共查询到20条相似文献,搜索用时 15 毫秒
1.
Wei Zhang Kaikai Wang Xiaodan Hu Xiaohong Zhang Shuquan Chang Haiqian Zhang 《先进技术聚合物》2020,31(10):2127-2135
The irradiation of tumors in radiotherapy requires accurate 3D dosimetry. The Fricke 3D dosimeters, which were considered to be high potential of application in 3D dosimetry, suffer from a reduced temporal integrity of dose distribution caused by Fe3+ ions diffusion. To overcome the drawback, we firstly synthesized a kind of amphiphilic molecules with critical micelle concentration of 0.45 g/L and hydrophile‐lipophile balance value of 10, then prepared multiple emulsions by self‐assembling those molecules in Fricke solution under liquid paraffin, and finally obtained Fricke hydrogel embedded with the multiple emulsions. The diffusion coefficient of Fe3+ ions in the embedded Fricke hydrogel was measured to be 0.17 mm2/h. The hydrogel dosimeter exhibits considerable potential for use in dose verification applications. 相似文献
2.
Cholesterol appended pyridinium urea 1 acts as low molecular weight gelator in DMSO:H2O (1:1, v/v) showing distinct colour change in the presence of aqueous solution of KF as well as tetrabutylammonium fluoride and recognises F? specifically. In addition, this hydrogel is noted to detect aqueous solution of Cu2+ and Pb2+ ions over a series of other metal ions and exhibits good semi-conducting property. 相似文献
3.
《Journal of polymer science. Part A, Polymer chemistry》2018,56(17):1907-1914
A facile synthetic strategy was developed for the preparation of thermoresponsive nanocomposite hydrogels comprising crosslinked chitosan (CS) networks and poly(N‐isopropylacrylamide) [p(NIPAAm)] nanogels. First, thermoresponsive p(NIPAAm) nanogels were synthesized via emulsion polymerization. The p(NIPAAm) nanogels were introduced into methacrylamide CS (MC) solution and the free‐radical initiated crosslinking reaction of MC produced nanogel‐embedded hydrogels. The last step involves the loading of the antibacterial model drug levofloxacin (LFX) into the prepared nanocomposite hydrogels by allowing the preformed hydrogels to swell to equilibrium in the drug's aqueous solution. The integration of p(NIPAAm) nanogel into CS networks facilitates thermoresponsive release of LFX with an enhancement of the drug‐loading capacity within the hydrogel. Notably, thermoresponsive drug‐release was achieved without unwarranted modification of the hydrogel's dimension and shape, although an increase in temperature caused the collapse of the p(NIPAAm) nanogels. The thermoresponsive property of the investigated nanocomposite hydrogel is beneficial and may offer broad opportunities for drug temperature‐triggered release for clinical applications. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1907–1914 相似文献
4.
In this review, we present a detailed study of the surface diffusion of adsorbed atoms and molecules on metal surfaces via the analysis of adsorbate density fluctuations in nanosized adsorption systems. Three different experimental approaches, all based on field emission techniques are presented: measurements of field emission current fluctuations, the analysis of local brightness fluctuations of digitized field emission images and the analysis of field ion rate fluctuations. 相似文献
5.
Thomas Spann Dietrich Bergner Bettina Teige Siegfried Däbritz Wolfgang Hauffe 《Mikrochimica acta》1997,125(1-4):381-387
To investigate processes of short circuit and uphill diffusion, low-temperature diffusion experiments were carried out with sandwich samples of CuSn6/Ni/Au in the kinetic regimeB after Harrison. Two kinds of base material CuSn6 with different grain sizes were chosen. The first material was cold rolled CuSn6 with a mean grain size of 3–4 m. The second was annealed CuSn6 with a mean grain size of 40 m. The Ni and Au layers with thicknesses in the m range were deposited by galvanization. The sheets were prepared by ion beam slope cutting, characterized by scanning electron microscopy and transmission electron microscopy. After annealing at 576 K up to 120 d, the samples were investigated with glow discharge spectroscopy and scanning electron microscopy. Concentration penetration plots made with glow discharge spectroscopy showed a different diffusion behaviour dependent on the CuSn6 material. The diffusion processes in the samples of cold rolled CuSn6 are more extensive than in the annealed CuSn6 samples. To find out causes of this phenomenon, a model of short circuit diffusion was developed and concentration penetration curves were calculated numerically with the finite difference method. Images of an ion beam slope cut sample show grain growth in the Au layer.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday 相似文献
6.
