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Multifunctional Polymer-Based Graphene Foams with Buckled Structure and Negative Poisson ’ s Ratio

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ABSTRACT

In this study, we report the polymer-based graphene foams through combination of bottom-up assembly and simple triaxially buckled structure design. The resulting polymer-based graphene foams not only effectively transfer the functional properties of graphene, but also exhibit novel negative Poisson’s ratio (NPR) behaviors due to the presence of buckled structure. Our results show that after the introduction of buckled structure, improvement in stretchability, toughness, flexibility, energy absorbing ability, hydrophobicity, conductivity, piezoresistive sensitivity and crack resistance could be achieved simultaneously. The combination of mechanical properties, multifunctional performance and unusual deformation behavior would lead to the use of our polymer-based graphene foams for a variety of novel applications in future such as stretchable capacitors or conductors, sensors and oil/water separators and so on.

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Mechanical characterization of PG foams and A-PG foams.(a) Measured Poisson’s ratio versus strain for as-prepared foams (red: PG foams; blue: A-PG foams). Inset: digital picture of PG and A-PG foams under 0 and ~50% strain. (b) Measured tensile stress of PG and A-PG foams as a function of strain. Insets show the in situ SEM imaging of a representative cell. Compared to PG foams, A-PG foams behave more flexible and stretchable due to rotational deformation of the buckled structure at initial 0–30% tensile strain. (c) Measured compressive stress of PG and A-PG foams as a function of strain. When compressive strain is applied up to 30%, Inset shows linear stress–strain curve for A-PG foams whereas two distinct modulus regions are observed for PG foams. All the strain here are engineering strain. two distinct modulus regions are observed. (d) Cushioning coefficients of PG and A-PG foams across a stress range of 0–180 kPa. Horizontal dashed line indicates a coefficient of 10.
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f2: Mechanical characterization of PG foams and A-PG foams.(a) Measured Poisson’s ratio versus strain for as-prepared foams (red: PG foams; blue: A-PG foams). Inset: digital picture of PG and A-PG foams under 0 and ~50% strain. (b) Measured tensile stress of PG and A-PG foams as a function of strain. Insets show the in situ SEM imaging of a representative cell. Compared to PG foams, A-PG foams behave more flexible and stretchable due to rotational deformation of the buckled structure at initial 0–30% tensile strain. (c) Measured compressive stress of PG and A-PG foams as a function of strain. When compressive strain is applied up to 30%, Inset shows linear stress–strain curve for A-PG foams whereas two distinct modulus regions are observed for PG foams. All the strain here are engineering strain. two distinct modulus regions are observed. (d) Cushioning coefficients of PG and A-PG foams across a stress range of 0–180 kPa. Horizontal dashed line indicates a coefficient of 10.

Mentions: Despite of multifunctional performance, many of applications such as flexible supercapacitors, pressure sensors and elastic conductors require that the 3D monoliths possess excellent mechanical performance during deformation. And unlike the functionalities mainly stemmed from the coated nanomaterials, the overall mechanical properties of this 3D porous template/nanomaterial system would be dominated by the cellular structures. As shown in Fig. 1g, the most prominent mechanical behaviors that caused by buckling structures within this 3D polymer template/graphene system are the improved flexibility and stretchability under tension, which are not surprising but intriguing for their applications. Moreover, distinctively, the response of the buckled structure in 3D A-PG foams to uniaxial tension also exhibits macroscopically lateral expansion, which is called auxetic behavior (means “expand laterally when stretched”) or negative Poisson’s ratio (NPR) effect. Interestingly, individual graphene nanosheets can be also made auxetic through vacancy defects tailoring48, but apparently the negative Poisson’s ratio of A-PG foams should be dominated by the buckling structures of the PU microfibers where the graphene assemblied upon. We thus measured Poisson’s ratios of our samples in Fig. 2a. Similar to that of PU foams in Figure S2, the Poisson’s ratios of PG foams are near +0.3 at small applied tensile or compressive strain level and approach +0.7 in tension and 0 in compression at high strain level. Comparatively, lateral expanding rather than necking is observed for A-PG foams (Fig. 2b insets), showing a minimum Poisson’s ratio of ~−0.5. This unique negative Poisson’s ratio of our A-PG foams could definitely cause the novel lateral expansion behaviors as well as many bulk mechanical properties.


