No abstract

Stretchable electronic materials have drawn strong interest due to their important applications in areas such as bioelectronics, wearable devices, and soft robotics. The stretchable electrode is an integral unit of stretchable systems. Intrinsically c o n d u c t i v e p o l y m e r s s u c h a s p o l y ( 3 , 4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) can have high mechanical flexibility and good biocompatibility. However, their electrical conductivity and mechanical stretchability should be greatly improved for its applications as the stretchable electrode. Here, we report highly conductive and highly stretchable PEDOT:PSS by incorporating biocompatible D-sorbitol. D-Sorbitol can serve as both the secondary dopant and plasticizer for PEDOT:PSS. It can not only significantly improve the conductivity but also the stretchability. D-Sorbitol-PEDOT:PSS (s-PEDOT:PSS) can have a conductivity of >1000 S/cm, and the conductivity could be maintained at a strain up to 60%. The resistance of s-PEDOT:PSS remains almost constant during repeated stretching−releasing cycles. The mechanism for the stretchability improvement by D-sorbitol is ascribed to the softening of PSSH chains. D-Sorbitol can position among the PSSH chains and thus destructs the hydrogen bonds among the PSSH chains. This makes the conformational change of the PSSH chains under stress become easy and thus increases the mechanical flexibility of PEDOT:PSS. This conductivity is the highest for biocompatible intrinsically conductive polymers with high stretchability.

Hydrophobic carbon nanotubes (CNTs) and hydrophilic nanofilaments such as oxidized CNTs, Pd nanowires (NWs), and MnO(2) NWs are transformed from wires to rings by a general methodology. We show that both oil-in-water and water-in-oil emulsions, so long as their droplet size is sufficiently small, can exert significant force to the entrapped nanostructures, causing their deformation. This effect can be easily achieved by simply mixing a few solutions in correct ratios. Even preformed oil droplets can take in CNTs from the aqueous solution converting them into rings, indicating the important role of thermodynamics: The question here is not if the droplets can exert sufficient force to bend the nanofilaments, because their random vibration may be already doing it. As long as the difference in solvation energy is large enough for a nanofilament, it would "want" to move away from the bulk solution and fit inside tiny droplets, even at the cost of induced strain energy. That said, the specific interactions between a droplet and a filament are also of importance. For example, when an oil droplet rapidly shrinks in size, it can compress the entrapped CNTs in multiple stages into structures with higher curvatures (thus higher strain) than that of a circular ring, which has minimal induced strain inside a spherical droplet.

No abstract

To understand complex sensory-motor behavior related to object perception by echolocating bats, precise measurements are needed for echoes that bats actually listen to during flight. Recordings of echolocation broadcasts were made from flying bats with a miniature light-weight microphone and radio transmitter (Telemike) set at the position of the bat's ears and carried during flights to a landing point on a wall. Telemike recordings confirm that flying horseshoe bats (Rhinolophus ferrumequinum nippon) adjust the frequency of their sonar broadcasts to compensate for echo Doppler shifts. Returning constant frequency echoes were maintained at the bat's reference frequency +/-83 Hz during flight, indicating that the bats compensated for frequency changes with an accuracy equivalent to that at rest. The flying bats simultaneously compensate for increases in echo amplitude as target range becomes shorter. Flying bats thus receive echoes with both stabilized frequencies and stabilized amplitudes. Although it is widely understood that Doppler-shift frequency compensation facilitates detection of fluttering insects, approaches to a landing do not involve fluttering objects. Combined frequency and amplitude compensation may instead be for optimization of successive frequency modulated echoes for target range estimation to control approach and landing.

For polymer composites to be used in electronic packaging, they must have a good combination of thermal and dielectric properties. A composite of aluminum-nitride (AlN) particles dispersed around polystyrene matrix particles has been synthesized in this study. The purpose of using this microstructure is to improve the thermal properties of the polymer at the low-filler content with a minimal increase in the dielectric constant of the polymer composite. The dielectric relaxation behavior of polystyrene–AlN composites has been investigated with broadband dielectric relaxation spectroscopy. The experimental results indicate that the dielectric property of polystyrene–AlN composites is a function of polystyrene particle size, AlN filler concentration, temperature, and frequency under this dispersion state. The dependence of Maxwell–Wagner–Sillars or interfacial polarization of polystyrene–AlN composites on AlN volume fraction has also been studied. The Davidson–Cole equation is used to fit the experimental Cole–Cole plot.

Point defects on a Si(001)-(2 x 1) surface were examined by scanning tunneling microscopy and ab initio pseudopotential calculations. The residual water molecules in the ultrahigh vacuum chamber are found to be the sole origin of the type-C defects. Most of the apparent dimer vacancies in the filled-state images were found to show a distinct U-shaped triple-dimer footprint in the empty-state images, which also originate from water adsorption. These two defects were identified as a single dissociated water molecule forming Si-OH and Si-H bonds in the interdimer (type-C defect) and the on-dimer (dimer-vacancy-like or U-shape defect) configurations.

Multiwall carbon nanotube reinforced poly (phenylene sulfide) (PPS) nanocomposites were successfully fabricated through melt compounding. Structural, electrical, thermal, rheological, and mechanical properties of the nanocomposites were systematically studied as a function of carbon nanotube (CNT) fraction. Electrical conductivity of the polymer was dramatically enhanced at low loading level of the nanotubes; the electrical percolation threshold lay between 1 and 2 wt % of the CNTs. Rheological properties of the PPS nanocomposites also showed a sudden change with the CNT fraction; the percolation threshold was in the range of 0-0.5 wt % of CNTs. The difference in electrical and rheological percolation threshold was mainly due to the different requirements needed in the carbon nanotube network in different stages. The crystallization and melting behavior of CNTfilled PPS nanocomposites were studied with differential scanning calorimetry; no new crystalline form of PPS was observed in the nanocomposites, but the crystallization rate was reduced. The thermal and mechanical properties of the nanocomposites were also investigated, and both of them showed significant increase with CNT fraction. For 5 wt % of CNT-filled PPS composite, the onset of degradation temperature increased by about 13.5 C, the modulus increased by about 33%, and tensile strength increased by about 172%.