Modify SWCNT IPMC by Hydrothermal Method

2016 International Conference on Manufacturing Science and Information Engineering (ICMSIE 2016) ISBN: 978-1-60595-325-0

Modify SWCNT-IPMC by Hydrothermal

Method

JIATIAN WANG, KE XIONG, KAN BIAN, HONGGUANG LIU

and MAN WANG

ABSTRACT

Modify SWCNT-IPMC by hydrothermal to improve the dispersion of SWCNT and solve the foaming problem. Study and analyze the morphology characteristics

and the basic mechanical properties and electrical properties of

0.1%wtSWCNT-IPMC modified before and after. The result shows, the dispersion of SWCNT in 0.1%wtSWCNT-IPMC modified is greatly improved, the foaming problem is completely solved, and the material has higher moisture content, tensile strength, modulus and tip force output, as well as lower swelling ratio, elongation and surface resistance.

INTRODUCTION

Ionic polymer metal composite material （IPMC), called "artificial muscle", has application prospect in the fields of medical, bionic, aerospace, etc. for the characteristics of low density, good flexibility, rapid response, easy miniaturization, and similar strain limit and damage limit[1-6].

Carbon nanotubes (CNT) as a typical one-dimensional modified materials, having excellent mechanical properties, often used as a material to modify the IPMC. However, the defect of CNT can’t be ignored. The dispersion of CNT is uneven and the bubble forms in the film forming process due to the large aspect ratio, causing the performance of CNT-IPMC becomes worse. To this end, the hydrothermal method is used to modify the CNT-IPMC in this paper[7-11].

________________________

PREPARATION AND MODIFICATION OF CNT-IPMC

In this paper, the Nafion117 solution of American DuPont company is used as the raw material. Its solvent is mixture of water and SEC butyl alcohol, the mixture ratio is 1:1, the solute is Nafion, and the solute concentration is 5%.Performance indicators are shown in table 1. Reinforced material is Single Wall Carbon Nanotubes (SWCNT) prepared by Chengdu science and technology research institute. Performance indicators are shown in table 2.

TABLEⅠ.PERFORMANCE INDEX OF NAFION(117).

Type perfluorosulfonic（H+）

Thickness/µm 100 ~ 200

Equivalent weight/(g / gmol)SO3- 1100

Electric conductivity/（S/cm） 0.1~ 0.12 Surface resistance/（Ω·cm2） 2 ~ 4.8

Water content/% 30

TABLEⅡ.PERFORMANCE INDEX OF SWCNT.

OD/nm 1~2

Length/µm 1~3

Purity/wt% >95

Ash/wt% <1.5

SSA/(m2/g) >340

Density/(g/cm3) 2.1

EC /(s/cm) >102

(1) Preparation Of CNT-IPMC By Solution Casting Method[12-13]:

A. Calculate Nafion solution volume according to the preset film size (length, width and thickness), volume solution;

B. Weigh SWCNT powder by mass ratio, add into the Nafion solution;

C. Volume DMSO solution, drop into the Nafion solution, the dosage of DMSO: Nafion=1:20;

D. Stir the mixture about 5 minutes, oscillate 1h with ultrasonic;

E. Pour the mixture into the mold, remove the bubbles, put the mold into the oven, slowly heated to 60℃, keep，ventilates lightly, evaporate to thick.

G. Heat up to 100℃, keep 3 hours, heat up to 140℃again, keep 1 hours, H. Cool to room temperature naturally.

(2) Preparation of Hydrothermal Modified CNT-IPMC by Solution Casting Method:

Add steps between (B) and (C):

a. Stir the mixture about 5 minutes, oscillate 1h with ultrasonic;

b. transfer the mixture to hydrothermal reactor, heat up to 120℃Slowly, keep 5h, cool to room temperature naturally

The rest of the process and the order remains unchanged.

MORPHOLOGY CHARACTERIZATIONS OF SWCNT-NAFION MODIFIED BEFORE AND AFTER

(1) Macroscopic Morphology Characterization

Figure 1.a Foaming film of unmodified

0.1%wtSWCNT-Nafion

Figure.1.b Unfoaming film of modified

0.1%wtSWCNT-Nafion

As shown in Figure 1.a and Figure 1.b, from the surface picture of 0.1%wt SWCNT-Nafion film modified before and after, we can see that the foaming problem of modified 0.1%wt SWCNT-Nafion film is almost solved.

(2) Microscopic Morphology Characterization

In this paper, Electron Microscope Scanning (SEM) was used to analyze the surface microstructure of IPMC modified before and after.

with the advantages of magnification range, regulation, high image resolution, large depth of field, stereoscopic image etc.

Figure 2.a. Local cross section SME of

unmodified 0.1%wt SWCNT-IPMC.

Figure 2.b. Local cross section SME of

modified 0.1%wt SWCNT-IPMC.

Figure 3.a. Local cross section SME of

electrode of unmodified 0.1%wt

SWCNT-IPMC.

Figure.3.b. Local cross section SME of

electrode of modified 0.1% wt

SWCNT-IPMC.

As shown in the Figure.2.a and Figure.2.b, from the local cross section SME of 0.1%wtSWCNT-IPMCmodified before and after, we can see that modified 0.1%wtSWCNT-IPMC has less agglomeration and better dispersion than unmodified.

