Dynamics of adsorption of hydroxypropyl methylcellulose at the air–water interface

Abstract

Surface dynamic properties (surface pressure and surface dilatational properties) of three commercial hydroxypropyl methylcellulose (HPMC) adsorbed at the air–water interface are presented in this paper as a function of adsorption time. Experiments were performed at constant temperature (20 °C), pH 7, and ionic strength 0.05 M. The dynamics of adsorption and the surface dilatational properties were measured simultaneously for different food-grade HPMC (called E4M, E50LV, and F4M), at bulk concentrations ( C HPMC) ranging from 1×10 −4 to 1% wt. It was found that the surface pressure ( π) increased with the HPMC bulk concentration, which may be associated with HPMC adsorption. These phenomena have been related to HPMC diffusion to the interface (at short adsorption time) and to molecular interactions (at long-term adsorption). The HPMC films behaved as viscoelastic as deduced from the surface dilatational elasticity ( E d) and the loss angle tangent (Tan δ) evolution upon time. The values of E d showed different behavior with the HPMC bulk concentration, which reflect structural differences in the adsorbed film. Differences in the dynamics of adsorption and surface dilatational properties between different HPMCs have been related to molecular differences, such as the molecular weight, degree of substitution, molar substitution, etc.