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51.
During the course of our investigation of the electron transfer properties of some redox species through highly hydrophobic
long chain alkanethiol molecules on gold in aqueous and non-aqueous solvents, we obtained some intriguing results such as
unusually low interfacial capacitance, very high values of impedance and film resistance, all of which pointed to the possible
existence of a nanometer size interfacial gap between the hydrophobic monolayer and aqueous electrolyte. We explain this phenomenon
by a model for the alkanethiol monolayer—aqueous electrolyte interface, in which the extremely hydrophobic alkanethiol film
repels water molecules adjacent to it and in the process creates a shield between the monolayer film and water. This effectively
increases the overall thickness of the dielectric layer that is manifested as an abnormally low value of interfacial capacitance.
This behaviour is very much akin to the ‘drying transition’ proposed by Lum, Chandler and Weeks in their theory of length
scale dependent hydrophobicity. For small hydrophobic units consisting of apolar solutes, the water molecules can reorganize
around them without sacrificing their hydrogen bonds. Since for an extended hydrophobic unit, the existence of hydrogen bonded
water structure close to it is geometrically unfavourable, there is a net depletion of water molecules in the vicinity leading
to the possible creation of a hydrophobic interfacial gap. 相似文献
52.
Basic principles of the generalized lattice model of multicomponent condensed systems are formulated. Short-range parts of interatomic interactions are taken into account by means of the geometric constraints method. Long-range parts of the interactions are taken into account in mean field approximation. The expression for Helmholtz free energy is obtained. A system of integral equations for the equilibrium distributions of components is derived. The asymptotic properties of its solutions are investigated. Moment expansion of interatomic interactions and localization of integral terms in free energy is obtained. A Ginzburg–Landau-like functional of free energy is derived. 相似文献
53.
In this paper the performances of inhomogeneous dielectric slabs as solar light collectors for both illumination and solar energy applications are analysed. 相似文献
54.
This paper presents an enhanced version of the elasto-plastic model for partially saturated soil first proposed by Bolzon,
Schrefler and Zienkiewicz in 1996, “BSZ” model, which uses the effective stress tensor and suction as independent stress variables.
It is recalled that the effective stress tensor proposed by Lewis and Schrefler in 1982 is thermodynamically consistent and,
compared with other choices of stress tensors, results particularly suitable for partially saturated soil mechanics. A hydraulic
constitutive relationship and a hydraulic hysteresis are introduced in the model, to take into account the irreversible deformation
during cyclic drying and wetting until structural collapse. For this reason the plastic rate of strain is split into the sum
of two components: one depending on the effective stress tensor and the other one on suction. This is the new feature of the
BSZ model. This enhanced model is then cast into a thermodynamical framework at macroscopic level and it is shown that it
is possible to derive the constitutive law from the Helmholtz free energy and a dissipation function, both for associative
and non- associative plasticity. Finally the model predictions have been compared with experimental data for Sion slime, with
particular emphasis on the deviatoric part, and model predictions of hysteretic behaviour have been investigated in case of
a wetting and drying cycle on compacted betonite–kaolin. 相似文献
55.
We obtain expressions for the energy spectrum widths of Rayleigh waves corresponding to their deformational coupling to Fermi and Boltzmann electrons in a two-dimensional layer near the surface of a semibounded solid. We evaluate the nonequilibrium energy of Rayleigh waves that depends on these widths and is caused by the same coupling to the corresponding hot electrons. We show that this energy is independent of the degeneracy degree of the electrons and is given by the mean energy of free Rayleigh waves heated up to temperature of the electrons. We find conditions under which the thermodynamics is determined by this nonequilibrium energy of Rayleigh waves in films of a certain thickness with Fermi electrons near the surface and by the equilibrium energy of bulk phonons in thicker samples. All the results are obtained using the Keldysh diagram technique applied to the case of semibounded media. 相似文献
56.
