Macromolecular colloids shape

Examples of typical coacervation are to be found among the "linear macromolecular colloids especially among those which belong to the highly viscous type This is an indication that it will be important for the theory of a typical coacervation to associate it with the skein shape of the macromolecule. With this disappears all serviceability of the scheme of Fig. 7 for an explanation of a typical coacervation in view of the fact that it is not only incorrect as regards the symbolisation of the hydration but also as regards the conception of the colloidal particles as solid spheres. 

Here P(q) is the particle scattering factor and q = (47i/Z0) sin (0/2) is the scattering vector. The value of P reflects the specific size and shape of the polymer particle. This parameter has been calculated and tabulated for many different kinds of idealized colloidal and macromolecular structures (Burchard, 1994 Evans, 1972 Tanford, 1961). 

In contrast to the above-described kinetic stability, colloids may also be thermodynamically stable. A stable macromolecular solution is an example we have already discussed. Formation of micelles beyond the critical micelle concentration is another example of the formation of a thermodynamically stable colloidal phase. However, when the concentration of the (say, initially spherical) micelles increases with addition of surfactants to the system, the spherical micelles may become thermodynamically unstable and may form other forms of (thermodynamically stable) surfactant assemblies of more complex shapes (such as cylindrical micelles, liquid-crystalline phases, bilayers, etc.). 

A relationship is shown to exist in viscometry experiments between particle size or molecular size and the viscosity of dispersions of inorganic colloids or the viscosity of macromolecular solutions. It is therefore possible to determine the molar mass from the viscosity of dilute macromolecular solutions. Since this experiment can be rapidly performed with simple equipment, it is, in practice, the most important molar mass determination method. However, the method is not an absolute one, since the viscosity depends on other molecular properties (for example, on the shape of the molecule), as well as on the molecular weight. 

Some liquid colloid systems show a double refraction when they are set in laminar flow. The classical example is the V2O5 sol which (at least after ageing) consists of needle-shaped particles with a crystalline character the sol itself with its particles randomly oriented by Brownian motion is isotropic if now one makes it flow through a tube or between two coaxial cylinders, one of which is rotating, it becomes double refracting The same is the case with many macromolecular sols This phenomenon, streaming double refraction of sols, is also reckoned as accidental double refraction, because it only occurs through a constraint exerted on the system ... 

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