Cylindrical polyelectrolyte-comb-surfactant complexes

Quaternized polymer combs based on poly(2-vinylpyridine-macromonomers) and the surfactant sodium dodecylsulfate are employed in the synthesis of a novel cylindrical polyelectrolyte-comb-surfactant complex (PECSC). The complex formed has 1:1 stoichiometry with respect to the ratio of dodecylsulfate to pyridinium units. It is soluble in organic solvents such as 2-butanol or chloroform. Characterization of single particle properties of the complex in organic solution is possible and yields a radius of gyration of 〈R_g〉_z = 78.4 nm, a hydrodynamic radius of 〈1/R_h〉_z⁻¹ = 51.4 nm and a cross-sectional radius of R_g,cross = 3.9 nm in chloroform. The characteristic ratio γ = 〈R_g〉_z/〈1/R_h〉_z⁻¹ decreases from γ = 1.73 for the original quaternized polymer comb, indicating the semi-flexible, cylindrical nature of the macromolecules in aqueous solution, to γ = 1.53 for the complex in chloroform. The effect of the main-chain stretching accompanied by the increase of the volume of the comb by introduction of the surfactant is smaller as compared to the electrostatic interactions in the parent comb. This is also reflected in the persistence length l_p, which is determined by SANS, and found to be 21.3 nm for the complex and 24.4 nm for the polyelectrolyte comb. In addition, AFM investigations of the polymers adsorbed onto mica showed a 2D-equilibrium adsorption for the complex and a kinetically dominated adsorption process in case of the polyelectrolyte comb.     

Forced translocation of polymer chains through a nanotube: A case of ultrafiltration

Translocation of polymer chains under the application of an external force has been studied through coarse-grained Monte Carlo simulations. The chains are pulled through a nanotube of finite length and diameter and their translocation times measured. The average translocation time, τ follows a scaling relation involving the chain length, N and applied force, F as, τ ∼ N^ν′F^−μ, where ν′ and μ are two different exponents (ν′ = 0.674, and μ = 0.95 ± 0.05). The scaling law is closely similar to the nanopore translocation scaling law reported by Milchev et al. [Ann N Y Acad Sci 2009;1161:95]. Characteristic signatures of the chain escape time have been exhibited by the square of end-to-end distance R², axial radius of gyration R_g−x and other constituent properties. The behavior of the linear polymers under the application of a pulling force has been exploited to gain insights into the ultrafiltration process of unentangled polymers in dilute solution. The generic pulling force-translocation time (F, τ) data obtained through simulation can be matched reasonably well with the hydrodynamic force-critical macroscopic flow time (f_h, Q_c⁻¹) data and also with the hydrodynamic force-reduced critical microscopic flow time (f_h, q_c⁻¹) data obtained in the ultrafiltration experiment on long linear polystyrene chains in cyclohexane, as recently reported by Ge et al. [Macromolecules 2009;42:4400] The simulation technique reported here may be extended to study biomolecular transports occurring in long protein channels, as studied experimentally through current-time or voltage-time traces.     

Electrospinning fabrication of partially crystalline bisphenol A polycarbonate nanofibers: The effects of molecular motion and conformation in solutions

Partially crystalline bisphenol A polycarbonate (BPAPC) nanofibers were successfully fabricated using a combination of a centrifugal field (1800 rpm) and an electrostatic field (25 kV). The BPAPC solution properties are key factors for adequately electrospinning the partially crystalline BPAPC nanofibers. The correlation times (τ_c) of methyl (τ_c = 9.3 ns) and of benzene-ring (τ_c = 15.3 and 15.8 ns) motions in the 14 wt.% BPAPC/THF solution were longer than in CH₂Cl₂ and CHCl₃, as determined by NMR. The distribution-peak maximum of the hydrodynamic radius of BPAPC in the 14 wt.% THF solution (R_h = 15 Å) was higher than in CH₂Cl₂ (R_h = 9.2 Å) and CHCl₃ (R_h = 7.9 Å), as evidenced by DLS data. We conclude that the BPAPC assumed a denser, more worm-like chain conformation in THF solvation.     

