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The change in charge on the addition of C12E6, acid (terephthalic acid) and salt (KCl) was studied using measurements of electrophoretic mobility and electrokinetic sonic amplitude (ESA). Electrophoretic mobilities were measured using conventional electrophoresis from a Penkem 3000 system. ESA measurements were made using a Matec, an electro acoustic technique. Zeta potentials of the order of −30 to −50 mV were obtained. This implies that the electrostatic contribution to stability cannot be neglected for non-aqueous systems of intermediate polarity. The surfactant showed very insignificant electrostatic stabilisation. C12E6 slightly increased the zeta potential at low levels. This is due to ionization of the silica particles on adsorption of the polar head group of the surfactant molecule. The surfactant, C12E6, reduced the zeta potential at high levels (above saturation of the silica surface) probably due to the shift in the shear (Stern) plane. Stabilisation of the particles is therefore by both electrostatic means and steric means (in the presence of surfactant). The thickness of the adsorbed layer was estimated to 8 nm indicative of globular aggregation. Water addition showed a constant zeta potential at low levels ( 2%, v/v). The acid gave an isoelectric point of about pH ∼4 and KCl additions gave a critical coagulation concentration of about 0.02 mol/dm3 (ζ ∼ 30 mV). Dodecane displayed a positive charge for the particles at low added concentrations of water (

An experimental programme is described that evaluated the role of charge and steric stabilisation in glycol and dodecane dispersions of colloidal silica particles on addition of trace water and acid. The surfactant used for steric stabilisation was a non-ionic surfactant, Dodecyl hexaethylene glycol monoether, C12E6 with a geometric head-to-tail length of 3.85 nm. The study showed using the self-consistent field theory of adsorption (SCFA), electrophoresis and electroacoustic sonic amplitude (ESA), that the C12E6 molecules adsorbed with the ethoxy group attached to the silica surface and the alkyl group in the bulk glycol solution. The thickness of the adsorbed layer as estimated from electrophoretic and viscosity measurements was found to be 8 and 10 nm, respectively, indicative of globular aggregation. The dispersions were stable at low levels of C12E6 concentrations due to electrostatic repulsions as deduced from the zeta potentials of silica which were of the order of about −30 to −50 mV in monoethylene glycol (MEG). Instability on further addition of C12E6 to the silica particles, a phenomenon normally obtained with high molecular weight polymers, was observed in MEG. Critical flocculation concentrations of C12E6, ϕfloc, increased with decrease in volume fraction of the silica particles in MEG. Instability is suggested to be from bridging interactions. Restabilisation observed at high surfactant concentration was due to steric repulsions of ethoxy groups of micellar aggregates adsorbed on silica particles. The study also revealed that the presence of trace water introduced charge repulsion which moderated rheological measurements in glycol media and introduced reversal of charge of silica particles in dodecane.

A series of six well characterised homopolymers of cis-polyisoprene (PIP) ranging from 1180 to 115,000 molecular weight were utilised to explore viscosity and the scaling relationship between viscosity and concentration in dodecane (good solvent). For each polymer molecular weight, the relative viscosity of PIP in dodecane at 298 K was measured at several polymer concentrations using capillary viscometry. The linear extrapolation of experimental data based on Huggins, Kramer, Martin and Schulz-Blaschke equations was used to find the intrinsic viscosity at infinite dilution for each polymer molecular weight. The single-point method of evaluation of the intrinsic viscosity was also used for comparison. The Mark-Houwink fit of the data gave power index of 0.72 indicating that dodecane is good solvent for PIP and the latter exists in solution as open flexible coil. Both the radius of gyration and critical chain overlap concentration, c*, were derived from measured intrinsic viscosities. Plot of the relative viscosities versus the scaled concentration c/c*, resulted in single curve with slope value 4.44 × 10−2 and correlation coefficient r2 = 0.996, indicating good linear fit.

The preparation of zwitterionic latex particles is reported by using a mixed anionic and cationic initiator system without requiring surface-active agents. Isoelectric points were found from microelectrophoresis experiments and were in the pH range of 3.5-5. Close to the isoelectric point, the latices coagulated as expected, and good stability was achieved outside this narrow range. This range of stability was in good agreement with predictions from current theory. Redispersion after coagulation was found to be difficult as was expected for a hydrophobic colloid. The electrokinetic behavior did not result in the maximum in zeta potential at an electrolyte concentration of 1 mM unlike the situation for other hydrophobic polystyrene latex particles, and hence these systems may be even better models for other colloidal studies.

