142 Advances in Polymer Science Editorial Board: A. Abe. A.-C ...

166 K. Ito, S. Kawaguchi
tion, q=q D . This means that the chain conformation for the grafts on the latex
particle will change with grafting density, as will be presented in Sect. 6.4. The S
value is closely related to the conformation of a single polymer chain as a stabilizer
grafted onto the surface of a latex particle. According to de Gennes' “mushroom”
model [130] for a polymer grafted to a noninteracting surface, the polymer
chain occupies a volume determined by its mean-squared radius of gyration
. When the surface becomes crowded with chains, additional energy is
needed to deform the polymer mushrooms into brushes. When the particle surfaces
are covered completely with random coils of the polymer, they are also
sterically stabilized against coagulation with other particles. One therefore defines
S crit as the maximum surface area occupied by a single polymer chain in the
continuous phase. In this approximation one may treat the polymer chain as a
rigid sphere composed of solvent and a random polymer chain, affixed on the
surface of latex particle. In this case, S crit is a cross section of the sphere and may
be written in terms of the square radius of gyration as
(29)
Figure 7 shows a comparison of Eq. (27) with the particle radius obtained by
dispersion copolymerization of styrene with PEO macromonomer 26 (m=4, n=
45) in methanol-water medium (9/1 v/v). One sees that the experimental particle
Fig. 7. Change of average particle radius (R) as a function of initial concentration (W Do in
g/l) of PEO macromonomer, 26 (m=4 and n=45). W Mo =100 g/l, [I] 0 =0.0122 mol/l, q=1, at
60 ˚C. A solid line is a theoretical curve calculated from Eq. (27) with S crit /r 1 =10 nm 2