Multifunctional Polymer-Based Graphene Foams with Buckled Structure and Negative Poisson ’ s Ratio
Mechanical characterization of PG foams and A-PG foams.(a) Measured Poisson’s ratio versus strain for as-prepared foams (red: PG foams; blue: A-PG foams). Inset: digital picture of PG and A-PG foams under 0 and ~50% strain. (b) Measured tensile stress of PG and A-PG foams as a function of strain. Insets show the in situ SEM imaging of a representative cell. Compared to PG foams, A-PG foams behave more flexible and stretchable due to rotational deformation of the buckled structure at initial 0–30% tensile strain. (c) Measured compressive stress of PG and A-PG foams as a function of strain. When compressive strain is applied up to 30%, Inset shows linear stress–strain curve for A-PG foams whereas two distinct modulus regions are observed for PG foams. All the strain here are engineering strain. two distinct modulus regions are observed. (d) Cushioning coefficients of PG and A-PG foams across a stress range of 0–180 kPa. Horizontal dashed line indicates a coefficient of 10.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5016781&req=5

f2: Mechanical characterization of PG foams and A-PG foams.(a) Measured Poisson’s ratio versus strain for as-prepared foams (red: PG foams; blue: A-PG foams). Inset: digital picture of PG and A-PG foams under 0 and ~50% strain. (b) Measured tensile stress of PG and A-PG foams as a function of strain. Insets show the in situ SEM imaging of a representative cell. Compared to PG foams, A-PG foams behave more flexible and stretchable due to rotational deformation of the buckled structure at initial 0–30% tensile strain. (c) Measured compressive stress of PG and A-PG foams as a function of strain. When compressive strain is applied up to 30%, Inset shows linear stress–strain curve for A-PG foams whereas two distinct modulus regions are observed for PG foams. All the strain here are engineering strain. two distinct modulus regions are observed. (d) Cushioning coefficients of PG and A-PG foams across a stress range of 0–180 kPa. Horizontal dashed line indicates a coefficient of 10.
Mentions: Despite of multifunctional performance, many of applications such as flexible supercapacitors, pressure sensors and elastic conductors require that the 3D monoliths possess excellent mechanical performance during deformation. And unlike the functionalities mainly stemmed from the coated nanomaterials, the overall mechanical properties of this 3D porous template/nanomaterial system would be dominated by the cellular structures. As shown in Fig. 1g, the most prominent mechanical behaviors that caused by buckling structures within this 3D polymer template/graphene system are the improved flexibility and stretchability under tension, which are not surprising but intriguing for their applications. Moreover, distinctively, the response of the buckled structure in 3D A-PG foams to uniaxial tension also exhibits macroscopically lateral expansion, which is called auxetic behavior (means “expand laterally when stretched”) or negative Poisson’s ratio (NPR) effect. Interestingly, individual graphene nanosheets can be also made auxetic through vacancy defects tailoring48, but apparently the negative Poisson’s ratio of A-PG foams should be dominated by the buckling structures of the PU microfibers where the graphene assemblied upon. We thus measured Poisson’s ratios of our samples in Fig. 2a. Similar to that of PU foams in Figure S2, the Poisson’s ratios of PG foams are near +0.3 at small applied tensile or compressive strain level and approach +0.7 in tension and 0 in compression at high strain level. Comparatively, lateral expanding rather than necking is observed for A-PG foams (Fig. 2b insets), showing a minimum Poisson’s ratio of ~−0.5. This unique negative Poisson’s ratio of our A-PG foams could definitely cause the novel lateral expansion behaviors as well as many bulk mechanical properties.

View Article: PubMed Central - PubMed

ABSTRACT

In this study, we report the polymer-based graphene foams through combination of bottom-up assembly and simple triaxially buckled structure design. The resulting polymer-based graphene foams not only effectively transfer the functional properties of graphene, but also exhibit novel negative Poisson’s ratio (NPR) behaviors due to the presence of buckled structure. Our results show that after the introduction of buckled structure, improvement in stretchability, toughness, flexibility, energy absorbing ability, hydrophobicity, conductivity, piezoresistive sensitivity and crack resistance could be achieved simultaneously. The combination of mechanical properties, multifunctional performance and unusual deformation behavior would lead to the use of our polymer-based graphene foams for a variety of novel applications in future such as stretchable capacitors or conductors, sensors and oil/water separators and so on.

No MeSH data available.


Related in: MedlinePlus