Effect of Volume Fraction and Particle Size on Depletion Flocculation of a Sterically Stabilized Latex Dispersion Induced by Addition of Poly(ethylene oxide)
✍ Scribed by W. Liang; Th.F. Tadros; P.F. Luckham
- Publisher
- Elsevier Science
- Year
- 1993
- Tongue
- English
- Weight
- 392 KB
- Volume
- 155
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
The effect of particle size, (a), and volume fraction, (\phi_{s}), of sterically stabilized polystyrene latex dispersions on depletion flocculation was studied using rheological measurements. Three latex particles with diameters of 147,435 , and (915 \mathrm{~nm}) were investigated using "free" poly(ethylene oxide) (PEO) with molecular weights of (20,000,35,000), and 100,000 . The results showed a linear relationship between the yield value (\tau_{\beta}) and ( (\phi_{\mathrm{p}}) (\left.-\phi_{p}^{*}\right)), where (\phi_{p}) is the free polymer volume fraction and (\phi_{p}^{+})is the critical value at which depletion flocculation begins. This linear relationship could be represented by a scaling law with an exponent of (\sim 2.8) in (\phi_{s}). From (\tau_{\beta}), the energy of separation of flocs into single units was calculated using a number of assumptions. The free energy of attraction due to depletion, (G_{\text {dep }}), was calculated using both the models of Asakura and Oosawa and of Fleer, Scheutjens, and Vincent. The latter theories show no dependence of (G_{\text {dep }}) on (\phi_{s}), whereas (E_{\text {sep }}) shows a clear increase with an increase in (\phi_{\mathrm{s}}). A scaling law could be used to illustrate the dependence of (E_{\mathrm{sep}}) on the various parameters of the system: the particle radius (a), the volume fraction of the dispersion (\psi_{s}). the concentration of free polymer (\phi_{p}), and the molecular weight of the free polymer. O 1993 Academic Press. inc.