Colloidal particles solution viscosity

The viscous flow of a polymer solution involves a shearing action in which different layers of the solution move with differing velocities. As we observed earlier, there is a pronounced increase in the viscosity of a polymer solution relative to that of the pure solvent even at low concentrations of the polymer. In this respect, the polymer solute behaves as a coUoidal dispersion, which is known to retard the flow of adjacent layers of a liquid under shearing force. For spherical colloidal particles, the viscosity of the solution, Tj, relative to that of the pure solvent, Tio, is referred to as the relative viscosity, given by... 

In support of the association theory, colloid chemists cited non-reproduceable cryoscopic molecular weight determinations (which were eventually shown to be caused by errors in technique) and claimed that the ordinary laws of chemistry were not applicable to matter in the colloid state. The latter claim was based, not completely without merit, on the ascerta-tion that the colloid particles are large aggregates of molecules, and thus not accessible to chemical reactants. After all many natural colloids were shown to form double electrical layers and adsorb ions, thus they were "autoregulative" by action of their "surface field" (29). Furthermore, colloidal solutions were known to have abnormally high solution viscosities and abnormally low osmotic pressures. 

Porous inkjet papers are in general created from colloidal dispersions. The eventual random packing of the colloid particles in the coated and dried film creates an open porous structure. It is this open structure that gives photographic-quality inkjet paper its apparently dr/ quality as it comes off the printer. Both the pore structure and pore wettability control the liquid invasion of the coated layer and therefore the final destination of dyes. Dispersion and stability of the colloidal system may require dispersant chemistries specific to the particle and solution composition. In many colloidal systems particle-particle interactions lead to flocculation which in turn leads to an increase in viscosity of the system. The viscosity directly influences the coating process, through the inverse relation between viscosity and maximum coating speed. 

With the viscosity of a liquid we mean the resistance to flow of that particular liquid. This resistance is caused by internal friction and other interactions between the particles. Among other things, viscosity is dependent on temperature, the solid volume fraction and the properties of the particles. The viscosity of normal liquids, solutions and lyophobic colloids which are not too concentrated and contain symmetrical particles is measured by allowing a certain volume to flow through a capillary and measuring the time required by the liquid to flow through it. In figure 5.10 you can see the instrument which is used for this measurement the Ostwald viscometer. 

Experimentally the increase in activation energy is quite evident, but the cause of this increase is not clear. It can be argued that the increase in activation energy is related to a strong increase in viscosity of the reactive medium or to phase separation in the reactive mass when a newly formed polymer precipitates from a solution and forms colloid particles. The experimental data described by Eqs. (2.23) - (2.25) can also be treated in ways other than those used in the original publication. For example, it is possible to linearize the exponential factor in Eq. (2.23), as was done above for other purposes. Then for the range of P from 0.35 to 0.8 we can write ... 

In a free solution, the electrophoretic mobility (i.e., peiec, the particle velocity per unit applied electric field) is a function of the net charge, the hydrodynamic drag on a molecule, and the properties of the solutions (viscosity present ions—their concentration and mobility). It can be expressed as the ratio of its electric charge Z (Z = q-e, with e the charge if an electron and q the valance) to its electrophoretic friction coefficient. Different predictive models have been demonstrated involving the size, flexibility, and permeability of the molecules or particles. Henry s theoretical model of pdcc for colloids (Henry, 1931) can be combined with the Debye-Hiickel theory predicting a linear relation between mobility and the charge Z ... 

The sedimentation of pharmaceutical dispersions in non-Newtonian polymer solutions is of some practical interest. These polymers are used not only to stabilize colloidal particles but also to slow down (or prevent) settling, thus preventing cake formation. Newtonian fluids are defined as simple fluids that show a linear relationship between the rate of flow or shear (G) and the applied (or shearing) stress (F) at a constant viscosity (p) as shown in Figure 4.38 ... 

Electrophoresis — Movement of charged particles (e.g., ions, colloidal particles, dispersions of suspended solid particles, emulsions of suspended immiscible liquid droplets) in an electric field. The speed depends on the size of the particle, as well as the -> viscosity, -> dielectric permittivity, and the -> ionic strength of the solution, and it is directly proportional to the applied electric field. In analytical as well as in synthetic chemistry electrophoresis has been employed to separate species based on different speeds attained in an experimental setup. In a typical setup the sample is put onto a mobile phase (dilute electrolyte solution) filled, e.g., into a capillary or soaked into a paper strip. At the ends of the strip connectors to an electrical power supply (providing voltages up to several hundred volts) are placed. Depending on their polarity and mobility the charged particles move to one of the electrodes, according to the attained speed they are sorted and separated. (See also - Tiselius, - electrophoretic effect, - zetapotential). 

