Mie scattering efficiency of a large spherical particle embedded in an absorbing medium

The Mie scattering calculations are usually performed for non-absorbing spherical particles embedded in a non-absorbing medium. We consider a case of an absorbing sphere placed in an absorbing medium. We find, by numerical calculation for large size parameter of the order of 10⁴, that the scattering efficiency of a spherical particle in an absorbing medium approaches the reflectance of a plane surface at perpendicular incidence.     

Morphology controlled open circuit voltage in polymer solar cells

We report a strong dependence of open circuit voltage on the altered morphology of block copolymer (P3HT‐b ‐PPerAcr) based solar cells. The open circuit voltage increases dramatically by about 300 mV by increasing the amount of acceptor homopolymer within the block copolymer/homopolymer blends. The change in open circuit voltage is found to be in correlation with the enrichment of acceptor moiety at the film surface as identified by Atomic force microscopy (AFM) and X‐ray photoelectron spectroscopy (XPS). Based on this fact, an additional increase in open circuit voltage to its maximum values is achieved by introducing an acceptor buffer layer at the cathode interface. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Improving polymeric microemulsions with block copolymer polydispersity

Recent experiments have demonstrated that block copolymers are capable of stabilizing immiscible homopolymer blends producing bicontinuous microemulsion. The stability of these polymeric alloys requires the copolymer to form flexible, nonattractive monolayers along the homopolymer interfaces. We predict that copolymer polydispersity can substantially and simultaneously improve the monolayers in both of these respects. Furthermore, polydispersity should provide similar improvements in systems, such as colloidal suspensions and polymer/clay composites, that utilize polymer brushes to suppress attractive interactions.     

Exact results for the adsorption of a semiflexible copolymer chain in three dimensions

Lattice model of directed self-avoiding walk has been solved analytically to investigate adsorption–desorption phase transition behaviour of a semiflexible sequential copolymer chain on a two-dimensional impenetrable surface perpendicular to the preferred direction of the walk of the copolymer chain in three dimensions. The stiffness of the chain has been accounted by introducing an energy barrier for each bend in the walk of the copolymer chain. Exact value of adsorption–desorption transition points have been determined using the generating function method for the cases in which one type of monomer is having interaction with the surface, namely (i) no interaction (ii) attractive interaction and (iii) repulsive interaction. Results obtained in each of the case show that for stiffer copolymer chain adsorption transition occurs at a smaller value of monomer surface attraction than a flexible copolymer chain. These features are similar to that of a semiflexible homopolymer chain adsorption.     

Tetramethylpolyarylate-polyarylate block copolymer: Synthesis and miscibility with polyarylate and poly(styrene-co-acrylonitrile)

Abstract

Tetramethylpolyarylate-polyarylate (TMPAr-PAr) block copolymers of various block lengths were synthesized by the coupling reaction of hydroxy-terminated TMPAr and hydroxy-terminated PAr using triphosgene. The phase behavior of these block copolymers are discussed based on the thermal properties observed by differential scanning calorimetry (DSC). The thermal properties of binary blends of these block copolymers with PAr homopolymer or poly(styrene-co-acrylonitrile) whose acrylonitrile content is 9.5 wt% (SAN 10) were observed by DSC. The compatibilizing effect of the microphase-separated TMPAr-PAr block copolymer in PAr/SAN 10 blends was observed from thermal properties and morphology.     

Localisation and damping in resonators with complex geometry

Based on numerical studies, we show that localisation is a common phenomenon in resonators exhibiting some kind of geometrical complexity. In two-dimensional (2d) shallow cavities of irregular shape, localisation effects are due to spatial decoherence in a major fraction of the volume. In 2d shallow cavities of regular geometry with embedded absorbing material of irregular shape, one observes the appearance of eigenmodes localised in both, the absorbing and the non-absorbing media. Those modes are thought to be responsible for increased dissipation. These results may be a hint to understand why natural or practical systems absorbing wave energy are found, or built, with complex geometry.     

