Bimodal distribution of particles

The optimum particle size lies in the range 0.1-10 /um and depends on the interparticle distance that must be lower than a critical value. The claim about the better effect achieved by the generation of a bimodal distributions of particle sizes has yet to be proved. 

The whitening developed in the 95/5 and 90/10 blends with the smallest particles (Figure la and lb) appears to be less than that in the 80/20 and 75/25 blends in which a bimodal distribution of particle sizes was observed (Figures lc and Id). These observations indicate that crazing is more pronounced in the blends with the largest particles. 

Figure 6.3 Relative viscosity as a function of the fraction of large spheres in a bimodal distribution of particle sizes with a 5 1 ratio of diameters, at various total volume percentages of particles. The arrow P Q illustrates the 50-fold reduction in viscosity that occurs when monosized particles in a 60 vol% suspension are replaced by a 50-50 mixture of large and small spheres. The arrow P S shows that if monosized spheres are replaced by a bimodal size distribution, the concentration of spheres can be increased from 60% to 75% without increasing the viscosity. (Reprinted from Barnes et al., An Introduction to Rheology (1989), with kind permission from Elsevier Science - NL, Sara Burger-hartstraat 25, 1055 KV Amsterdam, The Netherlands.)...

Figure 8.28 shows the pore size distributions for the PS formed on highly doped / -Si at different current densities." For the PS formed on heavily doped silicon, the pores at a given HF concentration have a narrower distribution at lower current at a given current density, the distribution is narrower at lower HF concentrations. A bimodal distribution of pore diameter is gena-ally associated with two-layer PS on lowly doped / -Si and iUmninated n-Si. The PS formed on p-Si has also been found to have a bimodal distribution of particles sizes small spherically shaped particles with a diameter of a few nanometers and large cylindrically shaped particles oriented with their axis perpendicular to the surface.The distribution of pore size with multiple peaks may be attributed to the fact that PS may have a surface micropore layer and smaller branched pores. Due to the hierarchical structure of the branched pores, the distribution of pore diameters for highly branched PS is found to be fractal-like. ° ... 

It is possible to obtain a bimodal distribution of final particles median diameter (distribution with two maxima), by seeded radical polymerisation. For example, if a polymer polyol having particle diameter of 0.3-0.6 pm is added to the poly ether before the radical polymerisation, after the normal polymerisation of the vinylic monomers, polymer polyols with a bimodal distribution of particles are obtained. As a general rule, a bimodal distribution leads to lower viscosities than an unimodal distribution of particle diameters, at the same solid content [32]. This is a method to obtain high, solid polymer... 

A PIPA polyol with a bimodal distribution of particle diameter is obtained by seeded polyaddition reaction [80]. 

If a PIPA polyol with 10% solids is used as initial polyol and to this polyol are added TEOA and TDI to obtain a PIPA polyol with 20% solids, a polymer polyol with a bimodal distribution of particle diameter is obtained. The solid particles from the initial polyol act as seeds and the diameter increases, beginning with the initial diameter of these particles and big particles result. By the reaction of TEOA with TDI new particles are also formed, which have smaller diameters. The global result is a bimodal distribution of particle diameters [80]. 

Particles can be monodisperse, or possess a certain distribution of sizes—wide, narrow, bimodal, and so on. Distribution can be irregular, typically a mix of particles of different sizes. This property of a particle mix largely depends on milling technology and classihcation (screening) of particles. A wide distribution or a bimodal distribution of particles of a mineral hller can be benehcial because it can provide a better packing density of particles in the matrix. Particle size distribution can affect viscosity of the hot melt. 

For example, in a recent work (13), ion exchange was proposed as a technique to remove emulsifier from latexes for electron microscopy, to improve the quality of the electron micrographs. The poly(vinyl chloride-co-ethyl acrylate) latex subjected to ion exchange was comprised of a bimodal distribution of particle sizes the average... 

Polymerizations with SSC (2). Previously NaSS-styrene copolymer latexes have been made, but <3% of NaSS could be incorporated without simultaneous formation of a soluble polyelectrolyte or a bimodal distribution of particle sizes (15-17), Hence, a lipophilic monomer that is freely miscible with styrene and VBC must be employed in order to achieve a high charge density styrenesulfonate latex. 

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