Homogeneous Poly Research Articles

Conformational dependence of the electronic coupling for singlet excitation energy transfer in DNA. An INDO/S study

Using the INDO/S method, we study the effects of structural fluctuations on the interaction of singlet excited states in homogeneous poly(dA)-poly(dT) and alternating poly(dAdT)(2) stacks. The coupling for excitation energy transfer (EET) between intra- and inter-strand nucleobases is derived with the fragment excitation difference scheme (Hsu, et al. J. Phys. Chem. C 2008, 112, 1204). In this approach, both Coulomb and short-range contributions to the EET coupling are properly accounted for. 15 000 conformations for each nucleobase dimer were considered. Conformational fluctuations of DNA are shown to result in a large variation of the transfer integral. The root mean square coupling values are used to characterize the interaction of pi-pi* states in DNA. The intra-strand and inter-strand couplings between adenines are found to be significantly smaller than those for thymines. Our findings suggest that (1) EET couplings in DNA are significantly more sensitive to conformational changes of the pi stack than is estimated within the dipole-dipole scheme; (2) singlet excitation energy transfer in poly(dA)-poly(dT) should dominantly occur through thymine bases; (3) pi-pi* excited states in homogeneous stacks are more delocalized than in alternating sequences; (4) structural fluctuations can strongly affect the exciton distribution.

Morphological and physicochemical properties of spin-coated poly(3-octylthiophene)/polystyrene composite thin films

Poly(3-octylthiophene) (P3OT) was synthesized by direct oxidation of 3-octylthiophene with FeCl 3 as oxidant. Molecular weight of P3OT polymer was measured by size exclusion chromatography. Homogeneous poly(3-octylthiophene) (P3OT) and polystyrene (PS) composite films have been synthesized by spin-coating technique from toluene with different polymer concentrations. The doped films were obtained by immersion for 30 s in a 0.3 M ferric chloride (FeCl 3) solution in nitromethane. A classical percolation phenomenon was observed in the electrical properties of these blends, it was smaller than 5% of P3OT in the blend. Surface topographical changes were studied by atomic force microscopy (AFM). AFM images of the composite films revealed surface morphology variation as a function of different P3OT concentration in PS, phase segregation was observed, and PS is shown to segregate to the surface of the films. The higher PS solubility, in comparison with the P3OT solubility, in toluene resulted in PS/P3OT bilayers. The films exhibited pit and island like topography, the pit size changed with the polymer concentration. Optical absorption properties of the polymeric films were analyzed in pristine and doped state. In doped state, the bipolaronic bands at 0.5 and 1.6 eV are shown in a 4% conductive polymer in the PS/P3OT film. Finally thermogravimetric analysis was also made on the simple and composite polymers.

Scanning Tunneling Spectroscopy of Single DNA Molecules

We briefly present the results of recent experiments of transverse scanning tunneling spectroscopy of homogeneous poly(dG)-poly(dC) DNA molecules and discuss them in the light of theoretical investigation. A semiempirical theoretical model is adopted to describe the transverse tunneling current across a DNA molecule placed between a metallic gold substrate and a metallic STM tip. We show that the main trends in the positions and relative magnitudes of the conductance peaks can be explained by a minimal model of a double tunnel junction with the molecule-electrode couplings and the applied voltage explicitly taken into account.

Effects of ingredients on thermal and mechanical properties of acrylic bone cements

AbstractThere is a very delicate relation between the amounts of all the ingredients present in the cement composition and the properties of the product. In this study, homogeneous poly(methyl methacrylate) (PMMA) microspheres were prepared by suspension polymerization technique, and used in cement formulations. Various acrylic cements with different compositions were prepared by using PMMA microspheres, methyl methacrylate (MMA) monomer, radiopaque agent of barium sulfate (BaSO4), inorganic particles of hydroxyapatite (HA), initiator and chain stopping agent of 1‐dodecyl mercaptan (DDM). The effects of these additives on mechanical and thermal properties of the resultant cements were examined. Addition of 8% HA relative to the solid parts caused an increase in both tensile and compressive strengths from 20.40 to 25.20 MPa, and from 84.04 to 89.57 MPa, respectively, while curing temperature was decreased about 3 degrees. Chain stopping agent of DDM caused a sharp decrease about 30 degrees in the curing temperature. Radiopaque agent of barium sulfate caused inverse effect on mechanical and thermal properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