Single layer homogeneous model for surface roughness by polarized light scattering

In this paper a homogeneous single layer model for surface roughness by polarized light has been developed. It has been shown that the reflectance change in non-absorbing layer is directly proportional to the refractive index of the ambient and substrate media for s polarization but inversely proportional to the p polarization and it is directly proportional to the square of the thickness of the layer for both the polarization. In an absorbing layer, it has been shown that the thickness of the layer is equal to the twice of surface roughness of the single layer identical system for s polarization but it is ratio of twice of surface roughness to the square of refractive index of thin film for p polarization. The extinction coefficient of the layer is directly proportional to the thickness of that layer for both the polarization. The consequence of the scattered light on the specular reflectance and transmittance for oblique incidence shows that there is reduction in reflectance (in both non-absorbing and absorbing cases) and transmittance (in the absorbing case for p polarization only), due to roughness on the surface under the Drude effective-medium approximation. Thus such an absorbing layer provides a valid model for the effect of scatter on the transmittance for p polarization only.     

最有效的相容剂是两嵌段还是多嵌段聚合物？

采用Monte Carlo模拟方法研究了多嵌段聚合物在A／B／嵌段聚合物三组份体系作为相容剂使用的有效性．占总体积19％的A组份在体系中为分散相．模拟结果显示了两嵌段和多嵌段聚合物在界面上的聚集行为,以及如何影响这个不相容体系的相形为．两嵌段聚合物趋于直立在相界面上,而多嵌段聚合物更容易横跨在相界面上并占据较大的界面积．从而导致多嵌段聚合物更有效的阻止体系相分离的发生．     

Self-induced transparency in diblock copolymer dispersions

We report on the versatile effect of weak red laser light impinging on diblock copolymer [poly(isoprene-b-styrene)] dispersions in two selective solvents for each block. In the strongly scattering but transparent micellar solutions in hexane (a good solvent for polyisoprene), higher refractive index copolymer-rich fibers were formed. In the turbid dispersions of the same copolymer in ethyl acetate (a good solvent for polystyrene), the effect of self-induced transparency was observed. A two-step patterning mechanism caused the generation of a transparent microchannel, increasing light transmission. The analogy between the current effect and that observed in homopolymer polyisoprene solutions in different solvents is discussed toward an understanding of the unanticipated light-soft-matter interaction.     

Determination of refractive indices and thickness of absorbing crystalline thin films by using prism coupler

An improved method has been implemented to study the refection of optical plane waves from anisotropic and absorbing films. The refection from anisotropic non-absorbing films and from isotropic non-absorbing films can be shown as some special cases. The method in this paper can be applied to almost all kinds of materials involved in optical films and integrated optics studies. Guided waves in the anisotropic and absorbing waveguides are determined, and the prism coupler method is employed to determine refractive indices and thickness of the anisotropic and absorbing films. The results show that when we only couple light beams into films with small effective indices, the effect of the absorption can be neglected.     

Dynamic mechanical and morphological studies of homopolymer/block copolymer blends

A triblock copolymer of styrene-butadiene-styrene (SBS) was blended with a high and a low molecular weight polybutadiene [designated as PB(H) and PB(L), respectively]. Electron micrographs of these blends show that PB(L) was solubilized into the butadiene domains of the SBS, while PB(H) was present in a separate phase. Dynamic mechanical data of the SBS&PB(L) blends indicate the presence of an intermediate loss peak between those of the glass transitions of the styrene and butadiene blocks in SBS, which can be attributed to the slippage of untrapped entanglements of PB(L) chains. Similar data for blends containing PB(H) also show an intermediate loss peak, which is, however, due to crystallization and melting of the polycisbutadiene chains. The peak due to the primary glass transition of the butadiene phase was shifted to lower temperatures upon incorporation of PB(L) as a result of plasticization effect of PB(L). The same transition for PB(H) blends is split into a doublet because of the presence of the homopolymer in a separate phase. Dynamic mechanical data for cross-linked blends were also taken for comparison.     

