Ionic-polymer metal composites (IPMCs) are a subset of ionic electroactive polymers (EAPs). They produce an actuation response based on the electrically induced flux of mobile ions through a parent-polymer matrix. This response is a result of the accumulation of cations and anions on opposing sides of the matrix and is directly related to the size disparity between the two types of ions. These factors impose a differential expansion across the matrix, which generates the macroscopic bending that is observed. It is well known that the motion of these EAPs is highly nonlinear and time dependent, making for a process that is difficult to model. A simplistic approach to modeling the physics behind this phenomenon and correlating that to experimental results is outlined, herein. This new methodology enables a comprehensive analysis of the boundary conditions (BCs) needed to be considered in order to accurately characterize the IPMC actuation response. The subsequent series of equations developed, which depict the ionic motion under these BCs, is presented. Empirical data for model analysis was acquired from IPMCs created using poly(ethylene oxide) (PEO), a well-known, biodegradable, solid-polymer electrolyte infused with lithium perchlorate, as the ionic salt. Experimental results fitted with this new model returned a favorable average adjusted-R2, goodness-of-fit, of 0.987, 0.994, and 0.992 when PEO films were tested under varying conditions, including: ionic concentration, applied voltage, and testing temperature, respectively.
Ionic electroactive polymers have been widely studied, wherein the electrically induced ionic motion generates an actuation response. The electromechanical bending observed in these polymers is due to the size difference between two types of ions which results in an unequal expansion and contraction between the two sides. Nanocrystalline cellulose (NCC) is a biodegradable, renewable, and inexpensive biomass derivative. Poly(ethylene oxide) (PEO) is also biodegradable and a well-known solid-state electrolyte capable of having both cations and anions diffuse through its matrix under an applied electric field. In this study, NCC is mixed with the PEO to make 0-3 composites with increased Young’s modulus and improved actuation performance. Experimental results showed that the time-dependent strain response for these composites followed an Arrhenius behavior. Using the Stokes- Einstein model, the flux of the ions within in the polymer matrix were defined as charged, spherical particles moving through a viscous medium with low Reynold’s number. This new approach makes it possible to calculate parameters that may otherwise have been difficult or impossible to obtain. In this work, calculations for these properties, such as: apparent ionic diffusion coefficient, ionic velocity, and the dynamic viscosity of the matrix material are analyzed and presented. For example, the parameters for PEO-NCC composites doped with 5.0 wt.% lithium were calculated to be 3.58e-10 cm2/s, 102 nm/s, and 275 Poise, respectively. Electroactive polyvinylidene fluoride films were also synthesized for comparison and refinement of the introduced model.
Poly(ethylene oxide) (PEO) has been widely studied as a solid-polymer electrolyte where both the cations and
anions can move inside of it under an applied electric field. The motion of these charge carriers in the PEO results in the
accumulation of ions close to the electrodes. The inherent size difference between the types of ions causes an unequal
volume change between the two sides which translates to an observed mechanical bending. This is similar to
electroactive polymers made from conducting polymers. Typically, PEO has a slow response. Some efforts have been
given to develop PEO-based polymer blends to improve their performance. In this work, a fundamental study on the
electromechanical response is conducted: the time dependence of the electromechanical response is characterized for
PEO under different electric fields. Based on the results, a new methodology to monitor the electromechanical response
is introduced. The method is based on the frequency dependence of the samples’ dielectric properties. To improve the
electromechanical response, the PEO is embedded with piezoelectric nanocrystalline cellulose (NCC). NCC is a biomass
derivative that is biodegradable, renewable, and inexpensive. The dielectric, mechanical, and electromechanical
properties of the NCC-PEO composites are characterized. It is found that the mechanical and electromechanical
properties of the PEO are significantly improved with adding NCC. For example, the composites with 1.5 vol.% of NCC
exhibit an electromechanical strain and elastic modulus that is 33.4% and 20.1% higher, respectively, than for PEO
without NCC. However, the electromechanical response decreases when the NCC content is high.
