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 approximately 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.

Interpolyelectrolyte complexes of dynamic multicompartment micelles

Dynamic core-shell-shell-corona micelles are formed between two oppositely charged block copolymer systems. Preformed polybutadiene-block-poly(N-methyl-2-vinylpyridinium)-block-poly(methacrylic acid) (PB-P2VPq-PMAA) block terpolymer micelles with a soft polybutadiene core, an interpolyelectrolyte complex (IPEC) shell made out of poly(N-methyl-2-vinylpyridinium) and poly(methacrylic acid), and a negatively charged PMAA corona were mixed in different ratios at high pH with positively charged poly(N-methyl-2-vinylpyridinium)-block-poly(ethylene oxide) (P2VPq-PEO) diblock copolymers. Under these conditions, mixing results in the formation of a second IPEC shell onto the PB-P2VPq-PMAA precursor micelles, surrounded by a PEO corona. The resulting multicompartmented IPECs exhibit dynamic behavior, highlighted by a structural relaxation within a period of 10 days, investigated by dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), and scanning force microscopy (SFM). After a short mixing time of 1 h, the IPECs exhibit a star-shaped structure, whereas after 10 days, spherical core-shell-shell-corona objects could be observed. To further increase complexity and versatility of the presented systems, the in situ formation of gold nanoparticles (Au NPs) in both the precursor micelles and the equilibrated IPEC was tested. For the PB-P2VPq-PMAA micelles, NP formation resulted in narrowly distributed Au NPs located within the PMAA shell, whereas for the core-shell-shell-corona IPEC, the Au NPs were confined within the IPEC shell and shielded from the outside through the PEO corona.

Double stimuli-responsive ultrafiltration membranes from polystyrene-block-poly(N,N-dimethylaminoethyl methacrylate) diblock copolymers

We report on the formation of self-supporting, double stimuli-responsive ultrafiltration membranes via the non-solvent-induced phase separation (NIPS) process. The polymers, polystyrene-block-poly(N,N-dimethylaminoethyl methacrylate) (PS-b-PDMAEMA), were synthesized via living anionic polymerization in THF using sec-butyllithium as initiator. Two amphiphilic diblock copolymers were used, S(81)D(19)(75) and S(68)D(32)(100). The membranes were cast from mixtures of THF and DMF. The influence of the solvent composition, the "open-time" before immersion into the coagulation bath, and the casting film thickness onto the membrane morphology were thoroughly investigated, and flux values obtained for the different membrane systems were compared. The higher content in hydrophilic polymer for S(68)D(32)(100) resulted in a better compatibility with the nonsolvent bath consisting of water, leading to a slower precipitation and thus an improved control of the phase separation occurring. Under certain conditions, ordered microphase-separated porous morphologies were observed in parts of the membrane cross-section. Further, the "smart" properties of those novel materials are shown for two representative systems. It could be demonstrated that both stimuli for PDMAEMA, pH and temperature, can be reversibly and independently applied in order to significantly change the transmembrane water flux.

Double stimuli-responsive ultrafiltration membranes from polystyrene-block-poly(N,N-dimethylaminoethyl methacrylate) diblock copolymers

We report on the formation of self-supporting, double stimuli-responsive ultrafiltration membranes via the non-solvent-induced phase separation (NIPS) process. The polymers, polystyrene-block-poly(N,N-dimethylaminoethyl methacrylate) (PS-b-PDMAEMA), were synthesized via living anionic polymerization in THF using sec-butyllithium as initiator. Two amphiphilic diblock copolymers were used, S(81)D(19)(75) and S(68)D(32)(100). The membranes were cast from mixtures of THF and DMF. The influence of the solvent composition, the "open-time" before immersion into the coagulation bath, and the casting film thickness onto the membrane morphology were thoroughly investigated, and flux values obtained for the different membrane systems were compared. The higher content in hydrophilic polymer for S(68)D(32)(100) resulted in a better compatibility with the nonsolvent bath consisting of water, leading to a slower precipitation and thus an improved control of the phase separation occurring. Under certain conditions, ordered microphase-separated porous morphologies were observed in parts of the membrane cross-section. Further, the "smart" properties of those novel materials are shown for two representative systems. It could be demonstrated that both stimuli for PDMAEMA, pH and temperature, can be reversibly and independently applied in order to significantly change the transmembrane water flux.

Alignment of tellurium nanorods via 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.

Silsesquioxane/polyamine nanoparticle-templated formation of star- or raspberry-like silica nanoparticles

Silica is an important mineral in biology and technology, and many protocols have been developed for the synthesis of complex silica architectures. The current report shows that silsesquioxane nanoparticles carrying polymer arms on their surface are efficient templates for the fabrication of silica particles with a star- or raspberry-like morphology. The shape of the resulting particles depends on the chemistry of the polymer arms. With poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) arms, spherical particles with a less electron dense core form. With poly{[2-(methacryloyloxy)ethyl] trimethylammonium iodide} (PMETAI), star- or raspberry-like particles form. Electron microscopy, electron tomography, and small-angle X-ray scattering show that the resulting silica particles have a complex structure, where a silsequioxane nanoparticle carrying the polymer arms is in the center. Next is a region that is polymer-rich. The outermost region of the particle is a silica layer, where the outer parts of the polymer arms are embedded. Time-resolved zeta-potential and pH measurements, dynamic light scattering, and electron microscopy reveal that silica formation proceeds differently if PDMAEMA is exchanged for PMETAI.

