Soft Materials~Application to Artificial Muscle~

Literature Seminar
H. Mitsunuma (D1)
06/18/2012

1

What Is “Gel” ?
Gels are defined as a substantially dilute cross-linked system, which exhibits
no flow when in the steady-state.
Ferry, John D. Viscoelastic Properties of Polymers. New York: Wiley, 1980.

Examples of “Gel” around us

KonjakContact lens

Nappy
2

Charactaristics of “Gel”
1. Solid + Liquid = “Soft material”+= ??

2. Open system in non-equiliblium state

3. Intelligent function

3

Today’s Topics
1. Basic concept and history of “Gel”

2. Application to artificial muscle

3. Future outlook
4Types of “Gel”

5

History of “Gel”

6

Evaluation of Gel Point
Flory-Stockmayer model

ゲル化点 =重量平均重合度無限大
7

Osmotic Theory of Gel
ゲル網目の変形に伴うギブス自由エネルギーの変化∆G = ∆Gm + ∆Ge∆Gm 網目と溶媒との混合からの寄与∆Ge 弾性からの寄与∆Gm = kBT[n1lnv1+n2lnv2+χn1v2]
kB:ボルツマン定数、n1 :溶媒分子数、 n2 :高分子鎖数v1:溶媒の体積分率、 v2:溶媒の体積分率
χ :高分子-溶媒相互作用パラメータ∆Ge = (3/2) kBTve (α2-1-lnα)ve:実在の網目中における鎖の有効数、α :変形因子∆G = n1kBT[lnv1+χv2]+ (3/2) kBTve (α2-1-lnα)(n2 =1よりn2を含む項は無視できる)

8Osmotic Theory of Gel
化学ポテンシャル変化∆µ1 = NA(∂∆Gm/∂n1)T, p + NA(∂∆Ge/∂α)T, p (∂α/∂n1)T, p= RT[lnv1+v2+χv22+V1(ve/V0)(v21/3-v2/2)]
V0:高分子網目の膨潤前体積、V1:溶媒のモル体積
α3 = V/V0 = 1/v2 (V:高分子網目の膨潤体積)
平衡膨潤状態のとき、 ∆µ1 = 0

9Equation of State of Gel
浸透圧
π = −∆µ1/V1 = -(RT/V2)[ln(1-v2)+v2+χv22]+RT(ve/V0)(v2/2-v21/3)=…
= -(NkT/v)[φ+ln(1-φ)+(∆F/2kT)φ2]+vkT[φ/2φ0-(φ/φ0)1/3]+fvkT(φ/φ0)= (網目高分子と溶媒の混合による圧力)+(弾性による圧力)+(対イオンによる圧力)
ただしR = kN, V1 = v, v2 = φ, χ = ∆F/2kT, ve/V0 = v,
f: 架橋点高分子鎖一本当たりの解離している対イオンの数平衡状態(π = 0)においてτ = 1-(∆F/kT)と定義すると、
τ= -vv/Nφ2 [(2f+1) (φ/φ0)-2 (φ/φ0)1/3 ]+1+2/φ+[2ln(1-φ)]/φ2(V/V0 = φ0/φ)10Volume Phase Transition
τ= -vv/Nφ2 [(2f+1) (φ/φ0)-2 (φ/φ0)1/3 ]+1+2/φ+[2ln(1-φ)]/φ2(V/V0 = φ0/φ, τ = 1-(∆F/kT))

体積相転移: 温度や溶媒組成などの外部条件の連続的な変化に応じて、ゲルの平衡膨潤度(体積)が大きな不連続変化を示す現象
T. Tanaka, Phys. Rev. Lett., 1978, 40, 820.

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Kinetics of Osmotic Theory
膨潤の緩和時間
τ= a2/π2D
a:半径、D:ポリマー網目の拡散係数(a) ink: diffusion (b) gel

12Summary of First Topic
Gel is essential for our life.

Volume phase transition(1978 T.Tanaka)

Explosive development
In the field of gel chemistry !!
(intelligent gel, actuator…)

13

Today’s Topics
1. Basic concept and history of “Gel”

2. Application to artificial muscle

3. Future outlook
14

The Structure of MuscleChemical reactions produce ATP molecules
which are used to power the movement ofthe myosin heads.

