Molecular force aggregation

At the same time K. H. Meyer and Mark (69) proposed an important structure for cellulose which is best described as a compromise between the aggregates of the association theory and Standinger s macromolecules. In an extensive paper, they carefully developed the idea of cellulose chains consisting of so called "primary valence chains". They further proposed that the primary valence chains were aggregated by molecular forces such as hydrogen bonding and van der Waal s forces. 

Equations (4.7) and (4.8) are both very useful when analysing surfactant aggregation behaviour and experimental cmc values. The difference in standard chemical potentials - Pi must contain within it the molecular forces and energetics of formation of micelles, which could be estimated from theory. These will be a function of the surfactant molecule and will determine the value of its cmc. 

This Chapter outlines some of the nature, delicacy and specificity of molecular forces, and how it is that these forces conspire with the geometry of molecules to organise self-assembled molecular aggregates. The shapes and topologies that set the physico-chemical environments for biochemistry are the subject of following chapters. The references provide a sufficient guide to the literature for the reader interested in exploring further complex technical issues. 

The authors suggest that computational chemistry offers the necessary tools to predict cluster energies associated with molecules designed for aggregation on the drawing board and we have seen that this goal has practically been achieved in the meantime. Furthermore, they stress, that tools to predict conformational trends are required, and argued that, therefore, the refinement of molecular force fields via quantum chemistry and the developments of better minimization techniques could be a major contribution. We hope that we have elaborated on these propositions in this account and that we were able to draw a more complete picture of what theoretical methods are capable of and into which directions they should evolve when the focus will be supramolecular chemistry. 

The hydrophobic effect is an aggregate phenomenon, distinguished from all other molecular forces (e.g., covalent, ionic, dipolar, hydrogen bonding, 7i interactions, van der Waals, and London forces) in that it arises from the collective behavior of many molecules by disruption of the hydrogen-bonded structure of water. 

The basis for the introduction of the notion of contactless flotation was the analogy with the well known phenomena of colloid particle coagulation in the secondary energetic minimum. Due to the predomination of the attractive molecular forces at large distances the particles can form aggregates in which some distance between particles is preserved. Thus, there is no direct contact between particles in this type of aggregation. However the notion of "contact" is not so simple. It is sufficient to point to the fact that a water monolayer remains on the hydrophobic surface. Thus the term "contactless" is maybe not suitable. 

In many cases, even if collisions between particles do take place, the naturally available binding mechanisms, mostly molecular forces, which are considerably lower in a liquid environment than in a gas atmosphere, do not create bonds with sufficient strength to withstand the various separating effects and satisfactory flocculation does not occur. For quite some time it has been known that polymers, added to liquid-based particulate systems, have a dramatic influence on particle interaction. Molecules may attach themselves to solid surfaces and, depending on the characteristics of the exposed radicals, can cause particle attraction [B.29] or dispersion [B.63]. The second, dispersion, is applied to avoid agglomeration (Chapter 4) or enhance disintegration of aggregates. 

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