Structure-tunable bidirectional hybrid nanowires via multicompartment cylinders

We present structure-tunable bidirectional inorganic-organic hybrid nanowires templated by soft multicompartment cylinders, possessing perfectly parallel compartments. The poly(2-vinylpyridine) compartments are used to bind nanoparticles via supramolecular coordination. The resulting hybrid nanowires are tunable in terms of the distribution of the inorganics in the corona. The two limiting cases are (a) perfectly aligned, parallel nanowires and (b) nanowires with one homogeneous corona. This approach demonstrates how advances in polymer architectures can be used to create novel hybrid materials of unprecedented complexity and very desirable architecture.

Smart organic-inorganic nanohybrids based on amphiphilic block copolymer micelles and functional silsesquioxane nanoparticles

Smart organic-inorganic nanohybrids are formed in aqueous solution by the interaction of amphiphilic block copolymer micelles of poly(n-butyl acrylate)-block-poly(acrylic acid) (PnBA(x)-b-PAA(y) with x = 90, 100 and y = 100, 150, 300) and diglycidylaminopropyl-functional silsesquioxane nanoparticles. We investigate the structure of the complex nanohybrids in dependence on pH and salinity. The complexation preserves the original size of the micelles according to dynamic light scattering (DLS) measurements. Cryogenic transmission electron microscopy (cryo-TEM) and Fourier-transform infrared spectroscopy (FT-IR) measurements unveil the formation of organic-inorganic nanohybrids. Furthermore, cryo-TEM micrographs provide evidence for the formation of a core-shell-corona structure of the nanohybrid system. Dialysis experiments with fluorescently labeled silsesquioxane nanoparticles clearly demonstrate the interaction between the micellar system and the silsesquioxane nanoparticles.

Interaction of cylindrical polymer brushes in dilute and semi-dilute solution

We present a systematic study of flexible cylindrical brush-shaped macromolecules in a good solvent by small-angle neutron scattering (SANS), static light scattering (SLS), and by dynamic light scattering (DLS) in dilute and semi-dilute solution. The SLS and SANS data extrapolated to infinite dilution lead to the shape of the polymer that can be modeled in terms of a worm-like chain with a contour length of 380 nm and a persistence length of 17.5 nm. SANS data taken at higher polymer concentration were evaluated by using the polymer reference interaction site model (PRISM). We find that the persistence length reduce from 17.5 nm at infinite dilution to 5.3 nm at the highest concentration (volume fraction 0.038). This is comparable with the decrease of the persistence length in semi-dilute concentration predicted theoretically for polyelectrolytes. This finding reveals a softening of stiffness of the polymer brushes caused by their mutual interaction.

Synthesis of dense poly(acrylic acid) brushes and their interaction with amine-functional silsesquioxane nanoparticles

Poly(acrylic acid) polyelectrolyte brushes were synthesized by surface-initiated atom transfer radical polymerization (SI-ATRP) of tert-butyl acrylate on planar gold surfaces and subsequent hydrolysis. Three types of monolayers with different numbers of thiol binding sites per initiating unit were used. The binding strength to the gold surface turned out to be of crucial importance for the formation of uniform brush layers after acidic hydrolysis. The monolayers and polymer brushes were characterized by ellipsometry, infrared spectroscopy, water contact angle measurements, atomic force microscopy, and X-ray photoelectron spectroscopy. Their interaction with [(diglycidylamino)propyl]silsesquioxane nanoparticles at various pH values was studied by surface plasmon resonance.

Water-soluble organo-silica hybrid nanowires

There has been growing interest in the past decade in one-dimensional (1D) nanostructures, such as nanowires, nanotubes or nanorods, owing to their size-dependent optical and electronic properties and their potential application as building blocks, interconnects and functional components for assembling nanodevices. Significant progress has been made; however, the strict control of the distinctive geometry at extremely small size for 1D structures remains a great challenge in this field. The anisotropic nature of cylindrical polymer brushes has been applied to template 1D nanostructured materials, such as metal, semiconductor or magnetic nanowires. Here, by constructing the cylindrical polymer brushes themselves with a precursor-containing monomer, we successfully synthesized hybrid nanowires with a silsesquioxane core and a shell made up from oligo(ethylene glycol) methacrylate units, which are soluble in water and many organic solvents. The length and diameter of these rigid wires are tunable by the degrees of polymerization of both the backbone and the side chain. They show lyotropic liquid-crystalline behaviour and can be pyrolysed to silica nanowires. This approach provides a route to the controlled fabrication of inorganic or hybrid silica nanostructures by living polymerization techniques.