Colloidal particles, characterization

Rowell and co-workers [62-64] have developed an electrophoretic fingerprint to uniquely characterize the properties of charged colloidal particles. They present contour diagrams of the electrophoretic mobility as a function of the suspension pH and specific conductance, pX. These fingerprints illustrate anomalies and specific characteristics of the charged colloidal surface. A more sophisticated electroacoustic measurement provides the particle size distribution and potential in a polydisperse suspension. Not limited to dilute suspensions, in this experiment, one characterizes the sonic waves generated by the motion of particles in an alternating electric field. O Brien and co-workers have an excellent review of this technique [65]. 

Colloidal particles can be seen as large, model atoms . In what follows we assume that particles with a typical radius <3 = lOO nm are studied, about lO times as large as atoms. Usually, the solvent is considered to be a homogeneous medium, characterized by bulk properties such as the density p and dielectric constant t. A full statistical mechanical description of the system would involve all colloid and solvent degrees of freedom, which tend to be intractable. Instead, the potential of mean force, V, is used, in which the interactions between colloidal particles are averaged over... 

The interactions between colloidal particles (see section C2.6.4) are central to tire understanding of suspension behaviour. Aitlrough most work has had to rely on ratlrer indirect ways to characterize tlrese interactions, novel teclmiques are emerging tlrat access tlrese interactions more directly. 

Surfaces can be characterized using scaiming probe microscopies (see section B1.19). In addition, by attaching a colloidal particle to tire tip of an atomic force microscope, colloidal interactions can be probed as well [27]. Interactions between surfaces can be studied using tire surface force apparatus (see section B1.20). This also helps one to understand tire interactions between colloidal particles. 

Real charge is always associated with well-defined physical carriers such as electrons and ions this is not so for the idealized physical charge considered in electrostatics. Each conductor can be characterized by stating the nature and concentration of the free charges. In the present section we consider free charged particles of atomic (or molecular) size, not larger, aggregated entities, such as colloidal particles. 

The alkaline EG S5mthesis method is a very effective technology for the chemical preparation of unprotected metal and alloy nanoclusters stabilized by EG and simple ions. This method is characterized by two steps involving the formation of metal hydroxide or oxide colloidal particles and the reduction of them by EG in a basic condition. The strategy of separating the core formation from reduction processes provides a valid route to overcome the obstacle in producing stable unprotected metal nanoclusters in colloidal solutions with high metal concentrations. Noble metal and alloy nanoclusters such as Pt, Rh, Ru, Os, Pt/Rh and Pt/Ru nanoclusters with small particle... 

The physicochemical forces between colloidal particles are described by the DLVO theory (DLVO refers to Deijaguin and Landau, and Verwey and Overbeek). This theory predicts the potential between spherical particles due to attractive London forces and repulsive forces due to electrical double layers. This potential can be attractive, or both repulsive and attractive. Two minima may be observed The primary minimum characterizes particles that are in close contact and are difficult to disperse, whereas the secondary minimum relates to looser dispersible particles. For more details, see Schowalter (1984). Undoubtedly, real cases may be far more complex Many particles may be present, particles are not always the same size, and particles are rarely spherical. However, the fundamental physics of the problem is similar. The incorporation of all these aspects into a simulation involving tens of thousands of aggregates is daunting and models have resorted to idealized descriptions. 

Several additional instrumental techniques have also been developed for bacterial characterization. Capillary electrophoresis of bacteria, which requires little sample preparation,42 is possible because most bacteria act as colloidal particles in suspension and can be separated by their electrical charge. Capillary electrophoresis provides information that may be useful for identification. Flow cytometry also can be used to identify and separate individual cells in a mixture.11,42 Infrared spectroscopy has been used to characterize bacteria caught on transparent filters.113 Fourier-transform infrared (FTIR) spectroscopy, with linear discriminant analysis and artificial neural networks, has been adapted for identifying foodbome bacteria25,113 and pathogenic bacteria in the blood.5... 

Oh, S.J. Cook, D.C. Townsend, H.E. (1998) Characterization of iron oxides commonly formed as corrosion products on steel. Hyper-fine Interactions 112 59-65 Ohmori, M. Matijevic, E. (1992) Preparation and properties of uniform coated inorganic colloidal particles. VII. Silica on hematite. J. Colloid Interface Sci. 150 594-598 Ohta, S. Effendi, S. Tanaka, N. Miura S. (1993) Ultisols of lowland Dipterocarp forest in East Kalimantan, Indonesia. Soil Sci. Plant Nutr. 39 1-12... 

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. 

The classic example of a NEAS is a supercooled liquid cooled below its glass transition temperature. The liquid solidifies into an amorphous, slowly relaxing state characterized by huge relaxational times and anomalous low frequency response. Other systems are colloids that can be prepared in a NEAS by the sudden reduction/increase of the volume fraction of the colloidal particles or by putting the system under a strain/stress. 

In subsequent chapters, we discuss some in situ techniques for the characterization of colloidal particles, especially with respect to particle size, structure, and molecular weight. 

Equation (9) is an important result since it describes the relationship among Rs, v, r/, and Ap, the density difference. Any one of these quantities may be evaluated by Equation (9) when the other three are known. Thus, Equation (9) can be used to determine the density difference between two phases or to determine the viscosity of a liquid. In this chapter, however, our interest is in the characterization of colloidal particles by means of observations of their sedimentation behavior. Therefore, we are primarily concerned with Equations (11) and (12), which are specifically directed toward this objective. 

Vol. 14 Complex Wave Dynamics on Thin Films. By H.-C. Chang and E.A. Demekhin Vol. 15 Ultrasound for Characterizing Colloids. Particle Sizing, Zeta Potential, Rheology. 

Sedimentation FFF implies application of the centrifugal field, which is produced by placing the channel in a centrifuge basket. SdFFF instruments can be linked readily to analytical instruments to provide analysis in real time. For the first time, Beckett (1991) introduced FFF-ICP-mass spectroscopy (MS) as a powerful analytical tool for characterizing macromolecules and particles. Taylor et al. (1992) illustrated the characterization of some inorganic colloidal particles and river-borne suspended particulate matter of size range <1 pm using SdFFF and ICP-MS. 

To characterize the complexes formed between molecular dispenser described in Sect. 2.2.4 and colloidal particles, the probability P(a, T) of finding a complex made from the copolymer envelope and the particle of a given size, a, was calculated as a function of temperature T [57]. 

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