Long-ranged Interaction Forces and Real Spaces Related to Them Including Anisotropic Cases

Interaction forces between charged interfaces in the presence of oppositely charged dendrimers are studied by experiment and simulation. The experiments involve direct force measurements with an atomic force microscope (AFM) between two negatively charged colloidal particles in the presence of adsorbed, positively charged globular dendrimers. The simulations are carried out by treating the macroions explicitly, while the small salt ions are treated implicitly through the Debye-Huckel approximation. The system undergoes overcharging, and at the isoelectric point long-ranged attractive electrostatic forces are present. The range of the attraction is on the order of half the Debye length at high salt concentration, but it becomes smaller at low salt concentration. Away from the isoelectric point, repulsive electrostatic forces are observed due to diffuse layer overlap. A semiquantitative agreement between experiment and simulation is obtained, despite the fact that the simple theoretical model does not involve any adjustable parameters. This study provides for the first time detailed comparison between experimental and simulation data of interaction forces between colloidal particles in the presence of multivalent macroions and monovalent salt ions.

Statistical mechanics of a lipid monolayer

A Study of Hydrophobic Interactions between Stainless Steel and Silanated Glass Surface Using Atomic Force Microscopy

The Poiseuille and thermal transpiration flows of a real gas confined between two parallel plates are investigated based on the Enskog–Vlasov kinetic equation under the diffuse reflection boundary condition. In contrast to an ideal gas, the gradients of pressure and normal stress components in the flow direction, as well as the density, are nonuniform in the direction normal to the plates. The net mass flows and the profiles of flow velocity and heat flow are obtained for various Knudsen numbers, molecular sizes, and magnitudes of the long-range intermolecular attractive force. Depending on the magnitude of the attractive force, the nondimensional net mass flow of the thermal transpiration flow exhibits a local minimum at an intermediate Knudsen number, analogous to the Knudsen minimum known for the Poiseuille flow. Both in the Poiseuille and thermal transpiration flows, the flow velocity and heat flow are enhanced due to the intermolecular attractive force, compared to the case of the Enskog equation for a purely repulsive hard-sphere dense gas. Unless the molecular diameter is sufficiently small compared to the distance between the plates, the enhancement is observed even at high Knudsen numbers, where the volume fraction of molecules is small. This occurs because, although the attractive force itself is small at high Knudsen numbers, its influence on molecules with small velocity components normal to the boundary remains significant. Due to the effect of intermolecular attractive force, the velocity distribution function of gas molecules becomes discontinuous not only on the boundary but also in the gas.

Chapter 7 - Tribological experiments with friction force microscopy

Residual long-range pseudoscalar forces between unpolarised macroscopic bodies

The Instability of the Solid–Liquid Interface and the Hydrophobic Force

Hydrophobic, hydrophilic and other interactions in epitope-paratope binding

Liquid helium wets almost all surfaces. This behaviour results from its small dielectric permittivity, e = 1.057, which leads to attractive forces between the helium atoms weaker than those between helium and other atoms [1]. In 1991 Cheng et al., however, predicted that 4He does not wet certain alkali metals. Instead, for some of these metallic substrates, a first-order wetting transition was foreseen [2]. In the alkali metals, weakly bound outer electrons cause a shortrange repulsion for the helium atoms. The resulting temperature-dependent balance between repulsive short-range and attractive long-range forces is at the origin of the wetting phenomenon in liquid helium.

We examine rotational transitions of HCl in collisions with H2 by carrying out quantum mechanical close-coupling and quasi-classical trajectory (QCT) calculations on a recently developed globally accurate full-dimensional ab initio potential energy surface for the H3Cl system. Signatures of rainbow scattering in rotationally inelastic collisions are found in the state resolved integral and differential cross sections as functions of the impact parameter (initial orbital angular momentum) and final rotational quantum number. We show the coexistence of distinct dynamical regimes for the HCl rotational transition driven by the short-range repulsive and long-range attractive forces whose relative importance depends on the collision energy and final rotational state, suggesting that the classification of rainbow scattering into rotational and l-type rainbows is effective for H2 + HCl collisions. While the QCT method satisfactorily predicts the overall behavior of the rotationally inelastic cross sections, its capability to accurately describe signatures of rainbow scattering appears to be limited for the present system.

Dissipative condensation of ion channels described by a Langevin-Kelvin equation

A new approach to surface modeling and reconstruction is developed which overcomes some important limitations of existing surface representations methods. The approach features two components. The first is a dynamic self-organizing oriented particle system which discovers topological and geometric surface structure implicit in visual data. The oriented particles evolve according to Newtonian mechanics and interact through long-range attraction forces, short-range repulsion forces, and coplanarity, conormality, and cocircularity forces. The second component is an efficient triangulation scheme that connects the particles into a continuous global surface model that is consistent with the inferred structure. A flexible surface reconstruction algorithm is developed that can compute complete, detailed, viewpoint-invariant geometric surface descriptions of objects with arbitrary topology. The algorithms are applied to 3-D medical image segmentation and to surface reconstruction from object silhouettes. >

Elasticity of Mutant Myosin Subfragment-1 Arranged on a Functional Silver Surface

The forces between a tungsten tip and a self-assembled monolayer of hexadecylthiol (C16H33SH) on a thin gold film have been studied using a newly developed interfacial-force microscope. Imaging of the surface, combined with spatially resolved force versus separation measurements, allow for the distinction of topographical and chemical features of the surface. Several distinct regions are observed for this system. The first, characterized by a very weak interfacial interaction between tip and sample, is representative of the self-assembled monolayer. The other regions show relatively strong, long-range attractive forces, which are associated with gross defects in the film.

Small-angle neutron scattering experiments were performed on concentrated binary dispersions of sterically-stabilized poly(methy1 methacrylate) particles of size ratio -0.31 dispersed in a mixture of cisdecalin-hl8 and octane-dl8. Using a contrast match technique, we have, for the first time, studied the local structure of small spheres in a simple (hard-sphere) colloidal mixture. In particular, our experiments demonstrate that the small spheres show evidence of particle clustering. We show that this observation is in accord with a long-ranged attractive force between the small spheres resulting from the depletion of larger particles from between the surfaces of the small spheres.