Coating with Surfactant

Heux et al. [20] have prepared suspensions of cotton and tunicate nanocrystals in nonpolar solvents, using surfactant as a stabilizing agent. The surfactant, a phosphoric ester of a poly(ethylene oxide) nonylphenyl ether, was added to aqueous 

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Figure C2.3.11 Key surfactant stmctures (not to scale) in emulsion polymerization micelles containing monomer and oligomer, growing polymer particle stabilized by surfactant and an emulsion droplet of monomer (reservoir) also coated with surfactant. Adapted from figure 4-1 in [67],...

Preparation 1) E.R. Rogers et al, Coated Ultrafine Ammonium Perchlorate Particles , USP 3954526(1976) CA 85,96630(1976) [Claimed is the prepn of AP particles of sub-micron size for propints by soln in a mixt of two volatile liquids, the second being less volatile than the first, and a non-AP solvent. The first liq is evapd to form an AP suspension in the second. The AP is subsequently coated with surfactants or polymers which are partially soluble in the second solvent, and this solvent is evapd to yield a powder or slurry. The average coated AP particle is 0.52 to 0.99 microns in... 

VCM and an emulsifier. These components are circulated through a mixing pump (homogeniser) which causes the mixture to disperse into very fine droplets, before being placed in the autoclave. The droplets are coated with surfactant which stabilises them during the reaction. Initiation and polymerisation occur within the droplets. After polymerisation, the autoclave contains a stable dispersion of fine particles of PVC in water. Thereafter the subsequent operations for obtaining the final product are similar to the emulsion polymerisation process. 

For example. Ilium et al. demonstrated that if microparticles were coated with surfactant block copolymers (e.g., Pluronic A-B-A polymers, where A is PEG and B is poly (propylene oxide) (PPO)), then the microparticles avoided uptake by the liver and therefore stayed in the blood circulation for long periods... 

The properties of ferrofluids seem now to be well understood, and numerous applications have been found. Unlike ER and MR fluids, particles in ferrofluids have permanent (magnetic) dipoles thus the particles must be small, around 10 nm, to prevent permanent clumping. If single-domain ferromagnetic particles this small are made, and coated with surfactant to prevent clumping by van der Waals forces, stable ferrofluids can be made whose properties are readily predicted from theory. 

The three surfactants commonly used in chlorofluro-carbon (CFC)-based MDI formulations are insoluble in the CFC-replacement propellants, hydrofluoroalk-ane (HFA) 134a and HFA 227. Possible formulation alternatives involve the use of an adjuvant such as ethanol to aid dissolution of the surfactant or a novel surfactant. Several companies have investigated novel materials among which are fluorosurfactants, poly-oxyethylenes and drugs coated with surfactant. ... 

Troster SD, Muller U, Kreuter J. Modification of the body distribution of poly(methylmethacrylate) nanoparticles in rats by coating with surfactants. Int J Pharm 1990 61 85-100. 

Maintenance of contact with neural cells is integral to the performance of the implant device and the use of biosynthetic CP coatings will potentially improve the long-term efficacy of such devices. Limited research is available on the long-term interactions of CPs with neural tissue. Two studies by the Martin research group at Michigan University have examined the chronic performance of nanostructured PEDOT on neural recording electrodes [52,144]. The microelectrode arrays coated with surfactant-templated PEDOT and... 

We have seen above that surface-force measurements provide important information about interactions between solid hydrophobic surfaces coated with surfactants and polymers, and that some of the informa tion obtained is directly relevant for oil-in-water emulsions. However, the details of the interaction pro files are expected to be different for liquid hydrocarbon droplets coated with the same molecules as the model solid surfaces. In particular, the coalescence behavior of the emulsion droplets cannot be modelled. It is even more difficult to make a solid model surface that mimieks the behavior of water-in-oil emulsions. At present, the best one can do is to use a polar surface that attracts the polar part of the emulsifier. In fliis way the orientation of the emulsifier on the model sur face and at the water-in-oil emulsion surface will be the same. This will allow us to draw some eonclusions about how polar solid surfaces coated with emulsifiers interact across oil, but care should be taken when using such results to draw conclusions about water-in-oil emulsions. 

Bonini C, Heux L, CavaiUe JY, Lindner P, Dewhurst C, Terech P. Rodhke cellulose whiskers coated with surfactant a small-angle neutron scattering characterization. Langmuir 2002 18 3311-3314. 

Relatively, efficient microemulsion formulations, typically those with less than 20 wt% surfactant, differ significantly from non-ideal solutions in that they contain a distinct type of microstructure, i.e. topologically ordered oil and water domains coated by surfactant. The microstructures within microemulsions typically range from 3 to 100 nm in size, and fluctuate rapidly in time. As the oil-to-water ratio in microemulsion phases is increased, many experimental studies indicate that a continuous progression of microstructures is observed. At low concentrations of oil, droplets of oil, coated with surfactant, swim in a continuous water domain (an oil-in-water microemulsion). As the concentration of oil is increased, the spherical droplets form oblong and globular structures. At intermediate ratios of oil to water (near 50/50), a so-called bicontinuous structure of oil and water domains is observed (12). As a... 

Fig. 34.11 Force-distance curves between two NPs with diameter d, coated with surfactant layers having separatirui s between chains of length L [18]. Thermodynamic self-assembly can be achieved when Iruig-range vdW attraction (red) is countered by short-range steric repulsion (green), which gives rise to a secondary minimum that defines the optimum distance between NPs in their self-assembled state (Reprinted with pmnission from the Royal Society of Chemistry)...

Another mechanism important in foam stability is the Gibbs-Marangoni effect, and this plays a role in preventing catastrophic thinning of the fluid films and subsequent bubble collapse. Consider two adjacent air bubbles in a foam, divided by a fluid film coated with surfactant molecules. As the bubbles grow, the dividing film will increase in area and become stretched. This means that the distribution of surfactant molecules... 

To find out why the hydrophilic platelets were located at the interface between a hydrophilic polymer and a hydrophobic continuous phase in the inverse latexes, cryo-TEM was used to examine the locations of the platelets in the starting inverse emulsions. Conventional TEM requires dried samples and cannot be used to characterize the starting inverse emulsions containing clay platelets. We examined a model inverse emulsion comprising water, cyclohexane and clay particles, with Span-80 as the surfactant. In the absence of clay particles, the cryo-TEM image showed that water droplets of 100-200 nm in diameter were coated with surfactant molecules. The surfactant-stabilized water droplets appeared to bundle together and formed cauliflower-like structures. When either LRD or MMT was added to the inverse emulsion, the cauliflowerlike structure appeared to remain intact, but the clay platelets were located at the interface between the water droplets and cyclohexane, not inside the water... 

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