electrochemically responsive nanoarchitected 3d microstructures

3d architected materials with their striking properties such as negative poisson’s ratios, negative linear thermal expansion 1,and negative reflective indexes have the potential to revolutionize the modern technologies. when the architected materials are incorporated with an internal mechanism to be geometrically reconfigurable triggered by an external stimulus, they can offer novel multifunctionalities. it has been shown that the architected structures can be actuated by various stimuli such as light, magnetic actuation, mechanical instability/deformation, temperature, and hydration-trigged swelling. however, most of stimulus-responsive architected structures have still some challenges such as (i) binary response and (ii) volatile actuation upon the removal of the stimulus. growing the advancement in micro/nanomanufacturing techniques such as microprinting, two-photon lithography, colloidal self-assembly, and stress-controlled buckling, has created the potential to address some of the challenges in manufacture of 3d architected microstructures and exploit them in emerging technologies such as microrobotics, biomedical devices, metamaterials, energy storage systems and integrated electronics. even though each of the above-mentioned fabrication techniques offers valuable and distinct features, none is without critical shortcomings; some in throughputs, features size/geometry, some are limited in use of high-performance materials and others in compatibility with the scalable 2d fabrication techniques such as photolithography, chemical/physical methods of deposition and growth. herein we exploit electrochemically driven alloying reaction to achieve reversible, non-volatile, and continues reconfiguration (with varying speeds) of the 3d carbon nanotube (cnt) microstructures coated with redox active materials. the developed the 3d architected microstructures reconfigure upon electrochemical alloying and de-alloying reactions. additive manufacturing of electrochemically responsive architectures has been developed by xia et al. using two-photon photopolymerization which is hardly applicable for printing a large number of microstructures and/or over the areas larger than few hundreds of microns. in this work, wafer-scale vertically aligned cnt forests were grown via thermal chemical vapor deposition (cvd) from 2d photolithography pattens as sturdy backbones for redox active materials. cnts are well known for their excellent tensile strength (100 gpa), high young's modulus (1 tpa), high fatigue resistance, and remarkable electrical and thermal conductivity. the alloying couple of lithium (li) and tin (sn) is used mainly because of the high volumetric expansion (+250%) and high capacity (~ 993 ma.h per gram of sn) of sn upon lithiation (from sn to li22sn5). we take the advantage of the elastocapillary mechanism initiated by reduction of sno2 to sn to transform the prismatic cnt forests to more intricate 3d microstructures. this additional geometric design can help to tune the degree of reconfiguration during lithiation. . the demonstrated approach for design and fabrication of the responsive architected materials can pave the way for development of emerging energy storage materials and micro-actuators