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1.
H. M. Tong K. L. Saenger C. J. Durning 《Journal of Polymer Science.Polymer Physics》1989,27(3):689-708
Using laser interferometry, we have determined in situ the thickness increase with time of thin supported polyimide films (4–8 μm in initial thickness) immersed in n-methyl-2-pyrrolidone (NMP) as a function of NMP temperature (22–120°C). Similar experiments were also performed in dimethyl sulfoxide (DMSO) at 22°C with polyimide films of 4.1 μm in thickness. For NMP, the equilibrium fractional thickness increase (about 20%) is independent of initial polyimide thickness and temperature. The time scale for reaching equilibrium sharply decreases with temperature from 2–3 days at 22°C to 30–60 min at 120°C. Compared with NMP, the rate of DMSO sorption is considerably faster, reaching equilibrium swelling of about 28% in about 5 h at 22°C. To describe the transport process, we applied a phenomenological model proposed by Astarita and Sarti1 but reformulated in polymer fixed frame to enable straightforward comparison with the thickness data. Our analysis indicated that the transport of NMP is best described as anomalous, that is, intermediate between diffusion controlled and case II transport. The effective diffusion coefficient Deff and the front velocity U0 at 22°C were found to be 3–6 × 10?12 cm2/s and 8 × 10?9 cm/s, respectively. Our front velocity is in good accord with the value of 6 × 10?9 cm/s obtained for a similar polyimide based on gravimetric measurements.2 Both Deff and U0 show an activation energy of ~56 kJ/mol. For DMSO, however, the transport is clearly case II. The front velocity at 22°C was found to be about 6 × 10?8 cm/s, which is about four times that obtained by Rutherford back-scattering spectrometry.3 相似文献
2.
Siu‐Ming Yuen Chen‐Chi M. Ma Chin‐Lung Chiang Yao‐Yu Lin Chih‐Chun Teng 《Journal of polymer science. Part A, Polymer chemistry》2007,45(15):3349-3358
Precursor of polyimide, polyamic acid has been prepared sucessfully. Acid‐modified carbon nanotube (MWCNT) was grafted with soluble polyimide then was added to the polyamic acid and heated to 300 °C to form polyimide/carbon nanotube composite via imidation. Morphology, mechanical properties and electrical resistivity of the MWCNT/polyimide composites have been studied. Transmission electron microscope microphotographs show that the diameter of soluble polyimide‐grafted MWCNT was increased from 30–60 nm to 200 nm, that is a thickness of 70–85 nm of the soluble polyimide was grafted on the MWCNT surface. PI‐g‐MWCNT was well dispersed in the polymer matrix. Percolation threshold of MWCNT/polyimide composites has been investigated. PI‐g‐MWCNT/PI composites exhibit lower electrical resistivity than that of the acid‐modified MWCNT/PI composites. The surface resistivity of 5.0 phr MWCNT/polyimide composites was 2.82 × 108 Ω/cm2 (PI‐g‐MWCNT) and 2.53 × 109 Ω/cm2 (acid‐modified MWCNT). The volume resistivity of 5.0 phr MWCNT/polyimide composites was 8.77 × 106 Ω cm (PI‐g‐MWCNT) and 1.33 × 1013 Ω cm (acid‐modified MWCNT).Tensile strength and Young's modulus increased significantly with the increase of MWCNT content. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3349–3358, 2007 相似文献
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4.
