Osmotic pressure value

The contribution of double-layer forces to the osmotic pressure of HIPEs was also investigated [98], These forces arise from the repulsion between adjacent droplets in o/w HIPEs stabilised by ionic surfactants. It was observed that double-layer repulsive forces significantly affected jt for systems of small droplet radius, high volume fraction and low ionic strength of the aqueous continuous phase. The discrepancies between osmotic pressure values observed by Bibette [97] and those calculated by Princen [26] were tentatively attributed to this effect. 

Table 8.1 shows osmotic pressure values of various solutes. Some generalizations may be made from this table. For example, comparing the osmotic pressures of... 

Gum arabic (acacia) has been used in pharmacy as an emulsifier. It is a polyelectrolyte whose solutions are highly viscous owing to the branched stmcture of the macromolecular chains its adhesive properties are also believed to be due to, or in some way related to, this branched stmcture. Molecular weights of between 200 000 and 250 000 (MJ have been determined by osmotic pressure, values between 250 000 and 3 x 10 by sedimentation and diffusion, and values of 10 by light scattering, which also points to the shape of the molecules as short stiff spirals with numerous side-chains. Arabic acid prepared from commercial gum arabic by precipitation is a moderately strong acid whose aqueous solutions have a pH of 2.2-2.7. It has a higher viscosity than its salts, but emulsions prepared with arabic acid cream are not as stable as those made with its salts. 

The osmotic pressure values given in Table 23 were obtained for 10% solutions of low-molecular povidones in water, using the equation given in Table 22. These values apply to pure povidone. As povidone contains only traces of impurities, e.g. 1 ppm vinylpyrrolidone, the osmotic pressure is hardly affected. This is confirmed by comparing the values measured for povidone K 17 with those calculated, in Table 23. The osmotic pressure calculated for a solution containing 1 ppm vinylpyrrolidone is given for reference. 

The osmotic pressure of solutions and especially the osmotic pressure in the boundary layer reduces the effective transmembrane pressure. To estimate the possible effect, ionic strength and osmotic pressure values for various salt solution compositions are summarised in Table 7.22. 

HBA and PhBA-Na were dissolved in pH 12 disodium hydrogenphosphate-NaOH buffer solution and in water, respectively. The drug concentration in injections was 215.3 ijmol/10 ml. The stability constants of drug-3-CD systems, and pH and osmotic pressure values of injections are listed in Table I. 

Consideration of the osmotic pressure values for components A and B adds one more correction Arios to the reological equation, which in contrast to Arjcr and Ar sp, is negative. It roots in a fact of better dispersal of fluctuations themselves due to osmotic pressure. The reduction of fluctuation correlation radiuses due to osmotic effect results in reduction of critical and spinodal corrections and therefore in reduction of the total system viscosity ... 

The phenomena we discuss, phase separation and osmotic pressure, are developed with particular attention to their applications in polymer characterization. Phase separation can be used to fractionate poly disperse polymer specimens into samples in which the molecular weight distribution is more narrow. Osmostic pressure experiments can be used to provide absolute values for the number average molecular weight of a polymer. Alternative methods for both fractionation and molecular weight determination exist, but the methods discussed in this chapter occupy a place of prominence among the alternatives, both historically and in contemporary practice. 

Since capillary tubing is involved in osmotic experiments, there are several points pertaining to this feature that should be noted. First, tubes that are carefully matched in diameter should be used so that no correction for surface tension effects need be considered. Next it should be appreciated that an equilibrium osmotic pressure can develop in a capillary tube with a minimum flow of solvent, and therefore the measured value of II applies to the solution as prepared. The pressure, of course, is independent of the cross-sectional area of the liquid column, but if too much solvent transfer were involved, then the effects of dilution would also have to be considered. Now let us examine the practical units that are used to express the concentration of solutions in these experiments. 

Osmotic pressure experiments provide absolute values for Neither a model nor independent calibration is required to use this method. Experimental errors can arise, of course, and we note particularly the effect of impurities. Polymers which dissociate into ions can also be confusing. We shall return to this topic in Sec. 8.13 for now we assume that the polymers under consideration are nonelectrolytes. 

