Dynamic Multicompartment-Core Micelles in Aqueous Media

We investigate micellar aggregates of amphiphilic block terpolymers, polybutadiene-block-poly(2-vinyl pyridine)-block-poly(methacrylic acid) (PB800P2VP190PMAA550) and their quaternized analogues polybutadiene-block-poly(N-methyl-2-vinylpyridinium)-block-poly(methacrylic acid) (PB800P2VPq190PMAA550) in aqueous solution using light scattering (DLS, SLS) and cryogenic transmission electron microscopy (cryo-TEM). At high pH, PB800P2VP190PMAA550 forms core−shell−corona micelles with a hydrodynamic radius Rh ∼ 100 nm and a continuous shell of P2VP. However, at pH 4 partial intramicellar interpolyelectrolyte complex (im-IPEC) formation between P2VP and PMAA results in a patchy, collapsed shell. This is far more pronounced for the quaternized analogue, PB800P2VPq190PMAA550, which forms aggregates of similar size, also exhibiting a noncontinuous, patchy shell. Here, these im-IPECs of the positively charged P2VPq and the partially negatively charged PMAA are present over the whole investigated pH range (4−10). We further demonstrate that size and charge of the corona can be tuned through the block terpolymer composition, in particular, the ratio between P2VPq and PMAA. These micelles are dynamic and able to react to changes in pH or salinity in terms of corona diameter and aggregation number

Stimuli-Responsive Organosilica Hybrid Nanowires Decorated with Metal Nanoparticles

We report on the synthesis and characterization of water-soluble stimuli-responsive organosilica hybrid nanowires that can be used as carriers for metallic nanoparticles. The nanowires were prepared from core−shell-structured cylindrical polymer brushes that served as templates with uniform size and shape. The core of the nanowires consists of a silsesquioxane network synthesized through a precursor route. The shell consists of a dense layer of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA). The hybrid nanowires exhibit pH-responsive behavior, because of the weak polyelectrolyte nature of the PDMAEMA shell. Simultaneously, the shell of PDMAEMA acts as a nanoreactor for the synthesis and immobilization of metal nanoparticles. It was further quaternized with methyl iodide, leading to a poly{[2-(methacryloyloxy)ethyl] trimethylammonium iodide} (PMETAI) cationic polyelectrolyte shell around the silsesquioxane core. The as-synthesized cationic organosilica hybrid nanowires are sensitive to salt concentration, in terms of their hydrodynamic radius. They can be functionalized with platinum nanoparticles as well, leading to stable composites of the nanowires and the platinum nanoparticles. The nanocomposites show high catalytic activity, as kinetically analyzed in the reduction of 4-nitrophenol by sodium borohydride

Template-Directed Synthesis of Hybrid Titania Nanowires within Core−Shell Bishydrophilic Cylindrical Polymer Brushes

Well-defined core−shell bishydrophilic cylindrical polymer brushes (CPBs) with a poly(2-hydroxyethyl methacrylate) (PHEMA) core and a poly(oligo(ethylene glycol) methacrylate) (POEGMA) shell were synthesized via the combination of anionic polymerization and atom transfer radical polymerization. They were used as a unimolecular cylindrical template for the controlled fabrication of linear assemblies of titania nanoparticles. The titania precursors were found localized mainly in the brush core via a transalcoholysis reaction and partially in the shell via a weak complexation force. After hydrolysis, the obtained titania−CPB hybrid nanowires are amorphous and soluble in organic solvents as well as water. A phase transition from amorphous titania to anatase titania was found by refluxing the hybrid nanowire solution for 5 days in a mixture of water/dioxane (vol. ratio = 1/3). They could also serve as in situ template for the pyrolytic formation of inorganic crystalline titania nanowires at 550 °C

Alignment of Tellurium Nanorods <i>via</i> a Magnetization−Alignment− Demagnetization (“MAD”) Process Assisted by an External Magnetic Field

Tellurium (Te) nanorods have been successfully aligned on a solid substrate via a magnetization−alignment−demagnetization (“MAD”) process in the presence of an external magnetic field. Te nanorods carrying a poly(tert-butyl methacrylate) shell were first converted into magnetic nanocylinders by assembling magnetite nanoparticles on their surface via a hydrophobic interaction in THF. We demonstrate that, below a critical concentration of the nanoparticles, this assembly process is able to quantitatively tune the magnetite nanoparticles’ density on the nanorods in terms of their stoichiometric ratio. Due to the polymer and surfactant on their surface, the formed magnetic nanocylinders are soluble in THF and aligned when dried on a solid substrate in the presence of an external magnetic field. The demagnetization of the prealigned nanocylinders was achieved via an acid-etching process, leaving Te nanorods in an aligned state. This MAD process can be extended as a general procedure for other nonmagnetic 1-D nanostructures. Additionally, the nonetched magnetic nanocylinders can be potentially applied in field of magnetorheology

Bis-Hydrophilic Block Terpolymers via RAFT Polymerization: Toward Dynamic Micelles with Tunable Corona Properties

We present the synthesis of well-defined bis-hydrophilic block terpolymers with two outer hydrophilic blocks and an inner hydrophobic block together with studies concerning their colloidal aggregates formed in water. The investigations aim at preparation of dynamic micelles with tunable corona properties. Highly functionalized poly(ethylene oxide) macro-chain-transfer agents (PEO-CTAs) of two molecular weights (2 and 5 kDa) are used as mediating agents in reversible addition fragmentation chain transfer (RAFT) polymerization. The synthesis is accomplished by first polymerizing n-butyl acrylate as a hydrophobic block and then chain extending the diblock copolymers further with various (meth)acrylamide derivatives, acrylamide (AAm), N-isopropylacrylamide (NIPAAm), N,N-diethylacrylamide (DEAAm,) and N-(2-hydroxypropyl)methacrylamide (HPMA). Due to the high degree of functionalization of the PEO-CTA, the blocking efficiency is near quantitative and the diblock copolymers can be obtained easily in a wide range of compositions and with an excellent control of the molecular weights and polydispersities (n-butyl acrylate). Depending on the hydrophilic-to-hydrophobic balance and the pair of hydrophilic end blocks employed, spherical micelles, worm-like micelles, and vesicles can be found. The corona structure of the micelles can be tuned by changing the length and type of hydrophilic polymers used