Dynamics of Thermally Induced Phase Separation in Polyvinyl Alcohol Aqueous Solutions: Impact of Viscosity Asymmetry on Scaling

This research presents an experimental analysis of thermally induced phase separation (TIPS) dynamics in a polymer aqueous solution with very different viscosities (a factor of about a thousand) between separated phases but with no elastic character. The study encompasses the determination of the phase diagram for the polymer-water system, and the exploration of phase separation (PS) dynamics in critical and off-critical systems using laser scanning confocal microscopy (LSCM). Thus, domain growth is analyzed through a fast Fourier transform (FFT) from the confocal images, providing insights into the characteristic size and the structure factor scaling. The study focuses on 10 and 12 wt. % polyvinyl alcohol (PVA) solutions, revealing distinct morphologies and growth mechanisms. Despite the huge difference in viscosities between separated phases, PVA₁₀ exhibits characteristics of spinodal decomposition with interconnected structures and linear growth (L_m (t) ∼ t¹), indicative of hydrodynamic coarsening. Conversely, PVA₁₂ shows a trend toward discontinuous structures with growth following L_m (t) ∼ t^1/3, suggesting a diffusion-driven coalescence mechanism. Notably, both systems demonstrate self-similar growth patterns despite the significant viscosity contrast, as confirmed by scaled structure factor analysis.