Nanoparticles triblock copolymer

Keywords Block copolymers ABC triblock copolymers Janus micelles Cylinder brushes Core-shell nanoparticles Graft copolymers Micelles Vesicles Copolyampholytes Polyelectrolyte block copolymers Aggregation... 

Janus micelles are non-centrosymmetric, surface-compartmentalized nanoparticles, in which a cross-linked core is surrounded by two different corona hemispheres. Their intrinsic amphiphilicity leads to the collapse of one hemisphere in a selective solvent, followed by self-assembly into higher ordered superstructures. Recently, the synthesis of such structures was achieved by crosslinking of the center block of ABC triblock copolymers in the bulk state, using a morphology where the B block forms spheres between lamellae of the A and C blocks [95, 96]. In solution, Janus micelles with polystyrene (PS) and poly(methyl methacrylate) (PMMA) half-coronas around a crosslinked polybutadiene (PB) core aggregate to larger entities with a sharp size distribution, which can be considered as supermicelles (Fig. 20). They coexist with single Janus micelles (unimers) both in THF solution and on silicon and water surfaces [95, 97]. 

Hales K, Chen Z et al (2008) Nanoparticles with tunable internal structure from triblock copolymers of PAA-b-PMA-b-PS. Nano Lett 8 2023-2026... 

Mesostructured alumina with hexagonal structure can be synthesized in the presence of sodium dodecyl sulfate (SDS), but it was not stable upon surfactant removal. Thermally stable mesoporous alumina has been obtained by nsing triblock copolymer as templates in ethanol solntion. Most alumina mesophases consist of amorphous or semicrystalline framework. Recently, Pinnavaia and coworkers developed a novel three-step assembly method to prepare mesostructured alumina with framework walls composed of crystalline, lathlike y-A Os nanoparticles. ... 

De Jaeghere, F. Allemann, E. Feijen, J. K. T. Doelker, E. Gumy, R. Cellular uptake of PEG surface-modified nanoparticles evaluation of nanoparticles made of PLA PEO diblock and triblock copolymers. J. Drug Target. 2000, 8, 143-153. 

The signiflcant recent advances in both colloidal and polymer chemistries have enabled the successful fabrication of complex, defect-free tianoslruclures following a bottom-up approach [353]. Two recent related examples are mentioned to stress the point. Recently, triblock copolymer with divalent counter-ions in mixed solvents led to the formation of particles with tunable internal structure mimicking lipid anphiphiles for potential use in drug delivery. The mechanism of formation involves either nanophase separation within the triblock copolymer nanoparticle upon addition of water or microemulsion formation similar to that in lipid systems... 

Apparent advantage of the prefabricated nanoparticles hes in the opportunity to use well-developed procedures to control particle size and particle size distribution and to characterize the particles by all possible means. Prefabricated particles can be introduced in the mesoporous materials in two ways. One avenue is direct incorporation of particles in sol-gel mixture as was recently reported in [60]. Here mesostructured nanoparticle-sihca monoliths have been synthesized by dispersing prefabricated Au or zeohte (sihcate) nanoparticles in sol-gel precursors containing SiCl4 and a Pluronic triblock copolymer template. To improve the compatibility of the Au nanoparticles with the poly(ethylene oxide) block, the nanoparticle surface was modified with a SiOj layer. Therefore, this technique requires good compatibihty of nanoparticles with the components of the sol-gel reaction, as it influences the distribution of nanoparticles through the material. Another hmitation of this method is encapsulation of particles within mesoporous material, but not necessary location in the pores. As was discussed above, this limitation is especially crucial for catalytic applications. 

Shi ZT, Pan DY, Zhao SF et al (2006) Self-assembly of ordered silver nanoparticle chains on triblock copolymer templates. Mod Phys Lett B 20(20) 1261-1266... 

D. Cheng, S.-C. Ng, and H. S. O. Chan, Morphology of polyaniline nanoparticles synthesized in triblock copolymers micelles. Thin Solid Films, 477, 19-23 (2005). 

Muller and coworkers prepared disc-like polymer Janus particles from assembled films of the triblock copolymer SBM and, after hydrolysis of the ester groups into methacrylic acid units, used these as Pickering stabilizer in the soap-free emulsion polymerization of styrene and butyl acrylate [111]. Armes and coworkers described the synthesis of PMMA/siUca nanocomposite particles in aqueous alcoholic media using silica nanoparticles as stabilizer [112], extending this method to operate in water with a glycerol-modified silica sol [113, 114]. Sacanna showed that methacryloxypropyltrimethoxysilane [115] in the presence of nanosized silica led to spontaneous emulsification in water, which upon a two-step polymerization procedure afforded armored particles with an outer shell of PMMA [116]. Bon and coworkers demonstrated the preparation of armored hybrid polymer latex particles via emulsion polymerization of methyl methacrylate and ethyl methacrylate stabilized by unmodified silica nanoparticles (Ludox TM O) [117]. Performance of an additional conventional seeded emulsion polymerization step provided a straightforward route to more complex multilayered nanocomposite polymer colloids (see Fig. 14). 

Chen K, Yang Y, SaQ, Shi L,Zhao H (2008) Suspension polymerization stabriized by triblock copolymer with CdS nanoparticles. Polymer 49(ll) 2650-2655... 

As we are interested in reversible Janus micelles, i.e. non-centrosymmetric nanoparticles with compartmentalised shells (Fig. 1), complex coacervate core micelles are a rather natural choice. As described in the previous section, electrostatic interaction is a rather weak driving force as compared to hydrophobic interaction. C3Ms may thus form under full thermodynamic control. Although ABC triblock copolymers in selective solvents (poor solvent for B good solvent for both A and C) may also yield Janus micelles, they most frequently aggregate into micelles with a quenched rather than a dynamic nature, such that the aggregation number is fixed and no reversible association/dissociation is observed (on experimental time scales). 

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