Particles surface chemistry

As already mentioned, the first step in any heterogeneous catalytic reaction is the adsorption of a gas molecule onto a solid surface. Adsorption heat measurements can provide information about the adsorption process not available using other surface analytical tools. For example, differential heat measurements can provide valuable insights into sites distribution on the catalyst surface as well as quantitative information on the changes in catalyst particle surface chemistry that result from changes in particle size or catalyst support material [148-150],... 

The content of amorphous phase and the small size of spherulites lead to an improvement of the fracture toughness of Polypropylene [16]. In presence of mineral filler, the particle surface chemistry can induce some specific microstructural characteristics of the PP matrix parameters such as degree of crystallisation, spherulite size, and p phase content (a/p ratio) [16]. 

With CaC03, the spherulite size is significantly reduced (Ds = 10-15 pm) and the particle surface chemistry induces some specific microstructural characteristics of the PP matrix small size surface treated CaC03 particles promote formation of the p phase. Without surface treatment, CaC03 has a nucleating effect the degree of crystallisation is increased by about 20%(X(. = 65%). 

Capillary forces develop when liquid bridges are formed in small gaps between two surfaces. Above a critical relative humidity, capillary forces are the dominant attractive force between aerosol particles [269,270]. The magnitude of this force depends on other parameters as well, such as particle surface chemistry and size. For two particles attached by a liquid bridge, the adhesive force is [260] ... 

See particle surface chemistry colloid chemistry sedimentation. 

Particles surface chemistry also plays a role in aging processes. Beyond the lithiation/delithiation mechanisms within the bulk of the particles leading to the phases described above, the particles surfaces undergo liieir own... 

Another interesting challenge remains in the area of describing the interactions. In the above studies, all interactions between particles and lipids were parameterized via their short-range potential. Moreover, particle surface chemistry was assumed to be uniform. It is possible to envision a variety of more interesting possibilities. One such possibility would include Janus or patchy particles, where the surface chemistry is nonuniform (there is a lateral phase separation into more hydrophobic and more hydrophilic areas). Very recently, Alexeev, Uspal and Balazs [75] used DPD simulations to study this problem, and some representative results of their... 

The true answer to this question is that everything depends on the particle size (and shape but, for simplidty, we concentrate on spherical partides here). If particle sizes are well in excess of characteristic polymer dimensions (Jip SOnm), particles would always aggregate and likely precipitate thus, the system would separate into three phases A-polymer-rich, B-polymer-ridi, and partide-rich. (Note that in the particle-rich phase, interstitial volume needs to be occupied by the polymer whether this is A-polymer, B-polymer, or a mixture of A and B would depend on the particle surface chemistry.) On the other hand, partides that are sufHdently small (Jip < 10 nm) can uniformly disperse in a polymer matrix, provided that van der Waals interactions between the particle and the polymer are not unfavorable. 

Note that the influence of particle surface chemistry is taken into account by means of introducing simple Flory-Huggins parameters between the particle and polymers... 

Obtaining ceramic parts, with satisfactory properties in a reproducible way by slip casting requires a judicious choice of the grain size and the control of the particle surface chemistry. The rheological behavior and the viscosity of the suspensions in fact depend directly on the grain size of the powders, the inter-particle interactions (state of dispersion) and the particle concentration. 

In order to incorporate the shape of the p>articles (e.g. cylinders) and the interaction between the particles, extensions of this Maxwell model were later developed by (Hamilton and Grosser, 1962) and (Hui et al., 1999). However, these classical models were found to be unable to accurately predict the anomalously high thermal conductivity of nanofluids (Murshed et al., 2008a). Thus, researchers have proposed several mechanisms to explain this phenomenon. For example, (Kebflnski et al., 2002) systematized the four different mechanisms for heat transfer to explain these enhancements, namely (i) Brownian motion of the nanoparticles (ii) liquid layering at the liquid/ particle interphase, (iii) the nature of the heat transport in the nanoparticles and (iv) the effect of nanoparticle clustering. From the analysis made in an exhaustive review paper on nanofluids (Murshed et al., 2008a) and other publications cited, therein, it is our belief that the effect of the particle surface chemistry and the structure of the interphase partide/fluid are the major mechanisms responsible for the unexpected enhancement in nanofluids. 

While the confirmation of the predicted long-range dispersion attraction between surfaces in air has been a major experimental triumph, the forces between particles in solution are of more general interest in colloid and surface chemistry. The presence of a condensed medium between the surfaces... 

