Bionic

Abstract

Introduction

Ionic polymeric materials suitably made into a functionally-graded composite with a conductor such as a metal, graphite or synthetic metal such as conductive polymers that act as a distributed electrode can exhibit large dynamic deformation if placed in a time-varying electric field (see Figs 1 and 2) [Shahinpoor 1992, 1993, Adolf, Shahinpoor, Segalman and Witkowski, 1993]. A recent book by Shahinpoor, Kim and Mojarrad (2004) and 4 fundamental review papers by Shahinpoor and Kim (2001, 2003, 2004 and 2005) presents a thorough coverage of the existing knowledge in connection with ionic polymeric cond uctor composites (IPCC's) including ionic polymeric metal composites (IPMC's) as biomimetic distributed nanosensors, nanoactuators and artificial muscles and electrically controllable polymeric network structures. Furthermore, in reference [Shahinpoor, Kim and Mojarrad, 2004], methods of fabrication of several electrically and chemically active ionic polymeric gel muscles such as polyacrylonitrile (PAN), poly(2-acrylamido-2-methyl-1-propane sulfonic) acid (PAMPS), and polyacrylic-acid-bis-acrylamide (PAAM) as well as a new class of electrically active composite muscle such as Ionic Polymeric Conductor Composites (IPCC's) or Ionic Polymer Metal Composites (IPMC's) made with perfluorinated sulfonic or carboxylic ionic membranes (chlor-alkali family) are introduced and investigated that have resulted in seven US patents regarding their fabrication and application capabilities as distributed biomimetic nanoactuators, nanotransducers, nanorobots and nanosensors. Theories and numerical simulations associated with ionic polymer gels electrodynamics and chemodynamics are also discussed, analyzed and modeled for the manufactured material.

Fig. 1.

Four-Fingered Robotic Grippers made With Plastic Muscles IPMC's

Fig. 2.

Successive photographs of an IPMC strip showing very large deformation (sample in a and b are 1cmx8cmx0.34mm under 4 volts). Note that Δt=0.5 sec between a.

In this paper we concentrate on perfluorinated sulfonic ionic membranes and ionic polyacrylonitrile materials only, as potentially powerful ionic polymers for biomimetic distributed nanosensing, nanoactuation, nanorobotics, nanotransducers for power conversion and harvesting, as well as artificial muscles for medical and industrial applications. It must be noted that widespread electrochemical processes and devices utilize poly(perfluorosulfonic acid) ionic polymers. These materials exhibit [Shahinpoor and Kim, 2001, 2002, 2003, 2004 and 2005], good chemical stability, remarkable mechanical strength, good thermal stability, and high electrical conductivity when sufficiently hydrated and made into a composite with a conductive phase such as metals, conductive polymers or graphite. As described in [Shahinpoor and Kim, 2005] a number of physical models have been developed to understand the mechanisms of water and ion transport in ionic polymersand membranes. Morphological features influence transport of ions in ionic polymers. These features have been studied by a host of experimental techniques including:small and wide-angle x-ray scattering, dielectric relaxation, and a number of microscopic and spectroscopic studies.

The emerging picture of the morphology of chlor-alkali ionic polymers is that of atwo-phase system made up of a polar fluid (water)-containing ion cluster network surrounded by a hydrophobic polytetrafluoroethylene (PTFE) medium. The integrity and structural stability of the membrane is provided by the PTFE backbones and the hydrophilic clusters facilitate the transport of ions and water in the ionic polymer. These nanoclusters have been conceptually described as containing an interfacial region of hydrated, sulfonate-terminated perfluoroether side chains surrounding a central region of polar fluids. Counterions such as Na+ or Li+ e are to be found in the vicinity of the sulfonates. It must be noted that the length of the side chains has a direct bearing on theseparation between ionic domains, where the majority of the polar fluids resides, andthe nonpolar domains. High resolution NMR of some perfluoroionomer shows an unusual combination of a non-polar, Teflon-like backbone, with polar and ionic side branches. It has also been well established [Shahinpoor and Kim 2004, 2005] that anions are tethered to the polymer backbone and cations (H+, Na+,Li+) are mobile and solvated by polar or ionic liquids within the nanoclusters of size 3–5 nanometers.

IPMC Manufacturing techniques

Manufacturing an IPMC begins with selection of an appropriate ionic polymeric material. Often, ionic polymeric materials are manufactured from polymers that consist of fixed covalent ionic groups. The currently available ionic polymeric materials that are convenient to be used as IPMC's are: (1)

Perfluorinated alkenes with short side-chains terminated by ionic groups [typically sulfonate or carboxylate (SO3- or COO-) for cation exchange or ammonium cations for anion exchange (see Fig. 3)]. The large polymer backbones determine their mechanical strength. Short side-chains provide ionic groups that interact with water and the passage of appropriate ions.

