RAFT polymerization and self-assembly of thermoresponsive poly(N-decylacrylamide-b-N,N-diethylacrylamide) block copolymers bearing a phenanthrene fluorescent α-end group

Phenanthrene α-end-labeled poly(N-decylacrylamide-b-N,N-diethylacrylamide) (PDcA_n-b-PDEA_m) block copolymers consisting in a highly hydrophobic block (n = 11) and a thermoresponsive block with variable length (79 ≤ m ≤ 468) were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. A new phenanthrene-labeled chain transfer agent (CTA) was synthesized and used to control the RAFT polymerization of a hydrophobic acrylamide derivative, N-decylacrylamide (DcA). This first block was further used as macroCTA to polymerize N,N-diethylacrylamide (DEA) in order to prepare diblock copolymers with the same hydrophobic block of PDcA (number average molecular weight: M_n = 2720 g mol⁻¹, polydispersity index: M_w/M_n = 1.13) and various PDEA blocks of several lengths (M_n = 10,000-60,000 g mol⁻¹) with a very high blocking efficiency. The resulting copolymers self-assemble in water forming thermoresponsive micelles. The critical micelle concentration (CMC) was determined using Förster resonance energy transfer (FRET) between phenanthrene linked at the end of the PDcA block and anthracene added to the solution at a low concentration (10⁻⁵ M), based on the fact that energy transfer only occurs when phenanthrene and anthracene are located in the core of the micelle. The CMC (∼2 μM) was obtained at the polymer concentration where the anthracene fluorescence intensity starts to increase. The size of the polymer micelles decreases with temperature increase around the lower critical solution temperature of PDEA in water (LCST ∼ 32 °C) owing to the thermoresponsiveness of the PDEA shell.     

The effect of chemistry on the polymerization, thermo-mechanical properties and degradation rate of poly(β-amino ester) networks

Poly(β-amino ester) networks are gaining attention as a scaffold material for tissue engineering applications where it is important to have tailorable degradation rate and elastic modulus. The objective of this work is to characterize and understand the relationships between chemical structure, polymerization, thermo-mechanical properties, and degradation in poly(β-amino esters) networks. The networks were synthesized from a primary amine with systematically varied molar ratios and chemical structures of diacrylates. Fundamental trends were established between the chemical structure, conversion during polymerization, macromer molecular weight, rubbery modulus, and degradation rate. The thermo-mechanical properties were dependent upon both polymerization steps. The rubbery modulus was tailorable over a range of several MPa by changing molar ratio and diacrylate molecular weight. The degradation rate ranged from hours to months depending upon the composition. Select chemical structures showed degradation rate independent of modulus. This work provides a basis for designing poly(β-amino esters) networks with specific thermo-mechanical properties and degradation rates for biomedical scaffolds.     

Synthesis of new N, N-diphenylhydrazone dyes for solar cells: Effects of thiophene-derived π-conjugated bridge

Four novel D-π-A hydrazone dyes (HT, HM, HE, and HO) with an N, N-diphenylhydrazone moiety as the electron donor, different thiophene-derived π-conjugated bridges and a cyanoacrylic acid moiety as the electron acceptor have been designed and synthesized for the application in dye-sensitized solar cells. The influences of thiophene-derived bridges on the photoelectrochemical and photovoltaic performance of these hydrazone dyes were investigated. Results demonstrate that the introduction of 3,4-dialkyloxythiophene could red-shift the dye’s absorption spectrum due to the enhancement of the electron-donating ability of π-conjugated bridges. Importantly, electrochemical impedance spectroscopy analysis reveal that 3,4-dialkyloxythiophene bridge could change the charge recombination resistance at the TiO₂/dye/electrolyte interface and as a result to improve the open-circuit photovoltage. Among the four dyes, HO exhibits the maximum power conversion efficiency of 5.83% (V_oc = 0.65 V, J_sc = 12.69 mA/cm², FF = 0.707) under simulated AM 1.5 irradiation (100 mW/cm²).     

