We present Raman spectroscopy analysis on laboratory and field sample analysis on several expeditions.
Our measurements in mineral and organic composition have demonstrated that both mineral and organic
species in low concentrations can be identified with Raman spectroscopy with no sample preparations
and without instrument probe contact to the samples. Our laboratory studies on cyanobacterial biomat,
and Mojave Desert rocks have demonstrated the promising potential for Raman spectroscopy as a nondestructive,
in situ, high throughput detection technique, as well as a desirable active remote sensing tool
for future planetary and space missions.
Polyaniline nanofibers (Pani nanofibers) have exhibited high performance and fault tolerant properties for dielectric
elastomer actuator devices. Electrodes comprised of uniformly sprayed Pani nanofibers in thicknesses 0.7 μm, 1.1 μm,
1.3 μm, and 1.5 μm have shown the following high strains: 65% in area for 0.7 μm electrodes at 3 kV, 97% in area for
1.1 μm thick electrodes at 3.5 kV, 84% in area for 1.1 μm thick electrodes at 3 kV, and 114.% in area for 1.5 μm thick
electrodes at 3.5 kV. Optimal performance was achieved with actuators with electrodes 1.1 μm thick, which
demonstrated self-healing properties at 3 kV. These actuators displayed a preserved strain of 91% after the clearing and
sustained a 93% area strain for 10 minutes at 3 kV. Devices with 1.1 μm thick electrodes were also able to perform 700
actuation cycles over a total duration of 75 minutes with a pulsed half-sinusoidal voltage of 3 kV. Mechanical
compliance tests performed on a film with a 1.1 μm thick Pani nanofiber electrode reveals that the electrode material
does not significantly alter the mechanical properties of the film. The estimated Young's modulus was found to be 32
MPa for the film with the electrode and 31 MPa for the film itself.
Dielectric elastomer actuators which consist of an electrode/dielectric elastomer/electrode sandwich structure show
greater than 100% electromechanical strain performance when high electrical field is applied. The strain in the dielectric
elastomer film occurs due to attraction of opposite charges across the dielectric film and repulsion of similar charges on
each compliant electrode. Structural defects present in these elastomers such as gel particles, uneven thickness, and stress
concentration may cause dielectric breakdown, leading to premature failure during continuous or repeated actuations.
Dielectric breakdown consequently reduces production yield and device lifetime. Carbon nanotubes (CNTs) have been
introduced as compliant electrodes for dielectric elastomers. Higher than 100% electromechanical strain was obtained
with ultrathin CNT electrodes due to the high aspect ratio and the high electrical conductivity of the nanotubes. These
ultrathin CNT electrodes also exhibit fault-tolerance in dielectric elastomers through the local degradation of CNTs
during dielectric breakdown. The degraded areas electrically isolate the defects, while keeping the rest of the elastomer
active. The "self-clearing" electrodes significantly increase the lifetime of the dielectric elastomers, making the dielectric
elasomer actuator much more reliable.
Dielectric elastomer actuators exert strain due to an applied electric field. With advantageous properties such as high efficiency and their light weight, these actuators are attractive for a variety of applications ranging from biomimetic robots, medical prosthetics to conventional pumps and valves. The performance and reliability however, are limited by dielectric breakdown which occurs primarily from localized defects inherently present in the polymer film during actuation. These defects lead to electric arcing, causing a short circuit that shuts down the entire actuator and can lead to actuator failure at fields significantly lower than the intrinsic strength of the material. This limitation is particularly a problem in actuators using large-area films. Our recent studies have shown that the gap between the strength of the intrinsic material and the strength of large-area actuators can be reduced by electrically isolating defects in the dielectric film. As a result, the performance and reliability of dielectric elastomers actuators can be substantially improved.
Electrochemical actuators were fabricated based on conducting polypyrrole (PPy) and acrylic elastomer substrate. An
ultrathin layer of single-wall carbon nanotubes (SWNT) was employed as the electrode for the electrochemical
deposition of PPy onto the substrate. The permeability of the nanoporous SWNT layer enabled the electrolyte solution to
penetrate the electrode and the polymerization of pyrrole both on the surface and at the interior of the substrate surface.
The resulting PPy was intimately attached to the substrate. The two materials could not be detached by any physical
means. Reversible and stable actuation has been demonstrated from the new PPy/SWNT/acrylic/SWNT/PPy bimorph structure.