the two-water model’s assumption and contribution. Under volume phase transition temperature (VPTT), $\tau _{\mathbf {h{2}}}$ is about 4 to $5\times $ larger than $\tau _{\mathbf {h{1}}}$ , and it does not change much even though the temperature is raised. However, $\tau _{\mathbf {h{2}}}$ rapidly increases above VPTT from 7 to 14, which reveals that the dynamics of heavy water are severely constrained inside the shrunken state of the PNIPAM microgel. The obtained results are compared to the dynamics of pure water in PNIPAM microgels aqueous suspension to better understand the effect of deuterium substitution for hydrogen on the dynamics of heavy water inside and outside of PNIPAM microgels.

A broadband dielectric spectroscopy study was conducted on a partially crystallized 10 wt% poly(N-isopropylacrylamide) [PNIPAM] microgel aqueous suspension to investigate the dielectric relaxation of ice in microgel suspensions. The measurements covered a frequency range of 10 mHz to 10 MHz and at temperatures ranging from 123 K to 273 K. Two distinct relaxation processes were observed at specific frequencies below the melting temperature. One is associated with the combination of the local chain motion of PNIPAM and interfacial polarization in the uncrystallized phase, while another is associated with ice. To understand the temperature-dependent behaviour of the ice relaxation process, the relaxation time of ice was compared with those observed in other frozen polymer water mixtures, including gelatin, poly-vinylpyrrolidone (PVP), and bovine serum albumin (BSA). For concentrations ≥ 10 wt%, the temperature dependence of the relaxation time of ice was found to be independent. Therefore, the study primarily focused on the 10 wt% data for easier comprehension of the ice relaxation process. It was found that the microgel and globular protein BSA had no significant effect on ice crystallization, while gelatin slowed down the crystallization process, and PVP accelerated it. To discuss the mechanism of the dielectric relaxation of ice, the trap-controlled proton transport model developed by Khamzin et al. [Chem. Phys., 2021, 541, 111040.] was employed. The model was used to discuss the dynamic heterogeneity of ice observed in this investigation, distinguishing it from the spatial heterogeneity of ice commonly discussed.

Free-radical precipitation polymerization was used to make non-ionic poly(N-isopropylacrylamide) (PNIPAM) microgel particles. On the synthesized PNIPAM microgel particles, a dynamic light scattering experiment was performed, and hydrodynamic radii were determined to be roughly 240 and 125 nm for temperatures of 298 and 313 K, respectively. Dielectric experiments were carried out on a 10 wt % PNIPAM microgel aqueous suspension at temperatures extending from 288 to 323 K, including volume phase transition temperature (VPTT) at 305 K in the frequency range of 40 Hz to 50 GHz. At frequencies of about 3-5 MHz and 16-18 GHz, two distinct relaxation processes were detected, in addition to electrode polarization and the contribution of dc conductivity. The local chain motion of PNIPAM (p-process) and the average relaxation mode of water located at the bulk solution and also within the microgel (w-process) are assumed to be the origins of the two relaxation processes. Furthermore, based on the idea of two kinds of water models, contributions of each of the two kinds of water, both free water outside the microgel (w1, with its relaxation time of tau(w1)) and confined water within the microgel (w2, with its relaxation time of tau(w2)), to the high-frequency relaxation spectrum were evaluated. The tau(w2) is only 2-2.7 times larger than tau(w1) above VPTT. This means that rotational motion of water molecules is not significantly constrained inside the microgel particle even above VPTT. The NMR rotational correlation time tau(c), which is comparable to the dielectric relaxation time, was estimated using Bloembergen-Purcell-Pound (BPP) theory. The 3 tau(c) value for the microgel suspension obeys BPP theory only up to VPTT; above that, due to anisotropy and/or loss of translational mobility of water induced by microgel shrinkage, precondition of BPP theory is broken. Furthermore, we obtained the concentration of PNIPAM in microgel particles using both the relaxation times and relaxation strengths of w1 and w2 above and below VPTT. Below VPTT, the p-process locates at the MHz region, and it shifts toward the lower-frequency side above VPTT due to the hindrance by microgel structural changes. The dynamics of the polymer and water inside and outside microgel particles in the solution bulk are observed simultaneously by the same physical quantities through the volume phase transition.

