Chapter Five - Polymer Chain Mechanics

Abstract

Force measurement at nanoscale is most often used by researchers concerned with synthetic and biological polymers. Long thread-like molecules have been a focus of intensive studies both from experimental and theoretical approaches. Most synthetic polymers have more or less uniform distributions of flexibly linked monomeric units and have freedom to rapidly change their shape in solution. It is only possible to refer to their structures based on time-averaged measurements of physical properties such as the end-to-end distance or radius of gyration. The ease of shape change determines the stiffness of polymer chains as characterized by the persistence length. Due to the freedom of shape change, polymer molecules in solution prefer to have a somewhat coiled conformation rather than an extended straight one. Thus averaged diameter is considerably shorter than the physical length of the chain from one end to the other. In contrast, most biological polymers, notably proteins and DNA, are characterized by accurately defined specific numbers and sequences of monomeric units within each individual molecule.