Kangseok Lee Sang Eun Shim Byung H. Lee Seong Uk Hong Soonja Choe 《Journal of Polymer Science.Polymer Physics》2004,42(6):1114-1126
The desorption behavior of a surfactant in a linear low‐density polyethylene (LLDPE) blend at elevated temperatures of 50, 70, and 80 °C was studied with Fourier transform infrared spectroscopy. The composition of the LLDPE blend was 70:30 LLDPE/low‐density polyethylene. Three different specimens (II, III, and IV) were prepared with various compositions of a small molecular penetrant, sorbitan palmitate (SPAN‐40), and a migration controller, poly(ethylene acrylic acid) (EAA), in the LLDPE blend. The calculated diffusion coefficient (D) of SPAN‐40 in specimens II, III, and IV, between 50 and 80 °C, varied from 1.74 × 10?11 to 6.79 × 10?11 cm2/s, from 1.10 × 10?11 to 5.75 × 10?11 cm2/s, and from 0.58 × 10?11 to 4.75 × 10?11 cm2/s, respectively. In addition, the calculated activation energies (ED) of specimens II, III, and IV, from the plotting of ln D versus 1/T between 50 and 80 °C, were 42.9, 52.7, and 65.6 kJ/mol, respectively. These values were different from those obtained between 25 and 50 °C and were believed to have been influenced by the interference of Tinuvin (a UV stabilizer) at elevated temperatures higher than 50 °C. Although the desorption rate of SPAN‐40 increased with the temperature and decreased with the EAA content, the observed spectral behavior did not depend on the temperature and time. For all specimens stored over 50 °C, the peak at 1739 cm?1 decreased in a few days and subsequently increased with a peak shift toward 1730 cm?1. This arose from the carbonyl stretching vibration of Tinuvin, possibly because of oxidation or degradation at elevated temperatures. In addition, the incorporation of EAA into the LLDPE blend suppressed the desorption rate of SPAN‐40 and retarded the appearance of the 1730 cm?1 peak. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1114–1126, 2004 相似文献
5.
《Electroanalysis》2002,14(23):1648-1653
An electrochemical equation suitable for examining the interaction of irreversible redox compounds with DNA is established. According to the equation, diffusion coefficients of both free and binding compounds (Df , Db), binding constant (K) and binding site size (s) of compounds with DNA could be obtained simultaneously by nonlinear fit analysis of electrochemical data. Bis‐benzimidazole derivative (Hoechst 33258), as an irreversible redox compound, was investigated for its electrochemical behavior and the interaction with natural fish sperm DNA (fsDNA) using cyclic voltammetry, chronocoulometry, bulk electrolysis and scanning electrochemical microscope technique. A nonlinear fit analysis of the experimental data yielded: Df=8.3×10?5 cm2 s?1, Db=6.0×10?6 cm2 s?1, K=2.1×108 cm3 mol?1, s=3.9. The overall results suggest that Hoechst 33258 binds tightly to the minor groove of fsDNA and covers four base pairs. 相似文献
6.
《Surface and interface analysis : SIA》2003,35(3):287-293
Calcium phosphate (CaP) coatings are used to improve the biological performance of an implant. A technique that is often used to measure the composition of this material is XPS. When extremely thin coatings are measured, for example to study the interface between CaP and a substrate, the quantification of the XPS results is complicated by the varying attenuation lengths (ALs) of the photoelectrons at different energies. To correct for this, AL data are needed. In this work we measured these ALs by comparing XPS yields with the coating coverage (as measured by Rutherford backscattering spectrometry). We were able to determine the AL for several calcium and phosphorus peaks. Determination of the oxygen ALs was not possible owing to diffusion of oxygen into the polymeric substrates. For the peaks that are most often used for quantification of XPS yields (the Ca 2p and the P 2p peak), we found ALs of 21.8 × 1015 atoms cm?2 and 26.8 × 1015 atoms cm?2, respectively. Concentration profiles near the interface, growth mode and interfacial roughness appeared to have no measurable effect on the measured ALs. For the ALs, an energy dependence with an exponent of 0.55 was found. The measured ALs are best predicted by the empirical CS1 equation of Cumpson and Seah. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
7.
