Isolated colloidal particle

Any biointeraction e.g. a standard hybridization is a useful tool to assemble colloidal particles in solution or at surfaces. By use of this technique arrays of colloids are easily obtained at a substrate surface. These particle arrays deviate in their optical and electrical behavior from single isolated colloidal particles. 

In extensively deionized suspensions, tliere are experimental indications for effective attractions between particles, such as long-lived void stmctures [89] and attractions between particles confined between charged walls [90]. Nevertlieless, under tliese conditions tire DLVO tlieory does seem to describe interactions of isolated particles at tire pair level correctly [90]. It may be possible to explain tire experimental observations by taking into account explicitly tire degrees of freedom of botli tire colloidal particles and tire small ions [91, 92]. 

Techniques used in bioseparations depend on the nature of the product (i.e., the unique properties and characteristics which provide a handle for the separation), and on its state (i.e., whether soluble or insoluble, intra- or extracellular, etc.). All early isolation and recovery steps remove whole cells, cellular debris, suspended solids, and colloidal particles, concentrate the product, and, in many cases, achieve some degree of purification, all the while maintaining high yield. For intracellular compounds, the initial harvesting of the cells is important... 

PVP, a water soluble amine-based pol5mer, was found to be an optimum protective agent because the reduction of noble metal salts by polyols in the presence of other surfactants often resulted in non-homogenous colloidal dispersions. PVP was the first material to be used for generating silver and silver-palladium stabilized particles by the polyol method [231-233]. By reducing the precur-sor/PVP ratio, it is even possible to reduce the size of the metal particles to few nanometers. These colloidal particles are isolable but surface contaminations are easily recognized because samples washed with the solvent and dried in the air are subsquently not any more pyrophoric [231,234 236]. 

To understand the origin of the attraction between colloidal particles, it is necessary to back off a bit and consider the interactions between individual molecules. Macroscopic interactions — as we shall call the interactions between colloids since these particles are large compared to atomic dimensions —are the summation of the pairwise interactions of the constituent molecules in the individual particles. Therefore we begin by examining the interactions between a pair of isolated molecules. 

Sampling and processing techniques designed to isolate and concentrate submicrometer-sized (colloidal) particles and associated elements were employed on 1989-1991 cruises. Three distinct approaches were exploited. 

Colloid stabilization with amphiphilic polymers [2,114,115] requires the formation of a thick polymer layer around each particle in order to create a repulsive steric force that overcomes the van der Waals attraction. This is usually done by adsorbing on the colloidal particle a polymer solution in a good solvent, which builds up on the surface a fluffy layer with a thickness of the order of the radius of gyration of isolated polymer chains, in general of the order of a few hundred angstroms. 

In practical applications of electrophoresis, collections of colloidal particles in bounded systems are usually encountered and the experimentally measured electrophoretic mobility is actually the average value for the entire suspension. It is therefore necessary to determine the average electrophoretic velocity for a suspension of colloidal particles. For dilute dispersions, the first order correction to the mobility of an isolated particle can be determined from the... 

We turn now to the other side of the colloidal particle interaction problem idealised to the case of two half spaces separated by salt water [3-10, 22-24]. Typically such particles will contain ionisable groups at their surfaces, so that the surfaces are charged. Imagine that the water, as before, retains its bulk properties up to the surface of the half spaces. The charged surfaces create an inhomogeneous profile of cationic and anionic density. For an isolated surface at the simplest level of approximation and schematically only, this distribution follows from the equation ... 

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