Embedding polyethylene oxide (PEO) in polypyrrole doped with dodecylbenzenesulfonate (PPy/PEO-DBS) leads to increase linear actuation due to improved ionic conductivity. In this research our goal is to investigate the effect of solvent exchange from aqueous (aq) to propylene carbonate (PC) using same concentration of electrolyte bis(trifluoromethane) sulfonamide lithium (LiTFSI). As previously observed for the case of PPy/DBS films, the actuation direction of PPy/PEO-DBS changed from purely cation-driven in (aqueous) LiTFSI-aq to purely anion driven in (propylene carbonate) LiTFSI-PC. Cyclic voltammetry driven electro-chemo-mechanical-deformation (ECMD) measurements showed that the strain in LiTFSI-PC was more than double than that of aqueous electrolyte consuming only half of the charge density. The diffusion coefficients were determined from the chronoamperometric measurements with higher values found in LiTFSI-PC. Energy dispersive X-Ray spectroscopy and scanning electronic microscopy measurements were performed to characterize the PPy/PEO-DBS films.
In this paper, we present a simple printing method for a highly resilient stretch sensor. The stretch sensors, based on multi-walled carbon nanotubes (MWCNT)/silicon rubber (Ecoflex® 00-30) polymer nanocomposites, were printed on silicon rubber (SR) substrate. The sensors exhibit good hysteresis with high linearity and small drift. Due to the biocompatibility of SR and is very soft, strong and able to be stretched many times its original size without tearing and will rebound to its original form without distortion, the proposed stretch sensor is suitable for many biomedical and wearable sensors application.
An investigation is reported into the electrochemomechanical deformation (ECMD) of polypyrrole (PPy) doped with
dodecylbenzenesulfonate (DBS) in the form of freestanding films and deposited onto conductive substrates (chemically
fixed poly-3,4-(ethylenedioxythiophene, PEDOT) based on PVdF (poly(vinylidenefluoride)). Linear actuation has been
achieved starting from a trilayer bending actuator design with a stretchable middle layer. To allow evaluation of the
proposed design, commercially available PVdF membranes were chosen as model material. For bending trilayer
functionality, electronic separation of both electrode layers is essential, but in order to obtain linear actuation, the CP
layers on either side are connected to form a single working electrode. The PPyDBS free standing films and PPyDBS
deposited on PEDOT-PVdF-PEDOT were investigated by electrochemical methods (cyclic voltammetry, square wave
potentials) in a 4-methyl-1,3-dioxolan-2-one (propylene carbonate, PC) solution of tetrabutylammonium
trifluoromethanesulfonate (TBACF3SO3). This study also presents a novel method of utilizing scanning ion-conductance
microscopy (SICM) to accurately examine the electrochemical redox behavior of the surface layer of the linear actuator
using a micropipette tip.
Carbide–derived Carbon (CDC) material is applied for super capacitors due to their nanoporous structure and their high
charging/discharging capability. In this work we report for the first time CDC linear actuators and CDC combined with
polypyrrole (CDC-PPy) in ECMD (Electrochemomechanical deformation) under isotonic (constant force) and isometric
(constant length) measurements in aqueous electrolyte. CDC-PPy actuators showing nearly double strain under cyclic
voltammetric and square wave potential measurements in comparison to CDC linear actuators. The new material is
investigated by SEM (scanning electron microscopy) and EDX (energy dispersive X-ray analysis) to reveal how the
conducting polymer layer and the CDC layer interfere together.
Novel bending actuators were made solely from electrochemically polymerized conducting polymer materials. The working principle for these free-standing conducting polymer (CP) films is based on different anion- and cation-dominated actuation for the two layers. Synthesis conditions for the two layers of the same polymer film have been chosen such that the mobility of cations and anions in the considered potential window is different. Polymerization of CP layers of this nature on top of each other results in a sandwich structure with bilayer functionality in a properly chosen electrolyte. The results of a comparative study of various combinations of sandwiched PEDOT films in terms of actuation properties are presented in this study. Free-standing films of PEDOT linear actuators electrodeposited in the same electrolyte at different polymerization potentials were investigated by means of electro-chemo-mechanical deformation measurements. PEDOT-PEDOT bilayer functionality is studied in this work with a view to their bending actuation properties.
