Latex colloidal, particle size

The object of this study was to clarify some aspects of the mechanism of shear-induced flocculation in colloidal dispersions. Vinyl chloride homopolymer and copolymer latices were prepared by emulsion polymerization using sodium dodecyl sulphate as emulsifier. Agglomeration behavior in these latices was studied by measuring the mechanical stability using a high speed stirring test. The latex particle size was measured by an analytical centrifuge. Molecular areas of emulsifier in the saturated adsorption layer at the surface of homopolymer and copolymer latex particles were estimated from adsorption titration data. 

Maron, S.H. and Elder, M.E., Determination of latex particle size by light scattering 1. Minimum intensity method, J. Colloid Set, 18, 107-118, 1963. 

The polymer latex stability obtained from the mini-emulsion polymerization with various ratios of SDS/CA decreases in the series l/3>l/10>l/l>l/6>l/0, which is consistent with the stability of monomer droplets reported by Ugelstad (l/3>l/2>l/l>l/6>l/0) [106]. The latex particle size decreases with increasing CA concentration. Furthermore, a two-dimensional hexagonal packing of surface-active molecules has been reported to be formed at a molar ratio of SDS/CA=l/3 in the colloidal system [107]. The good packing of the oil-water interfacial zone leads to satisfactory stability of monomer droplets, and it remains intact throughout the polymerization. 

Summarizing, the biosynthesis of PHB can be understood in terms of the kinetic processes of initiation, propagation and chain transfer and the affect of latex particle size on these. Rirther, the colloidal aspects of the formation of PHB latex particles can be explained by the homogeneous nucleation mechanism, well known in conventional emulsion polymerization processes. 

These polymers possess the characteristics of a true latex concerning colloidal stability, particle size uniformity, him forming properties, etc. However, the fact that they are not manufactured from monomers but by direct emulsification of already formed polymers makes them free of (pcHentiaiiy toxic) unreactcd monomers, and they can hence be used in the body without toxicity hazards (124.125). 

Surfactant keeps emulsion droplets and latex particles colloidally stable against coalescence/aggregation. The surfactant plays another important role in emulsion polymerisation besides stabilisation. Surfactant is critically involved in the nucleation mechanism (i.e., how the particles are formed) of the polymer latex particles (418,419). The amount of surfactant used is critical in controlling the latex particle size distribution. As surfactant is added to an emulsion, some remains dissolved in the aqueous phase, and some adsorbs onto the surface of the emulsion droplets according to an adsorption isotherm (e.g., Langmuir, Freundhch, or Frumkin adsorption isotherms) (173). 

The appropriate surfactant (stabiliser) for use in a particular emulsion polymerisation is selected based on several considerations (415). The surfactant controls the latex particle size and provides colloidal stability. Too much coagulum in the product may... 

The above latices were prepared by batch precipitation polymerisation of N-isopropylmethacrylamide using methylenebisacrylamide, as crosslinker, and potassium persulphate, as polymerisation initiator. The effect of the crosslinker on total conversion of polymer, latex particle size and morphological properties and colloidal properties of the final microgel particles were investigated. The relationship between the amount of water-soluble polymer and amount of crosslinker and the influence of temperature on the electrophoretic mobility of the latex are considered. 11 refs. 

Latex particles can be used for micromanipulation by taking into account that some of their colloidal properties (particle size and dielectric behavior) can be affected for instance imder the action of a laser beam or an electric field. 

Carboxyl and amino-functionalized latex particles were synthesized [67] by the miniemulsion polymerization of styrene and acrylic acid or 2-aminoethyl methacrylate hydrochloride, and the effect of hydrophilic comonomer and surfactant type (nonionic versus ionic) on the colloidal stability, particle size, and particle size distribution was analyzed. The reaction mechanisms of particle formation in the presence of nonionic and ionic surfactants were proposed. 

The compounding technique for latex differs from that of dry mbber and is fundamentally simpler. A critical factor of colloidal stabiUty makes necessary that each ingredient is of optimum particle size, pH, and concentration when added as an aqueous dispersion to the latex. Rubber latex is a colloidal aqueous emulsion of an elastomer and natural mbber latex is the milky exudation of certain trees and plants that of greatest commercial importance is the... 

This paper presents the physical mechanism and the structure of a comprehensive dynamic Emulsion Polymerization Model (EPM). EPM combines the theory of coagulative nucleation of homogeneously nucleated precursors with detailed species material and energy balances to calculate the time evolution of the concentration, size, and colloidal characteristics of latex particles, the monomer conversions, the copolymer composition, and molecular weight in an emulsion system. The capabilities of EPM are demonstrated by comparisons of its predictions with experimental data from the literature covering styrene and styrene/methyl methacrylate polymerizations. EPM can successfully simulate continuous and batch reactors over a wide range of initiator and added surfactant concentrations. 

In 1997, a Chinese research group [78] used the colloidal solution of 70-nm-sized carboxylated latex particles as a subphase and spread mixtures of cationic and other surfactants at the air-solution interface. If the pH was sufficiently low (1.5-3.0), the electrostatic interaction between the polar headgroups of the monolayer and the surface groups of the latex particles was strong enough to attract the latex to the surface. A fairly densely packed array of particles could be obtained if a 2 1 mixture of octadecylamine and stearic acid was spread at the interface. The particle films could be transferred onto solid substrates using the LB technique. The structure was studied using transmission electron microscopy. 

Fulda and Tieke [77] studied the effect of a bidisperse-size distribution of latex particles on the structure of the resulting LB monolayer. For this purpose, a mixed colloidal solution of particles la and lb was spread at the air-water interface. Particles la had a diameter of 434 nm, particles lb of 214 nm. The monolayer was compressed, transferred onto a solid substrate, and viewed in a scanning electron microscope (SEM). In Figure 10, SEM pictures of LB layers obtained from various bidisperse mixtures are shown. 

Table 10.4 summarizes the compositions of some experiments as well as the colloid-analytical data of the final polystyrene lattices. A particle diameter of about lOOnm (including the shell of the adsorbed block copolymers in an extended conformation) is rather low for the product of a dispersion polymerization in unpolar solvents. In addition, a mean deviation (a) of about 20% of the particle size indicates a well-controlled and stable latex. 

Because the latex solids in the saturation process are deposited in the struture of the paper web by drying, the colloidal system is not as critical as with beater addition. Nonionic and amphoteric surface-active materials can be effectively used in the latices. A low surface tension and small particle size are desirable features. 

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