In a prior work , fabrication of a nanofibrous sheet using electrospinning technique incorporating mixture of fatty acids (stearic and lauric acid) and polyvinyl alcohol was reported. PVA acted like a guiding polymer for electrospinning forming the fibrous matrix (forming a constrained environment for the fatty acid components) and fatty acids role was that of a phase change material. It was demonstrated that these sheets can act like flexible thermoregulating enclosures. A significant drop in eutectic temperature in the fatty acid binary mixtures was observed when in nanofibrous mats as compared to their bulk mixtures. Modeling suggested that the molecular interaction is altered in constrained environments as compared to bulk and it was conjectured that changing the hydrophilicity/oleophilicity of the constraining environment may further change the interaction between the two molecular components and thereby the eutectic point of the mixture. The PVA nanofibrous sheets incorporating the eutectic composition also showed poor mechanical strength thereby limiting its use as a thermoregulating enclosure. In this work, we incorporate PDMS (polydimethylsiloxane) as additional component in the spinning solution which serves to impart improved mechanical strength to these sheets as well as alter the hydrophilicity of the constrained environment and provides a route to test our conjecture. Both pure stearic acid and mixtures of lauric and stearic acid in PVA-PDMS nanofibrous sheets have been studied. Thermal, mechanical, morphological and wettability characterizations of these composite sheets have been performed using DMA, tensile tests, differential scanning calorimetry, surface profilometry, and SEM. In mats incorporating pure stearic acid, it was observed that mechanical strength improves by incorporating PDMS but only up to an optimal concentration of the stearic acid. PDMS-PVA mats incorporating stearic acid also exhibit good membrane properties and can be used to separate oil and water from emulsions. Detailed studies to construct a phase diagram for lauric and stearic acid mixtures in PVA-PDMS mats and compare it to the bulk phase diagram and the phase diagram obtained in PVA mats is under way. This comparison will be used to interpret the altered molecular interactions resulting from the change in the nature of the constraining environment.
Keywords: PVA/PDMS/Fatty Acids, Electrospinning, DMA, DSC, Tensile strength
 GUPTA R., KEDIA S., SHAURAKHIYA N., SHARMA A., RANJAN A., ELSEVIER 2016. Composite nanofibrous sheets of fatty acids and polymers as thermo-regulating enclosures. Solar Energy Materials and Solar Cells, 157, 676-685.