The chemical industry is one of the largest manufacturing industries in developed countries. The chemical industry produces mostly chemicals, like polymers, petrochemicals and basic inorganic chemicals to be used by other companies before ending up in consumer products.
Chemical substances and mixtures are part of all aspects of our lives and are found literally everywhere. In some cases, their behavior in a certain environment and in the meeting with certain surfaces can be relevant and of interest, since these may influence the chemical’s behavior to deviate from the one intended. Take, for example, surfactants and polymers, which are chemicals found in abundance in our daily lives. Surfactants are widely used as important components in detergents and other cleaning agents, in oil processing and recovery, and in pharmaceutical formations, to mention but a few.
Polymers are found in more areas than any other material, such as adhesives, coatings, foams, foods, cosmetics, clothes and many more. All of these areas are related to an interface in one way or the other, meaning that an understanding of the interfacial behavior and characteristics is important for the design and control of molecular behavior at the end user.
QSense QCM-D is a line of instrumentation for the real-time assessment of surface interaction analysis that will help you get the full picture of your surface-molecule interactions. Characterize phenomena and interactions at liquid/solid interfaces such as adsorption kinetics, layer thickness, morphological changes and the stability of the molecule-surface interactions
Polyoxyethylene surfactants are widely utilized in industrial applications, like coatings, food products, agriculture formulations, personal care and petroleum, where emulsion and foam stabilization is important. Alcohol ethoxylates are replacing more toxic alkylphenol ethoxylates that have been traditionally used as emulsifiers in many applications. However, straight-chain alcohol ethoxylates do not demonstrate as good emulsifier properties as alkylphenol ethoxylates, mainly due to the bulky tail of the latter. This is due to differences in the size of the polar head and the hydrocarbon tail that hinder the formation of a closely packed film at the interfaces.
The adsorption and surface rheology properties of two technical-grade non-ionic surfactants based on C10-Guerbet alcohol differing in the numbers of EO groups have been studied. They are denoted as, C10EO6 and C10EO14.
Surface pressure isotherms for both surfactants were fitted to the reorientation model. However, surface rheology data have to be interpreted differently. It will be shown that C10EO6 can be interpreted in the framework of diffusional relaxation process, whereas C10EO14 deviates from a diffusional controlled process. Its surface rheology response is closer to that of non-ionic polymer surfactants. Figure 1 (C10EO6) and Figure 2 (C10EO14) show the storage (E’) and loss (E’’) moduli of both surfactants obtained from the oscillation perturbation at two frequencies (0.02 and 0.5 Hz). The solid and dashed lines are the best fit to experimental data obtained from a diffusional model. It is shown that only the experimental data values of C10EO6 surfactant are in good agreement with the proposed model.
Figure 1. Storage, (E’, open symbols), and loss, (E’’, close symbols), moduli as a function of surfactant bulk concentration at two frequencies (0.02 Hz – triangles) and (0.5 Hz – diamonds) for the C10EO6 surfactant. Solid and dashed lines are the best fit of the experimental data to the diffusional model.
Figure 2. Storage, (E’, open symbols), and loss, (E’’, close symbols), moduli as a function of surfactant bulk concentration at two frequencies (0.02 Hz – triangles) and (0.5 Hz – diamonds) for the C10EO14 surfactant. Solid and dashed lines are the best fit of the experimental data to the diffusional model.
Surface rheology of both surfactants showed that they form a viscoelastic layer at the air/water interface. Nevertheless, the adsorbed films behave differently depending on the number of oxyethylene groups. Thus for the smaller surfactant, the adsorption and rheological data are well fitted to a diffusional model, whereas the larger C10EO14 surfactant shows a surface behavior closer to that of polymeric surfactants. Moreover, comparison of the dilatational elasticity and viscosity of both surfactants indicates that elasticity is enhanced by increasing the number of EO groups. The elasticity of adsorbed surfactant films are directly related to foam and emulsion stability. Therefore, the C10EO14 surfactant is likely to form more sable layers against coalescence than the shorter C10EO6 surfactant. Nevertheless, foam formation will be enhanced by using C10EO6 than C10EO14, due to the higher diffusivity of the former surfactant. Therefore, these results may find interesting applications in order to rationally develop stable foams and emulsions by using non-ionic surfactants containing oxyethylene groups.