Polyvinyltoluene latexes having uniform particle-diameters have been prepared. Diameters range from about 100 mμ to 1000 mμ. When such a monodisperse latex is dried down to the form of a friable film, the particles spontaneously arrange themselves in a close-packed crystalline array. The structure of these crystals has been investigated by means of the electron microscope, utilizing a surface replica technique.
The diameters of the particles were measured optically by three different methods: (1) for particles with diameters less than 276 mμ, the sizes were determined by dissymmetry of light scattering of dilute solutions, (2) for particles with diameters between 302 mμ and 481 mμ the sizes were determined by diffraction from the dried crystalline samples, (3) for particles greater than 595 mμ in diameter the sizes were determined by interference haloes from thin dried films of the samples. Agreement is good with particle-sizes determined from electron microscopy.
The diffraction from the crystalline samples of intermediate particle-size is shown to be that for a two-dimensional grating. It is suggested that these crystalline arrays be used as spectroscopic diffraction gratings.
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