file:EAP-example2.png, (a) Cartoon drawing of an EAP gripping device.
(b) A voltage is applied and the EAP fingers deform in order to release the ball.
(c) When the voltage is removed, the EAP fingers return to their original shape and grip the ball An electroactive polymer (EAP) is a polymer that exhibits a change in size or shape when stimulated by an electric field. The most common applications of this type of material are in

actuator An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover". An actuator requires a control device (controlled by control signal) a ...

s and sensors. A typical characteristic property of an EAP is that they will undergo a large amount of deformation while sustaining large

force In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a ...

s. The majority of historic actuators are made of

ceramic A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelai ...

piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word ' ...

materials. While these materials are able to withstand large forces, they commonly will only deform a fraction of a percent. In the late 1990s, it has been demonstrated that some EAPs can exhibit up to a 380% strain, which is much more than any ceramic actuator. One of the most common applications for EAPs is in the field of

robotics Robotics is an interdisciplinarity, interdisciplinary branch of computer science and engineering. Robotics involves design, construction, operation, and use of robots. The goal of robotics is to design machines that can help and assist human ...

in the development of artificial muscles; thus, an electroactive polymer is often referred to as an

artificial muscle Artificial muscles, also known as muscle-like actuators, are materials or devices that mimic natural muscle and can change their stiffness, reversibly contract, expand, or rotate within one component due to an external stimulus (such as voltage, cur ...

History

The field of EAPs emerged back in 1880, when

Wilhelm Röntgen Wilhelm Conrad Röntgen (; ; 27 March 184510 February 1923) was a German mechanical engineer and physicist, who, on 8 November 1895, produced and detected electromagnetic radiation in a wavelength range known as X-rays or Röntgen rays, an achie ...

designed an experiment in which he tested the effect of an electrostatic field on the mechanical properties of a stripe of natural rubber. The rubber stripe was fixed at one end and was attached to a

mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different element ...

at the other. Electric charges were then sprayed onto the rubber, and it was observed that the length changed. It was in 1925 that the first

polymer was discovered (

Electret An electret (formed as a portmanteau of ''electr-'' from "electricity" and ''-et'' from "magnet") is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric f ...

). Electret was formed by combining

carnauba wax Carnauba (; pt, carnaúba ), also called Brazil wax and palm wax, is a wax of the leaves of the carnauba palm '' Copernicia prunifera'' (synonym: ''Copernicia cerifera''), a plant native to and grown only in the northeastern Brazilian states of ...

, rosin and

beeswax Beeswax (''cera alba'') is a natural wax produced by honey bees of the genus ''Apis''. The wax is formed into scales by eight wax-producing glands in the abdominal segments of worker bees, which discard it in or at the hive. The hive workers ...

, and then cooling the solution while it is subject to an applied DC

electrical bias In electronics, biasing is the setting of DC (direct current) operating conditions (current and voltage) of an active device in an amplifier. Many electronic devices, such as diodes, transistors and vacuum tubes, whose function is processing ...

. The mixture would then solidify into a polymeric material that exhibited a

piezoelectric effect Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word '' ...

. Polymers that respond to environmental conditions, other than an applied

electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The movin ...

, have also been a large part of this area of study. In 1949 Katchalsky ''et al.'' demonstrated that when collagen filaments are dipped in acid or

alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of ...

solutions, they would respond with a change in

volume Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). Th ...

. The collagen filaments were found to expand in an

acidic In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a s ...

solution and contract in an

solution. Although other stimuli (such as pH) have been investigated, due to its ease and practicality most research has been devoted to developing polymers that respond to electrical stimuli in order to mimic biological systems. The next major breakthrough in EAPs took place in the late 1960s. In 1969 Kawai demonstrated that

polyvinylidene fluoride Polyvinylidene fluoride or polyvinylidene difluoride (PVDF) is a highly non-reactive thermoplastic fluoropolymer produced by the polymerization of vinylidene difluoride. PVDF is a specialty plastic used in applications requiring the highest pur ...