Ion induced controlled modifications in structural and optical properties of indium oxide thin films – studies with 25‐keV Co− and N+ beam implantations
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Riti Sethi Priya Darshni Kaushik Anver Aziz Azher M. Siddiqui Pravin Kumar 《Surface and interface analysis : SIA》2017,49(9):910-918
Two sets of indium oxide thin films (~150 nm) grown on quartz substrates using thermal evaporation technique were processed separately with 25‐keV Co? and N+ ions with several fluences ranging from 1.0 × 1015 to 1.0 × 1016 ions/cm2. The pristine and the ion implanted films were characterized by Rutherford backscattering spectroscopy (RBS), X‐ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV–Vis spectrometry. The RBS spectra reveal signature of only cobalt and nitrogen in accordance to their fluences confirming absence of any contamination arising due to ion implantation. An increase in the average crystallite size (from 13.7 to 15.3 nm) of Co? ions implanted films was confirmed by XRD. On the other hand, the films implanted with N+ ions showed a decrease in the average crystallite size from 20.1 to 13.7 nm. The XRD results were further verified by SEM micrographs. As seen in AFM images, the RMS surface roughness of the samples processed by both ion beams was found to decrease a bit (29.4 to 22.2 nm in Co? implanted samples and 24.2 to 23.3 nm in N+ implanted samples) with increasing fluence. The Tauc's plot deduced from UV–visible spectroscopy showed that the band gap decreases from 3.54 to 3.27 eV in Co? implanted films and increases from 3.38 to 3.58 eV for films implanted with N+ ions. The experimental results suggest that the modifications in structural and optical properties of indium oxide films can be controlled by optimizing the implantation conditions. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
8.
Yuhan Li Rizhe Jin Zhen Wang Zhiming Cui Wei Xing Lianxun Gao 《Journal of polymer science. Part A, Polymer chemistry》2007,45(2):222-231
A novel sulfonated diamine monomer, 2,2′‐bis(p‐aminophenoxy)‐1,1′‐binaphthyl‐6,6′‐disulfonic acid (BNDADS), was synthesized. A series of sulfonated polyimide copolymers containing 30–80 mol % BNDADS as a hydrophilic component were prepared. The copolymers showed excellent solubility and good film‐forming capability. Atomic force microscopy phase images clearly showed hydrophilic/hydrophobic microphase separation. The relationship between the proton conductivity and degree of sulfonation was examined. The sulfonated polyimide copolymer with 60 mol % BNDADS showed higher proton conductivity (0.0945–0.161 S/cm) at 20–80 °C in liquid water. The membranes exhibited methanol permeability from 9 × 10?8 to 5 × 10?7 cm2/s at 20 °C, which was much lower than that of Nafion (2 × 10?6cm2/s). The copolymers were thermally stable up to 300 °C. The sulfonated polyimide copolymers with 30–60 mol % BNDADS showed reasonable mechanical strength; for example, the maximum tensile strength at break of the sulfonated polyimide copolymer with 40 mol % BNDADS was 80.6 MPa under high moisture conditions. The optimum concentration of BNDADS was found to be 60 mol % from the viewpoint of proton conductivity, methanol permeability, and membrane stability. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 222–231, 2007 相似文献
9.
Virendra V. Singh M. Boopathi K. Ganesan Beer Singh R. Vijayaraghavan 《Electroanalysis》2010,22(12):1357-1363
Greener electrochemical detection method developed for chemical warfare agent (CWA) nitrogen mustard‐2 (NM‐2) using room temperature ionic liquid (RTIL). The diffusion coefficient calculated for NM‐2 in acetonitrile and RTIL was 1.57×10?4 cm2/s and 1.82×10?10 cm2/s, respectively. NM‐2 addition to RTIL enhanced RTIL conductivity. Moreover, heterogeneous rate constant (0.192 s?1), transfer coefficient (0.231) and the number of electron involved (1.0) were deduced for NM‐2 in RTIL. The calibration plot showed linearity between 2.94×10?5 and 1.17×10?3 M with detection limit 1.47 ×10?5 M (S/N=3). The large number of available RTIL can be used for greener detection of toxic CWAs. 相似文献
10.
