Osmotic pressure shear

The rheological properties of a fluid interface may be characterized by four parameters surface shear viscosity and elasticity, and surface dilational viscosity and elasticity. When polymer monolayers are present at such interfaces, viscoelastic behavior has been observed (1,2), but theoretical progress has been slow. The adsorption of amphiphilic polymers at the interface in liquid emulsions stabilizes the particles mainly through osmotic pressure developed upon close approach. This has become known as steric stabilization (3,4.5). In this paper, the dynamic behavior of amphiphilic, hydrophobically modified hydroxyethyl celluloses (HM-HEC), was studied. In previous studies HM-HEC s were found to greatly reduce liquid/liquid interfacial tensions even at very low polymer concentrations, and were extremely effective emulsifiers for organic liquids in water (6). 

Rgure 4.5. The computed shear modulus G (stars) and osmotic pressure (line), compared with the experimental values for (squares) and n (full circles). All data are normalized by Kint/a- (Adapted from [21].)... 

This article reviews the following solution properties of liquid-crystalline stiff-chain polymers (1) osmotic pressure and osmotic compressibility, (2) phase behavior involving liquid crystal phasefs), (3) orientational order parameter, (4) translational and rotational diffusion coefficients, (5) zero-shear viscosity, and (6) rheological behavior in the liquid crystal state. Among the related theories, the scaled particle theory is chosen to compare with experimental results for properties (1H3), the fuzzy cylinder model theory for properties (4) and (5), and Doi s theory for property (6). In most cases the agreement between experiment and theory is satisfactory, enabling one to predict solution properties from basic molecular parameters. Procedures for data analysis are described in detail. 

Hemolysis is the leakage of hemoglobin into liquid such as plasma, and is due to disruption of the erythrocytes. Within the body, hemolysis maybe caused by some diseases or poisons, whereas hemolysis outside the body, as in artificial organs, is caused by physical or chemical factors. If erythrocytes are placed in water, hemolysis will occur as the cells rupture due to the difference in osmotic pressure between water and the intracellular liquid. Hemolysis in artificial organs and their accessories occurs due to a variety of physical factors, including turbulence, shear, and changes of pressure and velocity. It is difficult, however, to obtain any quantitative correlation between the rates of hemolysis and such physical factors. 

The Maxwell construction would determine the condition of two phase coexistence or the points on the curves where the first-order phase change occurs [6,7]. It is the condition that the two phases have the same value of g or j d II = 0 from Eq. (2.6) at zero osmotic pressure, v2 and vx being the values of v in the two phases. However, this criterion is questionable in the case Kcritical point). This is because the shear deformation energy has not been taken into account in the above theory. See Sect. 8 for further comments on this aspect. 

In the case K > fi, the usual diffusion determines the kinetics for any gel shapes. Here the deviation of the stress tensor is nearly equal to — K(V u)8ij since the shear stress is small, so that V u should be held at a constant at the boundary from the zero osmotic pressure condition. Because -u obeys the diffusion equation (4.18), the problem is trivially reduced to that of heat conduction under a constant boundary temperature. The slowest relaxation rate fi0 is hence n2D/R2 for spheres with radius R, 6D/R2 for cylinders with radius R (see the sentences below Eq. (6.49)), and n2D/L2 for disks with thickness L. However, in the case K < [i, the process is more intriguing, where the macroscopic critical mode slows down as exp(- Q0t) with Q0 oc K. 

Cell lysis Mechanical methods pressure shearing, ultrasonic disintegration, bead-mill homogenizers Nonmechanical methods enzymatic lysis, osmotic lysis, freezing and thawing, detergent-based lysis and electroporation... 

The main mechanism for effecting triggered release is to use pressure to break the shell, and hence release the core contents into the external phase. This is particularly useful when the active material is a high MW molecule (e.g. a protein). The applied pressure can be in the form of simple mechanical pressure (e.g. in carbon paper copying) or high shear conditions. A more subtle method, however, is to use osmotic pressure to break the capsule. This can occur if solvent molecules from the external phase are able to diffuse across the shell into the core. If the core contains molecules (e.g. polymer) which are not able to diffuse across the shell, then clearly there will be an osmotic pressure difference across the shell, which will drive solvent to try to enter the core, leading to possible shell rupture. 

In a first step of the miniemulsion process, small stable droplets in a size range between 30 and 500 nm are formed by shearing a system containing the dispersed phase, the continuous phase, a surfactant, and an osmotic pressure agent. In a second step, these droplets are polymerized without changing their identity. 

Comparison of the normal osmotic pressure IT and the shear force in this regime is shown in Fig. 18 for chains of length N=100 for three values of vn, These... 

Fig. 18. Semilog plot of the normal osmotic pressure n, (O) and shear force/versus the plate separation D between polymer brushes of 100-mers in a solvent of free dimer molecules for pfl=0.03cr 2. The shear force is shown for uw=2.0X10 4 (A), 2.0X10-3 ( ), and 2.0X 10 2cr/r ( ). From ref. [63].

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... 

Figure 9 summarizes the simulation results for monodisperse packings. It shows a plot of Go, Goo and r, all scaled with , versus the packing fraction. These values of the shear moduli and the osmotic pressure were consistently reproduced over nine sample configurations for each fraction and show little spread, with error bars smaller than the symbols. Up to a packing fraction of around =0.64 (i.e., the close-packing density), there is no contact between particles, and both the moduli... 

Fig. 9 Simulation results for monodisperse packings. The high-frequency shear modulus Goo open circles, the low-frequency shear modulus Go closed circles, and the osmotic pressure TT diamonds are all scaled with the particle contact modulus E and plotted versus the packing fraction

Both the osmotic pressure and the high-frequency shear modulus can be calculated analytically from the radial distribution function derived above. The osmotic pressure n is related to the radial distribution function and the energy potential... 

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