This behaviour ean be quahtatively explained by Equation (12.7) since 4>m increases as the width of the size distribution increases. A good example of the ef-feets that particles and polymers have on the rheological behavior of liquids is cloudy apple juice (Genovese and Lozano, 2000). The aqueous milieu of the juice is a solution of sugar, acids and salts (i.e., the clarified juice) that contains charged particles (0.25-5 pm in size) and pectin as a colloidal dispersion. The viscosity of cloudy apple juice has been described by the expression ... 

Geoiogy. An example of electrochemistry in geology concerns certain types of soil movements. The movement of earth under stress depends on its viscosity as a siurry that is, a viscous mixture of suspended solids in water with a consistency of very thick cream. Such mixtures of material exhibit thixotropy, which depends on the interactions of the double layers between colloidal particles. These in turn depend on the concentration of ions, which affects the field across the double layer and causes the colloidal structures upon which the soil s consistency depends to repel each other and remain stable. Thus, in certain conditions the addition of ionic solutions to soils may cause a radical increase in their tendency to flow. 

Silicsol is a commercial product introduced in Europe this past decade. It is described as an activated silica liquor with a calcium-based reagent. As opposed to sodium silicate (colloidal silica particles dispersed in soda), silicsol is claimed to be a true solution. Viscosity and penetrability are similar to sodium silicate, but the reaction is different, resulting in a stronger end product more resistant to creep. There is no syneresis associated with silicsol. 

Polyvinyl alcohols (PVAl) are manufactured by saponification of vinyl acetate polymers (PVAc). Properties of PVC using PVAl as a protective colloid are influenced by the solution viscosity of the PVAl, i.e. the degree of polymerization of the PVAc and the degree of saponification. Polyvinyl alcohols of 75-90% hydrolysis are primary suspension agents for S-PVC, whereas polyvinyl alcohols of 25-40% hydrolysis are secondary suspension agents, which control the agglomeration of the primary particles. Partially hydrolyzed PVAc can be block or random polymers. 

Osmotic pressure measurements for the determination of MW were used in 1900 to characterize starch. Twenty years later, the solution viscosity measurements were introduced by Staudinger for this purpose. However, it was Mark and his collaborators who developed the concept of the intrinsic viscosity ([r ]) and demonstrated that it provides information on the volume of individual colloidal particles, thus on MW. For the freely rotating chains the dependence (today known as Mark-Houwink-Sakurada equation) was obtained [Guth and Mark, 1934] ... 

A relationship is shown to exist in viscometry experiments between particle size or molecular size and the viscosity of dispersions of inorganic colloids or the viscosity of macromolecular solutions. It is therefore possible to determine the molar mass from the viscosity of dilute macromolecular solutions. Since this experiment can be rapidly performed with simple equipment, it is, in practice, the most important molar mass determination method. However, the method is not an absolute one, since the viscosity depends on other molecular properties (for example, on the shape of the molecule), as well as on the molecular weight. 

A typical result of a calculation [127] of the complex viscosity rf(co) is shown in Fig. 11. The real part of the viscosity, / (w), which describes the dissipation of energy when the fluid is sheared, is approximately frequency-independent for small cu, i.e., the fluid behaves as a Newtonian fluid. There is a characteristic frequency co where f/ (o>) drops rapidly. The imaginary part of the viscosity, rf"(o)), which describes the elastic response of the fluid to an external perturbation, increases linearly for small co and reaches a maximum at CO = CO. This behavior is not specific to microemuisions but has been observed in other complex fluids as well, such as in suspensions of spherical colloidal particles [128,129] and in dilute polymer solutions [130]. 

As a colloidal particle diffuses or sediments through a solution containing nonadsorbing polymer chains, one may naively expect that the friction experienced by the particle is set by the bulk viscosity. In practice, it is smaller. An analysis of the... 

For polymer chains that are roughly as big as the particle, the apparent or effective viscosity experienced by a sphere is in between the viscosities of solvent and polymer solution. A similar finding was also reported for the rotational diffusion of colloidal particles [292] and for the sedimentation of colloids through a polymer solution [293]. 

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