PREPARATION OF NANOCOMPOSITE BASED ON FUNCTIONALIZED GRAPHENE - - PDF document

SLIDE 1

18TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS

• 1. Introduction

Graphene nanoplatelets (GNPs) based nanocomposites (NC) are attracting attentions of researchers because of their potential use in devices and other electronic applications [1,2]. Most of the processes for the preparation of GNPs based NC used graphene produced from oxidation method [3], in which oxidative intercalation/exfoliation normally destroys sp2 hybrids of graphitic carbon. Therefore a reduction step is needed in order to restore the

• xides to graphenes exhibiting inherent properties of

pristine graphenes. However the reduction process could not fully restore graphitic structures and many defects are still existed on graphene sheets resulting in an electrical conductivity several orders of magnitude lower than pristine graphene.[4] In order to develop graphene based NC with high electrical as well as thermal conductivity, an alternative production of “pristine” graphene is desirable. Our approach begins with natural graphite (NG) as graphene source. First, pristine GNP (p-GNP) was prepared by microwave exfoliation of reductive graphite intercalation compound (GICs) of NG intercalated with organic tetramethyl ammonium bromides (TMAB). Next, p-GNP was functionalized with 4-aminobenzoic acid (BA) through Friedel- Crafts acylation, resulting in the introduction of 4- aminobenzoyl groups on the egdes of graphene

• sheets. This functionalization could improve the

dispersion as well as physico-chemical interaction between GNPs with polymer matrix. A reactive polymer matrix based on epoxy-acrylate bifunctional polysiloxanes (EABFPS) was synthesized with unsaturated double bonds as reactive sites for grafting with graphene surfaces during the curing of

• nanocomposites. Hybrid of this polysiloxanes with

cycloaliphatic epoxy and pristine and/or functionalized GNPs was studied and electrical and thermo-mechanical properties of NCs are discussed in this paper.

• 2. Experimental

2.1 Synthesis and functionalization of graphene nanoplatelets 2.1.1. Synthesis of GICs and GNPs GICs of NG with lithium was prepared by stirring a 20 g of NG (98 %, 50 mesh, Hyundai Coma Ind. Co., Korea) in a solution of 2.31 g (0.277 mol) of lithium metal (99.5 %, Aldrich) dissolved in 100 ml tetrahydrofurane (THF, 99 %, Aldrich) containing 35.5 g (0.27 moles) of naphthalene (98 %, Aldrich) at room temperature for 24 hrs in a closed vial. Then, the GICs was filtered through the filtering funnel (0.2 µm pore size) under inert nitrogen environment and washed several times with fresh THF to remove

• naphthalene. Ion-exchange induced intercalations

were carried out in a closed vial with stoichiometric amount TMAB (99 %, Aldrich) in the presence of THF as solvent. The vials were stirred magnetically at room temperature for 12 hrs. The resulting product, GIC, was dried at 40oC in convection oven for 3 hrs. p-GNPs were prepared by microwave irradiation of GICs in an oven (LG Electronics, 700 watt) for 2 min under inert N2 gas. A volume expansion of 200 ml/g was observed. 2.1.2 Functionalization of GNPs via Friedel-Crafts acylation Functionalization of GNP was followed the process reported by Choi [5] as follows: p-GNPs (5.0 g, 0.42 mol) and 4-aminobenzic acid (5.0 g, 0.0364 mol, Aldrich) were introduced into 500 ml three necked round bottom glass reactor. Next, 200 g of polyphosphoric acid (83 % P2O5 basis, Aldrich) was added and the mixture was mechanically stirred at 500 rpm until homogenous mixture was obtained. Then, 50 g (0.5 mol) of

PREPARATION OF NANOCOMPOSITE BASED ON FUNCTIONALIZED GRAPHENE NANOPLATELET AND EPOXY-ACRYLATE BIFUNCTIONAL POLYSILOXANES

Quang-Trung Truong, Gwang Seok Song, and Dai Soo Lee* Division of Semiconductor and Chemical Engineering Chonbuk National Univeristy Jeonju, 561-756, South Korea

* Corresponding author: daisoolee@chonbuk.ac.kr

Keywords: graphene nanoplatelets, epoxy-acrylate bifunctional polysiloxanes, nanocomposite

SLIDE 2

p m th re a G v ti w re

• 2

E c F

p

m m

9

d th n re fo a re

• S

e A (t A T c w 2 g M 2 2 T d g p C d th a phosphorous maintaining hen heated eaction mixt and diluted GNPs (NH2-G vacuum suct imes with water/ethanol esulting pro

• vernight.