A systematic comparison of the diffusion coefficients of cations (Al, Cd, Co, Cu, Mn, Ni, Pb, Zn) and oxyanions (Al, As, Mo, Sb, V, W) in open (ODL) and restricted (RDL) diffusive layers used by the DGT technique was undertaken. Diffusion coefficients were measured using both the diffusion cell (Dcell) method at pH 4.00 and the DGT time-series (DDGT) method at pH 4.01 and 7.04 (pH 8.30 was used instead of 7.04 for Al) using the Chelex-Metsorb mixed binding layer. The performance of Chelex-Metsorb as a new DGT binding layer for Al uptake was also evaluated for the first time. Reasonable agreement was observed between Dcell and DDGT measurements for both ODL and RDL, except for V and W. The ratios of Dcell/DDGT for V of 0.44 and 0.39, and for W of 0.66 and 0.63 with ODL and RDL respectively, were much lower due to the formation of a high proportion of polyoxometalate species at the higher concentrations required with the Dcell measurements. This is the first time that D values have been reported for several oxyanions using RDL. Except for Al at pH 8.30 with ODL, all DDGT measurements were retarded relative to diffusion coefficients in water (DW) for both diffusive hydrogels. Diffusion in RDL was further retarded compared with ODL, for all elements (0.66–0.78) with both methods. However, the degree of retardation observed changed for cations and anions at each pH. At pH 7.04 cations had a slightly higher DDGT and oxyanions had a slightly lower DDGT than at pH 4.01 for both ODL and RDL. It is proposed that this is due to partial formation of acrylic acid functional groups (pKa ≈4.5), which would be fully deprotonated at pH 7.04 (negative) and mostly protonated at pH 4.01 (neutral). As Al changes from being cationic at pH 4.01 to anionic at pH 8.30 the results were more complex. 相似文献
7.
The system of equations describing ion transport in a binary electrolyte z
a-z
c with allowance for the linear dependence of the diffusion coefficients on the concentration was analyzed in the framework
of the phenomenological Nernst-Planck approach. The expressions are obtained that define concentration profiles of ions and
conditions favorable for the limiting current caused by the achievement of the concentration of a saturated solution (in the
case of the anodic reaction) and depletion of the near-electrode region in electroactive cations (in the case of the cathodic
reaction). The revealed theoretical dependence of the limiting current on the volume concentration of the salt agrees with
published experimental data. The voltammetric characteristics of the corresponding systems were calculated. The role of the
migrational component of the ion flow is discussed.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 638–642, April, 2006. 相似文献
8.
Initial and steady-state temperature coefficients of the voltage generated by thermogalvanic cells comprising silver chloride and quinhydrone electrodes in the systems HCl-H2O-C2H5OH and KCl-H2O-C2H5OH are determined. Standard thermal diffusion Soret coefficients, the entropy of thermal diffusion transport of electrolytes, and the entropy of mobile ions H+, K+, and Cl? are calculated for 298 K. The effect the nature of ions and the solvent composition exert on the obtained thermal diffusion transport characteristics is considered in terms of the De Bethune theory. 相似文献
9.
A theory of the staircase voltammetry in a thin-layer cell is developed. The influence of the cell thickness and the redox reaction rate constant on the current and the peak potentials is analyzed. For moderately thick cells, the kinetic maximum is predicted. The relationship between peak currents and the square root of the scan rate is not linear and the response may entirely vanish if the redox reaction is fast, the cell is very thin and the scan rate is slow. 相似文献
10.
Chang-Yeoul Kim Sung-Geun Cho Tae-Young Lim Duck-Kyun Choi 《Journal of Solid State Electrochemistry》2009,13(8):1165-1170
CeO2·TiO2 thin film is considered as an excellent candidate for a passive ion storage layer due to its good electrochemical stability
and comparatively great charge capacitance. When cerium-titanium oxide thin film is adopted as an ion storage layer against
cathodic tungsten oxide layer, the electrochromic device shows long term durability and cyclability. Therefore, many researchers
investigated the composition and crystallinity effects to the charge density. In our study, we prepared CeO2·TiO2 thin by sol–gel dip-coating method, varying thickness by controlling withdrawal speeds. As investigating results of cyclic
voltammetry and chronocoulometry, we found that there are three regions in the film thicknesses: (1) fast lithium ion diffusion
region under 100 nm, (2) slow diffusion region in the range of 100 to 150 nm, and (3) fast and great charge capacitance region
over 150 nm. In region 1, lithium ions diffuse very fast and reach into indium-tin oxide (ITO) layers, and slow diffusion
region follows in region 2, probably due to the remains or impurities within the film, and in region 3, lithium ion diffusion
gets fast again, accompanied with charge capacitance increase with thickness. 相似文献
11.
