Fillers particle complexity

Another interesting innovation is that developed by the Malaysian Rubber Producers Research Association. In this case the coupling agent is first joined to a natural rubber molecule involving an ene molecular reaction. The complex group added contains a silane portion which subsequently couples to filler particles when these are mixed into the rubber. 

Two points have to be stressed before considering the measurement of morphology. The first point to make in discussing filler morphology is that, except for rare instances such as monomodal glass spheres, the morphology of filler particles is complex and they will have a distribution of shapes and sizes which cannot be expressed as a single parameter. 

This paper is devoted to the study of a part of the complex phenomena of reinforcement, namely the behavior of the host elastomer in the presence of filler particles. The results of solid state NMR experiments and some other methods for filled PDMS are reviewed. The short-range dynamic phenomena that occur near the filler surface are discussed for PDMS samples filled with hydrophilic and hydrophobic Aerosils. This information is used for the characterization of adsorption interactions between siloxane chains and the Aerosil surface. Possible relations between mechanical properties of filled silicon rubbers on the one hand and the network structure and molecular motions at flie PDMS-Aerosil interface on the other hand are discussed as well. 

Composite density can be expected to vary because of the uneven distribution of filler particles in the manufactured product. This is very typical of the injection molding process where filler is distributed in a complex pattern of flow. In glass reinforced polystyrene parts, manufactured by injection molding, the density varied between 0.9 and 1.4 g/cm depending on the process conditions and locations Ifom which the sample was taken. ... 

Filler particles generated in situ can be perceived as ideally distributed within the matrix. Experimental studies show that the situation is more complex. Polyfdimethyl siloxane) network was swollen to equilibrium in tetraethyl-orthosilicate which was then hydrolyzed to produce an in situ filler. Such an experiment gives the almost ideal conditions of uniform distribution because both matrix and the filler precursor are chemically similar. There are numerous factors which affect how uniformly a filler is distributed. These include ... 

Polymer blends and alloys have more complex behavior in the presence of fillers than the binary mixtures of polymer and filler. The same factors, such as filler distribution, filler-matrix interaction, filler-matrix adhesion, particle orientation, nucleation, chemical reactivity, etc. have influence on properties, but this influence is complicated by the fact that there are two or more polymers present which compete for the same filler particles. These complex interactions result in many interesting phenomena discussed below. 

Hetero-coagulation This mechanism involves adsorption of oppositely charged particles, e.g., complexes of resin acids and aluminum sulfate, on the surfaces of fibers and filler particles. Hetero-coagulation is sensitive to soluble anionic wood polymers and electrolytes, with which cationic sizing particles, preferentially interact. 

Up to this point only the surface chemistry and size of the primary filler particles have been examined. However, important evidence exists that these particles are not randomly distributed throughout the elastomeric matrix. Indeed, much evidence shows that a complex state of aggregation is important for reinforcement in both carbon black and silica fillers. Two levels of structure have been identified in reinforcing fillers beyond the... 

In industrial practice it may be important to use mixtures of filler particles not only of spheroidal shape (as discussed above) but also of different shapes, e.g., filling and reinforcing polymer with CaCOs particles and glass fibers. The theoretical basis for optimization of such systems was developed by Wieckowski and Streg (1966) and later by MUewski (MUewski 1973, 1977, 1978 Milewski and Katz 1987). These studies are also important for polymer blends where at concentrations exceeding the percolation threshold the morphology is complex, comprising spheres, fibers, and lamellas. 

Not unexpectedly, Figure 1 shows that the behavior of p near the surface of the filler particles is qualitatively similar to that found for polymer melts near planar solid surfaces [22-24], i.e. it is characterized in all cases by a series of maxima and minima of progressively decreasing intensity with a periodicity approximately 0.8<7. This is true in particular for system Mg,10, in which p reaches its bulk value within approximately 2a from the surface of the particles, as found near planar solid surfaces. The behavior is quite different in the other two cases. In fact, the curve for system Mi6,36 shows a monotonous decrease following the initial series of maxima and minima, and the value of p for r = 20less than unity, while the curve for system Mg,50 shows a complex behavior characterized by the superposition of the series of maxima and minima with periodicity 0.8a with a second series of broad maxima and minima with a periodicity approximately 4complex behavior is observed for the other systems studied, such that intrinsically different p curves are obtained for different systems. In particular, the complexity of the curves is found to increase with increasing size and volume fraction of the filler. 

The next level of problems of equilibrium thermodynamics involve more complex properties, such as the tensorial mechanical properties described by compliance and stiffness tensors, as well as those entailing interactions between two or more phases. The latter properties include surface tension as well as phase separation and equilibria. There is great interest in using simulations to probe polymer behavior and properties in environments that are not readily accessible to measurement, such as those encountered in the confined spaces between filler particles. 

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