Micromechanical String Resonators: Analytical Tool for Thermal Characterization of Polymers

Abstract

Resonant microstrings show promise as a new analytical tool for thermal characterization of polymers with only few nanograms of sample. The detection of the glass transition temperature (T g) of an amorphous poly(d,l-lactide) (PDLLA) and a semicrystalline poly(l-lactide) (PLLA) is investigated. The polymers are spray coated on one side of the resonating microstrings. The resonance frequency and quality factor (Q) are measured simultaneously as a function of temperature. Change in the resonance frequency reflects a change in static tensile stress, which yields information about the Young’s modulus of the polymer, and a change in Q reflects the change in damping of the polymer-coated string. The frequency response of the microstring is validated with an analytical model. From the frequency independent tensile stress change, static T g values of 40.6 and 57.6 °C were measured for PDLLA and PLLA, respectively. The frequency-dependent damping from Q indicates higher T g values of 62.6 and 88.8 °C for PDLLA and PLLA, respectively, at ∼105 Hz. Resonant microstrings facilitate thermal analysis of nanogram polymer samples measuring the static and a dynamic glass transition temperature simultaneously.

Responsivity

“…Optimizing all parameters, K resolution can be achieved with nanostring resonators [13]. In the case of string made from multiple layers of different materials, the mass density and the temperature dependent tensile stress can be written in an effective form, which in the particular case of two materials are [26] …”

Detection methods for centrifugal microfluidic platforms

“…The high precision and small spot size make this system a powerful tool to read out a wide range of nano and micro-sized resonators. For example it could be used to realize compact mechanical IR spectrometers using string resonators (Larsen et al, 2013) and high-throughput platforms for studying thermal behavior of for example polymers (Bose et al, 2014;Jung et al, 2012).…”

Thermomechanical analysis of picograms of polymers using a suspended microchannel cantilever

“…17,18,21,22 Both of these techniques require special spray coating or ink jet printing to deposit nanograms of sample. 23 Another challenge (when using microstrings or microcantilevers) is sublimation of the sample during heating.…”