A MEMS dynamic mechanical analyzer for in situ viscoelastic characterization of 3D printed nanostructures

Abstract

Cellular metamaterial structures with sub-micron features have shown the ability to become excellent energy absorbing materials for impact mitigation due to the enhanced mechanical properties of materials at the nanoscale. However, in order to optimize the design of these energy absorbing metamaterial structures we need to be able to measure the dynamic properties of the sub-micron features such as storage and loss moduli and the loss factor. Therefore, at scale testing is required to capture the scale, temperature, and strain rate dependent material properties of these nanoscale materials. This paper presents the design, fabrication, and calibration of a MEMS-based dynamic mechanical analyzer (DMA) that can be directly integrated with the two photon lithography (TPL) process commonly used to fabricate metamaterial structures with nanoscale features. The MEMS-based DMA consists of a chevron style thermal actuator used to generate a tensile load on the structure and two differential capacitive sensors on each side of the structure used to measure load and displacement. This design demonstrated 1.5 ± 0.75 nm displacement resolution and 104 ± 52 nN load resolution, respectively. Dynamic mechanical analysis was successfully conducted on a single nanowire feature printed between the load and displacement stages of the MEMS device with testing frequencies ranging between 0.01–10 Hz and testing temperatures ranging between 22 °C–47 °C. These initial tests on an exemplar TPL part demonstrate that the printed nanowire behaves as a viscoelastic material wherein the transition from glassy to viscous behavior has already set in at the room temperature.

Power Spectral Density Analysis of Nanowire-Anchored Fluctuating Microbead Reveals a Double Lorentzian Distribution

“…In the limiting case of thin nanowires, the stochastic thermal forces exerted on the microbeads cause clearly detectable Brownian motion behavior (see Figure 1c), specifically in the direction perpendicular to the nanowire axis, as depicted in Figure 1d). Moreover, as recently demonstrated, photopolymer nanowires possess viscoelastic material properties [24,25], which define the specific confinement forces investigated in the present work. Our present work is closely related to the preceding study focused on the bending recovery motion of photopolymer microbead-nanowire systems [25].…”

“…As provided below in Section 4.5, the mean potential energy for the respective degrees of freedom can be compared to determine the equilibrium level of energy flow controlled by C FT1 and C FT2 . The Equation (24) given above is essentially the case of the general fluctuation-dissipation theorem introducing the natural heat unit k B T.…”

Assessing the Viscoelasticity of Photopolymer Nanowires Using a Three-Parameter Solid Model for Bending Recovery Motion

“…Viscoelastic behavior was reported recently for nanowires prepared by TPP-DLW [26,27]. In the work of Cayll et al, the nanowire properties were measured by a MEMS-based dynamic mechanical analyzer and were expressed in terms of the frequency dependent tensile storage and loss moduli [26]. Viscoelasticity of photopolymer nanowires was also reported in our previous work [27].…”

“…The process of downscaling experiments to microscopic dimensions is complex. Viscoelastic behavior was reported recently for nanowires prepared by TPP-DLW [26,27]. In the work of Cayll et al, the nanowire properties were measured by a MEMS-based dynamic mechanical analyzer and were expressed in terms of the frequency dependent tensile storage and loss moduli [26].…”