Electrically switchable metallic polymer nanoantennas

[Figure: see text].

From Understanding Mechanical Behavior to Curvature Prediction of Humidity-Triggered Bilayer Actuators

Nature will always be an endless source of bioinspiration for man-made smart materials and multifunctional devices. Impressively, even cutoff leaves from resurrection plants can autonomously and reproducibly change their shape upon humidity changes, which goes along with total recovery of their mechanical properties after being completely dried. In this work, simple bilayers are presented as autonomously moving, humidity-triggered bending actuators. The bilayers-showing reproducible bending behavior with reversible kinematics and multiway behavior-are studied in terms of their mechanical behavior upon humidity changes. The active layer consists of a highly conducting polymer film based on poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) with poly(dimethylsiloxane) (PDMS) as passive layer. The response to humidity is explored with dynamic mechanical thermal analysis and quartz crystal microbalance measurements. Introduction of a composite beam model allows to predict the curvature of the actuators with input from the rheological measurements. It is clearly demonstrated that volumetric strain and Young's modulus, both heavily influenced by the water uptake, dominate the bending behavior and therefore the curvature of the actuators. This loop of rheological characterization coupled with an analytical model allows to predict curvatures of in principle any complex geometry and material combination for moving parts in soft robotics.

Humidity-Controlled Water Uptake and Conductivities in Ion and Electron Mixed Conducting Polythiophene Films

Mixed conducting polymer films are of great interest in applications where an interface between electronic and ionic charge transport is needed, e.g., in bioelectronics, electrochemical energy applications, and photovoltaic device interfaces. The role of water on charge transport is of high relevance not only for aqueous environments but also for devices that are manufactured at ambient conditions with varying relative humidities. In this contribution, we present our results on the influence of controlled humidity changes on the mixed conductivity and correlation to the concomitant water uptake in the films. Two sulfonate-bearing polythiophene systems are studied: a self-made conjugated polyelectrolyte, poly(6-(thiophen-3-yl)hexane-1-sulfonate)-sodium (PTS-Na), and poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) with different ratios of PEDOT and the polyelectrolyte PSS. Our data give clear evidence of the similarities between the aforementioned polythiophene systems and pure ionic membranes such as Nafion used in fuel cells. As such, a phase separation between the hydrophobic electronically conducting polythiophene phase and the hydrophilic water-swellable ion-conducting phase is proposed. Changing the humidity from dry conditions up to ∼90% relative humidity results in extremely high water uptakes of more than 90 wt %, which corresponds to ∼13 water molecules per sulfonate unit at maximum water uptake. Conversely, the electronic conductivity is less sensitive to increasing humidity, which is due to percolation pathways. The ionic conductivity strongly increases from 10^-10 S/cm at dry conditions to 10^-3 S/cm at around 30 wt % water content and then levels off at maximum conductivities of 10^-3-10^-2 S/cm up to water contents of 90 wt %.

Levels and activities of nitrogenase proteins in Azotobacter vinelandii grown at different dissolved oxygen concentrations

Azotobacter vinelandii was grown diazotrophically at different dissolved oxygen concentrations (in the range of 3 to 216 microM) in sucrose-limited continuous culture. The specific nitrogenase activity, measured on the basis of acetylene reduction in situ, was dependent solely on the growth rate and was largely independent of oxygen and sucrose concentration. FeMo (Av1) and Fe (Av2) nitrogenase proteins were quantified after Western blotting (immunoblotting). When the cultures were grown at a constant dilution rate (D, representing the growth rate, mu) of 0.15.h-1, the cellular levels of both proteins were constant regardless of different dissolved oxygen concentrations. The same was true when the organisms were grown at D values above 0.15.h-1. At a lower growth rate (D = 0.09.h-1), however, and at lower oxygen concentrations cellular levels of both nitrogenase proteins were decreased. This means that catalytic activities of nitrogenase proteins were highest at low oxygen concentrations, but at higher oxygen concentrations they increased with growth rate. Under all conditions tested, however, the Av1:Av2 molar ratio was 1:(1.45 +/- 0.12). Cellular levels of flavodoxin and FeS protein II were largely constant as well. In order to estimate turnover of nitrogenase proteins in the absence of protein synthesis, chloramphenicol was added to cultures adapted to 3 and 216 microM oxygen, respectively. After 2 h of incubation, no significant decrease in the cellular levels of Av1 and Av2 could be observed. This suggests that oxygen has no significant effect on the breakdown of nitrogenase proteins.

Reversible and irreversible inactivation of cellular nitrogenase upon oxygen stress in Azotobacter vinelandii growing in oxygen controlled continuous culture

Azotobacter vinelandii growing in oxygen controlled chemostat culture was subjected to sudden increases of ambient oxygen concentrations (oxygen stress) after adaptation to different oxygen concentrations adjustable with air (100% air saturation corresponds to 225 +/- 14 microM O2). Inactivations of cellular nitrogenase during stress (switch off) as well as after release of stress (switch on) were evaluated in vivo as depending on stress duration and stress height (delta pO2). Switch off was at its final extent within 1 min of stress. The extent of switch off, however, increased with stress height and was complete at delta pO2 between 8-10% air saturation irrespective of different oxygen concentrations the organisms were adapted to before stress, indicating that switch off is adaptable. Inactivation of nitrogenase measureable after switch on represents irreversible loss of activity. Irreversible inactivation was at its characteristic level within less than 3 min of stress and at a delta pO2 of less than 1% air saturation. The level of irreversible inactivation increased linearly with the oxygen concentration the organisms were adapted to before stress. Thus adaptation of cells to increased oxygen concentrations did not prevent increased susceptibility of nitrogenase to irreversible inhibition during oxygen stress. The fast response of irreversible inactivation at low stress heights suggests that it takes place already during stress. Thus switch off comprised both a reversible and an irreversible phase. The data showed that reversible inactivation of nitrogenase was less susceptible to oxygen stress than irreversible inactivation.(ABSTRACT TRUNCATED AT 250 WORDS)