Aggregation dispersions

The term flotoflocculation is used to describe the process of aggregating dispersed oil droplets by the aid of polymeric flocculants (flocculation) then subjecting them to conventional flotation. It is also used, genericaHy, to describe situations where particles are first aggregated then floated. 

The use of ordered supramolecular assemblies, such as micelles, monolayers, vesicles, inverted micelles, and lyotropic liquid crystalline systems, allows for the controlled nucleation of inorganic materials on molecular templates with well-defined structure and surface chemistry. Poly(propyleneimine) dendrimers modified with long aliphatic chains are a new class of amphiphiles which display a variety of aggregation states due to their conformational flexibility [38]. In the presence of octadecylamine, poly(propyleneimine) dendrimers modified with long alkyl chains self-assemble to form remarkably rigid and well-defined aggregates. When the aggregate dispersion was injected into a supersaturated... 

The most popular tools for the visualization of engineered nanoparticles are electron and scanning probe microscopes. The visualization, the state of aggregation, dispersion sorption, size, structure, and shape can be observed by means of atomic force microscopy (AFM), scanning electron (SEM), and transmission electron microscopy (TEM). Analytical tools (mostly spectroscopic) can be coupled to... 

Closed, spherical, single-bilayer, 300- to 600-A-diameter surfactant and/or phospholipid aggregates dispersed in aqueous solutions. Ultrasonic dispersal of multilamellar vesicles (MLVs) or employing procedures such as French Press filtration result in SUV formation. 

Dispersants Keep contaminants of the lubricant in suspension and avoid their aggregation. Dispersants are amphiphilic molecules. Their long hydrocarbon tail helps to solubilize polar molecules in the base oil. The polar head group interacts with contaminants and facilitates the formation of (inverse) micelles around them. 

Fig. 25 a CD and UV spectra of poly n-hexyl(p-n-propoxyphenyl)silane (27) aggregates in toluene/(S)- (a solid line) or CR)-2-butanol (b dotted line)/methanol mixtures at 20 °C and b the ee purity dependency of 2-butanol to CD intensities at 354 nm of the polysilane aggregates dispersed in a ternary solvent composed of toluene/2-butanol ((S)-or CR)-form)/methanol at 20 °C... 

Magnetic biomaterials have different constraints than materials used for other applications. In vivo (in the body) applications require strict biocompatibility. In vitro (outside of the body) applications have less strict requirements, but techniques involving living cells still must consider the effect of the materials on the sample under study. In addition to biocompatibility, materials must be capable of being functionalized with one or more molecules, must retain their magnetic properties for a reasonable period of time in aqueous media with varying pH, must not be cleared too quickly from the bloodstream, and must form stable, non-aggregating dispersions [12, 13]. 

The model solutions discussed above were compared with experimental data collected using a laser diffraction particle size analyzer. Hematite was dispersed in solutions at various pH values and moderate ionic strength (0.02 M) such that aggregation rates varied from slow to fast, and aggregation was allowed to occur in quiescent solution. The aggregating dispersion was sampled over time, and data was represented in three dimensions as the change in particle size distributions over time. Figure 10a shows hematite... 

Fidder H, Wiersma DA. Exciton dynamics in disordered molecular aggregates dispersive dephasing probed by photon echo and Rayleigh scattering. J Phys Chem 1993 97 11603-11610. 

Ips typographica (bark beede) anti-aggregation (dispersal) pheromones... 

By electron microscopy the size of the primary particles in the aggregates is estimated to be about 10 nm. Particle size measurements using a nanosizer show the size of aggregates dispersed in a well wetting solvent to be in the range of 100 nm. Laser diffraction of fumed silica dispersed in air provides sizes of agglomerates larger than 5 pm. 

Although insect pheromone structures represent a myriad of chemical functionalities [6], the composite pheromones can be classified into six behaviourally functional groups sex, aggregation, dispersal (spacing or epideictic), alarm, recruitment (trail), and maturation. 

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 ... 

Semiochemicals can be placed into two distinct classes Pheromones control intraspecific interactions. These semiochemicals provide information regarding a range of behaviours including mate selection, aggregation, dispersal (alarm pheromones), oviposition and food sources (trail pheromones). Allelochemicals control interspecific interactions such as host and non-host identification by primary colonizers (plant or animal) and whether a food source is already exploited through tritrophic interactions (signals indicating the presence of primary colonizers). 

Figure 13.10 Schematic examples of the dependence of apparent viscosity >/a on the shear stress a applied for various non-Newtonian liquids. Curve (1) can represent a slightly aggregating dispersion of very small particles, (2) a solution of polymers that interact with each other to give a weak gel and hence produce a yield stress (of about 0.03 Pa), and (3) a nongelling polymer solution.

Takagi S, Yamagami T, Takeda K and Takagi T (1987) Helical configuration of lutein aggregate dispersed in liposomes of phosphatidyl choline and digalactosyldigliceride. Agric Biol Chem 51 1567-1572... 

In a block-selective solvent, the insoluble block or blocks of a copolymer agglomerate to form nanometer-sized aggregates [5,22,23]. Such aggregates disperse in the solvent and are protected from further agglomeration by the soluble block(s) that form(s) the aggregate corona. 

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