This thesis is concerned with the behaviour of the single phase (10) alkane oil-in- water (01W) microemulsions stabilised by nonionic surfactants of the general structure H-(CH2)n(OCH2CH2)m-OH, abbreviated to CnEm. The aims were to attempt to characterise their behaviour in terms of the effect of the different constituents n, m, and alkane oil chain length (x).Initially the limiting temperature phase boundaries of the 10 region were established by measurements of turbidity. Turbidity was found to be at a minimum at the lower temperature phase boundary (the solubilisation phase boundary, SPB), and at a maximum at the upper temperature phase boundary (UTPB). The temperature position of the 10 region was found to be increased by increasing m or x, and decreased by increasing n. The width of the temperature range was generally found to be decreased by increasing the ratio of oil to surfactant (R). For a series of decane-inwater microemulsions stabilised by surfactants having a constant ratio n/m=2, the SPB was found to be little affected by an increased overall surfactant length, whereas the UTPB was found to be increased.The microemulsion droplet sizes were determined by both static and dynamic light scattering (turbidity and PCS respectively). The particle size was measured at varying temperatures and was found to be at a minimum at the SPB and to increase with temperature (explaining the increase of turbidity with increasing temperature). The increased particle size was assumed to correspond to clustering or growth of the microemulsion droplets. The size measured at the SPB was assumed to be that of the individual droplets at their preferred size. The hydrodynamic radius (rh) of the droplet at the SPB was used to calculate the area (As) occupied per surfactant molecule at the interface between the droplet core and the surfactant monolayer. As was found to be increased by increasing n, and decreased by increasing x, whereas m was found to have little effect.Turbidity measurements were found to be a simple method of measuring the extent of clustering or growth of the droplets with increasing temperature. From this information the equilibrium constant (K) and the associated standard enthalpy, entropy and Gibbs free energy changes were obtained. A simple scheme of droplet aggregation was postulated in which K for the addition of one droplet to an existing cluster (equating to growth by the equivalent of one droplet at the preferred size) was constant regardless of cluster size. The model was found to fit well to a middle range droplet concentration of 0.04 - 0.10 M. Measurements at lower droplet volume fractions were found to be too inaccurate, and K was found to decrease for fractions greater than this range. A model which would accommodate the decrease in K with higher droplet volume fraction would be highly complex and include further estimated parameters. It was therefore deemed appropriate to employ the simple model for comparison within the relevant range of droplet volume fraction. As expected K was found to increase with increasing temperature for all systems. The large positive enthalpy (of the order of 1000 kJmol-1) obtained for all systems accounts for the strong temperature dependence of the behaviour of these microemulsions. The positive entropy change (of the order of 3 JK4mol-1) was attributed to the increasing disorder of the water molecules following dehydration from the surfactant head group region. The removal of water from the head groups has the additional effect of increasing inter-head group and therefore interdroplet attractions thus promoting clustering or growth. The resulting negative Gibbs free energy (of the order of -14 kJmol-1) indicates that the clustering/growth process is spontaneous and entropically driven. The clustering/growth process was found to be dependent on the packing density of the surfactant head groups at the droplet monolayer surface. Assuming clustering occurs the thermodynamic parameters were calculated per mole of surfactant molecules involved in the droplet contact zone of the clusters. Droplets having the more widely spaced (less closely packed) head groups were found to have a larger enthalpy and entropy change, probably as a result of the greater requirement for dehydration of the head groups.A temperature jump method was employed to study the kinetics of the clustering/growth process. The results were found to be consistent with the equilibrium data, in that the rates of the clustering/growth process were found to be dependent on the packing density of the surfactant head groups. Droplets having the less closely packed head groups were found to cluster more slowly, again an indication of the greater difficulty in dehydrating the head groups. The activation energy was also calculated for the clustering/growth process, and was found to be of the order of a few hundred kJmol4, but no discernible trends with molecular structure of the components were observed.

