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Cite This: ACS Appl. Mater. Interfaces 2017, 9, 40628-40637
Mechanically Robust Magnetic Carbon Nanotube Papers Prepared with CoFe2O4 Nanoparticles for Electromagnetic Interference Shielding and Magnetomechanical Actuation Guh-Hwan Lim,† Seongwon Woo,† Hoyoung Lee,† Kyoung-Seok Moon,‡ Hiesang Sohn,‡,§ Sang-Eui Lee,*,‡ and Byungkwon Lim*,† †
School of Advanced Materials Science and Engineering, Sungkyunkwan University (SKKU), Suwon 16419, Korea Samsung Advanced Institute of Technology (SAIT), Suwon 16678, Korea § Department of Chemical Engineering, Kwangwoon University, Seoul 01897, Korea ‡
S Supporting Information *
ABSTRACT: The introduction of inorganic nanoparticles into carbon nanotube (CNT) papers can provide a versatile route to the fabrication of CNT papers with diverse functionalities, but it may lead to a reduction in their mechanical properties. Here, we describe a simple and effective strategy for the fabrication of mechanically robust magnetic CNT papers for electromagnetic interference (EMI) shielding and magnetomechanical actuation applications. The magnetic CNT papers were produced by vacuum filtration of an aqueous suspension of CNTs, CoFe2O4 nanoparticles, and poly(vinyl alcohol) (PVA). PVA plays a critical role in enhancing the mechanical strength of CNT papers. The magnetic CNT papers containing 73 wt % of CoFe2O4 nanoparticles exhibited high mechanical properties with Young’s modulus of 3.2 GPa and tensile strength of 30.0 MPa. This magnetic CNT paper was successfully demonstrated as EMI shielding paper with shielding effectiveness of ∼30 dB (99.9%) in 0.5−1.0 GHz, and also as a magnetomechanical actuator in an audible frequency range from 200 to 20 000 Hz. KEYWORDS: carbon nanotube, cobalt ferrite, electromagnetic property, mechanical property, electromagnetic interference shielding, magnetomechanical actuation mechanical properties.32−34 In this work, we developed a facile and scalable route to the fabrication of mechanically robust magnetic CNT papers embedded with cobalt ferrite (CoFe2O4) nanoparticles. In this approach, magnetic CNT papers were fabricated by vacuum filtration of an aqueous suspension of CNTs, CoFe2O4 nanoparticles, and poly(vinyl alcohol) (PVA) and subsequent a hot press process. The resulting papers retained good mechanical properties even at a high content of CoFe2O4 nanoparticles and exhibited high electrical conductivity and magnetic permeability, which made it possible to apply them as multifunctional membranes for EMI shielding and magnetomechanical actuation.
1. INTRODUCTION Carbon nanotube (CNT) papers have received significant interest because of their potential applications in electronics,1−6 electromagnetic interference (EMI) shielding,7−9 thermal interface materials,10 actuators,11,12 sensors,13−18 supercapacitors,19−21 and batteries.22,23 Recently, CNT papers embedded with metal or metal oxide nanoparticles have been prepared in efforts to achieve improved electrical, mechanical, and/or electrochemical properties.24−29 For instance, CNT papers prepared with palladium and copper nanoparticles make a promising candidate for enhancement of EMI shielding properties.30 CNT papers consisting of gold nanoparticles showed enhancement in their mechanical and electrical properties.31 Despite recent progress, there have been few reports on the fabrication of a magnetic nanoparticle-embedded CNT paper, which is a promising candidate as both EMI shielding paper and magnetomechanical actuator. CNT papers are usually fabricated by vacuum filtration of CNT suspensions. However, the CNT papers prepared by this method often suffer from poor mechanical properties due to relative weak van der Waals interaction between constituent CNTs. Moreover, the introduction of inorganic nanoparticles into a CNT paper may lead to further reduction in its © 2017 American Chemical Society
2. EXPERIMENTAL DETAILS 2.1. Synthesis of CoFe2O4 Nanoparticles. In the synthesis of CoFe2O4 nanoparticles, 10 mL of an aqueous solution containing 0.275 mmol of cobalt chloride hexahydrate (CoCl2·6H2O, Acros) and 0.55 mmol of iron sulfate heptahydrate (FeSO4·7H2O, Sigma-Aldrich) was heated at 90 °C. After 40 min, 2 mL of an aqueous solution of sodium hydroxide (1.65 mmol, NaOH, Sigma-Aldrich) and potassium Received: August 14, 2017 Accepted: November 2, 2017 Published: November 2, 2017 40628
DOI: 10.1021/acsami.7b12147 ACS Appl. Mater. Interfaces 2017, 9, 40628−40637
Research Article
ACS Applied Materials & Interfaces
Figure 1. Fabrication process of magnetic CNT papers. The photograph shows flexibility of the magnetic CNT paper with 73 wt % of CoFe2O4 nanoparticles.
Figure 2. (a, b) Cross-sectional SEM images of dried CNT papers prepared (a) without and (b) with PVA. The inset in (a) shows a photograph taken after hot pressing of a dried CNT paper that had been prepared without PVA. (c) Stress−strain curves of CNT papers, and (d) comparison of mechanical properties of pristine CNT papers and CNT papers with polymers. nitrate (2.475 mmol, KNO3, Acros) was added to the above mixture solution. The mixture solution was kept at 90 °C for 3 h and then quenched to room temperature. 2.2. Fabrication of Magnetic CNT Papers. Thirty milligrams of multiwalled CNT (MWCNT) (10−20 nm in diameter,