Soret coefficients are measured conductimetrically for dilute aqueous solutions of the stepwise-associating ionic dyes methylene
blue (chloride salt) and methyl orange (sodium salt) at 25°C. In contrast to the behavior of other dilute aqueous electrolytes,
the Soret coefficients of the dyes increase with concentration. An approximate treatment of thermal diffusion of stepwise-associating
solutes is developed to interpret the results. The analysis is used to estimate the intrinsic enthalpies of transport of the
monomeric and the associated forms of the dyes. The enthalpy of association makes a large reactive contribution to the enthalpy
of transport of methyl orange. 相似文献
12.
This paper deals with frequency response (FR) analysis of a closed diffusion cell system with two resonators, that is both the LHS and RHS volumes are modulated. The analysis is made for a homogeneous particle described by a single effective diffusivity as well as a biporous pellet described by macropore and micropore diffusions. It is shown that if the perturbation of the volume of the reservoir #2 is lagged behind that of the reservoir #1 by 3/2, the pressure response in reservoir #1 is significantly enhanced with larger amplitude as well as phase angle. When the perturbations of the two reservoirs are out of phase, the heat effect is reduced and can become insignificant when the two perturbations are completely out of phase ( = ). Under such a condition, the pressure difference between the two reservoirs could be doubled. In the case of biporous pellets, it is shown that the FR behaviours obtained for micropore diffusion control and macropore diffusion control are well distinguished. In the former case, the FR system reduces to a traditional batch adsorber one while in the latter case, the FR behaviour is the same as for a two resonator system with homogeneous particles. This difference can be used for the discrimination of micropore and macropore diffusion processes. 相似文献
13.
Peter Fielitz Günter Borchardt Roger A. De Souza Manfred Martin Muayad Masoud Paul Heitjans 《Solid State Sciences》2008,10(6):746
18O/16O isotope exchange in combination with SIMS depth profiling was used to investigate oxygen transport in Li2O-deficient single crystalline LiNbO3 in the temperature range 983 ≤ T/K ≤ 1188 at 200 mbar oxygen. Within the limit of experimental error and for the investigated range of temperatures no significant differences between transport parallel and transport perpendicular to the c-axis were found. The following temperature dependencies were determined: for oxygen tracer diffusion D = 6.4 × 10−3exp[−333 kJ/mol/(RT)] m2/s; and for oxygen surface exchange k = 7.8 × 102exp[−288 kJ mol−1/(RT)] m/s. The activation enthalpy obtained for tracer diffusion can be interpreted as the enthalpy of migration of extrinsic oxygen vacancies induced by impurities with lower valency on niobium sites. 相似文献
14.
紫外光解/气膜扩散-离子色谱法测定废水中总氰和硫化物 总被引:1,自引:0,他引:1
建立了一种流动注射、紫外光解/气膜扩散净化与小柱富集、离子色谱-脉冲安培检测自动分析废水中总氰与硫化物的方法。样品被混合到硫酸和次磷酸组成的混合酸载流中,内含适量的氨基磺酸、抗坏血酸、EDTA与柠檬酸,经312 nm波长的紫外光解,使不同形态氰化物如Fe(CN)63-等变成氰化氢,硫化物变成硫化氢,通过孔径0.45 μm的聚丙烯膜片扩散,由稀碱溶液吸收,Metrosep A PCC 1 HC/4.0富集柱捕获,IonPac AS7分析柱分离,银电极三电位波形脉冲积分安培检测。总氰与硫化物在0.5~1000 μg/L范围内线性关系良好(相关系数分别为0.9989与0.9997),回收率在93%~102%,检出限(100 μL进样,信噪比为5)为0.5 μg/L与1.0 μg/L。利用该方法每小时可做6个样品,部分实际样品的测定结果与标准方法的测定结果具有较好的一致性。 相似文献
15.
