Colloids colloidal phenomena

The results obtained by MacLeod and by Church show, quite definitely, that the desire of addicts for morphine is not explainable on any sort of psychological basis it is a physiologico-colloidal phenomenon. The efficiency of the bromide ion in peptizing the reversibly coagulated nerve colloids is shown strikingly by Church s first case, for, while imder the influence of sodium bromide, 60 grains of morphine per day were administered. Despite this the cure was effected. 

The study of the coagulation of aqueous dispersions of sparingly soluble or insoluble solids (lyophobic colloids) has been one of the main streams of colloid research for over a century. This arises both from its practical importance and from the fact that it was the first colloidal phenomenon for which empirical rules governing its onset were established. Consequently it was also the first for which attempts were made to develop a theoretical interpretation. 

The sedimentation-diffiision equilibrium is not just a balance between difiusive transport and setding, but can also be regarded as equilibrium between chemical potential and gravity potential (RT dine = —gt V -Na dh). Based on this interpretation, Perrin (1909) employed this colloidal phenomenon to measure Avogradro s constant Na (and, thereby, to confirm the molecular origin of Brownian motion). It is rather fascinating that he obtained values between 6.5 x 10 moF and 7.5 x 10 moF, which ate close to the teal value. 

Detergency is unquestionably a surface and colloidal phenomenon reflecting the physicochemical behavior of matter at interfaces. Since the field is concerned principally with the removal of complex mixtures of soils and oily mixtures from equally complex soUd substrates, it is not surprising that such systems do not lend themselves readily to analysis by the more fundamental theories of surface and colloid science. A rigorous treatment of the current status of detergency theory would constitute a book itself. This section summarizes some of the most important aspects of detergency and illustrates how the chemical structure of the surfactants and other components in a formulation can affect overall performance. 

The most familiar type of electrokinetic experiment consists of setting up a potential gradient in a solution containing charged particles and determining their rate of motion. If the particles are small molecular ions, the phenomenon is called ionic conductance, if they are larger units, such as protein molecules, or colloidal particles, it is called electrophoresis. 

SERS. A phenomenon that certainly involves the adsorbent-adsorbate interaction is that of surface-enhanced resonance Raman spectroscopy, or SERS. The basic observation is that for pyridine adsorbed on surface-roughened silver, there is an amazing enhancement of the resonance Raman intensity (see Refs. 124—128). More recent work has involved other adsorbates and colloidal... 

If a dilute acid is added to this solution, a white gelatinous precipitate of the hydrated tin(IV) oxide is obtained. It was once thought that this was an acid and several formulae were suggested. However, it now seems likely that all these are different forms of the hydrated oxide, the differences arising from differences in particle size and degree of hydration. When some varieties of the hydrated tin(IV) oxide dissolve in hydrochloric acid, this is really a breaking up of the particles to form a colloidal solution—a phenomenon known as peptisation. 

As materials chemistry has developed, it has come to pay more and more attention to that archetypal concern of materials scientists, microstructure. That concern came in early when the defects inherent in non-stoichiometric oxides were studied by the Australian. I.S. Anderson and others (an early treatment was in a book edited by Rabenau 1970), but has become more pronounced recently in the rapidly growing emphasis on self-assembly of molecules or colloidal particles. This has not yet featured much in books on materials chemistry, but an excellent recent popular account of the broad field has a great deal to say on self-assembly (Ball 1997). The phenomenon of graphoepitaxy outlined in Section 10.5.1.1 is a minor example of what is meant by self-assembly. 

Freezing is a very general phenomenon. Upon increasing the interaction strength or increasing the density, colloidal suspensions undergo phase... 

The Group A emphases are those that inform the development of chemical literacy (DeBoer, 2000) and should be made available to all students (cf scientific literacy - (Roberts, 2007). These emphases all call for an imderstanding of a macro type of representation, so that learners appreciate what it is when they encounter a chemical phenomenon e.g. a solution, a colloid, a precipitate. This understanding would enable students to answer the question what is it and possibly what to do with it how to act when they encounter such a chemical phenomenon. These emphases also call for an understanding of the submicro type of representation, so that learners can qualitatively explain the nature of the macro phenomena that they encounter and hence be able to answer the question why is it as it is In order to explore these emphases, a chemistry curriculum would need to address a variety of contexts related to the three Group A emphases that have mearung in the everyday world. Pilot, Meijer and Bulte (2008) discuss three such contexts ceramic crockery, gluten-free bread and the bullet-proof vest. 