Anuj Mittal Swaminathan Sivaram 《Journal of polymer science. Part A, Polymer chemistry》2005,43(21):4996-5008
A tridentate ligand, BPIEP: 2,6‐bis[1‐(2,6‐diisopropyl phenylimino) ethyl] pyridine, having central pyridine unit and two peripheral imine coordination sites was effectively employed in controlled/“living” radical polymerization of MMA at 90°C in toluene as solvent, CuIBr as catalyst, and ethyl‐2‐bromoisobutyrate (EBiB) as initiator resulting in well‐defined polymers with polydispersities Mw/Mn ≤ 1.23. The rate of polymerization follows first‐order kinetics, kapp = 3.4 × 10?5 s?1, indicating the presence of low radical concentration ([P*] ≤ 10?8) throughout the reaction. The polymerization rate attains a maximum at a ligand‐to‐metal ratio of 2:1 in toluene at 90°C. The solvent concentration (v/v, with respect to monomer) has a significant effect on the polymerization kinetics. The polymerization is faster in polar solvents like, diphenylether, and anisole, as compared to toluene. Increasing the monomer concentration in toluene resulted in a better control of polymerization. The molecular weights (Mn,SEC) increased linearly with conversion and were found to be higher than predicted molecular (Mn,Cal). However, the polydispersity remained narrow, i.e., ≤1.23. The initiator efficiency at lower monomer concentration approaches a value of 0.7 in 110 min as compared to 0.5 in 330 min at higher monomer concentration. The aging of the copper salt complexed with BPIEP had a beneficial effect and resulted in polymers with narrow polydispersitities and higher conversion. PMMA obtained at room temperature in toluene (33%, v/v) gave PDI of 1.22 (Mn = 8500) in 48 h whereas, at 50°C the PDI is 1.18 (Mn = 10,300), which is achieved in 23 h. The plot of lnkapp versus 1/T gave an apparent activation energy of polymerization as (ΔE≠app) 58.29 KJ/mol and enthalpy of equilibrium (ΔH0eq) to 28.8 KJ/mol. Reverse ATRP of MMA was successfully performed using AIBN in bulk as well as solution. The controlled nature of the polymerization reaction was established through kinetic studies and chain extension experiments. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4996–5008, 2005 相似文献
57.
58.
59.
《Tetrahedron》2003,59(34):6415-6422
The Nuclear Independent Chemical Shift of each ring, as a criterion of aromaticity, is used to explain the stability order of benzopyrrole, benzofuran and benzothiophene, and their isomers. The results indicate that the benzene ring is aromatic in all the systems. The five-membered rings of benzopyrrole, benzofuran and benzothiophene are also aromatic, whereas those of isobenzopyrrole, isobenzofuran and isobenzothiophene are non-aromatic. This could be an explanation of the stability of the former molecules. The molecular orbitals and the condensed Fukui functions derived from the electronic structure calculations are also reported. These reactivity indices explain the expected electrophilic substitution of these compounds. The theoretical structure, ionization energies, order of aromaticity, stability and reactivity are in good agreement with the experimental results. The usefulness of this approach to determine the reactivity is discussed since their stability and reactivity may be understood. The reactivity indices are useful to explain and confirm the experimental information, and for molecules with unknown reactive behavior, this approach could help to predict some of the reactions. 相似文献
60.
为阐述放射性9C束流应用于治癌的物理基础, 运用一个球形生物组织等效正比计数器测量了9C束流不同贯穿深度上的线能谱, 得到了沿束流贯穿深度上的剂量平均线能分布. 将实验测量得到的线能谱转换成为不同传能线密度在吸收剂量中所占份额的分布, 得到了该9C束流在不同贯穿深度上的剂量平均传能线密度分布. 将生物组织等效正比计数器测量得到的与先前通过平行板正比计数器测量得到的该9C束流的剂量平均传能线密度分布进行比较, 发现: 在束流入射通道上, 两者测量数据符合很好, 而在束流Bragg峰附近9C离子的沉积区域, 由组织等效正比计数器测量得到的剂量平均传能线密度值大于由平行板正比计数器测量得到的值. 相似文献