Sulfonated Styrene-(ethylene-co-butylene)-styrene/Montmorillonite Clay Nanocomposites: Synthesis, Morphology, and Properties

Sulfonated styrene-(ethylene-butylene)-styrene triblock copolymer (SSEBS) was synthesized by reaction of acetyl sulfate with SEBS. SSESB-clay nanocomposites were then prepared from hydrophilic Na-montmorillonite (MT) and organically (quaternary amine) modified hydrophobic nanoclay (OMT) at very low loading. SEBS did not show improvement in properties with MT-based nanocomposites. On sulfonation (3 and 6 weight%) of SEBS, hydrophilic MT clay-based nanocomposites exhibited better mechanical, dynamic mechanical, and thermal properties, and also controlled water–methanol mixture uptake and permeation and AC resistance. Microstructure determined by X-ray diffraction, atomic force microscopy, and transmission electron microscopy due to better dispersion of MT nanoclay particles and interaction of MT with SSEBS matrix was responsible for this effect. The resulting nanocomposites have potential as proton transfer membranes for Fuel Cell applications

Kinetic studies of POSS–DGEBA precursors derived from monoamine functional POSS using dynamic dielectric sensing and nuclear magnetic resonance

Incorporation of pre‐reacted monofunctional polyhedral oligomeric silsesquioxane (POSS)–epoxy adducts dramatically improves dispersion of POSS in epoxy–amine networks. The relationship between reaction kinetics and mechanism for formation of POSS–epoxy adducts versus reaction temperature was investigated. Reactivities of epoxy–monoamine functional POSS molecules were determined using in situ reaction monitoring by dynamic dielectric sensing and 29Si NMR spectroscopy. The amine‐functional POSS–epoxy isothermal reaction showed reduced reactivity due to reduced molecular mobility, that is, diffusion limitations. Kinetic parameters were determined by fitting 29Si NMR data to the model of Kamal that was extended to include diffusion. Fitting of this model to experimental data showed very good agreement over the entire conversion range for pre‐reaction between amine‐functionalized POSS and epoxy. An autocatalytic mechanism, the same as that for the neat epoxy–amine systems, was indicated. Gel permeation chromatography, scanning electron microscopy and transmission electron microscopy were used to investigate molecular weight evolution and morphology of final networks cured by 4,4′ diaminodiphenyl sulfone using pre‐reacted POSS–epoxy adducts. POSS aggregate size decreased with increased pre‐reaction temperature; more homogenous POSS dispersion was observed with higher pre‐reaction temperature. Dynamic mechanical analysis demonstrated that Tg of composites decreased slightly compared to that of the neat matrix and there appeared to be little change in microstructural heterogeneity

PVA/chitosan/silver nanoparticles electrospun nanocomposites: Molecular relaxations investigated by modern broadband dielectric spectroscopy

In this study, we used broadband dielectric spectroscopy to analyze polymer nanofibers of poly(vinyl alcohol)/chitosan/silver nanoparticles. We also studied the effect of incorporating silver nanoparticles in the polymeric mat, on the chain motion dynamics and their interactions with chitosan nanofibers, and we calculated the activation energies of the sub-Tg relaxation processes. Results revealed the existence of two sub-Tg relaxations, the first gets activated at very low temperature (?90?C) and accounts for motions of the side groups within the repeating unit such as ?NH2, ?OH, and ?CH2OH in chitosan and poly(vinyl alcohol). The second process gets activated around ?10?C and it is thought to be related to the local main chain segments? motions that are facilitated by fluctuations within the glycosidic bonds of chitosan. The activation energy for the chitosan/PVA/AgNPs nanocomposite nanofibers is much higher than that of the chitosan control film due to the presence of strong interactions between the amine groups and the silver nanoparticles. Kramers?Kr?nig integral transformation of the ?" vs. f spectra in the region of the chitosan Tg helped resolve this relaxation and displayed the progress of its maxima with increasing temperature in the regular manner.This research was funded by the Qatar University support to postgraduate students under the grants #: QUST-CAS-SPR-14/15-4 and QUST-CAM-SPR-2017-6. The publication of this article was funded by the Qatar National Library.Scopu