CO hydrogenation to higher alcohols over Cu/Zn/Al catalysts without alkalis or Fischer–Tropsch elements: The effect of triethanolamine content

Cu/Zn/Al catalysts were prepared by a complete liquid-phase method with various triethanolamine (TEA) contents. Results showed that the mass fractions of higher alcohols in the total alcohols reached approximately 36.0% over Cu/Zn/Al catalyst without promoters and a suitable amount of TEA promoted the formation of higher alcohols. Characterization results showed that TEA mainly decreased the amount of weak acidic and increased the Cu content on the catalyst surface. It was speculated that a suitable amount of weak acid was beneficial to C–O hydrogenolysis and a relatively higher Cu content was beneficial for hydrogenation in the higher alcohols synthesis.     

Supported Ziegler–Natta catalyst for ethylene polymerization: Novel data on the effect of polymerization temperature on the number of active centers and propagation rate constant

The number of active centers at ethylene polymerization over highly active supported catalyst TiCl₄/MgCl₂ + AlEt₃ was determined at various polymerization temperatures. It was found that the increase in polymerization temperature in the range of 40–80 °C increases the number of active centers. The data on reversible changes in the polymerization rate with temperature in a single experiment give grounds for supposing that alteration of the number of active centers with temperature is a reversible process. The propagation rate constants and the activation energy of the propagation reaction (4.0 kcal mol^− 1) were calculated; the latter value being considerably lower than the effective activation energy of polymerization (16.5 kcal mol^− 1) due to the increase in C_P with rising temperature.     

The gadolinium effect on crystallization behavior and luminescence of β-NaYF4:Yb,Er phase

Single phase β-NaY_0.8-xGd_xYb_0.18Er_0.02F₄ nanoparticles with different concentrations of gadolinium ions were prepared via PVP-assisted solvothermal treating at 200°C (PVP- polyvinylpyrrolidone). With the increase in Gd³⁺ concentration, size of the nanoparticles decreased. The up-converting spectra recorded upon 980 nm irradiation showed the green (510-560 nm) and red (640-690 nm) emissions, due to ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions, respectively. The strongest up-conversion luminescence was detected in 15 mol% Gd³⁺-doped nanoparticles obtained after 20 hours of solvothermal treating. With the rise of Gd³⁺ content up-conversion emission decreased due to increased defect concentration in the NaYF₄ matrix. Fourier transform infrared spectroscopy proved in situ generation of hydrophilic nanoparticles as a result of PVP ligands retention at the particle surface.     

Pd/polyaniline as the catalysts for 2‐ethylanthraquinone hydrogenation. The effect of palladium dispersion

By doping of polyaniline (PANI) in PdCl₂ aqueous and ethanol solutions the catalysts containing crystalline and colloidal Pd particles of different sizes were prepared. The size of palladium particles present in Pd/PANI catalysts (characterised by SEM and XRD methods) influenced the course of 2‐ethylanthraquinone (eAQ) hydrogenation, a key step in the industrial production of H₂O₂. The presence of large palladium particles promotes reactions leading to the formation of the so‐termed “degradation products” not capable of hydrogen peroxide formation. This revised version was published online in July 2006 with corrections to the Cover Date.     

The method of moments used in polymerization reaction engineering for 70 years: An overview,tutorial, and minilibrary

In the last seven decades, the method of moments (MoM) has become an invaluable tool in the field of polymerization reaction engineering, due to the simplicity of translating a complex set of population balance equations (PBE) into a system with a limited number of equations. In this work, we offer an overview of the MoM, describing the derivation of the moment equations in a basic kinetic mechanism. Some tools and strategies for the derivation of the moment equations are reviewed and explained in detail, such as the binomial theorem, the method of series expansion and pattern identification (SEPI), extensively used by the community, and a graphical approach of summation inversion. The treatment for multivariate distributions is also exposed, taking advantage of the complete and partial moment techniques. The derivation of the MoM contribution by kinetic mechanisms beyond the basic ones or involving special difficulties, such as depropagation, long chain branching (LCB), random chain scission, LCB and β-scission, short chain branching (SCB) and scission, internal double bond (IDB) (polymerization), termination by combination, reversible deactivation radical polymerization (RDRP), and intermolecular transesterification reactions (ITRs), are explained in a tutorial way. Additionally, the fundamentals of the MoM in copolymerization and the application of the pseudo-homopolymerization approach are briefly described. An introduction of the MoM to emulsion polymerization is also presented. Finally, some advanced applications of MoM in recent works are exposed: MoM models with chain-length dependent or diffusion-controlled termination, and the extension of the MoM for the prediction of the molecular weight distribution (MWD ) .     

