Electronic structure and conduction properties of copolymers of silole based donor-acceptor polymers: effect of multi-neighbour interaction

Using the ab initio band structure results of two novel silole based donor-acceptor polymers PSICF (A)_x and PSICN (B)_x, the electronic structures and conduction properties of their various quasi-one-dimensional superlattices (copolymers) (A_mB_n)_x, belonging to the class of type-II staggered superlattices, have been investigated using negative factor counting method taking into account multi-neighbour interaction. Both PSICF and PSICN consist of a bicyclopentadisilole unit bridged by an electron-accepting group Y (Y=CCF₂ in PSICF and Y=CC(CN)₂ in PSICN). The trends in the electronic structures and conduction properties of these copolymers (A_mB_n)_x as a function of the (i) block sizes m and n; (ii) composition (m/n) and (iii) arrangement of blocks (periodic or aperiodic) in the copolymer chain are discussed. The results obtained are important guidelines for designing copolymers with tailor-made conduction properties.     

Approximate indexing of icosahedral polyhedra with fibonacci numbers

In general, indexing faces of icosahedral face-forms requires irrational numbers. However, for many practical purposes an approximate indexing based on triplets of integer numbers can be used. Two possible approaches called, respectively, “Fibonacci Matrix Methods” (FMM) and the “Linear Combination Method” (LCM) are described. FMM relies on the use of “auxiliary” matrices F_n, F² _n, F³ _n and F⁴ _n which have Fibonacci numbers as their elements. These matrices allow good approximation of the results usually obtained using the standard five-fold rotation matrices which are typical of icosahedral symmetry. LCM is based on the use of a classical crystallographic rule i.e. the so-called “Goldschmidt Complication Law” which is just a particular case of linear combination of triplets of face indices, with integers as coefficients. The occurrence of large integer indices is remarked.     

Comparison of Structure,Morphology, and Properties of Miktoarms Star Styrene-Butadiene Rubber and Star-Shaped Styrene-Butadiene Rubbe/Polybutadiene Rubber Blends

Four miktoarms star-shaped polybutadiene-Sn-poly(styrene-butadiene) rubber (MSS-PB-PSBR) with 1,1-diphenylhexyl at the ends of the arms were prepared by two different coupling techniques. One technique was a one-step technology, from which two miktoarms star styrene-butadiene rubbers, called AMSS-PB-PSBR, were obtained in which the four arm stars had varying ratios of PB:PSBR arms; another was a two-step technology, from which another two miktoarms star styrene-butadiene rubbers, called BMSS-PB-PSBR, were obtained in which all consisted of PB-Sn-(PSBR)₃ stars. The molecular structure parameters and morphology-properties of the four MSS-PB-PSBR were determined and studied, and compared with that of a star-shaped styrene-butadiene rubber (S-SSBR)/poly butadiene rubber (PBR) blend. The results showed that the total coupling efficiency (the ratio of the total number of polymer chains (arms) coupled by SnCl₄ to that of the total number of polymer chains) of the MSS-PB-PSBR was higher than 60%. However, the coupling efficiency of the polybutadiene arms of BMSS-PB-PSBR was obviously higher than that of the AMSS-PB-PSBR. Compared with the S-SSBR/PBR blend, MSS-PB-PSBR had a more uniform distribution of the PB phase and a smaller phase size of PB. It was found that MSS-PB-PSBR composites filled with carbon black (CB) had a lower Payne effect than the S-SSBR/PBR/CB composite, with the BMSS-PB-PSBR/CB composites being especially lower. The BMSS-PB-PSBR/CB composites had higher mechanical properties and lower rolling resistance than the AMSS-PB-PSBR/CB composites due to the high coupling efficiency of the polybutadiene arms; the results indicated that the two-step technology was better than the one-step technology for preparing the tread material of “green” tires.     