15

Artificial Muscle
Artificial muscle: actuators which mimic the muscles in our own
human bodies
Actuator: type of motor for moving or controlling a mechanismor system.
It is operated by a source of energy, usually in the formof an electric current, hydraulic fluid pressure orpneumatic pressure, and converts that energy into somekind of motion.

Functions needed for artificial muscles:
1. High compliance, flexiblity
2. High power density, small
3. Compact, mobile16

Types of Actuators
ElectroactivePolymers

Artificial
musclesPneumatic
artificialmuscles

Shapememoryalloys
17

Pneumatic Artificial Muscles
Pneumatic artificial muscles (PAMs) :contractile or extensional devices operated by pressurized air filling a pneumatic bladder.

Problems:
1. These systems require air compressors that are neither light nor small.
2. Their response speed is limited by the ability of compressors.
3. Consumable18

Shape Memory Alloys
Shape-memory alloys (SMAs):
an alloy that "remembers" its original, cold-forged shape: returning the pre-deformed
shape by heating.

Problems:
1. It takes time to cool the alloy and return to the rest position.
2. Low efficiency
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Types of Actuators
CompliancePower density

Mobility

Electroactivepolymes

Very goodNot so good

Possible

Penaumaticartificial muscles

Good

Very good

Difficult

Sharp memory
alloys

GoodGood

Possible(also see appendix for detail values)

Electroactive polymers are being developed as a prominent
candidate of artificial muscles !!
20Electroactive Polymers (EAPs)
Electroactive Polymers (EAPs):
polymers that exhibit a change in size or shape when stimulated by an electric field.

EAPs

Ionicpolymers

Fieldactivatedpolymers
21

Field-Activeted Polymers
Dielectronic elastomers

When a voltage is applied across these materials, the attraction between opposite
charges and the repulsion of like charges generates stress in the dielectric, known as
Maxwell stress, which compresses and elongates the dielectric.
DEs are one of the most studied polymer actuators and numerous applications are being
developed.
(electroactive fluid pumps, conformal skins for Braille screens, insect-like robots,
and Artificial Muscles’ autofocus lens positioner)
Mat. Today. 2007, 10, 30. 22Ionic Polymers
Ionic polymermetalcomposites
Ionic gels
Ionic polymers
Carbonnanotubes
Conductivepolymers
23

Ionic Polymer-Metal Composites
IPMCs consist of a solvent swollen
ion-exchange polymer membranelaminated between two thin flexible
metal or carbon-based electrodes

General basic ion exchange polymer:
Perfuluorinated alkanes with sidechains terminated by ionic groupEx) Nafion from DuPont
24

NafionNafion :sulfonated tetrafluoroethylene based fluoropolymer-copolymer discovered in the late 1960s by Walther
Grot of DuPont.

Structure of Nafion

State of Understanding of Nafion
Chem. Rev. 2004, 104, 4535.

25

Synthesis
Preparation
copolymerization of tetrafluoroethylene (TFE) and a derivative ofa perfluoro (alkyl vinyl ether) with sulfonyl acid fluoride.

FF+FF

FO2S

FFFF

CF3FO

FFFO

copol y mer i zat on
FFbasi c process

Synthesis of perfluorinated vinyl ether monomer: see appendix

N af i on26

Typical Bending Response of IPMC

When a water-saturated cantileverd strip of Nafion-based IPMC issubjected to a small DC Potential, it undergoes a fast bending
deformation towards the anode, followed by a slow relaxation in
the opposite direction.
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Effect of Different Cations

Effect of various cations on blocking force

28

Ionic Hydration EffectResult of IR analysis

J. Am. Chem. Soc. 1980, 102, 4665.
29

Ionic Hydration EffectFour-state model

1. Completely dissociated hydrated
ion pairs
2. Ion pairs at the contact of undisturbed
primary hydration shells
3. Outer-sphere complexes
4. Inner-sphere complexes

Lithium ion: stronger electrostatic fieldlarge hydration sphere
J. Am. Chem. Soc. 1980, 102, 4665.
30

Performance Improvement
1. Solvent loss in IPMC (electrolysis and evaporation)
2. Lowering surface resistance of IPMC surface electrode(gold coating)
3. Encapsulation of IPMC
4. Structure of membrane
Etc…
Int. J. Control. Autom. Syst. 2006, 4, 748.
International Journal of Precision Engineering and Manufacturing. 2012, 13, 141.
31

Mechanical Applications
Flapping device

Int. J. Control. Autom. Syst. 2006, 4, 748.