Determination of refractive indices and thickness of absorbing crystalline thin films by using prism coupler

Abstract

An improved method has been implemented to study the refection of optical plane waves from anisotropic and absorbing films. The refection from anisotropic non-absorbing films and from isotropic non-absorbing films can be shown as some special cases. The method in this paper can be applied to almost all kinds of materials involved in optical films and integrated optics studies. Guided waves in the anisotropic and absorbing waveguides are determined, and the prism coupler method is employed to determine refractive indices and thickness of the anisotropic and absorbing films. The results show that when we only couple light beams into films with small effective indices, the effect of the absorption can be neglected.     

Thermo-Sensitivity of poly-N-isopropylacrylamide with Statistically Introduced D,L-Allylglycine Betainic Units

Abstract

Statistical copolymers of N-isopropylacrylamide containing 2.2 – 2.7?mol % D,L-allylglycine were synthesized. The sample with 2.2?mol % allylglycine and molar mass 320000?g/mol was studied using light scattering and turbidimetry while heated in water and water–salt solutions. Temperature dependencies of light scattering intensity and optical transmission as well as hydrodynamic size and composition of the scattering entities were obtained in a wide range of pH. The onset temperatures of phase separation were independent of pH; however, in the basic pH region the phase transition was widened as compared to the neutral and acid media. It was shown that a small content of allylglycine results in a different thermoresponsive behavior of the copolymer as compared with N-isopropylacrylamide homopolymer. The addition of a physiological amount of NaCl shifts the copolymer thermo-sensitivity toward lower temperatures.     

Binary-component micelle and vesicle: Free energy and asymmetric distributions of amphiphiles between monolayers of vesicle

The real-space two-dimensional self-consistent field theory (SCFT) is employed to study the free energies of micelles and vesicles constituted by binary amphiphilic diblock copolymer AB in homopolymer A. With increasing volume fraction of copolymer AB, there are morphological transitions from the circle micelles to oblate circle-like micelles, to compound structure with inverted micelles in the inner center and micelles outer layer, and to vesicles. Special attentions are paid to the role of the copolymer AB in controlling free energies of the micelles and vesicles, by examining the effect of length ratio of A/B with the fixed whole chain length of AB copolymer, the length effect of A or B block with the corresponding fixed length of B or A block, for one component of copolymer, and the effect of different amphiphile compositions for binary-component copolymer system. The quantity η is provided to describe the asymmetric density distribution of amphiphiles between the inner and outer monolayers of vesicles, and to quantify the relative asymmetric extent of the density distribution between two species of copolymers in binary component vesicles.     

The effects of a laser field on phase transitions in liquid crystals

We investigate theoretically some phase transitions in liquid crystals in the presence of a laser beam. We found, in non-absorbing nematics, a laser-induced one-way transition from a paranematic to a nematic phase. In absorbing nematics we found, in addition to this transition, a one-way transition from a nematic to a paranematic phase with increasing laser intensity. Further, we found a reentrant nematic or a reentrant paranematic via paranematic or nematic phase respectively. In the case of smectic A, laser absorption results in a coupling between the positional and orientational orders. As a result, the smectic A to nematic transition can change from second order to first order and the smectic C to smectic A transition can become first-order in the field of a laser.     

Complexes of block copolymers in solution: Tree approximation

We determine the statistical properties of block copolymer complexes in solution. These complexes are assumed to have the topological structure of (i) a tree or of (ii) a line-dressed tree. In case the structure is that of a tree, the system is shown to undergo a gelation transition at sufficiently high polymer concentration. However, if the structure is that of a line-dressed tree, this transition is absent. Hence, we show the assumption about the topological structure to be relevant for the statistical properties of the system. We determine the average size of the complexes and calculate the viscosity of the system under the assumption that the complexes geometrically can be treated as porous spheres.     