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 focused beam reflectance (FBRM) method is a relatively new method, developed to perform particle size measurements in the range 0.8–1000 μm. The particle size determined is given in terms of a chord length. The relationship between chord length and particle size obtained using other methods (image analysis and Malvern Mastersizer) has been investigated. The advantage of the FBRM method is the ability to perform in-situ particle size analysis in real time, without the need for sampling or dilution. In this work, we study the effects of various experimental factors (e.g. agitation rate and particle concentration) on FBRM measurements, and compare the size distributions with those obtained by other sizing methods. FBRM has also been used for studying the formation of (oil-in-water) emulsion droplets (with a droplet size >100 μm) with time under shear, where both sampling and dilution may affect the droplet size distribution.

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.

two casebooks and two daily journals provide a snapshot of the life and times of J.C. Goodwin, a resident house surgeon or “houseman” in obstetrics and gynaecology at the Toronto General Hospital during 1927-28. No comparable record of that era survives. Ninety-one gynaecological cases have been meticulously recorded in the casebook for September 1927. They are largely concerned with pelvic floor problems, severe infections managed without antibiotics, and invasive cervical cancer. Similarly, 66 cases recorded in the casebook for March 1928 attest to the fact that obstetrical practice was an almost entirely mechanical affair. Even in Toronto, two-thirds of women still delivered at home and maternal mortality was one hundred times worse than today. Obstetric research was in its infancy. There was emerging emphasis on good prenatal care and concern about severe toxemia, but perinatology, neonatology, and sophisticated obstetric anesthesia were unheard of. The daily journals make no nostalgic exaggeration of the fact that a resident in training in the 1920s worked harder and longer than is the case today. Pay consisted of an absurd honorarium. No one could afford marriage. In those days, chiefs and chairmen valued common sense, enthusiasm, kindness, and a capacity for hard work far more than genius and erudition. Perhaps we are so obsessed today by evidence-based medicine, randomized clinical trials, and meta-analyses that we tend to overlook the cultivation of these attributes in our young residents.

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).

An opposed jets extensional rheometer, the Rheometrics RFX, was used to investigate the extensional flow properties of a series of solutions of polyvinylpyrrolidone (PVP) containing varying amounts of an anionic surfactant, sodium dodecylsulphate (SDS). The measurements were made in comparison with data collected for Newtonian fluids of similar viscosity to the polymeric systems of interest. The instrument was used to make measurements of the extensional viscosity as a function of extension rate, and a study of the effect of the residence time within the flow field was made. PVP has been shown to form a complex in aqueous solution with SDS. This study concentrated on the effect the addition of SDS has on the extensional rheology of semi-dilute solutions of PVP, with a molecular weight of 700 000. It was shown that increasing the amount of SDS increased the extensional thickening characteristics of solutions, as shown by a decrease in the critical extension rate for thickening. An increase in the viscosity of the solvent was shown to have an additional effect. By decreasing the distance between the opposed nozzles it was shown that a decrease in the residence time (and hence total average strain) diminished the extensional thickening character of these solutions.

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.

Fewer and fewer family physicians are delivering babies in rural Canada. Due to a serious shortage of obstetricians, general surgeons and rural physicians with advanced operative skills, some community hospitals have been forced to discontinue these operative services. In some instances, they have been obliged to close their maternity units entirely. Women must then deliver far from home in unfamiliar regional facilities. Two solutions to this provider access crisis have been suggested. It has been proposed that certain rural physicians be trained in advanced operative obstetric skills (chiefly the performance of Caesarean sections) for those community hospitals which require these skills. Candidates for a programme of this sort would be drawn from graduating family practice residents and from the ranks of practising rural physicians returning for reinforcement of this operative experience. This emerging initiative raises important questions about training, the scope of practice, specialist backup and maintenance of competence. An alternative remedy would stress much broader exposure to obstetrics in family practice residencies, the opportunity for additional training in more advanced skills, rural practice experience for senior residents in obstetrics and gynaecology, equitable alternative funding for consultant obstetricians in regional facilities and considerable strengthening of regional links for perinatal care delivery. The short-and long-term consequences of this crisis must not be underestimated by the profession, by regional health boards and particularly not by government.