Reduced graphene oxide for Li–air batteries: The effect of oxidation time and reduction conditions for graphene oxide

Reduced graphene oxide (rGO) has shown great promise as an air-cathode for Li–air batteries with high capacity. In this article we demonstrate how the oxidation time of graphene oxide (GO) affects the ratio of different functional groups and how trends of these in GO are extended to chemically and thermally reduced GO. We investigate how differences in functional groups and synthesis may affect the performance of Li–O₂ batteries. The oxidation timescale of the GO was varied between 30 min and 3 days before reduction. Powder X-ray diffraction, micro-Raman, FE-SEM, BET analysis, and XPS were used to characterize the GO’s and rGO’s. Selected samples of GO and rGO were analyzed by solid state ¹³C MAS NMR. These methods highlighted the difference between the two types of rGO’s, and XPS indicated how the chemical trends in GO are extended to rGO. A comparison between XPS and ¹³C MAS NMR showed that both techniques can enhance the structural understanding of rGO. Different rGO cathodes were tested in Li–O₂ batteries which revealed a difference in overpotentials and discharge capacities for the different rGO’s. We report the highest Li–O₂ battery discharge capacity recorded of approximately 60,000 mAh/g_carbon achieved with a thermally reduced GO cathode.     

The effect of two β-alanine dosing strategies on 30-minute rowing performance: a randomized,controlled trial

Background

β-alanine (βA) supplementation has been shown to increase intramuscular carnosine content and subsequent high-intensity performance in events lasting <?4?minutes (min), which may be dependent on total, as opposed to daily, dose. The ergogenic effect of βA has also been demonstrated for 2000-m rowing performance prompting interest in whether βA may be beneficial for sustained aerobic exercise. This study therefore investigated the effect of two βA dosing strategies on 30-min rowing and subsequent sprint performance.

Methods

Following University Ethics approval, twenty-seven healthy, male rowers (age: 24?±?2?years; body-height: 1.81?±?0.02?m; body-mass: 82.3?±?2.5?kg; body-fat: 14.2?±?1.0%) were randomised in a double-blind manner to 4?weeks of: i) βA (2.4?g·d^??1, βA1); ii) matched total βA (4.8?g on alternate days, βA2); or iii) cornflour placebo (2.4?g·d^??1, PL). Participants completed a laboratory 30-min rowing time-trial, followed by 3x30-seconds (s) maximal sprint efforts at days 0, 14 and 28 (T1-T3). Total distance (m), average power (W), relative average power (W·kg^??1), cardio-respiratory measures and perceived exertion were assessed for each 10-min split. Blood lactate ([La-]_b mmol·L^??1) was monitored pre-post time-trial and following maximal sprint efforts. A 3-way repeated measures ANOVA was employed for main analyses, with Bonferonni post-hoc assessment (P?≤?0.05).

Results

Total 30-min time-trial distance significantly increased from T1-T3 within βA1 only (7397?±?195?m to 7580?±?171?m, P?=?0.002, ?p²?=?0.196), including absolute average power (194.8?±?18.3?W to 204.2?±?15.5?W, P?=?0.04, ?p²?=?0.115) and relative average power output (2.28?±?0.15?W·kg^??1 to 2.41?±?0.12?W·kg^??1, P?=?0.031, ?p²?=?0.122). These findings were potentially explained by within-group significance for the same variables for the first 10?min split (P?≤?0.01), and for distance covered (P?=?0.01) in the second 10-min split. However, no condition x time interactions were observed. No significant effects were found for sprint variables (P?>?0.05) with comparable values at T3 for mean distance (βA1: 163.9?±?3.8?m; βA2: 161.2?±?3.5?m; PL: 162.7?±?3.6?m), average power (βA1: 352.7?±?14.5?W; βA2: 342.2?±?13.5?W; PL: 348.2?±?13.9?W) and lactate (βA1: 10.0?±?0.9?mmol·L^??1; βA2: 9.2?±?1.1?mmol·L^??1; PL: 8.7?±?0.9?mmol·L^??1).

