Physical Properties of Colloids

Colloidal dispersions owe their stability to a surface charge and the resultant electrical repulsion of charged particles. This charge is acquired by adsorption of cations or anions on the surface. For example, an ionic precipitate placed in pure water will reach solubility equilibrium as determined by its solubility product, but the solid may not have the same attraction for both its ions. Solid silver iodide has greater attraction for iodide than for silver ions, so that the zero point of charge (the isoelectric point) corresponds to a silver ion concentration much greater than iodide, rather than to equal concentrations of the two ions. The isoelectric points of the three silver halides are ° silver chloride, pAg = 4, pCl = 5.7 silver bromide, pAg = 5.4, pBr = 6.9 silver iodide, pAg = 5.5, pi = 10.6. For barium sulfate the isoelectric point seems to be dependent on the source of the product and its de ee of perfection.  

Lange and Berger studied the adsorption of potential-determining ions, or ions that carry a charge to the solid phase. For many substances, including silver iodide, they found that adsorption follows the equation 

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Chapter 8 presents evidence on how the physical properties of colloidal crystals organized by self-assembly in two-dimensional and three-dimensional superlattices differ from those of the free nanoparticles in dispersion. 

It will be noted that in the derivation of the transverse potential difference the product ijv should be constant for the same system under uniform conditions. A change in tj can be produced most conveniently by alteration of the temperature. Burton (Physical Properties of Colloidal Solutions, p. 145) gives the following data for colloidal silver solutions in support of the validity of the equation. 

The diminution of charge and eventual reversal of sign produced by the addition of electrolytes is more marked in the case of the polyvalent ions, and has been carefully investigated by Burton The Physical Properties of Colloidal Solutions, pp. 164-169) who in the case of a colloidal solution of copper obtained the following results ... 

A most important physical property of colloidal dispersions is the tendency of the particles to aggregate. Encounters between particles dispersed in liquid media occur frequently and the stability of a dispersion is determined by the interaction between the particles during these encounters. 

Brown, W.D., The Structure and Physical Properties of Colloids, Doctoral Thesis, Department of Physics, University of Cambridge, Cambridge, England, 1987. 

COLLOIDS (SECTION 13.6) Particles that are large on the molecular scale but stiU small enough to remain suspended indefinitely in a solvent system form colloids, or colloidal dispersions. Colloids, which are intermediate between solutions and heterogeneous mixtures, have many practical apphcations. One useful physical property of colloids, the scattering of visible hght, is referred to as the Tyndall effect. Aqueous colloids are classified as hydrophilic or hydrophobic. Hydrophilic colloids... 

The vehicle format we have used to produce aquasomes is the complex particulate multicomponent system. In general, complex particulate delivery systems are assemblies of simple polymers, complex lipid mixtures or ceramic materials that tend to measure individually between 30 and 500 nm in diameter. Being solid or glassy particles dispersed in an aqueous environment, they exhibit the physical properties of colloids their mechanism of action is controlled by their surface chemistry. They may deliver agents through a combination of specific targeting, molecular shielding, and slow release processes. 

In this paragraph the general physical properties of colloid systems are discussed in an introductory manner detailed treatment will only find a place in the later chapters. 

Russel W B, Seville D A and Schowalter W R 1989 Colloidal Dispersions (Cambridge Cambridge University Press) General textbook, emphasizing the physical equilibrium and non-equilibrium properties of colloids Shaw D J 1996 Introduction to Colloid and Surface Chemistry (Oxford Butterworth-Heinemann)... 

Chul, M Phillips, R McCarthy, M, Measurement of the Porous Microstructure of Hydrogels by Nuclear Magnetic Resonance, Journal of Colloid and Interface Science 174, 336, 1995. Cohen, Y Ramon, O Kopeknan, IJ Mizrahi, S, Characterization of Inhomogeneous Polyacrylamide Hydrogels, Journal of Polymer Science Part B Polymer Physics 30, 1055, 1992. Cohen Addad, JP, NMR and Statistical Structures of Gels. In The Physical Properties of Polymeric Gels Cohen Addad, JP, ed. Wiley Chichester, UK, 1996 39. 

Ueltmam, R.N. and Green, H. "Rheological Properties of Colloidal Solutions, Pigment Suspensions, and Oil Mixtures," J. Applied Physics. 1943, 14, 569-576. 

Among the purely physical properties of their materials, to which the chemist and the biologist have been compelled to pay an increasing amount of attention during recent years, surface tension undoubtedly occupies the first place. In a great measure this is due to the development of colloidal chemistry, which deals with matter in a state of extreme sub-division, and therefore with a great development of surface for a given mass, so that the properties of surfaces become important, and sometimes decisive, factors in the behaviour of such systems. 

Cadmium sulfate hydrate, 4 515 physical properties of, 4 509t Cadmium sulfate monohydrate, 4 515 physical properties of, 4 509t Cadmium sulfide, 4 503, 515-516, 518, 521 colloidal precipitation color, 7 343t color and bad gap, 7 335t physical properties of, 4 509t piezochromic material, 6 607 Cadmium sulfide photodetectors, 19 137 Cadmium sulfide photoconductor, fabrication and performance of, 19 155-156... 

Close contact was maintained with the schools at Darmstadt where E. Berl was actively involved in the evaluation of the technical properties of cellulose and its derivatives, and Karlsruhe. Mark was an associate professor at Karlsruhe, and accordingly observed G. Bredig and A. Reis studies of the physical chemistry of colloids and crystals. 

Interface and colloid science has a very wide scope and depends on many branches of the physical sciences, including thermodynamics, kinetics, electrolyte and electrochemistry, and solid state chemistry. Throughout, this book explores one fundamental mechanism, the interaction of solutes with solid surfaces (adsorption and desorption). This interaction is characterized in terms of the chemical and physical properties of water, the solute, and the sorbent. Two basic processes in the reaction of solutes with natural surfaces are 1) the formation of coordinative bonds (surface complexation), and 2) hydrophobic adsorption, driven by the incompatibility of the nonpolar compounds with water (and not by the attraction of the compounds to the particulate surface). Both processes need to be understood to explain many processes in natural systems and to derive rate laws for geochemical processes. 

The first step in the characterization of a new super-paramagnetic colloid is obviously the evaluation of its relaxometric properties, which determine its potential efficiency for MRI (27,28). Relating these valuable relaxometric data to morphological and physical properties of the particles may be carried out thanks to a proton relaxivity theory. 

Milk is a dilute emulsion consisting of an oil/fat dispersed phase and an aqueous colloidal continuous phase. The physical properties of milk are similar to those of water but are modified by the presence of various solutes (proteins, lactose and salts) in the continuous phase and by the degree of dispersion of the emulsified and colloidal components. 

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