Elasticity of macromolecules

Abstract Atomic force spectroscopy (AFM)-based single-molecule force spectroscopy (SMFS) was invented in the 1990s. Since then, SMFS has been developed into a powerful tool to study the inter- and intra-molecular interactions of macro-molecules. Using SMFS, a number of problems in the field of supramolecular chemistry and mechanochemistry have been studied at the single-molecule level, which are not accessible by traditional ensemble characterization methods. In this review, the principles of SMFS are introduced, followed by the discussion of several problems of contemporary interest at the interface of supramolecular chemistry and mechanochemistry of macromolecules, including single-chain elasticity of macromolecules, interactions between water and macromolecules, interactions between macromolecules and solid surface, and the interactions in supramolecular polymers. 

However, there are still some challenges in this field. Here are two examples. (1) The database of single-chain elasticity of macromolecules is not yet complete. As with the periodic table of elements, a complete database of macromolecules would certainly be helpful for the development of science and engineering. (2) The noise level of SMFS is still too high. A typical noise of 5-10 pN conceals some important data. However, it is greatly anticipated that, in the future, SMFS can contribute further to the development of supramolecular chemistiy and mechano-chemistry of macromolecules. 

The linkage between the enhancement of heat transfer at boiling of dilute polymer solutions and the elastic properties of the system is confirmed by the existence of the optimal concentration corresponding to (Figure 7.2.14). Similar optimal concentration was established in addition of polymers to water to suppress turbulence - the phenomenon that also owes its origin to elasticity of macromolecules. Therefore, it is possible to expect that the factors favoring the chain flexibility and increase in the molecular mass, should lead to strengthening of the effect. 

The diagram of the liquid-vapor phase equilibrium is eharacterized by a decrease in the derivative dp/dT with the polymer concentration (dp/dT —> 0 at k 0). This leads to increase in bofli die nucleation energy and the detachment size of a bubble (equation [7.2.59]) and, consequently, to reduction of the bubbles generation frequency. Note that in reality the critical work, W , for a polymeric liquid may exceed the value predicted by the formula [7.2.59] because of manifestation of the elasticity of macromolecules. 

The influence of molecular mass distribution, size and elasticity of macromolecules on friction reduction effect. 

The Influence of Molecular Mass Distribution, Size and Elasticity of Macromolecules on Friction Reduction Effect... 

In fig.3 curve 1 represents the dependence for turbulent friction reduction with increasing the rigidity (elasticity) of macromolecules. It has been found out that these data can be generalized by one and the same straight line for two different polymers (PAA and PMA) within the range of the sizes and... 

A large number of SAHs described in the literature combine synthetic and natural macromolecules in the network structure. The natural components are usually starch, cellulose, and their derivatives. It is assumed that introduction of rigid chains can improve mechanical properties (strength, elasticity) of SAH in the swollen state. Radical graft polymerization is one of the ways to obtain such SAH. 

In Geneva, he resumed with new energy his studies of macromolecules. He was able to obtain the cooperation of A. J. H. van der Wijk, who was one of his most devoted coworkers the latter s realistic criticisms were a valuable balance to Meyer s great enthusiasm. Studies on the thermodynamics of large molecules in solution, and on the structure of cellulose and chitin, were pursued with C. Boissonnas, W. Lothmar, and L. Misch. A theory of the elasticity of rubber evolved from his work with C. Ferri and his previous observations with Susich and Valk6. 

Intermolecular crosslinking between pendant vinyl groups and radical centers located on different macromolecules produce crosslinks that are responsible for the aggregation of macromolecules, which leads to the formation of a macrogel. It must be remembered that both normal and multiple crosslinks may contribute to the rubber elasticity of a network, whereas small cycles are wasted links. 

Ortiz C, Hadziioannou G. Entropic elasticity of single polymer chains of poly(methacrylic acid) measured by atomic force microscopy. Macromolecules 1999 32 780-787. 

Rusakov 107 108) recently proposed a simple model of a nematic network in which the chains between crosslinks are approximated by persistent threads. Orientional intermolecular interactions are taken into account using the mean field approximation and the deformation behaviour of the network is described in terms of the Gaussian statistical theory of rubber elasticity. Making use of the methods of statistical physics, the stress-strain equations of the network with its macroscopic orientation are obtained. The theory predicts a number of effects which should accompany deformation of nematic networks such as the temperature-induced orientational phase transitions. The transition is affected by the intermolecular interaction, the rigidity of macromolecules and the degree of crosslinking of the network. The transition into the liquid crystalline state is accompanied by appearence of internal stresses at constant strain or spontaneous elongation at constant force. 

A restriction will be made to polymer chains without strong and specific intersegmental forces, such as may exist in proteins and many other macromolecules. The reason is that the elasticity of networks composed of such chains cannot even be approached from the Gaussian coil point of view, since the chains are helical or at least partly so. At the moment no good theoretical treatment of these "proteinlike systems is available. 

---