The effect of surface microtopography of poly(dimethylsiloxane) on protein adsorption, platelet and cell adhesion

Chemical homogeneous poly(dimethylsiloxane) (PDMS) surface with dot-like protrusion pattern was used to investigate the individual effect of surface microtopography on protein adsorption and subsequent biological responses. Fibrinogen (Fg) and fibronectin (Fn) were chosen as model proteins due to their effect on platelet and cell adhesion, respectively. Fg labeled with 125I and fluorescein isothiocyanate (FITC) was used to study its adsorption on flat and patterned surfaces. Patterned surface has a 46% increase in the adsorption of Fg when compared with flat surface. However, the surface area of the patterned surface was only 8% larger than that of the flat surface. Therefore, the increase in the surface area was not the only factor responsible for the increase in protein adsorption. Clear fluorescent pattern was visualized on patterned surface, indicating that adsorbed Fg regularly distributed and adsorbed most on the flanks and valleys of the protrusions. Such distribution and local enrichment of Fg presumably caused the specific location of platelets adhered from platelet-rich plasma (PRP) and flowing whole blood (FWB) on patterned surface. Furthermore, the different combination of surface topography and pre-adsorbed Fn could influence the adhesion of L929 cells. The flat surface with pre-adsorbed Fn was the optimum substrate while the virgin patterned surface was the poor substrate in terms of L929 cells spread.

Pore Formation in Poly(divinylbenzene) Networks Derived from Organotellurium-Mediated Living Radical Polymerization

Macroporous cross-linked polymeric dried gels have been obtained by inducing phase separation in a homogeneous poly(divinylbenzene) (PDVB) network formed by organotellurium-mediated living radical polymerization (TERP). The living polymerization reaction of DVB with the coexistence of a nonreactive polymeric agent, poly(dimethylsiloxane) (PDMS), in solvent 1,3,5-trimethylbenzene (TMB) resulted in polymerization-induced phase separation (spinodal decomposition), and the transient structure of spinodal decomposition has been frozen by gelation. Well-defined macroporous monolithic dried gels with bicontinuous structure in the micrometer scale are obtained after removing PDMS and TMB by simple washing and drying. Inside the skeletons that comprise the macroporous structure, “skeletal pores” with various sizes in nanometer scale have also been found by gas sorption measurements. The skeletal pores are deduced to be formed by secondary phase separation in the skeletons due to the thermodynamic instability that ...

Kinetics Study of Mesophase-Crystal Transformation in Highly Oriented Homogeneous Poly(ethylene-co-1-octene) Filament

The thermal stability of highly oriented homogeneous poly(ethylene-co-1-octene) (h-PEO) fiber during annealing process was carefully studied by time-resolved two-dimensional wide-angle X-ray diffraction (WAXD) pattern. The experimental results show that three phases exist in h-PEO fiber, orthorhombic crystal phase, pseudo-hexagonal mesophase, and amorphous phase, which are stable at room temperature. As soon as the fiber is heated, the mesophase transforms to orthorhombic crystal phase. This transformation kinetics was analyzed in terms of Avrami phase transformation theory. The Avrami index was found to be 1, indicating one-dimensional growth. This can be explained by the bundle-like crystal morphology existing in h-PEO.

Pervaporation dehydration of alcohol–water mixtures: Optimization for permeate flux and selectivity by central composite rotatable design

