Imparting Polymeric Properties to Graphene Nanosheets bySurface Modification via p-p StackingJingquan Liu

College of Chemistry, Chemical and Environmental Engineering; Laboratory of FiberMaterials

andModern Textile, theGrowing Base for State Key Laboratory,QingdaoUniversity,Qingdao

266071, China. Email: jliu@qdu.edu.cn

Manuscript received: 9 March 2011.

Manuscript accepted: 18 May 2011.

Published online: 27 September 2011.

Jingquan Liu obtained his Ph.D. at theUniversity of New SouthWales (UNSW) under the supervision of Prof. JustinGooding in 2004 and thenworked as aCSIRO-UTS post-doctoral

fellow before returning to UNSW to work with Prof. TomDavis as a Vice-Chancellor’s Research Fellow in 2006. His research focusses on synthesis of various bio- and nano-hybrids

of versatile biodegradable and functional polymers.

Background

Graphene sheets have envisioned extensive applications in super-computer, novel

materials, nano-electronics and sensors etc., due to their excellent two dimensional

mechanical, structural, thermal and electrical properties.[1–5] The graphene sheets are

usually prepared by chemical reduction of graphite oxide platelets during which the

graphene sheets become more and more hydrophobic, leading to irreversible aggre-

gation via van der Waals interactions. Li et al. have successfully synthesized stable

aqueous dispersions of graphene nanosheets via electrostatic stabilization.[6] Graphene

sheets can also bemodified with polymers via several covalent linkages such as amides

or esters.[7,8] Ye and coworkers prepared amphiphilic graphene nanoplatelets using in

situ free radical polymerization method.[9] However, these covalent modification

methods will destroy the conjugated structure of graphene, leading to significant

compromization of its electrical conductivity. p-p Stacking interactions exhibit

incomparable advantages over other methods for graphene modification, particularly

in the protection of graphene conductivity. Several p-orbital rich aromatic molecules

such as 1-pyrenebutyrate,[10] have been attached onto graphene basal planes via p-p

stacking for various applications.

Applications

We have recently modified graphene via p-p stacking using thermal and pH sensitive

polymers[11,12] As an extension, in this focus paper, thermal sensitive copolymers of

oligoethylene glycol acrylate (OEG-A) and diethylene glycol ethyl ether acrylate

(DEG-A) were synthesized using the same RAFT mechanism as published[13]

(Scheme 1). The feed ratio was adjusted to achieve copolymers with controllable low

critical solution temperature (LCST) from 31 to 828C. These thermo-sensitive copo-

lymers were further used to prepare graphene/polymer composites, which exhibited

reduced LCST from 22 to 728C (Fig. 1a). High resolution SEM imaging revealed that

the graphene-polymer platelets are almost transparent under electron scanning (Fig 1b).

The result revealed that the polymeric properties could be imparted to graphene

composites via surface modification.

Acknowledgements

I thank Prof. Tom Davis for his guidance. I also thank Dr Wenrong Yang (Deakin

University) and Associate Professor Dan Li (Monash University) for collaboration on

the previous graphene projects.

Reference

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doi:10.1021/MA9013127

0

20

40

60

80

100

0 10 20 30 40 50 60 70Feed ratio of OEG-A/DEG-A

LCS

T [°

C]

Copolymers

Graphene/copolymer composites

(a) (b)

Fig. 1. (a) LCST of copolymer and graphene nanocomposites and (b) SEM micro-

graph of graphene nanocomposites.

SS

OS S

O

S

O

O AIBN/70°C

Graphenesheet

Polymer chain

Pyrene

OEG-A/DEG-A

SS

O

OO

O

S S

SO

O

OO

O

Om n =8 2

Scheme. 1. Preparation of graphene/polymer nanocomposites via p-p stacking.

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