Surface wetting behavior of the poly(styrene-b-isoprene-b-styrene) triblock copolymer with different chemical structures of the polyisoprene block chain

The relationship between the chemical structure of a block copolymer and its surface structure and properties is very important for the careful design of its outer surface layer. For this paper, a series of poly(styrene-b-isoprene-b-styrene) triblock copolymers (SIS), with different chemical structures in the polyisoprene block chain, were synthesized by anionic polymerization and their dynamic wetting behaviors were investigated. The dynamic contact angles of the polyisoprene homopolymer (PI) and the SIS were almost the same when the PI and the corresponding block in the SIS had similar chemical structures. The receding contact angle (θ_r) of SIS depended on the microstructure of the PI block chain, however, the advancing contact angles (θ_a) were almost the same regardless of the PI’s chemical structures. The receding contact angle (θ_r) of SIS containing 3,4-PI was far higher than that of SIS with 1,4-PI. Meanwhile, it gradually approached that of SIS with 1,4-PI as the of 3,4-PI content decreased or as the local temperature increased. Contact angle measurement is one of the most sensitive methods for providing information on the outer few angstroms of a polymer’s surface. Therefore, by designing SIS with different chemical structures in the PI block, it was confirmed that the properties and structure of the outermost layer of the SIS were controlled primarily by the PI block’s chemical structure. This demonstrates the possibility to modulate the surface structure and properties of SIS by adjusting the chemical structure of polyisoprene segment.     

Comparative study of liquid-crystalline ordering in a monomer,linear polymer,and graft copolymer by the photon transmission technique

The photon transmission technique was used to study the phase transitions of a liquid crystalline acrylate monomer, 6-(4-cyanobiphenyl-4′oxy)hexyl acrylate (LC6), its homopolymer (PLC6) and its graft copolymer (GLC6) with polytetrahydrofuran grafts. The phase transitions were also confirmed by DSC and polarizing microscopy. We observed the phase transition sequence isotropic–nematic–smectic A–smectic C in the LC6 monomer. In PLC6 and GLC6 polymers, the nematic and smectic A phases appear dominant. The apparent nematic–smectic A transition is of first order in PLC6 and of second order in GLC6, with the transition temperature remaining the same. The effects of quenched random constraints introduced in GLC6 are consistent with the theory of quenched random interactions. The critical exponents were also evaluated.     

Preparation and Characterization of Poly (Acrylonitrile-co-1-Acryloylpyrrolidine- 2-Carboxylic Acid) with High Molecular Weight

1-acryloylpyrrolidine-2-carboxylic acid (APCA) monomer was copolymerized with acrylonitrile (AN) by aqueous suspension polymerization. High molecular weight (HMW) copolymers of AN and APCA [poly(AN-co-APCA)] with different copolymer composition were successfully prepared by employing azobisisobutyronitrile (AIBN) as initiator and polyvinyl alcohol (PVA) as dispersant in a H₂O/N,N-dimethylformamide (DMF) mixture at 60°C. The PAN homopolymer and copolymers were characterized by elemental analysis (EA), nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The EA results indicated that the content of oxygen increased significantly in PAN copolymers with increasing APCA content. The APCA copolymer composition calculated from the EA was higher than that from ¹H NMR spectra. The FTIR spectra of PAN and poly(AN-co-APCA) with different monomer ratios confirmed that the contents of APCA units in the copolymer chains increased with increasing APCA content in the feed. The DSC exotherms revealed that copolymerization with APCA could slow the rate of the exothermic reactions during the heat-treatment processes. The XRD results indicated that the PAN homopolymer and copolymers poorly crystallized and the crystallinity decreased with increasing APCA contents.     

Some calculations of temperature profiles in thin films with laser heating

We present some calculations of heat flow in an absorbing film deposited on a non-absorbing substrate. The energy source is a Gaussian laser beam. We analyse the effects of film thickness, thermal conductivity, spot radius and forced cooling on the temperature profile and, in a special case, the time evolution of that profile. The emphasis is on applications in optical bistability.