Aggregates and structure

Byers J T, Meeting of the Rubber Division, ACS, CarPOn DlaCK anU tO apply tUlS JcnOWi- 

In the case of carbon black, the aggregates are distributed in the matrix rather than individual particles, it is therefore important in some applications (e.g., conductive plastics) to evaluate the distance between these aggregates. It is now possible to measure these distances by atomic force microscopy coupled with straining device. There is a linear relationship between the parallel distance between aggregates dispersed in SBR and strain value. For 10 phr of N 234, the mean distance between aggregates varied in a range from 1.85 to 3.42 jm. For practical purposes, a modified equation [5.4] is used to determine the interaggregate distance  

This is a complex area of investigations and far from being complete. Until mathematical criteria characterizing the structure are developed, the available quality control and research data is the only source of information that can be used to select carbon black for specific application. 

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Emerson WW, Foster RC, Oades JM (1986) Organo-mineral complexes in relation to soil aggregation and structure. In Huang PM, Schnitzer M (eds) Interactions of soil minerals with natural organics and microbes. Soil Sci Soc Am, Madison, WI, USA, pp 521-548... 

Once particles have been produced, it is possible to elucidate reasons for the observed variations in their habits. Specifically, different geometries of hematite particles were explained by the complex mechanisms of their formation, which consist of first precipitating akageneite precursors, subsequently undergoing controlled aggregation and structural transformation into hematite (95). Indeed, it was indicated that the morphological properties of the precursors were responsible for different shapes of the final products. 

An extension of the coupled-cluster approximation to the non-equilibrium classical systems [43-45] has allowed to study asymptotics of bimolecular reactions. It resulted in a rather unexpected conclusion that now the generally-accepted time dependence of the A+B —> 0 reaction for d = 3, n(t) oc f-3/4, is only the pre-asymptotic stage, with the true asymptotics n(t) oc f 1 Similar technique was used also for the study of diffusion-limited aggregation and structure formation processes [47],... 

Second, there are technical applications where amphiphile aggregates and structures are needed to promote a specific effect, while circumstances may prevent the particular use of water due to certain reactions, corrosion, or other specific... 

Summarizing our results on highly aggregated PECs, we can state that at nonstoichiometric mixing ratios electrostatically stabilized particles in the nm scale with controlled levels of aggregation and structural density can be prepared. These particles should be of interest as potential carrier systems for drugs and enzymes, because they offer an easy way to incorporate charged material by Coulomb interactions. 

The chief advantages usually realized from minimum tillage are that it (1) reduces compaction (2) lessens damage to soil aggregation and structure as cultivation is reduced ... 

Flores-Ferntodez, G.M., Sold, R.J., Griebenow, K. (2009) The relation between moisture-induced aggregation and structural changes in lyophilized insulin. J Pharm Pharmacol, 61 (11), 1555-1561. 

To obtain a final product with larger ultimate particles, before the particles are aggregated, it may be desirable to increase their size beyond that reached by spontaneous Ostwald ripening which is around 5 nm at 2S C and 10 nm at 80-I00 C. Ways of growing discrete particles have been described in Chapter 4 and the procedure when making silica from acid and sodium silicate was particularly discussed (402). This or another equivalent procedure is needed as an intermediate step prior to aggregation and structural reinforcement if the final product is to have a particle size much larger than 12-15 nm. 

The data on molecular mobility obtained from NMR measruements may be used for estimation of the structure of the adsorption layer for adsorption from mixtures.For the miscible system polycarbonate-fractions of immobilized segments have been estimated for various concentration of solution, i.e., for various points on isotherm. To characterize the structrue of the adsorption layer, we have used the fraction of immobilized segments, p, assuming that they correspond to the fraction of bound segments. In this way, we estimate the structrue of an adsorption layer at various states of aggregation and structure of solution (various concentrations of solution). In the case of a molecular-aggregative adsorption, the isotherms exhibit an absence of satruation. 

Chapters 10 and 11 are devoted entirely to aspects of colloid stabihty. First, the essential concepts of the electrical and van der Waals forces between colloid particles are presented with special emphasis on the concepts of the zeta potential, double-layer thickness and Hamaker constants. Then, the DLVO theory for colloidal stability is presented. This is a major tool in colloid chemistry and we discuss how stability is affected by manipulating the parameters of by the classical DLVO theory. Chapter 11 closes with a presentation of kinetics of colloid aggregation and structure of aggregates. Chapters 12 and 13 are about emulsions and foams, respectively - two important categories of colloid systems where DLVO and other principles of colloid and surface science are apphed. In this case, DLVO is often not sufficient. Steric forces and solvation effects are not covered by the classical DLVO and their role in colloid stabihty is also discussed in Chapter 12. 

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