R. H. Ottewill

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.

The preparation of poly(methyl methacrylate) latices in non-aqueous media

Abstract 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.

Preparation of monodisperse ellipsoidal polystyrene particles

A method is described for the preparation of monodisperse ellipsoidal particles of polystyrene in the colloidal size range. Monodisperse polystyrene particles were dispersed in a solution of polyvinyl alcohol. This dispersion was then allowed to form, by evaporation, a thin film of polyvinyl alcohol containing spherical polystyrene particles. Strips of this film were clamped into a metal frame, heated rapidly in an oil bath to 200°C and stretched to a predetermined extent in order to convert the spherical particles into ellipsoids; the film was then cooled. A wide range of axial ratios for a variety of initial particle sizes was obtained by this method.

Studies on the preparation and characterisation of monodisperse polystyrene latices

SummaryA series of polystyrene latices prepared by emulsion polymerisation have been characterised by electrophoresis. Dodecanoic acid, dodecylamine hydrochloride and dodecylphosphoric acid were used as emulsifying agents and hydrogen peroxide and potassium persulphate as initiators. After a preliminary dialysis to remove oxidation products formed in the polymerisation the mobility against pH curves showed regions which were characteristic of the adsorbed surface active agent. After extensive dialysis these regions were no longer present and the curves were characteristic of a carboxylic acid with a surface pK of 4.64. The experiments indicated that the carboxyl groups were an integral part of the polymer. This was confirmed by the preparation, using suspension polymerisation, of a dispersion of polystyrene particles in the complete absence of surface active agent. For this material the mobility — pH behaviour was very similar to that of the extensively dialysed latices. A detailed discussion is given of the problem of obtaining pK values from electrokinetic data.ZusammenfassungEs wurde versucht, Polystyrol-Latices, die durch Emulsionspolymerisation dargestellt worden waren, durch Elektrophorese zu charakterisieren.Als Emulsionsmittel wurden Dodecansäure, Dodecylamin, Dodecylphosphorsäure und Salzsäure, als Initiatoren Wasserstoffperoxid und Kaliumperoxiddisulfat verwandt. Wenn durch einmalige Dialyse die bei der Polymerisation gebildeten Oxydationsprodukte entfernt werden, zeigt die Beweglichkeit in Abhängigkeit vom pH-Wert Bereiche, die für die adsorbierten oberflächenaktiven Agentien charakteristisch sind. Nach intensiver Dialyse verschwinden diese Bereiche, und die Kurven nehmen die für Carbonsäuren mit einem Oberflächen-pK-Wert von 4,64 charakteristische Gestalt an. Die Versuche weisen darauf hin, da\ die Carboxylgruppen ein Bestandteil des Polymeren sind.Eine Bestätigung hierfür ergab sich aus der Darstellung einer Polystyroldispersion durch Suspensionspolymerisation bei völliger Abwesenheit grenzflächenaktiver Verbindungen. Diese Dispersion zeigt einen ähnlichen Zusammenhang zwischen Beweglichkeit und pH-Wert wie die ausgiebig dialysierten Latices. In einer detaillierten Diskussion wird die Frage behandelt, wie pK-Werte aus elektrokinetischen Daten ermittelt werden können.

The influence of non-ionic surface active agents on the stability of polystyrene latex dispersions