2.2. Synthesis EAFPS was s condensation First step: 50

polydimethy

mgKOH/g, f mol) of tetra

98 %, Aldr

dilaurate (98 he round bo nitrogen gas eaction flask for 3 hrs. A applied to th emove comp

• bserved.

Second step epoxycyclohe Aldrich) an trimethoxysi Aldrich) wer The reaction continuous st weight loss w 2.3. Preparati grapheme/EA Matrix resin w 26.67 wt % o 2021p- Dicel The mixture i density being graphene disp prepared by u Calculated am density of GN he matrix res and sonicated pentaoxide mechanical in oil bath ture was cool with de-ion GNPs) were tion, and r water until l mixture (1

• duct was d

s of novel EA synthesized n (Scheme 1) 0 g (0.044 m

ylsiloxanes

from Dow

aethoxyorth rich), and

%, Aldrich)

• ttom three n

inlet and d k was immer After 3 hrs he flask for pletely ethan p: 5.48 g exyl)ethyl] nd 5.524 ilyl) propyl m re added to t was carried tirring under was observed ion of functio ABFPS nanoc was a mixtur

• f cycloalipha

l Industry) a is transparen g 1.04 g/cm3. persion (0.1 w ultrasonicatio mount of gra NP was assum sin were mix d for 30 min. e was cau

• stirring. Th

at 130 oC f led to the roo ized water. collected by repeatedly w l neutral P 1/1 v/v) seve dried in vac ABFPS by two step ) as follows. mol) of hydro (OH valu

Corning), 2 hosilicate (R

d 1000 ppm ) as catalyst necked flask distillation c rged in an oi

• f reaction

several hou nol until no w (0.022 mo trimethoxys g (0.022 methacrylate the above re

• ut at 80 oC

r reduced pr d.

• nalized

composites re of 60 wt % atic epoxy re nd 13.33 wt nt even after c Pristine and wt %) in eth

• n at 200 wa

aphene disper med to be 2.2 xed in separa Then, solve utiously add he reactor w for 72 hrs,

• m temperat

Functionaliz y filtering un washed seve PH, then w eral times. T cuum at 80 non hydroly

• xy terminat

ue of 112 2.364 g (0.0

Reagent gra

m of dibuty were added k equipped w condenser,. T il bath at 80 n, vacuum w urs in order weight loss w l) of [2-(3 silane (97 mol)

• f

e (ETCS, 98 eaction mixtu C for 8 hrs w ressure until % of EABFP esin (Celloxi % of ETCS. cure, the d functionaliz anol was atts for 5 hrs. rsion (by vol 26 g/cm3), an ted beakers ent were ded was the ture zed nder eral with The

• C

ytic

ated

23.9 011

ade,

yltin d to with The 0 0C was r to was 3,4- %, 3- %, ure. with no S, ide . zed l %, nd ev 0.0 cat rad we Sa an 12

O

Sc 3. 3.1 na GN int Ex Ele Tr 20 Fig mi

N

aporated usin 04 wt % (bas talyst (Alum dical catalyst ere added and amples for th d cured at 11 0 ℃ and fina

O Si O O O Si Si Si H3C C O Si CH3 CH3 O H3C C O Si Si

n

H3CO O H3CO O OCH3 OCH3 O

n n

HO Si CH3 CH3 OH n

OH-PDMS-561.96 g/e

+ 4 mol

• cheme1. Two

Results and

• 1. Synthesis

noplatelets NPs were tercalation-m xfoliation cou ectron Mic ansmission 010). g.1. SEM im icrowave exf

NG

ng rotary eva sed on total c minium acetyl t (tert-butyl p d mixed by m e tests were 10 ℃ for 2 h ally post cur