BASIC MECHANICAL PROPERTIES AND ELECTRICAL PROPERTIES OF THE SWCNT-IPMC MODIFIED BEFORE AND AFTER

(1) Ratio of Moisture Content & Ratio of Swelling

The quality ratio of water loss to dried sample is called moisture content. The polymer absorbs the solvent and expands, the volume ratio of saturated sample to dried sample is called the swelling ratio. The swelling ratio is related to the factors such as pressure, temperature, and solvent properties.

In this paper, the moisture content and swelling ratio of the sample is measured under normal temperature and pressure. The moisture content of SWCNT-IPMC modified before and after was tested according to the GB/T1034-2008 "plastic water absorption test method". When the moisture content is less than 0.02%, that means, IPMC reached the state of water balance. Sample size: 50mm * 5mm * 0.3mm.

0 20 40 60 80 100

0 5 10 15 20 25

W

a

/%

t/min

Modified Unmodified

Figure 4. Moisture content change with time of 0.1%wtSWCNT-IPMC modified before and

after.

TABLE Ⅲ.SWELLING RATIO OF 0.1%WTSWCNT-IPMC MODIFIED BEFORE AND

AFTER.

Sample Unmodified Modified

Saturated volume/mm3 50×5×0.353 50×5×0.365

Dried volume/mm3 46×5×0.280 46×5×0.302

Tensile displacement/mm

F/

N

Tensile displacement/mm

F/N

Figure 4 shows that, moisture content of 0.1%wt SWCNT-IPMC modified before and after both decreases with time, and the equilibrium moisture content of modified 0.1%wt SWCNT-IPMC is higher than unmodified, increasing about 70%. From table 3, we can see that, the swelling ratio of modified SWCNT-IPMC decreases about 19.5% than unmodified.

(2) Property of Tensile

In this paper, the mechanical parameters of 0.1%SWCNT-IPMC modified before and after is tested according to the ASTM D882-02 "plastic sheet tensile properties test method" and GB/T 6673-2001 "plastic film and sheet length and width determination" . The loading rate is 5mm / min.

Figure 5.a Tensile curve of unmodified

0.1%wtSWCNT-IPMC.

Figure 5.b Tensile curve of modified

0.1%wtSWCNT-IPMC.

TABLE Ⅳ.TENSILE PERFORMANCE PARAMETERS OF 0.1%WT SWCNT-IPMC

MODIFIED BEFORE AND AFTER.

Sample Thickness

/mm

Gauge length

/mm

δ /MPa

E

/MPa

ε /%

Unmodified 0.280 25.02 25.25 408.99 87.93

Modified 0.286 24.88 26.38 481.50 73.15

(3) Resistance of Surface & Property of Actuation

In this peter, the inline four probe was used to measure the surface resistance change with time of 0.1%wt SWCNT-IPMC modified before and after. Tip force output performance of 0.1%wt SWCNT-IPMC modified before and after was tested under 3V DC.As usual, the sample size is : 50mm * 5mm * 0.3mm, and the free deformation length is 40 mm.

0 20 40 60 80 100

5 10 15 20 25

R/

Ohm

t/min

Modified Unmodified

Figure 6. Surface resistance change with time of 0.1%wt SWCNT-IPMC modified before and

after.

0 20 40 60 80

0.00 0.02 0.04 0.06 0.08 0.10 0.12

S/

mm

t/s

Modified Unmodified

Figure 7. Tip force output changes with time of0.1%wtSWCNT-IPMC

modified before and after under 3V DC.

From Figure 7, we can see that, the max tip force of modified 0.1%wt SWCNT-IPMCd is growth about 50% than unmodified.

RESULTS ANALYSIS

For 0.1wt SWCNT-IPMC:

It can be speculated that the environment of high temperature and high pressure in the process of hydrothermal makes the Nafion long chain fracture, more space between the molecules is easy to mobile for SWCNT. And, the hydrophilic makes the hydrophobic SWCNT hydrothermal. So the modified SWCNT disperses better and moisture content higher than unmodified.

Well dispersed SWCNT shows its mechanical properties of high strength and high modulus, so the strength and modulus is increased, the swelling ratio and elongation decreases of modified 0.1%wt SWCNT-IPMC.

Well dispersed SWCNT provides more attachment for metal particles, therefore, the electrode of modified 0.1%wt SWCNT-IPMC has better quality and smaller surface resistance than unmodified. Meanwhile, the decreased swelling to a certain extent alleviates the electrode continuity problems caused by volume expansion[14].

The solution of foaming problem is due to the environment of high temperature and high pressure in the process of hydrothermal as well. Cause blistering of the basement membrane of SWCNT-Nafion is that SWCNT aggregated to form a hollow structure, including air. SWCNT distributed evenly after modification, so the foaming problem no longer occurs in the process of film.

Further space between molecules and higher water content rate is conducive to the movement water cation, better quality of electrode and smaller surface resistance is conducive to electrical conduction, so the max output values of modified 0.1%wt SWCNT-IPMC is higher than unmodified[15-17].

CONCLUSION

Modified 0.1%wt SWCNT-IPMC overall performance is improved compared to the unmodified:

Morphology is better. The bubble problem solved, SWCNT agglomeration decreased, Sample continuity and homogeneity is better;

Mechanical property is strengthened. Moisture content, strength, modulus increases, swelling ratio, elongation decreases. The fatigue ability improved and life extend;

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