Unit 4 Surfaces and Colloids
In 1915 Wolfgang Ostwald described the subject matter of colloid and surface science as a "world of neglected dimensions". The reason for such a description stemmed from the unique nature of interfaces and colloidal phenomena, they could not be readily interpreted based on "classical" atomic or solution theories, and the regions of space involved were beyond the reach of existent experimental techniques. Science has since taken a firm theoretical and experimental hold on the nature of matter at its two extremes: at the molecular, atomic, and subatomic levels, and in the area of bulk materials, including their physical strengths and weaknesses and their chemical and electrical properties. Legions of chemists, physicists, materials scientists, engineers, and others are continuously striving to improve on that knowledge in academic and industrial laboratories around the world. Between those two extremes still lies the world referred to by Ostwald, and even with the latest advanced techniques for studying the region between phases, a great many mysteries remain to be solved. For that reason, I like to refer to the study of interfaces and colloids as entering the "twilight zone." That "region" of the physical world represents a bridge not only between chemical and physical phases, but also plays a vital but often unrecognized role in other areas of chemistry, physics, biology, medicine, engineering, and other disciplines.
Our understanding of the nature of the interfacial region and the changes and transormations that occur in going from one chemical (or physical) phase to another has historically lagged behind that in many other scientific areas in terms of the development and implementation of both theoretical and practical concepts. That is not to say, however, that we are particularly ignorant when it comes to interfacial and colloidal phenomena. Great strides were made in the theoretical understanding of interactions at interfaces in the late nineteenth and early twentieth centuries. Modern computational and analytical techniques made available in the last few years have led to significant advances toward a more complete understanding of the unique nature of interfaces and the interactions that result from their unique nature. However, because of the unusual and sometimes complex character of interfaces and associated phenomena, the development of fully satisfying theoretical models has been slow. By "fully satisfying" is meant a theory that produces good agreement between theory and experiment in situations that are less than "ideal" or "model" systems.
The degree of "satisfaction" one obtains from a given theory is quite subjective, of course, so there exists a great deal of controversy in many areas related to colloids and interfaces. For the surface and colloid scientist (as in all science), such controversy is not bad, since it represents the fuel for continued fundamental research, such uncertainty can sometimes complicate attempts to solve practical interfacial and colloidal problems.
It is likely that for every trained surface and colloid scientist in academic and industry, there are hundreds of scientists, engineers, and technicians whose work directly or indirectly involves some surface and/or colloidal phenomena. And very probably, of those hundreds, a relatively small percentage have been formally introduced to the subject in more than a cursory way during their scientifc training. It therefore becomes necessary for them to lean "on the fly" enough of the subject to allow them to attack their problems in a coherent way. This book has been designed in a way and at a level that will (hopefully) provide a useful introduction to surface and colloid science at an undergraduate or graduate level while at the same time serving as an accessible reference for those already trained in other fields of science but needing some initial guidance into the twilight zone.
It would be practically impossible to list all of the human activities (both technological and physiological) that involve surface and colloidal phenomena, but a few examples have been listed in Table 2. For purposes of illustration, the examples in Table 2 have been divided into four main categories, each of which is further divided (somewhat arbitrarily, in some cases) according to whether the main principle involved is "colloidal" or "interfacial". More exact definitions of what those two terms imply will be given in the appropriate chapters; however, for present purposes one can think of "colloidal" as being a state of subdivision of matter in which the particle (or molecular) size of the basic unit involved varies from just larger than that of "true" molecular solutions to that of coarse suspensions, that is, between 10 and 10000 nm. "Interfacial" phenomena may be defined in this context as those related to the interaction of at least one bulk phase (solid or liquid) with another phase (solid, liquid, or gas) or a vacuum in the narrow region in which the transition from one phase to the other occurs. As will quickly become apparent, the two classes of phenomena are intimately related and often cannot be distinguished. For present purposes (and according to this author's preference) the examples have been divided according to those definitions based on the principle phenomenon involved.
By examing each subdivision in Table 2, one can quickly see that interfacial and colloidal phenomena are ubiquitous. We and our world simply would not function or even exist as we know it in their absence.
Selected from "Surface, Interface and Colloids" 2nd edition, D.Meyer, Wiley Vch Inc. 1999
Words and Expressions
improve on 改善
twilight 微光
implementation 实现
suspension 悬浮液
surfactant 表面活化剂
emulsifier 乳化剂
stabilizer 稳定剂
aerosol 气溶胶
herbicide 除草剂
pesticide 杀虫剂
pharmaceutical 药的
lacquer 漆器
rheological 流变学的
emulsion 乳液
drilling mud 钻井泥浆
electrophoretic 电泳的
sewage 污物
respiration 呼吸作用
lubrication 润滑
capillary 毛细管
arteriosclerosis 动脉硬化
emulsification of nutrient 营养乳化
enzyme 酶
ubiquitous 普遍的
cell membrane 细胞膜
