Synthesis and electropolymerization of 9-tosyl-9<Emphasis Type="Italic">H</Emphasis>-carbazole,electrochemical impedance spectroscopic study and circuit modelling

This work reports on the newly synthesized 9-tosyl-9H-carbazole (TsCz) monomer. Capacitive properties of the electrochemically grown homopolymer, poly(TsCz) film on carbon fibre microelectrode (CFME), are characterised by cyclic voltammetry (CV), Fourier transform infrared reflectance-attenuated total reflection spectroscopy (FTIR-ATR), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Different monomer concentrations (1, 3 and 10 mM) were used for electrodeposition in 0.1 M sodium perchlorate (NaClO₄)/acetonitrile (ACN) solution. The capacitive behaviour of modified CFMEs was defined via Nyquist, Bode-magnitude and Bode-phase plots. An equivalent electrical circuit R(CR)(QR)(CR) for different concentrations of poly(TsCz)/CFME was proposed and experimental data were simulated to obtain the numerical values of the circuit components. The Nyquist plot for poly(TsCz) shows the highest specific capacitance (50.0 mF cm⁻²) at frequency of 0.01 Hz in the initial monomer concentration of 10 mM.     

Synthesis and electropolymerization of 9-(4-vinylbenzyl)-9H-carbazole on carbon fiber microelectrode: Capacitive behavior of poly(9-(4-vinylbenzyl)-9H-carbazole)

The synthesis of 9-(4-vinylbenzyl)-9H-carbazole (VBCz) monomer and surface characterizations of thin film coating of poly(9-(4-vinylbenzyl)-9H-carbazole), P(VBCz) homopolymer on carbon fiber microelectrode (CFME) was performed. Coatings of polymer thin films obtained, with different initial monomer concentrations, were characterized by cyclic voltammetry, scanning electron microscopy and Fourier transform infrared reflectance-attenuated total reflection spectroscopy. Different initial monomer concentrations (1, 3, 5, and 10 mM) were electrodeposited in 0.1 M lithium perchlorate/acetonitrile solution. The characterization of the thin polymer films was performed on the surface of carbon fiber, and composition of polymeric structure was proposed. Capacitor behavior of modified CFME was studied by electrochemical impedance spectroscopy. The deposition charge of polymer growth affected the redox parameters of resulting coated CFME.     

A Comparative study of redox parameters and electrochemical impedance spectroscopy of polycarbazole derivatives on carbon fiber microelectrode

In this study, N-Carbazole and its derivatives (N-Vinylcarbazole, N-Ethylcarbazole, N-Vinylbenzylcarbazole, and N-Benzylcarbazole) were electrochemically polymerized on carbon fiber microelectrodes (diameter ∼7 μm) by cyclic voltammetry within a potential range from 0.0 to 1.4 V. Redox parameters, Scanning electron microscopic (SEM) images were determined and also capacitance behaviors of polymers were examined via electrochemical impedance spectroscopy (EIS). EIS measurements of polycarbazole derivatives were given comparatively. The existence of a capacitance behavior is shown by Nyquist, Bode magnitude, Bode-phase, Admittance plots relationship. Although the highest low frequency capacitance (C_LF=12901 μA cm⁻²) and maximum phase angle of 81.9 ° at a frequency of 1 Hz were obtained for N-Vinylbenzylcarbazole, the lowest anodic and cathodic potential difference (ΔE=0.04 V) and double layer capacitance (C _dl =0.11 μA cm⁻²) were indicated in 0.1 M LiClO₄/PC.     

Polycarbazole modified carbon fiber microelectrode: Surface characterization and dopamine sensor

Electropolymerization of carbazole (Cz) by cyclic voltammetry (CV) onto carbon fiber microelectrodes (CFME) (diameter ∼7 μm) in dichloromethane (CH₂Cl₂) solution of 0.1 mol·dm⁻³ tetraethyl ammonium perchlorate (TEAP) results in the formation of polycarbazole (PCz) thin film coatings. CV results showed that these PCz thin films have reversible redox behavior in monomer-free electrolyte solution. The resulting thin polymer films were characterized using Fourier transform infrared attenuated total reflectance spectroscopy (FTIR-ATR) and atomic force microscopy (AFM). Results performed at optimum experimental conditions indicate that electrodes show a reversible and stable behavior over sixty eight days of testing for dopamine in 100 μmol·dm⁻³ buffer solution. A detection limit for PCz thin films as low as 0.1 μM (3S/N) was obtained for the polycarbazole (PCz) thin films formed using CV. Hence, this novel sensor can be considered as promising sensor for dopamine detection.     

