Adsorption of Surfactant Mixtures at Solid/Liquid Interface:A Comprehensive In-situ Spectroscopic, Microcalorimetric andTheoretical Modelling Study

Surfactant adsorption is an important phenomenon in many processes such as enhanced oil recovery, detergency, flotation, and molecular electronics and microstructure of the adsorbed layers a governing role in determining the efficiency of these processes. An approach combining advanced spectroscopic techniques such as luminescence, electron spin, resonance, Raman and NMR with conventional techniques of adsorption, electrokinetic, calorimetric and wettability has been used in recent studies to determine important microstructural properties such as micropolarity, microfluidity, aggregation number and surfactant and polymer orientation for several alumina-dodecyl sulfonate/polyacrylic acid systems for the first time. It is now possible to determine such properties in mixed surfactant systems that are invariably involved in practical systems. Mixed systems offer significant advantages in terms of high surface activity, salt tolerance, reduced precipitation loss etc. On the other hand, preferential adsorption from surfactant mixtures will cause chromatographic separation of the surfactant components resulting not only in loss of surfactants, but also in significant changes in the efficiency of the processes involved. Important questions to be answered include the effect of mixing, for example, anionics with nonionics, effect of relevant variables such as pH, ionic strength, multivalent ions concentration, temperature and order of addition of the components. It is most interesting to determine arrangement and rearrangement of the adsorbate species as the system is subjected to perturbations of composition, pH, etc. and to determine the resultant changes in the interfacial behavior of the systems. It is the aim of this work to investigate molecular level behavior of the species in mixed adsorbed films as a function of surfactant structure, PH, salinity, hardness, temperature using the comprehensive approach involving above spectroscopic and adsorption techniques. It will also be a major aim to model these systems with the help of additional information to be obtained from microcalorimetric investigation. Also, new techniques will be explored as in the past to determine additional micro and nano level properties of the adsorbed layers. With this multipronged approach, it should be possible to develop an accurate understanding of the adsorption mechanisms of real surfactant systems and to develop capability to control adsorption and to manipulate the configurational properties of the adsorbed species and their aggregates.