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Strain‐Induced Alignment Mechanisms of Carbon Nanotube Networks
Author(s) -
Downes Rebekah,
Wang Shaokai,
Haldane David,
Moench Andrew,
Liang Richard
Publication year - 2015
Publication title -
advanced engineering materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.938
H-Index - 114
eISSN - 1527-2648
pISSN - 1438-1656
DOI - 10.1002/adem.201400045
Subject(s) - materials science , carbon nanotube , microstructure , composite material , strain hardening exponent , waviness , nanotube , ductility (earth science) , deformation (meteorology) , creep
Random networks comprised of millimeter‐long multi‐walled carbon nanotubes (CNTs) have shown unique microstructure change mechanisms under uniaxial strain. These networks can be modified into highly aligned microstructures from strain‐induced plastic deformation. Applying a treatment consisting of an uncured resin as a load transfer enhancement medium leads to a dramatically increased degree of alignment and final mechanical properties of the CNT networks. The structural evolution of the CNT networks includes different modes: de‐bundling, elongation to reduce waviness, sliding friction, and packing for self‐assembly into large bundles. The high ductility of the treated networks, which allows the network to achieve high degrees of strain‐induced alignment is mainly because the extra high aspect ratios of the individual CNT and their bundles as well as enhanced load transfer. High aspect ratio causes high degrees of entanglement and locking points between the nanotubes in the random network, which are critical to provide adequate nanotube to nanotube load transfer for ductile deformation and lead to substantially increased CNT alignment during mechanical stretching. The classical strain strengthening mechanisms used in metals and polymers such as strain hardening and crystallization of long molecular chains are discussed and compared to CNT network deformation mechanisms. The CNT network strain hardening parameter n value is as high as 0.65, over three times that of annealed low‐carbon steel and more than four times of polycarbonate plastics. Strength coefficient K values for the CNT network also show high values up to roughly 450 MPa, comparable to that of annealed magnesium alloys. The results show how the high degree of alignment of CNT networks and strain strengthening can be achieved through simple uniaxial strain and load transfer medium.