(2)

Styrene/divinylbenzene-based polymers in which the ionic groups have been substituted from the phenyl rings where the nitrogen atom is fixed to an ionic group. These polymers are highly crosslinked and are rigid.

Fig. 3.

Perfluorinated sulfonic acid polymers

The preparation of ionic polymer-metal composites (IPMC's) requires extensive laboratory work including manufacturing polymer-metal composites by means of chemical oxidation-reduction (REDOX) operation. State-of-the-art IPMC manufacturing techniques [Shahinpoor and Mojarrad, 2000, Kim and Shahinpoor 2002] incorporate two distinct preparation processes: first initial oxidation process and then final reduction process. Different preparation processes result in morphologies of precipitated platinum that are significantly different. Fig. 4 shows illustrative schematics of two different preparation processes (top-left and bottomleft) and two top-view SEM micrographs for the platinum surface-electrode (top-right and bottom-right).

Fig. 4.

Two schematic diagrams showing different preparation processes

Note in Fig. 4 that (top-left) is a schematic showing the initial process of making the ionic polymer metal composite, (top-right) shows its top-view SEM micrograph, while (bottom-left) shows a schematic of the process of depositing surface electrodes on the ionic polymer and the (bottom-right) shows its top-view SEM micrograph where platinum deposited predominately on top of the initial Pt layer. The initial process of making the functionally-graded composite (IPMC's) requires an appropriate platinum salt such as Pt(NH₃)₄HCl or Pd(NH₃)₄HCl in the context of chemical reduction processes. The principle of the process of making a functionally graded composite is to metalize the inner surface of the material by a chemicalreduction means such as LiBH₄ or NaBH₄. The ionic polymeric material is soaked in a salt solution to allow platinum-containing cations to diffuse through via the ionexchange process (oxidation). Later, a reducing agent such as LiBH₄ or NaBH₄ is introduced to platinize the material (reduction). As can be seen in Fig. 5, the metallic platinum particles are not homogeneously formed across the membrane but concentrate predominantly near the interface boundaries. It has been experimentally observed that the platinum particulate layer is buried microns deep (typically 1–20 μm) within the IPMC surface and is highly dispersed. The fabricated IPMC's can be optimized to produce a maximum force density by changing multiple process parameters. These parameters include time-dependent concentrations of the salt and the reducing agents. The primary reaction is,

{LiBH}_{4} + 4 [PT ({NH}_{3})_{4}]^{2 +} + 8 {OH}^{-} \Rightarrow 1 P^{t} + 16 {NH}_{3} + {LiBO}_{2} + 6 H_{2} 0

(1)

Fig. 5.

Two SEM micrographs showing the cross section (left) and close-up (right) of a typical IPMC

In the subsequent placement of surface electrodes, multiple reducing agents are introduced (under optimized concentrations) to carry out the reducing reaction similar to Equation (1), in addition to the platinum layer formed by the initial process of making the composite. This is clearly shown in Fig. 4 (bottom-right), where the roughened surface disappears. In general, the majority of platinum salts stays in the solution and precedes the reducing reactions and production of platinum metal. Other metals (or conductive media), which are also successfully used, include palladium, silver, gold, carbon, graphite, and carbon nanotubes. To characterize the surface morphology of the IPMC, Atomic Force Microscopy (AFM) can be used. Its capability to directly image the surface of the IPMC can provide detailed information with a resolution of a few nano-meters. In Fig. 6, a number of representative AFM images (its surface analysis) reveal the surface morphology of the IPMC's.

Fig. 6.

An atomic force microscopy surface analysis image taken on the functionally-graded composite surface-electrodes of some typical IPMC's. The scanned area is 1 μm². The brighter/darker area corresponds to a peak/valley depth of 50 nm. The surface analysis image has a view angle set at 22 degrees

As can be seen, depending on the initial surface roughening, the surface is characterized by the granular appearance of platinum metal with a peak/valley depth of approximately 50 nm. This granular nanoroughness is responsible for producing a high level of electric resistance, yet provides a porous layer that allows polar liquid movement in and out of the ionic polymer.

During the AFM study, it was also found that platinum particles are dense and, to some extent, possess coagulated shapes. Therefore, the study was extended to utilize TEM (transmission electron microscopy), to determine the size of the deposited platinum particles. Fig. 7. shows a TEM image on the penetrating edge of the IPMC. The sample was carefully prepared in the form of a small size and was ion-beam treated. The average particle size was found to be around 47 nm.

Fig. 7.