A very important but rather complex application of surface chemistry is to the separation of various types of solid particles from each other by what is known as flotation. The general method is of enormous importance to the mining industry it permits large-scale and economic processing of crushed ores whereby the desired mineral is separated from the gangue or non-mineral-containing material. Originally applied only to certain sulfide and oxide ores. 

Mlcrofiltra.tlon, Various membrane filters have been used to remove viral agents from fluids. In some cases, membranes which have pores larger than the viral particle can be used if the filtration is conducted under conditions which allow for the adsorption of the viral particle to the membrane matrix. These are typically single-pass systems having pore sizes of 0.10—0.22 lm. Under situations which allow optimum adsorption, between 10—10 particles of poHovims (28—30 nm) were removed (34—36). The formation of a cake layer enhanced removal (35). The titer reduction when using 0.10—0.22 p.m membrane filters declined under conditions which minimized adsorption. By removal standards, these filters remove vimses at a rate on the low end of the desired titer reduction and the removal efficiency varies with differences in fluid chemistry and surface chemistry of viral agents (26). 

The properties of fillers which induence a given end use are many. The overall value of a filler is a complex function of intrinsic material characteristics, eg, tme density, melting point, crystal habit, and chemical composition and of process-dependent factors, eg, particle-si2e distribution, surface chemistry, purity, and bulk density. Fillers impart performance or economic value to the compositions of which they are part. These values, often called functional properties, vary according to the nature of the appHcation. A quantification of the functional properties per unit cost in many cases provides a vaUd criterion for filler comparison and selection. The following are summaries of key filler properties and values. 

In addition to surface area, pore size distribution, and surface chemistry, other important properties of commercial activated carbon products include pore volume, particle size distribution, apparent or bulk density, particle density, abrasion resistance, hardness, and ash content. The range of these and other properties is illustrated in Table 1 together with specific values for selected commercial grades of powdered, granular, and shaped activated carbon products used in Hquid- or gas-phase appHcations (19). 

Apart from manifold structures, carbons can have various shapes, forms, and textures, including powders with different particle size distributions, foams, whiskers, foils, felts, papers, fibers [76, 77], spherical particles [76] such as mesocarbon microbeads (MCMB s) [78], etc. Comprehensive overviews are given, for example in [67, 71, 72], Further information on the synthesis and structures of carbonaceous materials can be found in [67, 70, 72, 75, 79]. Details of the surface composition and surface chemistry of carbons are reviewed in Chapter II, Sec. 8, and in Chapter III, Sec. 6, of this handbook. Some aspects of surface chemistry of lithiated carbons will also be discussed in Sec. 5.2.2.3. 

Fig. 15-5 Comparative adsorption of several metals onto amorphous iron oxyhydroxide systems containing 10 M Fej and 0.1 m NaNOs. (a) Effect of solution pH on sorption of uncomplexed metals, (b) Comparison of binding constants for formation of soluble Me-OH complexes and formation of surface Me-O-Si complexes i.e. sorption onto Si02 particles, (c) Effect of solution pH on sorption of oxyanionic metals. (Figures (a), (c) reprinted with permission from Manzione, M. A. and Merrill, D. T. (1989). "Trace Metal Removal by Iron Coprecipitation Field Evaluation," EPRI report GS-6438, Electric Power Research Institute, California. Figure (b) reprinted with permission from Balistrieri, L. et al. (1981). Scavenging residence times of trace metals and surface chemistry of sinking particles in the deep ocean, Deep-Sea Res. 28A 101-121, Pergamon Press.)...

Balistrieri, L., Brewer, P. G. and Murray, J. W. (1981). Scavenging residence times of trace metals and surface chemistry of sinking particles in the deep ocean. Deep-Sea Res. 28A, 101-121. 

The formation of ordered two- and three-dimensional microstructuies in dispersions and in liquid systems has an influence on a broad range of products and processes. For example, microcapsules, vesicles, and liposomes can be used for controlled drug dehvery, for the contaimnent of inks and adhesives, and for the isolation of toxic wastes. In addition, surfactants continue to be important for enhanced oil recovery, ore beneficiation, and lubrication. Ceramic processing and sol-gel techniques for the fabrication of amorphous or ordered materials with special properties involve a rich variety of colloidal phenomena, ranging from the production of monodispersed particles with controlled surface chemistry to the thermodynamics and dynamics of formation of aggregates and microciystallites. 

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