Emulsions with poly based surfactants

Steric stabilization of poly(2-ethyl hexyl acrylate) (PEHA) emulsions in C02 was studied with static and dynamic light scattering (DLS) (O Neill et al., 1997 Yates et al., 1997). These emulsions were stabilized with PFOA-based surfactants. Figure 8.9 shows the average droplet size (hydrodynamic radius) measured by DLS for a liquid PEHA emulsion in C02 stabilized... 

Detailed studies were performed on the copper-catalyzed suspension or emulsion polymerizations.249 Living or controlled emulsion radical polymerization of nBMA can be achieved in the presence of nonionic poly(oxyethylene)-based surfactants such as Brij 97, Brij 98, and Tween 20 with the F21 (X = Br)/CuBr/ L-3 or L-4 system.249,251,252 The Mn increased in direct proportion to monomer conversion up to 5 x 104 (MJ Mn = 1.1 —1.2). The particle sizes are around 1000— 4000 nm, suggesting a suspension, but can be reduced to about 300 nm with the use of hexadecane as a cosurfactant along with ultrasonication.249 252... 

The anhydrous petrolatum base may be made more miscible with water through the use of an anhydrous liquid lanolin derivative. Drugs can be incorporated into such a base in aqueous solution if desired. Poly-oxyl 40 stearate and polyethylene glycol 300 are used in an anti-infective ointment to solubilize the active principle in the base so that the ointment can be sterilized by aseptic filtration. The cosmetic-type bases, such as the oil-in-water (o/w) emulsion bases popular in dermatology, should not be used in the eye, nor should liquid emulsions, owing to the ocular irritation produced by the soaps and surfactants used to form the emulsion. 

We have developed new reaction systems based on colloidal dispersions [23, 24], namely highly concentrated water-in-oil (gel) emulsions, which could overcome most of the disadvantages of the aqueoussolvent mixtures such as inactivation of the aldolase and incomplete aldehyde solubilization in the medium. These emulsions are characterized by volume fractions of dispersed phase higher than 0.73 [25] therefore, the droplets are deformed and/or polydisperse, separated by a thin film of continuous phase. Water-in-oil gel emulsions of water/Ci4E4/oil 90/4/6 wt%, where C14E4 is a technical grade poly(oxyethylene) tetradecyl ether surfactant, with an average of four moles of ethylene oxide per surfactant molecule and oil can be octane, decane, dodecane, tetradecane, hexadecane, or squalane, were typically chosen as reaction media [23, 26]. 

Water-based adhesives also encompass emulsion and dispersion adhesives in which polymer chains are dispersed and stabilized into tiny particles or spheres in aqueous medium with the aid of surfactants. Within this category there are low-cost poly(vinyl acetate) and acrylics, and more expensive higher-performance urethanes, which are typically made of two components. 

Probably the most widely used industrial emulsion or dispersion adhesives are those based on poly(vinyl acetate), commonly referred to as PVA. These product are normally manufactured by emulsion polymerization whereby, basically, vinyl acetate monomer is emulsified in water with a suitable colloid-emulsifier system, such as poly(vinyl alcohol) and sodium lauryl sulfate, and, with the use of water soluble initiator such as potassium persulfate, is polymerized. The polymerization takes place over a period of four hours at 70°C. Because the reaction is exothermic, provisions must be made for cooling when the batch size exceeds a few liters. The presence of surfactants (emulsifiers) and water-soluble protective colloids facilitates the process resulting in a stable dispersion of discrete polymer particles in the aqueous phase. 

A macromolecular surfactant based on poly(acrylic acid sodium salt) (HMWSP-A2) was used to prepare LDPE dispersions. The emulsion droplet size decreased with increasing surfactant concentration up to about 20 wt% of the oil phase. The first phase inversion from a water-in-polymer-melt emulsion to a polymer-melt-in-water emulsion occurred at a critical water phase volume of 20%. After phase inversion and subsequent dilution of the emulsion, if solidification of the melt was carried out during mixing, a second phase inversion occurred and water-in-solid polymer aggregates were formed even if the phase volume of the aqueous phase was well above the critical value. These aggregates contained an aqueous phase encapsulated by the polymer. The kinetics of the phase inversions were studied and the use of the technique to obtain microcapsules from aqueous solutions was discussed. 20 refs. 

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