James W. Goodwin

Studies on the preparation and characterisation of monodisperse polystyrene laticee: III. Preparation without added surface active agents

SummaryPreparative 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.

Scaling behaviour of the rheology of aggregate networks formed from colloidal particles

The instantaneous shear modulus G and compactive strength Py of aggregate networks formed from silica particles with a mean diameter of 26 nm have been determined as a function of particle concentration. The data are compared with similar data obtained earlier for a range of polystyrene spheres with diameters between 60 and 960 nm and with compactive strength data obtained for polystyrene spheres at higher volume fractions by Sutherland. It is shown that clusters of submicron spheres formed by rapid aggregation become spacefilling and form a network at a critical volume fraction Φg of ca. 0.05. Above this concentration the data for Py and G suggest that aggregate networks show universal behaviour which is consistent with the scalings G∼ϕµ, dPy(ϕ)//d ln ϕ∼G(ϕ), with µ= 4 ± 0.5. This latter value for the exponent agrees well with that predicted by Ball and Brown by assuming the clusters comprising the network are fractal. For diffusion-limited cluster–cluster aggregation (DCA) they obtained a value of µ= 3.6. The data for Py imply a particle size dependence of the type Py∼am with m between –2 and –3, where a is the particle radius. More data are required to establish the precise dependence; the observed trend is, however, not inconsistent with what might be expected from a consideration of interparticle forces which implies a scaling of a–2.3. The scaling behaviour of the yield stress in shear flow and the dependence of the shear modulus on strain for non-negligible strains is also discussed.

Studies on the Preparation and Characterization of Monodisperse Polystyrene Latices. VI. Preparation of Zwitterionic Latices

SummaryMethods are described for the preparation of monodisperse polystyrene latices using as initiators, 2-azo-bis-(2-methylpropamidinium) dichloride and 2-azo-bis-(2′-isopropyliminazolium) dichloride. The preparations were carried out in the absence of any added surface active agents. The effect on particle size of varying initiator concentration, monomer concentration, temperature and ionic strength was examined and the conditions defined for preparing monodisperse latices, with particles in the size range 0.2 to 1μm. Electrophoretic measurements confirmed that the latex particles were cationic. The evidence obtained suggested that the charged sites on the particle surface were amidinium groupings. The latices were not stable at pH values greater than 11 and prolonged heating at 90° also caused coagulation.ZusammenfassungEs wurden Methoden zur Darstellung monodisperser Polystyrol-Latices unter Verwendung von 2-azo-bis-(2-methylpropamidinium)-dichlorid und 2-azo-bis-(2′-isopropyliminazolium)-dichlorid als Initiator beschrieben. Die Darstellung erfolgte in Abwesenheit von grenzflächenaktiven Verbindungen. Der Einfluß unterschiedlicher Initiator- und Monomerkonzentrationen, der Temperatur und der lonenstärke auf die Teilchengröße wurde untersucht und die Bedingungen festgelegt, unter denen monodisperse Latices mit Teilchen im Größenbereich von 0,2-1μm erhalten werden. Elektrophoretische Messungen bestätigten, daß die Latexteilchen kationisch sind. Die Ladungen auf der Teilchenoberfläche sind Amidiniumgruppen. Die Latices waren bei pH-Werten über 11 nicht stabil; längeres Erhitzen auf 90° führte ebenfalls zur Koagulation.

The settling of particles through Newtonian and non-Newtonian media

Abstract 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.

Viscoelastic properties of concentrated latices. Part 2.—Theoretical analysis

Shear-modulus data for polystyrene latices at various volume fractions and sodium chloride concentrations are compared with a simple model based on the theory of interaction between electrical double layers. Stress relaxation and low shear-rate viscosity are also discussed in the context of particle interaction forces.

Viscoelastic properties of concentrated latices. Part 1.—Methods of examination

Concentrated polystyrene latices form strongly interacting systems, and under appropriate conditions of particle radii, volume fraction and ionic strength the repulsive forces can be strong enough to give rise to measurable viscoelastic behaviour. In this paper an experimental investigation of the viscoelastic behaviour of concentrated latices is described. The methods used included creep compliance and shear-wave propagation. The former was used to determine the low stress viscosities and the latter to determine the shear modulus. The particle radii were varied from 26 to 98 nm and the volume fraction range was 0.2–0.4.

Surface charge properties of colloidal titanium dioxide in ethylene glycol and water

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.

Production of porous suspension polymer beads with a narrow size distribution using a cross-flow membrane and a continuous tubular reactor

Abstract 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.

Functionalization of colloidal silica and silica surfaces via silylation reactions

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.

Shear field modification of strongly flocculated suspensions — Aggregate morphology

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.