Coupling Nanoscale Viscoelastic Measurements and Infrared Heating of Polymers with AFM-IR

In heterogeneous polymer systems, the viscoelastic response of polymers around interfaces or with nanostructured morphology may deviate from bulk values. However, current measurement techniques tend to mask these local variations, which are crucial for understanding and developing these materials. Coupling the high spatial resolution of atomic force microscopy (AFM) with dynamic mechanical analysis (DMA) offers an avenue to circumvent this limitation. We previously demonstrated the advantages of using a focused infrared (IR) laser on an AFM-IR system to locally heat a sample during nanomechanical measurements, with heating modulated by varying the IR repetition rate. [1] Herein, we present a brief demonstration of coupling nDMA with our previously demonstrated chemistry-selective IR heating. We first measured the storage and loss modulus of poly(propylene glycol) (PPG)-4,4′-methylenebis(phenyl urea) (MPU) at varying IR repetition rates, demonstrating a viscoelastic modulus response with typical heating characteristics upon crossing the glass transition temperature. We further demonstrated stress relaxation of an enaminelinked vitrimer possessing significant bond dynamicity at elevated temperatures. Overall, this method is in the preliminary stages of development, and this working paper aims to serve as a basis for feedback and discussion.