Solubilisation and emulsification of polydimethylsiloxane (PDMS) oils into aqueous surfactant solutions have been investigated with a series of nonionic surfactants and an anionic surfactant (AOT).For nonionic surfactants at oil-water interfaces, the effect of temperature, surfactant structure, electrolyte concentration and PDMS molecular weight on the emulsion phase inversion of water/PDMS/surfactant systems has been studied in detail. For certain nonionic surfactants the equilibrium phase behaviour of equal volumes of water and oil has been studied in Winsor systems. At air-water surfaces, the spreading behaviour of PDMS on aqueous nonionic surfactant solutions has been investigated for a range of surfactant structures. Above the critical micelle concentration (cmc) and with 50 cS PDMS, the initial and equilibrium spreading coefficients have been determined. For C12E5, the dependence of the spreading coefficients on oil molecular weight also was investigated. The complete adsorption isotherms of the volatile PDMS oils on C12E5 solutions have been measured, which yields the composition of the mixed layer of surfactant and oil. The competition for the surface between PDMS and surfactant has been studied by opening up the monolayer of C12E5 and L-77 by dilution below the cmc. The preliminary neutron reflectivity study showed that PDMS forms a thinlayer on top of the surfactant chain region.For the anionic surfactant AOT, the transition of Winsor systems at equilibrium for hexamethyldisiloxane (0.65 cS)+AOT+aqueous NaCI from I- 111-1is1 effected by increasing the electrolyte concentration. In single phase microemulsions, the uptake of oil into aqueous surfactant solutions and the solubilisation of water into surfactant solutions in oil are determined both as a function of salt concentration and temperature. The partitioning of salt between dispersed and excess water phases is considered. The stability of macroemulsions prepared from the coexisting phases in Winsor systems is investigated. Correlation between the emulsion phase inversion, Winsor phase transition and oil-water interfacial tension is discussed. The mixing behaviour of 0.65 cS PDMS oil and AOT at air-water surfaces has been studied as a function of oil activity, surfactant and electrolyte concentrations.

The thesis is concerned with aspects of the surface and colloid chemistry of various oil+water systems containing pure surfactants. In alkane plus aqueous NaCI systems containing the surfactant diethylhexyl sodium sulphosuccinate (AOT) , the alkane-aqueoussolution interfacial tension becomes constant at the onset of surfactant aggregation, which can occur in either the aqueous or alkane phase. This constant tension,Yc , can attain ultralow values ( < 10-3 mN m-1 )and can pass through a minimum value with respect to salt concentration, temperature and alkane chain length. Surfactant transfer between phases, and phase inversion of macroemulsions are shown to occur around the condition which produces minimum Yc.The origin of the low tensions is thought to be due to monolayer adsorption. Aggregatein equilibrium with the plane monolayer are shown to be spherical microemulsion droplets, whose sizes increase as a minimum in Yc is approached.The results are discussed in terms of the effective molecular geometry of the surfactant and how this is affected by the variables of interest. Minimum Yc occurs for the condition such that the effective headgroup area is equal to the effective chain area at a plane interface.A thermodynamic treatment has been used to describe the tension variations; minimum Ycis shown to result when there is some kind of equivalence between the plane oil-water interface and the surface of the aggregates. For example, minimum tension with respect to salt concentration occurs (in the case of ionic surfactants) when the degree of dissociation of surfactant in the micelle and at the plane oil-water interface are equal.For the single-chain surfactant sodium dodecyl sulphate, salt alone cannot yield a minimum in Yc , nor is Yc very low. Addition of octanol as cosurfactant however can produce very low values of Yc and a minimum as cosurfactant concentration is varied. A geometrical description of these effects is given which is in accord with the findings relating to the composition of interfacial monolayers emerging from thermodynamics.

No description available.

Thesis (D. Sc.)--University of Adelaide, Dept. of Chemistry, 1998. / Includes bibliographical references.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2008. / Includes bibliographical references. Also available in electronic version.

Thesis (Ph. D.)--Duke University, 2007.

Thesis (Ph. D.)--University of Toronto, 2008. / Includes bibliographical references.

Inaug.-diss.--University of Michigan. / Reprinted from the Physical review, vol. 29, no. 4, October, 1909. Includes bibliographical references.

Thesis (Ph. D.)--Syracuse University, 2007. / "Publication number: AAT 3295527."