Scattering and Osmotic Pressure

Most colloidal solutions, including proteins, show marked deviation from van t Hoff s law of osmotic pressure even at very low concentrations. However, in many fairly dilute solutions it is possible to express the osmotic pressure adequately by means of the two term equation 

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Theta temperature is one of the most important thermodynamic parameters of polymer solutions. At theta temperature, the long-range interactions vanish, segmental interactions become more effective and the polymer chains assume their unperturbed dimensions. It can be determined by light scattering and osmotic pressure measurements. These techniques are based on the fact that the second virial coefficient, A2, becomes zero at the theta conditions. 

Equation (22) has been confirmed by a variety of techniques including neutron scattering, dynamic light scattering, and osmotic pressured measurements [23]. As concentration increases the concentration blob decreases in size until the Kuhn length is reached and the coil displays concentrated or melt Gaussian structure. The coil accommodates concentrations between the overlap and concentrated through adjustment of the concentration blob size. 

Table I shows the molecular weight and the degree of end group substitution of the monofunctional polystyrene samples obtained. In Table II the corresponding data for the bifunctional samples are given. The samples were characterized by GPC in THF. and were calculated. Comparison with the corresponding nonfunctionalized control samples show good agreement. The results of the light scattering and osmotic pressure experiments with the acid form of the sulfonated polystyrenes were in agreement. No association was observed for THF solutions.

Polystyrene can be prepared as follows A mixture of styrene, detergent (Na-dodecanoate), and water is agitated ultrasonically to produce a fine emulsion. On the addition of hydrogen peroxide (initiator), PS is obtained as a polymer, which can be extracted after filtration. The polymer molecular weight is determined by various methods (such as light scattering and osmotic pressure). 

C 26 Cowie, J. M. G., D. J. Worsfeld and S. Bywater Light-scattering and osmotic pressure study on solutions of polystyrene of narrow molecular-weight distribution produced by anionic catalysis. Trans. Faraday Soc. 57,705 (1961). 

The conformational properties of polymer chains [1-4] are usually determined in dilute solutions of the polymers. Viscosity, light scattering, small-angle x-ray scattering, and osmotic pressure, are the main types of measurements made in solution. 

Methods for the determination of the molecular weight of a polysaccharide include gel-filtration (Andrews, 1970), ultracentrifugation, light scattering, and osmotic pressure determinations (Banks and Greenwood,... 

Cotton IP, Famoux B, Jannink G, Straziel C (1973) Dilute and semidilute solutions—light and neutron-scattering and osmotic-pressure. J Polym Sci Part C Polym Symp 42 981-985... 

Moltzer. Benoit and Doty (45) undertook the task of fractioning samples of nitrocellulose with 13.8-14.1% N. -llexane was added dropwise while stirring to 0.2% solution of nitrocellulose in acetone and several fractions were obtained. Their molecular weight was determined by light scattering, viscosity and osmotic pressure measurement. 

Some other methods have also been employed to observe the coil-globule transition for isolated polymer molecules (e.g., ordinary light scattering, viscosity and osmotic pressure measurements, and elastic neutron scattering off polymer solutions). However, the two techniques we mentioned before are the best for this purpose. They are very sensitive and allow measurements of solutions at extremely low concentrations. 

Information on micelle size and shape can be obtained from a variety of techniques such as light scattering, neutron scattering, viscosity measurements and osmotic pressures. Typically the micelles have a closely spherical shape in a rather wide concentration range above the CMC. Often there is no great change in shape until the surfactant solubility limit is reached, when a liquid-crystalline phase normally separates out. 

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