Weighted-density approaches for polymer structure at solid–polymer interfaces

Weighted-density approximations (WDAs), which are based on the weighting function for the second-order direct correlation functions (DCFs) of the uniform polymeric fluids, have been developed to investigate the structural and thermodynamic properties of polymer melts at interfaces. The advantage is the simplicity of calculation of the weighting functions and their accuracies in the applications. They were applied to study the local density distributions and adsorption isotherms of the freely jointed tangent hard-sphere chain, Yukawa chain, and hard-sphere chain mixture in slit pores. The polymer reference interaction model (PRISM) integral equation with the Percus–Yevick (PY) closure has been used to calculate the second-order DCF of the polymeric fluids required as inputs. The mean-field approximation (MFA) has been used to calculate the weighting function for the attractive contribution of a freely jointed tangent Yukawa chain fluid, having attraction among the beads. The calculated results show that (i) for the freely jointed tangent hard-sphere chain, the present theory is in excellent agreement with the computer simulations over a wide range of chain lengths and bulk densities, (ii) the WDA approach for the attraction provides an accurate method for the local density distributions of a freely jointed tangent Yukawa chain fluid, and that (iii) the present theory also yields a reasonably good result for the structural properties of the freely jointed hard-sphere chain mixtures composed of the chain and monomer.     

An opto-mechanical nanoshell–polymer composite

Metal nanoshells, which are nanoparticles consisting of a dielectric core surrounded by a metal shell, have an optical response dictated by the plasmon resonance. This optical resonance leads to large extinction cross-sections, which are typically several times the physical cross-section of the particles. The wavelength at which the resonance occurs depends on the core and shell sizes, allowing nanoshells to be tailored for applications. In this paper, we demonstrate how incorporating nanoshells transforms a thermoresponsivepolymer into a photothermally responsive nanoshell–polymer composite. When the thermoresponsive polymer, co-N-isopropylacrylamide-acrylamide (NIPAAm-co-AAm), is heated, the polymer undergoes a reversible decrease in volume. Pristine NIPAAm-co-AAm does not inherently absorb visible or near infrared light. However, by incorporating metal nanoshell particles with a resonance that has been placed at 832 nm into the NIPAAm-co-Aam, nanoshell–polymer composite hydrogels are fabricated. When the composite is illuminated with a diode laser at 832 nm, the nanoshells absorb light and convert it to heat. This induces a reversible and repeatable light-driven collapse of the composite with a weight change of 90% after illumination at 1.8 Wcm^-2. Received: 18 July 2001 / Published online: 10 October 2001     

Novel electrospun PAN�CPVC composite fibrous membranes as polymer electrolytes for polymer lithium-ion batteries

Composite fibrous membranes based on poly(acrylonitrile)(PAN)-poly(vinyl chloride)(PVC) have been prepared by electrospinning. The fibrous membranes are made up of fibers of 850- to 1,300-nm diameters. These fibers are stacked in layers to produce a fully interconnected pore structure. Polymer electrolytes were prepared by immersing the fibrous membranes in 1 M LiClO₄-PC solution for 60 min. The condition of pure PAN polymer electrolytes is jelly, which has poor mechanical performance and cannot be used. But when PVC with a good mechanical stiffener was added to PAN, the condition of composite PAN?CPVC polymer electrolytes becomes free-standing. In addition, the optimum electrochemical properties have been observed for the polymer electrolyte based on PAN?CPVC (8:2, w/w) to show ionic conductivity of 1.05?×?10^?3 S cm^?1 at 25 °C, anodic stability up to 4.9 V versus Li/Li⁺, and a good compatibility with lithium metal resulting in low interfacial resistance. The promising results showed that fibrous PEs based on PAN?CPVC (8:2, w/w) have good mechanical stability and electrochemical properties. This shows a great potential application in polymer lithium-ion batteries.     

One-pot biosynthesis of polymer–inorganic nanocomposites

A biological method is demonstrated to fabricate the polymer–inorganic nanocomposites (PINCs) utilizing bacterium as an efficient and versatile biofactory. Gluconacetobacter xylinum that can produce bacterial cellulose is incubated in the culture medium containing titanium or silica precursor. The PINCs can be acquired under the elaborate control of the culturing condition of G. xylinum, in which the formation of inorganic nanoparticles about several tens of nanometers in size synchronizes the fabrication of reticulated bacterial cellulose membrane composed of dense and finely branched nanofibers about 60–120 nm in diameter. The composition and chemical states, morphology, thermal stability of the inorganic nanoparticles, and nanocomposites were extensively characterized. A tentative mechanism for the formation of PINCs is proposed. It is hoped that this study may establish a generic platform toward facile and green synthesis of nanocomposite materials.     

