Interfacial properties of adsorbed films made of a PEG2000 and PLA50 mixture or a copolymer at the dichloromethane-water interface.

Adsorption kinetics of films of poly(ethylene glycol) (PEG2000) studied by the dynamic pendant drop method showed that PEG2000 was more tensioactive at the dichloromethane (DCM)-water interface than at the air-water interface. When initially solubilized into DCM, PEG2000 segments would form an adsorbed layer with hydrophobic segments buried into the polymer chains turned toward the organic phase. Compression of this layer, accompanied by viscoelastic effects, led to expulsion of some hydrophilic tails toward the water phase. When initially dissolved in water, adsorption of PEG2000 segments led to an elastic PEG2000 layer organized on both sides of the interface. Results showed that when the PEG2000-PLA50 (poly(D,L-lactide)) copolymer film was adsorbed at the DCM-water interface, it resulted in a mixed layer exclusively turned toward DCM and its rheological properties were governed by PLA50. When adsorption at the DCM-water interface resulted from a physical mixture of PEG2000 and PLA50, rheological properties of the film were influenced by the initial localization of PEG2000 in the bulk phases. In the case of a mixed film formed by the adsorption of PLA50 from DCM and PEG2000 from water, results showed that PEG2000 segments totally pushed those of PLA50 away from the interface and exclusively influenced the behavior of the mixed film.