TEM micrographs of IPMC (left-Pt particles; right-A Pt particle)

Advances in 3-D fabrication of IPMC's

In a previous work Kim and Shahinpoor [2002] have reported a newly developed fabrication method that can scale-up or down the IPMC artificial muscles in a strip size of micro-to-centi-meter thickness for various soft robotic applications, using liquid form of perfluorinated ionic polymers. By meticulously evaporating the solvent (isopropyl alcohol) out of the solution, recast ionic polymer can be obtained [Kim and Shahinpoor, 2002]. A number of these samples are shown in Fig. 8.

Fig. 8.

A various shapes of IPMCs having three-dimensional shapes

Modeling and simulation

We only report advances as recent as the year 2000. de Gennes, Okumura, Shahinpoor and Kim [2000] presented the first phenomenological theory for sensing and actuation in ionic polymer metal composites. Asaka and Oguro [2000] discussed the bending of polyelectrolyte membrane-platinum composites by electric stimuli and presented a theory on actuation mechanisms in IPMC by considering the electroosmotic drag term in transport equations. Nemat-Nasser and Li [2000] presented a modeling on the electromechanical response of ionic polymer-metal composites based on electrostatic attraction/repulsion forces in IPMC's. Later, Nemat-Nasser [2002] presented a revised version of their earlier paper and stressed the role of hydrated cation transport within the clusters and polymeric networks in IPMC's. Nemat-Nasser and Wu [2003] have presented a discussion on the role of back bone ionic polymer and in particular sulfonic versus carboxylic ionic polymers, as well as, the effect of different cations such as K+, Na+, Li+, Cs+ and some organometalic cations on the actuation and sensing performance of IPMC's. Tadokoro [2000], Tadokoro, Yamagami, Takamori and Oguro [2000] and Tadokoro, Takamori and Oguro [2001] have presented an actuator model of IPMC for robotic applications on the basis of physico-chemical phenomena.

A recent comprehensive review by Shahinpoor and Kim [2004] on modeling and simulation o $\underset{\sim}{E}$ onic polymeric artificial muscles discusses the various modeling approaches for the understanding of the mechanisms of sensing and actuation of ionic polymers. The most plausible mode of actuation and sensing is expected to be the following: under the field, the cations drift, and they carry with them a certain number of water molecules depending on the hydration number n of the cation M⁽⁺⁾. When these hydrated 1 $\underset{\sim}{E}$ lecules of water carried by cations pile up near the cathode, they create a local over-pressure (see Figs 9 and 10), which tends to deform the material. A thin membrane, which was originally flat, then tends to acquire a certain spontaneous curvature $C (\underset{\sim}{E}) = 1 / ρ_{c}$ where ρ_c is the radius of curvature.

Fig. 9.

Bending of an Ionic Gel Strip Due to an Imposed Electric Field Gradient

Fig. 10.

Illustration of the actuation principle of IPMC. (a) before a voltage is applied; (b) after a voltage is applied

These observations clearly establish that the main mechanism of actuation is polar plasticizer migration in the form of cationic hydrated water as well as loose water dragged by the migration of hydrated cations, and the Coulombic type ionic redistribution and forces may play a minor role. Note that the application of an electric field creates a potential according to the Poisson's equation, such that:

ρ^{*} (x, y, z, t) = (ρ_{M +} (x, y, z, t) - ρ_{s o 3} (x, y, z, t)) N_{e}

(2)

where φ(x,y,z,t) is an electric potential, ρ.(x,y,z,t) is an electric charge density and ε is the dielectric constant of the composite. ρ*(x,y,z, t) is determined by the equivalent weight of the precursor ion containing polymer and, in particular, the molar concentration of cations (Lithium) and the charge groups in the polymer (sulfonic or carboxylic) such that:

ρ^{*} (x, y, z, t) = (ρ_{M +} (x, y, z, t) - ρ_{s o 3} (x, y, z, t)) N_{e}

(3)

where ρ_M+(x,y,z,t) and ρ_so3(x,y,z,t) are, respectively, the molal density of cations and sulfons, N is the Avogadro's number (6.023 × 10²⁶ molecules per kilogram-mole in mks units), and e is the elementary charge of an electron (−1.602 × 10⁻¹⁹ coulomb). The electric field within the ionic polymeric structure is:

\underset{\sim}{E} (x, y, z, t) = - \nabla ϕ (x, y, z, t)

(4)

Balance of forces on individual cations hydrated with n molecules of water inside the molecular network, clusters and channels based on the diffusion-drift model of ionic media due to Nernst and Plank (Nernst-Plank equation) can be stated as:

\begin{array}{l} N_{e} ρ_{M +} E_{x} (x, y, z, t) = N (ρ_{M +} M_{M +} + n ρ_{w} M_{w}) (\frac{d v_{x}}{d t}) + N ρ_{M +} η v_{x} + \\ N ρ_{M +} k T (\frac{\partial \ln (ρ_{M +} + n ρ_{w})}{\partial x}) + (\frac{\partial P}{\partial x}) \end{array}