KEYWORDS: Sensors, Biosensors, Magnetic sensors, Scanning electron microscopy, Liquids, Particles, Microfabrication, Chemical elements, Magnetism, Gold
Food borne illnesses from the ingestion of S. typhimurium have been of primary concern due to their common
occurrence in food products of daily consumption. In this paper, micron size, magnetoelastic (ME) biosensors for the
detection of S. typhimurium were fabricated and tested in liquid solutions containing known concentrations of S.
typhimurium cells. The biosensors are comprised of a ME sensor platform and immobilized bio-molecular recognition
element (E2 phage) that has been engineered to bind the S. typhimurium multi-valently. The micron size ME sensor
platforms were manufactured using microelectronics fabrication techniques. Phage was engineered at Auburn
University and immobilized onto all surfaces of the sensor. The ME biosensor oscillates with a characteristic resonance
frequency when subjected to a time varying magnetic field. Binding between the phage and bacteria, adds mass to the
sensor that causes a shift in the sensor's resonance frequency. Sensors with the dimension of 500x100x4 μm were
exposed to S. typhimurium with increasing known concentrations ranging from 5 x101 to 5 x 107 cfu/ml. The ME
biosensor exhibited high sensitivity and a detection limit better than 50 cfu/ml.
To ensure the safety of food, a detection device, which can detect/monitor the present of bacteria in a real-time manner
and can be easily used for in-field tests, is highly desirable. Recently, magnetostrictive particles (MSPs) as a new type of
high-performance biosensor have been developed. The detection of various bacteria and spores in food with high
sensitivity has already been experimentally demonstrated. To fully use the technique for food safety, two miniaturized
interrogation systems based on frequency-domain and time-domain technique are developed to fabricate a handheld
detection device. The detection of Salmonella typhimurium (S. typhimurium) in liquid using a time-domain based
interrogation system was demonstrated.
In this paper, we report a wireless magnetoelastic (ME) biosensor with phage as the bio-recognition probe for real time
detection of Salmonella typhimurium. The ME biosensor was constructed by immobilizing filamentous phage that
specifically binds with S. typhimurium onto the surface of a strip-shaped ME particle. The ME sensor oscillates with a
characteristic resonance frequency when subjected to a time varying magnetic field. Binding between the phage and
antigen (bacteria) causes a shift in the sensor's resonance frequency. Sensors with different dimensions were exposed to
various known concentrations of S. typhimurium ranging from 5 x101 to 5 x 108 cfu/ml. The detection limit of the ME
sensors was found to improve as the size of the sensor became smaller. The detection limit was found to improve from
161 Hz/decade (2mm length sensors) to 1150 Hz/decade (500 μm length sensors). The stability of the ME biosensor was
investigated by storing the sensor at different temperatures (25, 45, and 65 °C), and then evaluating the binding activity
of the stored biosensor after exposure to S. typhimurium solution (5 x 108 cfu/ml). The results showed that the phage-coated
biosensor is robust. Even after storage in excess of 60 days at 65 °C, the phage-coated sensors have a greater
binding affinity than the best antibody coated sensors stored for 1 day at 45 °C. The antibody coated sensors showed
near zero binding affinity after 3 days of storage at 65 °C.
Microcantilevers (MCs) as state-of-art sensor platforms have been widely investigated. We recently introduced a
new type of MC, magnetostrictive microcantilever (MSMC), as high performance sensor platform. The MSMC is a
remote/wireless sensor platform and exhibits a high quality merit factor in liquid. In this paper, a MSMC-based
biosensor is developed for detecting B. anthracis spores in liquid, a potential biothreaten agent. The results
demonstrated the advantages of MSMCs as a sensor platform. MSMCs with different sizes were fabricated and
utilized in the experiments. The MSMCs were coated with the filamentous phage as a bio-recognition element to
capture the B. anthracis spores. The phage-coated MSMCs as biosensors were exposed to cultures containing target
spores with concentrations ranging from 5 * 104 spores/mL to 5 * 108 spores/mL. The resonance frequency of the
MSMC sensors in cultures was monitored in a real-time manner. The results showed that for MSMCs of 2.8 mm *
1.0 mm * 35 &mgr;m and with 1.4 mm * 0.8 mm * 35 &mgr;m have a detection limit of 105 and 104 spores/mL, respectively.
