Micromechanical String Resonators: Analytical Tool for Thermal Characterization of Polymers.

Area of Science:

• Materials Science
• Polymer Chemistry
• Analytical Chemistry

Background:

• Traditional thermal characterization methods often require larger sample sizes.
• Accurate determination of glass transition temperature (Tg) is crucial for polymer performance.
• Developing sensitive techniques for analyzing small polymer quantities is essential.

Purpose of the Study:

• To investigate resonant microstrings as a tool for thermal characterization of polymers.
• To detect the glass transition temperature (Tg) of amorphous poly(d,l-lactide) (PDLLA) and semicrystalline poly(l-lactide) (PLLA).
• To simultaneously measure static and dynamic Tg values using nanogram polymer samples.

Main Methods:

• Spray coating polymers onto resonant microstrings.
• Simultaneously measuring microstring resonance frequency and quality factor (Q) as a function of temperature.
• Utilizing changes in resonance frequency (Young's modulus) and Q (damping) for analysis.
• Validating the microstring frequency response with an analytical model.

Main Results:

• Static Tg values of 40.6 °C for PDLLA and 57.6 °C for PLLA were determined from frequency-independent stress changes.
• Dynamic Tg values of 62.6 °C for PDLLA and 88.8 °C for PLLA were observed at approximately 10^5 Hz from frequency-dependent damping (Q).
• Demonstrated simultaneous measurement of static and dynamic Tg for nanogram polymer samples.

Conclusions:

• Resonant microstrings provide a sensitive analytical tool for thermal characterization of polymers.
• The technique allows for the simultaneous determination of static and dynamic glass transition temperatures.
• This method is effective for analyzing very small polymer sample amounts (nanograms).