Interfacial Properties of Diglycerol Esters and Caseinate Mixed Films at the Air−Water Interface

Abstract

The surface pressure (π) at equilibrium (surface pressure isotherm) and surface dynamic properties (dynamic surface pressure and surface dilatational characteristics) of diglycerol ester (diglycerol-monocaprinate, diglycerol-monolaurate, diglycerol-monostearate, and diglycerol-monooleate) and protein (sodium caseinate) as emulsifiers, at different concentrations in the aqueous phase, were measured using tensiometry and a dynamic drop tensiometer, respectively. We have observed that (1) at equilibrium the value of critical micelle concentration (CMC) decreases and the maximum surface excess (Γmax) increases as the hydrocarbon chain increases because the hydrophobic character of the lipid also increases. The presence of a double bond in the hydrocarbon chain also increases the value of CMC and decreases those of Γmax. Caseinate presents higher adsorption efficiency but the surface activity is between those for lipids. The surface pressure isotherm of mixed systems is dependent on the emulsifier concentration and the protein/lipid ratio in the mixture. (2) The adsorption of pure emulsifiers at the air-water interface increases with emulsifier concentration in the aqueous phase via diffusion and penetration of the emulsifier at the interface. For mixed films, the rate of adsorption depends on the concentration and composition of the mixture. Competitive or cooperative phenomena were observed during the adsorption of both emulsifiers at the interface. (3) The surface dilatational characteristics of mixed films are viscoelastic. The surface dilatational modulus reflects the amount of emulsifier adsorbed at the interface and confirms the idea that the protein-lipid interactions at the air-water interface are somewhat weak, there even being the possibility of phase separation.

Dilational Properties of Novel Amphiphilic Dendrimers at Water–Air and Water–Heptane Interfaces

“…7,8 The properties of the interfacial film are governed by the composition and structure of the adsorbed material. 9 Furthermore, the interfacial rheological properties are the main characteristics of the dynamic properties of a film. The study of interfacial dilational properties is useful for better understanding the microcosmic properties of an interfacial film and has been proved to be a powerful technique for probing the interfacial adsorption behaviors.…”

“…The response of a film of molecules at an interface to expansion and compression is a key factor determining the ease of formation and stability of a multitude of colloidal systems such as emulsions and foams. , The properties of the interfacial film are governed by the composition and structure of the adsorbed material . Furthermore, the interfacial rheological properties are the main characteristics of the dynamic properties of a film.…”

Influence of Oleic Acid and Electrolyte on the Interfacial Dilational Properties of Surfactant/Polymer Systems at the Decane-Water Interface

“…Over the past 20 years, many studies have been dedicated to the dilational behavior of polymer solution at both water=air and water=oil interfaces. [6][7][8][9][10][11][12][13][14][15] The interfacial dilational properties are highly influenced by the polymer structure, by the nature of surfactants, and by the concentration ratio of both components. In previous work, we have investigated the interfacial dilational properties of hydrophobically modified polyacrylamide (HMPAM)-surfactant systems at oil-water interface.…”