(PVDF) exhibits a large piezoelectric effect. This sparked research interest in developing other polymers systems that would show a similar effect. In 1977 the first electrically

conducting polymer Conductive polymers or, more precisely, intrinsically conducting polymers (ICPs) are organic polymers that conduct electricity. Such compounds may have metallic conductivity or can be semiconductors. The biggest advantage of conductive polymer ...

s were discovered by

Hideki Shirakawa is a Japanese chemist, engineer, and Professor Emeritus at the University of Tsukuba and Zhejiang University. He is best known for his discovery of conductive polymers. He was co-recipient of the 2000 Nobel Prize in Chemistry jointly with ...

''et al.'' Shirakawa along with

Alan MacDiarmid Alan Graham MacDiarmid, ONZ FRS (14 April 1927 – 7 February 2007) was a New Zealand-born American chemist, and one of three recipients of the Nobel Prize for Chemistry in 2000. Early life and education MacDiarmid was born in Masterton, Ne ...

and

Alan Heeger Alan Jay Heeger (born January 22, 1936) is an American physicist, academic and Nobel Prize laureate in chemistry. Heegar was elected as a member into the National Academy of Engineering in 2002 for co-founding the field of conducting polymers a ...

demonstrated that

polyacetylene Polyacetylene (IUPAC name: polyethyne) usually refers to an organic polymer with the repeating unit . The name refers to its conceptual construction from polymerization of acetylene to give a chain with repeating olefin groups. This compound ...

was electrically conductive, and that by doping it with

iodine Iodine is a chemical element with the Symbol (chemistry), symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , ...

vapor, they could enhance its conductivity by 8 orders of magnitude. Thus the conductance was close to that of a metal. By the late 1980s a number of other polymers had been shown to exhibit a

or were demonstrated to be conductive. In the early 1990s,

ionic polymer-metal composite Ionic or Ionian may refer to: Arts and entertainment * Ionic meter, a poetic metre in ancient Greek and Latin poetry * Ionian mode, a musical mode or a diatonic scale Places and peoples * Ionian, of or from Ionia, an ancient region in western A ...

s (IPMCs) were developed and shown to exhibit electroactive properties far superior to previous EAPs. The major advantage of IPMCs was that they were able to show activation (deformation) at

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge t ...

s as low as 1 or 2

volt The volt (symbol: V) is the unit of electric potential, electric potential difference ( voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827). D ...

s. This is orders of magnitude less than any previous EAP. Not only was the

activation energy In chemistry and physics, activation energy is the minimum amount of energy that must be provided for compounds to result in a chemical reaction. The activation energy (''E''a) of a reaction is measured in joules per mole (J/mol), kilojoules p ...

for these materials much lower, but they could also undergo much larger deformations. IPMCs were shown to exhibit anywhere up to 380% strain, orders of magnitude larger than previously developed EAPs. In 1999,

Yoseph Bar-Cohen Yoseph Bar-Cohen is a physicist at the Jet Propulsion Laboratory who specializes in Electroactive polymers, electroactive materials and Ultrasonic testing, ultrasonic nondestructive evaluation (NDE), and is responsible for the Nondestructive Evalu ...

proposed the Armwrestling Match of EAP Robotic Arm Against Human Challenge. This was a challenge in which research groups around the world competed to design a robotic arm consisting of EAP muscles that could defeat a human in an

arm wrestling Arm wrestling (also spelled armwrestling) is a sport with two opponents who face each other with their bent elbows placed on a table and hands firmly gripped, who then attempt to force the opponent's hand down to the table top ("pin" them). The s ...

match. The first challenge was held at the Electroactive Polymer Actuators and Devices Conference in 2005. Another major milestone of the field is that the first commercially developed device including EAPs as an artificial muscle was produced in 2002 by Eamex in Japan. This device was a fish that was able to swim on its own, moving its tail using an EAP muscle. But the progress in practical development has not been satisfactory.

