Poly(vinyl alcohol) (PVA) with sulfosuccinic acid (SSA) membrane was prepared with different concentrations of SSA (wt.%) and thermally crosslinked successfully at 100 °C. Ion exchange capacity and proton conductivity were found to increase with increasing the SSA content in the meantime the water uptake and hydration number were declined with the rise in the degree of sulfonation. This anomalous behavior was discussed based on Nerst equation parameters which confirm the results discussion with enhancement with data of contact angle. Tensile strength results suggest the deterioration of the PVA/SSA membranes with increasing SSA content because of the chemical reaction of SSA and PVA chains. Positron annihilation results were found to enhance the electrochemical‐mechanical results of the membranes. The o‐Ps lifetime was found to increase with increasing degree of sulfonation while SO3 was working as an inhibitor agent of PS formation as o‐Ps Intensity was declined with an elevated percentage of SSA content. The o‐Ps lifetime as a function of temperature for different PVA/SSA membranes having different SSA content increased with increasing SSA content. Furthermore, the glass transition temperature of PVA/SSA membranes was found to decrease with increasing the SSA content. The results were discussed based on the free volume theory.

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Polyvinyl alcohol (PVA) with sulfophthalic acid (sPTA) as a proton exchange membrane (PEM) for fuel cell applications was prepared by the solvent casting method.The fabricated membranes were obtained by varying the concentration of sPTA from 5 to 30 wt.% of PVA and thermally crosslinked at a temperature of 100 C for 1 h.Crosslinked PVA/sPTA membranes were characterized by FTIR spectroscopy, scanning electron microscopy (SEM), and wide-angle X-ray diffraction (XRD). The transport properties were investigated by determining ion exchange capacity (IEC), water uptake, methanol permeability, and proton conductivity. Free volume hole size and its distribution of crosslinked PVA membrane were measured by positron annihilation lifetime spectroscopy (PALS). With an increase in sPTA concentration in the PVA membrane, both IEC and proton conductivity increased, but water uptake and methanol permeability decreased. At room temperature, IEC values were increased from 0.3 to 1.6 meq/g, and proton conductivity varied from 0.2 to 3.5 S/cm. According to PALS data, increasing the sPTA content causes the free volume content of crosslinked PVA membranes to decrease. The results were analyzed and presented in the context of free volume theory, in which the concentrations of nanostructure free volume defects are related to the membrane's transport capabilities.

Using the casting method, proton exchange membranes PEMs for fuel cell were prepared by thermal cross-linking of polyvinyl alcohol (PVA) with sulfophthalic acid (sPTA). The membranes were prepared with different cross-linking temperatures with thickness ranged between 100 to 150 μm. The prepared membranes were characterized by different techniques such as ion exchange capacity, thermal analyses, water uptake and proton conductivity. The prepared membranes showed proton conductivity between 8.46-32.7 mS/cm. Increasing the cross-linking temperature increased the cross-linking density, resulting in an enhancement in the tensile strength and thermal stability of the prepared membranes. The membrane hole sizes were obtained using positron annihilation lifetime spectroscopy (PALS) measurements. Cross-linked PVA/sPTA membranes showed a strong correlation between the free volume hole size with the mechanical stability and methanol permeability of the membranes.

Abstract:In this paper, the entropy-temperature curves are investigated for rotating boson gases in a 1D optical lattice with transverse harmonic confinement. Regimes at which the atomic sample can be significantly heated or cooled by adiabatically changing the lattice depth and the rotation rate are demonstrated. The suggested approach, which is the semiclassical approximation, includes the correction due to the finite size effect. The obtained results show that the entropy-temperature curves have a monotonically increasing nature for this system, in agreement with the standard thermodynamic arguments. For fixed temperature, entropy always increases with the increasing of the rotation rate or optical potential depth.