O Si CH3 CH3 CH3 O CH3 Si OCH3 OCH3 O OCH3 O OCH3

n

Mw = 5377.79 g/mo Epoxy EW = 2688.9

O CH3 O C

e

C2H5O Si OC2H5 OC2H5 OC2H5

TEOS 1 mol

• step synthes

discussion and function synthesize microwave uld be obser croscope ( Electron M mages of NG foliated GNP aporator at 6 composite) c l acetonate, A perbenzoate) mechanical s casted on Te hrs and additi red at 150 ℃

H3CO Si OCH OCH O

1 mol 2 m 2 m

• l

90

CH3

5

HO S C C

1st step

sis of EABF nalization of ed from N exfoliation rved employ (SEM, SM Microscope (scale bar 50 P (scale bar 2

p-GNP

60 ℃, finally ationic Aldrich) and ) of 0.1 wt % stirring. eflon mold ional 2 hrs at for 3 hrs.

H3 H3 O C O CH3 Si OCH3 OCH3 OCH3

mol mol

2nd s

i CH3 CH3 O n Si O Si CH CH OH Si CH3 H3C O n O Si CH3 H3C OH n

PS. graphene NG throug

• f

GIC ying Scannin M-5900) an (TEM, JEM 00 µm) and 2 mm) y a % t

step

H3 H3 OH n

gh C. ng nd M-

SLIDE 3

F 5

• m

e s F s m µ fu N d in th a c F s fo F c G N G a th A “ [6 fr

N

Fig.1 shows S 500-700 µm microwave expanded to tructures. Fig.2 shows T

• nication in

multilayers gr µm and thick functionalizat NH2-GNP be decreased to 4 ndicating fur hat the highl acid/P2O5 and caused exfoli Fig.2. TEM im cale bar is 50 focused at the Fig.3 shows F confocal micr GNP and NH NH2-GNP sh G and 2D (G assigned to th he D line is a A1g symmetr “fingerprint” 6] The 2D ba from its the N

p-GNP NH2-GNP

SEM images and p-GNP exfoliation

• several

TEM images

• ethanol. It sh

raphenes wit kness around tion with AB ecame less sta 4-5 µm and t rther exfoliat ly viscous me d the role of iation of GNP mages of p-G 00 nm) and h e edges (righ FT-Raman sp ro-spectrosco H2-GNP. Obv

• w three cha

’). The G lin he E2g phono a breathing m

• ry. 2D band

area for the and of the p- NG (~2690 n s of NG with

• btained aft

where the mm formi s of p-GNP a hows winkle th average la 5-10 nm. Af B, the multila acked, latera the thickness tion of p-GN edium of pol f AB as mole Ps during fun GNP and NH high resoluti ht, scale bar i pectra (Nano

• py, 633 nm

viously, all N aracteristic b ne (1580 nm)

• n of C- sp2

mode of κ-po is well know identificatio

• GNPs distin

nm) by shiftin

p-GNP NH2-GN

h particle size ter intercalat e C-axis w ing worm-l after 5 hrs ed structure o ateral length fter ayer graphen al length bein s around 5 nm

• NP. It seems

lysphosphori cular wedge nctionalizati H2-GNP (left

• n images

is 10 nm).

• finder-30

m) of NG, p- NG, p-GNP an ands named is usually atoms, while

• int phonons

wn as n of graphem nguishes itsel ng to lower

P

e of tion was like

• f

~7 nes ng m ic

• n.

t, and D, e

• f

me. lf wa for aro sho nm gra Th Fig (re 2D Fig Fu by pri NH wi ave length (~ rmation of gr

• und 10 [6].
• ws more sh

m) implying a aphene sheet hese results a

500

Intensity (a.u) N p N

g.3. FT- Ra ed) and NH2- D bands

4000 35

Transmittance (a.u)

333

g.4. FT- IR s unctionalizati y FT-IR sp istine GNP s H2-GNP exh ith primary a ~2648-2673 n raphene with After functio hift to lower w a further exfo t with the nu are consistent

1000 1500

10 20 30 Intensity (a.u)

Wave l NG p-GNP NH2-GNP

G D

aman spectra

• GNP (blue).

