The forces and viscosity between calcium benzene sulfonate surfactant-coated mica surfaces in various hydrocarbon liquids
containing a polyamine-functionalized hydrocarbon polymer (MW≈8000) have been measured using the surface forces apparatus technique. The polymer is found to adsorb to the substrate surfaces
by displacing the surfactant layer, and to produce forces that are monotonically repulsive. The forces have a maximum range
of 50–100 nm (>3RH), indicating that tails play a particularly important role in the interaction of this relatively low molecular weight polymer.
The forces become steeply repulsive below about 10 nm (∼0.6RH), at which point a “hard-wall” repulsion comes in that can sustain pressures greater than 100 atm. Thin-film viscosity measurements
indicate that the far-field positions of the slipping planes ΔH depend on the shear rate, showing that significant shear thinning/thickening effects occur within the outermost tail regions
of the adsorbed layers during shear. The position of the slipping plane, or hydrodynamic layer thickness ΔH, varies from 0.6RH to 2RH away from each surface (mica and surfactant-coated mica surfaces). Beyond the hydrodynamic layer the far-field fluid viscosity
is the same as that of the bulk polymer solution. At separations below D = 2ΔH the viscosity increases as each polymer layer is compressed. The static forces exhibited various time- and history-dependent
effects, which further indicate that a number of different relaxation/equilibration processes are operating simultaneously
in this complex multicomponent system. The results reveal that the interactions of tails of functionally adsorbed polymers
play a more important role than previously thought. This is especially true in this study where the adsorbed polymers are
of low molecular weight and where the tails may represent the largest fraction of interacting segments.
Received: 22 September 1998 Accepted: 11 January 1999 相似文献
The relative conductivities of solutions of poly(styrene-co-sodium styrene sulfonate) (PSSNa) in N,N-dimethylformamide + water have been measured as functions of temperature and at various concentrations. With the aid of the newly proposed theory related to the effect of solute adsorption on the relative conductivity measurement, the experimental data were analysed, and some interesting parameters describing the interfacial properties were deduced. The concentration of PSSNa data dependence of the reduced electrical conductivities has been fitted to an equation similar to the Vogel–Tammann–Fulcher based on the critical concentration model. The intrinsic electrical conductivity of Vogel [σV], the critical concentration and the concentration of Vogel CVFT were calculated. The behaviour of polymers close to interfaces has been studied with the parameter of [σV]. Two mechanisms of interaction between a polymer solution and a surface are in general distinguished, leading to the formation of adsorbed and grafted layers. 相似文献
Abstract In the development of electrochemical immunosensing strategies, stability or activity of the immobilized biocomponents and signal amplification of the immunoconjugates are two key factors. In this study, a comparative study of immunoglobulin G antibody (anti‐IgG) immobilization, as a model, was performed on cysteine (Cys), 2‐aminoethane thiol (AET), and 11‐mercaptoundecanoic acid (MUA) monolayers. The change of anti‐IgG layer formation on the three base layers as a function of the anti‐IgG concentration was investigated in parallel via electrochemical impedance spectroscopy, cyclic voltammetry, surface plasmon resonance, and quartz crystal microbalance. Through the parallel measurements, we demonstrate that the Cys‐modified layer is more suitable for the immobilization of the anti‐IgG molecules than the MUA or AET‐modified layer. Based on the CV and EIS analyses, it was determined that the current responses decreased with the increment of anti‐IgG concentration, while the resistance responses increased with the concentration of anti‐IgG increased. Moreover, the current and resistance shifts were more remarkable on the Cys layer than that of the other two layers. In the SPR and QCM measurements, the SPR and QCM response signals were similar in shape but differing in time scales, reflecting differences in detection mechanisms. With regard to the fundamental problem of comparing different measurement principles, the mechanism of the IgG immobilized on the three layers was proposed. Consequently, the surface concentration of anti‐IgG immobilized on the electrode should be optimized to improve the sensitivity of the immunosensors. 相似文献