Rhodamine 6G-doped polymer optical fiber amplifiers

Rhodamine 6G-doped step-index polymer optical fiber is fabricated. The characteristics of the amplification of rhodamine 6G-doped step-index polymer optical fiber amplifier have been studied. The high-gain optical amplification with a tunable wavelength range from 585 to 613 nm is obtained in a step-index polymer optical fiber doped with rhodamine 6G at 10-ppm level, which can be used for broadband amplifiers and tunable lasers.     

Resonantly enhanced off-specular X-ray scattering from polymer/polymer interfaces<Superscript>⋆</Superscript>

We have used measurements of the absolute intensity of diffuse X-ray scattering to extract the interfacial tension of a buried polymer/polymer interface. Diffuse scattering was excited by an X-ray standing wave whose phase was adjusted to have a high intensity at the polymer/polymer interface and simultaneously a node at the polymer/air interface. This method permits the capillary-wave-induced roughness of the interface, and hence the interfacial tension, to be measured independently of the polymer/polymer interdiffusion.     

Laser-induced condensation in colloid—polymer mixtures

We study a mixture of hard sphere colloidal particles and non-adsorbing polymers exposed to a plane wave external potential which represents a three-dimensional standing laser field. With computer simulations and density functional theory we investigate the structure and phase behaviour using the simple Asakura-Oosawa model. For varying laser wavelength λ we monitor the emergence of structure in response to the external field, as measured by the amplitude of the oscillations in the one-body density distribution. Between the ideal gas limit for small λ and the bulk limit of large λ there is a non-monotonic crossover that is governed by commensurability of λ and the colloid diameter. The theoretical curves are in good agreement with simulation results. Furthermore, the effect of the periodic field on the liquid-vapour transition is studied, a situation that we refer to as laser-induced condensation. Above a threshold value for λ the theoretical phase diagram indicates the stability of a ‘stacked’ fluid phase, which is a periodic succession (in the beam direction) of liquid and vapour slabs. This partially condensed phase causes a splitting of the liquid-vapour binodal leading to two critical and a triple point. All our predictions should be experimentally observable for colloid-polymer mixtures in an optical resonator.     

High photoluminescence efficiency in polymer containing rare earth

Organic electroluminescent (EL) devices were firstly demonstrated in the 1960s, but great interest was not shown until 1987 that Tang and Vanslyke succeeded in developing an effective device using tris(8-hydroxyquin oline) aluminum (Alq3) as the emitter[1-4]. Since then, different kinds of organic dyes, chelate metal com- plex and polymers were synthesized to fabricate higher efficiency devices. Polymers containing rare earth have been used to fabricate the full-color devices because the ver…     

Lipase-catalyzed polyester synthesis – A green polymer chemistry

This article is a short comprehensive review describing in vitro polyester synthesis catalyzed by a hydrolysis enzyme of lipase, most of which has been developed for these two decades. Polyesters are prepared by repeated ester bond-formation reactions; they include two major modes, ring-opening polymerization (ROP) of cyclic monomers such as cyclic esters (lactones) and condensation polymerization via the reaction between a carboxylic acid or its ester group and an alcohol group. Polyester synthesis is, therefore, a reaction in reverse way of in vivo lipase catalysis of ester bond-cleavage with hydrolysis. The lipase-catalyzed polymerizations show very high chemo-, regio-, and enantio-selectivities and involve various advantageous characteristics. Lipase is robust and compatible with other chemical catalysts, which allows novel chemo-enzymatic processes. New syntheses of a variety of functional polyesters and a plausible reaction mechanism of lipase catalysis are mentioned. The polymerization characteristics are of green nature currently demanded for sustainable society, and hence, desirable for conducting ‘green polymer chemistry’.     

