Colloidal emulsions

An aqueous colloid/emulsion of rubber particles can be up to 65% solids content generally low viscosity compared to polymer solutions. Only rubbers produced by emulsion polymerisation or natural rubber can be found in this form. 

Whether there is currently a nanotechnology is a question of definition. If one asks whether there are (or are soon likely to be) commercial electronic fluidic, photonic, or mechanical devices with critical lateral dimensions less than 20 nm, the answer is no, although there may be in 10 to 20 years. There is, however, a range of important technologies—especially involving colloids, emulsions, polymers, ceramic and semiconductor particles, and metallic alloys—that currently exist. But there is no question that the field of nanoscience already exists. 

Milk is an unusual colloid in comprising oil particles suspended in water. Adding, say, olive or sunflower oil to water will not produce a stable colloid. Two layers will re-form rapidly even after vigorous shaking, with the oil floating above the water. Milk is stable because it contains an emulsifier, i.e. a compound to promote the formation of a colloidal emulsion. 

Natural rubber can be found as a colloidal emulsion in a white, milky fluid called latex and is widely distributed in the plant kingdom. The Indians called it wood tears. It was not until 1770 that Joseph Priestly suggested the word rubber for the substance, since by rubbing on paper it could be used to erase pencil marks, instead of the previously used bread crumbs. At one time 98% of the world s natural rubber came from a tree, Hevea brasiliensis, native to the Amazon Basin of Brazil which grows to the height of 120 ft. Today most natural rubber is produced on plantations in Malaysia, Indonesia, Singapore, Thailand, and Sri Lanka. Other rubber-bearing plants... 

Latex An aqueous colloidal emulsion of an elastomer (natural or synthetic) or a plastic. It generally refers to the emulsion obtained from a tree or plant or produced by emulsion polymerization. 

The so-called bi-liquid foams described by Sebba and Vincent [17-20] will not be discussed since they are not true colloidal emulsions, but resemble conventional foams more closely, possessing polyhedral cells of centimetre dimensions. 

Alba, F. Crawley, G.M. Fatkin, J. Higgs, D.M.J. Kippax, P.G., Acoustic spectroscopy as a technique for the particle sizing of high concentration colloids, emulsions and suspensions Colloids and Surfaces A Physiochem. Eng. Asp. 1999, 15, 495-502. 

Steroids are lipids found in living systems that all have the ring system shown in Figure 3.8 for cholesterol. Steroids occur in bile salts, which are produced by the liver and then secreted into the intestines. Their breakdown products give feces its characteristic color. Bile salts act on fats in the intestine. They suspend very tiny fat droplets in the form of colloidal emulsions. This enables the fats to be broken down chemically and digested. 

Table 13.1 Some food colloids emulsions, foams, and suspensions. ...

With all polarization phenomena, the flux at a definite time is always less than the original value. When steady-state conditions have been attained a further decrease in flux will not be observed, i.e., the flux will become constant as a function of time. Polarization phenomena are reversible processes, but in practice, a continuous decline in flux can be observed. Such continuous decline is a result of membrane fouling, which may be defined as the irreversible deposition of retained particles, colloids, emulsions, suspensions, macro molecules, salts, etc. on or in the membrane. This includes adsorption, pore blocking, precipitation, and cake formation. 

Figure 12. Simplified illustrations of the electrical double layer around a negatively charged colloidal emulsion droplet. The left view shows the change in charge density around the droplet. The right view shows the distribution of ions around the charged droplet. (Courtesy of L. A. Ravina, Zeta-Meter, Inc., Long Island City, NY.)...

Oil and water [oil-in-water (0/W) or water-in-oil (W/0)] emulsions are utilized for the production of nanoparticle dispersions. The colloidal emulsions are stabilized by a film of surfactants and polymers, which interact with the oil and water phases to prevent aggregation and droplet growth. These microemulsions are typically used as templates for the production of nanoparticles and solid lipid nanoparticles (SLN). 

Colloids are categorized according to the phases of their dispersed particles and dispersing mediums. Milk is a colloidal emulsion because liquid particles are dispersed in a liquid medium. Other types of colloids are described in Table 15-6 and shown in Figure 15-20. How many of them are familiar to you Can you name others ... 