The title complex, [Zn(C5H6O4)(H2O)]n, has a two‐dimensional layer structure. The Zn atoms, in a geometry that is closer to trigonal bipyramidal than square pyramidal, are coordinated by two O atoms of a bidentate dimethylmalonate ligand, two O atoms of monodentate dimethylmalonate ligands and one O atom from the aqua ligand. The crystal structure is characterized by the intralayer motif of a hydrogen‐bonded network. Neighboring layers are linked together to build up a three‐dimensional network via van der Waals forces. 相似文献
A rigid, inherently chiral bilayer nanographene has been synthesized as both the racemate and enantioenriched M isomer (with 93 % ee) in three steps from established helicenes. This folded nanographene is composed of two hexa‐peri‐hexabenzocoronene layers fused to a [10]helicene, with an interlayer distance of 3.6 Å as determined by X‐ray crystallography. The rigidity of the helicene linker forces the layers to adopt a nearly aligned AA‐stacked conformation, rarely observed in few‐layer graphene. By combining the advantages of nanographenes and helicenes, we have constructed a bilayer system of 30 fused benzene rings that is also chiral, rigid, and remains soluble in common organic solvents. We present this as a molecular model system of bilayer graphene, with properties of interest in a variety of potential applications. 相似文献
The novel hydrophobic coating material was received for the first time by a two‐step synthetic route. Firstly, the 15‐functional brominated macroinitiator was prepared by the esterification methodology. Next step covers synthesis of star‐like polymers by poly(n‐butyl acrylate) (PBA) arms polymerization via three low‐ppm atom transfer radical polymerization (ATRP) approaches including application of copper and silver wire in SARA and ARGET ATRP, respectively, as driving forces in redox cycle of catalyst, and an external stimulus in the form of electric current (seATRP) as the third approach in copper(II) regeneration system. As expected, the electrochemically mediated technique allows synthesis of tannic acid‐inspired coating polymers in precisely controlled manner during the entire polymerization process, proved by linear first‐order kinetics plot in contrast to above‐mentioned methods, low dispersity (Ð = 1.18) of star‐shaped polymers, and high efficiency of initiation (?i = 81%) determined after detaching of polymers side arms. Macromolecules received by all low‐ppm ATRP solutions were characterized by preserved chain‐end functionality (theoretical dead chain fraction; DCFtheo <1%). Adhesive and hydrophobic properties of received polymer materials were investigated by contact angles (θ) and free surface energy (FSE) calculations. Prepared polymer films besides excellent hydrophobic properties have great potential as a self‐healing solution. 相似文献
The structural, electronic, and magnetic properties of the three possible terminated (001)‐oriented thin films of the double perovskite Pb2FeReO6 compound, 9‐L FeReO4 terminated, 10‐L FeReO4+PbO terminated, and 11‐L PbO terminated, have been studied by using the first‐principles calculations. An outward relaxation is observed for several layers near surface, and the relaxed fractional rumpling s of the PbO layer is larger than that of the adjacent FeReO4 layer, and both have a decrease tend from surface layer to inner layer. The O atom is closer to the adjacent Re atom than to the adjacent Fe atom. Except for Fe or Re transition‐metal (TM) atoms on the film's symmetrical central layer, the two axial TM‐O bond lengths are not equal in the survived FeO6 or ReO6 octahedra. The maintained HM‐FM character ensures the three possible terminated (001)‐oriented thin films of the double perovskite Pb2FeReO6 compound a potential application in magnetoresistive and spintronics devices. An FM coupling is obtained within each Fe or Re TM sublattice, whereas two TM sublattices are coupled AFM. The delocalized distribution of the spin/magnetic charge densities around the Fe atom on the first FeReO4 layer leads to a smaller magnetic moment. The remained two Re 5d2 electrons are mainly located on the down‐spin t2g (dxy, dyz, and dzx) orbitals. 相似文献
