Single-Walled Carbon Nanotube-Induced Lyotropic Phase Behavior of a Polymeric System

Temperature-Selective Self-Assembled Superlattices of Gold Nanoparticles Driven by Block Copolymer Template Guidance

Self-assembly of nanoparticles (NPs) into highly ordered structure can enhance their electronic and optical properties that provide great potential applications such as nanoelectronics and nanophotonics. However, the self-assembly of NPs upon external stimuli was still mainly continuous and irreversible, making various potential applications of NPs difficult. Herein, the self-assembled superlattices of gold nanoparticles (AuNPs) with a temperature-selective response had been investigated by using the amphiphilic block copolymer as a template. The AuNPs in the block copolymer template, which has the closed looplike phase behavior upon heating, self-assembled into the highly ordered body centered cubic (BCC) or face centered cubic (FCC) structures at a specific temperature region that means a temperature-selective responsiveness. The formation of highly ordered self-assembled superlattices (BCC or FCC symmetries) of AuNPs with the closed looplike phase behavior was controlled by the additive and temperature. This study is the first demonstration for temperature-selective response of the cooperative self-assembly of AuNPs in the block copolymer template.

Unexpected Phase Behavior of Pluronic Polymer-Organic Derivative Mixtures Depending on Temperature in Aqueous Solution

The phase behavior of amphiphilic Pluronic block copolymers in aqueous solution is of importance for a broad spectrum of practical applications but has not been fully exploited yet. Here, the phase behavior of the mixture of the Pluronic P65 and P105 triblock copolymer, (which have the same composition of PEO and PPO but the different molecular weight) and organic derivative, 5-methyl salicylic acid (5mS), in aqueous solution has been investigated by using small angle neutron scattering (SANS). According to the temperature and the 5mS concentration, SANS measurements showed that the P65-5mS mixtures sequentially transform into a random coil, sphere, vesicle, cylinder, and vesicle again, while the P105-5mS mixtures form spherical particles with two different sizes without any topological phase transition. Upon heating, the formation of two different kinds of the vesicle structure of amphiphilic block copolymer in aqueous solution is very unusual. This phase behavior was explained as the coupled effect of the simultaneous increase of the hydrophobicity of the polymer and the solubility of 5mS molecules upon heating. This result gives fundamental information for the practical use of Pluronic polymers in nano- and bio-science and it provides a simple route for the fabrication of the nanostructure without a complicated procedure.

Quantification of Carbon Nanotube Liquid Crystal Morphology via Neutron Scattering

Liquid phase assembly is among the most industrially attractive routes for scalable carbon nanotube (CNT) processing. Chlorosulfonic acid (CSA) is known to be an ideal solvent for CNTs, spontaneously dissolving them without compromising their properties. At typical processing concentrations, CNTs form liquid crystals in CSA; however, the morphology of these phases and their concentration dependence are only qualitatively understood. Here, we use small-angle neutron scattering (SANS), combined with polarized light microscopy and cryogenic transmission electron microscopy to study solution morphology over a range of concentrations and two different CNT lengths. Our results show that at the highest concentration studied the long CNTs form a highly ordered fully nematic phase, while short CNTs remain in a biphasic regime. Upon dilution, long CNTs undergo a 2D lattice expansion, whereas short CNTs seem to have an intermediate expansion between 2D and 3D probably due to the biphasic nature of the system. The average spacing between the CNTs scaled by the CNT diameter is the same in both systems, as expected for infinitely long aligned rods.

Selective distributions of functionalized single-walled carbon nanotubes in a polymeric reverse hexagonal phase

We have investigated the distributions of individually isolated and hydrophilically functionalized single-walled carbon nanotubes (p-SWNTs) in the Pluronic L121-water system at the reverse hexagonal phase using small-angle X-ray scattering (SAXS) and contrast-matched small-angle neutron scattering (SANS) measurements. As the p-SWNT-L121-water system is transitioned from the lamellar phase to the reverse hexagonal phase with temperature, p-SWNTs which were selectively distributed in the polar layers of the lamellar structure become selectively distributed in the cylindrical polar cores of the reverse hexagonal structure, forming a hexagonal array of p-SWNTs. This was clearly confirmed by the contrast-matched SANS measurements. The selective distribution of p-SWNTs in the reverse hexagonal phase is driven by the selective affinity of p-SWNTs to the polar domains of the block copolymer system. The method demonstrated in this study provides a new route for fabricating ordered SWNT superstructures and may be applicable for inorganic 1D nanoparticles such as semiconducting, metallic and magnetic nanorods which are of great interest.

Block-copolymer-induced long-range depletion interaction and clustering of silica nanoparticles in aqueous solution

Small-angle neutron scattering (SANS) has been carried out to examine the block-copolymer-induced depletion interaction of charged silica nanoparticles in aqueous solution. The measurements have been performed on fixed concentrations (1 and 10 wt. %) of anionic Ludox silica nanoparticles having sizes of 8 and 16 nm in the presence of 0.1M NaCl and varying concentration of polyethylene oxide-polypropylene oxide-polyethylene oxide P85 [(EO)(26)(PO)(39)(EO)(26)] block copolymer. The presence of the block copolymer induces an attractive depletion interaction between charge-stabilized nanoparticles. The effective interaction of silica nanoparticles is modeled by a combination of two Yukawa potentials accounting for attractive depletion and repulsive electrostatic forces. The depletion interaction is found to be a long-range attraction whose magnitude and range increase with block-copolymer concentration. The depletion interaction is further enhanced by tuning the self-assembly of the block copolymer through the variation of temperature. The increase of the depletion interaction ultimately leads to clustering of nanoparticles and is confirmed by the presence of a Bragg peak in the SANS data. The positioning of the Bragg peak suggests simple-cubic-type packing of particles within the clusters. The scattering from the clusters in the low-Q region is governed by the Porod scattering, indicating that clusters are quite large (order of microns). The depletion interaction is also found to be strongly dependent on the size of the nanoparticles.