Colloid properties osmotic pressure

As Morawetz puts the matter, an acceptance of the validity of the laws governing colligative properties (i.e., properties such as osmotic pressure) for polymer solutions had no bearing on the question whether the osmotically active particle is a molecule or a molecular aggregate . The colloid chemists, as we have seen, in regard to polymer solutions came to favour the second alternative, and hence created the standoff with the proponents of macromolecular status outlined above. 

Colligative properties are those properties of solutions that depend on the number of solute particles present and not their identity. Colligative properties include vapor pressure lowering, freezing point depression, boiling point elevation, and osmotic pressure. Colloids are homogeneous mixtures, in which the solute particles are intermediate in size between suspensions and true solutions. We can distinguish colloids from true solutions by the Tyndall effect. 

In order to utilise our colloids as near hard spheres in terms of the thermodynamics we need to account for the presence of the medium and the species it contains. If the ions and molecules intervening between a pair of colloidal particles are small relative to the colloidal species we can treat the medium as a continuum. The role of the molecules and ions can be allowed for by the use of pair potentials between particles. These can be determined so as to include the role of the solution species as an energy of interaction with distance. The limit of the medium forms the boundary of the system and so determines its volume. We can consider the thermodynamic properties of the colloidal system as those in excess of the solvent. The pressure exerted by the colloidal species is now that in excess of the solvent, and is the osmotic pressure II of the colloid. These ideas form the basis of pseudo one-component thermodynamics. This allows us to calculate an elastic rheological property. Let us consider some important thermodynamic quantities for the system. We may apply the first law of thermodynamics to the system. The work done in an osmotic pressure and volume experiment on the colloidal system is related to the excess heat adsorbed d Q and the internal energy change d E ... 

The analogue to one-component thermodynamics applies to the nature of the variables. So Ay S, U and V are all extensive variables, i.e. they depend on the size of the system. The intensive variables are n and T -these are local properties independent of the mass of the material. The relationship between the osmotic pressure and the rate of change of Helmholtz free energy with volume is an important one. The volume of the system, while a useful quantity, is not the usual manner in which colloidal systems are handled. The concentration or volume fraction is usually used ... 

It is important to note that the concept of osmotic pressure is more general than suggested by the above experiment. In particular, one does not have to invoke the presence of a membrane (or even a concentration difference) to define osmotic pressure. The osmotic pressure, being a property of a solution, always exists and serves to counteract the tendency of the chemical potentials to equalize. It is not important how the differences in the chemical potential come about. The differences may arise due to other factors such as an electric field or gravity. For example, we see in Chapter 11 (Section 11.7a) how osmotic pressure plays a major role in giving rise to repulsion between electrical double layers here, the variation of the concentration in the electrical double layers arises from the electrostatic interaction between a charged surface and the ions in the solution. In Chapter 13 (Section 13.6b.3), we provide another example of the role of differences in osmotic pressures of a polymer solution in giving rise to an effective attractive force between colloidal particles suspended in the solution. 

Formerly it was believed that in their physical properties, as for instance no increase in boiling point and in osmotic pressure, colloidal solutions of cellulose derivatives were radically different from solutions of crystalline substances having small molecules. Now, however it is clear that the difference is not so considerable and that a close analogy exists between solutions of cellulose and its derivatives and those of substances of low molecular weight. 

Effect of Pressure on Solubility 203 Effect of Temperature on Solubility 204 Colligative Properties of Solutions 205 Vapor Pressure 205 Boiling Point 207 Freezing Point 208 Osmotic Pressure 209 Colloids 212 Review Questions 213... 

For colloidal liquids, Eqs. (19-21) refer to the excess energy [second term of the right-hand side of Eq. (19)], the osmotic pressure and osmotic compressibility, respectively. They show one of the important features of the radial distribution function g(r), namely, that this quantity bridges the (structural) properties of the system at the mesoscopic scale with its macroscopic (thermodynamic) properties. 

The analysis of carbohydrates by CE has been reviewed by several authors as scientific papers or chapters of books. In fact, Chapter 7 by Khandurina in this handbook deals specifically with this topic. Carbohydrates have traditionally been classified by food researchers into sugars and polysaccharides, although mixtures of them such as glucose syrups are also used, taking advantage of their respective characteristics. Sugars are utilized for their sweetening power, preservative action (osmotic pressure), and crystallinity in foodstuffs polysaccharides provide foodstuffs with texture, body, and colloidal properties. 

We treat the extension of FVT and incorporate correct expressions for the (polymer concentration-dependent) depletion thickness and osmotic pressure, resulting in generalized free volume theory (GFVT). Expression (4.4) for the semigrand potential is still valid in GFVT it does not contain any assumption as yet on the physical properties of the depletants or the colloids. But now we need to... 

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