Latex particle size distribution

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. 

Particle size distribution of a latex has a pronounced influence on its rheological properties, storage stability, and film forming capabilities Q ). In addition, latex particle size distributions provide information on polymerization mechanisms and kinetics (2), and provide a means of polymerization control (3,4). 

The results reported herein indicate that hydrodynamic chromatography is an accurate, reproducible technique for latex particle size distribution analysis. Typical analysis requires 15-20 minutes to complete and reproducibility is generally better than 5% for both reported particle size and mass percent. Latex particle size distributions found using HDC provide useful information about end use performance of many types of material (see Table V). 

Figure 1. S/B latex particle-size distribution via HDC. with permission from Ref. 11. Copyright 1983 Tappi J.

Figure 8. Multi-component latex particle-size distribution.

Very often one does not require as much detail as presented in Figure 2 and the model can be simplified considerably. For example, one may only be interested in the first few moments of the latex particle size distribution, F(V,t) so as to get a mean and variance of the distribution. This can be readily calculated from the definition of the jth moment ... 

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). 

Industrial Engineering Chemistry Research 40, No.23,14th Nov. 2001, p.5177-83 NOVEL OPERATING METHOD FOR CONTROLLING LATEX PARTICLE SIZE DISTRIBUTION IN EMULSION POLYMERIZATION OF VINYLACETATE Ohmura N Kitamoto K Yano T Kataoka K Kobe,University... 

Details are given of a non-steady-state operation for controlling latex particle size distribution by using a continuous emulsion polymerisation of vinyl acetate. The experiment was conducted in a continuously stirred tank reactor under conditions below the critical micelle concentration of the emulsifier. The mean residence time was switched alternately between two values in the nonsteady-state operation to induce oscillations in monomer conversion in time. The effect of the switching operation on particle size distribution is discussed. 13 refs. 

G.E. Elicabe, L.H. Garcia-Rubio, Latex particle size distribution from tuibidimetry using inversion techniques. J. Coll. Int. Sci. 129(1), 192-200 (1989). doi 10.1016/0021-9797(89)90430-X... 

E. Gulari, G. Bazzi, E. Gulari, A. Annapragada, Latex particle size distributions from multiwavelength turbidity spectra. Part. Part. Syst. Charact. 4(1-4), %-100 (1987). doi 10. 10024 psc.l9870040120... 

Polymerization of fine emulsions achieved by using a combination of a typical surfactant such as sodium dodecyl sulfate and a long-chain fatty alcohol. This gives rise to spontaneous emulsification of the monomer into very fine droplets. In this case the polymerization can be carried out by using a water-soluble or a monomer-soluble initiator (27). The latex particle size distribution is the same as for microsuspension poljunerization. 

E-PVC is manufactured essentially by three polymerisation processes batch emulsion, continuous emulsion and microsuspension. All these processes are used to produce a range of latex particle size distributions and thus plastisol rheologies. Different paste applications demand different rheolog> profiles. The microsuspension process intentionally produces latexes with a significant content of coarser particles. 

The spray drying causes the agglomeration of the latex particles into secondary particles with a mean particle size of approximately 30 micrometres. These may be subsequently broken down by the use of a mechanical grinding process, to recover some or all of the original latex particle size distribution. 

After drying, suspension PVC is usually sieved to remove coarse particles which could cause problems during transformation. Emulsion PVC is classified and ground if required for the end application. Polymers for paste applications are normally ground those for general emulsion applications are not. The fracturing of the secondary particles formed in the dryer enables them to break down more easily in the plastisol and return to their original latex particle size distribution. 

The ability to predict latex particle size distributions is of significant practical importance as many physical and end use properties of the latex are directly related to this characteristic. 

M. J. Devon, E. Meyer, T. Provder, A. Rudin, B. B. VPfeiner, Detector Slit Width Error in Measurement of Latex Particle Size Distributions with a Disc Centrifuge , Chapter 10 in Particle Size Distribution II Assessment and Characterization, T. Provder (ed.), ACS Symposium Series 472,American Chemical Society, Washington D. C., 1991. 

The latex particle size distribution is narrow for both latexes and the particle sizes are, on average, around 60-80 nm. Comparing the two latexes, synthesized in absence (left] and in the presence of QDs [right], it is not immediately obvious which latex contains QDs. The distribution of QDs in the latex on the right is not homogeneous. A few particles appear to have darker structures within them [indicated with a white arrow] which, at least, points to the presence of some remaining, but clustered QDs after the polymerization. 

A number of studies endeavored to experimentally determine the values of the desorption rate constant. It is also interesting to note that Lee and Poehlein [46,48,49] modified the approach of Ugelstad et al. [8,9] and applied it to emulsion polymerization carried out in a single continuous stirred tank reactor (CSTR) system. The resultant latex particle size distribution data were then used to determine the value of A des. The k data obtained from other literature are summarized in Table 4.4. Significant variations in the values of k isi for the emulsion polymerizations of styrene at 60 °C are observed. 

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