Molecular assembly, entropic forces

The driving force for the molecular assembly of polymeric molecules into ID fiberlike objects stems from a fine balance between the entropic cost of forming ordered supramolecular structures with reduced flexibihty and the enthalpic gain resulting from intermolecular interactions [8]. Inter- and intrachain hydrogen bonding is by far the most important driving force for the association of biopolymer chains and the stabilization of fibrils in aqueous media. 

In general, molecular assembly formations are believed to be enthalpically driven, where favorable binding forces (enthalpy) compete with energy loss due to the decreased freedom of the individual subunits (entropy). The increased guest binding character of 2 at elevated temperature is due to the fact that more than one solvent molecule is involved in the initial complex and their substitution by a single large molecule is entropically favorable. 

If the backbone as well as the side chains consist of flexible units, the molecular conformation arises out of the competition of the entropic elasticity of the confined side chains and the backbone [ 153 -155]. In this case, coiling of the side chains can occur only at the expense of the stretching of the backbone. In addition to the excluded volume effects, short range enthalpic interactions may become important. This is particularly the case for densely substituted monoden-dron jacketed polymers, where the molecular conformation can be controlled by the optimum assembly of the dendrons [22-26,156]. If the brush contains io-nizable groups, the conformation and flexibility may be additionally affected by Coulomb forces depending on the ionic strength of the solvent [79,80]. 

The term self-assembly has become ubiquitous in materials science over the past few decades, particularly in the field of soft matter and in related fields at the convergence of soft and hard materials. It is important to define this concept here as it will be used frequently throughout this book. Self-assembly may be described as spontaneous molecular ordering resulting from the balance between entropic and intermolecular forces in a material. A self-assembled system or state is one that forms without external mechanical manipulation of the components. Instead, the elements of the material (molecules, particles, etc.) are subject to forces between these elements and thereby adopt a particular configuration by coming to an equilibrium state. 

---