C. Soluble in lower alcohols, acetic acid, and pyridine moderately soluble in dry acetone and dioxane almost insoluble in water, ether, and hydrocarbons. Depresses surface tension, forms a fairly stable colloidal emulsion in distilled water. 

Because the centrifugation forces are relatively weak for small molecules, sedimentation FFF is most applicable for molecules with molecular weights exceeding 10 . Such systems as polymers, biological macromolecules, natural and industrial colloids, emulsions, and subcelluar particles appear to be amenable to separation by sedimentation FFF. 

Plate 8 Total parental nutrition wherein up to three litres of a colloidal emulsion is administered intravenously per patient per day. Trace elements which are necessary for long-term TPjN include calcium, magnesium, iron, copper, zinc, cobalt, manganese, selenium, chromium, molybdenum, iodine, fluorine, phosphorus, chlorine, sodium, and potassium. Photograph provided by Kabi Pharmacia... 

Analysis of relaxation curves from fluids is of particular interest for the characterization of pores in rocks [Dav 1, Fori, Kle 1 ] and other porous materials such as packs of beads or grains, ceramics, zeolites, foods, colloids, emulsions, gels, suspensions, and is of interest to the retrieval of biochemical and biophysical information [Labi]. Because longitudinal and transverse relaxation rates can be significantly increased in the vicinity of solid-liquid interfaces, the relaxation behaviour of H and other nuclei of fluids confined in porous media can provide important information about porosity, pore-size distribution, and pore connectivity [Hiirl, Kiel, Kle2]. 

B.M. WC/Co B.M. Teflon B.M. polyamide contamination) industrial scale Hard + brittle Hard + abrasive Frozen or freeze-dried plant or animal tissues [ ] Soft + brittle suspensions, colloids, emulsions... 

It is particularly good for colloids, emulsions and particles. Samples separated thus far include lattices, latex aggregates, silica sols, alkyd resins, perfluorocarbon emulsions, milk, carbon particles, hematite, clay, water-borne particles, liposomes, subcellular particles, viruses, and polymerized proteins. 

Dispersions of pol5Tetrafluoroethylene are colloidal emulsions of small pol mier particles (<0.25 pm) in water which are negatively charged. They contain relatively high concentrations of PTFE, which increases their specific gravity. An estimate of solids content can be obtained from the specific gravity (Table 5.12). 

Polymer Colloids Emulsion polymerization produces monodisperse polymer spheres 50 to 500 nm in diameter by the scheme shown in Figure 11.9. Water-immiscible vinyl monomers such as styrene, acrylic esters, and methacrylic... 

Filler particles such as talc or carbon black are routinely incorporated in rubber compounds to improve mechanical properties. Guth [51] related this reinforcement effect to the Einstein viscosity law for colloidal emulsions... 

The stability of colloidal emulsions—also due to the unexplained sinic-ture—is very difficult to foresee, as particularly in mixtures for total parenteral nutrition (TPN) there are many interactions. In a. series of anictes Washington attempted to put the prediction of stability of emulsions in TPN regimes on a rational basis (183-189). To explain the stability of emulsions the following effects and theories are referred to ... 

SPBs can be prepared by surface-initiated ATRP with a variety of core particles, including organic latexes colloids emulsions, shells of shell-cross-linked micelles, and... 

C. H. Lu and S. K. Saha, Colloid emulsion of nanosized strontium bismuth tantalate powder,... 

Liquid Suspensions (Hydrosols and organosols) Colloidal emulsions (Oil/water, water/oil and microemulsions) Foams... 

Fig. 3.8. Organisation of a surfactant in an oil-in-water (0/W) colloidal emulsion. There also exist systems a little more complex than the simple surfactants (alcohol/surfactant mixtures) with the property that their co-adsorption at the O/W interface is energetically favoured (corresponding to a negative variation in free energy AG). In that case the system is thermodynamically stable and the dispersion forms spontaneously. The dispersed particles are extremely small (microemulsion) and the system remains stable indefinitely...

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