Long range attractive force

J. Klein and P.R Luckham Long-Range Attractive Forces Between Two Mica Surfaces in an Aqueous Polymer Solution. Nature 308, 836 (1984). 

Various diverse systems qualify as gels if one assumes that in these systems the common features are the solid-like behavior and the presence of a continuous structure of macroscopic nature (6,7). For the purpose of the discussion in this paper, we describe a gel as a colloidal system comprised of a dispersed component and a dispersion medium both of which the junction points are formed by covalent bonds, secondary valence bonds, or long range attractive forces that cause association between segments of polymer chains or formation of crystalline regions which have essentially infinite life time (8). 

The LB monolayers of dimethyldioctyadecylammonium ions on molecularly smooth muscovite mica surfaces were investigated. Direct measurements of the interaction between such surfaces were carried out using the surface force apparatus. A long-range attractive force considerably stronger than the expected van der Waals force was measured. Studies on the electrolyte dependence of this force indicate that it does not have an electrostatic origin but that the water molecules were involved in this. 

Hydrophobic forces are long-range attractive forces between macroscopic, hydrophobic surfaces in water. The force is significantly stronger than the Van der Waals attraction and can still be measured at surface separations as large as 70 nm. 

Later an exceptionally long-range attractive force between mica surfaces made hydrophobic by LB deposition of a monolayer of dimethyldioctadecyl-ammonium bromide (DODAB) was measured by Christenson and Claesson [82], It was shown to be an exponentially decaying force with a decay-length of 12-13 nm in the distance range 20-80 nm. This force was noted to be up to 100 times stronger than the expected van der Waals attraction (Fig. 5). 

Earlier evidence for the importance of V-R transfer in pure HC1 and DC1 had been reported by these and other investigators [222-225]. A theoretical treatment by Shin [226] of the energy-transfer problem in these gases, as well as in HBr and HI, shows clearly that long-range attractive forces play a significant role in the V-R exchange process. 

There are no electrostatic or induction forces between spherical molecules, such as argon, and yet there is clearly a long-range attractive force that causes the liquefaction of argon at low temperatures. This is the dispersion energy, the universal long-range force, which appears at second-order perturbation theory as ... 

Interpreting bulk properties qualitatively on the basis of microscopic properties requires only consideration of the long-range attractive forces and short-range repulsive forces between molecules it is not necessary to take into account the details of molecular shapes. We have already shown one kind of potential that describes these intermolecular forces, the Lennard-Jones 6-12 potential used in Section 9.7 to obtain corrections to the ideal gas law. In Section 10.2, we discuss a variety of intermolecular forces, most of which are derived from electrostatic (Coulomb) interactions, but which are expressed as a hierarchy of approximations to exact electrostatic calculations for these complex systems. 

Mineral or particle surfaces are enriched with As due to several processes that are collectively referred to as sorption (Parks, 1990), but the chemical properties of surface-associated As have been difficult to study directly. Outer-sphere, or physisorption, describes weak, long range, attractive forces between the surface and sorbing As inner-sphere, or chemisorption, refers to the formation of chemical bonds between the surface and adsorbing As. Stronger adsorption is expected by the formation of a bidentate (two bond) adsorbed complex rather than a monodentate (1 bond) complex. Selective chemical extraction methods have been useful for empirical determination of the dominant chemical/mineralogical compartments retaining As in aquifer... 

Surface complexes between As(V) or As(III) and B- and C-type hydroxyls are observed in IR studies but have not been verified by XAFS spectroscopy, probably because hydrogen bonding dominates the interaction between As and B- or C-type OH moieties (Sun and Doner, 1996) Fig. 8 d, e, and f). Hydrogen bonding is a long-range attractive force between atoms that does not involve direct bonding, and therefore would be classified as physisorption as opposed to chemisorption, which involves the formation of a chemical bond. 

The attachment of particles in a fluid suspension to a solid surface is extremely complex and involves long-range attraction forces to bring the particles to the surface and provide a basis for further interaction. The forces involved may include van der Waals forces... 

Molecules exhibit relatively long-range attractive forces between themselves which give rise to the cohesive forces in liquids. These forces arise because the electronic distribution in the molecule or atom making up the liquid is not uniform either on a time-averaged basis or with respect to its instantaneous value. Non-uniformity in the time-averaged electronic distribution in a molecule is a well-known phenomenon, and is discussed in terms of the experimentally measured dipole... 

Rather high electrolyte concentrations characteristic of natural and waste waters, substantially weaken non-equilibrium surface forces of the diffusion - electric nature but scarcely affect nonequilibrium surface forces caused by the dynamic adsorption layer of nonionic surfactant (Dukhin 1981). Therefore, we consider such forces are important and their mechanism deserves special attention. The flotation of tiny particles is, nevertheless, possible if the distance between the bubble and particle surfaces becomes smaller than a critical value h j-. The film of thickness h r is thiimed, becomes unstable, and collapses if long-range attractive forces exist between the particle and the bubble, drawing them together. 

The properties of a fluid are determined largely by short-range repulsive forces. The long-range attractive forces can be considered to be perturbations. Using these concepts, a perturbation theory of fluids is developed. In addition, the relationship of empirical equations of state to the perturbation theory is examined. The major weakness of most empirical equations is the use of the van der Waals free-volume term, (V-Nb) 1, to represent the contributions of the repulsive forces. Replacement of this term by more satisfactory expressions results in better agreement with experiment. 

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