High-Resolution Mapping of Thermal History in Polymer Nanocomposites: Gold Nanorods as Microscale Temperature Sensors

Abstract

A technique is reported for measuring and mapping the maximum internal temperature of a structural epoxy resin with high spatial resolution via the optically detected shape transformation of embedded gold nanorods (AuNRs). Spatially resolved absorption spectra of the nanocomposites are used to determine the frequencies of surface plasmon resonances. From these frequencies the AuNR aspect ratio is calculated using a new analytical approximation for the Mie-Gans scattering theory, which takes into account coincident changes in the local dielectric. Despite changes in the chemical environment, the calculated aspect ratio of the embedded nanorods is found to decrease over time to a steady-state value that depends linearly on the temperature over the range of 100-200 °C. Thus, the optical absorption can be used to determine the maximum temperature experienced at a particular location when exposure times exceed the temperature-dependent relaxation time. The usefulness of this approach is demonstrated by mapping the temperature of an internally heated structural epoxy resin with 10 μm lateral spatial resolution.

Thermal Reshaping Dynamics of Gold Nanorods: Influence of Size, Shape, and Local Environment

“…The values thus determined agree well with the spectroscopic analysis, as previously described. 16 Volumes were calculated from these dimensions assuming the GNR geometry to be a hemispherically capped cylinder, as evidenced by electron microscopy (see Figures S1 and S4). The results are tabulated in Table 1 with uncertainties reported as half the standard deviation for each set of measurements.…”

“…These values were then used to calculate the average aspect ratio (a) of the rods in the sample using the function a = f(E LSPR , E TSPR ) that we previously developed for gold nanorods in epoxy. 16 Representative spectroscopic data are given in the Supporting Information (Figure S3). The temperature and time dependence of the thermal reshaping for each sample were analyzed using computed values for the aspect ratio, and the initial and final aspect ratios in each case were verified with electron microscopy (see Figure S4 in the Supporting Information).…”

“…When subjected to elevated temperatures (above room temperature, but well below the melting temperature), GNRs tend to undergo thermal reshaping via surface diffusion, evolving toward lower aspect ratios that are closer to the energetically favorable Wulff construction geometry (approximately spherical). 4−10 In applications such as materials with tunable optical properties, 11−14 optical memory storage devices, 15 and highresolution temperature mapping, 16 GNR thermal reshaping is a key phenomenon. The ability to change GNR shapes with temperature enables complex spatial distributions of optical properties.…”

“…6 On the other hand, polymeric matrices allow the reshaping dynamics to be significantly modular, and the time constants for transformation of embedded gold nanorods can vary from minutes to days. 6,13,16,22,23 Recently, Danielsen et al compared the thermal reshaping rates between nanorods with cross-linked polymers directly grafted to the GNR surface and those with grafted but uncrosslinked polymer brushes. 22 They found that the crosslinked polymer shell retards the shape transformation to a notable degree, which demonstrates the importance of the specific surface interactions between the nanorods and the surrounding matrix toward thermal reshaping.…”

Current-Mode Self-Amplified CMOS Sensor Intended for 2D Temperature Microgradients Measurement and Imaging

“…Most temperature sensors are available for MEMS -based microscale measurements, and not all of them have the desired integration with the CMOS technology, to feature essential functions such as amplification and signal conditioning [ 11 , 15 , 17 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. Furthermore, there have been developments in the nanoscale thermal sensing [ 37 , 38 , 39 , 40 , 41 ]. Some of these nanoscale sensors are used in contact with the measured sample [ 27 , 28 , 31 , 33 , 34 , 36 , 37 , 38 ].…”