Metal Nanoparticles Acting as Light‐Activated Heating Elements within Composite Materials

Abstract

The photothermal effect of metal nanoparticles embedded in polymeric materials can be used to effi ciently generate local heat for in situ thermally processing within an existing material. Fluorescent probes are employed as thermal sensors to allow dynamical measurement of the amplitude and rate of temperature change within the polymer matrix. The effi cacy of this technique is demonstrated in polymer nanocomposite samples with different morphological characteristics, namely nanofi brous mats and thin fi lm samples. For similarly thick materials and both types of sample morphology, average temperature increases on the order of ≈ 100s ° C are readily obtained with dilute nanoparticle concentrations under relatively low irradiation intensity. Thus, the in situ photothermal heating approach has great potential for controllably driving a multitude of thermal processes, such as triggering phase transitions, generating site-specifi c cross-linking, or initiating chemical reactions from within a material.

Blending with Non‐responsive Polymers to Incorporate Nanoparticles into Shape‐Memory Materials and Enable Photothermal Heating: The Effects of Heterogeneous Temperature Distribution

“…Reported results are an average from the response of 12-15 separate specimens measured at three highest intensities. In all cases, the average temperature was greater than the melting temperature of PEO ( T m = 66 °C); as previously discussed, [ 5 ] for these conditions, the fi nal steady-state temperature under photothermal heating is only a weak function of laser intensity and particle concentration. 0.2 wt% AuNPs samples exhibited a more rapid increase in temperature than corresponding 0.1 wt% AuNPs samples up to the PEO melting transition.…”

“…As previously discussed, [ 5,12,13 ] photothermal heating from embedded metal nanoparticles in polymeric systems generates a heterogeneous spatial temperature distribution, with the warmest temperature in the region near the particle. In order to determine the average sample temperature, a molecular thermometer was utilized.…”

“…As an example, experiments with varying wt% of gold nanorods in neat PEO under a constant irradiation intensity resulted in average background sample temperatures of ≈10−30 °C lower than the temperature in the immediate vicinity of the particle, once a steadystate equilibrium temperature is established. [ 5,12,13 ] Thus, the hottest temperature in the sample could be as low as 10 °C or as high as ≈30 °C above the bulk temperature.…”

“…Thus, embedding low concentrations of metal nanoparticles (i.e., less than a few weight percent (wt%)) within polymeric materials potentially enables internal heating of the polymer (e.g., up to hundreds of °C). [ 5,12,13 ] In this work, spherical gold nanoparticles (AuNPs) with a relatively narrow distribution (32 ± 8 nm) were used as the photothermal heaters.…”

Nanoparticles for Mass Spectrometry Applications

“…Noble metal nanoparticles, such as gold or silver, possess an enhanced absorptivity in the ultraviolet-visible region, which favors transformation of photothermal energy during laser irradiation and provides a more effective ionization of analytes [6,34]. Photothermal properties and heat generation at the NP surface are directly dependent of NP volume, size, and incident energy, and heat generation at a given point is related to the distance to the center of the NP [35,36]. This way, ligands covalently bound to the NP surface will ionize easily as distance to the NP is minimal, but the desorption process is more difficult due to higher bonddissociation energy.…”