Viscoelastic Behavior of Poly(Methyl Methacrylate-Co-Methyl Acrylate) Random Copolymer Studied by Dynamic Mechanical Analysis and Nanoindentation

The viscoelastic behavior of poly(methyl methacrylate) (PMMA) homopolymer and poly(methyl methacrylate-co-methyl acrylate) random copolymers was characterized by dynamic mechanical analysis and nanoindentation. Differential scanning calorimetric results showed only one glass transition, indicating the random distribution of comonomers in the copolymers. The α relaxation temperature (T_α) and activation energy (H_α) decreased with increasing content of methyl acrylate monomers (C_MA%). The β relaxation temperature (T_β) also decreased whereas the activation energy (H_β) showed only small variations compared with H_α. Moreover, the indention displacement and creep compliance strongly depended on C_MA%. Two creep stages were found in the creep compliance curves.     

Kinetics of formation of green rust 2 in the steady acidic sulphated medium

The kinetics of formation of green rust 2, 4Fe(OH)₂.2FeOOH.FeSO₄.nH₂O, called “GR2, was followed by Mössbauer spectroscopy in the controlled aeration of a mixture of 0.4 M FeSO₄ and 0.4 M NaOH. Mössbauer spectra run at 78 K of the reaction products taken at different time intervals display an average of seven doublets. The initial products of reaction consists of a badly crystallized ferrous hydroxide, FE(OH)₂., called “FH”, which disappears first at about 1/3 of the total time of formation of GR2, and sulphated ferrous hydroxide, 4Fe(OH)₂.FeSO₄.nH₂O, called “SFH”. The kinetics of oxidation of SFH into GR2 can be described by a linear growth reaction and the transformation is considered to be in situ.     

Adhesion,morphology, and heat resistance properties of polyurethane coated poly(methyl methacrylate)/fullerene-C60 composite films

Novel polyurethane (PU) adhesive was prepared and coated on poly(methyl methacrylate) (PMMA) and poly(methyl methacrylate)/fullerene (PMMA/Full-C₆₀) composite. Dip-coating technique was employed as facile and cost-effective procedure to coat polyurethane on film substrate. The properties of PU/PMMA and PU/PMMA/Full-C₆₀ composite were studied using Fourier transform infrared spectroscopy, Field Emission Scanning Electron Microscopy, tensile, adhesion, thermal and flammability measurement. Testing polyurethane-coated PMMA exhibited crumpled surface while fullerene addition formed unique pattern of dispersed spherical structures. Fullerene nanofiller loading improved the adhesion and mechanical properties of composite films due to polymer–carbon interaction. In PU/PMMA/Full-C₆₀ 0.5 composite with 0.5 wt.% nanofiller, tensile strength (71.4 MPa) was increased by 18.6% while tensile modulus was increased by 143.85% compared with PU/PMMA. In PU/PMMA/Full-C₆₀ 0.5, T₀ of 473 °C and T_max of 655 °C were observed. Increasing the fullerene content up to 0.5 wt.% decreased the peak heat release rate to 131 kW/m². Novel polyurethane-coated PMMA/Full-C₆₀ composite have potential applications as adhesive coatings in electronic and automotive appliances.     

WAXS studies on crystalline behavior of polymethyl methacrylate-polyethylene oxide graft copolymers and their ionic complexes

A graphical multiple-peak resolution method for wide-angle x-ray scattering (WAXS) patterns is described and used to estimate the apparent crystallinities relative to the entire sample (Xca) in polymethyl methacrylate-polyethylene oxide graft copolymers (PMMA-g-PEO) and their ionic complexes with LiClO₄, KSCN and FeCl₂. The crystallinities (Xcg) and crystallite sizes (L ₁₂₀) in the PEO graft component, alone, were estimated at the same time. A concept of “reduced degree of crystallinity (Rc)” and “critical PEO content” is proposed and applied as a yardstick of the effects of PMMA backbone chains and salts on the crystalline behavior of the PEO graft chains. Xca and Xcg increase with both the content and molecular weight of the PEO graft chains. The critical PEO content, below which PEO crystallinity is not seen, is about 23.7%. PMMA backbone chains can reduce the crystallization of the PEO graft chains at any given PEO content. Xca and Xcg diminish after complexing with the salts and the order of reducing crystallinity is: LiClO4 > KSCN > FeCl₂; salts have two inverse effects, reduction and promotion, on the crystallization of the PEO graft chains. The salt effects depend on the salt concentrations and coordination of the cations. The crystallite sizes in the PEO graft chains are smaller than those in the PEO homopolymers but increase after complexing with salts. The PEO crystallite sizes are not noticeably affected by the content and molecular weight of the PEO graft chains but are noticeably affected by salt concentration.     

