Reinforcement of macroscopic carbon nanotube structures by polymer intercalation: The role of polymer molecular weight and chain conformation

C. J. Frizzell, M. in het Panhuis, D. H. Coutinho, K. J. Balkus, Jr., A. I. Minett, W. J. Blau, and J. N. Coleman

Phys. Rev. B 72, 245420 – Published 21 December 2005

Abstract

Novel polymer nanotube composites were fabricated by intercalating poly(vinylpyrrolidone) into Buckypaper from solution. This was carried out for both low $(10 k g ∕ mol)$ and very high $(1.3 M g ∕ mol)$ molecular weight polymers. Measurements of the polymer mass uptake as a function of time allowed the calculation of diffusion coefficients as $1.66 \times 10^{- 9} {cm}^{2} ∕ s$ and $3.08 \times 10^{- 12} {cm}^{2} ∕ s$ for the low and high molecular weight strands, respectively. Taking into account the molecular weights, comparison of these coefficients suggests that each polymer type undergoes a different mode of diffusion: normal diffusion for the $10 k g ∕ mol$ polymer, but reptation for the $1.3 M g ∕ mol$ polymer. This means that while the low weight polymer retains its randomly coiled conformation during diffusion and adsorption, the $1.3 M g ∕ mol$ molecule is forced to adopt an extended, high entropy state. These differences are reflected in the mechanical properties of the intercalated papers. While reinforcement was observed in all cases, modulus (increase $\sim \times 3.5$ ) and strength (increase $\sim \times 6$ ) enhancement occurred at lower polymer content for the longer chain polymer. However, the papers intercalated with the shorter chain molecules were much tougher (increase $\sim \times 25$ ). This is consistent with the conformation scheme described above.

Received 1 August 2005

DOI:https://doi.org/10.1103/PhysRevB.72.245420

Authors & Affiliations

C. J. Frizzell

Department of Physics & NanoTech Institute, The University of Texas at Dallas, 2601 N. Floyd Rd., Richardson, Texas 75083, USA and Department of Physics, Trinity College Dublin, Dublin 2, Ireland

M. in het Panhuis^*

Department of Physics & NanoTech Institute, The University of Texas at Dallas, 2601 N. Floyd Rd., Richardson, Texas 75083, USA and Department of Physical Sciences, the University of Hull, Hull, HU6 7RX, United Kingdom

D. H. Coutinho and K. J. Balkus, Jr.

Department of Chemistry, The University of Texas at Dallas, 2601 N. Floyd Rd., Richardson, Texas 75083, USA

A. I. Minett, W. J. Blau, and J. N. Coleman

Department of Physics, Trinity College Dublin, Dublin 2, Ireland

^*Author to whom correspondence should be addressed. Electronic address: M.Panhuis@hull.ac.uk

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Vol. 72, Iss. 24 — 15 December 2005

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Images

Figure 1
Scanning electron micrograph images of typical reference (pristine) and polymer soaked Buckypaper. (a) Surface and (c) cross section of reference paper. (b) Surface and (d) cross section of paper soaked in PVP $(10 000 g ∕ mol)$ solution for $12 h$ .Reuse & Permissions
Figure 2
Pore size distribution for annealed Buckypaper measured from $N_{2}$ adsorption-desorption isotherms. Pore sizes of $< 2 nm$ were calculated by the HK method while those of $> 2 nm$ were calculated using the BJH method. The point where the data sets were joined is shown by the arrow where a small mismatch can be seen. The peak around $6 Å$ is associated with internanotube pores; that is, the channels between nanotubes within bundles. The upper limit of this region is marked by the dotted line. The region of the graph to the right of the dotted line represents the interbundle pores.Reuse & Permissions
Figure 3
(a) Polymer mass uptake as a function of soak time for PVP with $M_{w} = 10 000 g ∕ mol$ . The dotted line is a fit to Eq. (2) with $D = 1.66 \times 10^{- 9} {cm}^{2} ∕ s$ and $l = 60 μ m$ . Note that the intercalation saturates after approximately $1 h$ . (b) Polymer mass uptake as a function of soak time for PVP with $M_{w} = 1.3 M g ∕ mol$ . The dotted line is a fit to Eq. (2) with $D = 3.08 \times 10^{- 12} {cm}^{2} ∕ s$ and $l = 60 μ m$ . In this case there is no sign of saturation even after $360 h$ . In both (a) and (b) the fraction of the internal surface coated by the polymer is shown as the right axis as calculated by Eq. (1). (c) Diffusion coefficients calculated from Figs. 3a, 3b as a function of $M_{w}$ . The solid line is a fit to $D_{M} \propto M_{w}^{- n}$ , giving $n = 1.29$ . Rouse diffusion $(n = 1)$ is depicted by the dotted line while reptation $(n = 2)$ is illustrated by the dashed line. The intersection of these two regimes occurs at $M_{w} = 313 566 g ∕ mol$ .Reuse & Permissions
Figure 4
Representative stress strain curves for the pristine paper, paper soaked in PVP with $M_{w} = 10 000 g ∕ mol$ , and paper soaked in PVP with $M_{w} = 1.3 M g ∕ mol$ . Note that no individual stress strain curve displayed the average behavior for modulus, strength, and toughness. These curves were chosen to illustrate the general shape of the stress strain curves and their relative toughness’.Reuse & Permissions
Figure 5
Mechanical properties of Buckypaper intercalated with PVP of $M_{w} = 10 000 g ∕ mol$ . (a) Young’s modulus, $Y$ , as a function of volume fraction. The line is a fit to Eq. (4) with $d Y ∕ d V_{f} = 7.49 GPa$ . (b) Ultimate tensile strength, $σ_{B}$ , as a function of volume fraction. At low volume fraction the data is linear with slope $d σ_{B} ∕ d V_{f} = 125 MPa$ . However, $σ_{B}$ tends to drop off above $V_{f} = 0.17$ . (c) Toughness, $T$ , as a function of volume fraction. At low volume fraction the data is linear with slope $d T ∕ d V_{f} = 1.91 MJ ∕ m^{3}$ . However, $T$ tends to drop off above $V_{f} = 0.17$ .Reuse & Permissions
Figure 6
Mechanical properties of Buckypaper intercalated with PVP of $M_{w} = 1.3 M g ∕ mol$ . (a) Young’s modulus, $Y$ , as a function of volume fraction. The line is a fit to Eq. (4) with $d Y ∕ d V_{f} = 57.5 GPa$ . However, $Y$ tends to saturate above $V_{f} = 0.04$ . (b) Ultimate tensile strength, $σ_{B}$ , as a function of volume fraction. At low volume fraction the data is linear with slope $d σ_{B} ∕ d V_{f} = 193 MPa$ . However, $σ_{B}$ tends to saturate above $V_{f} = 0.04$ . (c) Toughness, $T$ , as a function of volume fraction. At low volume fraction the data is linear with slope $d t ∕ d V_{f} = 321 kJ ∕ m^{3}$ . However, $T$ tends to saturate above $V_{f} = 0.04$ .Reuse & Permissions

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