Surface latexes, particles size

PVA and TaM -for the 88%-hydrolyzed PVA. The same dependence was found for the adsorbed layer thickness measured by viscosity and photon correlation spectroscopy. Extension of the adsorption isotherms to higher concentrations gave a second rise in surface concentration, which was attributed to multilayer adsorption and incipient phase separation at the interface. The latex particle size had no effect on the adsorption density however, the thickness of the adsorbed layer increased with increasing particle size, which was attributed to changes in the configuration of the adsorbed polymer molecules. The electrolyte stability of the bare and PVA-covered particles showed that the bare particles coagulated in the primary minimum and the PVA-covered particles flocculated in the secondary minimum and the larger particles were less stable than the smaller particles. 

The results showed that all batch polymerizations gave a two-peaked copolymer compositional distribution, a butyl acrylate-rich fraction, which varied according to the monomer ratio, and polyvinyl acetate. All starved semi-continuous polymerizations gave a single-peaked copolymer compositional distribution which corresponded to the monomer ratio. The latex particle sizes and type and concentration of surface groups were correlated with the conditions of polymerization. The stability of the latex to added electrolyte showed that particles were stabilized by both electrostatic and steric stabilization with the steric stabilization groups provided by surface hydrolysis of vinyl acetate units in the polymer chain. The extent of this surface hydrolysis was greater for the starved semi-continuous sample than for the batch sample. 

An ICI-Joyce Loebl Disc Centrifuge MK III, a photosedimento-meter, was used to measure the latex particle size distribution. The latex had a unimodal particle size distribution with a diameter of 1.05 micrometers (surface area average). The methods of separating latex particles by a centrifugal field and detecting the size distribution by a photocell may be found in the literature. 

Latex Particle Size, nm Surface Charge Density (sulfate group), yc/cm2 Electrophoretic Mobility in Deionized Water ym cm/sec volt... 

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. 

The surface activity of these compounds was not studied in detail. As mentioned in the Experimental Section, all were about equivalent in nucleating particles during emulsion polymerization. The resulting latexes when dialyzed to remove excess salt were stable against settling even at 10% solids over many months. Data on samples where both latex particle size and critical micelle concentration were measured is shown in Table II. 

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. 

A considerable amount of work has been published during the past 20 years on a wide variety of emulsion polymerization and latex problems. A list of 11, mostly recent, general reference books is included at the end of this chapter. Areas in which significant advances have been reported include reaction mechanisms and kinetics, latex characterization and analysis, copolymerization and particle morphology control, reactor mathematical modeling, control of adsorbed and bound surface groups, particle size control reactor parameters. Readers who are interested in a more in-depth study of emulsion polymerization will find extensive literature sources. 

In HEC-thickened formulations, low-shear-rate viscosities increase with decreasing latex particle size. This effect has been a major limitation in formulating small-particle latices. The phenomenon appears to arise from electro viscous, hydration, or flocculation effects, not a depletion layer mechanism. Associative thickeners achieve efficient viscosity in coating formulations via participation in synthesis and formulation surfactant micelles to form pseudo macromolecules and via an ion-dipole interaction between the cations of surface carboxylate groups on the latex and the ether linkages of the associative thickener. Generally, an excess of synthesis surfactant is found in the production of small-particle latices. The achievement of lower viscosities in small-particle ( 100 nm) latex coatings thickened with associative thickener appears to occur by extensive disruption of the polymer hydrophobe s participation in intermicellar networks. 

When conversion is determined gravimetrically. Interval I may be completed before the first sample is taken. When rates of emulsion polymerization are discussed it is the constant rate fi-equently observed during Interval II which is meant. Most commonly, practically all the emulsifier is adsorbed on the surface of the latex particles at the end of Interval I then the surface concentration of adsorbed emulsifier decreases as the latex particles grow. Soap titration [67], in which the volume of a standard emulsifier solution required to reduce the surface tension of the latex to the value characterizing the presence of micellar soap is determined can be used to determine the final surface concentration of emulsifier. The surface-average particle size can be calculated from a knowledge of the amount of surfactant adsorbed at this point and the area occupied at the interface by a surfactant molecule in a saturated monolayer. This area should... 

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 objective of this work was to characterise the sodium dodecyl allyl sulphosuccinate (Eliminol JS-2) stabilised poly(butyl acrylate) (PBA) lattices produced in a semibatch reactor. The PBA latex particles were prepared using a semibatch pulsion polymerisation process. It was found that the concentration of JS-2 or sodium dodecyl sulphate present in the initial reactor charge is very important in determining the final latex particle size. The higher the particle size polarity is, the larger is the saturated particle surface area covered by one JS-2 molecule. It was also found that at a common surfactant concentration, the JS-2 stabilised latex displays reduced chemical stability than the sodium dodecyl sulphate stabilised latex. The results of such research should be useful to tape and label manufacturers. 3 refs. 

Emulsion copolymerizations can be carried out using batch, semi-continuous, or continuous processes. The copolymers made by these processes differ according to the process used, the copoly-meriztion reactivity ratios of the monomers, and the monomer solubilities in the aqueous phase. To show the difference between batch and semi-continuous polymerization, the latex particle size, surface characteristics, latex stability, copolymer properties, and latex film morphology were investigated for the vinyl acetate-butyl acrylate system (37). The water solubilities are 290 mM and llmM for vinyl acetate and butyl acrylate, respectively, and the copoly-merization reactivity ratios of = 0-0.04 and r 2 show... 

In aqueous emulsion polymerization, amphiphilic polymers are widely used as polymeric surfactants to stabilize the latex particles, where the hydrophobic blocks can anchor on the particle surface while the hydrophilic blocks extend into the water phase and create a hydrophilic shell [47, 49-52]. Therefore, PS-PAA-PS and HB-(PAA)47-g-(PS)48 copolymers were further used as polymeric surfactants to explore the effect of chain topology on the emulsifying efficiency. The characterization results of solid contents (t), latex particle sizes ( R)) and numbers (A p) are summarized in Table 5.2, Figs. 5.29 and 5.30, where the average particle diameters were carefully determined by DLS at pH 3.2 to ensure the full collapse... 

The dispersion degree of the latex particles during the continuous emulsion polymerization of vinyl chloride depends on the emulsifier concentration in the system. Latex particle sizes vary around some average values in connection with the surface area which can be covered with emulsifier in a state of maximum packing. 

Xu and Chen [32] prepared two polymerizable surfactants, sodium 4-((o-acryloyloxyalkyl)oxy benzene sulfonate with the alkyl chain length equal to 8 or 10, and used them to stabilize the semibatch emulsion copolymerization of butyl methacrylate. A redox initiator system of ammonium persulfate and tetramethylethylenediamine was used to start the polymerization at room temperature. The latex particle size increases continuously, whereas the number of particles per unit volume of water remains relatively constant with the progress of polymerization. This is attributed to the predominant micellar nucleation mechanism. X-ray photoelectron spectroscopy data show that polymerizable surfactant molecules are preferably located near the latex particle surface layer. 

Taking latex particle size distribution as an example, nucleation of latex particles in the early stage of an ideal batch emulsion polymerization is normally very fast. Therefore, the total particle surface area generated is large enough to capture the free surfactant molecules and particle nucleation ceases quite early in the polymerization ( 2-10% monomer conversion). Latex particles thus formed would have approximately identical ages at the end of an ideal batch polymerization (Figure 7.5a). The particle size distribution of these... 

---