Simulation of surface-modified porous silicon photonic crystals for biosensing applications

In this work realistic biosensing structures based on the integration of porous silicon photonic crystals with polymer coating technology are presented. Microcavities and rugate filters are chosen as the photonic crystal configuration. The deposition of a polymer layer on the pore walls of these structures is proposed to improve the selectivity and sensitivity of the sensing function. A complete effective refractive index model including the polymer layer, the target and external effects like silicon oxidation has been developed in order to accurately simulate the structures. It is expected that the proposed structures could be used as low cost, highly integrated and highly sensitive biological sensors.     

Formation of periodic polymer structures on the surface of optical fibers

The self-organization of solutions of organic and inorganic polymers on the surface of round fibers during the evaporation of a solvent leads to the formation of longitudinal and transverse periodic structures. The structure period ranges from several tens to several hundreds of microns and depends on the type of polymer, the initial solution composition, and the fiber diameter. Nanoporous periodic structures made of inorganic materials can be formed from a suspension of inorganic nanoparticles in a polymer solution upon thermal decomposition of the polymer. These processes are shown to be used to create long-period fiber gratings for fiber sensor systems and fiber optical filters.     

Polymer photonic band-gaps fabricated by nanoimprint lithography

We report on the fabrication and characterization of photonic band-gaps structures by nanoimprint lithography in a dye-doped polymer. Photonic band calculations show that photonic crystal slabs composed of a triangular array of polymer pillars could exhibit photonic band-gaps for the magnetic-like modes. The resulting structures show that the nanoimprint lithography process is well-suited to fabricate in a single-step process, these challenging photonic structures opening perspectives to realize integrated photonic band-gap circuits.     

Nanostructures of colloidal complexes formed in oppositely charged polyelectrolyte/surfactant dilute aqueous solutions

Small-angle neutron scattering measurements were performed on dilute solutions of carboxymethylcellulose/DTAB complexes in water in order to determine their size, shape and internal structures. At low polymer content, the complexes are spherical, rather monodisperse and probably made of polymer chains intercalated between surfactant micelles. Moreover, we show that these micelles have a similar cubic arrangement than found in polymer/surfactant precipitates formed at higher surfactant concentrations. At larger polymer content, in the semi-dilute polyelectrolyte regime, the complexes are larger, softer and polydisperse. However, they possess a similar internal structure in both regimes. Carboxymethylcellulose/CTAB complexes are also large, soft and polydisperse but do not seem to exhibit well-defined internal structures.     

Phase separated composite films of liquid crystals

Phase separation of liquid crystals from a solution with polymers has long been studied and used to prepare polymer stabilized and polymer dispersed structures. They are formed by spatially isotropic phase separation. A new mode, in which the phase separation proceeds anisotropically, has recently been discovered. Known as phase separated composite films (PSCOF), the resultant structures are made of adjacent parallel layers of liquid crystal and solidified polymer. PSCOFs have been made with nematic, ferroelectric (FLC), and antiferroelectric (AFLC) liquid crystals. Liquid crystals in PSCOFs exhibit electro-optical properties not observed in devices prepared by conventional methods, polymer dispersion, or polymer stabilization methods. Devices incorporating FLCs possess grey scale and switch 100 times faster at low fields than conventional surface stabilized devices. This method makes it possible to prepare very flexible devices and devices with liquid crystal film thickness comparable to optical wavelengths with great ease.     

Mechanism of polymer drag reduction using a low-dimensional model

Using a retarded-motion expansion to describe the polymer stress, we derive a low-dimensional model to understand the effects of polymer elasticity on the self-sustaining process that maintains the coherent wavy streamwise vortical structures underlying wall-bounded turbulence. Our analysis shows that at small Weissenberg numbers, Wi, elasticity enhances the coherent structures. At higher Wi, however, polymer stresses suppress the streamwise vortices (rolls) by calming down the instability of the streaks that regenerates the rolls. We show that this behavior can be attributed to the nonmonotonic dependence of the biaxial extensional viscosity on Wi, and identify it as the key rheological property controlling drag reduction.     

Metallic nanostructures in a polymer matrix and substrate fabrication and structural characterization

Metal nanostructures are of considerable interest in the field of plasmonics and metamaterials and could have a wider impact if they are successfully embedded in a stable, inert and flexible polymer matrix. Fabrication of such structures is challenging for a variety of reasons including thermal stability, material compatibility with processing steps and general handling of material. In this work we have demonstrated the fabrication of metal nanostructures and embedded them in a polymer. Furthermore, these structures were fabricated on a flexible polymer membrane and detached from a carrier substrate. Characterization of these structures was performed with SEM, TEM and EDS.     

