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A series of well characterised cis -poly(isoprene) (PIP) polymers ( M w =1180, 8000, 28 300, 31 500, 86 000, 115 000 and 130 000) have been added to dispersions of poly(12-hydroxystearic acid) (PHS) coated poly(methylmethacrylate) (PMMA) particles in dodecane. The ratio of particle size to adsorbed layer was also varied. For a given added polymer molecular weight, the polymer concentration in the continuous phase covered the dilute, semi-dilute and concentrated regimes as defined by the critical concentrations c ∗ and c ∗∗ . The viscosity behaviour of latex dispersions with added polymer were similar for all latex/polymer combinations except when polymer M w =1180 was added. In the latter case, the effect of adding polymer reduced both the viscosity and shear thinning behaviour. This supports the contention that the lower molecular weight polymer acts more like a diluent than a depletent. The behaviour of the viscosity ratio (the viscosity of the dispersion relative to that of the medium) as a function of polymer concentration increased with an increase in the polymer concentration until some critical concentration ( c max ) for all polymers except for a polymer molecular weight 1180 Daltons. The addition of the polymer M w =8000 gave the highest viscosity ratio values in the polymer concentration range studied. It was found that the viscosity of all latex/polymer combinations decreased with an increase in temperature. The results suggest that the viscosity behaviour cannot be explained on the basis of a simple steric–elastic model and require a modified theoretical treatment.

The surface charge properties of colloidal titanium dioxide dispersions in ethylene glycol and water have been studied. The effect that silica and alumina coatings have on anatase particles is discussed, along with the difference in behaviour between anatase and rutile. Surface charge properties determined by electrophoresis show significant differences between each type of particle and between the two dispersion media. Small amounts of water have a significant effect on the behaviour of the particles, including the ability to change the sign of the charge for uncoated samples.

The work described focuses on a two-stage process for the production of large porous suspension polymer beads of defined particle size and narrow size distribution. Emulsification has been performed using purpose built cross-flow membrane equipment, which allows controlled production of large emulsion droplets with a much narrower size distribution. The work described compares the production of large emulsion droplets of monomer prepared both by agitation and using a cross-flow membrane. The effects of variations in the pore size of the membrane and flow-rates on the size of the emulsion droplets produced are also investigated. The second stage of the process is polymerisation of performed monomer emulsion droplets using a continuous tubular reactor. Samples polymerised using such a method show a narrower size distribution than similar systems polymerised as a batch.

The conventional method for the synthesis of porous cross-linked copolymer beads is by suspension polymerisation. Suspension polymerisation reactions are generally performed in a stirred tank, which generally results in a large size distribution. By careful control of the polymerisation conditions, polymer beads can be produced using a tubular poly(tetrafluoroethylene) continuous reactor. Such beads are produced with the same average pore size, but with a lower degree of polydispersity than analogous systems produced in a batch reactor (stirred tank). This is achieved by density-matching the droplet and continuous phases (by the use of a brominated monomer or a porogenic diluent) and increasing the viscosity of the monomer phase (with the addition of small amounts of polystyrene).

A series of well characterised cis -polyisoprene polymers have been added to dispersions of PHS coated PMMA particles in dodecane. At a molecular weight of 8000 g mol −1 and above, these systems showed phase separation at low particle volume fractions and above a critical polymer concentration. The rate of separation has been shown to be influenced by the viscosity of the polymer. At high polymer and particle volume fractions long lived metastable phases occurred. Above a critical concentration these were viscoelastic indicating an appreciable change in diffusion dynamics with two relaxation processes present. A significant Bingham yield stress was also observed. The Asakura Oosawa potential was not able to describe the observed rheological properties. At a molecular weight of 1000 g mol −1 no phase separation was observed. At high particle concentrations the yield stress was found to reduce with the addition of polymer. This was due to the polymer acting as a ‘solvent’ and penetrating the stabilising layer on the particles.

Large, cross-linked polymer beads have been produced by suspension polymerization. The surface area of the beads can be increased by making the structure porous by the addition of an inert solvent to the droplet phase. Kinetic measurements have been performed with systematic changes in monomer ratio (styrene–glycidyl methacrylate), with an increase in glycidyl methacrylate concentration leading to an increase in reaction rate. The effects of changing the initiator type have also been studied, the use of azobisisobutyronitrile, as opposed to benzoyl peroxide, results in higher reaction rates and higher yields. The effects of these variations on both the emulsion and bead droplet size distributions have also been studied. An increase in styrene concentration has no significant effect on the average size of the emulsion droplets, but increases the final bead size. The average pore size and specific surface areas of the polymer beads (determined from BET isotherms) have also been investigated.

The rheology of flocculated dispersions is dependent on the suspension microstructure and its time evolution as well as the type and magnitude of the interparticle forces. Much of the current work focuses on this microstructure as recent developments in experimental techniques have made this type of information more accessible. Simulation continues to add breadth to our understanding of the behaviour of flocculated suspensions.

