Elsevier

Polymer

Volume 51, Issue 15, 8 July 2010, Pages 3431-3435
Polymer

Synthesis and characterization of layer-aligned poly(vinyl alcohol)/graphene nanocomposites

https://doi.org/10.1016/j.polymer.2010.05.034Get rights and content

Abstract

Layer-aligned poly(vinyl alcohol)/graphene nanocomposites in the form of films are prepared by reducing graphite oxide in the polymer matrix in a simple solution processing. X-ray diffractions, scanning electron microscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry and thermogravimetric analysis are used to study the structure and properties of these nanocomposites. The results indicate that graphene is dispersed on a molecular scale and aligned in the poly(vinyl alcohol) (PVA) matrix and there exists strong interfacial interactions between both components mainly by hydrogen bonding, which are responsible for the change of the structures and properties of the PVA/graphene nanocomposites such as the increase in Tg and the decrease in the level of crystallization.

Introduction

Graphene, as a single layer of carbon atoms in a two-dimensional honeycomb crystal lattice, has been attracting tremendous interest in the fields of electronics and composite materials because of its fascinating properties [1], [2]. It has been found that electrons move ballistically in the graphene structure with a mobility exceeding 15,000 m2V−1s−1 [3]. Theoretical and experimental results show that single-layered graphene sheets are the strongest materials developed thus far [4]. Graphene nanosheets also have high thermal conductivity and high specific surface area [5]. These particular properties make graphene an excellent additive to dramatically enhance the mechanical, thermal, and electrical properties of polymer materials [6], [7], [8]. Great efforts have been made in the use of solution-processable graphene materials for highly conducting composite [9], transparent electrode [10], and photovoltaic device [11] applications.

So far, technological and engineering applications of graphene sheets usually require graphene solutions (or dispersions) either in water or in an organic solvent. However, as-prepared graphene itself is not soluble and therefore, cannot be dispersed in water or in any organic solvent. A main challenge for realizing the large-scale potential for polymer/graphene nanocomposites is to homogeneously disperse thin nanosheets of graphene within the polymeric matrix. Moreover, the control of the interfacial interaction is crucial. In this respect, graphene oxide (GO), the oxygenated counterpart of graphene, has already been explored as an attractive intermediate to synthesize graphene nanocomposites [12]. GO bears various oxygen functional groups (e.g. hydroxyl, epoxide, and carbonyl groups) covalently bonded on their basal planes and edges of carbon atoms. Therefore, GO is hydrophilic and can be readily dispersed in water as individual sheets to form stable colloidal suspensions [13]. Meanwhile, these oxygen-containing groups impart GO sheets with the function of strong interaction with polar small molecules or polymers to form GO intercalated or exfoliated composites [14], [15]. More important, GO can be readily reduced chemically to graphene by a variety of common reagents [16], [17], [18].

Herein, we report an investigation into the aqueous solution processing of graphene nanosheets in the polymer matrix. A simple and practical approach to synthesize well-dispersed nanocomposites with aligned graphene nanosheets in a poly(vinyl alcohol) (PVA) matrix is demonstrated. The effect of graphene content on the structures and properties of PVA/graphene nanocomposites is investigated. Although the addition of graphene significantly decreases the crystallinity of PVA matrix, the film of the PVA/graphene nanocomposite is strong and ductile. These results demonstrate that the change of structure and properties of the PVA/graphene nanocomposites could be ascribed to the uniform dispersion on a molecular scale and alignment of graphene in the polymer matrix and strong interfacial interactions between both components.

Section snippets

Materials

Graphite powder was purchased from Uni-Chem. PVA (99+% hydrolyzed, Mw ∼ 89,000–98,000) and hydrazine (∼35% water solution) were purchased from Aldrich. Other reagents were of analytical grade and used without further purification.

Synthesis of PVA/graphene nanocomposites

GO was synthesized from graphite powder by the modified Hummers method [19], [20]. The procedures for preparing PVA/graphene nanocomposite films are described as follows. GO was dissolved in 10 mL of water and treated with ultrasound for 45 min to make a homogeneous

Results and discussion

In one-step approach, when hydrazine was added, the brownish solution of PVA/GO changed immediately to black, suggesting graphene formation by reduction of GO. Moreover, no precipitate was observed a few hours after the magnetic stirring had been stopped, which indicated that no aggregates of the graphene sheets were formed. This behavior suggests the presence of interactions between the PVA matrix and graphene for avoiding graphene sheets aggregation. Fig. 1 shows the photographs of PVA/1 wt%

Conclusions

In conclusion, we have successfully prepared layer-aligned PVA/graphene nanocomposites by the reduction of graphene oxide in the presence of PVA and subsequently cast from aqueous solution. Though the addition of graphene significantly decreases the crystallinity of PVA, the film of the PVA/graphene nanocomposite is strong and ductile. The modulus and tensile stress of PVA/3.5 wt% graphene nanocomposite are 16% and 32% higher than those of pure PVA. And the glass transition temperature and the

Acknowledgments

The work is supported by a grant (Economic Production of Carbon Nanotubes) of The Hong Kong Polytechnic University, Key Project in Science & Technology Innovation Cultivation Program of Soochow University, Educational Bureau of Hubei Province (Q20091508), Scientific Research Foundation for Returned Overseas Chinese Scholars of MOE ([2009]1341), Scientific Research Key Project of MOE (209081) and National Natural Science Foundation of China (20904044).

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