To improve the oil absorbency of caster oil‐based polyurethane foam, nano‐organic‐montmorillonite (OMMT) was used for the additives. The aim of this study is to evaluate the oil diffusion mechanism and dispersion uniformity of OMMT modified caster oil‐based polyurethane (MPU) using experiments and molecular dynamic simulation. Molecule movement and molecule trajectory of oil was investigated by molecular dynamic simulation and numerical simulation. According to the quantitative analyzing results, the diffusion model was put forward. The average diffusion coefficient of crude oil in 0, 1, 2 wt%, 4, and 6 wt% MPU is 2.4 × 10?4 cm2/s, 2.6 × 10?4 cm2/s, 3.0 × 10?4 cm2/s, 3.2 × 10?4 cm2/s, and 3.3 × 10?4 cm2/s, respectively. It indicated that crude oil appeared gradient in the MPU. The optimal diffusion direction of crude oil is (0, 0, 1) crystal face, and the small particles of crude oil are easy to be adsorbed. The two‐dimensional diffusion trajectory of crude oil is nonlinear. The diffusion model includes the diffusion of crude oil at the interface of oil and polyurethane, surface diffusion and pore diffusion, and pore adsorption. Furthermore, the diffusion model showed that the van der Waals force was the main reason for crude oil diffusion or adsorption. OMMT could improve the ability of oil/water separation of polyurethane. 相似文献
11.
M. C. del Barrio S. G. García C. E. Mayer D. R. Salinas 《Surface and interface analysis : SIA》2008,40(1):22-26
The Cd underpotential deposition (UPD) process on Au(111) was analyzed by means of combined electrochemical measurements and in situ scanning tunneling microscopy (STM). In the underpotential range 300?ΔE (mV) ?400, 2D Cd islands are formed on the fcc regions of the Au(111)‐(√3 × 22) reconstructed surface without lifting the reconstruction. At lower underpotentials, the 2D Cd islands grow and, simultaneously, new 2D islands nucleate and coalesce with the previous ones forming a complete condensed Cd monolayer (ML). STM images and long time polarization experiments performed at ΔE = 70 mV demonstrate the formation of an Au? Cd surface alloy. At ΔE = 10 mV, the formation of the complete Cd ML is accompanied by a significant Au? Cd surface alloying and the kinetic results reveal two different solid‐state diffusion processes. The first one, with a diffusion coefficient D1 = 4 × 10?17 cm2 s?1, could be ascribed to the mutual diffusion of Au and Cd atoms through a highly distorted (vacancy‐rich) Au? Cd alloy layer. The second and faster diffusion process (D2 = 7 × 10?16 cm2 s?1) is associated with the appearance of an additional peak in the anodic stripping curves and could be attributed to the formation of another CdzAux alloy phase. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
12.
《Electroanalysis》2004,16(4):289-297
The polymer film of N,N‐dimethylaniline (DMA) is deposited on the electrochemically pretreated glassy carbon (GC) electrode by continuous electrooxidation of the monomer. This poly N,N‐dimethylaniline (PDMA) film‐coated electrode can be used as an amperometric sensor of ascorbic acid (AA). The polymer film (thickness (?): 0.3±0.02 μm) having positive charge in its backbone attracts the anionic species AA. Thus, the anodic peak potential (350 mV vs. Ag|AgCl|NaCl(sat)) for the oxidation of AA at the bare electrode is largely shifted to the negative value (150 mV) at this electrode. The PDMA film‐coated electrode is stable in acidic, alkaline and neutral media and can sense AA at different pH's. The diffusion coefficients of AA in solution (D) and in film (Ds) were estimated by rotating disk electrode voltammetry: D=(5.5±0.1)×10?6 cm2 s?1 and Ds=(6.3±0.2)×10?8, (6.0±0.2)×10?8 and (4.7±0.2)×10?8 cm2 s?1 for 0.5, 1.5 and 3.0 mM AA, respectively. A permeability of AA through the PDMA film was found to decrease with increasing the concentration of AA in the solution. In the chronoamperometry, the current response for the oxidation of AA at different times elapsed after potential‐step application is linearly increased with the increase in AA concentration in a wide range of its concentration from 25 μM to 1.65 mM. In the hydrodynamic amperometry, a successive addition of 10 μM AA caused the successive increase in current response with equal amplitude and the sensitivity was calculated as 0.178 μA cm?2 μM?1. So, the fouling of the electrode surface caused by the oxidized product of AA is markedly eliminated at this PDMA film‐coated electrode. A flow injection analysis based on the present electrode was performed to estimate the concentration of vitamin C in fruit juice. 相似文献
13.