The influence of thermal stabilization stage on the molecular structure of polyacrylonitrile fibers prior to the carbonization stage

Structural transformation from a linear chain structure to crosslinked chain structure, occuring during the thermal stabilization stage of carbon fiber manufacture, was followed through the use of infrared spectroscopy, differential scanning calorimetry (DSC), elemental analysis and gel-fraction measurements. The results obtained from the analysis of IR spectroscopy showed the gradual and continuous loss of intensity of the nitrile (C≡N) vibration at 2242 cm⁻¹ closely associated with the cyclization reactions whereas the intensity loss of the methylene (CH₂) groups vibration around 2920–2939 cm⁻¹ has been attributed to the loss of hydrogen atoms as part of the dehydrogenation reactions. The dehydrogenation index, evaluated using the absorbance ratio of A₁₄₅₂/A₁₃₆₈, also indicated the gradual loss of hydrogens in agreement with decreasing hydrogen content with progressing stabilization process. IR spectroscopy also showed the emergence of new absorption bands attributed to the formation of crosslinked ladder-like structure in the 1590–1600 cm⁻¹ region. The amount of newly formed crosslinked structure was characterized using DSC conversion index, IR conversion index and gel-fraction measurements. The results are compared and discussed in detail.     

Characterization of conductive poly(acrylonitrile-<Emphasis Type="Italic">co</Emphasis>-vinyl acetate) composites: Matrix polymerization of pyrrole derivatives

In this study, poly(acrylonitrile-co-vinyl acetate) (P(AN-co-VAc)) composite films were prepared by chemical polymerization of pyrrole(Py), N-methyl pyrrole (NMPy) and N-phenyl pyrrole (NPhPy) with cerium(IV) [Ce(IV)] on P(AN-co-VAc) matrix. An increase was observed in the absorbances of CN ring stretching vibration (1451 cm⁻¹) by introducing pyrrole (Py) derivatives on P(AN-co-VAc) matrix. The nitrile (CN) and carbonyl (C=O) groups played a significant role on the interactions with cationic sites of Py derivatives. Conductivity was increased in the presence of carbonyl (C=O) groups due to their additional negative charges on P(AN-co-VAc) matrix compared to PAN. Poly(N-Phenyl Pyrrole) (PNPhPy) exhibited higher dielectric constant and AC conductivity in the frequency range between the 10⁻²–10⁷ Hz. The TGA results exhibited shifts of peak to higher temperatures by the presence of Py derivatives by increasing the weight loss %.     

Structure and properties of silk fibroin modified cotton

In this research, a novel cotton fiber with a silk fibroin (SF) coating was prepared by the oxidation of a cotton thread with sodium periodate and subsequent treatment in a solution of silk fibroin. The structures of both the oxidized cotton samples and the SF modified cotton samples were investigated by Fourier transform infrared (FT-IR) in combination with X-ray photoelectron spectroscopy (XPS) analysis. Other performances such as surface morphology and breaking strength were also studied. The results indicated that the weight of the oxidized cotton samples increased during SF treatment, while that of the un-oxidized cotton (pure cotton) samples reduced after SF treatment. Compared with the pure cotton samples, the oxidized cotton clearly showed a characteristic absorption band at 1730 cm⁻¹ due to the stretching vibration of the C=O double bond of the aldehyde group. After being treated with the SF solution, the oxidized cotton fiber showed a weakened characteristic absorption band at 1730 cm⁻¹ and a new absorption band at round 1540 cm⁻¹, suggesting the formation of C-N bond between aldehyde groups in the oxidized cotton and primary amines in the silk fibroin. The results were also confirmed by XPS analysis. Compared with the oxidized cotton samples, the SF treated cottons had relatively smooth surfaces, similar breaking strength, and the improved wrinkle recovery angles. The results in this research suggest that cotton based materials with protein coating can be achieved without using any other crosslinking agents by the method introduced.     

The effects of nitrogen supply and stem density on leaf attributes and stem branching in potato (Solanum tuberosum L.)

Summary The interaction between nitrogen supply and stem density on leaf attributes and branching was studied in two field experiments. Stem densities included 8, 16, 24, 32 and 40 stems m⁻². The low-N treatments received 5 or 10 g m⁻² nitrogen, and the high-N treatments 20 or 25 g m⁻². The sizes of mature individual leaves on the main stem declined with increase in stem density and were larger for greater N supply, with additive effects of nitrogen and stem density. The specific leaf area was not affected by nitrogen supply and increased with stem density (range of values: 210 to 310 cm² g⁻¹). The leaf weight ratio was not affected by the treatments. At 8 and 16 stems m⁻² basal branches contributed substantially to the total leaf area per stem: at 24 stems m⁻² and higher densities the development of basal branches was negligible. Leaf area on apical branches was always smaller for higher plant densities and lower rates of N supply.     