500 3000 2500

Wave nu

39-3328

p-GNP NH2-GNP

spectra of p-G ion of p-GN ectra (JASC shows a feat hibits charac mines (–NH nm) indicatin h the number

• nalization, N

wave length foliation to th umber of laye nt with the im

2000 2

2500 2550 2600 2650 2 000 000 000 Wave length (nm

length (nm)

a of NG (b . The inset sh

2000 1500

150 1600 1657

umber (cm

• 1)

GNP and NH NP was furth CO, FT/IR- atureless spec cteristic ban H2) occurring ng the r of layers NH2-GNP (2640-2670 hinner ers around 5- mages by TEM

500 3000

2700 2750 2800 )

2D

black), p-GN hows enlarge

1000 500

08

H2-GNP her confirme

• 4100) Whi

ctrum (Fig.4 nds associate at 3328-332

3

• 7.

M. NP ed ed ile 4), ed 29

SLIDE 4

Scheme.2. Schematic for Friedel-Crafts acylation - functionalization of GNPs. cm-1 (N-H stretching vibration) and at 1600 cm-1 (N– H bending vibrations). Furthermore, NH2-GNP clearly showed an aromatic carbonyl (C=O) peak centered at 1657 cm-1 due to the covalent junctions between the AB and graphene. These results provided further evidence that the ABs were covalently linked to the graphene sheets as given in Scheme 2. The degree

• f

functionalization could be quantitatively estimated using thermogravimetric analysis (TGA, Q50, TA Instruments). Fig. 5 shows TGA thermograms of p-GNP and NH2-GNP. The p- GNP showed almost no weight loss (~3.0 wt %) up to a 600 oC in N2. On the other hand, NH2-GNP showed a stepwise weight loss commencing at 423

• C. This early weight loss was attributed to the AB

moiety that was covalently attached to the edges of the graphenes. The amount of weight loss at 600 oC was approximately 15 wt%. It means that the amount of AB moiety introduced into graphenes was 12 % by weight.

100 200 300 400 500 600 700 800 50 55 60 65 70 75 80 85 90 95 100

Temperature (

• C)

Weight (%)

0.00 0.05 0.10 0.15 0.20 0.25 0.30

• Der. weight (%/
• C)

p-GNP NH2-GNP

Fig.5. TGA thermograms of p-GNP and NH2-GNP . (Ramping rate was 10 ℃/min under nitrogen) 3.2. Synthesis of novel EABFPS The synthesis of EABFPS through two steps (scheme 1) was monitored by measuring the IR spectra during the reaction progress. Fig. 6 shows the IR spectra of the first step reaction product (c) in comparison with starting reactants, OH-PDMS in (b) and TEOS in (a). The peak at 3294 cm-1 attributed to OH groups stretching vibration of Si-OH of the starting OH-PDMS. This peak intensity of Si-OH groups largely decreases after 5 hrs of reaction, indicating the non-hydrolytic condensation reaction between Si-OH and Si-OC2H5 of TEOS. Furthermore, the two characteristic peaks of TEOS at 1391 cm-1 (C-H bending in CH3 of TEOS) and 1169 cm-1(C-H rocking in CH3 of TEOS) almost disappeared in IR spectrum of the 1st step product means the complete reaction of TEOS with OH- PDMS.

4000 3500 3000 2500 2000 1500 1000 500

c b Transmittance (a.u) Wave number (cm

• 1)

OH-PDMS 1

st step product

TEOS

a 3294 1391 1160

Fig.6. IR spectra of the 1st step product (c) in comparison with starting materials, (a) and (b).

