Colloids, freezing properties

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. 

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... 

The nature of the colloidal dispersion can have important influences on other food properties. For example, a 50/50 % emulsion of oil (fat) and water has a very different thermal properties in O/W versus W/O form. The O/W emulsion would be expected to have the greater thermal conductivity, water being the external phase and, other factors being equal, should freeze at a faster rate [811]. O/W food emulsions tend to be quite fluid, whereas W/O food emulsions tend to be more viscous, sometimes solid-like. 

A study of the freezing points of solutions of the tannins has yielded results that lead to the conclusion that they all possess very high molecular weights,—a fact in accord with their colloidal properties. Since the number of compounds formed as the result of their hydrolysis is relatively small it is probable that they are the result of the condensation, with the loss of the elements of water, of hydroxy benzoic acids, such as gallic acid and protocatechnic acid. Emil Fischer who studied this class of... 

Chem. Descrip. Acrylic resin Uses Thickener, anti-skinning agent for coatings Features AlkalFsoluble freeze/lhaw stable improves non-blistering props. Properties Colloidal disp. dens. 8.8 Ib/gal vise. 25 cps acid no. 128 (on solids) pH 6.0 39.5% NV Joncryl 507 [S.C. Johnson Polymer]... 

Clearly, there are also numerous other areas which could be included in a chapter devoted to the application of surface and colloid chemistry in pharmacy, in particular relating to the surface properties of dry formulations, such as spray or freeze-dried powders, wettability of drug crystals, etc. Flowever, in order to harmonize with the scope of the volume as a whole, these aspects of surface chemistry in pharmacy will not be covered here. Furthermore, even with the restriction of covering only wet systems, the aim of the present chapter is to illustrate important and general effects, rather than to provide a complete coverage of this vast field. 

Now the changes of the osmotic properties (lowering of the freezing point etc.) do not run parallel to the electrochemical properties and from these differences Me Bain calculates the number of colloidal particles at various concentrations. Colloidal soap can exist in two forms the anions can associate, but it is also possible that undissociated soap molecules form an aggregate. In a soap solution (for example Na-palmitate, NaP) the following particles can therefore occur ... 

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