BYBYABHIJIT.R.C.ABHIJIT.R.C.

S7M1S7M1ROLL NO:27101ROLL NO:27101

INTRODUCTION

Electro active polymers (EAP) are actuation materials that are used to drive mechanisms and are fastly replacing conventional methods. Several investigations are in its way to utilize the excellent properties of the polymer. These materials are now applied in various fields including robotics, medicine, defense etc:-and are effective alternatives for conventional sensors and actuators such as motors, gears, bearings, screws etc:- EAP’s can change all the paradigms of design.

EAP’s are soft actuators consists mainly of a ionic polymer background with metallic electrodes deposited on the surface. When an external voltage is applied, it causes the bending or actuation towards the anode side, whose deflection can be conveniently controlled.

MICROSTRUCTURE AND COMPOSITION (IONOMERS AS BENDING EAP

ACTUATORS)

• The bending EAP actuator is composed mainly of perflourinated ion exchange membrane metallic composite backbone called ionic polymer metallic composite or IPMC(0.18µm)

• IPMC have commercial name Nafion®.• The ionomer background or matrix is

coated on both sides with metallic electrodes made of noble metals such as Pt,Au or Pt/Au(5-10µm).

• It is then neutralized with a certain amount of counter-ions such as monovalent cations of alkali metals such as Li+ ,Na+ ,K+ and Rb+.

• A finishing layer of gold is provided to increase surface conductivity.

• It is then fully solvated. The most common solvent used is water but we can also use organic solvents like Ethylene glycol or Glycerol.

• An IPMC has to be kept moist continuously for long working(4 months) and it is done by providing a polysilicon coating.

MANUFACTURING TECHNIQUES The current manufacturing techniques of IPMC’sIncorporates 2 distinct processes:1.Initial compositing process2.Surface electroding process Rectangular silicone wells with size 1cm by 3cm by 2-5mm is used as

containers for IPMC fabrication. It is deposited on glass slides.

Initial compositing process• It is to metallize the inner surface of polymer by a chemical reduction process.

• Ionic polymer is soaked in salt solution of a complex salt Pt(NH3)4HCl

• a proper reducing agent such as LiBH4 or NaBH4 is introduced to metallize the polymer

• LiBH4 + 4[Pt(NH3)4]2+ + 8OH- ==> 4Pt + 16NH3 + LiBO2 + 6H2O.

• The metallic platinum particle 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.

Schematic showing Initial compositing process

Surface electroding process

• In the subsequent surface electroding process, multiple reducing agents are introduced (under optimized concentrations) to carry out the reducing reaction similar to previous equation in addition to the initial platinum layer formed by the initial compositing process.

• The roughened surface disappears.• Platinum will deposit predominately on top of

initial Pt layer.• Other metals which are also successfully used

include palladium, silver, gold, carbon, graphite etc:-

Schematic of Surface electroding process

• After the upper electrode material is deposited and allowed to air dry, the glass slide is placed in an oven and annealed at 700C for 45minutes.

• The silicone well is filled with deionized water for 30 minutes to saturate the IPMC.

• The device is lifted from the well with tweezers and tested

• A low modulus poly silicon coating is applied to the surface to trap the solvent inside IPMC.

MECHANISM FOR ELECTRICAL ACTUATION

• When an external voltage is applied on an IPMC film, it causes bending towards the anode

• The IPMC strip bends due to these ion

migration induced hydraulic actuation and redistribution.

• Nafion IPMC has the ability to absorb considerable amount of water, which increases the cations mobility and conductivity.

• The cations will get hydrated while the anions sulfonate(SO3

-) group remains fixed to the polymer matrix.

• When a voltage(1-3V) is applied the hydrated cations will move towards the cathode side.

• The swelling or expansion at the cathode side results due to the increase in volume at the cathode side of IPMC, as a result of the transfer of hydrated cations.

• This swelling is followed by a slow back relaxation towards cathode.

• This is because that the weak bonds associated with the hydrated cations break after prolonged exposure to the applied electric field causing the inherent ‘relaxation.’

• This will cause the re-orientation of the cations in the boundary layer.

• Finally the EAP will come to an equilibrium position.