(5)

\begin{array}{l} N_{e} ρ_{M +} E_{y} (x, y, z, t) = N (ρ_{M +} M_{M +} + n ρ_{w} M_{w}) (\frac{d v_{y}}{d t}) + N ρ_{M +} η v_{y} + \\ N ρ_{M +} k T (\frac{\partial \ln (ρ_{M +} + n ρ_{w})}{\partial y}) + (\frac{\partial P}{\partial y}) \end{array}

(6)

\begin{array}{l} N_{e} ρ_{M +} E_{z} (x, y, z, t) = N (ρ_{M +} M_{M +} + n ρ_{w} M_{w}) (\frac{d v_{z}}{d t}) + N ρ_{M +} η v_{z} + \\ N ρ_{M +} k T (\frac{\partial \ln (ρ_{M +} + n ρ_{w})}{\partial z}) + (\frac{\partial P}{\partial z}) \end{array}

(7)

where, M_M+ and M_w are the molecular weight of cations and water, respectively, P is the local osmotic fluid pressure P_f minus the local swelling pressure or stress σ*, such that P=P_f−σ*, and

e \underset{\sim}{E} (x, y, z, t) = {[e E (x, y, z, t)_{x}, e E (x, y, z, t)_{y}, e E (x, y, z, t)_{z}]}^{T}

(8)

is the force vector on an individual cation due to electro-osmotic motion of an ion in an electric field, k is the Boltzmann's constant and,

\underset{\sim}{v} (x, y, z, t) = {[v_{x} (x, y, z, t)_{x}, v_{y} (x, y, z, t), v_{z} (x, y, z, t)_{z}]}^{T}

(9)

is the velocity vector of the hydrated cations, and

\underset{\sim}{\nabla} p (x, y, z, t) = \frac{L}{K} \underset{\sim}{E} (x, y, z, t)

(10)

is the force vector of the viscous resistance to the motion of individual hydrated cations in the presence of a viscous fluid medium with a viscosity of η, and

k T \underset{\sim}{\nabla} [\ln (ρ_{M +} (x, y, z, t) + n ρ_{w} (x, y, z, t)]

(11)

is the force vector due to diffusion of individual cations and accompanying molecules of hydrated water in the polymer network with the following x, y, and z components, respectively:

k T (\frac{\partial \ln [ρ_{M +} (x, y, z, t) + n ρ_{w} (x, y, z, t)]}{\partial x})

(12)

k T (\frac{\partial \ln [ρ_{M +} (x, y, z, t) + n ρ_{w} (x, y, z, t)]}{\partial y})

(13)

k T (\frac{\partial \ln [ρ_{M +} (x, y, z, t) + n ρ_{w} (x, y, z, t)]}{\partial z})

(14)

and the force vector due to inertial effects on an individual hydrated cation is:

(M_{M +} + n M_{w}) (\frac{d v}{d t})

(15)

such that in a compact vectorial form the force balance equation reads:

\begin{array}{l} N_{e} ρ_{M +} \underset{\sim}{E} = N (ρ_{M +} M_{M +} + n ρ_{w} M_{w}) (\frac{d \underset{\sim}{v}}{d t}) + N ρ_{M +} η \underset{\sim}{v} + \\ N ρ_{M +} k T \underset{\sim}{\nabla} \ln (ρ_{M} + n ρ_{w}) + \underset{\sim}{\nabla} P_{f} \cdot {\underset{\approx}{σ}}^{*} \end{array}

(16)

where the stress tensor ${\underset{\approx}{σ}}^{*}$ can be expressed in terms of the deformation gradients in a non-linear manner such as in Neo-Hookean or Mooney-Rivlin type constitutive equations as suggested by Segalman, Adolf, Witkowski and Shahinpoor, [1991–1993]. The flux of hydrated cations is given by:

\underset{\sim}{Q} = [ρ_{M +} (x, y, z, t) + η ρ_{w} (x, y, z, t)] \underset{\sim}{v} (x, y, z, t)

(17)

Such that the equation of continuity becomes:

(\frac{\partial [ρ_{M +} (x, y, z, t) + η ρ_{w} (x, y, z, t)]}{\partial t}) = - \underset{\sim}{\nabla} \underset{\sim}{Q}

(18)

Equations 2 through 18 are the governing equations for the dynamics of ionic polymer metal composites as biomimetic distributed nanosensors, nanoactuators, soft nanorobots and artificial muscles.