Free-radical propagation and termination kinetics of the butyl acrylate dimer studied by pulsed laser polymerization techniques

The propagation and termination rate coefficients for bulk polymerization of the butyl acrylate dimer (BA dimer) are determined by pulsed laser techniques. The rate coefficient for propagation, k_p, is deduced for temperatures from 20 to 90 °C via the pulsed laser polymerization-size exclusion chromatography (PLP-SEC) method at pulse repetition rates between 1 and 10 Hz. The Arrhenius parameters were found to be: E_A(k_p) = (34.2 ± 1.0) kJ mol⁻¹ and A(k_p)/L mol⁻¹ s⁻¹ = (1.08 ± 0.49) × 10⁷ L mol⁻¹ s⁻¹. The termination rate coefficient, k_t, has been measured via SP-PLP-ESR, single pulse-pulsed laser polymerization in conjunction with time-resolved electron spin resonance detection of radical concentration. The resulting Arrhenius parameters as deduced from the temperature range −15 to +30 °C are: E_A(〈k_t〉) = (22.8 ± 3.7) kJ mol⁻¹ and log(A/L mol⁻¹ s⁻¹) = 10.6 ± 1. The chain-length dependence of k_t was studied at 30 °C. For short chains a significant dependence was found which may be represented by an exponent α = 0.79 in the power-law expression k_t(i) = k_t⁰i^−α.     

Hydrolytic degradation of oligo(lactic acid): a kinetic and mechanistic study

This study shows that the degradation mechanism and kinetics of monodisperse oligo(lactic acid)s esterified with N-(2-hydroxypropyl)methacrylamide (HPMAm) are strongly influenced by the nature of the chain end. Oligomers with free hydroxyl chain ends degraded predominantly by chain end scission via a backbiting mechanism with a pseudo first-order rate constant k_bb=2.7 h⁻¹ in aqueous buffer (37 °C, pH 7.2). Once the hydroxyl groups were protected by acetylation, random chain scission became the rate limiting step with k_r=0.022 h⁻¹ under the same conditions. Using these rate constants, the theoretical time-resolved degradation profile was calculated for every (intermediate) degradation product and corresponded very well with the experimental results. The rate of formation of HPMAm was independent of the chain length for the acetylated oligomers, while the hydroxyl terminated oligomers with an even number of lactic acid units formed HPMAm more rapidly than oligomers with an odd number of units. The possibility to fine-tune the degradation rate is relevant when applied as e.g. hydrogels for controlled release or tissue engineering materials.     

Termination rate coefficients for acrylamide in the aqueous phase at low conversion

The kinetics of acrylamide (AAm) free radical polymerization at low conversion of monomer to polymer in the aqueous phase was investigated at 50 °C using γ-radiolysis relaxation, which is sensitive to radical-loss processes. The values of the termination rate coefficients for AAm ranged from 8×10⁶ to 3×10⁷ M⁻¹ s⁻¹ as the weight fraction of polymer ranged from 0.002 to 0.0035, which is significantly lower than the low-conversion values for monomers such as styrene (2×10⁸ M⁻¹ s⁻¹) and methyl methacrylate (4×10⁷ M⁻¹ s⁻¹) in organic media. These can be quantitatively explained by applying a chain-length-dependent model of free-radical polymerization kinetics [Russell GT, Gilbert RG, Napper DH. Macromolecules 1992;25:2459. [19]] in which termination kinetics are expressed in terms of a diffusion-controlled encounter of radicals which ultimately yields an expression for the chain-length-averaged termination rate coefficient, 〈k_t〉. The lower 〈k_t〉 for AAm arises due to a combination of the high k_p value, promoting rapid formation of slower terminating long chains, and the slow diffusion of short propagating chains, relative to other common monomers. The chain transfer to monomer constant for AAm in water at 50 °C, C_M, was estimated using the chain-length-distribution method with correction for band-broadening [Castro JV, van Berkel KY, Russell GT, Gilbert RG. Aust J Chem 2005;58:178. [21]] and found to be 1.2×10⁻⁴ (±10%). The diffusion characteristics for AAm were adapted from those obtained for a similar aqueous system (hydroxyethyl methacrylate) together with a 0.5 exponent for the power law dependence on penetrant degree of polymerization at zero weight fraction polymer. This provides an adequate fit to the 〈k_t〉 data. This is the first application of the chain-length-dependent model to describe experimental termination rate coefficients for an aqueous system at low conversion to polymer. The result that the experimental termination rate coefficients can be reproduced with an a priori model with physically reasonable parameters supports the physical assumptions underlying that model.     