DARPA The Defense Advanced Research Projects Agency (DARPA) is a research and development agency of the United States Department of Defense responsible for the development of emerging technologies for use by the military. Originally known as the Ad ...

-funded research in the 1990s at

SRI International SRI International (SRI) is an American nonprofit organization, nonprofit scientific research, scientific research institute and organization headquartered in Menlo Park, California. The trustees of Stanford University established SRI in 1946 as ...

and led by Ron Pelrine developed an electroactive polymer using silicone and acrylic polymers; the technology was spun off into the company

Artificial Muscle Artificial muscles, also known as muscle-like actuators, are materials or devices that mimic natural muscle and can change their stiffness, reversibly contract, expand, or rotate within one component due to an external stimulus (such as voltage, cur ...

in 2003, with industrial production beginning in 2008. In 2010, Artificial Muscle became a subsidiary of

Bayer MaterialScience Covestro AG is a German company which produces a variety of polyurethane and polycarbonate based raw materials. Products include isocyanates and polyols for cellular foams, thermoplastic polyurethane and polycarbonate pellets, as well as polyure ...

Types

EAP can have several configurations, but are generally divided in two principal classes: Dielectric and Ionic.

Dielectric

Dielectric EAPs are materials in which actuation is caused by

electrostatic Electrostatics is a branch of physics that studies electric charges at rest (static electricity). Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for am ...

forces between two electrodes which squeeze the polymer. Dielectric elastomers are capable of very high strains and are fundamentally a capacitor that changes its capacitance when a voltage is applied by allowing the polymer to compress in thickness and expand in area due to the electric field. This type of EAP typically requires a large actuation voltage to produce high electric fields (hundreds to thousands of

s), but very low

electrical Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...

power consumption. Dielectric EAPs require no power to keep the actuator at a given position. Examples are electrostrictive polymers and dielectric elastomers.

Ferroelectric polymers

Ferroelectric polymers Ferroelectric polymers are a group of crystalline polar polymers that are also ferroelectric, meaning that they maintain a permanent electric polarization that can be reversed, or switched, in an external electric field. Ferroelectric polymers, s ...

are a group of crystalline polar polymers that are also

ferroelectric Ferroelectricity is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. All ferroelectrics are also piezoelectric and pyroelectric, with the ad ...

, meaning that they maintain a permanent electric polarization that can be reversed, or switched, in an external electric field. Ferroelectric polymers, such as

(PVDF), are used in acoustic transducers and electromechanical actuators because of their inherent

response, and as heat sensors because of their inherent pyroelectric response. Figure 1: Structure of Poly(vinylidene fluoride)

Electrostrictive graft polymers

300px, left, Figure 2: Cartoon of an electrostrictive graft polymer. Electrostrictive graft polymers consist of flexible backbone chains with branching side chains. The side chains on neighboring backbone polymers cross link and form crystal units. The backbone and side chain crystal units can then form polarized monomers, which contain atoms with partial charges and generate dipole moments, shown in Figure 2. When an electrical field is applied, a force is applied to each partial charge and causes rotation of the whole polymer unit. This rotation causes electrostrictive strain and deformation of the polymer.

Liquid crystalline polymers

Main-chain liquid crystalline polymers have mesogenic groups linked to each other by a flexible spacer. The mesogens within a backbone form the mesophase structure causing the polymer itself to adopt a conformation compatible with the structure of the mesophase. The direct coupling of the liquid crystalline order with the polymer conformation has given main-chain liquid crystalline elastomers a large amount of interest. The synthesis of highly oriented elastomers leads to have a large strain thermal actuation along the polymer chain direction with temperature variation resulting in unique mechanical properties and potential applications as mechanical actuators.