Conclusions

Whilst daily βA may confer individual benefits, these results demonstrate limited impact of βA (irrespective of dosing strategy) on 30-min rowing or subsequent sprint performance. Further investigation of βA dosage >?2.4?g·d^??1 and/or chronic intervention periods (>?4–8?weeks) may be warranted based on within-group observations.

     

Cobalt catalysts for Fischer–Tropsch synthesis: The effect of support,precipitant and pH value

In this report,Co-based catalysts supported on ZnO,Al_2O_3 and ZrO_2 as well as the ZrO_2 derived from different precipitants and different pH values were prepared by co-precipitation method.Their catalytic Fischer–Tropsch synthesis(FTS)performance was investigated in a fixed-bed reactor.The results revealed that Co catalyst supported on ZrO_2 exhibited better FTS catalytic performance than that supported on ZnO or Al_2O_3.For the Co/ZrO_2catalyst,different precipitants showed the following an activity order of NaOHNa_2CO_3NH_4OH,and the best pH value is 13.The catalysts were characterized by N_2adsorption–desorption,XRF,XRD,H_2-TPR,H_2-TPD and TEM.It was found that the main factor affecting the CO conversion of the catalyst was the amounts of low-temperature active adsorption sites.Moreover,the selectivity of C_5~+hydrocarbons had a positive relationship with the peak temperature of the weak hydrogen adsorption sites.The higher the peak temperature,the higher the C_5~+selectivity is.     

The effect of Al–O substitution for Si–N on the luminescence properties of YAG:Ce phosphor

The present paper describes the effect of various Si–N substitution degree on the crystal structure and optical properties of yellow YAG:Ce phosphor commonly used with combination of InGaN in white LEDs. It has been found that the course of silicon/nitrogen YAG:Ce garnet doping as well as formation of the liquid phase and its chemical composition controlled formation of the side phase besides YAG:Ce. Substitution of Al–O for Si–N chemical bonds according to the general formula Y_2.94Ce_0.06Al_(5?x)Si_xO_(12?x)N_x was confirmed by changes of the unit cell parameter and formation of the Si–N bonds as detected by FT-IR studies. Formation of the nitrogen ligand in cerium arrangement resulted in a red shift in emission spectrum of trivalent cerium if nominal x value was in the range of 0.2–0.3. Above x = 0.3 only decrease of emission intensity was observed because of the secondary phase precipitation but further solution of Si–N in YAG:Ce crystal lattice cannot be excluded.     

Immobilization of Titanium Tetrachloride on Mixed Support of MgCl2 · xEB/Poly(methyl acrylate-co-1-octene): Catalyst for Synthesis of Broad MWD Polyethylene

TiCl₄ immobilization on different compositions of mixed support of MgCl₂ · xEB and poly(methyl acrylate-co-1-octene) (PMO; synthesized through ARGET ATRP) resulted in the formation of solid catalysts having variation in incorporation of titanium. The effect of mixed support composition onto the titanium immobilization, catalyst morphology and performance for ethylene polymerizations has been evaluated. The polyethylenes synthesized showed broad to bimodal MWD in GPC and DSC where the broadness was found to be dependent upon the ratio of mixed support MgCl₂ · xEB/PMO. The morphological features of PE as elucidated using SEM lead to postulation of polymer formation mechanism.     

