Precipitate, cohesive

Asphaltenes are obtained in the laboratory by precipitation in normal heptane. Refer to the separation flow diagram in Figure 1.2. They comprise an accumulation of condensed polynuclear aromatic layers linked by saturated chains. A folding of the construction shows the aromatic layers to be in piles, whose cohesion is attributed to -it electrons from double bonds of the benzene ring. These are shiny black solids whose molecular weight can vary from 1000 to 100,000. 

For a given slurry, the maximum filtration rate is determined by the minimum cake thickness which can be removed—the thinner the cake, the less the flow resistance and the higher the rate. The minimum thickness is about 6 mm (0.25 in) for relatively rigid or cohesive cakes of materials such as mineral concentrates or coarse precipitates like gypsum or calcium citrate. Sohds that form friable cakes composed of less cohesive materials such as salts or coal will usually require a cake thickness of 13 mm (0.5 in) or more. Filter cakes composed of fine precipitates such as pigments and magnesium hydroxide, which often produce cakes that crack or adhere to the medium, usually need a thickness of at least 10 mm (0.38 in). 

Reinforcing fillers (active) Fumed Silica (Si02) precipitated calcium carbonate (CaCOi) carbon black Thixotropic reinforcing agents (non-slump), adjustment of mechanical properties (cohesion) provide toughness to the elastomer as opposed to brittle materials. 

In some cases, so called direct plasma injection techniques may be used23 83 104 108 instead of protein precipitation for loading plasma samples onto an HPLC/MS/MS system. Some direct plasma injection systems use a column switching technique in which the plasma is loaded onto an extraction column that retains the small molecules. The other plasma components are sent to waste and the flow is switched so that the small molecules are eluted onto an analytical column that connects to the MS/MS.23 83 108 One variation of the column switching method is turbulent flow chromatography commercialized by Cohesive Technologies (now part of Thermo, San Jose, CA).23... 

Because the instability of the N-oxide metabolite, which was subjected to decomposition during sample preparation (solvent evaporation during offline SPE), online SPE LC/MS became the method of choice for the application. Hsieh et al. (2004) built a system with two TFC cartridges and one analytical column, and another system with two TFC cartridges and two analytical columns for GLP quantitative bioanalysis of drug candidates. A Turbo C18 (50 x 1.0 mm, 5 /.mi, Cohesive Technologies), an Xterra MS C18 (30 x 2.0 mm, 2.5 /mi), and a guard column were used. Protein precipitation preceded injection. The cycle times for the two systems were 0.8 and 0.4 min. 

To keep the precipitating polymers in the dispersed state throughout the polymerization, requires steric stabilizers. This problem is classically tackled via copolymerization with fluoroalkylmethacrylates or the addition of fluorinated surfactants, both being only weak steric stabilizers. DeSimone el al. also applied a fluorinated block copolymer,9 proving the superb stabilization efficiency of such systems via a rather small particle size. One goal of the present chapter is therefore an investigation of our fluorinated block copolymers as steric stabilizers in low-cohesion-energy solvents. 

These block copolymers can act as effective steric stabilizers for the dispersion polymerization in solvents with ultralow cohesion energy density. This was shown with some polymerization experiments in Freon 113 as a model solvent. The dispersion particles are effectively stabilized by our amphi-philes. However, these experiments can only model the technically relevant case of polymerization or precipitation processes in supercritical C02 and further experiments related to stabilization behavior in this sytem are certainly required. 

When the attachment of the substrate to the precipitate to be formed is strong, the clusters tend to spread themselves out on the substrate and form thin surface islands. A special limiting case is the formation of a surface nucleus on a seed crystal of the same mineral (as in surface nucleation crystal growth). As the cohesive bonding within the cluster becomes stronger relative to the bonding between the cluster and the substrate, the cluster will tend to grow three-dimensionally (Steefel and Van Cappellen, 1990). 

The difference in properties when the aliphatic chain of amine oxide contains more than 14 carbons is attributed to the mismatch of the hydrophobic chain with that of the SDS. The extra terminal segment results in a disruptive effect on the packing of the surface active molecules. The observed association behavior in the case of 0 2 C14-DAO with SDS is then also due to the maximum cohesive interaction between hydrocarbon chains in addition to the reduced electrostatic repulsion in the head groups. Solubilization of the 1 1 association is also determined by this chain length compatibility effect which may contribute to the absence of visible precipitation in C12/C12 and C2 2/ -14 mixtures. Chain length compatibility effects in different systems have been discussed by other investigators (24,25,26). 

A variety of admixtures and additives are used to accelerate strength development, cohesiveness, bond, freeze-thaw and abrasion resistance, and to reduce rebound. Most of the accelerating admixtures used probably act by precipitating as insoluble hydroxides or other salts - a form of false set. Conduction calorimetric studies show that their main effect on early strength is due to the action on the C3 A fraction of the cement. The reaction of... 

After ethanol precipitation, digest the pTDl vector with another restriction endonuclease to produce the same cohesive end as that introduced in the C-terminal primer. 

Such small particles usually are generated by air-jet micronization and less frequently by controlled precipitation or spray drying. As bulk powder, they usually tend to be very cohesive and exhibit poor flow and insufficient dispersion because of large interparticle forces such as van der Waals and electrostatic forces (Zeng et al. 2001 Podczeck 1998 Hickey et al. 1994). The control of sufficient powder flow and deaggregation (dispersion) is thus of utmost importance to ensure efficient therapy with a dry-powder aerosol. Two different formulation approaches are used currently in marketed DPI preparations to fulfill the requirements. Most often, coarse particles of a pharmacologically inactive excipient, usually a-lactose monohydrate, are added that act as a carrier and provide sufficient powder flow to the mixture. Other carbohydrates, amino acids, and phospholipids have been suggested frequently (Crowder et al. 2001). 

The class of methods used for preparing colloidal dispersions in which precipitation from either solution or chemical reaction is used to create colloidal species. The colloidal species are built up by deposition on nuclei that may be of the same or different chemical species. If the nuclei are of the same chemical species, the process is referred to as homogeneous nucleation if the nuclei are of different chemical species, the process is referred to as heterogeneous nucleation. See also Dispersion Methods. An empirical or qualitative term referring to the relative ease with which a material can be deformed or made to flow. It is a reflection of the cohesive and adhesive forces in a mixture or dispersion. See also Atterberg Limits. 

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