FACTORS AFFECTING ACTUATION

1. Counter ion species.

2. Hydration

3. Frequency

4. Potential

5. Temperature

6. Platinum penetration & dispersion

APPLICATIONS OF EAP1.EAP actuating a dust wiper in NASA mission

INDUSTRIAL APPLICATIONS:

• Miniature Robotic arm

• EAP was used to

make android heads that could mimic facial expressions.

• Robotic swimming fish:

This remotely controllable stealthy, noiseless, biomimetic swimming robotic fish made with IPMC’s, can be used for naval applications.

• Linear actuators:

• Slithering device: Snake-like locomotion can be accomplished by arranging appropriate segments of the IPMC in series and controlling each segment’s bending by applying sequential input power to each segment in a cascade mode.

• Resonant flying machines: By providing a suitable oscillator frequency close to the resonant frequency we can cause large displacements similar to flapping of wings like insects.

• Electromechanical relay switches: Non-magnetic, self-contained, electromechanical relay switches can be made from IPMC’s by utilizing their good conductivity and bending characteristics in small applied voltages to close a circuit.

• Diaphragm pumps using flexing IPMC strips and diaphragms: Single or multiple IPMC’s can function as the diaphragms that

create positive volume displacement. The applied voltage amplitude and frequency can be adjusted to control the flow and volume of fluid being pumped. Such a pump produces no noise and has a controllable flow rate in the range of a few micro liters per minute.

BIO-MEDICAL APPLICATIONS: Target applications include compact pumps, including

prosthetic blood pumps, and robotic instruments for minimally invasive surgery

• Heart compression device:

Ionic polymeric metal composite (IPMC) biomimetic sensors, actuators and artificial muscles integrated as a heart compression device which can be implanted external to the patient’s heart, and partly sutured to the heart without contacting or interfering with the internal blood circulation. Thus, the potential IPMC device thereby can avoid thrombosis and similar complications.

• Artificial smooth muscle actuator: By arranging IPMC materials segments, we can provide skeletal joint mobility.

• Correction of refractive errors of the human eyes and bionic eyes and vision.

• Surgical tool:

The IPMC actuator can be adopted for use as a guide wire or a micro-catheter in biomedical applications for intra-cavity endoscopic surgery and diagnostics. Small internal cavities in the body can be navigated by using small strip or fiber-like IPMC actuators.

ADVANTAGES• Lighter compared to other actuators and

sensors.• Soft and flexible, hence find wide

application in bio-medical field• EAP’s can be mass produced. Hence it

results in low cost.• EAP’s can be easily fabricated in various

shapes.• Inherent vibration damping.

• Response speed is significantly higher.

• Superior fatigue characteristics

• Large actuation strains

• Can withstand extreme conditions esp. up to -1400C.This suits EAP in planetary applications.

DISADVANTAGES

• No effective and robust EAP material is currently commercially available.

• Selection of suitable and satisfying materials poses a problem as new and new materials emerge.

• A compromise between stress and strain needed

CONCLUSION• Electroactive polymers have emerged with great potential

enabling the development of unique biomimetic devices. As artificial muscles, EAP actuators are offering capabilities that are currently considered science fiction. Developing such actuators is requiring development on all fronts of the field infrastructure. Enhancement of the performance of EAP will require advancement in related computational chemistry models, comprehensive material science, electro-mechanics analytical tools, and improved material processing techniques.

Making robots that are actuated by EAP as artificial muscles that are controlled by artificial intelligence would create a new science and technology realities. While such capabilities are expected to significantly change future robots, significant research and development effort is needed to develop robust and effective EAP-based actuators.

REFERENCES

• www.ndeaa.jpl.nasa.gov/nasa-nde/lommas/aa-hp.htm - 19k

• www.spie.org/web/meetings/ programs/ss00/courses/sc125.html

• www.hmc.psu.edu/artorg/electrop/ • www.azom.com/details.asp?ArticleID=885• www.unm.edu/~amri/SMSReview-4 • www.mae.cornell.edu/ccsl/papers/SFF05_Malone • www.teccenter.org/electroactive_

polymers/licensingterms.html • www.materialsnetbase.com/ejournals/

books/book_summary/summary.asp?id=1047 - 22k