Colloids core micelles

The hard-core reverse micelles considered in this chapter are composed of an amorphous Ca (Mg) carbonate (or borate) colloidal core surrounded by benzensulfonate, phenate or salicylate molecules strongly bonded to the colloidal... 

Synthesis of oil soluble micellar calcium thiophosphate was performed in a one-step process involving the reaction of calcium oxide, tetraphosphorus decasulfide and water in the presence of an alkylaryl sulfonic acid. This product could be defined as a calcium thiophosphate hard-core surrounded by a calcium alkylarylsulphonate shell in accordance with a reverse micelle type association in oil. Three micellar products with the same chemical nature core were prepared, each with different core/shell ratio of 0.44, 0.92 and 1.54. Better performances are expected with products of higher core/shell ratios. The antiwear performance of micellar calcium carbonates is directly linked to the size of the mineral CaC03 colloidal particles. At a concentration of 2 % micellar cores, no antiwear effect is observed whatever the micellar size. At an intermediate concentration of 4 % of micellar cores, the wear scar diameter is clearly dependent on the micellar size, slipping from 1.70 mm to 1.10 mm, then to 0.79 mm when the core diameter moves from 4.37 nm to 6.07 nm, then to 6.78 nm. Size dependence is increased at a concentration of 5 % in colloidal cores. This clearly confirms the size dependence of the micellar cores on their antiwear performance (Delfort et al.,... 

Micellar dispersions, which contain micelles along with individual surfactant molecules, are the typical examples of lyophilic colloidal systems. Micelles are the associates of surfactant molecules with the degree of association, represented by aggregation number, i.e. the number of molecules in associate, of 20 to 100 and even more [1,13,14]. When such micelles are formed in a polar solvent (e.g. water), the hydrocarbon chains of surfactant molecules combine into a compact hydrocarbon core, while the hydrated polar groups facing aqueous phase make the hydrophilic shell. Due to the hydrophilic nature of the outer shell that screens hydrocarbon core from contact with water, the surface tension at the micelle - dispersion medium interface is lowered to the values othermodynamic stability of micellar systems with respect to macroscopic surfactant phases. 

Voets IK, Keizer DA, Cohen Stuart MA (2009) Complex coacervate core micelles. Adv Colloid Interface Sci 147-148 300-318... 

Brzozowska AM, de Keizer A, Norde W, Detremblenr C, Cohen Stuart MA (2010) Grafted block complex coacervate core micelles and their effect on protein adsorption on silica and polystyrene. Colloid Polym Sci 288 1081-1095. doi 10.1007/s00396-010-2228-4... 

Brzozowska AM et al (2009) Reduction of protein adsorption on silica and polystyrene surfaces due to coating with complex coacervate core micelles. Colloids Surf A 347 146-155. doi 10.1016/j.colsurfa.2009.03.036... 

Force curves measured between (A) silica (a) and polystyrene (b) substrates coated with C3M-PEO204/PAA139 and a silica probe at 10 mM NaCl, pH 7 (B) silica (a) and polysulfone (b) substrates coated with C3M-PVA445/P2MVPI228, and a silica probe at 10 mM NaCl, pH 7. Closed symbols correspond to approach and open to retraction. C3M corresponds to complex coacer-vate core micelles. (Reproduced from Brzozowska, A. M., et al.. Journal of Colloid and Interface Science, 353,380-91,2011. With permission from Elsevier.)... 

The next two chapters concern nanostructured core particles. Chapter 13 provides examples of nano-fabrication of cored colloidal particles and hollow capsules. These systems and the synthetic methods used to prepare them are exceptionally adaptable for applications in physical and biological fields. Chapter 14, discusses reversed micelles from the theoretical viewpoint, as well as their use as nano-hosts for solvents and drugs and as carriers and reactors. 