Banana fiber strands–reinforced polymer matrix composites

Banana fiber (BF)-reinforced low-density polyethylene (LDPE) unidirectional composites were fabricated by the compression molding process with 40 wt% fiber loading. The fibers were modified with methylacrylate (MA) mixed with methanol (MeOH) along with 2% benzyl peroxide under thermal curing method at different temperatures (50–90 °C) for different curing times (10–50 min) in order to have better compatibility with the matrix. The effect of fiber surface modification on the mechanical properties (tensile and impact properties) of the composites were evaluated. Monomer concentration, curing temperature, and curing time were optimized in terms of polymer loading and mechanical properties. The mechanical properties were found to be improved based on the improved interaction between the reinforcement and the matrix. Optimized BFs were again treated with 2–5 wt% starch solutions and composites made of 4% starch treated BF showed the highest mechanical properties than that of MA treated composites. Scanning electron microscopy (SEM) was performed to get an insight into the morphology of the composites. Water uptake and soil degradation test of the composites were also investigated.     

Guiding mode in elliptical core microstructured polymer optical fiber

A kind of microstructured polymer optical fiber with elliptical core has been fabricated by adopting in- situ chemical polymerization technology and the secondary sleeving draw-stretching technique.Microscope photography demonstrates the clear hole-structure retained in the fiber.Though the holes distortion is visible,initial laser experiment indicates that light can be strongly confined in the elliptical core region, and the mode field is split obviously and presents the multi-mode characteristic.Numerical modeling is carried out for the real fiber with the measured parameters,including the external diameter of 150μm,the average holes diameter of 3.3μm,and the average hole spacing of 6.3μm by using full-vector plane wave method.The guided mode fields of the numerical simulation are consistent with the experiment result. This fiber shows the strong multi-mode and weak birefringence in the visible and near-infrared band,and has possibility for achieving the fiber mode convertors,mode selective couplers and so on.     

Statistical mechanics of inhomogeneous model colloid—polymer mixtures

We describe two strategies for tackling the equilibrium statistical mechanics of inhomogeneous colloid—polymer mixtures treated in terms of the simple Asakura—Oosawa—Vrij (AO) model, in which colloid—colloid and colloid—polymer interactions are hard-sphere like, whereas the polymer—polymer interaction is zero (perfectly interpenetrating polymer spheres). The first strategy is based upon integrating out the degrees of freedom of the polymer spheres to obtain an effective one-component Hamiltonian for the colloids. This is particularly effective for small size ratios q = σ_p/σ_c < 0.1547, where σ_p and σ_c are the diameters of colloid and polymer spheres, respectively, since in this regime three and higher body contributions to the effective Hamiltonian vanish. In the second strategy we employ a geometry based density functional theory (DFT), specifically designed for the AO model but based on Rosenfeld's fundamental measure DFT for additive mixtures of hard-spheres, that treats colloid and polymer on an equal footing and which accounts for the fluid-fluid phase separation occurring for larger values of q. Using the DFT we investigate the properties of the ‘free’ interface between colloid-rich (liquid) and colloid-poor (gas) fluid phases and adsorption phenomena at the interface between the AO mixture and a hard-wall, for a wide range of size ratios. In particular, for q = 0.6 to 1.0, we find rich interfacial phenomena, including oscillatory density profiles at the free interface and novel wetting and layering phase transitions at the hard-wall-colloid gas interface. Where appropriate we compare our DFT results with those from computer simulations and experiment. We outline several very recent extensions of the basic AO model for which geometry based DFTs have also been developed. These include a model in which the effective polymer sphere—polymer sphere interaction is treated as a repulsive step function rather than ideal and one in which the depletant is a fluid of infinitely thin rods (needles) with orientational degrees of freedom rather than (non-interacting) polymer spheres. We comment on the differences between results obtained from these extensions and those of the basic AO model. Whilst the interfacial properties of the AO model share features in common with the those of simple (atomic) fluids, with the polymer reservoir density replacing the inverse temperature, we emphasize that there are important differences which are related to the many-body character of the effective one-component Hamiltonian.     

Phenolic polymer–surface interactions from ab initio computations

Test calculations show that the diamond surface binding energy of C₁₃H₁₁O₂, the simplest model for phenolic, is virtually the same as that of C₆H₅. Using the C₆H₅ model, we compare the binding to a diamond surface, a graphene sheet, a (10, 0) nanotube, and a silica surface. The binding energy is more than 5?eV for the silica and 2.85?eV for the diamond surface. As expected, the binding energy of a second molecule at a site adjacent to the first molecule is larger than the first binding energy for the graphene sheet and the carbon nanotube, since the first C₆H₅ bond breaks a π bond and the second molecule bonds to the unpaired π electron created by adding the first molecule. For all of the systems, adding a C₂ unit between the surface and the C₆H₅ group increases the binding by at least 0.51?eV and up to 2.3?eV. Part of this increase is due to the intrinsically stronger bonding for the sp hybridization and part due to a decrease in the surface–C₆H₅ repulsion.     

