Osmotic pressure and diffusion

The recent systematic investigations carried out by Newman et al. [37] were devoted to the viscosity, sedimentation, diffusion and osmotic pressure of nitro-celluloses prepared by nitrating non-purified cotton, purified cotton, and viscose fibres with mixed add containing phosphoric acid and phosphoric anhydride. 

Interstitial fluid flow, ion diffusion and osmotic pressure... 

Thus, the solvent flux was expressed as a sum of contributions from diffusive and osmotic pressure terms. The osmotic pressure in the solvent flux expression depends upon the viscoelastic properties of the polymer. The relationship between the osmotic pressure and the stresses within the polymer was derived by writing momentum balances as... 

In the previous sections, the impact of the material properties of emulsions and spray process parameters on the dispersion was described. It provided information about the dispersion of secondary droplet of DE, rather than the release of an encapsulated component. The release of functional components during spray processing may also be influenced by shear-induced diffusion and osmotic pressure. Therefore, an iron-salt (FeS04) encapsulated DE was sprayed and the retained amount of iron in the sprayed emulsion detected. Conductivity and Atomic Adsorption Spectroscopy (AAS) methods were used for measuring the concentration of iron. The retained amount of iron is defined as follows (23.15) ... 

The reason for using the two different molecular weights is that some properties, such as freezing points, vapor pressure, and osmotic pressure of dilute solutions, are related directly to M , whereas other properties, such as lightscattering, sedimentation, and diffusion constants, are related directly to Mu-... 

Equation (6.173) implies that the release rate is governed by the porosity of the membrane, which influences the permeability the polymer material, which influences the semipermeability of the membrane the thickness and surface area of the membrane the solubility and osmotic pressure and the amount of drug in the core. Figure 6.41 shows the effect of osmotic pressure on the release of KC1 from MPOPS. By extrapolating the linear line to zero osmotic pressure, the release rate of drug by diffusion through the microporous membrane structure can be obtained. 

Rejection of protein adsorption to the outermost grafted surface is attributed to a steric hinderance due to the tethered chains. A grafted surface in contact with an aqueous medium, a good solvent of the chains, has been identified to have a diffuse structure [67]. Reversible deformation of tethered chains due to invasion of mobile protein molecules into the layer would lead to a repulsive force which is governed by the balance of entropic elasticity of the chains and osmotic pressure owing to the rise in the segment concentration. The overlapped repulsive force would prevent the direct contact of protein molecules with the substrate surface. 

Further, the criterion that equilibrium is reached when (8A)XV = o, applies to reactions in solutions Take the simplest case of diffusion of a solute from a region of high concentration to one of low Equilibrium is reached when the work entailed by a small virtual change m the system can be equated to zero Suppose we have a solute at concentrations Cy and and osmotic pressures Px and P2 in the same vessel By means of osmotic membranes (the whole vessel being supposed to be surrounded by solvent of infinite extent) we can imagine 8 moles transferred from Px to P2 the work being < j WP, which will be zero... 

Both the concentration polarization and osmotic pressure descriptions can be applied to polymer solutions that form well-defined gels at high concentrations. In a gel the thermodynamic osmotic pressure results from the solvent-mediated interactions between the randomly moving gel monomers, and this pressure tends to swell the gel. Both descriptions have been calculated in some detail for gelling macromolecular solutions and shown to produce similar behaviors (Probstein et al. 1979, Trettin and Doshi 1981). Actually a relatively simple argument shows that the two approaches are equivalent if the diffusion... 

The bicarbonate ions are replaced in the plasma by chloride ions that diffuse out of the blood cells. This step, called the chloride shift, maintains charge balance and osmotic pressure relationships between the plasma and red blood cells. 

An extremely thin piece of material such as a sheet of synthetic polymer or animal tissue can allow some molecules to pass through it. Such a material is called a membrane and is said to be permeable to those molecules and ions that can pass through. Permeability is dependent on the presence of tiny passages within the membrane. A membrane permeable to water molecules but not to ions or molecules larger than water molecules is called a semipermeable membrane. Many membranes made from synthetic polymers have this characteristic. One such polymer is cellulose acetate. If a semipermeable membrane is placed between seawater (brine) and pure water, the pure water will pass through the membrane to dilute the seawater. This is a process called osmosis. The hquid level on the seawater side rises as more water molecules enter than leave, and pressure is exerted on the membrane until the rates of diffusion of water molecules in both directions are equal. Osmotic pressure is defined as the external pressure required to prevent osmosis. Figure 11.10a and 11.1 Ob illustrates the concepts of osmosis and osmotic pressure. 

Non-electrolvtes. a- Dilute solutions. Taking into account the hydrodynamic theory of diffusion, Nernst (27) considered a relationship between pressure in gases and osmotic pressure in liquids and derived. 

---