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Notes: Abstract  A simple procedure for the preparation of styrene-in-water and methylmethacrylate (o/w) micro-emulsions was established. This consisted of the preparation of a w/o emulsion using a low HLB number surfactant (Synperonic NP4, nonyl phenyl with 4 mol ethylene oxide) and a small amount of an anionic surfactant (Aerosol OT, diethyl hexyl sulphosuccinate, or sodium dodecyl benzene sulphonate). The w/o emulsion was then titrated with an aqueous solution of a high HLB number surfactant (Synperonic NP15, nonyl phenyl with 15 mol ethylene oxide). The droplet size and poly-dispersity were determined using photon correlation spectroscopy (PCS). The temperature range within which a microemulsion remained stable decreased with increase in the concentration of styrene or methylmethacrylate and this could be explained in terms of the phase diagram of the microemulsion system. Conductivity measurements as a function of temperature showed that the systems are oil-in-water microemulsions.

Notes: Abstract  The interaction of a nonionic polymeric surfactant with an anionic surfactant at the oil–water interface has been studied by its effects on the droplet size, stability and rheology of emulsions. Oil-in-water (o/w) emulsions were prepared using isoparaffinic oil and mixtures of a nonionic polymeric surfactant with an anionic surfactant. The macro-molecular surfactant was a graft copolymer with a backbone of polymethyl methacrylate and grafted polyethylene oxide (a graft copolymer with PEO chains of MW=750). The anionic surfactant was sodium dodecyl sulfate (SDS). The stabiliza-tion of the emulsion droplets was found to be different when using one or the other surfactant. The mechanism of stabilization of emulsion droplets by the macro-molecular surfactant is of the steric type while the stabilization by anionic surfactant is of the electrostatic repulsion type. Emulsions stabilized with mixtures present both types of stabilization. Other effects on the preparation and stabilization of emulsions were found to be dependent on properties associated with the surfactant molecular weight such as the Marangoni effect and Gibbs elasticity. The initial droplet size of the emulsions showed a synergistic effect of the surfactant combination, showing a minimum for the mixtures compared to the pure components. Emulsion stability also shows a synergistic interaction of both surfactants. Rheological measurements allow for the estimation of the interparticle interaction when measured as a function of volume fraction. Most of the effects observed can be attributed to the differences in interfacial tension and droplet radius produced by both surfactants and their mixtures. The elastic moduli are well explained on the basis of droplet deformation. Ionic versus steric stabilization produce little difference in the observed rheology, the only important differences observed concerned the extent of the linear viscoelasticity region.

Notes: Abstract  The polymerization of styrene-in-water and methylmeth-acrylate-in-water microemulsions stabilized by nonionic surfactants was investigated using different initiation techniques. Thermally induced initiation was carried out using potassium persulfate (water soluble) and azobisiso-butyronitrile (AIBN) (oil soluble) at 60° and 50°C, respectively. When the monomer concentration was kept below a certain limit, the particle size of the nanolatex was similar to the droplet size of the microemulsion precursor. At higher monomer concentrations, the latex produced was significantly larger than the microemulsion droplets, as a result of the possible coalescence of the microemulsion droplets during polymerization. By using chemically induced polymerization (hydrogen peroxide+ascorbic acid) at temperatures below the cloud point temperature of the microemulsion or by photochemically induced initiation at room temperature, it was possible to obtain nanolatex particles with similar size to the droplets up to 10% monomer content. In all cases, the particle size was determined using photon correlation spectroscopy (PCS). Electron micrographs of the microlatex particles were taken and these confirmed the measurements obtained by PCS. The molecular weight of the polymers produced was determined by gel permeation chromatography. The average number of polymer molecules per particle was calculated. It was shown in some cases that the nanolatex contained one polymer chain per particle. A mechanism was suggested for polymerization and particle growth.

Notes: Abstract The preparation of microlatex dispersions from microemulsions of a monomer (styrene, methylmethacrylate or vinyl acetate) is described. A simple method for preparing the microemulsion has been devised. This consists of forming a water-in-oil (w/o) emulsion using a low (HLB) surfactant (nonylphenol with 5, 6 or 7 moles ethylene oxide) and then titrating with an aqueous solution of a high HLB surfactant (nonylphenol with 15 or 16 moles ethylene oxide). A small amount of anionic surfactant (sodium lauryl sulphate, sodium dodecyl benzene sulphonate or dioctyl sulphosuccinate) was also incorporated to enhance the stability of the w/o emulsion and facilitate the inversion to an o/w microemulsion. The droplet-size distribution of the resulting microemulsion was determined using photon-correlation spectroscopy. Three different methods of polymerising the microemulsion were used. These were thermally induced polymerisation using potassium persulphate, azobis-2-methyl propamidinium dichloride (AMP-water-soluble initiators) or azobisisobutyronitrile (AIBN, an oil-soluble initiator). All these initiators required heating to 60°C, i.e. above the stability temperature of the microemulsion. In this case, the microlatices produced were fairly large (37–100 nm diameter) and had a broad particle-size distribution. The second polymerisation procedure was chemically induced using a redox system of hydrogen peroxide and ascorbic acid. This produced microlatices with small sizes (18–24 nm diameter) having a narrow-size distribution. The microlatex size was roughly two to three times the size of the microemulsion droplets. This showed that collision between two or three microemulsion droplets resulted in their coalescence during the polymerisation process. The third method of polymerisation was based on UV irradiation in conjunction with K2S2O8, AMP or AIBN initiators. In this case, the microlatex size was also small (30–63 nm) with a narrow particle-size distribution. Microlatex particles were also prepared using a mixture of monomers (styrene plus methylmethacrylate) or mixture of monomers and a macromonomer, namely methoxy (polyethylene glycol)methacrylate. The latter was used to produce “hairy” particles, i.e. with grafted polyethylene oxide (PEO) chains. The stability of the microlatices was determined by adding electrolytes (NaCl, CaCl2, Na2SO4 or MgSO4) to determine the critical flocculation concentration (CFC). The nonionic latices were very stable giving no flocculation up to 6 mol dm−3 NaCl or CaCl2 and a CFC of 0.6 mol dm−3 for Na2SO4 or MgSO4. Charged latices were less stable than the nonionic ones. The critical flocculation temperatures (CFT) of all latices were determined as a function of electrolyte concentration. With the nonionic latices, CFC was higher than the θ-temperature for polyethylene oxide at the given electrolyte concentration. This indicated enhanced steric stabilisation as a result of the dense packing of the chains and hence an elastic contribution to the steric interaction. This was not the case with the charged latex, which showed CFT values lower than the θ-temperature. The “hairy” latices [i.e. those containing methoxy polyethylene glycol (PEG) methacrylate] were also less stable towards electrolyte (CFT was much lower than θ-temperature), indicating a low density of PEO layers.