To develop biosensors with the capability of detecting very small mount of biological agents, such as single or several cells, magnetostrictive bars or stripes in size from nanometer to micrometer are required. In this paper, magnetostrictive nanobars and nanobar arrays, with a diameter from 50 to 200 nm and a length of 2~5 μm, were fabricated based on template-based synthesis. The amorphous Fe-B alloy was selected as the magnetostrictive material to fabricate the nanobars. The study on resonance behavior and magnetic properties of plated Fe-B thin films indicate that amorphous Fe-B alloy is a good candidate for fabricating high performance sensor platform. The magnetization hysteresis loop of
Fe-B nanobars was characterized. It is found that all the nanobar arrays exhibit easy axis of magnetization along bar length direction but with smaller coercivity, which is different with bulk materials. The physics behind the phenomena is discussed.
High sensitivity and high Q value, as well as working well in liquid, make the newly developed magnetostrictive
microcantilevers (MSMCs) a great candidate for developing a high performance biosensor. In this paper, blood
cell identification by the MSMCs was demonstrated. The MSMCs were fabricated and their surface was
functionalized by immobilizing anti-B antibody as the bioreceptor for blood cells inspection. By immersing the
MSMCs into different type blood cells and monitoring the resonance frequency shift, due to blood cell binding,
the blood cells A and B were distinguished.
There is an urgent need for biosensors that are able to detect and quantify the presence of a small amount of biological threat agents in a real-time manner. The magnetostrictive microcantilever (MSMC) as the biosensor platform is reported in this paper. The resonance behavior and the sensitivity of MSMC as sensor platform were characterized and compared to the theoretical calculation. The stability and the performance of the MSMC in liquid are studied. The feasibility of MSMC as a high performance biosensor platform is demonstrated by detecting yeast cells in real-time manner used MSMC based-biosensor. Compare to current microcantilevers, the MSMCs have following advantages: 1) remote/wireless driving and sensing; 2) easy to fabricate. More importantly, the MSMC exhibits very high quality merit factor (Q value).
The performance of new biosensor design -- Micro-ElectroMechanical Diaphragm (MEMD) -- made from PVDF piezoelectric polymer is reported. The resonant frequencies changing with featured size of MEMD are characterized. The resonant behavior in liquid media shows that the damping effect of MEMD is lower than that of MC. Yeast cell detection demonstrated the feasibility of using this platform as biosensor in real time detection. Finally, the preliminary study on microelectronic fabrication of MEMD is presented.
There is an urgent need for biosensors that are able to detect and quantify the presence of a small amount of biological threat agents in a real-time manner. The magnetostrictive microcantilever (MSMC) as the biosensor platform is reported in this paper. The resonance behavior and the sensitivity of MSMC as sensor platform were characterized and compared to the theoretical calculation. The stability and the performance of the MSMC in liquid are studied. The feasibility of MSMC as a high performance biosensor platform is demonstrated by detecting yeast cells in real-time manner used MSMC based-biosensor. Compare to current microcantilevers, the MSMCs have following advantages: 1) remote/wireless driving and sensing; 2) easy to fabricate. More importantly, the MSMC exhibits very high quality merit factor (Q value).
The understanding of the electromechanical response in electroactive polymers (EAPs) will lead the development of new materials or the improvement of existing materials. The recent development of electrostriction based high performance EAPs, such as irradiated P(VDF-TrFE) and dielectric elastomers, makes it more interesting to understand the micro-mechanism that contribute the observed strain response. However, the current widely accepted mechanisms, such as electric field induced phase transition and the Maxwell effect, could not explain some of the observed phenomena. In this paper, the structure and property of recrystallized P(VDF-TrFE) 65/35 copolymer which was previously irradiated with high-energy electrons are reported. It is found that the interfacial layer existing between the crystalline regions and amorphous regions plays an important role. This concept is further extended to explain the pre-stress dependence of the electromechanical response observed in dielectric elastomers. That is, partially ordered regions are induced in the dielectric elastomer by the pre-stress. These partially ordered regions are the key to the observed high electromechanical performance dielectric elastomers.
In an effort to develop very inexpensive electroactive polymers, P(VDF-CTFE) and its blends with P(VDF-TrFE) copolymer are studied and reported. A high electrostrictive strain of 5% was observed in the treated P(VDF-CTFE) and its blends with blend ratio 10/90 wt% [P(VDF-TrFE)/P(VDF-CTFE)]. Combined with Young’s modulus, dielectric constant, and the piezoelectric constant, the electromechanical coupling factor and energy density of this blend system are evaluated and compared with irradiated P(VDF-TrFE) and terpolymer P(VDF-TrFE-CTFE).