Adsorption phenomena from solutions onto sohd surfaces have been one of the important subjects in colloid and surface chemistry. Sophisticated application of adsorption has been demonstrated recently in the formation of self-assembhng monolayers and multilayers on various substrates [4,7], However, only a limited number of researchers have been devoted to the study of adsorption in binary hquid systems. The adsorption isotherm and colloidal stabihty measmement have been the main tools for these studies. The molecular level of characterization is needed to elucidate the phenomenon. We have employed the combination of smface forces measmement and Fomier transform infrared spectroscopy in attenuated total reflection (FTIR-ATR) to study the preferential (selective) adsorption of alcohol (methanol, ethanol, and propanol) onto glass surfaces from their binary mixtures with cyclohexane. Om studies have demonstrated the cluster formation of alcohol adsorbed on the surfaces and the long-range attraction associated with such adsorption. We may call these clusters macroclusters, because the thickness of the adsorbed alcohol layer is about 15 mn, which is quite large compared to the size of the alcohol. The following describes the results for the ethanol-cycohexane mixtures [10],... 

As early as 1848, it had been suggested that sensory receptors transduce only one sensation, independent of the manner of stimulation. Behavioral experiments tend to support this theory. In 1919, Renqvist proposed that the initial reaction of taste stimulation takes place on the surface of the taste-cell membrane. The taste surfaces were regarded as colloidal dispersions in which the protoplasmic, sensory particles and their components were suspended in the liquor or solution to be tested. The taste sensation would then be due to adsorption of the substances in the solution, and equal degrees of sensation would correspond to adsorption of equal amounts. Therefore, the rate of adsorption of taste stimulants would be proportional to the total substances adsorbed. The phenomenon of taste differences between isomers was partly explained by the assumption that the mechanism of taste involves a three-dimensional arrangement for example, a layer of fatty acid floating on water would have its carboxylic groups anchored in the water whereas the long, hydrocarbon ends would project upwards. 

Colloidal suspensions stabilized by electrostatic repulsion are very sensitive to any phenomenon able to disrupt the double layer like ionic strength or thermal motion. 

Thirdly, a stable icing foam requires a tendency for the surface of the extended protein film to solidify, thereby giving structure and permanence to the foam. Egg albumen is a hydrophilic (water-loving) colloid, for it is readily soluble in water. However, when subjected to heat, egg albumen becomes insoluble in water or is said to be hydrophobic (water-hating). Through this phenomenon of changing solubility, egg whites make very stable foams if used at sufficient concentration. 

If the electric field E is applied to a system of colloidal particles in a closed cuvette where no streaming of the liquid can occur, the particles will move with velocity v. This phenomenon is termed electrophoresis. The force acting on a spherical colloidal particle with radius r in the electric field E is 4jrerE02 (for simplicity, the potential in the diffuse electric layer is identified with the electrokinetic potential). The resistance of the medium is given by the Stokes equation (2.6.2) and equals 6jtr]r. At a steady state of motion these two forces are equal and, to a first approximation, the electrophoretic mobility v/E is... 

This paper reviews the experiences of the oil industry in regard to asphaltene flocculation and presents justifications and a descriptive account for the development of two different models for this phenomenon. In one of the models we consider the asphaltenes to be dissolved in the oil in a true liquid state and dwell upon statistical thermodynamic techniques of multicomponent mixtures to predict their phase behavior. In the other model we consider asphaltenes to exist in oil in a colloidal state, as minute suspended particles, and utilize colloidal science techniques to predict their phase behavior. Experimental work over the last 40 years suggests that asphaltenes possess a wide molecular weight distribution and they may exist in both colloidal and dissolved states in the crude oil. 

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