SummaryThe influence ofn-dodecyl hexaoxyethylene glycol monoether on the stability of dispersions of polystyrene latices has been investigated by measuring the rates of flocculation, by lanthanum nitrate and hydrochloric acid, in the presence of various concentrations of the surface active agent. The adsorption isotherm for the non-ionic surface active agent on the latex surface showed that saturation adsorption was reached at about the critical micelle concentration to give a monolayer of vertically orientated molecules. A determination of the thickness of the adsorbed layer by an ultracentrifuge method confirmed the vertical orientation. In order to explain the results a theory has been developed based on the interaction between the adsorbed layers which includes a term to account for the interaction between the surface active molecule and the solvent.ZusammenfassungDer Einfluß vonn-Dodecyl-hexaoxyäthylen-glycolmonoäther auf die Stabilität von Dispersionen von Polystyrol-Latices wird durch Messung der Flockungsgeschwindigkeit durch Lanthannitrat und hydrochlorische Säure in Gegenwart von verschiedenen Konzentrationen überflächenaktiver Agentien untersucht. Die Adsorptionsisothermen von nichtionischen oberflächenaktiven Agentien an die Latexoberfläche zeigt, daß etwa bei der kritischen Micellkonzentration Sättigungsadsorption erreicht wird, die eine monomolekulare Schicht senkrecht orientierter Moleküle gibt.Die Bestimmung der Dicke der adsorbierten Schicht durch eine Ultrazentrifugenmethode stellt die senkrechte Orientierung sicher. Um die Ergebnisse zu erklären, wird eine Theorie entwickelt, die auf der Wechselwirkung zwischen den adsorbierten Schichten beruht, einschließend einen Term, um der Wechselwirkung zwischen den oberflächenaktiven Molekülen und dem Lösungsmittel Rechnung zu tragen.

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.

Studies on the preparation and characterization of monodisperse polystyrene latices

SummaryA description is given of the methods used for the preparation of monodisperse polystyrene latices using hydrogen peroxide as an initiator and sodium dodecanoate, sodium dodecyl hydrogen phosphate and dodecylamine hydrochloride as surface active agents for the emulsification of styrene. The latices prepared had a small coefficient of variation on particle diameter as measured by electron microscopy. The range of particle sizes investigated was from 500–5000 Å. The diameters of the particles determined, where possible, from Higher Order Tyndall Spectra were in reasonable agreement with those determined by electron microscopy. Determination of the surface area of one latex by krypton adsorption gave a surface area in close agreement with that obtained from electron microscope observations.ZusammenfassungDie Methoden zur Präparation monodisperser Polystyrol-Latices werden beschrieben, wobei als Initiator Wasserstoffsuperoxid und als Emulgator Natriumdodecanoat, Natriumdodecyl-Hydrogenphosphat und Dodecylamin-Hydrochlorid Verwendung fanden. Die erhaltenen Latices haben einen kleinen Koeffizienten der Variation des Teilchen-Durchmessers, bestimmt mit Elektronenmikroskopie. Die Partikelgröße schwankte innerhalb 500–5000 Å. Die Teilchen-Durchmesser aus höheren Ordnungen des Tyndall-Spektrums stehen in vernünftigerÜbereinstimmung mit denen aus elektronenmikroskopischen Untersuchungen. Die Bestimmung der Oberflächengröße eines Latex durch Krypton-Adsorption gab eine Oberfläche ebenfalls in guter Übereinstimmung mit der elektronenmikroskopischen Beobachtung.

Stability and Instability in Disperse Systems

Abstract The balance of the forces of interaction between colloidal particles determines, in general, whether a colloidal dispersion remains stable or undergoes coagulation or flocculation. A review of interaction forces is given and it is then shown how such forces can be measured experimentally using either macroscopic systems or particulate dispersions. Particular attention is given to the repulsive forces which arise from electrostatic charges and/or adsorbed layers. From an understanding of these forces some rationalization can be made of the many phenomena which constitute colloid and interface science.

Small angle neutron scattering studies on non-aqueous dispersions of calcium carbonate

Colloidal dispersions of calcium carbonate in toluene, with the particles stabilised by an alkyl aryl sulphonic acid, have been examined by small angle neutron scattering. On the basis of the assumption that the adsorbed layer of stabilising surface active agent formed a concentric shell around a spherical calcium carbonate core particle, a method was developed to determine both the radius of the core particle and the thickness of the adsorbed layer. For the two series of particles examined the calcium carbonate core particles were found to have radii of 22 and 67 å respectively and in both cases the adsorbed layer thickness was found to be 19.0±1 å. The method provides a means of obtaining adsorbed layer thicknesses under conditions where particle and layer cannot be separated.