There is an urgent need for real-time bio-detectors with high performance, such as high sensitivity, small size, easy deployment. Sensor platforms based on MEMS, such as microcantilevers (including piezoelectric and silicon-based cantilevers), have been studied. Piezoelectric-based micro-diaphragm, micro-electromechanical diaphragm (MEMD), used as micro-sensor platform, is reported in this article. It is found that the sensitivity of the sensor based on micro-diaphragm is much higher than that based on the micro-cantilever. Since a lower density of material used in the diaphragm results in a better sensitivity, PVDF-based piezoelectric polymer was chosen to fabricate the devices. Both cantilevers and diaphragms made of the same piezoelectric polymer were characterized in order to compare the difference of quality merit factor (Q-value) between the cantilever and diaphragm. It is experimentally found that the Q-value of the diaphragm is higher than that of the cantilever. More importantly, the damping effect of liquid media on diaphragm is much smaller than that that on cantilever. All these indicate that as a sensor platform the micro-diaphragm is much better than the micro-cantilever.
Biosensors for detecting and quantifying the presence of a small amount of biological threat agents in a real-time manner are urgently needed for a wide range of applications. In this paper, a novel type of micro-biosensor platform - magnetostrictive microcantilever (MMC) - is reported. The resonance behavior and the sensitivity of MMC are characterized and compared to the theoretical calculation. Additionally, the quality merit factor (Q value) was characterized. It is found: 1) the MMC exhibits a sensitivity of about 50% higher than that of piezoelectric-based microcantilevers and 2) the MMC has a high Q value (~140 in air and 50 in yeast suspension). A biosensor for detecting yeast cells in water is built based on MMC. The performance of the biosensor is characterized.
A study of recrystallization on high-energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer with composition 65/35 mol% is reported in this paper. Electron irradiated copolymer P(VDF-TrFE) exhibits a high electromechanical performance that is attractive for many applications. The structure and morphology of the recrystallized samples were determined using DSC, X-ray diffraction and FTIR. The polarization behavior of the recrystallized samples was also studied. The nonpolar phase content in the recrystallized samples was much lower than that in the irradiated samples. For irradiated samples that exhibited the best electromechanical performance, the corresponding recrystallized material had a high polar phase content, correspondingly a high remanent polarization was observed. For samples irradiated with higher doses, which have low polarization levels, after recrystallization the material exhibited a much higher polarization level with a very small remanent polarization, an attractive combination for many electromechanical applications.
In this paper, we report a new electroactive polymer system, blends of P(VDF-TrFE) and P(VDF-CTFE). The thermal transition behavior and crystalline structure of the polymer blends were studied using the DSC and X-ray diffraction. The optimized thermal treating condition and composition for the blends were identified to have homogeneous materials. In order to find blends with high electromechanical performance, the maximum polarization level and the ratio of maximum polarization to remnant polarization are employed as key parameters to optimize the composition and process. Uniaxially stretching technique was employed to modify the morphology of the polymer blends and to enhance the electromechanical performance. The phase transition behavior can be significantly modified using thermal treating condition. In a stretched polymer blend, a polarization level about 60 mC/m2 at external electric field of 150 V/μm was obtained with a small remnant polarization, less than 10 mC/m2. This is very attractive for electromechanical applications.
This paper reports two classes of electroactive polymers developed recently which exhibit very high strain and elastic energy density. In the first class of the electroactive polymer, i.e., the defects modified poly(vinylidene fluoridetrifluoroethylene)(P(VDF-TrFE)) polymers, an electrostrictive strain of more than 7% and an elastic energy density above 1 J/cm3 can be induced under a field of 150 MV/m. The large electrostrictive strain in this class of polymers originates from the local molecular conformation change between the trans-gauche bonds and all trans bonds, which
accompanies the field induced transformation from the non-polar phase to the polar phase. The second class of the polymer is an all organic composite, which shows a very high dielectric constant (>400) and high strain induced with a low applied field (2% strain under 13 MV/m). The strain is proportional to the applied field and the composite has an elastic modulus near 1 GPa.
