pubs.acs.org/Langmuir © 2010 American Chemical Society
Hydrogen-Bond-Induced Heteroassembly in Binary Colloidal Systems Frank M. Bayer, Karl Hiltrop, and Klaus Huber* Department of Chemistry, Physical Chemistry, University of Paderborn, Warburger Strasse 100, 33098 Paderborn, Germany Received May 7, 2010. Revised Manuscript Received July 9, 2010 A new binary colloidal system is designed with each colloidal component being able to exclusively interact with the colloids of the second component, respectively. The colloids are based on cross-linked polystyrene and polymerized by means of surfactant-free emulsion polymerization with either 4-hydroxyl styrene or 4-vinyl pyridine as comonomers. The comonomers are selected to decorate the colloids with complementary H-bond donors or acceptors. Characterization of the colloids by light scattering in CHCl3 results in particle radii covering a regime of 130 nm < R < 270 nm and indicates a narrow particle size distribution for all prepared samples. The colloids are slightly swollen compared to their state in H2O. The corresponding size ratio expressed as the radius of the small colloids divided by the radius of the large colloids in CHCl3 extends over a regime of 0.52 < RS/RL < 0.85. IR analysis indicates strong hydrogen bonds between a colloidal component and the complementary molecular functions, that is, phenol or pyridine. If both colloidal components are directly combined as suspension in CHCl3 a fast heteroaggregation is observed. This aggregation slows down and becomes accessible to an analysis by means of time-resolved static light scattering if the suspensions get sufficiently dilute. Fast aggregation can be totally inhibited if capping agents like phenol to cap the 4-vinyl pyridine functions are added as highly concentrated solutions. Dried samples of those binary suspensions equilibrated with an appropriate amount of phenol show the first indication for an ordered binary assembly.
Introduction Spherical colloids bear striking similarities to the phase behavior of atomic and molecular systems.1 In close analogy to atoms and molecules, highly monodisperse hard spheres like colloids in liquid suspensions exhibit crystallization or even liquid-gas phase transitions with a critical point once the particles are equipped with a suitable interaction potential.2 One step further along this analogy is the generation of binary colloidal systems with the capability to form binary composite systems with specific stoichiometries in analogy to “chemical compounds”.3 A simple example for such binary superlattices is the formation of a NaCl lattice from a 1:1 mixture of two monodisperse colloidal samples, a larger component (L) and a smaller component (S) which only forms with a size ratio in the regime of 0.2
