Experimental and Theoretical Studies of Light-to-Heat Conversion and Collective Heating Effects in Metal Nanoparticle Solutions

Abstract

We perform a set of experiments on photo-heating in a water droplet containing gold nanoparticles (NPs). Using photo-calorimetric methods, we determine efficiency of light-to-heat conversion (η) which turns out to be remarkable close to 1, (0.97< η <1.03). Detailed studies reveal a complex character of heat transfer in an optically-stimulated droplet. The main mechanism of equilibration is due to convectional flow. Theoretical modeling is performed to describe thermal effects at both nano- and millimeter-scales. Theory shows that the collective photo-heating is the main mechanism. For a large concentration of NPs and small laser intensity, an averaged temperature increase (at the millimeter-scale) is significant (~ 7 °C) whereas, on the nanometer scale, the temperature increase at the surface of a single NP is small (0.02 °C). In the opposite regime, a small NP concentration and intense laser irradiation, we find an opposite pictures: a temperature increase at the millimeter-scale is small (0.1 °C) but a local, nanoscale temperature has strong local spikes at the surfaces of NPs (3 °C). These studies are crucial for the understanding of photo-thermal effects in NPs and for their potential and current applications in nano-and bio -technologies.

Nanoparticles Heat through Light Localization

“…(6) It has been suggested that collective thermal effects are important in explaining the response of such systems. (7)(8)(9)(10)(11) Here we show, however, that collective thermal effects alone are not sufficient to explain the thermal response of these systems. Rather, light trapping by solutions of particles that simultaneously absorb and scatter light results in highly localized heating, an unanticipated effect that, when combined with classical heat transfer, provides an accurate theoretical description of the system.…”

Physiological Fluid Specific Agglomeration Patterns Diminish Gold Nanorod Photothermal Characteristics

“…Au-NRs also possess the shapespecific advantages of tunable aspect ratio (AR) and strong longitudinal surface plasmon (LSP) absorbance in the near infrared (NIR) range [4]. Due to the fact that NIR light excites the LSP resonance of the Au-NRs, they possess exceptional photothermal capabilities, converting absorbed light into thermal energy with high efficiency [5,6]. This nanophotonic characteristic, coupled with the fact that NIR light is minimally absorbed by tissues, makes Au-NRs an ideal candidate for photothermal based therapies and applications.…”

Compact solar autoclave based on steam generation using broadband light-harvesting nanoparticles

“…A variety of nanoparticles such as metallic nanoshells, nanoshell aggregates, and conductive carbon nanoparticles, when dispersed in aqueous solution and illuminated by sunlight, has been shown to convert absorbed solar energy to steam at an efficiency of just over 80%, where less than 20% of the energy contributes to heating the liquid volume (7). This effect depends on the highly localized, strong photothermal response of these types of nanoparticles, a characteristic that is being used to effectively ablate solid tumors by irradiation with near-IR laser light with near-unity tumor remission rates (8)(9)(10)(11)(12)(13)(14)(15)(16). In the solar steam generation process, broadband light-absorbing nanoparticles create a large number of nucleation sites for steam generation within the fluid.…”