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Anisotropic Adsorption of Molecular Assemblies on Crystalline Surfaces Jaehun Chun, Je-Luen Li, Roberto Car, Ilhan A. Aksay, and Dudley A. Saville*,
 

Summary: Anisotropic Adsorption of Molecular Assemblies on Crystalline Surfaces
Jaehun Chun, Je-Luen Li, Roberto Car, Ilhan A. Aksay, and Dudley A. Saville*,
Departments of Chemical Engineering and Chemistry, Princeton UniVersity, Princeton, New Jersey 08544-5263
ReceiVed: April 26, 2006; In Final Form: June 20, 2006
Orientational order of surfactant micelles and proteins on crystalline templates has been observed but, given
that the template unit cell is significantly smaller than the characteristic size of the adsorbate, this order
cannot be attributed to lattice epitaxy. We interpret the template-directed orientation of rodlike molecular
assemblies as arising from anisotropic van der Waals interactions between the assembly and crystalline surfaces
where the anisotropic van der Waals interaction is calculated using the Lifshitz methodology. Provided the
assembly is sufficiently large, substrate anisotropy provides a torque that overcomes rotational Brownian
motion near the surface. The probability of a particular orientation is computed by solving a Smoluchowski
equation that describes the balance between van der Waals and Brownian torques. Torque aligns both micelles
and protein fibrils; the interaction energy is minimized when the assembly lies perpendicular to a symmetry
axis of a crystalline substrate. Theoretical predictions agree with experiments for both hemi-cylindrical micelles
and protein fibrils adsorbed on graphite.
Introduction
Surfactants in aqueous solution form micelles due, in part,
to the limited solubility of their hydrocarbon tails. Spherical,
cylindrical, bilayer, and bicontinuous structures occur, depending
on the characteristics of the molecules and their concentrations.1

  

Source: Aksay, Ilhan A. - Department of Chemical Engineering, Princeton University

 

Collections: Materials Science