Interaction of self-assembling β-sheet peptides with phospholipid monolayers: The effect of serine, threonine, glutamine and asparagine amino acid side chains

The dioleoyl phosphatidylcholine (DOPC) monolayer activities of 11 systematically altered 11 residue β-sheet tape-forming peptides were studied. Peptide-DOPC interactions were characterised by electrochemical impedance spectroscopy (EIS). An impedance model combining the constant phase element approach with dielectric relaxation in the surface layer was used to analyse the data. The facilitation of DOPC layer permeability to ions by the peptides was monitored by both EIS and the Tl(I)/Tl(Hg) and Cd(II)/Cd(Hg) faradaic reactions. It was found that peptides with side chains of serine and threonine interact with DOPC layers more strongly and in a well characterised manner compared to peptides with side chains of glutamine and asparagine. Cationic and neutral peptides containing serine and threonine penetrate the DOPC to give a maximum plateau monolayer capacitance. At higher solution concentrations of these peptides the growth of a well-defined secondary element in the impedance data indicates the segregation of secondary DOPC-peptide phases. Cationic and neutral peptides containing serine and anionic peptides containing threonine interact with the DOPC layers leading to a selective increase in the layer's permeability to Tl⁺ ions. Impedance measurements at higher solution concentrations of anionic peptides with serine and threonine show that these peptide modified DOPC layers associate with electrolyte ions.     

The effect of grain boundary on the visible light absorption of BaTi1-x[Ni1/2Nb1/2]xO3-δ ferroelectric ceramics

(Ni²⁺, Nb⁵⁺) co-doped BaTiO₃ ceramics BaTi_1-x(Ni_1/2Nb_1/2)_xO_3-δ (BTNN-100x) are prepared by a solid-state reaction method, and their electrical and light absorption properties are investigated. The results show that BTNN-100x can generate oxygen vacancies which pin the domain walls. BTNN-100x bulk ceramics show strong visible light absorption. However, the phenomenon of visible light absorption disappear for BTNN-100x ceramic powders, and the band gap of doped ceramic powders are nearly unchanged. The experiments demonstrate that stress and density have little effect on the band gap. And the grain boundary shows stronger cathodoluminescence (CL) emission. Actually, oxygen vacancies can be enriched at grain boundaries, and defect [V_o-Ni_Ti-V_o] complex structures can be form and give rise to the visible light absorption as demonstrated by First-principles calculations. Thus, the engineering design of ferroelectric grain boundaries may pave the way for the application of coupled ferroelectric-photovoltaic processes.     

The effect of precursor composition and sintering additives on the formation of β-sialon from Al, Si and Al2O3 powders

A study was performed to investigate the effect of increasing the Al or Al₂O₃ precursor content, above the stoichiometric amount, on the formation of β-sialon by pressureless sintering of Al, Si and Al₂O₃ powders in flowing nitrogen gas. The effect of adding Y₂O₃ or Fe to the precursor mixture, on the β-sialon formation, was also studied. The phase morphology and yield produced by the various compositions were examined using X-ray diffraction (XRD). Additional Al₂O₃ decreases the β-sialon phase yield and results in a greater amount of Al₂O₃ in the final sintered material. Additional Al improved the conversion to β-sialon up to a maximum of 4 wt% Al beyond which the β-sialon:15R sialon ratio in the sintered material decreases. 1 wt% Y₂O₃ was determined to be the optimum sintering additive content, as yttrium aluminium garnet (YAG) was found to be present in materials formed from higher Y₂O₃ containing precursors. The presence of Fe in the precursor powder retards the formation of β-sialon by preferentially forming Fe silicides at low temperatures, thus depleting the reaction system of elemental Si, favouring the formation of 15R sialon.     