A central composite rotatable design (CCRD) of response surface methodology was used to analyze pervaporation performance of homogeneous poly(vinyl alcohol) (PVA) membranes. A regression model was developed for the pervaporation flux and selectivity as a function of the operating conditions: temperature, concentration and flow-rate. Dehydration experiments were performed on two different alcohol–water systems: isopropanol–water (IPA–water) and ethanol–water (Et–water) mixtures around their azeotropic concentrations. Based on preliminary experiments and CCRD design, the ranges of values of the operating conditions were selected: temperature 33–67 °C, feed flow-rate 46–114 L/h, and concentration 83–92 wt% for IPA and 93–98 wt% for Et in feed mixtures. A total of 20 pervaporation experiments were conducted for each alcohol–water system. Judged by the lack-of-fit criterion, the analysis of variance (ANOVA) showed the regression model to be adequate. From the regression analysis, the flux and selectivity were expressed with quadratic equations of temperature, feed concentration and flow-rate. The predicted flux and selectivity from the regression model were presented in 3D surface plots. For both alcohol–water systems, quadratic terms of temperature and feed alcohol concentration showed significant ( p < 0.0001) influence on the flux and selectivity. A strong interaction effect of temperature and concentration was observed on the selectivity for the Et–water system. However, the interaction of flow-rate with temperature or concentration was found to be less significant. In order to optimize the pervaporation flux and selectivity of azeotropic alcohol–water mixtures, the desirability function approach was applied to analyze the regression model equations by commercial software. For the azeotropic IPA–water mixture (87.5 wt% IPA), the optimized dehydration variables were found to be 50.5 °C and 93.7 L/h for temperature and flow-rate, respectively. For the azeotropic Et–water mixture (95.5 wt% Et), the optimized temperature and flow-rate were found to be 57 °C and 89.2 L/h, respectively. Compared with experiments performed at optimized temperature and flow-rate, the predicted flux and selectivity of the azeotropic mixtures showed errors to be within 3–6%.

Homogeneous Poly(acrylamide) Hydrogels Made by Large Size, Flexible Dimethacrylate Cross-Linkers

Figure 1. (A) G′(filled symbols) and G′′(open symbols) of the reaction system in the presence of DMA-4 shown as a function of the reaction time. DMA-4 ) 0.3 (9), 2.0 (b), 3.3 ((), and 5 mol % (.). (B) The effective cross-link density νe of the hydrogels shown as a function of the cross-linker concentration. The solid curves are a guide to the eye. x ) 1( ∆ ), 2( 2 ), 4( b ), 9( O), and 14 (1).

Theoretical Verification of Surface Cross-Linking as an Effective Method To Reduce Initial Burst Release from Swellable Hydrogels

In this paper, we extend a mathematical model previously proposed for drug release from homogeneous swellable hydrogels to surface cross-linked hydrogels. This new model predicts the simultaneous water uptake into and drug diffusion from a cross-linked hydrogel with a bulk inner core surrounded by a highly cross-linked surface layer. The model verifies our experimental work to show that the treatment of surface cross-linking can be used to reduce the initial burst observed in homogeneous poly(vinyl alcohol) hydrogels and achieve near zero-order release. In the model, the parameter that has the greatest impact on reduced burst release is the water partition coefficient between the surface cross-linked and bulk layers.

Mathematical Model to Predict Drug Release, Including the Early-Time Burst Effect, from Swellable Homogeneous Hydrogels

In this work, we present a mathematical model for the simulation of water uptake by and drug release from homogeneous hydrogels. This model successfully predicts the shape of the water uptake profile (including Super Case II transport) as well as the initial burst release observed experimentally in homogeneous poly(vinyl alcohol) hydrogels. Parameter sensitivity studies were performed on the modeling of homogeneous hydrogels, showing the polymer relaxation constant had a profound effect on water uptake and drug release.

Conformations of poly{G}–poly{C} π stacks with high hole mobility

Charge transfer properties of DNA depend strongly on the pi stack conformation. In the present paper, we identify conformations of homogeneous poly-{G}-poly-{C} stacks that should exhibit high charge mobility. Two different computational approaches were applied. First, we calculated the electronic coupling squared, V(2), between adjacent base pairs for all 1 ps snapshots extracted from 15 ns molecular dynamics trajectory of the duplex G(15). The average value of the coupling squared <V(2)> is found to be 0.0065 eV(2). Then we analyze the base-pair and step parameters of the configurations in which V(2) is at least an order of magnitude larger than <V(2)>. To obtain more consistent data, approximately 65,000 configurations of the (G:C)(2) stack were built using systematic screening of the step parameters shift, slide, and twist. We show that undertwisted structures (twist<20 degrees) are of special interest, because the pi stack conformations with strong electronic couplings are found for a wide range of slide and shift. Although effective hole transfer can also occur in configurations with twist=30 degrees and 35 degrees, large mutual displacements of neighboring base pairs are required for that. Overtwisted conformation (twist> or =38 degrees) seems to be of limited interest in the context of effective hole transfer. The results may be helpful in the search for DNA based elements for nanoelectronics.

