Osmoti£pressure

If we again define P — fo as the osmotie pressure, tt and substitute from Equation (19.48) into Equation (19.46), we obtain... 

Higher molecular mass dextrans (partieularly dextran 70, 75 and 110) are used to promote short-term expansion of plasma volume thus preventing/treating shoek due to blood loss. A 6% w/v solution of these dextrans exerts an osmotie pressure similar to that of plasma proteins. Generally, an initial dose of 500 ml 1 litre is administered by i.v. infusion. Dextrans also inhibit the aggregation of red blood eells. Thus, they are often used to prevent/treat post-operative thrombo-embolic disorders (see later in this ehapter) and to improve blood flow. 

The lower molecular mass dextran 40 (40kDa) exhibits similar therapeutic effects to the higher molecular mass dextrans, although it must be used at slightly higher concentrations (10%, w/v) in order to aehieve the same osmotie pressure. 

Osmose plays an essential role in a wide teehnologieal and espeeially in biologieal systems represented by solutions of biopolymers. That is why understandable is interest of seientists to the problem of osmotie pressure of polymerie solutions whieh permits eomparatively easy experimentally to determine the advantages and defieieneies of theoretieal imaginations about thermodynamieal properties of polymerie solutions. 

Two main approaehes for osmotie pressure of polymerie solutions theoretieal deseription ean be distinguished. First is Flory-Huggins method [1, 2], whieh afterwards has been determined as method of self-eonsistent field. In the initial variant the main attention has been paid into pair-wise interaetion in the system gaped monomerie links - moleeules of solvent . Flory-Huggins parameter y was a measure of above-said pair-wise interaetion and this limited applieation of presented method by field of eoneentrated solutions. In subsequent variants sueh method was extended on individual maeromoleeules into diluted solutions with taken into aeeount the tie-up of ehain links by Gaussian statisties [1]. 

For deseription of the osmotie pressure 71 of polymerie solutions the virial deeomposition is used in the Flory-Huggins method... 

Further development of the Flory-Huggins method in direetion of taking into accoimt the effects of far interaction, swelling of polymeric ball in good solvents [4, 5], difference of free volumes of polymer and solvent [6, 7] leaded to eomplieation of expression for virial eoefficient A and to growth of number of parameters needed for its numerical estimation, but weakly reflected on the possibility of equation (1) to deseribe the osmotie pressure of polymerie solutions in a wide range of eoncentrations. 

In general case v is eomplieated and independent function on solution composition. However, in narrow purposes of investigations the influence of macromolecules chemical potential eonformation component on osmotie pressure we use the approximation v = const. Then after the integration of (30) we will obtain... 

The relation between osmotie pressure and solvent aetivity is to be found from the ehemieal potential equilibrium eondition, taking into aeeount the pressure dependenee of ti. From the rules of phenomenologieal thermodynamies, one obtains ... 

Integration is performed between Pq, i.e., the ordinary pressure or measuring pressure, and TZ, the osmotie pressure, and results in Equation [4.4.35]. 

Figure 2 (A) Osmosis (B) osmotic equiiibrium (C) reverse osmosis. M, semipermeabie membrane ph, hydrostatic pressure n, osmotis pressure p, externai pressure, D, aqueous sait soiution, A, water.

Write the equation relating osmotie pressure to the concentration of a solution. Define all the terms and specify their units. 

A protein has been isolated as a salt with the formula Na2oP (this notation means that there are 20 Na ions associated with a negatively charged protein p20-) osmotie pressure of a 10.0-mL solution containing 0.225 g of the protein is 0.260 bar at... 

In the mean-field approximation the field-dependent potential (osmotie pressure) can be presented in the form of a truncated Landau expansion in powers of the order parameter... 

The number of solvent molecules exchanged during the reaetion is due to the variation of the concentration of ions inside the polymer, being quantified by the osmotie pressure (77), which follows the van t Hoff equation ... 

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