Ionic

* Ionic EAPs, in which actuation is caused by the displacement of ions inside the polymer. Only a few volts are needed for actuation, but the ionic flow implies a higher electrical power needed for actuation, and energy is needed to keep the actuator at a given position. Examples of ionic EAPS are

conductive polymer Conductive polymers or, more precisely, intrinsically conducting polymers (ICPs) are organic polymers that conduct electricity. Such compounds may have metallic conductivity or can be semiconductors. The biggest advantage of conductive polymer ...

s (IPMCs), and responsive gels. Yet another example is a Bucky gel actuator, which is a polymer-supported layer of

polyelectrolyte Polyelectrolytes are polymers whose repeating units bear an electrolyte group. Polycations and polyanions are polyelectrolytes. These groups dissociate in aqueous solutions (water), making the polymers charged. Polyelectrolyte properties are th ...

material consisting of an

ionic liquid An ionic liquid (IL) is a salt in the liquid state. In some contexts, the term has been restricted to salts whose melting point is below a specific temperature, such as . While ordinary liquids such as water and gasoline are predominantly made of ...

sandwiched between two

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials ...

layers consisting of a gel of ionic liquid containing single-wall

carbon nanotube A scanning tunneling microscopy image of a single-walled carbon nanotube Rotating single-walled zigzag carbon nanotube A carbon nanotube (CNT) is a tube made of carbon with diameters typically measured in nanometers. ''Single-wall carbon nan ...

s. The name comes from the similarity of the gel to the paper that can be made by filtering carbon nanotubes, the so-called buckypaper.

Electrorheological fluid

Electrorheological fluids change the viscosity of a solution with the application of an electric field. The fluid is a suspension of polymers in a low dielectric-constant liquid. With the application of a large electric field the viscosity of the suspension increases. Potential applications of these fluids include shock absorbers, engine mounts and acoustic dampers.

Ionic polymer-metal composite

Ionic polymer-metal composites consist of a thin ionomeric membrane with noble metal electrodes plated on its surface. It also has cations to balance the charge of the anions fixed to the polymer backbone. They are very active

s that show very high deformation at low applied voltage and show low impedance. Ionic polymer-metal composites work through electrostatic attraction between the cationic counter ions and the cathode of the applied electric field, a schematic representation is shown in Figure 3. These types of polymers show the greatest promise for bio-mimetic uses as collagen fibers are essentially composed of natural charged ionic polymers. Nafion and Flemion are commonly used ionic polymer metal composites.

Stimuli-responsive gels

Stimuli-responsive gels (hydrogels, when the swelling agent is an aqueous solution) are a special kind of swellable polymer networks with volume phase transition behaviour. These materials change reversibly their volume, optical, mechanical and other properties by very small alterations of certain physical (e.g. electric field, light, temperature) or chemical (concentrations) stimuli. The volume change of these materials occurs by swelling/shrinking and is diffusion-based. Gels provide the biggest change in volume of solid-state materials. Combined with an excellent compatibility with micro-fabrication technologies, especially stimuli-responsive hydrogels are of strong increasing interest for microsystems with sensors and actuators. Current fields of research and application are chemical sensor systems, microfluidics and multimodal imaging systems.

Comparison of dielectric and ionic EAPs

Dielectric polymers are able to hold their induced displacement while activated under a DC voltage. This allows dielectric polymers to be considered for robotic applications. These types of materials also have high mechanical energy density and can be operated in air without a major decrease in performance. However, dielectric polymers require very high activation fields (>10 V/µm) that are close to the breakdown level. The activation of ionic polymers, on the other hand, requires only 1-2 volts. They however need to maintain wetness, though some polymers have been developed as self-contained encapsulated activators which allows their use in dry environments. Ionic polymers also have a low electromechanical coupling. They are however ideal for bio-mimetic devices.

Characterization

While there are many different ways electroactive polymers can be characterized, only three will be addressed here: stress–strain curve, dynamic mechanical thermal analysis, and dielectric thermal analysis.

