Effect of molecular weight and diffusivity on the adsorption of PEO-PPO-PEO block copolymers at PTFE-water and oil-water interfaces

The diffusion and adsorption behaviors of a few PEO-PPO-PEO type triblock copolymers, namely, PluronicsA (R) L62, L64, F68, F87, and F88 at solid-liquid and liquid-liquid interfaces is investigated using water penetration through packed PTFE powder, dynamic surface tension (DST), interfacial tension (IFT), dynamic light scattering (DLS), and contact angle measurements. The water penetration and DST data reveal that the diffusivity of these block copolymers to the interface decreases with increase in the PEO molecular weight of the polymer and is governed by adsorption of surfactant molecules at the interface through PPO blocks. The DST and IFT results reveal faster diffusion to the interface for low molecular L62 and L64. The adsorption behaviors at isopropyl myristate (IPM)-water and PTFE-water interfaces are in good agreement, where lower molecular weight and lower PEO content favor the faster diffusion kinetics. The size of the formed emulsion droplets in presence of different surfactant molecules is measured using DLS, which shows bigger emulsion droplet size for high molecular weight and PEO containing polymer F88. Thus, it was found that surfactant having lower DST will result in higher wettability, lower contact angle, and lower interfacial tension.