A new fast methodology to measure total diene content in gasoline

The rate constants for the quenching of biacetyl phosphorescence by a series of conjugated dienes were measured. 1,3-cyclohexadiene (k_qP = 2.94 × 10⁹ s⁻¹ mol⁻¹ L), 2,5-dimethyl-2,4-hexadiene (k_qP = 1.91 × 10⁹ s⁻¹ mol⁻¹ L), 2,4-dimethyl-1,3-pentadiene (k_qP = 1.78 × 10⁸ s⁻¹ mol⁻¹ L), 3-methyl-1,3-pentadiene (k_qP = 1.22 × 10⁸ s⁻¹ mol⁻¹ L), 2,4-hexadiene (k_qP = 1.35 × 10⁸ s⁻¹ mol⁻¹ L) and trans-2-methyl-1,3-pentadiene (k_qP = 3.84 × 10⁸ s⁻¹ mol⁻¹ L). Cyclooctene also quenched biacetyl phosphorescence but with a lower rate (k_qP = 1.97 × 10⁷ s⁻¹ mol⁻¹ L). Quenching was not observed with 1-methylnaphthalene. Since conjugated dienes quench biacetyl phosphorescence preferentially, this method was studied using gasoline samples with known diene composition. A good correlation was found between the rate of quenching of biacetyl by the gasoline samples and the quantity of conjugated dienes present.     

Hydrodynamic and mass transfer characterization of a flat-panel airlift photobioreactor with high light path

This work evaluates the volumetric mass transfer coefficient (k_La), the gas hold-up (?) and the mixing time (t_m) as a function of superficial gas velocity (U_G) in a flat-panel photobioreactor (PBR) with high light path. CO₂ utilization efficiency and volumetric power consumption (P/V) were also evaluated. A 50 L working volume photobioreactor was developed, 0.67 m in length, 0.57 m in height and 0.15 m in width (light path). The height-width ratio was 3.8, which is lower than reported in most PBRs. Initially, experiments were performed with air and tap water (biphasic system) and, subsequently, using a Spirulina sp. culture (triphasic system: air, culture medium, cells). Minimum and maximum superficial gas velocity values were 5 × 10⁻⁵ and 8.4 × 10⁻³ m s⁻¹, respectively. Maximum values for k_La and ? were 20.34 h⁻¹ (0.0057 s⁻¹) and 0.033 in the biphasic system, and 31.27 h⁻¹ (0.0087 s⁻¹) and 0.065 in the triphasic system. CO₂ utilization efficiency was 30.57%. Results indicate that the hydrodynamic and mass transfer characteristics of this photobioreactor are more efficient than those reported elsewhere for tubular and other flat-plate PBRs, which opens the possibility of using PBRs with higher light paths than yet proposed.     

Investigation of the intra-particle sintering kinetics of a mainly agglomerated alumina powder by using surface area reduction

An alumina precursor was prepared by the aluminium sulphate (0.20 M) and excess urea reaction in boiling aqueous solution. The precursor was calcined at 900 °C for 2 h and then δ-Al₂O₃ powder having volumetric agglomeration degree of 80% was obtained. Cylindrical compacts having diameter of 14 mm were prepared under 32 MPa by axial pressing using oleic acid as binder. Each compact was fired isothermally at various temperatures between 950 and 1400 °C. The firing time was changed from zero to 2 h. The fired compacts were examined by scanning electron microscopy (SEM) and nitrogen adsorption techniques. The specific surface areas (S/m² g^− 1) of the samples were calculated using the Brunauer, Emmett, and Teller (BET) procedure. The rate constant (k) and mechanism-characteristic parameter (n) were obtained for different temperatures between 950 °C and 1150 °C from the application of the neck-growth sintering rate (NGRM) model on the surface area reduction data. An Arrhenius equation and the parameter n for the sintering were found in the forms of k = (7.648 × 10⁶ h^− 1) exp (− 186,234 J mol^− 1 / RT) and n = 4.0 × 10^− 7 T³-1.7 × 10^− 3 T² + 2.3 T − 1030.8 respectively. The parameter n changes in the interval 0.61 <  n < 1.34 with rising temperature having maximum at about 1025 °C. Based on the SEM images and NGRM data, the intra-particle sintering was discussed.     