Recent applications of the scanned pipette to materials science problems have included its quantification of the ion flux
resulting from conducting polymer actuation. However, in order to correlate this flux with the precise height changes
arising from actuation, a separate experiment must be carried out. Herein we propose a new design that may be capable
of simultaneously determining both ion flux and topography, on the basis of subtle current density magnitude shifts and
precisely chosen experimental positioning parameters. A simulation of the geometrical model - consisting of the pipette,
conducting polymer film and electrodes - was setup and solved in 2D axi-symmetrical domain. The ion concentrations,
voltage potentials and current densities were determined as a function of time, with three key parameters varied: the
maximum ion flux value Jmax, conducting polymer swelling Tp and overall separation distance d between pipette and
polymer. It was found that the separation Tp - d should be around 50 to 150 nm, roughly the same as the actuation itself.
Furthermore, the current density component arising from geometrical changes due to actuation was on the order of a few
percent, and was highly sensitive to Jmax levels.
A novel flexible strain sensor was developed using a conducting polymer coated on rubber for large strain
measurements. A coating of the conducting polymer, polypyrrole, was deposited on a strip of natural rubber through the
process of vapour phase polymerisation while the rubber is in a stretched state. This process involves depositing a layer
of oxidant on the rubber surface, followed by exposure to pyrrole monomer vapours that polymerize on the oxidantcoated
rubber to produce polypyrrole.
The change in electrical resistance of the strain sensor was recorded while cyclic strain from 0% to 20% was exerted on
it. The gauge factor of the strain sensor was calculated to be 1.86. From repeated electrical resistance-strain
measurements, the repeatability of the strain sensor was studied. A hysteresis was observed in a single extensionretraction
strain cycle. Further study showed that the observed hysteresis is dependent on the strain rate where lower
strain rate resulted in higher hysteresis and vice versa for a higher strain rate. There is also an electrical resistance drift
between consecutive extension-retraction cycles.
Owing to the flexibility of the rubber, the strain sensor can be used in complex configurations. The strain sensor can also
be mounted or attached directly on surfaces to provide low-profile installation where space constraint is an issue. These
characteristics offer advantages over traditional strain sensors to be used in applications that were not previously
possible.
We demonstrate an electrochemical switching of conformation of surface-bound polymer brushes, by grafting
environmentally sensitive polymer brushes from an electrochemically-active conducting polymer (ECP). Using atom
transfer radical polymerization (ATRP), we grafted zwitterionic polymer brushes, poly(3-(methacryloylamino)propyl)-
dimethyl(3-sulfopropyl)ammonium hydroxide) (MPDSAH), from a surface initiated poly(pyrrole-co-pyrrolyl butyric
acid) film. The changes in ionic solution composition in electrical double layer at the surface resulting from oxidation
and reduction of the ECP trigger a switch in conformation of surface-bound poly(MPDSAH), demonstrated here by
electrochemical impedance spectroscopy (EIS). The switch is also dependent upon temperature. We speculate that the
synergistic combination of properties embodied in these "smart" materials may find application in electrochemical
control of surface wetting and of interaction with biomolecules and living cells.
A novel flexible large strain sensor was developed to be use with an air muscle. A piece of butyl rubber was coated with
the conducting polymer, polypyrrole through bulk solution and chemical vapour deposition method. The strain sensor
was able to response to sudden movements represented by the multiple step functions of the applied strain. Consistency
of the sensor's output was studied and the average error in the change of resistance was calculated to be 0.32% and
0.72% for elongation and contraction respectively for the sample made using chemical vapour deposition. However, a
hysteresis was observed for this sample for a single cycle of elongation and contraction with the highest error calculated
to be 3.2% at a 0% applied strain. SEM images showed the propagation of surface micro-cracks as the cause of the
variation in surface resistance with applied strain. In addition, slower relaxation rate of the rubber prevented the surface
micro-cracks to open and close at the same rate. The idea of utilizing conducting polymer coating can be applied to the
inner rubber tube of the air muscle. As such, a complete integration between actuator and sensor can be realized.
Trilayer actuators were constructed using polypyrrole (PPy) films doped with dodecylbenzene sulfonate (DBS). Identical
5-20 μm PPy/DBS films were grown on either side of a 110 μm poly(vinylidene fluoride) (PVDF) membrane to serve as
working and counter electrodes with respect to each other. The performance of the trilayer actuator was tested using
potential step experiments between -0.8 and +0.8 V at different frequencies (0.03 to 10 Hz) and trilayer lengths (1 to 2.5
cm), and the extent of deflection was measured using a CCD camera. Satisfactory deflections in the range of 1-3 mm
were observed for 10 μm thick PPy layers on trilayers 1.5 to 2.5 cm in length when operated at 1-5 Hz for over 40,000
cycles. The trilayer actuators were examined in a fluidics channels, and mathematical modelling using finite element
analysis was used to predict overall fluid movement and flow rates. The trilayers were also used to construct a 'fish-tail'
positioned at the back of a self-driven robotic fish.
