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Overbased detergents (OD) are oil-soluble nanoparticles consisting of a calcium carbonate core and surfactant outer shell. They are important additives in automotive and marine engine oils. Langmuir trough (LT) and molecular dynamics (MD) simulations have been carried out to characterise the interaction between OD particles made from a range of surfactants. We also explore the factors that determine the shape of the particles, in particular by the level of overbasing (amount of calcium carbonate in the core), surfactant type and the presence of stearate co-surfactant. Clint and Taylor (J. H. Clint and S. E. Taylor, Colloids Surf., 1992, 65, 61) derived expressions for the particle size, contact angle and interparticle interaction between spherical particles at the air/water interface in a Langmuir trough surface pressure experiment. We extend this mathematical treatment to encompass the more general case of oblate and prolate ellipsoidal particles. On reinterpreting the experimental data, the derived expressions suggest that the largest deviations from spherical symmetry occur for the phenate and calixarate particles without co-surfactant. This is supported by molecular modelling studies also reported herein. The evidence from the combined LT and MD studies is that the co-surfactant makes the particles more spherical, by disrupting any tendency of the surfactants to self-assemble in an ordered fashion around the surface of the carbonate core.

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Molecular dynamics (MD), simulations have been carried out of crystalline aragonite and calcite, and of finely dispersed calcium carbonate in the form of nanosized inorganic core-organic shell particles. The latter, called overbased detergents commercially, are used as acid-consuming components in automotive and marine engine oils. We have modelled several types of these particles using different surfactant types. We compare the internal structure of the calcium carbonate in these particles with calcite and aragonite crystalline forms using MD in each case. The atomic force-field adopted accounts reasonably well for the crystalline phases, although under unconstrained (constant stress) conditions some distortion of the aragonite structure was noticed. The microstructure of the nanoparticles appears to be quite different to the crystals, and seemingly amorphous. For these small clusters it appears that there is probably no thermodynamic benefit in forming local crystalline order in the cores. The relatively large surface to volume ratio found in these particles lends itself to a more amorphous microstructure.

New intercalation compounds of the pseudo-layered oxides Uv'Te'v05 and UV'Se'V05 have been prepared and characterised At ambient temperatures products of the type AxUM05 (x < 1, A = Li, Na, H, NH,) are formed by both host oxides with minimal structural change Magnetic susceptibility measurements confirm that Uv species are formed on intercalation Several metal oxides, MO,, where M is a transition metal (or uranium) in a high oxidation state, have tunnelled or layered structures which undergo insertion or intercalation reactions at ambient temperatures These result in the formation of products, AxMO,, in which a electropositive element A is incorporated interstitially into the host oxide with minimal