Residues of free and bound maleic hydrazide in potato tubers

Summary The method of Vadukul (1991) for determining maleic hydrazide (MH) was modified and gave recoveries of free MH of 89%±4%. The values recorded on individual tubers ranged from 2–14 mg kg⁻¹. Maleic hydrazide was evenly distributed throughout the tuber (peel, outer and inner flesh) but concentration increased slightly as tuber size increased. The concentration of free MH decreased from 7 to 3 mg kg⁻¹ over the storage period of 5 1/2 months. Acid hydrolysis released substantial amounts of MH particularly from older potatoes (13 mg kg⁻¹) compared with 6 mg kg⁻¹ from new potatoes, implying that free MH is gradually converted to a bound form with time after treatment. No evidence was found for the presence of a β-glucoside of MH.     

Diffusion of oxygen through lenticels in potato tuber

Summary Diffusion into the potato tuber of oxygen for respiration takes place only through lenticels, and not through the rest of the periderm. The number of lenticels which were capable of injection with methylene blue solution was observed to be about 100 per tuber. Rates of oxygen diffusion per lenticel varied from 0.024 to 0.296 cm³ h⁻¹ atm⁻¹ with a mean of 0.1105±0.013 cm³ h⁻¹ atm⁻¹.     

Microorganism repair after UV-disinfection of secondary-level effluent for agricultural irrigation

A pilot study of microorganism repair after UV disinfection was performed for agricultural reuse of secondary-level effluent in paddy rice fields in Korea. Effluent from the bio-filter of a 16-unit apartment was used in a flow-through type UV-disinfection system. The average concentration of suspended solids (SS) and biochemical oxygen demand (BOD) were 3.4 and 5.9 mg L⁻¹, respectively. The mean total coliform level was in the range of 1.5 × 10⁴ MPN 100 mL⁻¹. Photoreactivation and dark repair were apparent at a low UV dose (6 mW s cm⁻²). In low-dose UV disinfection, microorganisms increased within 12 h by approximately 5 and 1% due to photoreactivation and dark repair, respectively. This increase was not significant at a high UV dose (16 mW s cm⁻²). The repaired microorganisms were further inactivated, rather than reactivated, by solar irradiation, and numbers decreased to non-detectible levels after 4 h of exposure to solar irradiation. Based on UV disinfection and repair studies, a UV dose of 30 mW s cm⁻² is recommended as sufficient to produce reclaimed water virtually free of pathogens and may be adequate for disinfection of secondary effluent for agricultural irrigation in paddy rice culture.     

Preparation of PHEMA/nHAP nanocomposites via <Emphasis Type="Italic">in situ</Emphasis> polymerization in supercritical carbon dioxide for biomedical applications

Poly(2-hydroxyethylmethacrylate) (PHEMA)/hydroxyapatite (HAP) nanocomposites were synthesized through a new route involving nano-sized HAP (nHAP) particles or modified nHAP mixed with monomer 2-hydroxyethylmethacrylate via in situ polymerization in supercritical carbon dioxide (scCO₂). Fourier-transform infrared spectroscopy showed phosphate peak increased with nHAP content in composite. X-ray diffraction patterns of PHEMA/nHAP revealed the presence of crystallized nHAP. Thermogravimetric analysis showed that the ultimate nHAP content in PHEMA/nHAP composites is consistent with its initial amount. Scanning electron microscopy revealed that nanocomposite particles are much smaller than PHEMA particles. PHEMA/nHAP composites with average diameter of approximately 600 nm were obtained in scCO₂ with 94 % yield. Mechanical properties of PHEMA/nHAP nanocomposites were better than those of PHEMA, and compressive modulus and strength of composites with 30 wt.% nHAP were 193 and 29 MPa, respectively. Nanocomposite adsorption toward bovine serum albumin was evaluated, and results indicated that analyte adsorption amount can reach up to 282 mg/g.     

Poly(vinylidene fluoride)/poly(ethylene-co-vinyl acetate) (20/80) blend. I. Miscibility and crystallization behavior

The miscibility and crystallization behavior of the blends of poly(vinylidene fluoride) (PVDF) and ethylene/vinyl acetate(20/80) copolymer (EVAc80) have been studied using a differential scanning calorimeter and a polarizing microscope equipped with a heating stage. From the melting point depression, the values of interaction energy densityB were calculated to be −1.3004 (cal/cm³) and the Flory-Huggins interaction parameterχ ₁₂ was found to be −0.0818 at 445.6 K. With increasing concentration of EVAc80, the radial growth rate of spherulite was reduced drastically. The FT-IR analysis of samples quenched from the melt to various temperatures showed increasing content ofβ-phase with increasing amount of blended EVA80 along with lower quenching temperature.     