Here below, a linear steady state version of the formulation is presented to obtain some preliminary understanding of the complex ionic diffusion and drift in these electronic materials. Figs 9 and 10 depict the general structure of the IPMC's after chemical plating and compose manufacturing. The structure bends towards the anode. The nature of water and hydrated ions transport within the IPMC can affect the moduli at different frequencies.

Let us now summarize the underlying principle of the IPMC's actuation and sensing capabilities, which can be described by the standard Onsager formulation using linear irreversible thermodynamics. When static conditions are imposed, a simple description of mechanoelectric effect is possible based upon two forms of transport: ion transport (with a current density $\underset{\sim}{J}$ , normal to the material) and solvent transport (with a flux $\underset{\sim}{Q}$ we can assume that this term is water flux). The conjugate forces include the electric field $\underset{\sim}{E}$ , and the pressure gradient, $- \underset{\sim}{\nabla} p$ . The resulting equation has the concise form of,

\underset{\sim}{J} (x, y, z, t) = σ \underset{\sim}{E} (x, y, z, t) - L_{12} \underset{\sim}{\nabla} p (x, y, z, t)

(19)

\underset{\sim}{Q} (x, y, z, t) = L_{21} \underset{\sim}{E} (x, y, z, t) - K \underset{\sim}{\nabla} p (x, y, z, t)

(20)

where σ and K are the material electric conductance and the Darcy permeability, respectively. A cross coefficient is usually L= L₁₂ = L₂₁. The simplicity of the above equations provides a compact view of the underlying principles of both actuation, transduction and sensing of the IPMCs as also shown in Fig. 10. When we measure the direct effect (actuation mode, Fig. 6. 29), we work (ideally) with electrodes which are impermeable to water, and thus we have $= \underset{\sim}{Q}$ . This gives:

\underset{\sim}{\nabla} p (x, y, z, t) = \frac{L}{K} \underset{\sim}{E} (x, y, z, t)

(21)

This $\underset{\sim}{\nabla} p (x, y, z, t)$ will, in turn, induce a curvature $\underset{\sim}{κ}$ proportional to $\underset{\sim}{\nabla} p (x, y, z, t)$ The relationships between the curvature $\underset{\sim}{κ}$ and pressure gradient $\underset{\sim}{\nabla} p (x, y, z, t)$ are fully derived and described in de Gennes, Okumura, Shahinpoor and Kim [2000]. Let us just mention that (1/ρ_c)=M(E)/YI, where M(E) is the local induced bending moment and is a function of the imposed electric field E, Y is the Young's modulus (elastic stiffness) of the strip which is a function of the hydration H of the IPMC and I is the moment of inertia of the strip. Note that locally M(E) is related to the pressure gradient such that in a simplified scalar format:

\nabla \nabla p (x, y, z, t) = (\frac{2 P}{t^{*}}) = (\frac{M}{I}) = \frac{Y}{ρ_{c}} = Y_{\underset{\sim}{K}}

(22)

Now from equation (22) it is clear that the vectorial form of curvature ${\underset{\sim}{k}}_{E}$ is related to the imposed electric field E by:

{\underset{\sim}{k}}_{E} ≅ [\frac{2 {\underset{\sim}{δ}}_{max}}{l_{g}^{2} + {\underset{\sim}{δ}}_{max}^{2}}] ≅ \frac{2 {\underset{\sim}{δ}}_{max}}{l_{g}^{2}} ≅ (\frac{L}{K Y}) \underset{\sim}{E}

(23)

Based on this simplified model the tip bending deflection δ_max of an IPMC strip of length l_g should be almost linearly related to the imposed electric field due to the fact that:

{\underset{\sim}{k}}_{E} ≅ [\frac{2 {\underset{\sim}{δ}}_{max}}{l_{g}^{2} + {\underset{\sim}{δ}}_{max}^{2}}] ≅ \frac{2 {\underset{\sim}{δ}}_{max}}{l_{g}^{2}} ≅ (\frac{L}{K Y}) \underset{\sim}{E}

(24)

The experimental deformation characteristics depicted in Fig. 11. Note that the results depicted in Fig. 11 are clearly consistent with the above predictions obtained by the above linear irreversible thermodynamics formulation which is also consistent with equation 23 and 24 in the steady state conditions and has been used to estimate the value of the Onsager coefficient L to be of the order of 10⁻⁸ m²/V-s. Other parameters have been experimentally measured to be K~10⁻¹⁸m²/CP, σ~1A/mV or S/m. Fig. 12 depicts the experimental results of IPMC deflection under a step voltage with and without a dispersant polyvinyl pyrolidone (PVP). This completes our coverage of mechnoelectrical phenomena in ionic polymers artificial muscles. More extensive modeling is reported in Shahinpoor and Kim (2004).

Fig. 11.