Theory of square-wave voltammetry of quasireversible electrode reactions using an inverse scan direction

The standard rate constant of a simple electrode reaction Ox + ne⁻ ↔ Red, in which both Ox and Red are solution soluble, can be determined by the variation of frequency in the square-wave voltammetry with inverted scan direction: log k_s = log f₀^1/2 + log D^1/2 − 0.60 ± 0.01. In this equation log f₀ is the abscissa of the intersection of straight lines E_p,2 = a log f + b and E_p,2 = E⁰, where E_p,2 is the potential of the second peak of the net response, E⁰ is the standard potential, a = 2.3RT/2(1 − α)nF, b = E⁰ − 2a log k_s + a log D − 0.0353/(1 − α)n and D is a common diffusion coefficient.     

Dynamics of amylopectin in semidilute aqueous solution

The dynamic behaviors of potato amylopectin and waxy corn amylopectin in semidilute solution were investigated by laser light scattering and viscometer. For potato amylopectin with relatively smaller molecular weight, only pure diffusion motion of amylopectin was found by LLS in dilute regime. When the concentration was above the critical overlapping concentration (C^∗), three relaxation modes were found. The line-width of fast mode (Γ_f) had a q² dependence, where q is the scattering vector, and the correlative length (〈ξ_h〉) could be scaled to concentration (C) as 〈ξ_h〉 ∼ C^−0.79±0.1 when C > 2%. This mode was attributed to the cooperative relaxation motion of the “blobs” in the transient network. The line-width of slow relaxation mode (Γ_s) could be scaled with q as Γs∼qαs, α_s varying from 2.0 to 2.66 as the concentration increased. The relaxation time of slow relaxation mode (τ_s) had a C^1.8±0.1 dependence. This mode was originated from the association of the amylopectin. The medium mode was found when C > 4%. The line-width of medium relaxation mode (Γ_m) could be scaled to q as Γm∼qαm, α_m varying from 2.7 to 2.5 with the increasing concentration. The relaxation time of medium relaxation mode (τ_m) had C^0.7±0.1 dependence. The relative intensity contribution of the medium relaxation mode decreased with a rise in the concentration. This mode was attributed to the thermally agitated density fluctuation in semidilute solution induced by heterogeneities of the transient network. For waxy corn amylopectin with relatively huge molecular weight (∼10⁸ g/mol), only the internal motion of the single amylopectin molecule was found in dilute regime when qR_g ≥ 2, where R_g is the gyration radius of amylopectin. It was also found that there were three relaxation modes in semidilute solution of waxy corn amylopectin. The fast relaxation mode was found to be caused first by the internal motion of the single amylopectin molecule, and then, with the increasing concentration, by the cooperative motion of the transient network. The medium and slow relaxations for waxy corn amylopectin have the same physical origin as those for potato amylopectin. However, the C dependence and the q dependence of the medium and slow relaxation times for waxy corn amylopectin were different from those for potato amylopectin. This was attributed to the strong dynamic coupling effect in semidilute solution of the waxy corn amylopectin. The concentration dependence of the viscosity of amylopectin in semidilute solution indicated that the topological entanglement of amylopectin was weak due to the highly branching.     

