Comparative Study on the Aggregation Behaviors of X-Shaped and Linear Block Polyethers at the Air/Water and <em>n</em>-Heptane/Water Interfaces

Abstract

Linear block polyethers, i.e., poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-PEO (LPE), and X-shaped block polyethers, i.e., PEO-PPO-PEO (TPE), with same EO/PO ratios and molecular masses were synthesized by anionic polymerization. The aggregation behaviors at air/water and n-heptane/water interfaces were systematically studied. The results show that LPE is more efficient at decreasing the surface tension of water and n-heptane than TPE is. The dynamic interfacial tension curves indicate that the lag-time of the adsorption of the block polyethers at the n-heptane/water interface is smaller than that at the air/water surface, implying that immersion of the PO groups in the oil phase is more energetically favorable than immersion in the air phase. The oil molecules can insert into the adsorption layer, and hydrophobic interactions between oil molecules and PO moieties lead to a relatively ordered arrangement of adsorbed polyether molecules. At the n-heptane/water interface, diffusion of the block polyethers is faster than that at the air/water surface. The dilatational elasticity at the n-heptane/water interface is much higher than that at the air/water surface.