Suspensions osmotic pressure

Ophthalmic Dosage Forms. Ophthalmic preparations can be solutions, eg, eye drops, eyewashes, ointments, or aqueous suspensions (30). They must be sterile and any suspended dmg particles must be of a very fine particle size. Solutions must be particle free and isotonic with tears. Thus, the osmotic pressure must equal that of normal saline (0.9% sodium chloride) solution. Hypotonic solutions are adjusted to be isotonic by addition of calculated amounts of tonicity adjusters, eg, sodium chloride, boric acid, or sodium nitrate. 

Colligative properties are those properties of solutions that depend on the number of solute particles present and not their identity. Colligative properties include vapor pressure lowering, freezing point depression, boiling point elevation, and osmotic pressure. Colloids are homogeneous mixtures, in which the solute particles are intermediate in size between suspensions and true solutions. We can distinguish colloids from true solutions by the Tyndall effect. 

Consider the equilibrium in a vertical cylinder of suspension of density pi in a suspension medium of density of unit cross-section and height. o o. If at a height x there are n particles per unit volume and at a height xJr x,n->cM particles per unit volume the difference in osmotic pressures due to the particles on the assumption that the suspension conforms to the laws of an ideal solution will be... 

The force acting on a particle suspended in a solution will be caused by the osmotic pressure differences in the suspension or... 

The osmotic pressure of the saturated salt solution is high, on the order of tens of atmospheres, and the small pressure required to pump the suspension of active agent is insignificant in comparison. Therefore, the rate of water permeation across the semipermeable membrane remains constant as long as sufficient solid salt is present in the salt chamber to maintain a saturated solution and hence a constant osmotic pressure driving force. 

Barton [41] has assembled a well-referenced source book for the derivation and use of x and cohesion parameters for various polymer solvent pairs. There are many ways to measure solvent activity, the simplest being boiling point elevation, freezing point depression, and osmotic pressure discussed in Section 11.5, Solution and Suspension Colligative Properties. ... 

The osmotic pressure of solutions are discussed here as an introduction to the concept of osmotic pressme in suspension [21]. The phenomena of osmotic pressure is illustrated by a semipermeable membrane filled with a sugar solution immersed in water. The pressure inside the membrane, p + it, is large than that in the water, p, according to the formula... 

Osmotic Pressure of the Double Layer in a Colloidal Suspension... 

An aqueous colloidal suspension also has an osmotic pressure associated with both the double layer of the particles in solution and the structure of the particles. The osmotic pressure term for the structure is given in Section 11.6 for both ordered and random close packing. The osmotic pressure associated with the double layer surrounding the ceramic particles in aqueous solution is discussed here. 

If we consider a spherical cell containing at its center a spherical particle of radius, a, and a shell of fluid of radius, /B, as a one-partide example of the suspension with a volume fraction d> [= (a//3f], then the osmotic pressure of the suspension is given by [23]... 

Because the particle lattice is assumed to be static, the osmotic pressure term due to particle conformation for the disordered suspension derived by Carnahan and Starling [25] and used by Dickinson [26] and Evans and Napper [27] must be added to the previous equation ... 

Strauss et al. [28] has developed a numerical method for the nonlinear Poisson-Boltzmann equation 4 > 25 mV for this spherical particle in a spherical cell geometry. Figure 11.5 is a plot of the osmotic pressure for a suspension of identical particles with 100 mV surface potential and KU = 3.3. In this figure, the configurational osmotic pressure is also given and is much smaller than that of the osmotic pressure due to the double layer. The osmotic pressure increases with increased volume fraction due to the further overlap of the double layers sur-roimding each particle. 

In addition, Strauss s work developed the means to determine the osmotic pressure for a polydisperse suspension corresponding to a lognormal size distribution. With this S5/stem a particular osmotic pressure, II(= 4cksT sinh [ezt/ (j8)/2A BT]), is assumed specifying a value of i/ (j8). The volume fraction is then calculated. For a particular particle size, a, the volume of fluid associated with the particle is determined by the specified value of t//(j8) and the boimdaiy conditions. With the outer boundary condition, dt/ /dr r=(3 = 0 and //(j8) = constant for a specific value of the osmotic pressure, the total volume firaction, can be determined by summation of the volume fraction associated with... 

Figure 11.6 is a plot of the osmotic pressure versus volume fraction for a suspension with different widths, tr = In a-g, of the log-normal particle size distributions where Og is the geometric mean size and a-g is the geometric standard deviation. As the width of the size distribution increases, the osmotic pressure decreases for a particular volume fraction. With this osmotic pressure, we can evaluate the order—disorder transition for an electrostatically stabilized suspension, which is discussed next. 

Osmotic Pressure (and Other Thermodynamic Properties) of a Ceramic Suspension... 

FIGURE 11.10 Gibbs free energy, G, versus osmotic pressure, II, for a suspension of hard spheres showing the intersection of the disordered and the ordered curves corresponding to the disorder-order transition with 4a-a%/3 = 0.74. Adapted from Cast et al. [63]. Reprinted with permission Academic Press. 

Determine the osmotic pressure for a suspension of 0.001 ftm hard spheres at a volume fraction of 0.74. 

Using a linearized flat plate solution to the Poisson—Boltzmann equation for the potential distribution of a sphere, what is the osmotic pressure of a 0.01 volume fraction suspension of 0.1 /an spheres immersed in a 1 1 salt solution at 0.1 M. The surface potential of the particle is 25 mV. Compare this value with that for the salt solution only. 

This then gives a direct link between the thermodynamic stress and the osmotic pressure (or the compressibility) of the suspension. As a result of this stress, the viscosity will depend directly upon the structure, and the interpartide potential, V(ry). Using this interrelationship Batchelor has been able to evaluate the ensemble averages of both the mechanical and thermodynamic stresses by renormalizing the integrals. As a result, he has developed truncated series expressions for the low shear limit viscosity, and the high shear limit viscosity, t) , corresponding to... 

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