Effect of Nanoclay on the Morphology and Properties of Nylon 6 and Poly(Methyl Methacrylate) (PMMA) Blends

The effect of organomodified nanoclay on the morphology and properties of a (70/30 w/w) nylon 6/poly(methyl methacrylate) (PMMA) blend prepared by a melt processing method was investigated. The number average domain diameter (D_n ) of the dispersed PMMA phase was found to decrease with the addition of a small amount [0.5 per hundred resin (phr)] of clay in the blend. A much finer dispersion of the minor phase in the presence of a higher amount (5 phr) of clay indicated better mixing efficiency and improved morphology in the blend. X-ray diffraction indicated the exfoliation of the clays in the nylon 6 matrix, whereas PMMA chains only intercalated into the clay layers. However, the same effect of the clay was not observed in a (30/70 w/w) nylon 6/PMMA blend when nylon 6 became the dispersed domains. In the (30/70 w/w) nylon 6/PMMA blend, the addition of organomodified nanoclay (up to 2 phr) increased the D_n of the nylon 6 domains by preferential location of the clays inside the nylon 6 domains. Addition of styrene-maleic anhydride (SMA) copolymer effectively reduced the D_n of disperse phases in both compositions of the nylon 6/PMMA blends. Thus, in nylon 6/PMMA blends, clay platelets could prevent the coalescence of dispersed domains during melt mixing as long as it was dispersed in the matrix phase of the blend. Mechanical properties and thermal stability of the blends were also improved in the presence of clay.     

Current switching in bistable structures: Heavily doped n +-polysilicon-tunnel-oxide layer-n-silicon

Switching from a state with a steady-state nonequilibrium depletion and low current into the “on” state with a high current and low voltage drop on the structure is observed in highly doped n ⁺-polysilicon-tunnel-oxide-n-silicon structures. The structures were prepared on n-silicon substrates with a resistivity of 25 Ω·cm. A structure with an oxide thickness of 23 Å can be switched on both by a radiation pulse with small reverse bias on the structure (50 V) and under dark conditions by increasing the reverse bias to 250–300 V. In the “on” state Auger carrier production is the internal source of minority carriers that is required for compensating tunnel leakage of holes into the n ⁺-polysilicon and for maintaining a quasiequilibrium inversion layer of holes at the n-Si-SiO₂ boundary.     

Role of salt concentration on conductivity optimization and structural phase separation in a solid polymer electrolyte based on PMMA-LiClO4

Although a large number of ionic conductors based on poly(methyl-methacrylate) (PMMA) are reported in literature, an optimization of salt concentration with respect to conductivity and stability properties remains by and large neglected. We report, perhaps for the first time, such an optimization of salt (LiClO₄) concentration on structural, morphological, electrical, and ion–polymer interaction in PMMA-based solid polymer films. The active coordination site for the cation (Li⁺), out of the two possible electron donating functional groups (i.e. C=Ö and Ö–CH₃) in PMMA, has been ascertained on the basis of evidences recorded in Fourier transform infrared spectrum. The results suggested C=Ö as the only possible site in PMMA matrix for coordination with Li⁺ cation. The X-ray diffraction results have clearly indicated an optimum limit of salt dissolution in PMMA matrix corresponding to O/Li = 4 (i.e., ~21wt.%) above which “phase-separation” occurs distinctly. The effect of salt concentration on amorphous → crystalline phase changes in PMMA and its correlation to morphology have been clearly observed in terms of their impact on electrical properties. An optimum electrical conductivity of ~7.2 × 10^?5S cm^?1 has been recorded at 100°C (~PMMA glass transition). The temperature dependence of conductivity follows typical Vogel–Tamman–Fulcher behavior.     

