Structure and Mechanical Properties of a Polyglycerol Ester at the Air−Water Surface

Abstract

We studied the structure and mechanical properties of surface films resulting from the adsorption of a dispersed L beta phase at the air-water interface. This L beta phase corresponds to multilamellar vesicles and is formed by a commercial polyglycerol fatty acid ester (PGE) in aqueous solution at temperatures below the main chain-melting temperature (Tm=58 degrees C). We measured the adsorption kinetics using the pendant drop technique and mechanical properties of PGE films using oscillatory surface shear and dilatational rheometric methods. Though the adsorption kinetics are very slow, we show that the L beta phase of PGE is surface-active and forms viscoelastic films at the air-water surface after sufficiently long adsorption times. The rheological response functions to shear and dilatational deformation are reminiscent of those of temporary networks, indicating an intermolecular connectivity at the surface. This temporary network is probably created by hydrophobic interactions of alkyl chains. We obtained more detailed information about the properties of this network by comparing the rheological signature of an adsorbed PGE film (unknown structure) with a solvent-spread monolayer (known structure). We characterized the structural features of spread PGE films by recording the Langmuir isotherm and Brewster angle micrographs (BAM).We show that the rheological responses of the adsorbed film and the solvent-spread monolayer are very close to each other, indicating a structural similarity. From this study, we conclude that a dispersed L beta phase of PGE is able to adsorb at the air-water surface at T<T m. The structure of the resulting film is a composite consisting of a monomolecular layer at the surface and eventually further bimolecular sublayers in the bulk. At T<T m, the alkyl chains within the layers are noncovalently connected and provide mechanical film stability measured as a viscoelastic response under small-amplitude shear or dilatational deformation.

Binary coalescence of gas bubbles in the presence of a non-ionic surfactant

“…This stabilizing force could be interpreted as a steric or structural repulsive force, which acts against forced film drainage as two bubbles are pressed against each other. As reported in an earlier article [16], PGE self-assembles at the air-water surface into a mesoscopic structure consisting of stacked mono-and bilayers. After sufficient adsorption time, this structure is no longer confined to the two-dimensional interface but extends into the surrounding bulk liquid (here: thin film).…”

“…More details about the phase behavior and of the importance of residues of anionic fatty acid soaps are given elsewhere [15]. Recently, it was shown that despite the restricted molecular mobility in the gel-like state, PGE molecules are able to adsorb at the air-water interface at ambient temperature [16].…”

“…In an earlier study [16], the elastic or solid-like response under both modes of deformation, was related to formation of a crystal in the surface and sub-surface. This crystal has a three-dimensional nature and consists of a monolayer in the interfacial plane and several bilayers, which extend in the sub-surface bulk.…”

Influence of pH on colloidal properties and surface activity of polyglycerol fatty acid ester vesicles

“…Consequently, the foaming power is determined by the ability of PGE to adsorb at the newly created surface within equally short time scales. However, it has been recently shown that the adsorption kinetics of native solutions of this surfactant, at temperatures typical for processing, are very slow [18]. Yet in that article, the influence of the ion content of the solution on the adsorption kinetics was not considered.…”

Filmes De Langmuir De Ésteres De Polietilenoglicol Derivados De Ácidos Graxos

“…Duerr-Auster et al, em 2008 tem relatado estudos sobre a estrutura e propriedades mecânicas de filmes superficiais resultado da adsorção ou dispersão de ésteres de poliglicerol (PGE) na interface ar-água através de métodos de reologia dilatacional e métodos oscilatórios de cisalhamento. Neste trabalho eles concluem que esses filmes moleculares são ativos na interface e possuem propriedades viscoelásticas provenientes da conectividade intermolecular de uma rede interfacial formada na monocamada, provavelmente devida à interações hidrofóbicas das cadeias alquílicas destes compostos (Duerr-auster et al, 2008). Anton, et al, em 2013 apresentaram um estudo que contribui grandemente ao melhor entendimento da reologia bi-dimensional das monocamadas de surfactantes não iônicos a base de polietilenoglicol (PEG) adsorvidos na interface óleo-água.…”