Ion transport plays an important role in solar-to-electricity conversion, drug delivery, and a variety of biological processes. Carbon nanotube (CNT) is a promising material as an ion transporter in the applications of the mimicking of natural ion channels, desalination, and energy harvesting. Here, we demonstrate a unique, enhanced ion transport through a vertically aligned multiwall CNT membrane after the application of an electric potential across CNT membranes. Interestingly, electrowetting arising from the application of an electric potential is critical for the enhancement of overall ion transport rate through CNT membranes. The wettability of a liquid with high surface tension on the interior channel walls of CNTs increases during an electric potential treatment and promotes the formation of water channels in CNTs. The formation of water channels in CNTs induces an increase in overall ion diffusion through CNT membranes. This phenomenon is also related to a decrease in the charge transfer resistance of CNTs (Rct) after an electric potential is applied. Correspondingly, the enhanced ion flow rate gives rise to an enhancement in the capacitive performance of CNT based membranes. Our observations might have profound impact on the development of CNT based energy storage devices as well as artificial ion channels.Keywords: capacitive performance; electrowetting; ion flow; multiwall carbon nanotubes; water channels;

This report describes a technique for fabricating dual-structured hierarchical surface topography on the surface of polydimethylsiloxane (PDMS) films through simply replicating prefabricated patterns and wrinkling PDMS films. To enhance the biocompatibility of PDMS films, we synthesize a biocompatible dopamine-glycopolymer, which is utilized to modify the chemical feature of the PDMS surface. Dopamine component in this copolymer is introduced for the formation of a carbohydrate layer on the surface of PDMS films because of its excellent adhesion. The carbohydrate component in this copolymer enhances the interactions between cells and PDMS films. We investigate the influence of the chemical and topographical surface properties of the extracellular matrix on fibroblast cell growth. The coupling of the dopamine-glycopolymer coating and hierarchical topography produces the best induction effect on the alignment of cells.Keywords: cell behaviors; dopamine; dual-structured hierarchical topography; glycopolymer; surface modification; wrinkle films;

Our study on poly(methyl methacrylate) (PMMA) films with fixed nanoparticles (NPs) on the supporting substrate, where the nanoparticles span the film thickness, reveal a three-stage evolution of wavelike undulations on the film surface: early stage, intermediate stage and late stage. The wavelike height undulations are induced by the compressive stresses, which are enhanced by introducing fix constrians (NPs) that resist the in-plane thermal expansion of the polymer film. We quantified the evolution of surface undulations, in an effort to understand the effect of solvent annealing on the undulations. The polymer chains in PMMA films prepared by spin coating are not fully equilibrated due to the rapid solvent evaporation during drying. Solvent annealing increases the molecular mobility and enables relaxation of the polymer network. This solvent treatment could perhaps give rise to an increase in entanglement density and associated film modulus. The surface undulations increase with the solvent annealing time before they reach the equilibrium values. The wavelike surface undulations might be associated with the entanglement density of polymer chains.The overall evolutionary process of wavelike surface undulations of nanoparticle-filled polymer thin films annealed in solvent vapor.

We demonstrate a general approach for attaining the bottom morphology of block copolymer (BCP) thin films. In our former measurements on PS-b-PMMA films, surface morphology maps of the BCP films revealed distinct ordering regimes where the cylinders orient predominantly perpendicular or parallel to the interface and an ‘intermediate’ regime where these morphologies coexist. However, this earlier work did not explore the bottom morphology of BCP thin films. In this study, we investigated the block copolymer morphology near the solid substrate in the cast block copolymer film having a perpendicular cylinder morphology on the surface.

We demonstrate a novel nano-porous membrane of 10 nm diameter multiwall carbon nanotubes (MWCNTs) filled with thermally sensitive poly(N-isopropylacrylamide) (PNIPAm) hydrogel. High-resolution transmission electron microscopy (HRTEM), micro FT-IR spectroscopy and confocal laser scanning fluorescence microscopy are used to confirm that the MWCNTs are filled with the hydrogel. An improvement in the hydrophilicity of the gel-filled nano-channels is expected to promote the migration of aqueous solutions and the transportation of water. Meanwhile a decrease in ion flux is observed after the nano-pores of MWCNTs are filled with the hydrogel. This new hydrogel filled-CNT material shows potential for nano-chromatography, water purification and use as intelligent ionic channels.

We have investigated the interdiffusion of two dissimilar polymer species with different molecular masses, Mw, thus having different self-diffusion coefficients D*. A net mass flux across the interface and displacement of the original interface, Δx, between the two polymer films are observed. The displacement of the original interface moves toward the side containing the faster moving polymer species. We also examine the effect of an in-plane stationary temperature gradient on the interdiffusion of two dissimilar polymer species. As the low Mw polymer species is in the region of high temperature under the thermal gradient temperature field, the interface between the two polymer films moves faster compared with the system with the low Mw polymer species in the cold region of the temperature gradient field. We suggest that the in-plane thermal gradient accelerates polymer migration through the enhancement in polymer diffusion along the direction of the temperature gradient due to the Soret effect. We also find that the interdiffusion of polymers depends on the composition in the blend system. For a statistical copolymer system of plastic poly(ethylene-co-hexene) (PEH) and elastic poly(ethylene-co-butene) (PEB), having technologically interesting plastic and elastic properties, the diffusion of the relatively slow diffusion species (PEH) increases with the increase of PEB composition. Under the thermal gradient field the net mass flux across the interface and the movement of original interface between two polymer films can be controlled by the direction of the temperature gradient and composition of the blend system.

We investigate the effect of a temperature gradient on the orientation of phase-separated structures in a polyolefin blend system. Phase contrast optical microscopy (PCOM) has been used to measure the morphology of phase separation via spinodal decomposition as a function of phase separation time and temperature gradient. The bicontinuous and interconnected tubelike structure, the characteristic morphology of the spinodal decomposition process, exhibits a preferential alignment along the direction of temperature gradient after phase separation. The orientation of the bicontinuous and interconnected tubelike structures gradually increases with phase separation time and temperature gradients. Also the orientation of phase-separated domains can respond really quickly to the change in the direction of external temperature gradient field. The results suggest that “thermal force” induced by the temperature inhomogeneity might play an important role in aligning phase-separated domains preferentially along the temperature gradient direction.

We demonstrate a novel nano-porous membrane of 10 nm diameter multiwall carbon nanotubes (MWCNTs) filled with thermally sensitive poly(N-isopropylacrylamide) (PNIPAm) hydrogel. High-resolution transmission electron microscopy (HRTEM), micro FT-IR spectroscopy and confocal laser scanning fluorescence microscopy are used to confirm that the MWCNTs are filled with the hydrogel. An improvement in the hydrophilicity of the gel-filled nano-channels is expected to promote the migration of aqueous solutions and the transportation of water. Meanwhile a decrease in ion flux is observed after the nano-pores of MWCNTs are filled with the hydrogel. This new hydrogel filled-CNT material shows potential for nano-chromatography, water purification and use as intelligent ionic channels.