Preparation and Characterization of an Organic/Inorganic Composite Based on Ferrospinel with Poly(Methyl Methacrylate) and Polyaniline

A novel organic/inorganic composite based on LiNi–ferrospinel with poly(methyl methacrylate) (PMMA) and polyaniline (PANI), PANI/PMMA/LiNi_0.5Fe₂O₄ composite, was synthesized via a facile in-situ polymerization process. The structures of the resulting samples were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, and atomic force microscopy. The optical and thermal properties of the PANI/PMMA/LiNi_0.5Fe₂O₄ composite were studied by fluorescent spectroscopy and thermogravimetry analysis. It was indicated that the existence of LiNi_0.5Fe₂O₄ (LFNO) in the PANI/PMMA/LFNO composite resulted in changes in the fluorescence spectra. The as-obtained composite may have potential for electrical and electromagnetic applications in antistatic materials, electromagnetic shields, radar absorbers, and so forth.     

New approach in synthesis,characterization and release study of pH-sensitive polymeric micelles,based on PLA-Lys-<Emphasis Type="Italic">b</Emphasis>-PEGm,conjugated with doxorubicin

Amphiphilic block copolymers are well established as building blocks for the preparation of micellar drug carriers. The functional polymer micelles possess several advantages, such as high drug efficiency, targeted delivery, and minimized cytotoxicity. The synthesis of block copolymers using nano-structured templates has emerged as a useful and versatile approach for preparing drug carriers. Here, we report the synthesis of a smart polymeric compound of a diblock PLA-Lys-b-PEG copolymer containing doxorubicin. We have synthesized functionalized diblock copolymers, with lysinol, poly(lactide) and monomethoxy poly(ethylene glycol) via thermal ring-opening polymerization and a subsequent six-step substitution reaction. A variety of spectroscopic methods were employed here to verify the product of our synthesis. ¹H-Nuclear magnetic resonance and Fourier transform infrared studies validated the expected synthesis of copolymers. Doxorubicin is chemically loaded into micelles, and the ex vitro release can be evaluated either in weak acidic or in SBF solution by UV–vis spectroscopy. Dynamic light scattering, thermo gravimetric analysis, and size exclusion chromatography have also been used.     

End group effect on surface and interfacial segregation in PS-PMMA blend thin films

Thin films of polystyrene (PS)/poly (methyl methacrylate) (PMMA) blends with different end groups were investigated using ToF-SIMS and AFM. PS with -OH and -NH₂ end groups were blended in toluene solvent with pure PMMA homopolymer, and PMMA having anhydride end group. The ToF-SIMS spectra of PS-OH/PMMA resembled that of pure PS-PMMA blends showing an increase of PMMA intensity after annealing. On the contrary, the PS-NH₂ blended with PMMA showed an increase in PS intensity on the surface after annealing. The ToF-SIMS spectra were similar to that of a pure PS-PMMA di-block copolymer. These results indicate copolymer formation at the surface. The PS-NH₂ with PMMA-anhydride blend spectra showed very slight changes in spectra before and after annealing and the AFM images revealed spinodal bi-continuous structures on the surface before and after annealing. The copolymer formation is found to occur in the as-cast film itself and not after thermal treatment.     

Surface-grafted block copolymer gradients: Effect of block length on solvent response

We outline a method to fabricate gradient combinatorial libraries that explore architectural parameters of surface-grafted block copolymers (BCs). In addition, we demonstrate the utility of such libraries for the rapid, thorough assessment of the response of grafted BCs to solvent exposure. Our fabrication route uses surface-initiated controlled radical polymerization to produce a tethered polymer block with uniform length (in this case, poly(n-butyl methacrylate), PBMA), followed by a graded synthesis that adds a second block that varies in its length over the library (here, poly(2-(N,N′-dimethylamino)ethyl methacrylate), PDMAEMA). Our demonstration study maps the response of PBMA and PDMAEMA blocks to hexane and water, and defines regimes of behavior to this respect. Moreover, our study illuminates a narrow BC composition window that exhibits the strongest possible response to water and hexane treatment.     