Optical and photoluminescent properties of plasma polymer films used in electroluminescent display structures

The optical and photoluminescent properties of plasma polymer layers synthesized from hexamethyldisiloxane are examined. The value of the polymer layer transparence is in the limits from 55% at 400 nm to 88% at 800 nm. Photoluminescence is stimulated by using the spectral line λ=365 nm emitted by a Hg spectral lamp.The organosilicon plasma polymers are included as protective and capsulating layers in electroluminescent (EL) structures. The structure obtained is characterized by a significant increase in emission brightness, compared to inorganic protective layers. For EL structures with a chalcogenide protective layer the increase is more than 6 times and for structures with heterogeneous matrix on the base of TiO₂ it is more than 20 times. As a stable covering the organosilicon plasma polymer increases the lifetime of the EL structures too.     

聚合物结构转变中的介电信息

聚合物的一级结构为理想完整的长分子链；其中的电子和离子贡献快极化效应.长链的拓扑形变给出二级结构，而三级结构由许多形变后的链组成，聚合物的二和三级结构贡献的都是慢极化.冷冻时域介电谱方法证明，在聚合物的β转变中二和三级结构软化，但一级结构不变.这种方法可将冷冻于聚合物中的各快和慢分量分开. 关键词：     

Nanostructural self-organization and dynamic adaptation of metal–polymer tribosystems

The results of investigating the effect of nanosize modifiers of a polymer matrix on the nanostructural self-organization of polymer composites and dynamic adaptation of metal–polymer tribosystems, which considerably affect the wear resistance of polymer composite materials, have been analyzed. It has been shown that the physicochemical nanostructural self-organization processes are developed in metal–polymer tribosystems with the formation of thermotropic liquid-crystal structures of the polymer matrix, followed by the transition of the system to the stationary state with a negative feedback that ensures dynamic adaptation of the tribosystem to given operating conditions.     

Directed assembly of nanostructured carbon materials on to patterned polymer surfaces

Directed assembly of single-walled carbon nanomaterials on to polymer surfaces has been achieved. The approach relies on selective interactions of the polymer functionalities with the surface structures present on the carbon materials. The successful immobilization of the carbon structures was confirmed by scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. By generating patterned polymer surfaces with chemically distinct components through the control of polymer–polymer or polymer–substrate interactions, directed assembly of single-walled carbon nanohorns and single-walled nanotubes was demonstrated. This new type of carbon assembly might open up new avenues in the construction of functional polymer/carbon composites and flexible nanocarbon nano-electronics.     

Nanomechanical modeling of interfaces of polyvinyl alcohol (PVA)/clay nanocomposite

Abstract

We study interfacial debonding of several representative structures of polyvinyl alcohol (PVA)/pyrophillite-clay systems – both gallery-interface (polymer/clay interface in the interlayer region containing polymer between clay layers stacked parallel to each other) and matrix-interphase (polymer/clay interphase-region when individual clay layers are well separated and dispersed in the polymer matrix) – using molecular dynamics simulations, while explicitly accounting for shearing/sliding (i.e. Mode-II) deformation mode. Ten nanocomposite geometries (five 2-D periodic structures for tension and five 1-D periodic structures for shearing) were constructed to quantify the structure-property relations by varying the number density of polymer chains, length of polymer chains and model dimensions related to the interface deformation. The results were subsequently mapped into a cohesive traction–separation law, including evaluation of peak traction and work of separation that are used to characterise the interface load transfer for larger length scale micromechanical models. Results suggest that under a crack nucleation opening mode (i.e. Mode-I), the matrix-interphase exhibits noticeably greater strength and a greater work of separation compared to the gallery-interface; however, they were similar under the shearing/sliding mode of deformation. When compared to shearing/sliding, the tensile peak opening mode stresses were considerably greater but the displacement at the peak stress, the displacement at the final failure and the work of separation were considerably lower. Results also suggest that PVA/clay nanocomposites with higher degree of exfoliation compared with nanocomposites with higher clay-intercalation can potentially display higher strength under tension-dominated loading for a given clay volume fraction.     

Fabrication of optical devices in poly(dimethylsiloxane) by proton microbeam

Optical diffraction grating and micro Fresnel zone plate type structures were fabricated in relatively thin poly(dimethylsiloxane) (PDMS) layers using proton beam writing technique and the performance of these optical devices was tested. PDMS is a commonly used silicon-based organic polymer, optically clear, generally considered to be inert, non-toxic and biocompatible. PDMS has been used as a resist material for direct-write techniques only in very few cases. In this work, PDMS was used as a resist material; the structures were irradiated directly into the polymer. We were looking for a biocompatible, micropatternable polymer in which the chemical structure changes significantly due to proton beam exposure making the polymer capable of proton beam writing. We demonstrated that the change in the structure of the polymer is so significant that there is no need to perform any development processes. The proton irradiation causes refractive index change in the polymer, so diffraction gratings and other optical devices like Fresnel zone plates can be fabricated in this way. The observed high order diffraction patterns prove the high quality of the created optical devices.     