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Mechanical Applications
Flapping device
Applied voltage: 3~4 V
Square wave form: 0.5~10 Hz

Maximum flapping angle:
85 degree (1 Hz input)
Flapping angle:
15 degree (3V, 15 Hz input)

The flapping device should be useful for mimicking an insect flying at low frequency.
Int. J. Control. Autom. Syst. 2006, 4, 748.

33

Mechanical Applications
IPMC valve-less micro pump
Biomimetic jellyfish robot
Mechanical gripper
Fish robot (developed by Eamax, a Japanese company)
etc…

34

Ionic Polymers
Ionic polymermetalcomposites
Ionic gels
Ionic polymers
Carbonnanotubes
Conductivepolymers
35

Carbon Nanotube Actuators
Carbon nanotubes: very good conductors of both electricity and heatvery strong and elastic molecules in certain directions
tensile modulus (640 GPa), tensile strength (20-40 GPa)

An applied potential injects charge in theTwo nanotube electrodes in solution

Charge injection at the surface of ananotube bundle

Coulombic forces resulted in actuation !!

Science. 1999, 284, 1340.

36

Carbon Nanotube Aerogel Muscles
Actuation in sheet width

50-mm-long 2-mm-wide
nanotube aerogel sheet

Applying a field of 5kV
width: 220% elongation !!
(3.7*104)% per second

25-mm-long nanotube sheet(1500 K by applying 3kV)
Science. 2009, 323, 1575. 37

Carbon Nanotube Aerogel Muscles
Carbon nanotube sheet

Carbon nanotube forest plane

90 degree rotation of MWNTs in aa forest to form a sheet

The measured gravimetric strength of orthogonally oriented sheet arrays exceeds thatof sheets of high-strength steel.
Science. 2005, 309, 1215. 38

Torsional CNT Artificial Muscles
Carbon nanotube yarn

Carbon nanotube yarn provides a reversible
15000 degree rotation and 590 revolutions
per minute !!
Science. 2011, 334, 494.

39

Summary of Second Topic
1. Electroactive polymers appear to provide the best conbinationof properties for muscle like actuation.

2. The field of EAPs is under development.

3. CNT artificial muscles show the best result.

40

Today’s Topics
1. Basic concept and history of “Gel”

2. Application to artificial muscle

3. Future outlook
41

Current Trends of Gel
Medical field
Biochemistry

Actuator

Biomaterial, DDS,
Microallay etc…

Functional gel

Applicationof Gel
Strong Gel

Analysis

TP gel, NC gel etc…

Theory42

Future Outlook
Gel with “emergence” functionality

Actin
MyosinSarcomere

Actual forceInteraction

Pico newton

Centi meter, kg

Nano meter

Gel has the potential to artificially mimic “biological emergence” !!
43

Future Outlook
Gel with “emergence” functionality

1. Artificial biological machine systemEx) muscle like gel engine, brain like computer, biomining…etc

2. Recognition of “life”

44Reference
1.
2.
3.
4.

「驚異のソフトマテリアル 最新機能性ゲル研究」 日本化学会「ゲルハンドブック」 エヌティエス 長田義仁他「高分子ゲル」 高分子学会 吉田亮「図解 人工筋肉 ソフトアクチュエーターが拓く世界」 日刊工業新聞社 中村太郎

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Appendix 1

Macromol. Rapid Commun. 2010, 31, 10.

46

Appendix 2
Preparation procedure for IPMCs
Supply: Nafion, NaBH4, Aqueous solution of platinum ammine complex, Hydrazine hydrateHydroxylamine hydrochloride, Diluted ammonium hydroxide solution,Diluted hydrochloric acid, Deionized water

1. Surface roughening of the membrane
a.
b.
c.
d.

Mild sandblast
Ultrasonic washing
Treatment with HCl
Treatment with water

2. Ion-exchange
3. Primary plating
4. Secondary plating47

Appendix 3
Synthesis of comonomer

J. Fluorine. Chem. 2004, 125, 1211.

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