Fine dispersed suspensions characteristics

The changes of character of distribution on nanoparticles sizes take place depending on the nature of nanocomposites, dielectric penetration and polarity of liquid phase. Below characteristics of finely dispersed suspensions of metal/carbon nanocomposites are given. The distribution of nanoparticles in water, alcohol and water-alcohol suspensions prepared based on the above technique are determined with the help of laser ana-... 

This chapter is dedicated to the development of Nanochemistry methods for the Metal/Carbon Nanocomposites Synthesis as well as for the Materials modification by these Nanocomposites. The perspectives of the scientific trend introducing with the organization of modem Nanocomposites production in Nanoindustry are discussed. Nanochemistry methods for the creation of Metal/Carbon Nanocomposites in nanoreactors of polymeric matrixes are considered. The principal characteristics of nanocomposites obtained are given. With the help of IR and X-ray photoelectron spectroscopies it is found that the media respond to the introduction of super small quantities of nanostructures. The results of the modification of inorganic and organic materials with super small quantities of fine dispersed suspensions of Metal/Carbon Nanocomposites are presented. 

CHARACTERISTICS OF METAL/CARBON NANOCOMPOSITES FINE DISPERSED SUSPENSIONS... 

The short information about nanostructures formation mechanism in polymeric matrix nanoreactors as well as about the methods of synthesis and control during metal/carbon nanocomposites production represents. The main attention is given for the ability of nanocomposites obtained to form the fine dispersed suspensions in different media and for the distribution of nanoparticles in media. The examples of improving technical characteristics of foam concretes and glue compositions are given. 

Below characteristics of finely dispersed suspensions of metal/carbon nanocomposites are given (Figs. 12.1-12.4). 

Coagulation structures are formed by pigments and fillers of paints, varnishes and polymers. Spacial networks that form during coagulation of clay suspensions by electrolytes represent a characteristic example of thixotropic systems. Due to their ability to undergo structuring in aqueous media, finely dispersed bentonite and montmorillonite clays are widely used as main components of drilling liquids (see Chapter IX, 3) [32]. 

The viscosity characteristics of liquids can be altered considerably by the presence of finely dispersed solid particles, especially of colloidal size. The viscosity of a suspension of rigid spherical particles in a liquid, when the distance between the spheres is much greater than their diameter, may be expressed by the Einstein equation ... 

An alternative way to improve the mechanical properties of a polymer gel and retain its good absorption capacity consists in forming a composite stmcture comprising a rigid matrix embedded into the flexible-chain network. Such gels were obtained, for example, by acrylamide polymerization in aqueous suspensions of a finely dispersed clay sodium mon-tmorillonite. In the course of polymerization in this system, the PAAm gel is incorporated into the clay platelets, which resulted in the formation of a sufficiently strong composite stmcture with good mechanical characteristics. 

Fine suspensions are reasonably homogeneous and segregation of solid and liquid phases does not occur to any significant extent during flow. The settling velocities of the particles are low in comparison with the liquid velocity and the turbulent eddies within the fluid are responsible for the suspension of the particles. In practice, turbulent flow will always be used, except when the liquid has a very high viscosity or exhibits non-Newtonian characteristics. The particles may be individually dispersed in the liquid or they may be present as floes. 

The fineness characteristic of a powder on a cumulative basis is represented by a straight line from the origin to 100 per cent undersize at a particle size of 50 un. If the powder is initially dispersed uniformly in a column of liquid, calculate the proportion by mass which remains in suspension in the time from commencement of settling to that at which a 40 i m particle falls the total height of the column. It may be assumed that Stokes law is applicable to the settling of the particles over the whole size range. 

DISPERSANTS. Dispersants are materials that help maintain fine solid particles in a state of suspension, and inhibit their agglomeration or settling in a fluid medium. With the help of mechanical agitation, dispersants can also hit-.tk up agglomerates of particles to form particle suspensions. Another use of dispersants is to inhibit the growth of crystallites in a supersaturated solution. This characteristic is also known us precipitation... 

The physical properties of the solid state seen in crystals and powders of both drugs and pharmaceutical excipients are of interest because they can affect both the production of dosage forms and the performance of the finished product. Powders, as Pilpel reminded us, can float like a gas or flow like a liquid but when compressed can support a weight. Fine powders dispersed as suspensions in liquids are used in injections and aerosol formulations. Both liquid and dry powder aerosols are available and are discussed in Chapter 9 some properties of compacted solids are dealt with in Chapter 6. In this chapter we deal with the form and particle size of crystalline and amorphous drugs and the effect these characteristics have on drug behaviour, especially on drug dissolution and bioavailability. 

Suspensions are defined as the stable dispersions of fine solid particles in liquids. Due to the widespread use of suspensions in industry, accurate analysis of their fluid dynamical behavior is needed to carry out the design calculations in many flow processes. According to the theoretical considerations the fluid dynamical behavior of a suspension may depend on a very large number of factors. In this respect, material characteristics of liquids and solids in the dispersion and the composition of the mixture in terms of solid volume fraction, particle size distribution, and interactions between solid particles can be mentioned. 

Newtonian theory provides the simplest cases of viscous behavior, in which the stresses are related to the velocity gradients existing at time of the observation. For an incompressible fluid in a simple shear, such theory may be stated, according to Figure 10.1, by the first function in Table 10.1. In the most general sense, any fluid response not explainable by Newtonian theory may be termed non-Newtonian. In practice, however, non-Newtonian fluids, as opposed to Newtonian, are those in which the viscosity is not a constant value, but is a function of the imposed shear rate. The dispersions resultant of dissolving solids in liquids, are normally of non-Newtonian characteristics. In the same manner, the suspensions of finely divided solids into continuous liquid phases are usually non-Newtonian. 

Dispersion Polymerization - This technique is a heterogenous regime where a significant amount of surfactant is added to the polymerization medium. Characteristics of the process include small uniform polymer particles which may be unstable and coagulate if they are not stabilized. Hydrocarbon oil is added to the dispersion polymerization reactor to stabilize the polytetrafluoroethylene emulsion. Temperature and agitation control are easier in this mode than suspension polymerization. Polytetrafluoroethylene fine powder and dispersion are produced by this technique. 

---