Preliminary measurements of the triplet diffusivity tensor in crystalline pyrene at 300 K are reported. Maximum diffusivity occurs along the b axis and Dab = (1.25 ± 0.3) × 10?4 cm2 s?1. Diffusion in the ac′ plane is nearly isotropic with D ≈ (0.3 ± 0.1) × 10?4 cm2 s?1. These results are tentatively interpreted as diffusion dominated by nonlocal scattering. 相似文献
14.
Carlin Geor Malar Muthulingam Seenuvasan Kannaiyan Sathish Kumar 《Applied biochemistry and biotechnology》2018,186(1):174-185
Herein, the magnetite nanoparticles (MNs) were prepared by facile solvothermal method and its porous nature was modified using 3-(2-aminoethyl)-3-aminopropyl trimethoxysilane (AEAPS). Magnetite formation, successful amino tagging, and urease conjugation on the surface were confirmed from the presence of certain functional groups in Fourier transform infrared (FT-IR) spectra. Also, nanosize (13.2 nm) and spherical morphology of MNs were evaluated from diffraction patterns and electron micrographs respectively. Lower retentivity and coercivities in magnetization curve revealed the superparamagnetic behavior, and nitrogen adsorption/desorption curves exhibited decrease in its surface porosity. Conductivity measurements showed lower diffusion coefficient (De?=?1.9?×?10?17 cm2/min) and higher diffusion with limited hydrolytic reaction in native urease and improved activity of conjugated urease with higher De (12.62?×?10?16 cm2/min). Hence, this study revealed that the surface porous nature of MNs can be altered effectively by amino tagging in order to overcome diffusional limitations thereby enhancing enzyme activity. 相似文献
15.
The electrochemical behaviour of hydrazine at a 1‐benzyl‐4‐ferrocenyl‐1H‐[1,2,3]‐triazole‐triazole/carbon nanotube modified glassy carbon electrode has been studied. The modified electrode shows an excellent electrocatalytic activity for the oxidation of hydrazine and accelerates electron transfer rate. The electrocatalytic current increases linearly with hydrazine concentration in the range 0.5–700.0 μm and the detection limit for hydrazine was 33.0 ± 2.0 nm . The diffusion coefficient (D = 2.5 ± 0.1 × 10?5 cm2 s?1) and kinetic parameters such as the electron transfer coefficient, (α = 0.52) and the heterogeneous rate constant (k′ = 5.5 ± 0.1 × 10?3 cm s?1) for hydrazine were determined using electrochemical approaches. Finally, the method was employed for the determination of hydrazine in water samples. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
16.
《Electroanalysis》2006,18(18):1778-1785
This work examines the charge transport properties of redox films of the immobilized enzyme mediator [Os(bpy)2(picolinate)]Cl ([Os(bpy)2Pic]+). Chronoamperometry was used to calculate DCT values (typically of the order of 1.5×10?8 cm2 s?1) and the effect of %loading of redox material was determined for three electrolytes over a range of concentrations. The data obtained implies that charge transfer within the film occurs via a redox site diffusion mechanism. The concentration of redox sites was determined using an approximate film thickness of 7 μm, as determined from profilometry studies. Experiments were also performed using immobilized carbon nanotubes within the redox film in order to examine the impact of the increased surface area and conductivity. The presence of the carbon nanotubes had the effect of doubling the surface coverage values and enhancing DCT1/2 CM values from 1.9×10?9 to 16.1×10?9 mol cm?1 s?1. 相似文献
17.