Chemical Modification of a Nafion(R) Sulfonyl Fluoride Precursor Via In Situ Sol-Gel Reactions

The melt-processible sulfonyl fluoride precursor of a Nafion(R) ionomer was utilized as a sol-gel reaction medium for 3-aminopropyltriethoxysilane (APrTEOS). The diffusion-mediated reaction of APrTEOS with SO2F groups can be controlled with high degree of reaction. Fourier transform infra-red/attenuated total reflection studies show that sulfonamide linkages are formed and condensation reactions of SiOR groups provide covalent crosslinking of chains. Formic acid treatment plus high temperature plus long time resulted in a high degree of polymer crosslinking as seen in Si-29 solid state nuclear magnetic resonance spectra. Mechanical modulus and strength increase, and elongation-to-break decreases with increasing filler. Hybrids with \u3c18% uptake accumulate cracks with crosslinked outer layers, each event signalled by a drop in stress followed by stress recovery. While there are sharp visual material fronts inward from both surfaces, EDAX (energy dispersive analysis of X-rays) showed that there are no sharp Si composition boundaries. Differential scanning calorimetry (d.s.c.) revealed a broad, weak endothermic event peaking at 67 degrees C for the precursor and shifting to higher temperatures while broadening with increasing filler content, indicating progressively-restrictive glass-transition-temperature-related molecular motions within an increasingly nonhomogeneous environment. For the unreacted precursor, this d.s.c. transition occurs at a temperature just above a glass transition detected by dynamic mechanical means. (C) 1997 Elsevier Science Ltd

Nafion/ORMOSIL Hybrids via In Situ Sol-Gel Reactions .3. Pyrene Fluorescence Probe Investigations of Nanoscale Environment

Pyrene (Py) photophysical probes were used to interrogate structural diversity within [1] Nafion/[silicon oxide] and [2] Nafion/[ORMOSIL] hybrids. The interior of the silicon oxide phase in [1] has the most polar environment wherein Py is trapped in silicon oxide cages in the vicinity of -SO3- groups. Polar/nonpolar interphase regions in [1] are next in order of decreasing polarity. The interior of the ORMOSIL phase in [2] displays lowest polarity, reflecting CH3 groups in Py-encapsulating ORMOSIL cages, and the interphase ranks somewhat higher in polarity. Water uptake is ordered: Nafion/ORMOSIL \u3c unfilled Nafion-H+ \u3c Nafion/[silicon oxide]. The hydrophilicity of unfilled Nafion-H+ is adjustable by tailoring the organic content of the incorporated sol-gel-derived nanophase as polarity determined from fluorescence emission and water uptake correlate well. Fluorescence emission of Py monitored nanostructural polarity shifts that result from secondary in situ gel growth induced by annealing. Additional condensation of SiOH groups and liberation of volatiles is promoted by increasing temperature/time, as evidenced by diminishing polarity. Polarity decrease with annealing is more profound for Nafion/[ORMOSIL incorporating Py] than for Nafion/[silicon oxide incorporating Py] as polar solvents are removed more easily from the less polar ORMOSIL nanophase

Microstructural Evolution of a Silicon-Oxide Phase in a Perfluorosulfonic Acid Ionomer by an \u3ci\u3eIn Situ\u3c/i\u3e Sol-Gel Reaction

Nanocomposites were produced via sol-gel reactions for tetraethylorthosilicate within the cluster morphology of perfluorosulfonic acid films. Small-angle x-ray scattering revealed that the polar/nonpolar nanophase-separated morphological template persists despite invasion by the silicon oxide phase. Scanning electron microscopy (ESEM-EDAX) studies have indicated that the greatest silicon oxide concentration occurs near the surface and decreases to a minimum in the middle. Optical and ESEM micrographs revealed a brittle, surface-attached silica layer at high silicon oxide contents. (C) 1995 John Wiley & Sons, Inc