Polystyrene sphere, preparation conditions

For example, spheres of narrow size distribution of polyl/Mm-butylstyrene) were obtained by exposing the corresponding monomer droplets to the trifluorometh-anesulfonic acid initiator vapor (Fig. 1.5.8). The polymer particles ranged in diameter from I to 3 p,m, and their uniformity was sensitive to the monomer-to-initiator mass ratio. Under certain conditions the normally smooth spheres appeared connected through polymer whiskers (Fig. 1.5.9) (67). Using styrene monomer and adjusting the boiler temperature, uniform polystyrene particles up 10 xm in diameter and spheres of 20 p,m of broader size distribution could be prepared (67). 

Monodisperse spheres are not only uniquely easy to characterize, but also very rarely encountered. Polymerization under carefully controlled conditions allows the preparation of the polystyrene latex shown in Figure 1.8. Latexes of this sort are used as standards for the size calibration of optical and electron micrographs (also see Section 1.5a.3). However, in the majority of colloidal systems, the particles are neither spherical nor monodisperse, but it is often useful to define convenient effective linear dimensions that are representative of the sizes and shapes of the particles. There are many ways of doing this, and whether they are appropriate or not depends on the use of such dimensions in practice. There are excellent books devoted to this topic (see, for example, Allen 1990) and, therefore, we consider only a few examples here for the purpose of illustration. 

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