Voids in a medium are defined as the regions that are located outside an appropriately defined occupied space associated with molecules. Dynamical properties like diffusion can be related to the structure and distribution of voids present in the medium. This work deals with an analysis of voids and diffusion in liquid ammonia. The analysis of voids is done by the construction of Voronoi polyhedra and Delaunay tessellation. We have performed a series of molecular dynamics simulations of monovalent cations and anions of varying size in liquid ammonia at two different temperatures of 210 and 240 K to investigate the effects of ion size on the diffusion of ions and roles of voids in determining the observed diffusion behavior. It is found that with the increase of ion size, the diffusion coefficients first increase and then pass through a maximum similar to the behavior observed earlier for diffusion in water. The observed results are explained in terms of passage through voids and necks that are present in liquid ammonia. © 2012 Wiley Periodicals, Inc. 相似文献
16.
E. G. Kulapina N. M. Makarova O. V. Mikhaleva 《Russian Journal of Electrochemistry》2008,44(12):1339-1344
Relationships are established for the permeability and flux of ionic surfactants with the concentration of electroactive compounds (EAC), the nature and concentration of solutions adjacent to the membrane, and membrane thickness. Values of permeability and ion fluxes decrease with decreasing EAC concentration and increasing membrane thickness. As the EAC concentration increases, i.e., as the number of charged centers in the membrane increases, permeabilities and ion fluxes also increase proportionally. The quantitative properties of membrane transport are an order of magnitude lower under conditions of diffusion mass transfer than with constant current. 相似文献
17.
A simple direct enzyme immunoassay for semiquantitative detec tion of antibodies is suggested. It is based on the difference
in diffusion rates in a gel for a synthetic low-mol-wt antigen and of its complexes with antibodies to be detected. Sensitivity
and specificity of the devel oped assay are equal to an ELISA method. The assay has been tested with antibodies against HIV
protein gp41 in rabbit serum. Possible applications and limitations of the method are discussed. 相似文献
18.
The importance of intraparticle convection during and after the pressurization step of a pressure swing adsorption process is assessed by considering a single, cylindrical, closed-end pore with adsorptive walls exposed to a binary mixture of an adsorbable component and an inert gas. Gas-phase mass transfer is comprised of pore diffusion and convection, and surface diffusion occurs in the adsorbed phase. Concentration, velocity, and flux profiles are obtained inside the pore both during and after pressurization. Solutions are obtained analytically for the limiting cases of no adsorption, no diffusion, and no inert gas. Complete solutions of the material balance equations are obtained by orthogonal collocation. The pressurization rate, the adsorptive capacity of the pore wall, and the gas-phase mole fraction are varied over a wide range to study the relative importance of convection and diffusion under different conditions. Results show that convection makes a large contribution to transport in the pore except when the adsorbable component has a small mole fraction. 相似文献
19.
M. A. Krykin A. A. Dadaly O. V. Gasyuk A. N. Ozerin A. V. Rebrov R. A. Shmukler I. P. Storozhuk A. M. Wasserman 《Journal of Polymer Science.Polymer Physics》1995,33(2):309-314
The rotational diffusion of spin-probes and the translational diffusion of n-pentane in a series of random-block copolymers (BSP) have been studied as a function of composition and block lengths. It was shown that the local diffusion properties of the BCP microphases depend on these two characteristics of BCP. © 1995 John Wiley & Sons, Inc. 相似文献
20.
Surface diffusion in reversed-phase liquid chromatography (RPLC) using silica gels bonded with C1 and C18 alkyl ligands of different densities was studied from the viewpoints of two extrathermodynamic relationships, i.e., enthalpy-entropy compensation (EEC) and linear free energy relationship (LFER). First, according to the four methods proposed by Krug et al., the values of surface diffusion coefficient (Ds) were analyzed to confirm that an actual EEC resulting from substantial physico-chemical effects takes place for surface diffusion. Then, it was also demonstrated that a LFER is observed between surface diffusion and the retention equilibrium. The establishment of EEC and LFER suggests a mechanistic similarity of molecular migration by surface diffusion, irrespective of the alkyl chain length and the densities of C1 and C18 ligands. Finally, a thermodynamic model for the LFER based on the real EEC was used to estimate Ds values under various RPLC conditions. The Ds values can be estimated with a mean square deviation of about 25–30%. The agreement between the Ds values estimated and those experimentally measured suggests that the total mass flux by surface diffusion consists of the two contributions due to C1 and C18 ligands and that the contribution of each ligand is proportional to the ligand density. 相似文献