A series of copolymer latices synthesized from pyrrole and N-methylpyrrole were prepared with similar particle sizes. After a detailed characterization of the particles the systems were prepared as...

Rheological and microscopical studies have been made to elucidate the effects of shear fields on the morphology of concentrated, aggregated model colloids. The models employed are well-characterised, predominantly chargestabilised polymer latices, coagulated by the addition of excess electrolyte. Continuous shear rheological and viscoelastic measurements indicate a very significant decrease in shear yield stress, apparent viscosity and shear modulus following prolonged shearing. Electron microscopy reveals the source of these changes. Freshly coagulated suspensions form networks that are porous, strong and qualitatively similar to simulated structures for diffusion limited aggregation. Following protracted shearing, the network structure is rearranged to yield discrete, tightly packed aggregates with a characteristic size, which is principally a function of the primary particle size.

We have extended some previous studies, carried out in this laboratory, of the colloidal stability of polystyrene latex particles (carrying terminally-anchored polyethylene oxide chains) in the presence of sodium polyacrylate, to similar studies with Ludox silica particles plus sodium polyacrylate. In particular, we show that the stability / instability depletion flocculation boundaries depend on the way in which the system is assembled, as does the nature of the flocs formed. The observed behaviour also depends strongly on the presence of background electrolyte. We have also extend the earlier latex work, on depletion effects in the presence of sodium polyacrylate, to investigate two rheological parameters as a function of particle volume fraction: the dynamic shear stress and the high-frequency plateau modulus. Reasonable fits to the experimental data, for both these parameters, could only be obtained if the background visco-elastic nature of the polyelectrolyte solution, continuous phase is taken into account.

An experimental investigation has been made of the settling rate of polystyrene latex dispersions containing particles of radius = 1.55 μm in salt solutions and in shear thinning polymer solutions. The volume fraction of the dispersion was varied from dilute, ca. 0.01, to concentrated, ca. 0.5. The experimental data are compared with theoretical predictions for dispersions of hard spheres. It was found that the relative velocity of settling U U o for concentrated systems could be represented by the equation U U 0 = 1 — φ/p) kp with p = the latex volume fraction at close packing, φ = the volume fraction of the latex, and k a constant. In shear thinning polymer solutions it was concluded that the zero shear rate viscosity controlled the rate of settling of the particles.

A small angle neutron scattering investigation has been carried out on aqueous polystyrene latices containing particles of mean diameter, 360 A. At low volume fraction, 0.01, in 10−3 mol dm−3 sodium chloride solution particle—particle interactions were minimized and the results were used to obtain the particle size. In a concentrated dispersion at a very low electrolyte concentration the arrangement of the particles was probed by determination of the structure factor. The radial distribution function was obtained from the latter by Fourier transformation of the data. Comparison with theoretical models showed that the particles in the concentrated system behaved essentially as hard spheres with an effective interaction radius much greater than the actual radius of the particles. The arrangement of the particles was found to be “liquid-like.”

A single-stage method is described for preparing monodisperse poly(methyl methacrylate) latices stabilised by poly(12-hydroxy-stearic acid) in hydrocarbon media. By variation of solvency conditions, it was possible to obtain a variation in particle size. At high monomer concentrations, a range of particle diameters between 178 nm and 2.6 μm was obtained with a small coefficient of variation on the number average size. At low monomer concentrations, stable latices were obtained with diameters of ∼ 80 nm. Some suggestions are made for the mechanism of particle formation and growth in non-aqueous latices.

Concentrated latices can show a short range liquid-like order of the particles. The rheological properties of such a concentrated polystyrene latex, with a particle diameter of 170 nm, have been examined using a variety of techniques. Shear-wave propagation was used to determine the high-frequency limiting modulus while creep compliance was employed to determine the viscosity as a function of applied stress and hence the zero shear viscosity. Dynamic moduli over a frequency range of 0.05 to 20 Hz have been determined by means of a continuous forced oscillation technique. The volume fraction range studied was from 0.1 to 0.35 and the electrolyte concentration was 5 × 10 −4 mole dm −3 with respect to sodium chloride. The loss modulus curves were Fourier transformed to give relaxation spectra which were found to move to longer times and become narrower as the volume fraction was increased. The spectra were integrated to give both the high-frequency limiting modulus and the zero shear viscosity. The experimental data were then compared with curves predicted from a quasi-static lattice model for the microstructure using pair-wise additivity for the interparticle pair potentials. Concordance with the experimental data was found if diffuse layer potentials within the range 40–95 mV were used in the calculations.

Concentrated latices form the end-product of emulsion polymerisation processes. The structural arrangement of the particles in such latices and the interactions between them determine the bulk behaviour of the system. The use of small angle neutron scattering to determine the structure factor for concentrated latices is discussed and the form of the radial distribution function and its dependence on electrolyte concentration and volume fraction for electrostatically stabilised system described. In addition, the correlation between the structure factor, a microscopic property, and the shear modulus, a bulk property, is illustrated.