Polystyrene nanocomposites viaIn-situ intercalated free radical polymerization

Organically modified montmorillonite (C₈PPh-MMT) was obtained using the ion exchange reaction between Na⁺-montmorillonite (Na⁺-MMT) and 1-octenyltriphenyl phosphonium chloride (C₈PPh-Cl⁻). Polystyrene nanocomposites were then prepared by in-situ free-radical polymerization of the styrene containing intercalated C₈PPh-MMT. The resulting polystyrene hybrids with various organoclay contents were investigated with FT-IR, which confirmed that PS hybrids were successfully prepared via the reaction of styrene monomer in the interlayers of the clays. The variations of the thermal behaviors of the hybrids with increases in the organoclay content from 0 to 8 wt% were determined. The glass transition temperatures (T_g) and initial thermal degradation temperatures (T_D ⁱ) of the PS hybrids were found to increase linearly with increases in the organoclay loading. Regardless of the organoclay content of the hybrids, the clay was found to be dispersed homogeneously in the matrix polymer. This is direct evidence that the PS hybrids formed nanocomposites. This result was confirmed with XRD and TEM.     

Simulation of salt and water movement and estimation of water productivity of rice crop irrigated with saline water

The HYDRUS-ID model was experimentally tested for water balance and salt build up in soil under rice crop irrigated with different salinity water (ECiw) of 0.4, 2, 4, 6, 8 and 10 dS m⁻¹ in micro-lysimeters filled with sandy loam soil. Differences of means between measured (M) and HYDRUS-1D predicted (P) values of bottom flux (Q _o) and leachate EC as tested by paired t test were not found significant at P = 0.05 and a close agreement between RMSE values showed the applicability of the HYDRUS-1D to simulate percolation and salt concentration in the micro-lysimeters under rice crop. Potential ET values of rice as obtained from CROPWAT matched well with model predicted and measured one at all ECiw treatments. The model predicted root water uptake varied from 66.1 to 652.7 mm and the maximum daily salt concentration in the root zone was 0.46, 2.3, 4.5, 6.7, 8.4 and 10.2 me cm⁻³ in 0.4, 2, 4, 6, 8 and 10 dS m⁻¹ ECiw treatments, respectively. The grain production per unit evapotranspiration ( \textWP_{\textET\texta} {\text{WP}}_{{{\text{ET}}_{\text{a}} }} ) value of 2.56 in ECiw of 0.4 dS m⁻¹ treatment declined to 1.31 with ECiw of 2 dS m⁻¹. The \textWP_{\textET\texta} {\text{WP}}_{{{\text{ET}}_{\text{a}} }} reduced to one-fifth when percolation was included in the productivity determination. Similarly, the water productivity in respect of total dry matter production (TDM) was also reduced in different treatments. Therefore, the model predicted values of water balance can be effectively utilized to calculate the water productivity of rice crop.     

Surface modification of okra bast fiber and its physico-chemical characteristics

The effect of chemical treatment i.e. bleaching, alkalization and graft copolymerization on the morphology changes of okra bast fiber has been investigated by means of infrared spectroscopy (IR), scanning electron microscopy (SEM), water absorption and tensile properties measurements. The graft copolymerization reaction of bleached fiber with acrylonitrile monomer (AN) has been carried out under the catalytic influence of K₂S₂O₈ and FeSO₄ redox system. The maximum graft yield (11.43 %) has been found at 70°C temperature, 3×10⁻² mol/l acrylonitrile, 5×10⁻³ mol/l K₂S₂O₈, 5×10⁻³ mol/l FeSO₄ and for 90 min. On the contrary, the fiber has been treated with 10 % NaOH solution, which is much effective to remove the impurities. Based on findings of water absorption, tensile properties and SEM micrograph, the AN-grafted fiber has been showed better properties than bleached and alkali treated fibers. The degree of modification of okra bast fiber by chemical treatment has been evaluated by IR measurement.     

