Particle, small colloidal

Micro filtration Pressure gradient 0.1-10 xm Small particles, large colloids, microbial cells... 

These problems have been improved in recent years by the microfabrication of sharp tips with radii less than 10 nm, the observation in an SEM or STEM of the exact radius before and after the experiment, the use of robust carbon-nanotube probes, and general improvements in control electronics. However, another method used initially was the attachment of a small colloid particle in place of the AFM tip. These particles were considered a reasonably good approximation to a single-asperity contact their radii were accurately known and remained the same for the duration of the experiment. Such probes have also been used to investigate colloids where surface roughness is an important aspect of the colloid interaction. 

The hydrodynamic forces acting on the suspended colloids determine the rate of cake buildup and therefore the fluid loss rate. A simple model has been proposed in literature [907] that predicts a power law relationship between the filtration rate and the shear stress at the cake surface. The model shows that the cake formed will be inhomogeneous with smaller and smaller particles being deposited as the filtration proceeds. An equilibrium cake thickness is achieved when no particles small enough to be deposited are available in the suspension. The cake thickness as a function of time can be computed from the model. 

For small colloidal particles, which are subject to random Brownian motion, a stochastic approach is more appropriate. These methods are based on the formulation and solution of the diffusion equation in a force field, in the presence of convection... 

More recently, Wells and Goldberg (1991) report that very small marine colloids (d < 120 nm) are, by at least three order of magnitudes, more abundant. A vertical stratification of these particles was found (very high concentrations in the thermodine and season-dependent in the bottom-waters). This stratification indicates that these very small colloidal particles are reactive. The apparent close association of metals with these colloids suggests that they may play an important part in the transport and fate of trace elements in seawater (Wells and Goldberg,... 

Henglein A (1989) Small-particle research - physicochemical properties of extremely small colloidal metal and semiconductor particles. Chem Rev 89 1861-1873... 

A colloidal solution is defined as a solution intermediate in character between a suspension and a true solution. Particles with diameters < 10 pm are usually called colloids [19,65], although the distinction based on size is arbitrary. The size of particles is a continuum and the point at which large macromolecules end and small colloids begin is subject to judgment, as is the upper end of the size continuum, where colloids and suspended particles merge. The tendency of suspended particles to settle out of solution is not really a function of size alone, rather the relative density of the particles and the motion of the water will determine what is suspended and what settles. 

Donnan equilibrium phys chem The particular eq ul 11 bri u m set up when two coexisting phases are subject to the restriction that one or more of the ionic components cannot pass from one phase into the other commonly, this restriction is caused by a membrane which is permeable to the solvent and small ions but impermeable to colloidal ions or charged particles of colloidal size. Also known as Gibbs-Donnan equilibrium. dO-non e-kwo lib-re-om ... 

After delivery to the ocean, clay minerals react with seawater. The processes that alter the chemical composition of the terrigenous clay minerals during the first few months of exposure are termed halmyrolysis. These include (1) cation exchange, (2) fixation of ions into inaccessible sites, and (3) some isomorphic substitutions. Another important transfiarmation is flocculation of very small (colloidal-size) clay particles into larger ones. 

Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) are the techniques most widely used for the characterization of crystallinity and polymorphism of solid lipid particles. Although DSC is usually more sensitive in detecting crystalline material, XRD is much more reliable in determining the type of polymorph present in the dispersions because it provides structural data. In contrast, DSC can detect the type of polymorph only indirectly via the transition temperatures and enthalpies. Because these parameters may be different from those observed in the bulk material, particularly for small colloidal particles [1,62], assigmnent of polymorphic forms in DSC curves should be supported by x-ray data. 

Colloidal supports, such as small colloidal Si02 particles, restrict the interparticle difinsion of silver atoms when formed by radiolysis of the ions at their surface. The silver oligomers absorbing at 290 and 330 nm are observed by pulse radiolysis. They are stable with respect to coalescence but they are oxidized by MV ", O2, Cu, and Ru(NH3)6 [101]. 

Albert Einstein derived a simple equation for the viscosity of a solution of spherical particles, and from this result it is obvious that if we could make the polymer in small colloidal-sized balls, then the solution would be much less viscous. Also, if we could use surfactants to stabilize (e.g. by charging) the polymer particles in water, then there would be no need for organic solvents. Both these conditions are neatly obtained in the emulsion polymerization process, which is schematically explained in Figure 5.3. A polymer latex is produced by this process and can contain up to 50% polymer in the form of 0.1-0.5 im size spherical particles in water. A typical starting composition is ... 

The tiny particles in colloidal gold were not seen directly until the early twentieth century, when the Austrian chemist Richard Adolf Zsigmondy invented the ultramicroscope, a device capable of resolving such small objects. For elucidating the nature of colloids Zsigmondy was awarded the Nobel Prize in chemistry in 1925. 

However, there are a number of difficulties associated with the synthesis of colloidal semiconductor particles. The preparation of stable, monodispersed, well-characterized populations of nanosized, colloidal semiconductor particles is experimentally demanding and intellectually challenging. Small and uniform particles are needed to diminish non-productive electron-hole recombinations the mean distance by which the charge carriers need to diffuse to reach the particle surface from which they are released is necessarily reduced in small particles. Monodispersity is a requirement for the observation of many of the spectroscopic and electro-optical manifestations of size quantization in semiconductor particles. Small semiconductor particles are difficult to maintain in solution in the absence of stabilizers flocculations and Ostwald ripening... 

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