A brief survey is given of the methods which can be used to produce polymer latices with a narrow size distribution. The factors which control both the particle size and the nature of the chemical groupings on the latex particle surface are discussed for latices prepared without the addition of an emulsifier. In particular, it is demonstrated experimentally that the ionic strength of the aqueous phase plays a major role in controlling particle size and that the free radicals produced by thermal decomposition of the initiator become incorporated as end-groups on the polymer chains and hence form the surface groups on the particle. A theoretical explanation is given which indicates the reasons for the importance of ionic strength in controlling particle size.

The translational diffusion coefficients of single spheres, and aggregates of polystyrene latex spheres have been measured. The measurements were made using an apparatus constructed for the direct microscopic examination of colloidal particles. A time-lapse method was developed using a pin registered cinematographic camera and the method was tested using spherical polystyrene particles with diameters of 2.00 and 3.47 μm. The movements of linear- and clustered-type aggregates of the smaller diameter latex particles were observed for aggregates containing up to six primary particles. The diffusion coefficients were calculated from the movement of the common centre of mass of each aggregate and evidence was obtained to show that linear, chain-like aggregates are more mobile than cluster-type aggregates containing the same number of primary particles.

The fluid used for these studies consisted of lithium poly(methacrylate) dispersed in a chlorinated hydrocarbon oil. Shear wave propagation was employed to measure the storage and loss moduli at a frequency of 1200 rad s−1. The parameters varied were field strength, volume fraction and water content of the particles. Optical microscopy was used to measure the particle size distribution whilst electrophoresis was used to enable the electro-kinetic potential to be measured. This showed that the particles were positively charged with a potential of circa + 45 m V. Further characterisation of the suspensions was carried out by conductivity measurements and the conductivity of the systems was shown to be due to the counter-ions in the diffuse layer which balances the surface charge. The moduli of the suspensions were found to increase with applied field to a maximum value and then decrease. In addition, the storage moduli were much higher than the loss moduli for all samples at low applied fields, but at high fields both moduli were of similar magnitude. These experimental data will be discussed in terms of the inter-particle forces and the structure in the suspensions.

Preparative methods have been developed in order to obtain monodisperse polystyrene latices in the absence of added surface active agents. By suitable adjustment of the ionic strength of the aqueous phase the initiator concentration and the polymerisation temperature it was found possible to obtain a range of particle sizes, ca. 0.1 to 1.0 ,um, by single-stage reactions. The total initial ionic strength of the aqueous phase was found to play a critical function in determining particle size. A formula has been derived from the experimental data which enables the preparative conditions required to form a latex, containing particles of a particular size, to be predicted.

Poly(methylmethacrylate) particles stabilised by poly(12-hydroxystearic acid) in a hydrocarbon medium provide, as a polymer latex, a useful system for investigating the properties of a sterically stabilised concentrated dispersion. In the present work these latices were investigated by small angle coherent neutron scattering and by quasielastic incoherent scattering. The former technique was used to probe the dimensions of the surface layer of poly(12-hydroxystearic acid) and to determine the diameter of the core particle of poly(methylmethacrylate) using dilute dispersions. In concentrated dispersions it was used to determine the structure factor. The latter was compared with that expected for an interacting system of hard spheres and reasonable agreement obtained. The quasielastic technique was used to probe the translational diffusion of the poly(12-hydroxystearic acid) molecules on the surface and the diffusion of the total particles in the concentrated systems.

Methods have been devised for the formation of monodisperse polystyrene latices in the absence of added surface active agents. The particles are stabilised, as a colloidal dispersion, by surface groupings which are an integral part of the particle and are not removed by dialysis. By suitable variation of the ionic strength of the aqueous phase, the initiator concentration and the polymerisation temperature, the final particle size obtained in single-stage reactions was varied between c. 0.15 and 1.0 μm. The coefficient of variation on particle diameters was usually less than 5%. The ionic strength of the aqueous phase was found to play an important part in determining particle size; this was explained in terms of a limited coagulation process occurring at the stage involving the nucleation of polymer particles. Conductometric titration experiments revealed the presence of sulphate, carboxyl and hydroxyl groups on the particle surfaces. Molecular weight determination of the polystyrene formed showed that this was lower than that formed in conventional emulsion polymerisation.

The flow properties of dispersions are a function of both particle number density and interparticle potential. At high number densities suspensions change from fluid-like behaviour to solid-like. The number density where this transition occurs is controlled by the shape of the interparticle potential function. The material state is clearly indicated from the rheological measurements. Wave propagation, stress relaxation and continuous shear viscometry have been used to study a variety of suspensions of monodisperse particles. Hard sphere, weakly attractive and strongly repulsive systems are discussed.

The use of the high frequency elastic modulus, G∞, to probe particle interactions in weakly agglomerated, concentrated suspensions is discussed. We show that a model based on pair interaction potentials and a statistical description of pair spatial distribution yields accurate prediction of the volume fraction dependence of G∞. The use of statistical treatments of particle distributions as predicted from particle interaction potentials is found to provide insight on how surface chemistry affects the uniformity of powder compacts.