Molecularly dispersed

Starches. Starch (qv) granules must be cooked before they wiU release their water-soluble molecules. It is common to speak of solutions of polysaccharides, but in general, they do not form tme solutions because of their molecular sizes and intermolecular interactions rather they form molecular dispersions. The general rheological properties of polysaccharides like the starch polysaccharides are described below under the discussion of polysaccharides as water-soluble gums. Starch use permeates the entire economy because it (com starch in particular) is abundantly available and inexpensive. Another key factor to its widespread use is the fact that it occurs in the form of granules. 

Cold- Water Swelling Starches. Special physical treatment produces starch granules that will sweU in water without heating. Molecular dispersions can be formed by appHcation of shear to the swoUen granules. 

Acid Leveling Dyes. These are molecular dispersions at low temperatures (tme solutions) and are simple molecules. They have low affinity at neutral pH and exhibit ionic attraction at acidic pH when the wool becomes charged. They exhibit good leveling and migration behavior. Their low affinity however also results in low fastness. 

Figure 12-15. Hole mohilily in molecular dispersion of 75% (hy weighi) of TAPC in polycarbonalc as a function of (lie dearie field parametric in lempcra-lure (Kef. [56]).

In order to complete the discussion of methodical problems, we should mention two more methods of determining yield stress. Figure 6 shows that for plastic disperse systems with low-molecular dispersion medium, when a constant rate of deformation, Y = const., is given, the dependence x on time t passes through a maximum rm before a stationary value of shear stress ts is reached. We may assume that the value of the maximal shear stress xm is the maximum strength of the structure which must be destroyed so that the flow can occur. Here xm as well as ts do not depend or depend weakly on y, like Y. The difference between tm and xs takes into account the difference between maximum stress and yield stress. For filled polymer melts at low shear rates Tm Ts> i,e- fhese quantities can be identified with Y. 

PMo 12-polymer composite film catalyst [9]. This demonstrates that PM012 catalyst was not in a crystal state but in an amorphous-like state, indicating that PM012 catalyst was molecularly dispersed on the PS support via chemical interaction. As attempted in this work, it is believed that heteropolyanions (PMoi204o ) were strongly immobilized on the cationic sites of the PS bead as charge-compensating components. 

The electrokinetic processes can actually be observed only when one of the phases is highly disperse (i.e., with electrolyte in the fine capillaries of a porous solid in the cases of electroosmosis and streaming potentials), with finely divided particles in the cases of electrophoresis and sedimentation potentials (we are concerned here with degrees of dispersion where the particles retain the properties of an individual phase, not of particles molecularly dispersed, such as individual molecules or ions). These processes are of great importance in particular for colloidal systems. 

Independent self-diffusion measurements [38] of molecularly dispersed water in decane over the 8-50°C interval were used, in conjunction with the self-diffusion data of Fig. 6, to calculate the apparent mole fraction of water in the pseudocontinuous phase from the two-state model of Eq. (1). In these calculations, the micellar diffusion coefficient, D ic, was approximated by the measured self-dilfusion coefficient for AOT below 28°C, and by the linear extrapolation of these AOT data above 28°C. This apparent mole fraction x was then used to graphically derive the anomalous mole fraction x of water in the pseudocontinuous phase. These mole fractions were then used to calculate values for... 

X 10 cm by measuring molecularly dispersed water in toluene and by correcting for local viscosity differences between toluene and these microemulsions [36]. Values for Dfnic were taken as the observed self-diffusion coefficient for AOT. The apparent mole fraction of water in the continuous toluene pseudophases was then calculated from Eq. (1) and the observed water proton self-diffusion data of Fig. 9. These apparent mole fractions are illustrated in Fig. 10 (top) as a function of... 

Thereby, photogeneration of singlet oxygen molecules from the quartz surface containing molecular dispersed molecules of pentoxide... 

Polymer-bound antioxidants must be molecularly dispersed (i.e. infinitely soluble) and cannot be physically lost from the substrate. High-MW phenolic AOs are preferred for applications requiring FDA approval, minimal discoloration, and long service life at high temperatures. Antioxidants are used for protection of polymers, plastics, elastomers, foods, fuels and lubricants. 

Properly functionalised additives can react with polymer substrates to produce polymer-bound functions which are capable of effecting the desired modification in polymer properties, hence the use of the term reactive modifiers. As an integral part of the polymer backbone, reactive modifiers are useful vehicles for incorporating the desired chemical functions to suit the specialised application. Being molecularly dispersed, the problem of solubility expressed under 2 above is avoided. Implicitly, the bound-nature of the function is not subjected to the normal problems of the loss of additives from the surface which are common with both high and low molecular mass additives. The bound nature of the function must be fully defined for the conditions of service. 

The defined size ranges and limits are somewhat arbitrary since there are no specific boundaries between the categories. The transition of size ranges, either from molecular dispersions to colloids or from colloids to coarse dispersions, is very gradual. For example, an emulsion may exhibit colloidal properties, and yet the average droplet size may be larger than 1 pm. This is due to the fact that most disperse systems are heterogeneous with respect to their particle size [1-2]. 

Molecular dispersion < 1.0 nm Particles invisible by electron microscopy pass through semipermeable membranes generally rapid diffusion Oxygen molecules, potassium and chloride ions dissolved in water... 

Disperse systems can also be classified on the basis of their aggregation behavior as molecular or micellar (association) systems. Molecular dispersions are composed of single macromolecules distributed uniformly within the medium, e.g., protein and polymer solutions. In micellar systems, the units of the dispersed phase consist of several molecules, which arrange themselves to form aggregates, such as surfactant micelles in aqueous solutions. 

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