Stress–strain curve

250px, Figure 4: The unstressed polymer spontaneously forms a folded structure, upon application of a stress the polymer regains its original length. Stress strain curves provide information about the polymer's mechanical properties such as the brittleness, elasticity and yield strength of the polymer. This is done by providing a force to the polymer at a uniform rate and measuring the deformation that results. An example of this deformation is shown in Figure 4. This technique is useful for determining the type of material (brittle, tough, etc.), but it is a destructive technique as the stress is increased until the polymer fractures.

Dynamic mechanical thermal analysis (DMTA)

Both dynamic mechanical analysis is a non destructive technique that is useful in understanding the mechanism of deformation at a molecular level. In DMTA a sinusoidal stress is applied to the polymer, and based on the polymer's deformation the

elastic modulus An elastic modulus (also known as modulus of elasticity) is the unit of measurement of an object's or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. The elastic modulus of an object i ...

and damping characteristics are obtained (assuming the polymer is a damped harmonic oscillator). Elastic materials take the mechanical energy of the stress and convert it into potential energy which can later be recovered. An ideal spring will use all the potential energy to regain its original shape (no damping), while a liquid will use all the potential energy to flow, never returning to its original position or shape (high damping). A viscoeleastic polymer will exhibit a combination of both types of behavior.

Dielectric thermal analysis (DETA)

DETA is similar to DMTA, but instead of an alternating mechanical force an alternating electric field is applied. The applied field can lead to polarization of the sample, and if the polymer contains groups that have permanent dipoles (as in Figure 2), they will align with the electrical field. The

permittivity In electromagnetism, the absolute permittivity, often simply called permittivity and denoted by the Greek letter ''ε'' ( epsilon), is a measure of the electric polarizability of a dielectric. A material with high permittivity polarizes more i ...

can be measured from the change in amplitude and resolved into dielectric storage and loss components. The

electric displacement field In physics, the electric displacement field (denoted by D) or electric induction is a vector field that appears in Maxwell's equations. It accounts for the effects of free and bound charge within materials. "D" stands for "displacement", as i ...

can also be measured by following the current. Once the field is removed, the dipoles will relax back into a random orientation.

Applications

EAP materials can be easily manufactured into various shapes due to the ease in processing many polymeric materials, making them very versatile materials. One potential application for EAPs is that they can potentially be integrated into

microelectromechanical systems Microelectromechanical systems (MEMS), also written as micro-electro-mechanical systems (or microelectronic and microelectromechanical systems) and the related micromechatronics and microsystems constitute the technology of microscopic devices, ...

(MEMS) to produce smart actuators.

Artificial muscles

As the most prospective practical research direction, EAPs have been used in artificial muscles. Their ability to emulate the operation of biological muscles with high

fracture toughness In materials science, fracture toughness is the critical stress intensity factor of a sharp crack where propagation of the crack suddenly becomes rapid and unlimited. A component's thickness affects the constraint conditions at the tip of a ...

, large actuation strain and inherent vibration damping draw the attention of scientists in this field. EAPs have even successfully been used to make a type of hand.

Tactile displays

In recent years, "electro active polymers for refreshable

Braille Braille (Pronounced: ) is a tactile writing system used by people who are visually impaired, including people who are blind, deafblind or who have low vision. It can be read either on embossed paper or by using refreshable braille display ...

displays" has emerged to aid the visually impaired in fast reading and computer assisted communication. This concept is based on using an EAP actuator configured in an array form. Rows of

s on one side of an EAP film and columns on the other activate individual elements in the array. Each element is mounted with a Braille dot and is lowered by applying a voltage across the thickness of the selected element, causing local thickness reduction. Under computer control, dots would be activated to create tactile patterns of highs and lows representing the information to be read.

Visual and tactile impressions of a virtual surface are displayed by a high resolution tactile display, a so-called "artificial skin" (Fig.6) . These monolithic devices consist of an array of thousands of multimodal modulators (actuator pixels) based on stimuli-responsive hydrogels. Each modulator is able to change individually their transmission, height and softness. Besides their possible use as graphic displays for visually impaired such displays are interesting as free programmable keys of touchpads and consoles.

