Biomimetic Carbon Nanotube Films with Gradient Structure and Locally Tunable Mechanical Property

Abstract

Naturally existing materials often acquire unique functions by adopting a gradient structure with gradual change in their microstructure and related properties. Imparting such an elegant structural control into synthetic materials has been a grand challenge in the field. Here, the concept of gradient structure into macroscopic carbon nanotube (CNT) films is employed and the CNT arrangement from well‐aligned array to completely random distribution, in a continuous and smooth way, is changed. Gradient films with tailored aligned‐to‐random transition rate or multilevel hierarchical structures with repeated transition have been fabricated. Local deformation and mechanical properties are directly related to the arrangement of CNTs and can be tailored by Herman's orientation factor; in particular, the elastic modulus and stiffness span over several orders of magnitude from aligned to random regions within a single monolithic film. Controlled synthesis of macroscopic CNT gradient structures with tunable mechanical properties opens a potential route toward manufacturing biomimetic functional materials with locally optimized design.

Biomimetic Materials with Multiple Protective Functionalities

“…A mechanical gradient is often obtained by varying the structures or components along an axis of materials, including filler content, degree of orientation, and crosslinking density . Here, we introduced mechanical gradients by varying Cu‐DOU hard phase content.…”

Carbon Nanotube Sponges, Aerogels, and Hierarchical Composites: Synthesis, Properties, and Energy Applications

“…[ 104 ] In this report, a pre-designed pattern of MWNT arrays was contacttransferred to a PDMS sheet, and then a complementary pattern of SWNT arrays was transferred onto the MWNT-PDMS substrate, resulting in a 3D microarchitecture containing the SWNT and MWNT components with tunable nanotube orientation (Figure 4 d). [ 105 ] The fabrication process was similar except that we gradually and smoothly varied the volume ratio between the two carbon sources (xylene and dichlorobenzene) during feeding. Furthermore, inspired by the gradient structure of natural materials with gradual change in their macrostructure and related properties (bamboo shows a gradient structure in its cross section), our group reported a gradient CNT fi lm in which the nanotube distribution changed from aligned to completely random in a smooth and continuous way.…”

“…Reproduced with permission. [ 105 ] Copyright 2015, Wiley-VCH. c) SEM images of the sponge-array parallel structure in which the sponge blocks are enclosed by the patterned arrays.…”

“…The above efforts were focused on the performance improvement by directly combining different CNT‐based structures into one integral composite. Furthermore, inspired by the gradient structure of natural materials with gradual change in their macrostructure and related properties (bamboo shows a gradient structure in its cross section), our group reported a gradient CNT film in which the nanotube distribution changed from aligned to completely random in a smooth and continuous way . The fabrication process was similar except that we gradually and smoothly varied the volume ratio between the two carbon sources (xylene and dichlorobenzene) during feeding.…”

Large Continuous Mechanical Gradient Formation via Metal–Ligand Interactions

“…Some lateral gradients are able to obtain smooth transitions, but there are few examples due to the complex synthetic effort required to generate them. Notable examples of previously reported lateral gradients include photoinduced crosslinking of cellulose nanocrystals, ordering of carbon nanotube films, and cellulose nanofibril/polymer nanopapers . While these and other synthetic analogs are functional mechanical gradients, they often suffer from relatively small ranges in stiffness (∼1 order of magnitude), non‐continuous stepwise transitions, and require specialty equipment to fabricate.…”