Collapse of polymer brushes grafted onto planar ... - Wageningen UR

SURFACE FORCES, SUPRAMOLECULAR POLYMERS, AND DIRECTIONALITY
J. van der Gucht 1,2) , N.A.M. Besseling 1) , M.A. Cohen Stuart 1)
1)
Laboratory of Physical Chemistry and Colloid Science, Wageningen University,
Dreijenplein 6, 6703 HB Wageningen, The Netherlands
2)
Dutch Polymer Institute,
Postbus 902, 5600 AX Eindhoven, The Netherlands
email: klaas@fenk.wau.nl
ABSTRACT
Interactions between surfaces, e.g. of dispersed colloidal particles are crucial in all heterogeneous soft
matter.(1) Supramolecular equilibrium polymers (sometimes denoted as living polymers) are polymeric chains
formed by reversible, non-covalent association of special small molecules.(2) The main purpose of this
presentation is to point out the relevance of the symmetry of the monomers for their behaviour at surfaces.
Monomers that are symmetric in the sense that their two binding sites are self-complementary form nondirectional
chains, but monomers with mutually complementary binding sites, often denoted as donor and
acceptors sites (or as host and guest, lock and key) form directional chains. In solution or in bulk this
difference will not lead to any difference in behaviour. However, in the presence of surfaces, and especially
when two surfaces approach each other, the directionality of the monomers and the ensuing chains may be
crucial.
Figure 1. Non-directional chains between two surfaces (a), and directional chains between two similar surfaces that bind
preferentially to the acceptor binding sites of the monomers (b).
Phenomenological Landau analysis indicates that non-directional equilibrium polymers always yield attractive
surface forces, but that directional equilibrium polymers may yield repulsion between surfaces that binds
preferentially either the donors or the acceptors. More detailed information is deduced from a lattice model
analysed in a Bethe-Guggenheim approximation. The strength and the range of the surface force, and their
concentration dependencies is predicted to be different for the directional and the non-directional cases.
These principles may explain certain observations on heterogeneous systems, and might be used to
manipulate the properties of such systems.
References
1. J. Israelachvili, Intermolecular and Surface Forces, Academic Press, 1991.
2. A. Ciferri, Supramolecular Polymers, Marcel Dekker, 2000.
3. J. van der Gucht, N.A.M. Besseling, M.A. Cohen Stuart, 2002. Surface forces, supramolecular polymers,
and inversion symmetry. J. Am. Chem. Soc. 124, 6202-6205.