Microstructural Fluids and Simple Fluids at Interfaces

In the first part of this work the self-assembly structure of three amphiphilic Systems is studied using various experimental techniques. After a general introduction given in Chapter 2, the theoretical and practical aspects of the experimental methods are outlined in Chapters 3 and 4, respectively. In Chapter 5 the nature of spontaneously formed aggregates in the binary DDAOH/water system is explored quantitatively by classical and dynamic light scattering as well as electron microscopy. It is shown that these solutions self-assemble into dilute monodisperse unilamellar vesicles in equilibrium with micelles. The experimental data are explained in terms of a model in which most of the micelles are confined to the interior of the vesicles, indicating the existence of a supra-self-assembly mechanism. In Chapter 6 the phase diagram of binary didodecyldimethylammonium acetate/ water system is studied using classical and dynamic light scattering and electrical conductivity measurements. These data are supplemented by SANS studies in the region of high surfactant concentration. The existence of a dilute vesicular phase is demonstrated at concentrations below 0.005 surfactant volume fraction. With increased concentration of surfactant the isotropic sponge (L3) phase and lamellar phase are observed separated by a two phase region. Analysis of the light scattering results indicates the existence of a second order phase transition between the asymmetric and symmetric sponge phase. In the sponge phase region SANS data are consistent with the membrane thickness of 25 A and electrical conductivity results are in agreement with theoretical predictions for charge carriers scattering on large oblate objects. For surfactant concentrations larger than 0.03 volume fraction a mixture of L3 and lamellar phase is observed. In Chapter 7 the thermodynamic consequences of the structure of ternary DDAB/water/cyclohexane system in the microemulsion region (L2) and cubic phase region are studied using microcalorimetric specific heat measurements. The calorimetric technique is demonstrated to produce results consistent with the structural information derived from direct observations of the phase diagram and the DOC structural model. Two or possibly three separate cubic phases are distinguished in the cubic phase region. The results indicate that the values of specific heat per surfactant molecule reflect changes in both the surfactant film topology and geometry. The second part of this work is devoted to the study of adsorption of three simple liquids on molecularly smooth mica using an angle-averaging, refractive index-matching ellipsometric technique. A general outline is given in Chapter 8 followed by discussion of the ellipsometric method (Chapter 9). In Chapter 10 experimental results are presented and discussed. For water and cyclohexane the isotherms are structureless. For octamethylcyclotetrasiloxane a layering upon adsorption is observed, showing no qualitative change on passing through the triple point of the bulk liquid. The isotherms for all three liquids studied do not agree with the Lifshitz theory of van der Waals forces and are qualitatively interpreted using the surface phase diagrams of Pandit, Schick and Wortis. (author)