Hydroxypropylmethylcellulose surface activity at equilibrium and adsorption dynamics at the air-water and oil-water interfaces

The surface behaviour of hydroxypropylmethylcelluloses (HPMC) was studied at the air-water (A/W) and oil-water (O/W) interfaces. At the A/W interface, the pi-C isotherms were sigmoidal and presented inflexions as the HPMC bulk concentration increases, related with different structural patterns adopted by the biopolymer segments. The behaviour of these biopolymers at the O/W interface resulted different. No inflections in the adsorption isotherm were observed, denoting the absence of any change in the structure of the adsorbed monolayer. The order in the interfacial activity was different at the two interfaces. The dynamics of adsorption showed that the surface pressure (pi) values and the rate of adsorption/penetration were lower at the O/W interface. Analogously to pi values, the surface dilatational modulus was smallest at the O/W interface, however at long-term adsorption strong viscoelastic films are formed at the O/W interface. (C) 2009 Elsevier Ltd. All rights reserved.