熵驱动下柱状高分子刷螺旋结构的研究

自然界中广泛存在螺旋结构,在特定情形下熵能驱动高分子链形成螺旋结构.本文采用分子动力学方法研究柱状高分子刷吸附在无限长圆柱表面时的构象行为.发现其构象与嫁接支链条数、柱状高分子刷与圆柱表面之间的吸附能密切相关.在较弱的吸附能下,具有较多支链条数的柱状高分子刷能形成完整的螺旋结构,其本质就是熵驱动下形成的螺旋结构.该研究有助于加深对生物大分子螺旋结构的理解.     

Direct opal-like structures consisting of monodisperse polymer particles and synthesis of the related inverse structures

Three-dimensional periodic solid-state film structures with a face-centered cubic lattice and a high degree of perfection have been prepared from monodisperse particles of styrene copolymers with methacrylic acid. It has been shown that these structures can be successfully used not only as model objects for studying specific features of light propagation in photonic crystals but also as templates for synthesizing inverse opal-like structures. The influence of the degree of hydrophilization of the surface layer of polymer particles forming a polymer template and the template synthesis conditions on the quality of an inverse opal-like TiO₂-based structure has been analyzed.     

The uses of diversity: non-crystalline arrays in microstructured optical fibres

Microstructured polymer optical fibres (mPOFs) can be more easily fabricated in unusual geometries than their silica counterparts, allowing a more diverse range of structures to be explored. We have used evolutionary algorithms to explore a variety of fibre structures, including non-periodic structures.     

On the morphological similarities between networklike structures in viscoelastic polymer systems and the large-scale structure of the universe

Networklike structures are observed in various materials and nature. The networklike structures in viscoelastic phase separation of polymer mixtures have been explained by a model with a couple of hydrodynamic equations. On the other hand, the large-scale structure of the universe has been explained by a multi-dimensional extension of the Burgers equation. The networklike structures of the two very different systems have some morphological similarities. To see origins of the similarities and differences, the Burgers equation is derived from the model of the polymer mixtures using several approximations. The meaning of the approximations is discussed in connection with the morphology.     

半刚性高分子链螺旋结构诱导纳米棒的有序结构

在自然界中, 螺旋结构广泛存在. 在熵的驱动下, 高分子链能在某些特殊情形下形成螺旋结构. 采用分子动力学方法研究了高分子链诱导纳米棒的自组装行为, 发现纳米棒/高分子链体系的构象与纳米棒的数量、高分子链的刚性等密切相关. 当纳米棒与高分子链之间存在适度吸附能时, 纳米棒能够形成三种完全不同的构象, 特别是在半刚性高分子链诱导下纳米棒能够形成线型排列. 研究结果对新型材料制备具有一定指导意义.     

Large-eddy simulations of a forced homogeneous isotropic turbulence with polymer additives

Large-eddy simulations （LES） based on the temporal approximate deconvolution model were performed for a forced homogeneous isotropic turbulence （FHIT） with polymer additives at moderate Taylor Reynolds number. Finitely extensible nonlinear elastic in the Peterlin approximation model was adopted as the constitutive equation for the filtered conformation tensor of the polymer molecules. The LES results were verified through comparisons with the direct numerical simulation results. Using the LES database of the FHIT in the Newtonian fluid and the polymer solution flows, the polymer effects on some important parameters such as strain, vorticity, drag reduction, and so forth were studied. By extracting the vortex structures and exploring the flatness factor through a high-order correlation function of velocity derivative and wavelet analysis, it can be found that the small-scale vortex structures and small-scale intermittency in the FHIT are all inhibited due to the existence of the polymers. The extended self-similarity scaling law in the polymer solution flow shows no apparent difference from that in the Newtonian fluid flow at the currently simulated ranges of Reynolds and Weissenberg numbers.     

Thin film polymer photonics: Spin cast distributed Bragg reflectors and chirped polymer structures

Polymer based photonic structures were produced by spin coating up to 50 alternating layers of polystyrene (PS) and poly(vinylpyrrolidone) (PVP) from mutually exclusive (orthogonal) solvents. The resulting thin film multi-layer structures were studied using a simple optical reflectivity apparatus and were shown to have narrow (10-20nm wide) reflectance bands in the visible region. The position of the reflectance bands was controlled by varying the spin speed used during production of the multi-layers and peak reflectance values of 55% were obtained for samples containing 50 layers. The results were shown to be in agreement with modified optical transfer matrix method calculations which include the effects of diffuse polymer interfaces. This modelling approach revealed that the width of the polymer/polymer interfaces formed by spin coating was in the range 15-20nm. Data and calculations were also obtained for chirped polymer photonic structures. These results were also shown to be in good agreement. These experiments demonstrate that simple processing methods such as spin coating can be used to produce organic photonic structures with tailored optical properties.