Actuation under a Low Frequency Electric Field to Minimize the Effect of Loose Water Back Diffusion

Fig. 12.

Step Response Displacement Characteristics of IPMC Samples (δ: arc length, Lo: effective beam length), Lo = 1.0 inch (left) and Lo = 1.5 inch (right)

Advances in sensing and transduction

A recent paper by Shahinpoor [2004] presents a review on sensing and transduction properties of ionic polymer conductor composites. Shahinpoor (1995 and 1996), reported that IPMC's by themselves and not in a hydrogen pressure electrochemical cells as reported by Sadeghipour, Salomom and Naogi [1992] can generate electrical power like an electromechanical battery if flexed, bent or squeezed. Shahinpoor [1995, 1996] reported the discovery of a new effect in ionic polymeric ionic polymeric gels, namely the ionic flexogelectric effect in which flexing, compression or loading of IPMC strips in air created an output voltage like a dynamic sensor or a transducer converting mechanical energy to electrical energy. Keshavarzi, Shahinpoor, Kim and Lantz [1999] applied the transduction capability of IPMC to the measurement of blood pressure, pulse rate, and rhythm measurement using thin sheets of IPMC's. Motivated by the idea of measuring pressure in the human spine, Ferrara, Shahinpoor, Kim, Schreyer, Keshavarzi, Benzel, and Lantz [1999] applied pressure across the thickness of an IPMC strip while measuring the output voltage.

Typically, flexing of such material in a cantilever form sets them into a damped vibration mode that can generate a similar damped signal in the form of electricalpower (voltage or current) as shown in Fig. 13. The experimental results for mechanoelectrical voltage generation of IPMC's in a flexing mode are shown in Fig. 14(a). Fig. 14(a) also depicts the current output for a sample of thin sheets of IPMC's. Fig. 14(b) depicts the power output corresponding to the data presented in Fig. 14(a).

Fig. 13.

A typical voltage response of an IPMC

Fig. 14.

Typical voltage/current output (a) and power output (b) of IPMC samples. Fig. 15 depicts the output voltage of the thin sheet IPMC batteries under 200N normal load. The output voltage is generally about 2 mV/cm length of the IPMC sheet

Fig. 15.

Out voltage due to normal impact of 200N load on a 2cmx2cmx0.2mm IPMC sample

The experimental results showed that almost a linear relationship exists between the voltage output and the imposed displacement of the tip of the IMPC sensor (Fig. 11). IPMC sheets can also generate power under normal pressure. Thin sheets of IPMC were stacked and subjected to normal pressure and normal impacts and were observed to generate large output voltage. Endo-ionic motion within IPMC thin sheet batteries produced an induced voltage across the thickness of these sheets when a normal or shear load was applied.

A material testing system (MTS) was used to apply consistent pure compressive loads of 200N and 350N across the surface of an IPMC 2 × 2cm sheet. The output pressure response for the 200N load (73 psi) was 80mV in amplitude and for the 350N (127 psi) it was 108 mV. This type of power generation may be useful in the heels of boots and shoes or places where there are a lot of foot or car traffic.

Product development

Environmental Robots Incorporated (www.environmental-robots.com) is currently the world's leader in developing medical and industrial products based on ionic polymer metal composites (IPMC's) and ionic polymer conductor composites (IPCC's) as distributed biomimetic nanosensors, nanoactuators, nanotransducers and artificial muscles. These products include two artificial muscle science kits for bothcontractile fiber bundles of PAN muscles as well as bending flexing and sensing Silver and Platinum based IPMC's, assortment of ionic polymeric artificial muscles, assortment of polymeric micro muscles, sensor and actuators packages, deluxe packages of ionic polymeric muscles, dynamic signal generators to drive the ionic polymeric muscles and a host of other ionic polymeric muscle products.

Some medcial and industrial applications

Due to space and size limitation for papers in this publication, no detailed explanation of the current medical and industrial products based on ionic polymeric nanosensors, nanoactuators, nanotransducers and artificial muscles can be presented here.

But it can be briefly categorized in to the following list: Mechanical Grippers, Biomimetic Noiseless Swimming Robotic Fish and Fin Actuators, Diaphragm Pump Designs, Linear Actuators Metering Valves, Musical Instruments, Flat Key Boards, Data Attire and Braille Alphabet, Artificial Ventricular or Cardiac-Assist Muscles, Surgical Tool, Peristaltic Pumps, Artificial Smooth Muscle Actuators, Composite Wing-flap, Resonant Flying Machine and a host of others, as discussed in references [Shahinpoor, Kim and Mojarrad, 2004] and [Shahinpoor and Kim, 2004]. Figs 16 and 17 depict some of these products.

Fig. 16.