Morphology of Fractured Polymer‐Polymer Interfaces Bonded at Ambient Temperature as Studied by Atomic Force Microscopy

The amorphous polymer surfaces of polystyrene (PS, M _n=200 kg/mol, M _w/M _n=1.05) and poly(methyl methacrylate) (PMMA, M _n=51.9 kg/mol, M _w/M _n≤1.07) were brought into contact at 21°C to form PS‐PS (for 54 days) and PMMA‐PMMA auto‐adhesive joints (for 11 days). After contact at that temperature corresponding to T _g‐bulk ?81°C for PS and to T _g‐bulk–88°C for PMMA, where T _g‐bulk is the calorimetric glass transition temperature of the bulk sample, the bonded interfaces were fractured and their surfaces were analyzed by atomic force microscopy (AFM). The surface roughness, R _q, of the fractured interfaces was larger by a factor of 3–4 than was that of the free PS and PMMA surfaces aged for the same period of time. A similar increase in R _q was found by comparison of the free PS surface aged at T _g‐bulk+15°C for 1 h and of the surface of the PS‐PS interface fractured after healing at T _g‐bulk+15°C for 1 h. These observations, indicative of the deformation of the fractured interfaces, suggest the occurrence of some mass transfer across the interface even below T _g‐bulk ?80°C.     

Linear and nonlinear optical properties of luminescent ZnO nanoparticles embedded in PMMA matrix

ZnO nanoparticles embedded in the PMMA matrix were prepared by wet chemical synthesis. The optical band gap of the ZnO nanoparticles decreases with increase in NaOH concentration. The photoluminescence spectra of the ZnO colloids show strong UV, green and blue emissions. The optical absorptive nonlinearity of the ZnO:PMMA composites was analyzed using an open aperture Z-scan technique which shows optical limiting type nonlinearity due to the two photon absorption in ZnO. The efficiency of limiting is found to increase with decrease in the band gap. ZnO:PMMA shows a negative value for nonlinear refractive index n₂ and the magnitude of n₂ increases with decrease of band gap. Stability as well as the mechanical properties of the nanoparticles embedded in the PMMA matrix makes it more suitable for device fabrication as compared to the ZnO nanoparticles dispersed in solution.     

On the electronic structure and conduction properties of polymeric quasi-one-dimensional model superlattices: Study of Type I and Type II-staggered superlattices

The electronic spectrum of the various quasi-one-dimensional model compositional superlattices (copolymers) (A_mB_n)_x belonging to class of Type I and Type II-staggered superlattices have been calculated in the tight binding approximation using the direct numerical approach. The trends in their electronic structure and conduction properties as a function of (i) composition (m/n), (ii) block sizes m and n and (iii) arrangement of the blocks in the copolymer chain are discussed. The results obtained are important guidelines for designing copolymers with tailor made conduction properties.     

Bonding at Compatible and Incompatible Amorphous Interfaces of Polystyrene and Poly(Methyl Methacrylate) Below the Glass Transition Temperature

Abstract

Films of high‐molecular‐weight amorphous polystyrene (PS, M _w = 225 kg/mol, M _w/M _n = 3, T _g‐bulk = 97°C, where T _g‐bulk is the glass transition temperature of the bulk sample) and poly(methyl methacrylate) (PMMA, M _w = 87 kg/mol, M _w/M _n = 2, T _g‐bulk = 109°C) were brought into contact in a lap‐shear joint geometry at a constant healing temperature T _h, between 44°C and 114°C, for 1 or 24 hr and submitted to tensile loading on an Instron tester at ambient temperature. The development of the lap‐shear strength σ at an incompatible PS–PMMA interface has been followed in regard to those at compatible PS–PS and PMMA–PMMA interfaces. The values of strength for the incompatible PS–PMMA and compatible PMMA–PMMA interfaces were found to be close, both being smaller by a factor of 2 to 3 than the values of σ for the PS–PS interface developed after healing at the same conditions. This observation suggests that the development of the interfacial structure at the PS–PMMA interface is controlled by the slow component, i.e., PMMA. Bonding at the three interfaces investigated was mechanically detected after healing for 24 hr at T _h = 44°C, i.e., well below T _g‐bulks of PS and PMMA, with the observation of very close values of the lap‐shear strength for the three interfaces considered, 0.11–0.13 MPa. This result indicates that the incompatibility between the chain segments of PS and PMMA plays a negligible negative role in the interfacial bonding well below T _g‐bulk.