Correlating the fineness and residual gum content of degummed hemp fibres

It is well known residual gum exists in degummed or retted hemp fibres. Gum removal results in improvement in fibre fineness and the properties of the resultant hemp yarns. However, it is not known what correlation if any exists between the residual gum content in retted hemp fibres and the fibre fineness, described in terms of fibre width in this paper. This study examined the mean width and coefficient of variation (CV) of fibre width of seventeen chemically retted hemp samples with reference to residual gum content. The mean and CV of fibre width were obtained from an Optical fibre diameter analyser (OFDA 100). The linear regression analysis results show that the mean fibre width is directly proportional to the residual gum content. A slightly weaker linear correlation also exists between the coefficient of variation of fibre width and the residual gum content. The strong linear co-relation between the mean of fibre width and the residual gum content is a significant outcome, since testing for fibre width using the OFDA is a much simpler and quicker process than testing the residual gum content. Scanning Electron Microscopy (SEM) reinforces the OFDA findings. SEM micrographs show a flat ribbon like fibre cross-section hence the term “fibre width” is used instead of fibre diameter. Spectral differences in the untreated dry decorticated skin samples and chemically treated and subsequently carded samples indicate delignification. The peaks at 1370 cm⁻¹, 1325 cm⁻¹, 1733 cm⁻¹, and 1600 cm⁻¹ attributed to lignin in the untreated samples are missing from the spectra of the treated samples. The spectra of the treated samples are more amine-dominated with some of the OH character lost.     

An adsorption study of alum-morin dyeing onto silk yarn

Silk yarn was dyed with morin (2′,3,4′,5,7-pentahydroxyflavone) by using alum as mordant. In order to optimize the process, three methods of dyeing involving: pre-mordanting, simultaneous mordanting, and post-mordanting were assessed and compared with a mordant-free process. The adsorption of alum-morin dye onto silk fibers indicated that the adsorption capacities were significantly affected by pH, the initial dye concentration, and temperature. The initial dye adsorption rates of alum-morin dye on silk before equilibrium was reached increased with higher dyeing temperatures. The pseudo second-order kinetic model was indicated for alum-morin dyeing (simultaneous mordanting) of silk at pH 4.0 with an activation energy (E _a ) of 45.26 kJ/mol. The value of the enthalpy of activation (ΔH ^#) for alum-morin dyeing on silk at pH 4.0 was −31.29 kJ/mol. Also, the free energy (ΔG ^o) and entropy changes (ΔS ^o) for alum-morin dyeing on silk were −17.73 kJ/mol and −45.7 J/molK, respectively, consistent with a spontaneous and exothermic adsorption process.     

Synthesis and characterization of acrylic fibers-<Emphasis Type="Italic">g</Emphasis>-polyacrylamide

Graft copolymerization of acrylamide onto commercial acrylic fibers was carried out using benzoyl peroxide as a free-radical initiator in aqueous medium within the 75–95 °C temperature range. In this study, the effects of initiator and monomer concentration, the amount of fiber, polymerization time, and temperature on the graft yield were investigated. The optimum concentration for initiator was found to be 2.0×10⁻³ mol/l and the optimum temperature of 85 °C. The activation energy of the reaction was calculated to as 35.81 kJ/mol at the temperature interval of 75–95 °C. The structures and morphologies characterization of grafted fibers was investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The thermogravimetric analysis data showed that the thermal stability of the acrylic fibers increased with graft yield. The scanning electron photographs showed that the homogeneous appearance of the fiber surface changed and a shell-like heterogeneous structure occurred at the surface with an increasing degree of grafting. The moisture content, water absorption, dyeability, and antimicrobial activity of grafted acrylic fibers were also reported. The results showed that grafting of polyAAm improved the moisture contain, water absorption, dyeability, and antimicrobial activity of fiber.     

The degree of starch phosphorylation as influenced by phosphate deprivation of potato (Solanum tuberosum L.) plants

Summary The levels of starch phosphorylation in potato tubers were investigated in relation to fertilization with phosphorus (P) of field-grown and greenhouse-grown plants. The field-grown plants received 0, 15 or 30 kg P ha⁻¹. Starch from plants grown without P-fertilizer contained 15.6 nmol P (mg starch)⁻¹ whereas starch from plants grown with 30 kg P ha⁻¹ contained 20.6 nmol P (mg starch)⁻¹. The greenhouse-grown plants were cultured in inert media and received nutrient solutions containing 0, 3, 12 or 24 mg P l⁻¹, respectively. Plants grown with no P-fertilizer produced tuber starch with phosphorylation levels reduced to approximately 30% of the level found in plants grown with an ample supply of P. Thus, the level of starch phosphorylation can be modified by limiting the P-supply through the root system. Application of foliar P-fertilizer to the greenhouse-grown plants had no significant effect on the phosphorylation of the tuber starch.