Photoinduced Heating of Freestanding Azo-Polymer Thin Films Monitored by Scanning Thermal Microscopy

Abstract

Despite numerous attempts to capture a temperature rise in azobenzene-functionalized polymer thin films exposed to laser irradiation, so far no attention has been paid to direct temperature measurements. Here, we characterize a photoinduced heating of freestanding thin films using nanoscale resolution scanning thermal microscopy. The polymer films under study are composed of epoxy-based oligomers with chemically attached nitroazobenzene chromophores. A temperature change of 1.7 K only is observed when an 800 nm thick film is subject to resonant 532 nm illumination with a modest intensity of 25 mW/cm2. A freestanding and glass substrate supported 20 nm azo-polymer films exhibit an anomalous depression of the glass transition temperature by approximately 80 and 70 K, respectively, that is probed with thermally assisted atomic force microscopy. Our results show that the photoinduced heating can negatively affect an ordered state of the azo dyes within the polymer ultrathin film (<100 nm) at room temperature.

A Review on Principles and Applications of Scanning Thermal Microscopy (SThM)

“…Another kind of polymers, like the Azobenzene‐functionalized polymers, show nonlinear properties. By measuring the temperature rise of thin films in free‐standing state, the azo‐polymer thin film was concluded to have increasing photoinduced heating when it is laminated by a larger phonon intensity . Researchers also combined thermally conductive fillers into polymers and built thermal percolation pathways to promote internal heat transfer in the composites.…”

Nanoscale Sensing Vitrification of 3D Confined Glassy Polymers Through Refractory Thermoplasmonics

“…Most conventional methods for probing the glass–rubber transitions, for example, differential scanning calorimetry (DSC), possess high sensitivity but insufficient resolution. At first glance, it can be done with scanning probe microscopy methods such as atomic force microscopy , and scanning thermal microscopy, , which allow one to probe a specimen at a higher spatial resolution. However, these tools often require macroscopic heating/cooling of the whole specimen.…”

Light-printable epoxy oligomer wrinkle-forming surface for rewritable information storage

“…5a and c), which was similar to the values in previous reports. [40][41][42] And the surface temperature increase on the corresponding blank PDMS substrate was about 2 C during light irradiation (64 mW cm À2 ) ( Fig. 5a and d).…”