Some of the proposed and developed products. (a) biomimetic robotic fish and caudal fin actuators, (b) diaphragm micropump, (c) one string musical instrument, (d) linear robotic platform actuators made with IPMC's

Fig. 17.

Some of the proposed and developed products. (a) is a data glove (attire), (b) IPMC heart compression/assist band, (c) IPMC mini-heart compression and assist device, (d) wing flapping flying system made with IPMC's, courtesy of ERI and Ohio Aerospace Institute (OAI)

Conclusions

Table 1 below depicts the general properties of ionic polymeric muscles for soft robotic applications

Table 1.

Current Capabilities of IPMC Materials

Young's Modulus, E	Up to 2 GPa
Shear Modulus, G	Up to 1 GPa
Poisson's ratio, ν	Typical: 0.3–0.4
Power density (W/volume))	Up to 200 mW/cc
Max force density (Cantilever Mode)	Up to 50 Kgf/Kg
Max displacement/strain	Up to 4% linear strain
Bandwidth (speed)	Over kHz in a cantilever vibratory mode for soft robotic actuation Over MHz for soft sensing in cantilever mode
Resolution (force and displacement control)	Displacement accuracy down to 1 micron Force resolution down to 1 mg
Efficiency (electromechanical)	More than 25 % (frequency dependent) for actuation More than 90% for sensing
Density	Down to 1.8 g/cm³

Footnotes

Acknowledgement

This research was partially supported by Ohio Aerospace Institute in Cleveland, Ohio and Environmental Robots Inc. in Albuquerque, New Mexico. Thanks are extended to Anthony Colozza and Curtis Smith of OAI for their support and encouragement.

References

Adolf

Shahinpoor

Segalman

, and Witkowski

, (1993). Electrically Controlled Polymeric Gel Actuators, US Patent and Trademark Office, U.S. Patent #5,250,167, October 13

Asaka

, and Oguro

, (2000). Bending of Polyelectrolyte Membrane Platinum Composites By Electric Stimuli, Part II. Response Kinetics, J. Electroanalytical Chemistry, vol. 480, pp. 186–198

de Gennes

P. G.

Okumura

Shahinpoor

, and Kim

K.J.

, (2000) presented the first phenomenological theory for sensing and actuation in ionic polymer metal composites.

Ferrara

Shahinpoor

Kim

K. J.

Schreyer

Keshavarzi

Benzel

and Lantz

Jeffrey

, (1999). Use of Ionic Polymer-Metal Composites (IPMCs) As A Pressure Transducer In the Human Spine, Proc. Elactroactive Polymers Symposium, San Diego, Calif., SPIE Publication Number3669-45, pp. 394–401

Keshavarzi

Shahinpoor

Mohsen

Kim

Kwang J.

, and Lantz

Jeffrey

, (1999). Blood Pressure, Pulse Rate, and Rhythm Measurement Using Ionic Polymer-Metal Composite Sensors, Proc. Elactroactive Polymers Symposium, San Diego, Calif., SPIE Publication Number 3669-36, pp. 369–376

Kim

K. J.

and Shahinpoor

, (2002). A Novel Method of Manufacturing Three-Dimensional Ionic Polymer-Metal Composites (IPMC's) Biomimetic Sensors, Actuators and Artificial Muscle, Polymer, Vol. 43/3, pp.797–802

Kim

K.J.

and Shahinpoor

, (2003). Ionic Polymer-Metal Composites – II. Manufacturing Techniques, Smart Materials and Structures Int. J., Institute of Physics (IOP) Publication, Philadelphia, PA., USA, Vol. 12, No. 1, pp. 65–79.

Nemat-Nasser

, (2002). Micro-Mechanics of Actuation of Ionic Polymer-metal Composites (IPMCs), Journal of Applied Physics, Vol. 92, No. 5, pp. 2899–2915

Nemat-Nasser

, and Li

J. Y.

, (2000). Electromechanical Response of Ionic Polymer-Metal Composites, J. Applied Physics, Vol. 87, No. 7 pp. 3321–3331.

10.

Nemat-Nasser

, and Wu

, (2003). Comparative Experimental Study of Ionic Polymer-Metal Composites With Different Backbone Ionomers And In Various Cation Forms, J. Applied Physics, Vol. 93, pp. 5255–5267

11.

Sadeghipour

Salomon

and Neogi

, (1992). Development of A Novel Electrochemically Active Membrane and Smart Material based Vibration Sensor/Damper, Smart Materials and Structures Journal, Institute of Physics Publication, Philadelphia, Pa., vol. 1, pp. 172–179

12.

Segalman

D. J.

Witkowski

W. R.

Adolf

D. B.

Shahinpoor

, (1992). Theory and Application of Electrically Controlled Polymeric Gels, Smart Materials and Structures, Institute of Physics Publication, Philadelphia, Pa., vol. 1, pp.95–100

13.