Structure design for high performance n-type polymer thermoelectric materials

Organic thermoelectric(OTE)materials have been regarded as a potential candidate to harvest waste heat from complex,low temperature surfaces of objects and convert it into electricity.Recently,n-type conjugated polymers as organic thermoelectric materials have aroused intensive research in order to improve their performance to match up with their ptype counterpart.In this review,we discuss aspects that affect the performance of n-type OTEs,and further focus on the effect of planarity of backbone on the doping efficiency and eventually the TE performance.We then summarize strategies such as implementing rigid n-type polymer backbone or modifying conventional polymer building blocks for more planar conformation.In the outlook part,we conclude forementioned devotions and point out new possibility that may promote the future development of this field.     

Aqueous polymer–nitrate solution deposition of YBCO films

High critical current density YBa₂Cu₃O_7?x (YBCO) films were prepared by solution deposition of aqueous non-fluorine precursors. Non-fluorine polymer-assisted deposition (PAD) processes utilizing rheology modifiers and chelating agents were used to produce 50 nm films with a critical current density (J_c) over 3 MA/cm² and 400 nm films with J_c > 1 MA/cm²_. T_c measurements indicated that films have T_c values near 90 K. The total heat treatment time to produce these high performance films was less than 4 h. Rheology modifiers such as polyvinyl alcohol (PVA) and hydroxyethyl cellulose (HEC) were used to increase the thickness of deposited films independent of the solution cation concentration. Chelating agents such as polyethylene glycol (PEG) and sucrose increased the barium ion solubility. Nitrate crystallization during deposition was controlled through rapid drying with vacuum and coating with hot solutions.     

All-optical switching effect based on azodye-doped polymer thin films

A simple all-optical switch based on photoinduced birefringence effect is demonstrated in azo dye (DR1) doped polymer (PMMA) thin films. The all-optical switching effect has been studied at different control beam power and different temperatures of the sample. With a control power of 30.7 mW and at 56 ℃, the response time of the switching is less than 5 ms, and the depth of the modulation reaches 80%.     

Optically inscribed surface-relief zone plates in azo polymer films

We describe a simple and cost-effective holographic method for the fabrication of surface-relief zone plates. The zone plate is inscribed by interference between the first- and second-order diffracted waves from an ion-etched Fresnel zone plate. The inscribed surface-relief zone plates are observed by atomic force microscope (AFM). The formation process of the surface grating and the mass diffusion in azo polymer are analyzed.     

Charge transport across the metal–polymer film boundary

Thin polyaniline films were fabricated by thermal vacuum evaporation from a Knudsen effusion cell. The conducting properties of films synthesized under different evaporation conditions were studied. The enhancement of the emission capacity of a wolfram tip coated with a polyaniline film of a nanometer thickness was demonstrated experimentally. A model of the discovered effect was proposed. The obtained Fowler–Nordheim current–voltage characteristics were used to estimate the change in the electronic work function occurring when a thin film is deposited on the tip surface. The effective temperature of electrons emitted from the polyaniline film was determined based on the results of analysis of energy distributions, and the specific features of charge transport in the metal–polyaniline–vacuum system were examined. A model of energy bands of the metal–polymer film contact was also constructed.     

Femtosecond fabrication of waveguide-like micro-structures in a photorefractive polymer

In this letter, we report on, for the first time, the successful femtosecond micro-fabrication of continuous waveguide-like channels in the photorefractive polymer consisting of the nonlinear chromophore 2,5-dimethyl-4-(p-nitrophenylazo)anisole (DMNPAA), the photosensitive compound 2,4,7-trinitro-9-flourenone (TNF), and the plasticiser N-ethylcarbazole (ECZ) all doped in the polymer matrix poly (methyl methacry-late) (PMMA). These channels are caused by the change in refractive index as a result of the localised heating of the polymer and therefore have an important potential for micro-photonic devices in future.