Surface Interactions between Propylene Glycol and Sodium Dodecyl Sulfate during Coalescence of MMA/nBA/AA Colloidal Dispersions:  A Spectroscopic Study

These studies focus on the behavior of methalmethacrylate/n-butyl acrylate (MMA/n-BA) and methyl methacrylate/n-butyl acrylace/acrylic acid (MMA/nBA/AA) colloidal dispersions stabilized by sodium dodecyl sulfate (SDS). In MMA/n-BA, migration of SDS is apparent, but the presence of AA suppresses SDS mobility even at elevated temperatures. However, the addition of propylene glycol (PG) promotes SDS mobility. Internal reflection infrared imaging (IRIRI) data indicate that PG and SDS occupy the same areas, suggesting that both components reach the surface at the same time through the same transport mechanisms. As PG evaporates, SDS remains on the surface and likely forms crystalline phase. Using IRIRI imaging, with a spatial resolution of 1 μm, coalescence of MMA/nBA/AA was followed as a function of time. These studies show that the presence of AA in colloidal particles significantly alters not only film formation processes, but also SDS-particle interactions, thus minimizing mobility of SDS to the film−air (F−A) interfacial regions during coalescence. This behavior is attributed to the presence of localized ionomeric clusters (LIC) at the particle interstices that exhibit higher thermal stability.