The popularity of minimally invasive surgical procedures over traditional open procedures motivates us to develop new instruments that address the limits of existing technology and enable more widespread use of minimally invasive approaches. Robotic surgical instruments have the potential to provide improved dexterity and range of motion within the confines of the human body when compared with manually actuated instruments. The high strain response and elastic energy density of electron-irradiated P(VDF-TrFE) make it a candidate actuator material for robotic instruments that provide electronic mediation and multiple degrees of freedom of tip movement. We are currently studying both active and passive properties of P(VDF-TrFE) with the goal of constructing a mathematical model of the material's behavior. Studies have been conducted on 15 micron thick film samples in rolled and rolled-flattened configurations. Passive properties can be represented by a 5 parameter viscoelastic model with two time constants on the order of ten and 200 seconds. Active responses were found to have strong dependence upon field and modest dependence upon load. We suggest means by which the active and passive responses can be combined in a model of steady-state response that would be of value in positioning tasks. The time course of the active response appears to contain components on two time scales, but further studies are required to characterized it in more detail.
KEYWORDS: Polymers, Actuators, Data modeling, Silicon, Electrodes, Selenium, Solids, Digital video recorders, Performance modeling, Microelectromechanical systems
We report on the performance of micromachined unimorph actuators (PMAT) based on the electrostrictive poly(vinylidene fluoride-trifluoroethylene) copolymer. Because of the high electrostrictive strain and high elastic energy density of the active polymer, the PMAT exhibits a very high stroke level with high load capability and high displacement voltage ratio. In addition, the experimental data also demonstrate that the PMAT is capable of operating over a broad frequency range. The PMAT performance was modeled and the agreement between the modeling results and experimental data confirms that the response of the PMAT indeed follows the design parameters.
The recent discovery of high electromechanical performance in high-energy electron irradiated P(VDF-TrFE) copolymers opens a new avenue for developing high performance electroactive polymers. From basic materials consideration, it is expected that one can achieve high electromechanical performance by means of nonirradiation approach, such as introducing ter-monomer to form PVDF based terpolymer. The basic requirement for the ter-monomer is discussed in order to achieve a high electromechanical performance in P(VDF-TrFE) based terpolymer. Based on the conclusion, P(VDF-TrFE-CFE) terpolymer has been synthesized and the experimental results indicate that the terpolymer exhibits better electromechanical performance compared with irradiated copolymers. For example, both the electric induced strain and Young's modulus in P(VDF-TrFE-CFE) terpolymer could be higher than that in irradiated copolymers. X-ray diffraction, DSC and FTIR were employed to determine the structure and molecule conformation. Furthermore, a serious theoretical simulation was carried out for P(VDF-TrFE) based terpolymers with different ter-monomers. The results show that indeed the terpolymer with CFE favors gauche conformation, consistent with the experimental results.
In our earlier work, we have demonstrated that the high- energy electron irradiation modifies (VDF-TrFE) copolymers from a normal ferroelectric to a relaxor ferroelectric with high electromechanical response. Here, we present two approaches we are taking recently. One is to explore the non-irradiation approach to modify the PVDF-based material to achieve high electromechanical response. A ter-monomer (HFP and CTFE are used here) with a relative large size is added to the copolymer to act as modifiers. The electromechanical and dielectric properties in the terpolymers seem to be similar to those in irradiated copolymers. The other approach addresses the fundamental issue of the low dielectric constant in the currently available electroactive polymers. By making use of composite approach and ultra-high dielectric constant in CuPc, a polymeric composite with very high dielectric constant but the elastic modulus similar to polymer has been demonstrated. The preliminary results indicate that the polymer composite has the potential to generate high strain under much lower field. In parallel to the material development, we investigated device performance based on the irradiated copolymers. The performance of irradiated copolymer multilayers with a thickness up to 1 mm was characterized. The design and device performance of a flextensional actuator fabricated from the irradiated copolymer multiplayer are presented. The flextensional actuator, whose resonance frequency is at a frequency of a few kHz to more than 10 kHz, exhibits more than 1 mm displacement and high force output, which are attractive for many applications.
