Polystyrene microgel particles

Fig. 16.2. Three component diagrams at 25 °C for polystyrene microgel particles (M) in ethylbenzene (S) in the presence of free polystyrene (P) (a) free polystyrene of various molecular weights curves 1, 1 800 2, 18 000 3, 2 x lO (b) different particle sizes curves 1, 520 nm 2, 460 nm 3, 403 nm (after Clarke and Vincent, 1981b).

The concentration dependence of q of hard-sphere suspensions is the same as the concentration dependence of q found in many polymer solutions, namely t](c) is a stretched exponential in c at smaller c and a power law in c for larger c. The frequency dependences of G (a>) and G"(co) for a colloid suspension and for a polymer solution are also very nearly the same, namely a stretched exponential in (o at smaller a>, a power law in co at large a> and various high-frequency small additive components. At the extreme large-concentration limit, the dynamic moduli of a soft-sphere melt composed of polystyrene microgel particles have very nearly... 

M. Rasmusson, A. Routh, and B. Vincent, Flocculation of microgel particles with sodium chloride and sodium polystyrene sulfonate) as a function of temperature, Langmuir 20, 3536-3542 (2004). 

FIGURE 12.28 The reduction adsorbed amount of nucleic acids onto high cationic polystyrene latexes and low cationic poly(NIPAM) microgel particles as a function of pH at 20°C and M ionic strength. (From Ganachaud, F. et ah, Langmuir, 13, 701, 1997. With permission.)... 

The first attempts to investigate the consequences of the addition of free polymer to model colloidal systems were undertaken by Sieglaff (1959). He studied microgel particles composed of polystyrene cross-linked by 0-3% divinylbenzene dispersed in toluene. Free polystyrene of weight average molecular weight 5 x 10 or 2 x 10 was dissolved into the dispersion medium. 

The cross-linking of the polystyrene latex particles prevented their complete dissolution when dispersed in toluene, although significant sweUing still ensued (hence the designation microgel )-... 

In more recent times, Clarke and Vincent (1981b) have extended the studies of Sieglaff on microgel particles. They used ethyl benzene and n-butyl formate, rather than toluene, as the dispersion medium. Their various samples of relatively narrow molecular weight free polystyrene spanned the molecular weight range 1-8 x 10 to 2 x 10 . The microgel particles when swollen had a diameter of between 500 and 1150 nm, as determined by photon correlation spectroscopy. 

Clarke and Vincent in these studies established the phase diagrams for the free polystyrene-microgel-ethyl benzene systems, two of which are displayed in Fig. 16.2a and b. In all cases, only the stability/instability boun ry is shown. These lines correspond to the locus of the critical volume fraction of free polymer required to induce flocculation (vj ) as a function of the volume fraction of the microgel particles (< 3). 

The molecular weight dependence of vz for the flocculation of microgel particles by polystyrene in ethyl benzene... 

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