Finally, we have designed and synthesized a series of block copolymer surfactants for C02 applications. It was anticipated that these materials would self-assemble in a C02 continuous phase to form micelles with a C02-phobic core and a C02-philic corona. For example, fluorocarbon-hydrocarbon block copolymers of PFOA and PS were synthesized utilizing controlled free radical methods [104]. Small angle neutron scattering studies have demonstrated that block copolymers of this type do indeed self-assemble in solution to form multimolecular micelles [117]. Figure 5 depicts a schematic representation of the micelles formed by these amphiphilic diblock copolymers in C02. Another block copolymer which has proven useful in the stabilization of colloidal particles is the siloxane based stabilizer PS-fr-PDMS [118,119]. Chemical... 

A number of diblock copolymers of NIPAM and hydrophobic comonomers have been prepared by various groups and assessed in terms of micellar structure, thermosensitivity, and applications. For example, PS-fo-PNIPAM was shown to form either micelles consisting of a PS core and a PNIPAM corona, or vesicles. The assemblies were colloidally stable at elevated temperature [262-266]. 

Surfactants are well known as stabilizers in the preparation of metal nanoparticles for catalysis in water. Micelles constitute interesting nanoreactors for the synthesis of controlled-size nanoparticles from metal salts due to the confinement of the particles inside the micelle cores. Aqueous colloidal solutions are then obtained which can be easily used as catalysts. 

Colloidal catalysts in alkyne hydrogenation are widely used in conventional solvents, but their reactivity and high efficiency were very attractive for application in scC02. This method, which is based on colloidal catalyst dispersed in scC02, yields products of high purity at very high reactions rates. Bimetallic Pd/Au nanoparticles (Pd exclusively at the surface, while Au forms the cores) embedded in block copolymer micelles of polystyrene-block-poly-4-vinylpyridine... 

The new connective sites provide the opportunity to destroy or disconnect other regions of the nanostructure without destruction of the entire nanoscale entity. This was demonstrated by the excavation of the core of shell crosslinked polymer micelles, by the removal of the colloid from colloidally templated... 

A promising strategy towards stable and catalyticaUy active metal colloids is their preparation inside the core of micelles formed by amphiphilic block copolymers. This strategy offers a number of advantages (i) micelles represent a nano-structured environment which can be exactly tailored by block copolymer synthesis (ii) polymers act as effective steric stabilizer ]36] (iii) metal leaching might be avoided (iv) micelles allow control over particle size, size distribution and particle solubility [37] and (v) micelles are also supposed to effect catalytic activity and selectivity [38]. 

More recently, micelles have also been proposed as contrast agents. They are colloidal particles with a hydrophobic core and a hydrophilic shell, formed by amphiphilic compounds 102). 

Bimetallic colloids (Pd-Au, Pd-Pt and Pd-Zn) stabilized into the micelle cores of PS-b-P4VP were investigated to determine the influence of the second metal (18). In this case, during the preparation of the catalyst, the addition of both metals salts occurs simultaneously, followed by reduction of metal compounds. 

Micelles are colloidal dispersions that form spontaneously, under certain concentrations, from amphiphilic or surface-active agents (surfactants), molecules of which consist of two distinct regions with opposite afL nities toward a given solvent such as water (Torchilin, 2007). Micelles form when the concentration of these amphiphiles is above the critical micelle concentration (CMC). They consist of an inner core of assembled hydrophobic segments and an outer hydrophilic shell serving as a stabilizing interface between the hydrophobic core and the external aqueous environment. Micelles solubilize molecules of poorly soluble nonpolar pharmaceuticals within the micelle core, while polar molecules could be adsorbed on the micelle surface, and substances with intermediate polarity distributed along surfactant molecules in intermediate positions. 

It should be noted that the development of such polymer systems is stimulated by existing experimental works. In particular, the experimental methods of preparation of nanometer-sized hollow-sphere structures have been suggested [58-63] because of their possible usage for encapsulation of molecules or colloidal particles. The preparation of hollow-sphere structures, generally, is based on self-assembling properties of block copolymers in a selective solvent, i.e., on the formation of polymer micelles with a nanometersized diameter. Further cross-finking of the shell of the micelle and photodegradation [64] of the core part produce nanometer-sized hollow cross-linked micelles. 

---