Experiments on Spherical Polymer Particles

Of course, it is impossible to find particles with zero adhesion to confirm the theoretical argument that spheres should form a face-centered cubic structure above 0.49 volume fraction. However, certain types of polymer latex can be made to approximate to the theoretical nonadhesion conditions above. Polymethyl methacrylate particles were polymerized in a dispersion and polymer molecules were grafted to the surface to provide a steep repulsive force on close approach. The solvent was chosen to reduce the van der Waals force to a low level, by matching the refractive index to the spheres, obtaining an almost transparent suspension from the milky preparation. 

Pusey and his colleagues then investigated the detailed structure of the crystalline regions by examining the diffraction patterns of the scattered light to distinguish fee from hep and rhep structures. Under dilute conditions of slow 

It was a surprise to find that a sample of packing 0.537 did not give fee packing in space, but rhep instead, whereas it gave fee on earth. Also, samples crystallized quicker in space than on earth. For example, a glassy packing of 0.619 volume fraction remained random for a year on Earth whereas it crystallized in space in 4 d. Some of these odd effects require further investigation. One possible cause of these problems is the time required for the crystallization process, which is considered next. 

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