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

Abstract

Photopolymer nanowires prepared by two-photon polymerization direct laser writing (TPP-DLW) are the building blocks of many microstructure systems. These nanowires possess viscoelastic characteristics that define their deformations under applied forces when operated in a dynamic regime. A simple mechanical model was previously used to describe the bending recovery motion of deflected nanowire cantilevers in Newtonian liquids. The inverse problem is targeted in this work; the experimental observations are used to determine the nanowire physical characteristics. Most importantly, based on the linear three-parameter solid model, we derive explicit formulas to calculate the viscoelastic material parameters. It is shown that the effective elastic modulus of the studied nanowires is two orders of magnitude lower than measured for the bulk material. Additionally, we report on a notable effect of the surrounding aqueous glucose solution on the elasticity and the intrinsic viscosity of the studied nanowires made of Ormocomp.

3D-printed ultra-small Brownian viscometers

“…The micro-viscometers investigated in this study are made of OrmoComp, a bio-compatible photoresist material with exceptional flexibility 39 . Our previous work investigated the viscoelastic properties of OrmoComp nanowire cantilevers by measuring the recovery motion of structures deflected by an optical tweezer setup 40 , 41 . It was shown that the cantilever mechanics can be described by a three-parameter viscoelastic model.…”

“…The effective Young’s modulus of polymer nanowires is four orders of magnitude lower than that of silicon, which is commonly used in AFM and/or MEMS cantilever applications. The stiffness of nanowires employed in our viscometers is extremely low, on the order of 0.001 pN/nm 41 . At the same time, because of significant dissipation caused by the surrounding liquid and the cantilever material's internal viscoelasticity, low frequency motion dominates the system dynamics.…”

“…Figure 1 d depicts the mechanical scheme of the micro-bead attached to the viscoelastic cantilever; only a single oscillation direction is considered. The nanowire viscoelasticity is characterized by the upper (red) arm, which evolves from the Kelvin form of a three-parameter standard linear solid 40 , 41 with two spring constants (stiffnesses) k 1 , k 2 , and a single internal damping coefficient δ . The lower (blue) arm containing the hydrodynamic resistance γ represents the Newtonian liquid that damps the micro-bead fluctuations.…”

Fabrication and Characterization of a Magnetic 3D‐printed Microactuator

“…This is because polymerized photoresins, similar to numerous other polymeric materials, display viscoelastic behavior. [54,55] The structures thus show typical characteristics such as creep and relaxation when load is applied and subsequently removed.…”

Estimation of Tensile Modulus of a Thermoplastic Material from Dynamic Mechanical Analysis: Application to Polyamide 66

“…This task is more difficult, since these models must take into account the variation in the behavior of materials at different frequencies and temperatures [ 2 , 6 , 20 ]. Although dynamic mechanical analysis (DMA) is a well-established option for obtaining material-response data over a broad spectrum of frequencies and temperatures [ 21 ], new methods are currently being tested and developed to identify the material parameters: for applications at the micro- and nanoscale by atomic force microscopy [ 22 , 23 , 24 ] or optical tweezer [ 25 ]; for biological materials (challenging because of their intrinsic softness and labile nature) [ 26 ]; and for noncontact methods such as magnetic mechanical testing for biomaterials [ 27 ] or ultrasonic DMA for nondestructive inspection [ 28 ]. On the other hand, a number of studies have examined simpler methods to be able to estimate the properties of materials, reducing the experimental cost and complexity [ 18 , 29 , 30 ].…”