Osmotic compressibility curves

As the attractive potential V between droplets increases, g decreases. The normalized osmotic compressibility curves v/kT.3tt/3tf> versus cf pass closer and closer to the axis and become tangent to... 

Still one may wonder how much this shift depends on the applied pressure. Indeed the new concentrations were measured under an osmotic stress of 5 atmospheres would they have been substantially different if the applied pressure was more or less This requires a measurement of the complete osmotic compression curve for floes. 

The complete osmotic compression curve was determined through a set of "Parsegian" experiments. At equilibrium the osmotic pressures inside and outside the bag are equal. Thus when the concentration of macromolecules in the reservoir is raised tiie osmotic pressure in the bag increases as well. The response of the dispersion inside the bag is a further deswelling. In this way the concentration inside the bag was measured at different osmotic pressures for two compositions of the dispersion. The first composition is the O.F.C and the other one corresponds to the saturation of the... 

Figure 4 compares osmotic compressibility data for isotropic schizophyllan-water solutions [63] with the scaled particle theory. The ratios of the z-average to the weight-average molecular weights of these schizophyllan samples are ca. 1.2. The solid curves, calculated with d taken to be 1.52 nm and other molecular parameters (Lc, v, and c ) estimated from Mw and the wormlike chain parameters in Table 1, are seen to come close to the data points for all samples. 

In this case, the structure function is given by eqn (16.4.4) and we verify that this curve has a downward concavity. Figure 16.8 shows us that the osmotic compressibility... 

Figure 19-6. Inverse osmotic compressibility of inorganic silicotungstic acid solutions as a function of volume fraction for dijferent concentrations of added lithium chloride as measured by static light scattering. The decreasing and ultimately negative slope of the curves is an indication of reduction of repulsive interactions and increasing strength ofattraction between the STA particles (Ramakrishnan, 2000).

The isoelectric regime (ct, > a3 Fig. 1, curve 3). Here the network remains in compressed state even in good solvent a. m-1/6. The attractive electrostatic interaction due to the term Fei s, < 0 (see Eq. (9)) and very small osmotic pressure of counter ions due to their low concentration are the reasons. 

For an athermal case, the continuous deswelling of the network takes place (Fig. 9, curve 1) which in the result of compressing osmotic pressure created by linear chains in the external solution (the concentration of these chains inside the network is lower than in the outer solution, cf. Ref. [36]). If the quality of the solvent for network chains is poorer (Fig. 9, curves 2-4), this deswelling effect is much more pronounced deswelling to strongly compressed state occurs already at low polymer concentrations in the external solution. Since in this case linear chains are a better solvent than the low-molecular component, with an increase of the concentration of these chains in the outer solution, a decollapse transition takes place (Fig. 9, curves 2-5), which may occur in a jump-like fashion (Fig. 9, curves 3-4). It should be emphasized that for these cases the collapse of the polymer network occurs smoothly, while decollapse is a first order phase transition. 

The shape of the curve determined by 3-D osmotic pressure measurements is similar to that determined by the 2-D compression studies. This congruence is strongly suggestive of the absolute validity of this shape for steric stabilization in better than 0-solvents. 

That the tail region indeed is dilute is emphasized by the low force required to compress the layers and by the exponential decay of the long-range part of the force curve. We note that the segment density in the tail region has been predicted to decay exponentially with distance from the surface [31] Thus an exponential decay of the force is predicted in the weak overlap model [29] where the force is only due to the increased osmotic pressure caused by the increased segment density (including counterions) at the midpoint between the surfaces. Of course, at small distances the weak overlap approximation breaks down and other contributions, e.g. loss of conformational entropy, become important and the measured force is expected and... 

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