Segalman

Witkowski

Adolf

and Shahinpoor

, (1992). Numerical Simulation of Dynamic Behavior of Polymeric Gels, Proc. 1st. Int. Conf. Intelligent Materials, ICIM'92, Tsukube, Japan, July, Technomic Publishing Co., pp. 310–313

14.

Segalman

Witkowski

Adolf

and Shahinpoor

, (1992). Theory of Electrically Controlled Polymeric Muscles As Active Materials in Adaptive Structures, Int. J. Smart Materials & Structures, Institute of Physics Publication, Philadelphia, Pa., vol.1, no.1, pp.44–54

15.

Segalman

Witkowski

Rao

Adolf

Doug

and Shahinpoor

, (1993). Finite Element Simulation of the 2D Collapse of A Polyelectrolyte Gel Disk, Proc.(1993) SPIE North American Conference on Smart Structures and Materials, February 93, Albuquerque, NM, vol. 1916, pp. 14–22

16.

Segalman

Witkowski

Adolf

Shahinpoor

, (1991). Electrically Controlled Polymeric Gels as Active Materials in Adaptive Structures, Proceedings of the ADPA/AIAA/ASME/SPIE Conference on Active Materials and Adaptive Structures, pp.335–345

17.

Shahinpoor

, (1992). Conceptual Design, Kinematics and Dynamics of Swimming Robotic Structures Using Ionic Polymeric Gel Muscles, Smart Materials and Structures, Institute of Physics (IOP) Publication, Philadelphia, PA., USA, Vol. 1, No. 1. pp. 91–94

18.

Shahinpoor

, (1993). Microelectro-Mechanics of Ionic Polymeric Gels As Artificial Muscles For Robotic Applications, Proc. (1993) IEEE International Conference on Robotics & Automation, Atlanta, Georgia, May 93, Vol. 2, pp.380–385

19.

Shahinpoor

, (1995). A New Effect in Ionic Polymeric Gels: The Ionic Flexogelectric Effect, Proc. SPIE (1995) North American Conference on Smart Structures Materials, February 28 March 2 (1995), San Diego, California, vol. 2441, paper No. 05.

20.

Shahinpoor

, (1996). The Ionic Flexogelectric Effect, Proc. (1996) Third International Conference on Intelligent Materials, ICIM'96, and Third European Conference on Smart Structures and Materials, Lyon, France, pp. 1006–1011

21.

Shahinpoor

, (2004). Smart Thin Sheet Batteries Made With Ionic Polymer-Metal Composites (IPMC's), IMECE2004-60954, Proceedings of ASME-IMECE2004, 2004 ASME International Mechanical Engineering Congress and RD&D Exposition, ASME Publication, November 13–19, 2004, Anaheim Convention center/Hilton, Anaheim, California

22.

Shahinpoor

, and Kim

K. J.

, (2001). Ionic Polymer-Metal Composites – I. Fundamentals,” (Review Paper), Smart Materials and Structures Int. J., Institute of Physics (IOP) Publication, Philadelphia, PA., USA, Vol. 10, pp. 819–833

23.

Shahinpoor

, and Kim

K. J.

, (2004). Ionic Polymer-Metal Composites – III. Modeling and Simulation As Biomimetic Sensors, Actuators, Transducers and Artificial Muscles (Review Paper), Smart Materials and Structures Int. J., Institute of Physics (IOP) Publication, Philadelphia, PA., USA, vol 13, No. 4, pp. 1362–1388.

24.

Shahinpoor

, and Kim

K. J.

, (2005). Ionic Polymer-Metal Composites – IV. Industrial and Medical Applications, (Review Paper), Smart Materials and Structures Int. J., Institute of Physics (IOP) Publication, Philadelphia, PA., USA, Vol. 14, No. 1, pp. 197–214.

25.

Shahinpoor

Kim

K.J.

and Mojarrad

, (2004). Ionic Polymeric Artificial Muscles, ERI/AMRI Press, Albuquerque, New Mexico.

26.

Tadokoro

, (2000). An Actuator Model of ICPF For Robotic Applications On the Basis of Physico-Chemical Hypotheses, Proc. IEEE, ICRA, pp. 1340–1346

27.

Tadokoro

Takamori

, and Oguro

, (2001). Application of the Nafion-Platinum Composite Actuator, Proceedings of the SPIE, SPIE Publication, Vol. 4329, pp. 28–42

28.

Tadokoro

Yamagami

Takamori

, and Oguro

, (2000). Modeling of Nafion-Pt Composite Actuators (ICPF) by Ionic Motion, Proceedings of the SPIE, SPIE Publication, Vol. 3987, pp. 92–102