Percolation
Percolation is a process by which paths are formed that pass through random media. Water, electrical current, or fire can all travel via percolative paths (i.e., water within rocky soil, current within a composite materials, or fire jumping from tree top to tree top). For a composite material, conducting paths are formed within a non-conducting matrix with the addition of a conducting dopant, enabling an insulating polymer matrix to conduct current. This process occurs in three stages (illustrated below). At low loading levels, dopant is isolated and thus no paths are formed. As the dopant level is increased a single path forms, which is associated with a dramatic increase in conductivity. The conductance of the composite will increase as more paths are formed until the network has been saturated. This "cartoon" illustration shows percolation in a homogeneous medium; however the data is from a sample with 80% porosity. We are interested in how volume confinement and changes in dimensionality affect the percolation process for such complex samples. We are also interested in new electrospinning techniques, techniques to post-process such nanocomposites to improve their properties, and the use of composites for biological applications.
S D McCullen et. al., Int. J. Nanomedicine 2, 253 (2007).
S D McCullen et. al., J. Appl. Poly. Sci. 105, 1668 (2007).