Adhesion, forces and the stability of interfaces.

Robin Guttmann,Alexander F Sax,Johannes Hoja,Reinhard J Maurer,Christoph Lechner

doi:10.3762/bjoc.15.12

Robin Guttmann, Alexander F Sax + Show 3 more

Open Access

https://doi.org/10.3762/bjoc.15.12

Copy DOI

Abstract

Weak molecular interactions (WMI) are responsible for processes such as physisorption; they are essential for the structure and stability of interfaces, and for bulk properties of liquids and molecular crystals. The dispersion interaction is one of the four basic interactions types – electrostatics, induction, dispersion and exchange repulsion – of which all WMIs are composed. The fact that each class of basic interactions covers a wide range explains the large variety of WMIs. To some of them, special names are assigned, such as hydrogen bonding or hydrophobic interactions. In chemistry, these WMIs are frequently used as if they were basic interaction types. For a long time, dispersion was largely ignored in chemistry, attractive intermolecular interactions were nearly exclusively attributed to electrostatic interactions. We discuss the importance of dispersion interactions for the stabilization in systems that are traditionally explained in terms of the “special interactions” mentioned above. System stabilization can be explained by using interaction energies, or by attractive forces between the interacting subsystems; in the case of stabilizing WMIs, one frequently speaks of adhesion energies and adhesive forces. We show that the description of system stability using maximum adhesive forces and the description using adhesion energies are not equivalent. The systems discussed are polyaromatic molecules adsorbed to graphene and carbon nanotubes; dimers of alcohols and amines; cellulose crystals; and alcohols adsorbed onto cellulose surfaces.

Highlights

Any change of the state of motion of a particle, described in an inertial frame, is caused by a force acting on the particle
In general, the magnitude of adhesive forces does not depend on the whole contact zone (CZ)
Dispersion interactions play a dominant role in Weak molecular interactions (WMI), there are fields of chemistry in which dispersion interaction are systematically ignored as soon as polar atom groups occur, such as those involved in hydrogen bridges, at which point all stabilizing interactions are attributed to the hydrogen bridges

Summary

Introduction

Any change of the state of motion of a particle, described in an inertial frame, is caused by a force acting on the particle. By this procedure many-body contributions are captured that go beyond the three-body ATM term and improve, for example, cohesive energies considerably [37,41], some open questions concerning the calculation of correlation energies using the MBD method remain It is not yet clear how well fluctuating dipoles represent fluctuations of anisotropic charge in general, or whether molecular polarizabilities entering the expressions for dispersion interaction in the single-center expansion can be replaced by fragment polarizabilities, analogous to the multicenter expansion of charge distributions [38]. Large range located at different positions in space are equivalent to high-rank multipoles with a much shorter range This is frequently ignored in chemistry, where, for example, interactions between two molecular quadrupoles (1/r5 distance dependence) are reduced to interactions between bond dipoles having a 1/r3 distance dependence. Are they describing static attractive multipole–multipole interactions between orbital contributions to the molecular electron densities, as Anthony Stone suggests [2]; or are they describing constructive or destructive interference of orbitals as for the explanation of reactions using the Woodward–Hoffmann rules? Are they describing attractive dispersion interactions between the π-densities, or the exchange repulsion of π-densities?

Methods to describe WMI

Results

Discussion