Super-tough artificial nacre based on graphene oxide via synergistic interface interactions of π-π stacking and hydrogen bonding
Graphical abstract
Introduction
Natural nacre demonstrates extraordinary fracture toughness ranging to 3000 times higher than the intrinsic toughness of its constituent of CaCO3 platelets. This level of toughness is attributed to the interfacial interactions between organic protein matrix and CaCO3 platelets [1], [2], [3]. Inspired by this relationship of extraordinary toughness and abundant interface interactions, a range of bioinspired nanocomposites based on different inorganic platelets have been demonstrated, including flattened double-walled carbon nanotubes [4], man-made CaCO3 [5], [6], nanoclay [7], [8], Al2O3 flakes [9], [10], and layered double hydroxides [11]. Graphene oxide (GO) nanosheets with numerous oxygen-containing groups are an ideal candidate for achieving the artificial nacre construction through the design of different interface interactions, including hydrogen bonding, ionic bonding, π-π interaction, and covalent bonding. Many GO-based artificial nacre with excellent mechanical properties have been produced by constructing different interface interactions [12], [13], [14], [15], [16], [17], [18], for example, the GO-Borate, rGO-PCDO, PGO-PDA, rGO-SL, and rGO-PAPB. In our previous report [16], [17], we demonstrated ultra-tough GO-based artificial nacre with long linear molecules of PCDO, which absorbs much energy when the coiled structure is stretched under loading. However, constructing much tougher GO-based artificial nacre remains a great challenge.
Recently, our group has developed a new route to toughen brittle epoxy thermosets with the block ionomer, sulfonated polystyrene-block-poly (ethylene-co-butylene)-block-polystyrene (SSEBS) via sulfonating polystyrene-block-poly (ethylene-co-butylene)-block-polystyrene (SEBS) with 67 wt% of polystyrene (PS) [19], [20]. Moreover, styrene segments in SEBS can form strong π-π stacking [21] whereas sulfoacid groups can form hydrogen bonds with oxygen-containing groups on the GO surface, which can guarantee strong interfaces between GO and SSEBS and thus facilitate the stress transfer and energy dissipation upon external load.
In this work, we have demonstrated super-tough GO-based artificial nacre through synergistic toughening of π-π interaction and hydrogen bonding. A new water-soluble long chain molecule, sulfonated styrene-ethylene/butylene-styrene (SSEBS), with many benzene groups was synthesized through sulfonating SEBS triblock copolymers. Then the SSEBS and GO nanosheets were assembled into artificial nacre via vacuum assisted-filtration. The strong π-π interaction is formed between the benzene groups with GO nanosheets, and hydrogen bonding network is formed between hydroxyl groups, carboxyl groups of GO nanosheets, and sulfonic groups of SSEBS [19], [20], [21] as well. The resultant synergistic effect of π-π interactions and hydrogen bonding improves the efficiency of stress transfer, and long soft SSEBS segments easily deform and extend under loading, dissipating much more fracture energy. The toughness of GO-SSEBS reaches as high as 15.3 MJ/m3, which is eight times higher than that of natural nacre [22], and superior to other GO-based artificial nacre. This bioinspired synergistic toughening of π-π interactions and hydrogen bonding strategy opens a new avenue for constructing high performance GO-based nanocomposites in the near future.
Section snippets
Materials
Graphene oxide (GO) was prepared according to our previous work [23]. Detailed preparation process of sulfonated styrene-ethylene/butylene-styrene (SSEBS) is provided in Supporting Information.
Fabrication of SSEBS-toughened GO-based artificial nacre
Firstly, 1.5 g of each polymer (GO, SSEBS) was dispersed in 1000 ml deionized water with the aid of sonication for 30 min, and then stirring for 3 h and to prepare 1.5 mg/ml aqueous solutions of GO, and SSEBS, respectively. Then, a certain amount of SSEBS solution was added into the GO solution according
Results and discussion
The size of GO nanosheets is in the range of 1.0–5.0 μm with a thickness of ∼1 nm (Figure S1), and the water-soluble SSEBS was synthesized via sulfonating SEBS (Scheme S1). After sulfonation, four new absorption peaks appear in the infrared spectrum (IR), respectively locating at 3397 cm−1 (the stretching vibration of OH in SO3H), 1126 cm−1, 1032 cm−1 and 1003 cm−1 (stretching vibration of SO) [24], [25] (Figure S2A). Elemental analysis results show that SSEBS contains 5.14 wt% S element, and
Conclusions
Inspired by natural nacre, we created super-tough GO-based artificial nacre via synergistic interface interactions. The synthesized water-soluble sulfonated SEBS copolymer provides numerous functional groups, resulting in formation of π-π interaction and hydrogen bonding with GO nanosheets. This kind of synergistic interface interactions achieves high toughness of 15.3 MJ/m3, superior to natural nacre and other GO-based nanocomposites. This work provides a novel bioinspired toughening strategy
Acknowledgements
Z. Xu is the co-first author and P. Song and Z. Xu contributed equally to the work.
This work was financially supported by the Natural National Science Foundation of China (51522301, 51303162, 51304166 and 51628302) and the Non-profit Project of Science and Technology Agency of Zhejiang Province of China (Grant No. 2013C32073). P.S. was also supported by an Alfred Deakin Postdoctoral Research Fellowship at Deakin University (Grant No. 0000025468).
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P. Song and Z. Xu contributed equally to the work.