A Links‐Nodes‐Blobs (L‐N‐B) model, based on the fractal and percolation concepts, is used to study the electrically conductive mechanism of conductive filler loaded polymer composites. The change in the conductivity of polymer composites during the mixing process can be explained as the competition between the breakdown of filler aggregates and the diffusion of ingredients of matrix material and impurities onto the surface of the filler. The value of the fractal dimension μ, which is the exponent in the power‐law relationship of the electrical conductivity σ = σ0·(ϕ – ϕc)μ, is calculated as 1.88. This value is close to the values obtained directly from experiments or from other simulations. The positive temperature coefficient (PTC) behavior in the conductivity of composite material is also explained by this model as the breakdown of the conductive filler network. If the thermo‐expansion induced strain is greater than the apparent on‐set strain εonset = mQ + 2 G/2d G·εb of the L‐N‐B model, a strong PTC effect would happen. 相似文献
In the title coordination polymer, {[Cd(C6H8O4S)(C13H14N2)]·H2O}n, the CdII atom displays a distorted octahedral coordination, formed by three carboxylate O atoms and one S atom from three different 3,3′‐thiodipropionate ligands, and two N atoms from two different 4,4′‐(propane‐1,3‐diyl)dipyridine ligands. The CdII centres are bridged through carboxylate O atoms of 3,3′‐thiodipropionate ligands and through N atoms of 4,4′‐(propane‐1,3‐diyl)dipyridine ligands to form two different one‐dimensional chains, which intersect to form a two‐dimensional layer. These two‐dimensional layers are linked by S atoms of 3,3′‐thiodipropionate ligands from adjacent layers to form a three‐dimensional network. 相似文献
The role of theory level in prediction of benzene magnetic indexes of aromaticity is analysed and compared with calculated nuclear magnetic shieldings of 3He used as NMR probe. Three closely related nucleus‐independent chemical shift (NICS) based indexes were calculated for benzene at SCF‐HF, MP2, and DFT levels of theory and the impact of basis set on these quantities was studied. The changes of benzene NICS(0), NICS(1), and NICS(1)zz parameters calculated using SCF‐HF, MP2 and several density functionals were within 1 to 3 ppm. Similar deviations between magnetic indexes of aromaticity were observed for values calculated with selected basis sets. Only very small effect of polar solvent on benzene aromaticity was predicted. The 3He nuclear magnetic isotropic shielding (σ) and its zz‐components (σzz) of helium atom approaching the centre of benzene ring from above produced similar curves versus benzene‐He distance to NICS parameters calculated for similarly moving Bq ghost atom. We also propose an experimental verification of NICS calculations by designing the 3He NMR measurement for benzene saturated with helium gas or in low temperature matrices. 相似文献
The structure of a new magnesium nitridoboride, MgNB9, has been refined from single‐crystal X‐ray data. The Mg and N atoms lie on sites with crystallographic 3m symmetry. The structure consists of two layers alternating along the c axis. The NB6 layer, with B12 icosahedra, has the C2B13 structure type. Within this layer, boron icosahedra are bonded to N atoms, each coordinating to three boron polyhedra. Another MgB3 layer, with B6 octahedra, does not belong to any known structure type. The boron icosahedra and octahedra are connected to each other, thus forming a three‐dimensional boron framework. 相似文献
Summary: We describe molecular dynamics simulations of α‐tetrathiophene molecules deposited on a flat graphite substrate, at two different temperatures (300 K and 400 K) and several degrees of coverage (from approximately one to three molecular layers). The simulations employ a modified version of the CFF91 force field, with the torsion parameters tailored on high‐level ab initio calculations on 2,2′‐bithiophene. We found that the molecules in the first layer were relatively planar and packed against the underlying surface, while those outside it were not arranged in well‐defined layers and were more conformationally disordered. On the time scale of the simulation, the molecules did not crystallize but rather achieved a liquid crystalline‐like state with their average director parallel to the surface.
Side view of the final configuration in the simulation of 24 tetrathiophenes at 300 K. Molecules are depicted with different shades of gray according to their z coordinate (first, second or third layer). 相似文献