Dielectric relaxation studies of acetate buffer solutions of Sodium Dodecyl Sulphate (SDS- anionic), Cetyl Trimethyl Ammonium Bromide (CTAB- cationic), Tween 80 (TW-80-non-ionic), Betaine Anhydrous (BA- zwitterionic) surfactants have been examined in the frequency region between 1GHz and 25GHz for various concentrations of surfactants at the temperatures of 283, 288, 293 and 298K using time domain dielectric spectroscopy. The obtained corrected loss spectra of all the amphiphiles except betaine anhydrous in acetate buffer solution depicted peaks near 1-2GHz and 15GHz, respectively. For betaine anhydrous, expected peak was not observed in the 1-2GHz frequency region. The peak ascertained near 15GHz, and another peak about 1-2GHz was accorded to free water relaxation and bound water reorientation of the surfactant micelles, and has acquired the reliance of temperature with concentration in detail. Single Debye and Cole-Cole function was employed to compute the relaxation times of free water and bound water, respectively. The Arrhenius plot was used to calculate the enthalpy and entropy for the micelle forming surfactants.

In this study, ZnO–Fe 2 O 3 nanocomposites were prepared by high-energy ball milling technique and characterized through X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), UV–visible spectroscopy and dielectric spectroscopy. The amount of Fe 2 O 3 in the ZnO–Fe 2 O 3 nanocomposites was varied at the rates of 1[Formula: see text]wt.%, 3[Formula: see text]wt.% and 5[Formula: see text]wt.% in order to investigate its influence on the structural, optical and dielectric properties of the nanocomposites. XRD patterns of nanocomposites revealed no shift in peak positions and hence confirmed the formation of composites after ball milling. Further, it was observed from FESEM analysis that Fe 2 O 3 particles were distributed randomly on the ZnO matrix of the nanocomposites. ZnO–Fe 2 O 3 nanocomposites reveal extended optical absorption in the range of 400–600[Formula: see text]nm from UV studies. The dielectric constant and loss of the nanocomposites decrease exponentially with increase in frequency. The composition and frequency dependences of the dielectric constant, dielectric loss and AC conductivity are explained based on the Maxwell–Wagner effect and Koop’s theory.

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Composites of polypropylene with different weight percentages of ZnO-TiO2 core-shell nanoparticles were prepared by the combination of solution and mixture melting methods. Dielectric properties of polypropylene composite films were studied at frequencies ranging from 50 Hz to 5 MHz at four different temperatures (313, 333, 353, and 373 K). It is observed that the dielectric constant reduces quickly in the low-frequency range followed by a near frequency independent behavior above 1 KHz. The dielectric properties of composites at low frequency can be explained by interfacial polarization or Maxwell-Wagner-Sillars effect. It is also observed that the dielectric constant reaches the maximum value at 3 wt% of ZnO-TiO2, which is the percolation threshold of nanocomposite. As the weight percentage of ZnO-TiO2 increases beyond the percolation threshold up to 7%, the dielectric constant of the nanocomposites decreases. The dielectric loss of the composites follows the similar trend with frequency as the dielectric constant. A sharp increase in the dielectric loss of the nanocomposite observed near the percolation threshold is due to leakage current produced by the formation of conductive network by ZnO-TiO2 core-shell nanoparticles. Further, peaks in the loss tangent observed for the nanocomposite systems indicating the appearance of a relaxation process. These relaxations peaks were shifted to higher frequencies as the particle content increased, since relaxation processes were influenced by the interfacial polarization effect which generated electric charge accumulation around the ZnO-TiO2 core-shell nanoparticles.

Dielectric relaxation studies of rat tail tendon collagen with anionic sodium dodecyl sulphate (SDS), cationic cetyltrimethyl ammonium bromide (CTAB) and nonionic Tween 80 in aqueous buffer solutions at four different temperatures have been carried out in the frequency range 1 GHz to 25 GHz using time domain dielectric spectroscopy. The frequency dependent normalized dielectric modulus function P of the collagen and surfactant solutions show up as peaks around 1-2 GHz which is due to the bound water around collagen macromolecule and surfactant micelles. For the collagen - surfactant complexes, the peak in normalized dielectric modulus function P is shifted towards high frequency side near 2-3 GHz upon addition of surfactants to collagen in buffer solution. The water structure around collagen is altered in the presence of micelle forming surfactant additives and this change may affect the degrees of freedom of their motion. Hence the significant changes are observed in the relaxation time of bound water around collagen macromolecule in the presence of surfactants. Further, it was observed that no considerable change in relaxation time of hydration water of the complexes with respect to change in temperature within the studied temperature range. The activation enthalpy and activation entropy for the dipolar orientation corresponding to the free water for the surfactants and their complexes with collagen have been calculated from the Arrhenius plot. Our thermodynamic results suggest that the two-hydrogen-bonded model may be possible in SDS and Tween 80 environments, whereas the one-hydrogen-bonded model is likely to be possible in buffer and CTAB environments. (C) 2019 Elsevier B.V. All rights reserved.