Two Laponite clays, of general formula [Mn+]x/n [Lix Mg6-x Si8 O20 Fy (OH)4-y], were prepared with different Li+ levels (0.57 and 0.70% w/w) and F- levels (9.5 and 9.9% w/w). The clays were characterized by measurements of nitrogen adsorption isotherms, cation exchange capacity, and conductometric titration data. The clay with higher Li+ and F- levels had a higher (more negative) face charge and a lower (less negative) edge charge. Small-angle X-ray scattering (SAXS) data obtained from dilute aqueous dispersions indicate that both clays are of similar particle size (diameter ca. 40 nm and thickness ca. 3.5 nm). Experimental structure factors for concentrated Laponite dispersions were calculated using the ratio of scattered X-ray intensities from concentrated and dilute dispersions. Maxima in the experimental structure factors were observed at scattering angles of 0.14−0.2 nm-1 under favorable solution conditions (pH ≥ 9 and ionic strength ca. 5 × 10-3 mol dm-3) for one of the Laponite clays. These results...

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.

Advocates of midwifery have claimed, rather aggressively, that the only remedy for the apparently widespread dissatisfaction felt by women with hospital delivery experiences and obstetricians is a return to the traditional place of birth, the home. They maintain that pregnant women suitable for home delivery can be selected with sufficient accuracy using antenatal risk identification methods. However, women assessed as being of low antenatal risk can suddenly develop dangerous complications in labour, necessitating (if possible) transfer to hospital. Clearly, transfers of this sort inflate hospital perinatal mortality and morbidity statistics and give rise to the fallacious conclusion that home birth is much safer than delivery in hospital. Evidence is presented which convincingly refutes this assumption. Professional midwives urgently require an organization similar to the Canadian Medical Protective Association (CMPA), providing immediate counselling from experienced lawyers and adequate liability insurance to give medico-legal protection far perinatal misadventure in the home. It would appear that professional midwives have mare time to give to the care of pregnant women than do many family physicians. The so-called "low intervention" unit in regional (Level II) hospitals staffed by both midwives and family physicians wouid seem a superior substitute far the home as a setting for birth.

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...

The steady shear viscosity, dynamic viscoelasticity, and high shear wave rigidity modulus were measured for silica dispersions stabilized by a nonionic surfactant, dodecyl hexa ethylene glycol monoether (C(12)E(6)). Electrokinetic measurements were also obtained to help understand the role of charge on the stability of the silica particles in nonaqueous media. The dispersions were found to be stable at low levels of C(12)E(6) concentrations due to electrostatic repulsions as deduced from zeta potential data. Zeta potentials of silica particles in mono ethylene glycol (MEG) were of the order of (-)20-(-)70 mV, signifying the importance of electrostatic stabilization normally reported in aqueous media. Instability on further addition of C(12)E(6) to silica particles in MEG, a phenomenon normally obtained with high molecular weight polymers, is explained in terms of micellar bridging and hydrophobic interactions. The extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory is used to model the effect of C(12)E(6) on particle stability. Viscoelasticity of silica in MEG in the presence of C(12)E(6) is also reported. Viscoelasticity was found to be due to weak flocculation resulting in a free energy increase and a decrease in configurational entropy as the dispersion was weakly strained. Viscoelastic measurements are modeled using a mode-coupling model.

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.

An apparatus, that allows simultaneous measurements to be made of excess osmotic pressure and optical diffraction of polymer colloid dispersions, has been constructed. Results are reported for monodisperse polystyrene latices at several salt concentrations. An interesting feature of the results is a clear indication of a co-existence region occurring with particles of 182 nm diameter in sodium chloride concentrations of 10−4 mol dm−3

A series of trialkoxysilane compounds tipped with primary amine groups were used to functionalize the surfaces of glass and colloidal silica. Streaming potential and microelectrophoretic mobility measurements were used to monitor the stability of the functionalized surfaces. Hydrolytic breakdown of the surface-to-silane coupling was induced by either successively increasing and decreasing the pH of the solution in contact with the surface, or by aging the derivatised surfaces in aqueous solution over prolonged periods of time. The chemistry of the spacer units between the trialkoxysilane group and the primary amine tip had a major influence on the subsequent hydrolytic stability. Large hydrophobic spacer groups showed small changes in the electrokinetic properties on storage, but large changes when successively titrated with acid and base through the pH range. The behavior observed with small hydrophobic spacer groups was that large changes in electrokinetic properties were obtained on storage and with pH titration.

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.