Preparation of Macroporous Poly(divinylbenzene) Gels via Living Radical Polymerization

AbstractMacroporous cross-linked polymeric dried gels have been obtained by inducing phase separation in a homogeneous poly(divinylbenzene) (PDVB) network formed by organotellurium-mediated living radical polymerization (TERP). The living polymerization reaction of DVB with the coexistence of a non-reactive polymeric agent, poly(dimethylsiloxane) (PDMS), in solvent 1,3,5-trimethylbenzene (TMB) resulted in polymerization-induced phase separation (spinodal decomposition), and the transient structure of spinodal decomposition has been frozen by gelation. Well-defined macroporous monolithic dried gels with bicontinuous structure in the micrometer scale are obtained after removing PDMS and TMB by simple washing and drying. The properties of the macropores have been controlled by changing starting composition.

A simple method for preparing porous carbon by PVDC pyrolysis

A simple method for preparing porous carbon with high surface area was presented in this paper. The homogeneous poly(vinylidene chloride) (PVDC) was used as starting material. After being carbonized at high temperature under the protection of inert atmosphere, porous carbon with surface area higher than 1200 m 2/g has been simply prepared without activation or any other additional processes. The effect of carbonization temperature on the microstructure of the porous carbon was investigated by measuring the BET surface area, pore size distribution, XRD and SEM, etc. The electrochemical measurements showed that the PVDC-based carbon exhibits outstanding high volume capacitance (214 F/cm 3) and good rate performance, indicating that it is a promising electrode material for electric double layer capacitors.

Preparation and recovery of polysulfone affinity membrane with mercapto as chelating group for Hg2+ cations

AbstractHighly qualified homogeneous poly(benzylsulfone) plate affinity membrane with mercapto group (PSF‐SH) was prepared successively through reactions between chloromethyl polysulfone matrix membrane and thiourea, and then alkalic hydrolysis. The mercapto‐functionalized polysulfone affinity membrane was utilized for the adsorption of Hg2+ cations through the coordination of the mercapto group and Hg2+ cations, in which the effects of the morphological and the structure of the affinity membrane on the chelating properties were investigated. The chelating conditions, including concentration of Hg2+, and temperature and pH of the introductory solution had significant influence on the chelating capacity of PSF‐SH affinity membrane. The highest static and dynamic chelating capacity of PSF‐SH plate membrane for Hg2+ cations were 398 and 403 μg/cm2 per membrane, respectively, which demonstrated that the resultant polymer membrane was a highly efficient affinity chromatography for Hg2+. The affinity membrane containing mercapto group can be conveniently recovered by dilute hydrochloric acid for coordination of Hg2+ cations, which would have wide application for the treatment of waste water containing heavy metal cations. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2514–2522, 2007

Simple Ways to Characterize Non-isothermal Crystallization of Homogeneous Poly(ethylene-1-co-octene) Copolymer

Non-isothermal crystallization of homogeneous poly(ethylene-co-1-octene) copolymers with different octene contents was studied using power-compensating differential scanning calorimetry as functions of cooling rate and comonomer content. With increasing cooling rate, the crystallization temperature decreases for all polymers. A single crystallization peak was observed for polyethylene, while multiple crystallization peaks were observed for copolymers. The non-isothermal crystallization rate of these copolymers was estimated by continuous cooling transformation (CCT) curves, crystallization rate coefficient (CRC), and crystallization rate parameter (CRP). With increasing comonomer content, the CRC value decreases and CCT curves shift to longer time under the same degree of supercooling, indicating the crystallization rate decreases. However, the CRP value can't successfully estimate the crystallization rate of these copolymers.