4000 3500 3000 2500 2000 1500 1000 500

e d Transmittance (a.u) Wave number (cm

• 1)

3296 1723 1637 3427 a b c

Fig.7. IR spectra of the 2nd step product in comparison with starting reactants:(a) ETCS;(b) TMSMC; (c) 1-st step product; (d) 2nd step product after 4 hrs; (e) 2nd step product after 8 hrs

SLIDE 5

F p w a O s a h S s in (C s b 3 F

• F

G S F

• N

in th th a Fig.7. shows product (e) at with starting and 1st step pr OH group str tep product ( almost flatten hydrolytic co Si-OCH3 in E hows other p ntroduction o C=O), and at uccessful syn by 29Si-NMR 3.3. Propertie

0.0 0.5 1 4 6 8 10 12 14

Log (surface resistivity) Ohm/sqr

Fig.8. Electri

• f graphene c

Fig.9.TEM im GNP 1 vol % Scale bar is 2 Fig.8 shows e

• f graphene c

NC showed e nsulating to c han NH2-GN hat p-GNP h agglomerate s IR spectra o t different rea reactants, ET roduct in (c) retching vibra (c) decreased ned after 8 hr

• ndensation r

ETCS and TM peaks at 1723

• f carbonyl g

t 1637 cm-1 o nthesis of EA R spectroscop es of nanocom

.0 1.5 2.0 2.5 3.0

Grahene conten

cal surface r contents mages of slic % (left) and N 200 nm.. electrical res

• content. It is

electrical per conducting a NP based NC has higher asp structure con f the 2nd step action time i TCS in (a), T . The peak a ation of Si-O d with reactio rs indicating reaction betw

• MSMC. The

3, 1704 cm-1 groups of acr

• f double bo

ABFPS was py method (n mposites

3.5 4.0 4.5 5.0 5.5

nt (vol %) p-GNP NH2-GNP

esistivity of ced nanocom NH2-GNP-1 isitivity of N

• bserved tha

colation tran at threshold ( C (4 vol %). I pect ratio wi ntributing to p reaction in compariso TMSMC in (b at 3296 cm-1 o OH in the 1st

• n time and

the non- ween Si-OH a final EABFP indicating t rylate units

• nd (C=C). T

also confirm not shown he

6.0

NC as functi mposites of p- vol % (right NC as functio at p-GNP bas nsition from (0.5 vol %) It is speculate th a better way

• n

b)

• f

and PS the The med ere). ion

• t),
• n

sed ed y of

• f

ha co res ne sec im pre im dis Fig

• f

Th usi TA film Th sum p-G sig co tem shi co GN sof percolating n s smaller asp ntributied to sulting in mo

• twork. This p

ction TEM im mages of p-GN esence of lar mages of NH2 spersion. g.10. DMA t different p-G hemo-mechan ing Dynamic A2900, TA in m tension cla he results are mmary of DM GNPs to this gnificant imp mpared with mperature of ifted to highe

• ntents. It is a

NPs restrictin ft segmentso

• 100 -80

Tan delta (a.u) a b c d e

• 100 -80

10 100 1000 10000 p

Storage modulus (MPa)

• network. On

pect ratio and a better disp

• re difficultie

postulation c mages of NC NP based NC ge graphene

2-GNP system

thermograms GNP content nical propert c Mechanical nstrument) at amp and a ra showed in F MA data. It i s EABFPS sy provement of h the polymer f NC at lower er temperatu attributable to ng the molec

• f the matrix
• 60 -40 -20

20 40 6

Temp a- Matrix b- p-GNP-0.5 c-p-GNP-1.0 d-p-GNP-2.0 e-p-GNP-3.0

• 60 -40 -20

20 40 6 p-GNP-3.0

Tempara p-G

n other hand, d polar funct persion in the es in forming can be suppo C shown in F C 1vol % (le e agglomerate m (right) sho s of NC base t (vol%) ties of NC w l Analysis (D at frequency amping rate o Fig.10. Table is shown tha ystem showe f storage mod r matrix. Gla r temperatur ure with incre

• the platelet

cular motions resin.

