Adsorbent morphology

Adsorption isotherms from surfactant solutions have been reported to often exhibit maximum and sometimes even minimum in the region around critical micelle concentration (1-4). The phenomenon of maximum and minimum is of such theoretical interest as well as practical importance in such areas as enhanced oil recovery using surfactant flooding. The presence of maximum has been attributed in the past to mechanisms involving micellar exclusion from interfacial region due to electrostatic repulsion or structural incompatibility, presence of impurities, surfactant composition, adsorbent morphology, etc. (1,2). None of these mechanisms is, however, fully substantiated to be considered as a confirmed mechanism for surfactant adsorption from concentrated solutions particularly due to serious possibilities for experimental arti-... 

The effects of foreign surfaces on platelets has been intensively studied because of the place of platelets in thrombotic processes and because the visible deposition of platelets is evidence of some surface-platelet interaction. This latter is not strictly true because protein adsorption precedes platelet adsorption so that in reality it is a platelet-protein adsorbate reaction in which the nature of the adsorbate reflects the nature of the underlying surface. In vitro studies, primarily using platelet-rich plasma, have involved measurement of the adsorption rate, number adsorbed, morphological changes, and more recently, the release reaction. 

The first stage in the interpretation of a physisorption isotherm is to identify the isotherm type and hence the nature of the adsorption process(es) monolayer-multilayer adsorption, capillary condensation or micropore filling. If the isotherm exhibits low-pressure hysteresis (i.e. at p/p° < 0 4, with nitrogen at 77 K) the technique should be checked to establish the degree of accuracy and reproducibility of the measurements. In certain cases it is possible to relate the hysteresis loop to the morphology of the adsorbent (e.g. a Type B loop can be associated with slit-shaped pores or platey particles). 

The external surface area of the filler can be estimated from a psd by summing the area of all of the equivalent spheres. This method does not take into account the morphology of the surface. It usually yields low results which provide Htde information on the actual area of the filler that induences physical and chemical processes in compounded systems. In practice, surface area is usually determined (5) from the measured quantity of nitrogen gas that adsorbs in a monolayer at the particle surface according to the BET theory. From this monolayer capacity value the specific surface area can be determined (6), which is an area per unit mass, usually expressed in m /g. 

Characterization. The proper characterization of coUoids depends on the purposes for which the information is sought because the total description would be an enormous task (27). The foUowiag physical traits are among those to be considered size, shape, and morphology of the primary particles surface area number and size distribution of pores degree of crystallinity and polycrystaUinity defect concentration nature of internal and surface stresses and state of agglomeration (27). Chemical and phase composition are needed for complete characterization, including data on the purity of the bulk phase and the nature and quaHty of adsorbed surface films or impurities. 

A number of approaches are available to improve the morphology and homogeneity of electrochemically deposited conducting polymer films. Priming of the electrode surface with a monolayer of adsorbed or covalently bonded monomer leads to more compact deposits of polyaniline,87,88 poly thiophene,80 and polypyrrole.89,90 Electrode rotation has been shown to inhibit the deposition of powdery overlayers during poly(3-methylthiophene) deposition.81... 

Optimum conditions for the formation of CdS by the acidic method on metallic A1 substrate at 25 °C have been reported as follows pH 2.3, potential -1 V vs. SCE, and electrolysis time > 2 h [44]. Thermal treatment improved the characteristics of the films and their photovoltaic properties, which were evaluated by evaporating a CU2S layer on the CdS/Al film, to form a heterojunction cell. The influence of the deposition substrate on the formation and morphology of CdS was found to be important. The aluminum substrates gave the best results among Pt, Mo, and Al. In the case of molybdenum, surface blocking by adsorbed sulfur was considered. 

Other scientists took up Oparin s ideas, used them for their own concepts, and tried to form organic molecules from inorganic starting materials. The Mexican scientist A. L. Herrera reported in 1942 in an article entitled A New Theory of the Origin and Nature of Life on his investigations with sulphobes (Herrera, 1942). These are morphological units ( lifelike forms ) which he obtained from reactions between thiocyanates and formalin. Sulphobes are spherical in form, with a diameter between 1 and 100 pm, and can interact with their surroundings thus they can adsorb dyestuffs. In some ways, they resemble the coacervates studied by Oparin and his school (Sect. 10.2.2). 

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