The Origin of Osmotic Pressure

however, it is put in water, solvent molecules penetrate the fine Assures and cracks of the crystal surface, interact with the hydroxyl groups of the glucose or fructose residues and thereby interfere with the cohesion of the crystal to such an extent that the average kinetic energy is sufficient to detach the individual C12H22O11 molecules from the solid phase and drive them into the liquid. There, combined with a few water molecules, they execute molecular motion under the influence of random impacts, which push them hither and thither and make them victims of chance. In a short time the solid sugar crystal disappears with the automatic formation of a homogenous solution. 

On thermodynamic principles the cause will be attributed to the increase in entropy consequent on solution while the statistical-kinetic mode of consideration will recognize as decisive the predominance of the random molecular motion over the acting forces. 

We shall now assume that the solution is very dilute and that the sugar molecules constitute only a few per thousand of the water molecules present. If there is a wall which allows the molecules of the solvent to pass but is impermeable to the particles of the solute (semi-permeable), energy will be imparted to the wall by the dissolved particles and their pressure—the osmotic pressure—is observable by direct experiment. 

Let us imagine now a dilute sugar solution brought in contact with the pure solvent through a semi-permeable membrane and inquire what happens. 

We give the answer first by thermodynamic principles and then by statistical-kinetic considerations. 

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These capillary and electro capillary views, it must be understood, refer only to the possible mechanism of semipermeability of membranes This is quite distinct from the origin of osmotic pressure itself, which has been attributed to a difference between the value of the solvent pressure throughout the body of the pure solvent, and the value of the solvent pressure throughout the body of the solution... 

Stress must be laid on the fact that the views expressed in the foregoing sections regarding the origin of osmotic pressure are at the present... 

In the meantime, the intense study of the simpler vesicle systems has unravelled novel, unsuspected physicochemical aspects - for example growth, fusion and fission, the matrix effect, self-reproduction, the effect of osmotic pressure, competition, encapsulation of enzymes, and complex biochemical reactions, as will be seen in the next chapter. Of course the fact that vesicles are viewed under the perspective of biological cell models renders these findings of great interest. In particular, one tends immediately to ask the question, whether and to what extent they might be relevant for the origin of life and the development of the early cells. In fact, the basic studies outlined in this chapter can be seen as the prelude to the use of vesicles as cell models, an aspect that we will considered in more detail in the next chapter. 

As noted above, all of the colligative properties are very similar in their thermodynamics if not their experimental behavior. This similarity also extends to an application like molecular weight determination and the kind of average obtained for nonhomogeneous samples. All of these statements are also true of osmotic pressure. In the remainder of this section we describe osmotic pressure experiments in general and examine the thermodynamic origin of this behavior. 

Exxon products appear to release via a unique mechanism. Like other polymer-coated technologies, the penetration of water iato the granule is purely by diffusion. However, as water enters the particle, an osmotic pressure is created as the fertilizer is solubilized. This pressure causes an expansion of the elastomeric coating and the particle swells to many times its original diameter. As the particle swells, the coating becomes increasingly thinner to the point where it caimot contain the internal pressure and the nutrient is released. 

The origin of the structural disjoining pressure is osmotic in nature. When nanoparticles/surfactant micelles are conflned in a thin film, they tend to ar-... 

If you have a class with biochemists, clearly the area of enzyme kinetics is practically mandatory. If biologists are mixed in with the biochemists, osmotic pressure is an important concept to cover carefully and a concept typically not well covered in general chemistry and in most physical chemistry texts or classes. A quick example what is a 2 Osmolar solution of sodium chloride Such concentration units are used when dispensing various saline solutions in hospitals. What is the origin of the unit A 1 M NaCl solution dissociates into two ions that would double the osmotic pressure of a non dissociating solute. Thus, the 1 M solution of NaCl becomes a 2 Osmolar solution. Other examples abound - the bursting pressure of a cell relates to the osmotic pressure of the serum in which the cell finds itself. 

Binding and transport. There are four binding sites on the albumin molecule, with varying specificity for different snbstances (snch as fatty acids and bilirubin). Competitive binding of drugs may occur at the same site, with displacement of the originally bound substance. Maintenance of colloid osmotic pressure. Albumin is responsible for 75-80 % of osmotic pressure. 

As osmosis proceeds, pressure builds up on the side of the membrane where volume has increased. Ultimately, the pressure prevents more water from entering, so osmosis stops. The osmotic pressure of a solution is the pressure needed to prevent osmosis into the solution. It is measured in comparison with pure solvent. The osmotic pressure is directly related to the different heights of the liquid on either side of the membrane when no more change in volume occurs. Osmotic pressure depends on the temperature and the original concentration of solute. Interestingly, it does not depend on what is dissolved. Two solutions of different solutes, for example alcohol and sugar, will each have the same osmotic pressure, provided they have the same concentration. Osmotic pressure is therefore a colligative property of solutions, one which depends only on the concentration of dissolved particles, not on their chemical identity. 

We would like to stress that the physical reason of the polyelectrolyte gel expansion is the osmotic pressure of counterions, which originates from their translational entropy. Counterions possessing high translational entropy would like to leave the network sample. However, this is forbidden because of the condition of total electroneutrality. So the counterions create osmotic pressure on the sample of the polymer network. 

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