J. K. Gillie M. D. Newsham A. Sen R. A. Bubeck 《Journal of Polymer Science.Polymer Physics》1995,33(11):1621-1626
Diffusion of aqueous and nonaqueous coagulants into lyotropic/nematic solutions of poly(phenylene benzobisoxazole) in polyphosphoric acid using fluorescence microscopy is reported. The fluorescence microscopy technique offers advantages in that the experiment is independent of the coagulant and the experiments can be performed in a front surface mode so that optically thin samples are not required. The diffusion process is modeled as Case II diffusion as described by Crank and Park. The apparent diffusion coefficients are found to range from ~ 2 × 10?6 cm2/s to ~ 2 × 10?7 cm2/s for aqueous and nonaqueous coagulants. The apparent diffusion coefficients can be varied by several orders of magnitude (e.g., down to ~ 3 × 10?10 cm2/s) by varying the concentration of polyphosphoric acid in the coagulant. © 1995 John Wiley & Sons, Inc. 相似文献
18.
The transport properties of oxygen in poly(dimethyl siloxane) have been measured using the method of quenching of fluorescence. This paper discusses the uniqueness of this method and its use in measuring the diffusion coefficient of oxygen in unfilled PDMS. The results show (1) a large value for the diffusion coefficient of oxygen in pure PDMS at 25°C, D = 3.55 × 10?5 cm2/s, (2) a low value of the acitivation energy, ED = 4.77 kcal/mole, which was not temperature dependent in the ranges evaluated, and (3) a large value of the preexponential term, D0 = 0.115 cm2/s. The diffusion coefficient was found to be independent of both the oxygen concentration and fluorophor concentration in the pressure and temperature ranges used in these experiments. The import of these experiments lies in their application to a unique biomedical oxygen sensor which is fast, sensitive, and does not consume oxygen. 相似文献
19.
《Analytical letters》2012,45(13):2207-2216
Abstract A simple and selective spectrophotometric method has been developed for the determination of trace amounts of arsenic using azure B as a chromogenic reagent. The proposed method is based on the reaction of arsenic(III) with potassium iodate in acid medium to liberate iodine. The liberated iodine bleaches the violet color of azure B and is measured at 644 nm. This decrease in absorbance is directly proportional to the As(III) concentration, and Beer's law is obeyed in the range 0.2–10 µg ml?1 of As(III). The molar absorptivity, Sandell's sensitivity, detection limit, and quantitation limit of the method were found to be 1.12×104 l mol?1cm?1, 6.71×10?3 µg cm?2, 0.02 µg ml?1 and 0.08 µg ml?1, respectively. The optimum reaction conditions and other analytical parameters were evaluated. The proposed method has been successfully applied for the determination of arsenic in various environmental and biological samples. 相似文献
20.
《Electroanalysis》2004,16(10):860-865
The electrocatalytic oxidation of sulfite has been studied on the cobalt pentacyanonitrosylferrate modified glassy carbon electrode (CoPCNF). The CoPCNF films on the glassy carbon electrodes show an excellent electrocatalytic activity toward the oxidation of sulfite in 0.5 M KNO3. The kinetics of the catalytic reaction was investigated by using cyclic voltammetry, rotating disk electrode (RDE) voltammetry and chronoamperometry. The average value of the rate constant, K, for the catalytic reaction and the diffusion coefficient, D, were evaluated by different approaches for sulfite and found to be 2.9×102 M?1s?1 and 4.6×10?6 cm2s?1, respectively. At a fixed potential under hydrodynamic conditions (stirred solutions), the oxidation current is proportional to the sulfite concentration and the calibration plot was linear over the concentration range 5×10?6–1×10?4 M. The detection limit of the method is 3×10?6 M., low enough for the trace sulfite determination. 相似文献