Experimental studies and molecular modelling of the stress-optical and stress-strain behaviour of poly(ethylene terephthalate). Part II: Molecular modelling of birefringence of poly(ethylene terephthalate) networks

The Monte-Carlo (MC) approach of Paper I is developed to predict the birefringence of PET. An extension of the modelling of polarisability is used that accounts for chain flexibility and for structural units containing several types of bonds. The rotational-isomeric-state (RIS) model for PET chains in melts is employed to calculate the polarisability of the terephthaloyl segment and of each of the 27 possible conformations of the five skeletal bonds of the glycol segment. These polarisabilities then enable the birefringent properties of drawn PET melts to be predicted. A method of pre-averaging the individual glycol polarisabilities that greatly reduces the length of the calculation is shown to be valid.It is found that shorter PET chains produce higher values of birefringence (Δñ) for a given deformation. This trend is due to greater proportions of the chains reaching higher conformational extensions and therefore becoming more oriented. In disagreement with Kuhn and Grün theory, Δñ is not linearly related to λ² − λ⁻¹. This non-linear behaviour is related to the non-linear behaviour of the orientation functions of the terephthaloyl and glycol segments, 〈P₂(cos ζ_ter)〉 and 〈P₂(cos ζ_gly)〉, with λ² − λ⁻¹. The non-linear behaviour of 〈P₂(cos ζ_ter)〉 with λ² − λ⁻¹ was confirmed experimentally in Paper I, where the measured values of 〈P₂(cos ζ_ter)〉 were found to be closely predicted by the present MC modelling.In the present paper, the predicted values of Δñ, calculated according to various published values of bond polarisabilities are presented and discussed. They will be used in Paper III to model the measured birefringence of drawn PET.     

Kinetic study of hydrogen sulfide absorption in aqueous chlorine solution

Hydrogen sulfide (H₂S) is currently removed from gaseous effluents by chemical scrubbing using water. Chlorine is a top-grade oxidant, reacting with H₂S with a fast kinetic rate and enhancing its mass transfer rate. To design, optimize and scale-up scrubbers, knowledge of the reaction kinetics and mechanism is requested. This study investigates the H₂S oxidation rate by reactive absorption in a mechanically agitated gas–liquid reactor. Mass transfer (gas and liquid sides mass transfer coefficients) and hydrodynamic (interfacial area) performances of the gas–liquid reactor were measured using appropriated physical or chemical absorption methods. The accuracy of these parameters was checked by modeling the H₂S absorption in water without oxidant. A sensitivity analysis confirmed the robustness of the model. Finally, reactive absorption of H₂S in chlorine solution for acidic or circumneutral pH allowed to investigate the kinetics of reaction. The overall oxidation mechanism could be described assuming that H₂S is oxidized irreversibly by both hypochlorite anion ClO⁻ (k = 6.75 × 10⁶ L mol⁻¹ s⁻¹) and hypochlorous acid ClOH (k = 1.62 × 10⁵ L mol⁻¹ s⁻¹).     

Glass transition and free volume in the mobile (MAF) and rigid (RAF) amorphous fractions of semicrystalline PTFE: a positron lifetime and PVT study

The structure of the free volume and its temperature dependence in poly(tetrafluoroethylene) (PTFE) and of its copolymer with perfluoro(propyl vinyl ether) (PFA) was studied by pressure-volume-temperature (PVT) experiments (T=27-380 °C, P=0.1-200 MPa) and positron annihilation lifetime spectroscopy (PALS, T=−173-250 °C, P=10⁻⁵ Pa). From the analysis of these experiments we conclude on the volumetric properties of the mobile (MAF) and rigid amorphous fractions (RAF) in these semicrystalline polymers. The specific volumes of the MAF and RAF, V_MAF and V_RAF, were estimated assuming that V_MAF agrees with the specific volume of the melt extrapolated down to lower temperatures using the Simha-Somcynsky equation of state (S-S eos). V_RAF was then estimated from the specific volume of the entire amorphous phase, V_a, and the known V_MAF. The specific free volume V_f=V_a−V_occ was also estimated from V_a using the S-S eos hole fraction h, V_occ=(1−h)V_a. From the analysis of PALS data with the routine LT9.0 the mean volume, 〈v_h〉, and the width, σ_h, of the local free volume size distribution (holes of subnanometre size) were obtained. A comparison of 〈v_h〉 with V_f delivered the hole density N^′h. The volume parameters show that the RAF which is formed during crystallisation from the melt has a distinctly smaller specific free and total volume than the MAF. During cooling the contraction of the RAF slows down and finally, below room temperature, the RAF possesses a larger free volume than the MAF shows. Obviously, the restriction of the segmental mobility in the RAF by the crystals limits at high temperatures the free volume expansion and at low temperatures dense packing of the polymer chains. These conclusions from the analysis of the specific volume are confirmed by PALS experiments.     