The actuation properties of free standing films of poly-3,4-ethylenedioxythiophene (PEDOT) prepared from propylene
carbonate (PC) solutions of tetrabutylammonium trifluromethanesulfonate have been studied in a range of aqueous and
organic (PC) solvent electrolytes. The following electrolyte salts were investigated: TBACF3SO3, LiCF3SO3, TBAPF6,
NaPF6, NaDBS and TMACl. The best actuation performance was achieved in TMACl (aq.) with >4 % strain, 0.18 % s-1
strain rate and a low creep of 2.3 % after 50 cycles using potential step experiments. The PEDOT film morphology was
significantly changed from an open sub-micron pore polymer network to a morphology with fewer and less open pores when the solvent was changed from PC to water.
Investigations of the actuation properties of free standing PPy and PEDOT films in a propylene carbonate-triflate electrolyte (PC/TBACF3SO3) under isotonic (constant load)
conditions are presented in this work. The PPy film showed mixed ion movement during charging and discharging in cyclic voltammetric and chronoamperometric experiments. At a potential of -1.0 V the maximum strain was in the range of 1-2 % whereas at the anodic potential of +1.0 V strains in the range of 3-4 % were observed. Cyclic voltammetry experiments at higher scan rates to 10 mV/s led to a decrease in the anodic strain and an increase in the cathodic strain before it declined at higher scan rates. The free-standing PEDOT films showed mainly cathodic actuation at the potential -1.0 V and the size of actuation was again dependent upon the scan rate. Cation movement is discussed in terms of
the immobilisation of CF3SO3- anions during polymerisation. Extended potential step experiments showed good actuation and low creep in the potential range between 0.0 and
+1.0 V. The surface morphology (SEM) showed an open porous structure for PEDOT in contrast to the smooth morphology of PPy.
The availability of rapid and specific biosensors is of great importance for many areas of biomedical
research and modern biotechnology. This includes a need for DNA sensors where the progress of molecular
biology demands routine detection of minute concentrations of specific gene fragments. A promising
alternative approach to traditional DNA essays utilizes novel smart materials, including conducting
polymers and nanostructured materials such as quantum dots. We have constructed a number of DNA
sensors based on smart materials that allow rapid one-step detection of unlabeled DNA fragments with high
specificity. These sensors are based on functionalized conducting polymers derived from polypyrrole (PPy)
and poly(p-phenylenevinylene) (PPV). PPy based sensors provide intrinsic electrical readout via cyclic
voltammetry and electrochemical impedance spectroscopy. The performance of these sensors is compared
to a novel self-assembled monolayer-PNA construct on a gold electrode. Characterization of the novel PNA
based sensor shows that it has comparable performance to the PPy based sensors and can also be read out
effectively using AC cyclic voltammetry. Complementary to such solid substrate sensors we have
developed a novel optical DNA essay based on a new PPV derived cationic conducting polymer. DNA
detection in this essay results from sample dependent fluorescence resonance energy transfer changes
between the cationic conducting polymer and Cy3 labeled probe oligonucleotides. As an alternative to such
fluorochrome based sensors we discuss the use of inorganic nanocrystals ('quantum dots') and present data
from water soluble CdTe quantum dots synthesized in an aqueous environment.
To construct practical devices based on the actuating properties of conducting polymers we need to understand the underlying mechanism of the reversible length change and the effect of numerous synthetic and processing parameters on the extent of actuation, reversibility and durability. Here, we have investigated the out-of-plane actuation of polypyrrole (PPy) doped with dodecylbenzenesulfonate (DBS) in an aqueous electrolyte, and the linear actuation of PPy/DBS (aq.) and PPy/ hexafluorophosphate (PF6) in a propylene carbonate (PC) based electrolyte. The out-of-plane actuation was examined by means of AFM, and linear actuation was evaluated by a combination of electrochemomechanical deformation (ECMD) measurements, cycling voltammetry, chronoamperometry and conductivity measurements. The results revealed a very large actuation for PPy/DBS (aq.) in the out- of-plane mode, but a very limited actuation in the linear direction with low reversibility. PPy/PF6 (PC) showed much higher linear actuation than PPy/DBS, with reversible ECMD characteristics.
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