A population balance model for emulsion polymerisation has been developed. This model captures PSD and MWD, both of which are key performance indicators for the end latex product. The model employs purely mechanistic kernels and is aimed at maximising predictive capacity. The model is validated against a multi-objective experimental target. The aim is to predict data for PSD, solids, particle number as well as global molecular weight. The experimental system investigated is a vinyl acetate/butyl acrylate copolymerisation with ionic emulsifier and thermal initiator. The predictive capacity is tested by tuning the model to one set of experimental data, then trying to predict results from a further perturbed experiment, with no further tuning. The results of this study indicate that the model is able to capture the main process trends as well as providing an accurate representation of quantitative data.

Ozonolysis of tetramethyl ethene, trans-4-octene or 1-octene in water leads to species, which after thermolysis at 60°C, generate radicals that initiate radical emulsion polymerization of methyl methacrylate (MMA). The course of the reaction is dependent on the structure of the alkene used. Tetramethyl ethene ozonates give the highest final yield of polymer, although the rates of polymerization observed from 0 to approximately 60% conversion are found to be essentially equivalent, regardless of the structure of the alkene employed. The difference in final conversion is attributed to changes in the half life of the generated peroxy species as a function of alkene structure. From these differences it is inferred that the initiating species are organo peroxides, probably hydroxy hydroperoxides, rather than hydrogen peroxide. Two latex systems, one stabilized by a cationic surfactant and the other by an anionic surfactant, were successfully prepared. Ozonolysis of water followed by heating in the presence of MMA does not produce polymer. However, ozonolysis of an aqueous sulphonate surfactant solution does produce a species that forms radicals on thermolysis and these radicals initiate radical polymerization of MMA, which proceeds to high conversion in emulsion.

Experimental results are reported concerning the effect of coverage of grafted polymer chains on the stability of dispersions of soft sphere particles to depletion flocculation in the presence of free polymer. Two sets of experiments are described. In the first set a direct comparison of soft spheres with equivalent hard spheres (zero coverage) is made, for cases where the free polymer is the same as the grafted polymer and for cases where it is different. In the second set of experiments, the effect of varying the actual number of grafted chains per unit area is investigated. It is found that the stability of the dispersions to depletion flocculation goes through a maximum with increasing coverage. This is in line with earlier predictions from two major theories (but is only partly accounted for by scaling theory) and is the first set of reported data to show this effect.

Dispersions of hydrophilic silica particles, which are charge-stabilised in ethanol, may be flocculated on the addition of sufficient cyclohexane. The primary mechanism is the reduction in the zeta potential. The flocculation observed is kinetically controlled; it is irreversible and time dependent. By way of contrast, dispersions of hydrophobised particles (i.e., silica particles carrying terminally-grafted n-octadecyl chains) in cyclohexane are uncharged and behave virtually as dispersions of hard-sphere particles. Addition of ethanol, beyond a critical concentration leads to particle “phase separation” (weak flocculation); this is thermodynamically controlled.

Phase separation may be induced in dispersions of hydrophobic silica particles in cyclohexane upon the addition of non-adsorbing polymer (polydimethylsiloxane). The origin of this effect is ascribed to the depletion interaction. Depending on the particle size and molecular weight of the polymer, the analogues of the molecular gas/solid, gas/liquid and liquid/solid co-existing phase regions may each be observed. It is demonstrated that using relatively simple, mean-field theories for both the fluid state (random phase approximation or adhesive sphere model), and also the solid state (cell model), all these transitions may be predicted. Although the quantitative agreement between experiment and theory is not exact, qualitatively all the observed trends in behaviour are accounted for.

Monodispersed stearylated silica suspensions of various particle sizes have been examined for their sedimentation behaviour, and for the order which is produced when the sediment compacts under gravity. The phase behaviour is complex, and crystalline and glassy phases can apparently coexist over long periods. The rate of accretion of the sediment is one controlling factor in deciding which phases appear; the more rapid the build-up, the less likely are crystalline sediments to be formed. By increasing the particle volume fraction, and so slowing the rate of accumulation, we show that the extent of crystallisation can thus be increased.

A new approach is described for calculating the depletion interaction in systems of sterically-stabilised particles (“soft spheres”) plus added free polymer. By combining the depletion interaction with the steric interaction, the overall interparticle pair potential is calculated. Variations in the amount of free polymer required to induce flocculation is predicted for these systems, in particular as a function of the nature of the solvent (through the χ parameter) and the properties of the adsorbed polymer layer (through the thickness and the average segment volume fraction). Some experimental results are presented for the system silica—g—polystyrene plus solvent plus free polystyrene, which confirm, at least in a qualitative way, the predictions of the new theory.