60 80 100 120 140 160 180

perature (

• C)

60 80 100 120 140 160 180 p-GNP-2.0 p-GNP-1

ature (

• C)

matrix GNP-0.5

NH2-GNP tional groups e resin matr g percolating

• rted by cross
• Fig. 9. TEM

ft) shows the e while

• ws better

ed on p-GNP were studied DMA, 1Hz using a

• f 5 oC.min-1

e 1 is the at addition of ed a dulus ass transition e, Tg1 was easing p-GN t structure of s of PDMS

0 200 220 0 200 220 1.0

5

s ix, g s e s

1.

f n P f

SLIDE 6

However the second glass transition temperature at higher temperatures due to overall chain mobility shows slight decrease with increasing p-GNPs contents and attributed to the grafting of double in acrylate unit in EABFPS to graphene nanoplatelets forming a new network structures. Table 1. Summary of the DMA analysis result of NC At low concentration of NH2-GNP, notably 0.5 vol %, NC showed large increase of storage modulus (107 %) in comparison with p-GNP-0.5 vol % (31.9 %). It is attributable to the strong interaction between NH2-GNP and polymer matrix due to the reactive amino groups introduced by functionalization. However, at higher concentration of NH2-GNP, % storage modulus improvement is decreased. It seems that the amino groups in NH2-GNPs inhibited cationic curing reaction of cycloaliphatic epoxy

• resin. Therefore, higher concentration of NH2-GNP

resulted in stronger inhibition effects.

• 4. Conclusion

We successfully prepared and characterized GNPs and AB-functionalized GNP through a non-oxidative method yielding less defect GNPs which can be used as electrical conductive fillers for polymer

• nanocomposites. Furthermore, a novel reactive

epoxy acrylate bifunctional polysiloxane based resin matrix was synthesized and formulated for GNPs based NC. It is showed that both p-GNPs and NH2- GNP could be dispersed well in the matrix giving many advantageous properties such as low viscosity, high electrical conductivity and possibly high thermal conductivity for many potential applications. Further investigation of curing kinetics and thermal conductivity of NCs are underway. Acknowledgements It is acknowledged that this work was supported by Ministry of Education and Science Technology through Human Resources Training Project for Regional Innovation and Ministry of Environment through Environmental Technology Development Project.

References

[1] A. K. Geim and K. S. Novoselov “The rise of

graphene”, Nature Materials, Vol. 6(3), pp 183- 191, 2007.

[2] J.R. Potts , D. R. Dreyer, C. W. Bielawski, R. S. Ruoff, “Graphene-based polymer nano

composites”, Polymer., vol. 52, pp. 5-25, 2011. [3] W. S. Hummers “Preparation of Graphitic Oxide”, J. Am. Chem. Soc., vol. 80, No.6, pp. 1339, 1958. [4] C.G. Navarro, R. T. Weitz,, A. M. Bittner, M. Scolari, A. Mews, M. Burghard and K. Kern “Electronic Transport Properties of Individual chemically Reduced Graphene Oxide Sheets”, Nano Lett., vol.7 No (11), pp. 3499–3503, 2007. [5] E. K. Choi, I.Y. Jeon, S.Y. Bae, H.J. Lee, H. S. Shin, L.Dai and J.B. Baek “High-yield exfoliation of three-dimensional graphite into two-dimensional graphene-like sheets”, Chem. Commun., Vol. 46, pp. 6320-6322, 2010. [6] A. C. Ferrari, J. C. Meyer, V. Scardaci, C. Casiraghi, M. Lazzeri, F. Mauri, S. Piscanec, D. Jiang, K. S. Novoselov, S. Roth, and A. K. Geim “Raman Spectrum of Graphene and Graphene Layers” Phys. Rev. Lett. Vol.97, pp.187401, 2006.

Sample code Storage modulus (MPa) ΔM (%) Tg1 ( oC) Tg2 (oC) Matrix 251.4

• 40.5

91.5 p-GNP-0.5 331.8 31.9

• 38.7

76.7 p-GNP-1.0 563.8 124.2

• 38.6

65.6 p-GNP-2.0 573.2 128.0

• 38.0

75.6 p-GNP-3.0 596.8 137.3

• 25.0

111.9 NH2-GNP-0.5 521.4 107.4

• 35.9

75.9 NH2-GNP-1.0 410.8 63.4

• 30.4

84.1 NH2-GNP-2.0 304.7 21.2

• 35.1

78.2 NH2-GNP-3.0 306 21.7

• 34.0

155.2

ΔM % denoted the % improvement of storage modulus.