(618bm) Hierarchical Bio-Inspired Vascular Networks: Electrical Treeing

Vascular networks provide a
method to distribute fluid throughout a system. Artificial vascular materials
with enhanced properties are being developed that could ultimately be
integrated into systems reliant upon fluid transport while retaining their
structural properties. An uninterrupted and controllable supply of liquid is
optimal for many applications such as continual self-healing materials, in-situ
delivery of optically index matched fluids, thermal management (sweating)
and drug delivery systems could benefit from a bio-inspired approach that
combines complex network geometries with minimal processing parameters. One
such approach to induce vascular networks whilst mimicking nature's design is electrical
treeing (ET).

                (a)
     (b)                                         (c)
(d)

Figure 1. Optical image of ET (a) in a EPON 828/PACM system,
(b) under AC driven electrical current showing ?bush-like? features, (c) under
DC driven electrical current showing ?tree-like? features and filling of an ET
grown vascular network with a UV visualization dye.

Electrical treeing (ET) is
the result of partial discharges in a dielectric material. In the vicinity of a
small diameter electrode, the local electric field is greater than the global
dielectric strength, causing a localized, step-wise, breakdown to occur forming
a highly branched interconnected structure (Fig. 1a). The growth of
these structures is influenced by the configuration of the electrodes, with
geometries of a point lead electrode to a point or plane ground electrode being
of most interest. ET is a viable method to produce networks in 2D systems and
in more robust 3D systems on a smaller, micron, scale than the products of the EHVF
method. AC driven electrical current (Fig. 1b), harnessing a sine wave
at 100 Hz, grows a ?bush-like? structure with many branches and therefore a
larger volume within the epoxy samples. DC driven electrical current (Fig. 1c)
produces a more ?tree-like? structure with fewer branches and bifurcations. The
surface of the electrodes were modified with dispersed multi-walled carbon
nanotubes (MWCNTs) to aid in increasing the local electric field, and thus
enable a higher rate of tree initiation and growth. Inclusion of particles was
investigated to determine if the growth direction can be manipulated. The use
of self-clearing electrodes (as a grounding material) was investigated with the
infiltration of a UV dye through the hollow channels produced by ET resulting
in a vascularized network capable of repeated fillings and evacuations. Fluid
delivery (Fig. 1d) can be tailored through the applications of different
electrode and ground manufacturing techniques for optimized flow rates for a
given application.