Monodisperse latex particles

Most technological suspensions consist of very polydisperse particles. In order to simplify his experimental system Stotz employed monodispersed latex suspensions (particle diameter = 6 or 30y). In an interesting comparative experiment, he also measured the particle mobilities using the simple... 

Polymerization. Figure 1- shows how the formation of particles during the polymerization depends on the initial concentration of SDS in the aqueous phase. In order to achieve a monodisperse latex, the particle nucleation must be confined to the initial stage of the polymerization. No new particles can be permitted to form during the reaction, and agglomeration of latex particles must be prevented- Thus both a too high and a too low emulsifier concentration must be avoided (I6). This was accomplished by careful postaddition oT emulsifier. 

The porous latex seed particles are obtained via the dynamic swelling method followed by an emulsion polymerization process. A volatile solvent that has no tendency to take part in the polymerization is used in the swelling process and is followed by evaporation to prepare the porous microspheres [99]. The monodisperse particles can be swollen up to 50-1000 times with respect to their initial volume by a vinyl monomer solution, sometimes in combination with other reactants such as a porogen solvent. All reactants are present inside the swollen particles before polymerization. 

Numerical calculations by Mic s theory for model gamma distribution of particles and experiments with bimodal latex suspensions have shown (Khlebtsov and Mel nikov, 1992) the mean particle size determined by the turbidity spectrum method from n(r) calibrations for monodisperse particles to correspond to the relationship... 

The dispersion polymerisation of styrene was studied in a mixed ethanol-water medium using 0.1-2 wt% of omega-methoxy poly(ethylene oxide)40 undecyl-alpha-methacrylate macromonomer as a steric stabiliser. The polymerisation rate reached a maximum at a styrene conversion of around 18% and remained almost constant up to about 55% conversion. The molecular weight of the polymer increased with increasing conversion of styrene up to about 55%. The polymerisation rate and activation energies were studied and discussed. Spherical monodisperse particles of around 250 nm diameter were obtained for the final stable latices.The grafted poly(ethylene oxide) macromonomers were enriched and anchored on the surface of PS latex particles with a top surface composition of 28% macromonomer. 33 refs. SINGAPORE Accession no.665916... 

Emulsion polymerization produces latexes whose particles are almost perfectly spherical polymer latexes of highly uniform particle size have been knovm since their accidental discovery in 19 7 l y scientists at the Dow Chemical Company. Concentrated monodisperse latexes are frequently iridescent, whereas heterodisperse latexes are white. The iridescence was correctly attributed by Luck, Wesslau and Klier (l) to Bragg reflection of visible light from ordered arrays of particles. Because of the approximate equivalence of their measured Bragg spacing to that expected for a packed array at the same particle diameter (and also beca ase the... 

The prospects are alluring. Colloidal polymer patterning is similar to very well-established painting and coating processes, so that existing equipment could be adapted for the production of coatings and materials with new properties. The polymer latex formulations that form the basis of the process are well-known in industry, and the step to monodispersed particles and controlled deposition seems viable. For applications where molding methods are inapplicable, particle-based polymer patterns could form the basis of industrial processes. 

Rgure 7.3. A schematic representation for a continuous emulsion polymerization process, in which the relatively monodisperse particle size distribution of seed latex particles introduced into a continuous stirred tank reactor becomes broader at the exit of the reactor. 

---