By delayed sedimentation is meant the rapid collapse of a colloidal gel following a period of either little or no sedimentation. The delay or collapse time can range from seconds to many months, depending upon the strength of the gel. Delayed collapse is generally presumed to be a consequence of steady coarsening which somehow brings the gel to a critical state. Earlier work on very weak depletion gels demonstrated an exponential dependence of the collapse time on depletant concentration, implying that the activation energy for coarsening is equal to the mean binding energy of the particles, θ. This correlation is not however followed by the somewhat stronger secondary-minimum gels studied originally by Partridge, who first reported the phenomenon of delayed collapse. It is demonstrated here that the scaling on the mean binding energy becomes progressively more and more sub-Arrhenius as the latter is increased above ca. 10 kBT, also that the width of the potential well has an important effect. Between them, these two effects account for the faster than expected collapse shown by the secondary-minimum gels and by more strongly-flocculated depletion gels. It is suggested that apparent departures from Arrhenius scaling are a consequence of heterogeneity which causes the mean activation energy and the mean binding energy to differ as the energies become larger.

Two major difficulties in using default logics are their intractability and the problem of selecting among multiple extensions. We propose an approach to these problems based on integrating nonmonotonic reasoning with plausible reasoning based on triangular norms. A previously proposed system for reasoning with uncertainty (RUM) performs uncertain monotonic inferences on an acyclic graph. We have extended RUM to allow nonmonotonic inferences and cycles within nonmonotonic rules. By restricting the size and complexity of the nonmonotonic cycles we can still perform efficient inferences. Uncertainty measures provide a basis for deciding among multiple defaults. Different algorithms and heuristics for finding the optimal defaults are discussed.

The use of various modern techniques to examine particle–particle interactions in concentrated colloidal dispersions is reviewed. The analogy between colloidal dispersions and molecular fluids is drawn and the conditions for the formation of colloidal crystals discussed. The latter part of the article examines the role played by particle–particle interactions in determining the macroscopic properties of colloidal dispersions such as viscosity, viscoelasticity and elasticity.

A water-soluble carbodiimide has been used to end-graft aminated poly (ethylene oxide)(PEO) chemically onto colloidal polystyrene particles. Two particle sizes (115 and 347 nm diameter) and two PEO molecular weights (112 000 and 615 000 g mol–1) were combined to give suspensions with four different ratios of polymer layer thickness to particle radius. Electrophoresis demonstrated that the PEO was grafted, not just adsorbed. Dynamic light scattering showed that the adsorbed and grafted layers had similar structures and that non-ionic surfactant perturbed the PEO configurations. Steady shear and oscillatory rheometry indicated that long-ranged polymeric forces between particles governed the variation of viscosity and storage modulus with applied stress and PS volume fraction. Hard-sphere and effective hard-sphere scaling helps rationalize the rheological behaviour in terms of the variation of the polymeric force among the different suspensions and hydrodynamic deformation of the polymer layers.

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.”

The rate of aggregation of monodisperse polystyrene latices in various electrolyte concentrations has been studied. A charge stabilised polystyrene latex dispersion was used and comprised 3.47 μm spheres in water. In perikinetic conditions a finite amount of aggregation of the latex dispersion occurred until a plateau in the single particle number concentration was reached. It was found that a critical flocculation concentration, or at least a narrow range of concentrations existed. Below this region, slow aggregation took place and above, the aggregation was more rapid. Orthokinetic aggregation was studied as a function of shear rate and electrolyte concentration. The initial rate of aggregation increased with increasing electrolyte concentration and shear rate. The aggregation kinetics of the dispersion in prolonged periods of Couette flow at low shear rates was studied. It was shown that the plateau in the single particle number concentration could be altered to higher or lower values depending on the conditions used. The phenomena observed were explained in terms of the secondary minimum flocculation.

Monodisperse polystyrene lattices, at high electrolyte concentrations and with an adsorbed layer of nonionic surface active agent, produced weakly flocculated dispersions which sedimented rapidly to give a final sediment concentration of ∼30% by volume. Three lattices were used with particle sizes in the range 1–2 μm. The surface active agent used was C12E6. Optical microscopy of dilute systems showed that dense flocs were formed which were easily disrupted by small shear stresses. Shear wave propagation experiments were used to give the volume fraction dependence of the wave rigidity modulus, G, of these systems at high frequency. The high frequency limit to the shear modulus, G(∞), was calculated from the particle pair potential and the particle pair distribution function determined by using one of the current perturbation theories. The interparticle pair potential was calculated from a combination of van der Waals’ attraction, and both steric and electrostatic repulsion. Good agreement was obtained be...

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.