Macromolecular colloids

Preparation of X-ray amorphous ZSM-5 crystallites according to procedure BT It is important that the gel formation takes place as homogeneously as possible. Because of the particular sensitivity of various silica and alumina species to the pH (63,64), the pH range between 4.5 and 8.5 was avoided. Nucleation was performed at pH 3.5-4, where a low viscous gel containing essentially monomeric silica species is rapidly formed (65).The, pH is theii raised to about 9, in order to form tetrahedral A1(0H) entities and to favour the further A1 incorporation within the zeolitic framework. NaCl was used to increase the (super)saturation of the gel, which will flocculate into a macromolecular colloid (V) and initiate the nucleation. This procedure yields 100 % crystalline zeolite after... 

The flux of many macromolecular colloidal and particulate solutions is too high (sometimes by an order of magnitude) to be rationalized by a reasonable value of the diffusion coefficient and the boundary layer thickness in Equation (6.2). 

Figure 13.14 Relationship between A14C and C N ratios in macromolecular colloidal organic matter (COM) fractions (COMj = >1 kDa <0.02 pm, COMio = >1 kDa <0.02 pm) in Galveston Bay, July 1993. (Modified from Guo et al., 1997.)...

Giddings, J.C., Field-flow fractionation Analysis of macromolecular, colloidal, and particulate materials, Science, 260, 1456, 1993. 

Meerschaum, Solid foam expanded plasties Microporous oxides, Xerogels 1 silica gel , porous glass, microporous carbons, zeolites Macromolecular colloids Gas Solid... 

A somewhat more complex situation arises when osmotic equilibrium is set up between two electrolyte solutions, one of which contains ions to which the membrane is impermeable. These ions may be macromolecular (colloidal electrolytes) or in the limit... 

Differentiation between dissolved, macromolecular colloidal and particulate is arbitrary and based on our difficulties in retrieving samples (Cauwet, Chapter 4). Information concerning the detailed organic chemical composition of suspended material is only recently developing with the application of deep-sea collection techniques for particulate material (S. Honjo, J. Farrington and coworkers. Woods Hole, Mass., U.S.A. Wakeham et al., 1980). 

Macromolecular colloid solutions also play an important role in ensuring the stability of disperse systems (e.g. suspensions, emulsions). In the case of emulsions the polymer decreases the rate of separation by increasing viscosity on the one hand, and it has an enthalpy stabilizing effect by adsorption on the surface of the droplets on the other hand [3, 4, 7]. Depending on the concentration of the polymer, a protecting and flocculating effect can be observed during the interaction between suspensions and polymers. If the polymer concentration is low, the polymer adsorbed on the surface of the particles connects the particles into loose floccules. Thereby, the rate of... 

Association and macromolecular colloidal solutions have a number of conunon properties... 

Unlike that of normal molecules, the composition of the particles in an association colloid is not perfectly defined. Composition is variable from one solution to another and depends on the preparation method. In water at least, there is a single sodium chloride, whereas there may be a whole series of ferric phosphates with dimensions varying from 1 to 10. Furthermore, the ions present in the solution are fixed to variable degrees by adsorption at the interfaces. The components of macromolecular colloids, however, are less variable. 

The presence of macromolecular colloids (carbohydrate polymers) may also affect the stability of association colloids. Carbohydrate polymers may either act as protective coUoids, preventing flocculation, or possibly destabilize the colloids and cause them to precipitate (Section 9.4.1). 

In some instances, an entire solution may be stabilized when a macromolecular colloid (polysaccharide) and an unstable colloid are pnt together. Macromolecular colloids with this property are known as protective colloids . 

Equilibria can be studied in two ways thermodynamically or molecular-kinetic-ally, in which last case a thorough knowledge of the ultimate kinetic units — the single molecules — may be of primary importance. Especially in the case of macromolecular colloids an intimate knowledge of their structure and configuration opens indeed wide perspectives. 

The elimination procedure, which in the case of sols did not give new points of view, however does so when we apply it to polyphase systems which occur in the domain of macromolecular colloids. 

In the following discussion we shall use the term macro-units for the kinetic units fulfilling the definition of colloid particles (p. 3 1 b) and micro-units for those smaller than them. Almost all colloid systems of macromolecular colloids consist of an intimate mixture of macro- and micro-units, and we shall now apply the elimination procedure to them. 

In the course of this chapter three different liquid macromolecular colloid systems have been met with, which fulfil the definition of Sol in 1 b (p. 2) ... 

Still more grave objections could be made from the point of view of rigid classification, as in the last named three Chapters IX, X and XI, colloids have often been considered (phosphatides) which do not at all belong to macromolecular colloids, but to association colloids, the latter belonging to Part II of this Volume. 

If we were free to write a general physical chemistry of soaps or soaplike substances — thus not hindered by the necessity in this book of paying only special attention to particles falling within an arbitrarily chosen range of masses — then an analogous classification as above for macromolecular colloids would suit us. 

So there remain only a very restricted number of subjects analogous to those in macromolecular colloids. Moreover we have already discussed the fact that with the association colloids only the associated low molecular units form the kinetic units of the colloidal system. 

Thus association — and not the molecule — forms the basic idea of this class of colloids. Therefore in the chapter on association colloids (Chapter XIV) no effort is made to follow an analogous division into subjects as in macromolecular colloids. Indeed the association phenomenon itself is put in the centre of the discussion and an attempt will be made to explain the properties of sols and coacervates from this point of view. 

VII. SOLS OF MACROMOLECULAR COLLOIDS WITH ELECTROLYTIC NATURE... 

In this and in the succeeding chapters we shall deal with the various properties of the sols of macromolecular colloids in so far as they depend on the charge of the particles. 

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