Mesoscopic Disorder
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MRS BULLETIN/MAY 1994
on the disordered structure of the random network of fibers that compose it because the characteristic length scale is much larger. This complicates the description of the behavior and properties of these and similar disordered materials. A larger length scale of the disorder influences a much greater range of properties. This issue of the MRS Bulletin is devoted to disordered materials whose characteristic length scale of disorder is larger than microscopic. We label this "mesoscopic disorder" to distinguish the larger length scale (100 A and larger) of the disorder from that which characterizes materials such as molecular glasses. The larger length scales inherent in mesoscopically disordered materials imply that their properties will not be dominated by their behavior on the atomic or molecular scale. Rather, their properties will be dominated by their behavior on more macroscopic length scales. This complicates the study of their properties and structure; only at very large length scales can these materials be considered homogeneous. Typically, their properties are dominated by their behavior on smaller length scales, and thus the disorder in their structure plays a dominant role. Therefore, knowledge of their properties on a wide range of length scales is often essential to describe their behavior. Despite the inherent complexity of mesoscopically disordered materials, they are increasingly the subject of studies by the materials science community, and considerable progress has been achieved in describing their behavior. Their importance derives partly from their role as components in the modern age of advanced materials; it also derives from the fascinating behavior often observed. Advances in our understanding have arisen because of increasingly sophisticated modern theoretical tools, such as computer simulation and statistical methods; they have also arisen because of increasingly sophisticated experimental methods and techniques which allow us to probe the properties of mesoscopically disordered materials on all the relevant length scales, and to assimilate the necessarily large amount of data that is collected. Many experimental and theoretical ad-
vances can be applied to a large number of different systems; moreover, many different mesoscopically disordered materials share key properties and behavior, so that advances in the study of one can often aid our understanding of others. A key goal in choosing the articles in this issue is to highlight this synergy. The article by D. Asnaghi, M. Carpineti, and M. Giglio describes recent progress in our understanding of colloid aggregation, a subject of scientific research for most of this century. The considerable progress achieved over the last decade was largely stimulated by the realization that the highly disordered structure of colloidal aggregates can be quantitatively described as a fractal. The authors describe an additional form of ordering they observed in the structure of the colloidal aggregates. Colloids at a sufficiently hi
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