MD simulations of heterogeneous reduction of the tert-butyl bromide molecule

This paper reports results of molecular dynamics simulations on the electrochemical reduction of the tert-butyl bromide molecule according to the scheme: (CH₃)₃CBr + e → (CH₃)₃C + Br⁻. A model Hamiltonian is proposed, that is based on the Anderson-Newns concept of the electron transfer process and on quantum calculations performed for the (CH₃)₃CBr molecule and the (CH₃)₃CBr·⁻ radical anion. The rate constants k and the transfer coefficients α obtained at different solvent frictions γ_x, temperatures T and overpotentials η, are presented. At η = 1.3 V, which corresponds to the experimental conditions, the α estimates obtained from the simulations with low solvent frictions are very close to the measured value of 0.2; in more viscous solvents they are slightly higher. The α coefficient is found to depend non-linearly on η. It is also shown to depend on the temperature: at lower overpotentials the transfer coefficient decreases with T: α (348 K) < α (298 K) < α (248 K), while for high η the reversed order appears. In all simulations strong saddle point avoidance was observed. The choice of the effective reaction paths is shown to be responsible for some trends found in the results.     

Determination of the kinetic parameters of oxygen reduction on copper using a rotating ring single crystal disk assembly (RRDCu(h k l)E)

The kinetics of the oxygen reduction reaction (orr) on Cu(h k l) surfaces are investigated in perchloric acid and sulfuric acid solutions using rotating ring disk electrode (RRD_Cu(h k l)E). Parameters, such as reaction order, kinetic current, rate constant, Tafel slopes as well as the number of electrons transferred are determined. The variation in the activity and reaction pathway with the crystal faces in different electrolytes is related to the surface characteristics of Cu(h k l) and the structure-sensitive inhibiting effect of the adsorbed anions on their surfaces. In 0.1 M HClO₄, the difference in activity is clearly observed on Cu(h k l) surfaces (Cu(1 0 0) > Cu(1 1 1) although it is relatively small). The higher activity of Cu(1 0 0) arises from its more open characteristics which may facilitate the co-adsorption of O₂. On the other hand, the adsorption of oxygenated species on Cu(1 1 1) at E > −0.35 V induces a 2 e⁻ pathway; while a 4 e⁻ reduction is observed on Cu(1 0 0) in the entire potential region (−0.70 V < E < −0.10 V). In 0.5 M H₂SO₄, the sequence in activity between Cu(1 1 1) and Cu(1 0 0) varies with the potentials, i.e., Cu(1 0 0) is initially more active than Cu(1 1 1) at −0.35 V < E < −0.15 V, however, the reversal in the activity between Cu(1 1 1) and Cu(1 0 0) is observed at more negative potentials (−0.45 V < E < −0.35 V). The desorption of strongly adsorbed (bi)sulfate anions on Cu(1 1 1) induces the 2 e⁻ reduction via peroxide formation, however, a 4 e⁻ reduction is dominant on the Cu(1 0 0) surfaces. The major effect of (bi)sulfate anions and oxygenated species on the orr kinetics and reaction pathway on Cu(h k l) surfaces is the blocking of active copper sites for the adsorption of O₂ molecules.     

The ultrasonic electropolymerization of an 5-[o-(4-bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) film electrode and its electrocatalytic properties to dopamine oxidation in aqueous solution