Amperometric Biosensors for Glucose Based on Layer‐by‐Layer Assembled Functionalized Carbon Nanotube and Poly (Neutral Red) Multilayer Film

Multiwalled carbon nanotubes (MWNTs) were treated with a mixture of concentrated sulfuric and nitric acid to introduce carboxylic acid groups to the nanotubes. Conducting polymer film was prepared by electrochemical polymerization of neutral red (NR). By using a layer‐by‐layer method, homogeneous and stable MWNTs and poly (neutral red) (PNR) multilayer films were alternately assembled on glassy carbon (GC) electrodes. With the introduction of PNR, the MWNTs/PNR multilayer film system showed synergy between the MWNTs and PNR, with a significant improvement of redox activity due to the excellent electron‐transfer ability of carbon nanotubes (CNTs) and PNR. The electropolymerization is advantageous, providing both prolonged long‐term stability and improved catalytic activity of the resulting modified electrodes. The MWNTs/PNR multilayer film modified glassy carbon electrode allows low potential detection of hydrogen peroxide with high sensitivity and fast response time. As compared to MWNTs and PNR‐modified GC electrodes, the magnitude of the amperometric response of the MWNTs/PNR composite‐modified GC electrode is more than three‐fold greater than that of the MWNTs modified GC electrode, and nine‐fold greater than that of the PNR‐modified GC electrode. With the immobilization of glucose oxidase onto the electrode surface using glutaric dialdehyde, a biosensor that responds sensitively to glucose has been constructed. In pH 6.98 phosphate buffer, nearly interference‐free determination of glucose has been realized at −0.2 V vs. SCE with a linear range from 50 µM to 10 mM and response time <10s. The detection limit was 10 µM glucose (S/N=3).

Synthesis and Characterization of UV-Induced Interpenetrating Polymer Network (IPN) Structure of Poly(urethane acrylate) (UA Polymer)/Silica Hybrids

High transparent and homogeneous poly(urethane acrylate) (UA Polymer)/silica hybrids were obtained by using strong ionic interaction between carboxylic acid groups of the UA Polymer and amino moieties of silica resulting from 3-aminopropyltriethoxysilane (APTEOS). The ionic interaction was directly confirmed by FT-IR measurement. The homogeneity of the obtained UA Polymer/silica hybrids was examined by SEM, TM-AFM and nitrogen adsorption porosimetry studies. Thermal property of the polymer hybrids was also checked by TGA study. Furthermore, the semi-interpenetrating polymer network (semi-IPN) structured UA Polymer/silica hybrids, where UA Polymer was dispersed in silica gel matrix, were changed to the IPN structured polymer hybrids by photo-induced cross-linking between UA Polymers. The change of the surface hardness, solvent-resistant property, and surface roughness on nanometer scale depending on the formation of IPN structure was investigated.

Synthesis of poly(vinylidene fluoride) (PVdF)/silica hybrids having interpenetrating polymer network structure by using crystallization between PVdF chains

AbstractHigh transparent and homogeneous poly(vinylidene fluoride) (PVdF)/silica hybrids were obtained by using an in‐situ interpenetrating polymer network (IPN) method. The simultaneous formation of PVdF gel resulting from the physical cross‐linking and silica gel from sol–gel process prevented the aggregation of PVdF in silica gel matrix. To form the physical cross‐linking between PVdF chains, the cosolvent system of dimethylformaide (DMF) and γ‐butyrolactone was used. The obtained PVdF/silica hybrids had an entangled combination of physical PVdF gel and silica gel, which was called a “complete‐ IPN” structure. The physical cross‐linking between PVdF chains in silica gel matrix was confirmed by differential scanning calorimetry (DSC) measurements. The miscibility between PVdF and silica phase was examined by scanning electron microscopy (SEM) and tapping mode atomic force microscopy (TM‐AFM) measurements. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3543–3550, 2005

Morphological interpretation of n-hexane diffusion in polyethylene

The diffusion of small-molecule penetrants in polyethylene is retarded by the detour caused by the crystals and by the segmental constraints imposed by the crystals on the penetrable phase. The earlier reported n-hexane diffusivity data for a series of homogeneous poly(ethylene-co-octene)s showed unexpectedly that the detour was greatest in the low crystallinity polymers. The crystal width-to-thickness ratio and the crystallinity were assessed by electron microscopy and differential scanning calorimetry and used in the Fricke model. The calculations showed that the geometrical impedance factor followed the same trend with increasing crystallinity as the data obtained from n-hexane desorption. The high geometrical impedance factor shown by the low crystallinity samples was due to the presence of crystals with an unusually high crystal width-to-thickness ratio. A unified relationship, including data for both linear and branched polyethylene was found between the fractional free volume and the phase composition of the penetrable phase including the liquid-like, interfacial liquid and the interfacial crystal core.