Micromachined unimorph actuators based on the electrostrictive P(VDF-TrFE) copolymer have been fabricated. The performance of the devices has been modeled and characterized. The experimental results on the device responses are very close to the prediction of the model, indicating a high actuator displacement and voltage sensitivity. For a typical unimorph device with 1 mm length, the displacement at the center of the device can reach 30 micrometers , and the ratio of the displacement/applied voltage is more than 30nm/V. Furthermore, over more than 3 frequency decades, the dispersion of the displacement is less than 20%, which indicates the high frequency capability of this polymer based MEMS. To demonstrate the high force capability of the device, the displacement response of the device was evaluated at 200 Hz ina fluid medium and there is no observable change in the displacement response in fluid medium when compared with that measured in air. Due to the large field induced electrostrictive strain and high frequency capability of the electrostrictive P(VDF-TfFE), the device is capable of operating at no-resonance model with high displacement and force output, and over a broad frequency range (DC to >10 kHz). The observed performance of the device indicates that this type of electrostrictive P(VDF-TrFE) based MEMS is attractive for micro-pump, values, and air coupled ultrasonic transducer array, etc.
In order to characterize the electromechanical properties of newly developed electrostrictive poly(vinylidene fluoride- trifluorethylene) copolymers for practical device applications, the following results are presented: 1) The driving field amplitude dependence of the material response. It was found that M(S = ME2) exhibits the driving field amplitude dependence and that the apparent piezoelectric coefficient for the material under DC bias depends on both the driving field amplitude and DC field. 2) Load capability. The copolymer film has a high mechanical load capability. For example, the transverse strain remains 0.6% at 47MV/m under a tensile load of 45 MPA. The load dependence of the material response prove that the electric field induced strain in the copolymer films mainly originates from the electric field induced phase transition in the crystal regions. 3) Frequency dependence of the material response. Although the strain response decreases with increasing frequency, it is found that the strain response at 1 kHz can reach more than 80% of the response at 1Hz.
Peizoelectric and electrostrictive polymers are widely used in many areas of electromechanical actuation and transduction. This paper summarizes the current status and recent works in this class of polymers. For the piezoelectric polymers, the electromechanical properties of poly(vinylidene fluoride-trifluoroethylene) copolymers (P(VDF-TrFE), which possess the best piezoelectric performance among the known piezopolymers, are presented. In order to improve the strain capability and other electromechanical properties, the large electrostrictive response and high electromechanical conversion efficient near a first order ferroelectric-paraelectric transition of P(VDF-TrFE) copolymer were exploited. It is shown that the copolymer, treated with high energy electron irradiation, exhibits high electrostrictive strains (-5% longitudinal strain under 150 MV/m and 3.5% transverse starin under 100 MV/m) with high strain energy density, high load capability and improved electromechanical coupling factor. For the comparison, the works related to the Maxwell stress induced strain response in soft polymers are also discussed.
An exceptionally high electrostrictive response was observed in electron irradiate polyvinelidene fluoride- trifluoroethylene [P(VDF-TrFE)] copolymer. Moreover, the transverse strain of the material can be tuned over a large range by different sample treatment conditions. For example, in films uniaxially stretched, the strain can be comparable or even larger than the longitudinal strain, while in films unstretched, the transverse strain is quite small. In addition, when the films are completely clamped mechanically in the lateral directions, the films can still generate large longitudinal strains. Due to relatively high elastic modulus of the films, high elastic strain energy densities, which are much higher than those in conventional piezo and electrostrictive ceramics and magnetostrictive materials.
All-polymer electrostrictive systems are developed. Two typical electro-active polymers, poly(vinyldiene- trifluoroethylene) P(VDF-TrFE) of high elastic modulus and polyurethane of low elastic modulus, are studied. The conducting polymers used as electrodes in the system are polypyrrole and polyaniline respectively. The compatible interface between the electrode polymer and electrostrictive polymer produces acoustic transparency of the all-polymer films. The dielectric and electromechanical properties of the system are characterized and compared with that of the electroactive polymer with gold electrodes. It is found that the dielectric loss of the system is a litter bit higher than that of the sample with gold electrodes at high frequency since the conductivity of the conductive polymer is lower than that of the gold. The electric field induced longitudinal strain response of the all-polymer system is the same as that of the electroactive polymer with gold electrodes. However, the electric field induced transverse strain response of the all-polymer system is higher than that of the electroactive polymer with gold electrodes.
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