The effect of Fe-acceptor doping on the electrical properties of Na1/2Bi1/2TiO3 and 0.94 (Na1/2Bi1/2)TiO3–0.06 BaTiO3

Na_1/2Bi_1/2TiO₃ (NBT) based ceramics are amongst the most promising lead-free ferroelectric materials. It was expected that the defect chemistry and the effect of doping of NBT would be similar to that observed for lead based materials, however, acceptor doping does not lead to ferroelectric hardening. Instead, high oxygen ionic conductivity is induced. Nevertheless, for solid solutions with BaTiO₃ (BT), which are more relevant with respect to ferroelectric applications, such a drastic change of electrical properties has not been observed so far. To rationalize the difference in defect chemistry between NBT and its solid solution 94(Na_1/2Bi_1/2TiO₃)–0.06 BaTiO₃ (NBT–6BT) compositions with different concentrations of Fe-dopant were investigated. The study illustrates that the materials exhibit very similar behavior to NBT, and extraordinarily high oxygen ionic conductivity could also be induced in NBT–6BT. The key difference between NBT–6BT and NBT is the range of the dependence of ionic conductivity with dopant concentration. Previous studies of NBT–6BT have not reached sufficiently high dopant concentrations to observe high conductivity. In consequence, the same defect chemical model can be applied to both NBT and its solid solutions. This will help to rationalize the effect of doping on ferroelectric properties of NBT-ceramics and defect chemistry related degradation and fatigue.     

Broadened effect of Dy around 3 μm of Yb/Er/Dy: PbF2 crystal for broadband tunable lasers

It is well known that the laser crystal with mid-infrared (MIR) broadened and enhanced luminescence is of great significance for various applications, such as atmospheric monitoring, medical surgery and compact, and efficient coherent sources. Herein, we exploit the sensitization and deactivation effects of Yb³⁺/Dy³⁺ ions to achieve broadening and enhancement ~3 μm emission of Er³⁺: ⁴I_11/2→⁴I_13/2 transition in Yb³⁺/Er³⁺/Dy³⁺: PbF₂ crystal. The energy transfer (ET) mechanism between Yb³⁺, Er³⁺, and Dy³⁺ was studied. A broadened and enhanced emission with a full width at half maximum of 265 nm was obtained at ~3 μm due to the fact that Er³⁺ and Dy³⁺ ions were used as the emission center at the same time. On the one hand, the incorporation of Dy³⁺ ion can solve the self-termination bottleneck effect of Er³⁺ ion, reducing the lifetime of Er³⁺: ⁴I_13/2 level. On the other hand, Dy³⁺ ion can simultaneously serve as the emission center of 3 μm, broadening and enhancing the emission of 3 μm. The experiments show that the corresponding ET efficiency Er³⁺: ⁴I_13/2→Dy³⁺: ⁶H_11/2 level is as high as 98.0%, indicating that Dy³⁺ ion can be used as an effective deactivating ion, benefitting to achieve broadening and enhancing MIR emission around 3 μm. Hence, the Yb³⁺/Er³⁺/Dy³⁺: PbF₂ crystal is an attractive laser medium for MIR broadband tunable laser applications.     

An emerging approach for the targeting analysis of dimethoate in olive oil: The role of molecularly imprinted polymers based on photo-iniferter induced “living” radical polymerization

This study concerns the first attempt to prepare molecularly imprinted polymers for the selective recognition of dimethoate using an iniferter polymerization technique (Inif-MIP). The synthesized polymers were fully characterized. SEM micrographs show a large accessibility to the binding sites with a significant improvement in MIP morphology. Inif-MIPs displayed high adsorption capacity (Q = 5.3 mg g⁻¹). The selectivity of this imprinting system was also assessed by means of cross-selectivity assays and the results obtained show that Inif-MIP displays a high selectivity for dimethoate, whereas some structural analogues (omethoate, malathion and methidathion) are poorly retained (6.3–28.7%) or not retained at all (fenthion). Inif-MISPE methodology was implemented by packing Inif-MIPs particles into a Solid Phase Extraction (SPE) cartridge and the loading, washing and eluting steps were optimized. The suitability of this sample preparation technique was demonstrated, as concentrations of dimethoate close to the tolerated maximum residue limits in the olive oil samples could be satisfactorily analyzed with good precision and accuracy. Some remarkable characteristics, like the sorbent reusability (at least 20 cycles without the lost of selectivity), low solvent consumption, reduced sample handling and, moreover higher recovery rates reaching 88% could be ascribed to the Inif-MISPE methodology.