The interfacial structure of polymeric surfactant stabilised air-in-water foams

Small-angle neutron scattering was used to probe the interfacial structure of nitrogen-in-water foams created using a series of tri-block polymeric surfactants of the poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (EOx–POy–EOx) range, from which the nature of the polymeric interface could be characterised. The data follow a pronounced Q−4 decay, along with a number of inflexions and weak but well-defined peaks. These characteristics were well-described by a model embodying paracrystalline stacks of adsorbed polymer layers, whose formation is induced by the presence of the air–water interface, adsorbed at the flat air–water (film lamellae) interface. A minimum of approximately five paracrystalline polymer layers of thickness of the order of 85–160 Å, interspersed with somewhat thicker (400 Å) films of continuous aqueous phase were found to best fit the data. The thickness of the layer (L) was shown to follow a relationship predicted by anchor block dominated polymer adsorption theories from non-selective solvents, L EO1PO1/3. The insight gained from these studies should permit a more rational design of polymeric stabilisers for hydrophilic polyurethane foams

Segregation versus interdigitation in highly dynamic polymer/surfactant layers

Many polymer/surfactant formulations involve a trapped kinetic state that provides some beneficial character to the formulation. However, the vast majority of studies on formulations focus on equilibrium states. Here, nanoscale structures present at dynamic interfaces in the form of air-in-water foams are explored, stabilised by mixtures of commonly used non-ionic, surface active block copolymers (Pluronic®) and small molecule ionic surfactants (sodium dodecylsulfate, SDS, and dodecyltrimethylammonium bromide, C12TAB). Transient foams formed from binary mixtures of these surfactants shows considerable changes in stability which correlate with the strength of the solution interaction which delineate the interfacial structures. Weak solution interactions reflective of distinct coexisting micellar structures in solution lead to segregated layers at the foam interface, whereas strong solution interactions lead to mixed structures both in bulk solution, forming interdigitated layers at the interface

Probing the behaviour of poly(ethylene oxide)- poly(propylene oxide)-poly(ethylene oxide) surfactants in the formation of hydrophilic polyurethane foam

Polyurethane (PU) foams are widely used in the medical industry in the treatment of chronic wounds but the role of surfactants in the reaction process, which strongly influences foam structure and properties, is not well understood. In this research, a homologous series of non-ionic poly(ethylene oxide)-poly(propylene oxide)- poly(ethylene oxide) (Pluronic) block copolymer surfactants were studied, in order to elucidate the influence of surfactant structure on PU foam performance. The behaviour of aqueous surfactant stabilised foams was investigated using a combination of surface science techniques (foaming ability / stability, surface tension) and small-angle neutron scattering (SANS). SANS has been successfully implemented to probe the adsorbed Pluronic surfactant layer of dynamic foams in-situ in the neutron beam. We propose the air-water interface comprises a paracrystalline stack consisting of a minimum of 5 adsorbed surfactant layers, with thickness ranging from 80-200Å interspersed with somewhat thicker (200Å) films of water. Total adsorbed layer thickness correlates directly with aqueous foam stability. Correlations of aqueous behaviour to the cell structure and performance of PU foams manufactured on an industrial line were made in an attempt to determine the features of surfactant necessary to produce ‘ideal’ PU foam wound dressings. Analysis of foam cell size and fluid absorption properties demonstrated that greatest absorption was observed for small, fine cell size. This was typically produced by the smallest molecular weight,most hydrophobic surfactants of the series implying that the surface activity of the surfactant (i.e. its ability to reduce the surface tension of the system) is more important than its foaming behaviour. This study should provide a more rational approach when designing surfactant formulations for polyurethane foam systems

AN EXPLORATORY STUDY OF THE PREDICTORS OF COPING AND PSYCHOLOGICAL WELL-BEING IN FEMALE PARTNERS OF EXCESSIVE DRINKERS

The study was a cross-sectional questionnaire survey of 29 women with a recent experience of coping with excessive drinking in a male partner. A number of cognitive and environmental factors were studied to determine the extent to which they predicted coping style and psychological well-being in this group. Results of multiple regression analysis indicated that “engaged” coping (characterized by attempts to change the drinker) was best predicted by a single cognitive variable (self-demands). In contrast, “tolerant” coping was best predicted by a combination of participant’s beliefs about their ability to withdraw from the drinker and the degree of drink-related hardship experienced within the family. “Withdrawal” coping, characterized by avoidant and independent behaviours by the women, was best predicted by a combination of beliefs about the necessity of withdrawal and the duration of time the participants had been coping with the excessive drinking. Finally, psychological well-being was best predicted by a single environmental variable (the degree of hardship caused by the drinking). A number of significant correlations were found to exist between the predictor and criterion variables and are discussed. Limitations of the study and clinical implications of the findings are examined.</jats:p