Altered phase behavior of the lauric acid–stearic acid binary mixtures in electrospun PVA–PDMS mats

Abstract

In this work, we study and report the phase behavior of the mixture of lauric acid (LA) and stearic acid (SA) inside polyvinyl alcohol (PVA)–polydimethylsiloxane (PDMS) nanofibrous mats woven using the electrospinning technique. Incorporating PDMS in the fibers prevents the mechanical properties from degrading due to the eutectic melting of the fatty acid mixtures present in the mats. Based on the results from scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), and Raman studies a phase diagram of the binary LA–SA mixture inside the PVA–PDMS nanofibrous mat environment has been constructed. The phase behavior suggests a eutectic composition in these mixtures of approximately 75 mole percent of LA, an intermediate composition between those obtained for the same mixture in a pure PVA nanofibrous environment (∼50 mole percent) and in the bulk (∼90 mole percent). We conjecture that the hydrophilicity/hydrophobicity of the surrounding fiber environment to which the fatty acid molecules are subjected influences the interactions between the fatty acid molecules and thereby their phase behavior. This work suggests that we can engineer the phase behavior of a fatty acid mixture by altering the properties of its nanoconfinement. From an application point of view, PDMS–PVA mats incorporating LA–SA can be used for fabricating sheets with the desired mechanical integrity and impregnated with phase change materials (PCMs) for thermal energy storage applications.