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Nanoconfinement of a polymer film affords a reduction of the glass transition temperature ( T g ) and effective viscosity (η eff ). Early on, Prof. Tisato Kajiyama pioneered the idea of enhanced polymer mobility at the free surface. This concept is now well established, and accounts for the T g and η eff reductions of thin polymer films. To pay tribute to Prof. Kajiyama's seminal contribution, it is fitting to report in this special issue the use of ultraviolet ozone (UVO) to chemically modify the surface of polymer films and thereby alter their dynamical properties for the first time. Specifically, we show that with a brief exposure time of only 1.0 s under typical UVO treatment conditions, the η eff of polystyrene (PS) films supported by silica changes from decreasing to rapidly increasing as the film thickness is decreased upon the UVO treatment. As such, the tendency of the films to spontaneously rupture on heating is significantly lessened. Considering the simplicity and inexpensiveness of the method, our results demonstrate that UVO treatment is an attractive method to refine the dynamical properties of polymer films and improve their thermal stability.

The significant volumetric change of electrically conducting polymers (ECPs) during the cyclic charging–discharging process causes the capacitance to decrease and electrodes to degrade. Herein we introduce a new strategy for the synthesis of a flexible supercapacitor device based on conducting polyaniline (PANI) nanowires confined within a 10 nm-diameter multiwall carbon nanotube (MWCNT) porous membrane. The PANI nanowires with a diameter of 8 nm and an aspect ratio over 100 are deposited inside the hollow channels of MWCNTs through an in situ electro-polymerization method. The aligned nanostructure of graphitic CNTs provides both protection to the organic polymers and efficient pathways for charge transfer. More importantly, the confined CNT nano-channels suppress the structural change of the PANI chains during multiple charging–discharging cycles and increase the lifetime of the device. Conducting polymers encapsulated inside MWCNTs as such have significant potential to be manufactured into thin, flexible supercapacitor films. The films we made showed a good electrochemical capacitance of 296 F g−1 at a current density of 1.6 A g−1 and considerable stability with the capacitance loss being less than 5% after 2000 charging–discharging cycles.

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 demonstrate a method to fabricate microscopic topographic patterns over a large area. The idea is based on anisotropic dewetting of a previously rubbed polymer film. Two types of patterns are demonstrated. One contains well aligned parallel micro-grooves with widths and separations of about 1 μm. The other contains striped domains of micro-grooves oriented parallel and orthogonal to the stripes in alternation. Although the pattern formation had been demonstrated on 2×2 cm 2 substrates, this method is scalable to any substrate size and could offer an attractive low-cost alternative to photolithography and soft lithography in very large area applications.

PACS. 47.20.Hw Morphological instability; phase changes - 68.15.+e Liquid thin films -68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces.

In a previous study, we reported observation of the novel inverted phase (the minority blocks comprising the continuum phase) in kinetically controlled phase separating solution-cast poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer films [Zhang et al. Macromolecules 2000, 33, 9561−7]. In this study, we adopt the same approach to investigate the formation of inverted phase in a series of solution-cast poly(styrene-b-butadiene) (SB) asymmetric diblock copolymers having nearly equal polystyrene (PS) weight fraction (about 30 wt %) but different molecular weights. The microstructure of the solution-cast block copolymer films resulting from different solvent evaporation rates, R, was inspected, from which the kinetically frozen-in phase structures at qualitatively different block copolymer concentrations and correspondingly different effective interaction parameter, χeff, can be deduced. Our result shows that there is a threshold molecular weight or range of molecular weight below which the unusual...

Rubbing-induced molecular alignment and its relaxation in polystyrene (PS) thin films are studied with optical birefringence. A novel relaxation of the alignment is observed that is distinctly different from the known relaxation processes of PS. First, it is not the Kohlrausch–Williams–Watts type but instead is characterized by two single exponentials plus a temperature-dependent constant. At temperatures several degrees or more below the glass-transition temperature (Tg), the relaxation time falls between that of the α and β relaxations. Second, the decay time constants are the same within 40% for PS with weight-average molecular weights (Mw's) of 13,700–550,000 Da at temperatures well below the sample Tg's, indicating that the molecular relaxations involved are mostly local within the entanglement distance. Nonetheless, the temperature at which the rubbing-induced molecular alignment disappears (T0) exhibits a strong Mw dependence and closely approximates the Tg of the sample. Furthermore, T0 depends notably on the thickness of the polymer in much the same way as previously found for the Tg of supported PS films. This suggests that the α process becomes dominant near Tg. Preliminary spectroscopic studies in the mid-infrared range show a significant degree of bending of the phenyl ring toward the sample surface, with the CC bond connecting the phenyl ring and the main chain tends to lie along the rubbing direction, which indicates that the relaxation is connected with the reorientation of this CC bond. We exclude the observed relaxation, as predominantly a near-surface one, because detailed studies on the effects of rubbing conditions on the degree of molecular alignment indicate that the alignment is not local to the polymer–air surface. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2906–2914, 2001

Scanning probe microscopy was used to simultaneously determine the molecular chain structure and intrinsic mechanical properties, including anisotropic elastic modulus and friction, for lamellae of highly oriented high-density polyethylene (HDPE) obtained by the melt-drawn method. The molecular-scale image of the highly oriented lamellae by friction force microscopy (FFM) clearly shows that the molecular chains are aligned parallel to the drawing direction, and the periodicities along and perpendicular to the drawing direction are 0.26 and 0.50 nm, respectively. The results indicate that the exposed planes of the lamellae resulting from the melt-drawn method are (200), which is consistent with results of transmission electron microscopy and electron diffraction. Because of the high degree of anisotropy in the sample, coming from alignment of the molecular chains along the drawing direction, the measured friction force, F, determined by FFM is strongly dependent on the angle, θ, between the scanning direct...