Microfluidics

EAP materials have huge potential for microfluidics e.g. as drug delivery systems, microfluidic devices and

lab-on-a-chip A lab-on-a-chip (LOC) is a device that integrates one or several laboratory functions on a single integrated circuit (commonly called a "chip") of only millimeters to a few square centimeters to achieve automation and high-throughput screening. ...

. A first microfluidic platform technology reported in literature is based on stimuli-responsive gels. To avoid the electrolysis of water hydrogel-based microfluidic devices are mainly based on temperature-responsive polymers with lower critical solution temperature (LCST) characteristics, which are controlled by an electrothermic interface. Two types of micropumps are known, a diffusion micropump and a displacement micropump. Microvalves based on stimuli-responsive hydrogels show some advantageous properties such as particle tolerance, no leakage and outstanding pressure resistance. Besides these microfluidic standard components the hydrogel platform provides also chemical sensors and a novel class of microfluidic components, the chemical transistors (also referred as chemostat valves). These devices regulate a liquid flow if a threshold concentration of certain chemical is reached. Chemical transistors form the basis of microchemomechanical fluidic integrated circuits. "Chemical ICs" process exclusively chemical information, are energy-self-powered, operate automatically and are able for large-scale integration. Another microfluidic platform is based on

ionomeric An ionomer () ('' iono-'' + '' -mer'') is a polymer composed of repeat units of both electrically neutral repeating units and ionized units covalently bonded to the polymer backbone as pendant group moieties. Usually no more than 15 mole perce ...

materials. Pumps made from that material could offer low voltage ( battery) operation, extremely low noise signature, high system efficiency, and highly accurate control of flow rate. Another technology that can benefit from the unique properties of EAP actuators is optical membranes. Due to their low modulus, the mechanical impedance of the actuators, they are well-matched to common optical

membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. ...

materials. Also, a single EAP actuator is capable of generating displacements that range from micrometers to centimeters. For this reason, these materials can be used for static shape correction and jitter suppression. These actuators could also be used to correct for

optical aberration In optics, aberration is a property of optical systems, such as lenses, that causes light to be spread out over some region of space rather than focused to a point. Aberrations cause the image formed by a lens to be blurred or distorted, with th ...

s due to atmospheric interference. Since these materials exhibit excellent electroactive character, EAP materials show potential in

biomimetic Biomimetics or biomimicry is the emulation of the models, systems, and elements of nature for the purpose of solving complex human problems. The terms "biomimetics" and "biomimicry" are derived from grc, βίος (''bios''), life, and μίμησ ...

-robot research, stress sensors and acoustics field, which will make EAPs become a more attractive study topic in the near future. They have been used for various actuators such as face muscles and arm muscles in humanoid robots.http://eap.jpl.nasa.gov/ NASA WorldWide Electroactive Polymer Actuators Webhub

Future directions

The field of EAPs is far from mature, which leaves several issues that still need to be worked on. The performance and long-term stability of the EAP should be improved by designing a water

impermeable Permeability, permeable, and semipermeable may refer to: Chemistry *Semipermeable membrane, a membrane which will allow certain molecules or ions to pass through it by diffusion *Vascular permeability, the movement of fluids and molecules betwe ...

surface. This will prevent the evaporation of water contained in the EAP, and also reduce the potential loss of the positive counter ions when the EAP is operating submerged in an

aqueous An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would ...

environment. Improved surface conductivity should be explored using methods to produce a defect-free conductive surface. This could possibly be done using metal vapor deposition or other doping methods. It may also be possible to utilize conductive polymers to form a thick conductive layer. Heat resistant EAP would be desirable to allow operation at higher voltages without damaging the internal structure of the EAP due to the generation of heat in the EAP composite. Development of EAPs in different configurations (e.g., fibers and fiber bundles), would also be beneficial, in order to increase the range of possible modes of motion.