Chemistry Reference
In-Depth Information
CHAPTER 3
SUPRAMOLECULAR CONTROL
OF MECHANICAL PROPERTIES IN
SINGLE MOLECULES, INTERFACES,
AND MACROSCOPIC MATERIALS
DAVID M. LOVELESS, FARRELL R. KERSEY, and STEPHEN L. CRAIG
3.1. INTRODUCTION AND BACKGROUND
Molecular recognition and aggregation, whether highly specific and directional in
nature as in some of the examples discussed in Chapter 1, or less so as in the case
of solvophobic interactions discussed in Chapter 2, have been demonstrated to be
capable of leading to useful, stress-bearing materials with properties that are
similar to those of traditional covalent polymers. Rehage and Hoffmann published
a series of studies in the 1980s that described the viscoelasticity of aqueous wormlike
micellar aggregates (Rehage and Hoffmann 1988, 1991) that were known to
form gels at low concentrations (Hayashi and Ikeda 1980; Porte 1980; Candau
et al. 1984). These noncovalent aggregates of small, amphiphilic molecules
possess mechanical properties typically associated with high molecular weight
polymers, properties that are not observed in comparable solutions of nonaggregated
small molecules.
Dramatic examples have also been reported for main-chain supramolecular
polymers (SPs; Lehn 1993; Ciferri 2005; Fig. 3.1), in which specific and directional
molecular recognition events between end groups define the main chain of a linear
polymeric assembly. Although main-chain SPs had been created and characterized
previously (Broze et al. 1983; Fouquey et al. 1990; Alexander et al. 1993; Bladon
and Griffin 1993; St Pourcain and Griffin 1995), it was a groundbreaking paper in
1997 that demonstrated the mechanical potential of supramolecular interactions
and catalyzed much of the current interest in the field (Sijbesma et al. 1997).