Force−distance curves were obtained using a home-built atomic force microscope (AFM) at different temperatures (T = 30−65 °C) and probe rates (f = 31.25−50 000 Hz) on a 150 nm thick film of a model sample, poly(tert-butyl acrylate) (Mw = 148K Da, Mw/Mn = 17, and Tgbulk = 50 °C according to DSC). The pull-off force, Fad, at which detachment between the AFM tip and the sample occurred was measured as adhesion. By limiting the loading force, F, to ∼2.5 nN, the tip penetrated by no more than 2 nm into the sample in the glassy state. Therefore, evolution of the rheological properties of the polymer at the free surface with increasing T could be studied. In the vicinity of Tgbulk, Fad was seen to increase rapidly with increasing T or decreasing f. Equivalence between T and f was found using time−temperature superposition in which, upon rescale of f by a temperature-dependent shift factor aTAFM(T), a master curve Fad(aTAFM(T) f) resulted. We showed that Fad(aTAFM(T)f) could be fully accounted for by using an app...

The dependence of the Josephson plasma frequency ωp in Bi2Sr2CaCu2O8 on a tilted field H is reported. Measurements over a large range of B and tilt angle θ allow a detailed comparison with a recent calculation by Koshelev. With a slight modification of the model, close agreement is obtained. From the fits, we find values for the in-plane correlation length and the zero-field critical current density Jc0 (4600 A/cm2 at 30 K). An analogy to Bragg diffraction is described, as well as a picture for the fractional-exponent behavior of ωp vs. H

We report x-ray intensity fluctuation spectroscopy (XIFS) measurements of the equilibrium dynamics of colloidal suspensions of charge-stabilized ${\mathrm{Sb}}_{2}{\mathrm{O}}_{5}$ spheres of radius $250\ifmmode\pm\else\textpm\fi{}40 \mathrm{\AA{}}$ in glycerol. The dynamics were investigated for times between 4 and several thousand seconds, and for wave vectors, $Q$, from 0.003 to 0.012 ${\mathrm{\AA{}}}^{\mathrm{\ensuremath{-}}1}$, well beyond wave vectors that can be studied with visible light. The unique advantages of XIFS for studies of concentrated suspensions composed of refractive-index-mismatched components have not previously been explored. Here, we study a dilute sample (sample I) and a concentrated sample (sample II). For sample I, the diffusion coefficient is independent of $Q$, with a value consistent with the Stokes-Einstein relation. For sample II (effective hard-sphere volume fraction, $\ensuremath{\varphi}=0.18)$, the diffusion coefficient exhibits a minimum at the peak of the structure factor, indicating modifications to Brownian behavior due to interparticle interactions.

We present data on the Josephson plasma resonance in Bi 2 Sr 2 CaCuO 8+δ in a field nominally aligned with the CuO 2 planes (the tilt angle θ smaller than that in sweep-down scans. The hysteresis has a sign opposite to that usually encountered in isotropic superconductors. A second unusual aspect of the hysteresis is that the turning field (maximum or minimum field in a particular scan cycle) influences the value of one of the resonance fields. We propose an explanation in which the critical field for vortex pancake nucleation and the existence of the vortex lock-in state generate a hysteresis loop in the B y −B z plane. The model accounts for the anomalous sign as well as other features observed. The experiment clarifies plasma resonance experiments performed close to alignment at low temperatures. We discuss the importance of zero-field cooling the sample in resonance measurements in this geometry.

We study the driven flow of an unentangled glassy polymer film with a free upper surface and supported below by a substrate using nonequilibrium molecular dynamics simulations based on a bead-spring model. Above the glass transition temperature T(g), simple Poiseuille laminar flow is observed with the film mobility defined as the flow current density per unit pressure gradient scaling as h(3) with the film thickness h. Below T(g), the film mobility becomes independent of h, signifying surface transport. This is in full agreement with recent experiments on the time evolution of capillary waves in polystyrene films supported by silica. A mobile layer is found responsible for the surface transport, as previously conjectured. Our result also shows that it has a velocity profile decaying exponentially into the bulk.

We present a versatile method for continuous-flow, on-chip biological processing of cells, large bio-particles, and functional beads. Using an asymmetric post array in pressure-driven microfluidic flow, we can move particles of interest across multiple, independent chemical streams, enabling sequential chemical operations. With this method, we demonstrate on-chip cell treatments such as labeling and washing, and bacterial lysis and chromosomal extraction. The washing capabilities of this method are particularly valuable because they allow many analytical or treatment procedures to be cascaded on a single device while still effectively isolating their reagents from cross-contamination.