The ratio n/c2 is called the reduced osmotic pressure-and can be plotted with or without the RT-and the zero-intercept value (subscript 0) is the limiting value of the reduced osmotic pressure. Quite an assortment of different pressure units are used in the literature in reporting n values, and the units of R in Eq. (8.88) must be reconciled with these pressure (as well as concentration) units. 

Use the method described in Problem 9 to obtain values of and p from these data. How do the values of these parameters compare with the values obtained for the same system from osmotic pressure data in Problem 8 ... 

Table 9.3 lists the intrinsic viscosity for a number of poly(caprolactam) samples of different molecular weight. The M values listed are number average figures based on both end group analysis and osmotic pressure experiments. Tlie values of [r ] were measured in w-cresol at 25°C. In the following example we consider the evaluation of the Mark-Houwink coefficients from these data. 

Sweetness is primarily a function of the levels of dextrose and maltose present and therefore is related to DE. Other properties that increase with increasing DE value are flavor enhancement, flavor transfer, freezing-point depression, and osmotic pressure. Properties that increase with decreasing DE value are bodying contribution, cohesiveness, foam stabilization, and prevention of sugar crystallization. Com symp functional properties have been described in detail (52). 

The test of the validity of the theory of Arrhenius is not therefore to be found in the agreement between the values of i obtained from measurements of any properties of solutions which are conditioned by the osmotic pressure it is in quite another field—that of electrochemistry—that a comparison of known relations with the deductions from the theory may be instituted. 

Then if any two phases are separately in equilibrium with a third phase, they are also in equilibrium when placed in contact, so that if any one phase (e.y., the vapour) is taken as a test-phase, and the other phases are separately in equilibrium with this, the whole system will be in equilibrium. Under the conditions imposed, it is sufficient that the vapour pressure, or osmotic pressure, of each component has the same value at all the interfaces, for we may consider each component separately by intruding across the interface a diaphragm permeable to that compo- -nent alone. Then if the vapour, or osmotic pressures, are not equal at the third interface to their values at the first and second interfaces, i.e., at the interfaces on the test-phase, we could carry out a reversible isothermal cycle in which any quantity of a specified component is taken from the test-phase to the phase of higher pressure, then across the interface to the phase of lower pressure, and then back to the test-phase. In this cycle, work would be obtained, which however is impossible. Hence the two phases which are separately in equilibrium with the test-phase are also in equilibrium with each other. This may be called the Law of the Mutual Compatibility of Phases (cf. 106). 

For practical purposes, the colligative property that is most useful for measuring relative molar masses of polymers is osmotic pressure. As Table 6.2 shows, all other properties take such small values that their measurement is impractical. 

The high osmotic pressure of seawater, 27.6 atm, makes it clear that osmotic pressures can be quite large. Thus, an osmotic pressure of 6.9 atm is a reasonable value for a solution such as blood. 

This is a large value for a molar mass, but it is reasonable because biological molecules often are quite large. As in any calculation, be careful to express all data in appropriate units. The osmotic pressure was measured to two significant figures, so the result has two significant figures. 

They showed further that the limiting slope (RTA2) of the plot of the osmotic pressure-concentration ratio tz/c against the polymer concentration in a binary solvent mixture should be proportional to the value of the quantity on the left side of Eq. (17),f with V2 representing the volume fraction of solvent in the nonsolvent-solvent mixture which is in osmotic equilibrium with the solution. The composition of the liquid medium outside the polymer molecules in a dilute solution must likewise be given by V2. The composition of the solvent mixture within the domains of the polymer molecules may differ slightly from that outside owing to selective absorption of solvent in preference to the nonsolvent. This internal composition is not directly of concern here. If the solution is made sufficiently dilute, the external nonsolvent-solvent composition v2 = l—Vi) will be practically equal to the over-all solvent composition for the solution as a whole. Hence... 

The results of osmotic pressure measurements are shown in Fig. 145 for poly-(4-vinyl-N-butylpyridinium bromide) in alcohol, and for the parent uncharged polymer, poly-(4-vinylpyridine), likewise in alcohol. The value of /c for the former (note difference in scales) is much larger than for the latter, and it increases with dilution. The... 

At high Q values the contribution from osmotic pressure predominates. This is shown by the ratio of the two forces which is given by... 

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