Modeling Menisci and Capillary Forces from the Millimeter to the Micrometer Size Range
Original Entry by Michelle Borkin, AP225 Fall 2009
Bartosz A. Grzybowski, Ned Bowden, Francisco Arias, Hong Yang, and George M. Whitesides. J. Phys. Chem. B, 2001, 105 (2), pp 404–412.
The research presented in this paper investigates capillary interactions from the millimeter to sub-millimeter scales (0.1 to 10 mm) to gain a better understanding of self-assembly driven by capillary forces at the macroscopic scale. They examine the shape of PFD (perfluorodecalin) and water interfaces (i.e. immiscible fluid-fluid interface) and its interactions with hydrophobic and hydrophilic materials. By studying the shapes of these interfaces, energy profiles can be derived to characterize the different types of interactions (e.g. attraction, repulsion). The investigators use both computer simulations as well as experimental evidence to draw conclusions. For the computer modeling, when finding an analytical solution using the Laplace equation applied to two infinite surfaces was impossible, the menisci shapes were determined numerically using Surface Evolver which applies a Finite Element Method (FEM) to model the contours of the menisci. For the experimental measurements of the menisci shapes, the water layer was solidified with gelatin, then a cast was made using a UV-curable polymer (NOA), and then the cast was imaged with both optical and SEM microscopes. Menisci of varying sizes from millimeter to submillimeter were created and computer modeled in order to determine how the decay length scaled with the menisci dimensions.