5-[o-(4-Bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) was electropolymerized on a glassy carbon electrode (GCE), and the electrocatalytic properties of the prepared film electrode response to dopamine (DA) oxidation were investigated. A stable o-BrPETPP film was formed on the GCE under ultrasonic irradiation through a potentiodynamic process in 0.1 M H₂SO₄ between −1.1 V and 2.2 V versus a saturated calomel electrode (SCE) at a scan rate of 0.1 V s⁻¹. The film electrode showed high selectivity for DA in the presence of ascorbic acid (AA) and uric acid (UA), and a 6-fold greater sensitivity to DA than that of the bare GCE. In the 0.05 mol L⁻¹ phosphate buffer (pH 6.0), there was a linear relationship between the oxidation current and the concentration of DA solution in the range of 5 × 10⁻⁷ mol L⁻¹ to 3 × 10⁻⁵ mol L⁻¹. The electrode had a detection limit of 6.0 × 10⁻⁸ mol L⁻¹(S/N = 3) when the differential pulse voltammetric (DPV) method was used. In addition, the charge transfer rate constant k = 0.0703 cm s⁻¹, the transfer coefficient α = 0.709, the electron number involved in the rate determining step n_α = 0.952, and the diffusion coefficient D_o = 3.54  10⁻⁵ cm² s⁻¹ were determined. The o-BrPETPP film electrode provides high stability, sensitivity, and selectivity for DA oxidation.     

Polymer translocation through a nanopore in mesoscopic simulations

Dissipative particle dynamics (DPD) simulations are carried out to study the translocation of a single polymer chain through a pore under fluid field. The influences of the field strength E, the chain length N, the solvent quality α_sp, and the pore size h on the translocation time are evaluated. The translocation time τ, which is defined as the time that the chain moves through the pore completely in the direction of the driving force, scales with the field strength E as τ ∼ E^{−0.48±0.01}. We find that the translocation time is proportional to the chain length, which is in agreement with the experimental results and theoretical predictions. Tracing the variation of the square radius of gyration, , and the polymer configuration during translocation, we observe that the chain is elongated when it is passing through the pore, which manifests that the chain is not in equilibrium during the translocation process. We also find that the worse the solvent quality is, the less time it will take to translocate, no matter what the size of the pore is. If the size of the pore is enlarged, the translocation time will be shorter. The information we gain from this study may benefit to the DNA sequencing.     

Nucleic acid biosensor for DNA hybridization detection using rutin-Cu as an electrochemical indicator

The complex of rutin-Cu (C₈₁H₈₆Cu₂O₄₈, abbreviated by Cu₂R₃, R = rutin) was synthesized and characterized by elemental analysis and IR spectra. Cyclic voltammetry (CV) and fluorescence spectroscopy were used to investigate the interaction of Cu₂R₃ with salmon sperm DNA. It was revealed that Cu₂R₃ could interact with double-stranded DNA (dsDNA) by a major intercalation role. Using Cu₂R₃ as a novel electroactive indicator, an electrochemical DNA biosensor for the detection of specific DNA fragment was developed and its selectivity for the recognition with different target DNA was assessed by differential pulse voltammetry (DPV). The target DNA related to coliform virus gene could be quantified ranged from 1.62 × 10⁻⁸ mol L⁻¹ to 8.10 × 10⁻⁷ mol L⁻¹ with a good linearity (r = 0.9989) and a detection limit of 2.3 × 10⁻⁹ mol L⁻¹ (3σ, n = 7) was achieved by the constructed electrochemical DNA biosensor.     

Dilute solutions and phase behavior of polydisperse A-b-(A-co-B) diblock copolymers

The effect of polydispersity on dilute solution properties and microphase separation of polydisperse high-molecular-weight (M_w > 10⁵ g mol⁻¹) polystyrene-block-poly(styrene-co-acrylonitrile) diblock copolymers, PS-block-P(S-co-AN), was studied in this work. For experiments, a series of diblock copolymers with variable weight fractions of acrylonitrile units (w_AN = 0.08-0.29) and length of block P(S-co-AN) was synthesized using nitroxide-mediated radical polymerization (NMP) technique, namely, by chain extension of nitroxide-terminated polystyrene (PS-TEMPO). According to light scattering and viscometry measurements in dilute tetrahydrofuran (THF) solutions the studied diblock copolymers assumed random coil conformation with the values of characteristic structure factor R_g/R_h = 1.50-1.76. It was found that polydisperse diblock copolymers being in strong segregation limit (SSL) self-assembled into microphase-separated ordered morphologies at ordinary temperature. The long periods of lamellar microdomains were larger compared to theoretical predictions for hypothetical monodisperse diblock copolymers. It was demonstrated by means of SAXS and TEM that a transition from a lamellar (LAM) to irregular face-centered-cubic (FCC) morphology occurred with increasing volume fraction of P(S-co-AN) block.