Development of a photoacoustic instrument for the determination of the photothermal properties of nanoparticles

Open Access
Author:
Wrubel, Joshua Michael
Graduate Program:
Chemistry
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 08, 2013
Committee Members:
  • Benjamin James Lear, Thesis Advisor
  • David Lawrence Allara, Thesis Advisor
  • John B Asbury, Thesis Advisor
Keywords:
  • chemistry
  • analytical
  • photoacoustic
  • nanoparticles
  • gold
  • iron oxide
  • laser
  • TEM
Abstract:
Chemical reactions that typically require heating of a bulk solution in order to proceed are one recent target of the push towards greener chemical methods. One method employed to reduce the amount of energy input needed for such reactions is to use the photothermal effect in nanoparticles (NPs) to heat the reactant molecules locally without heating the whole reaction mixture. Determining the amount of thermal energy produced by NPs is of concern in order to maximize the efficiency of such methods, but most approaches to date only indirectly report on this heat by monitoring the progress of the target reaction. I used photoacoustic (PA) analysis to measure the heat produced by NPs, specifically dodecanethiol-functionalized gold nanoparticles (AuNPs) and oleylamine-functionalized iron oxide nanoparticles (Fe3O4 NPs). PA analytical techniques use microphones or vibration-sensitive piezoelectric detectors to acoustically measure the pressure front caused by the propagation of thermal energy away from an analyte. For such measurements, thermal energy is generated by the non-radiative (thermal) relaxation pathways in the analyte of interest. Using a frequency-doubled pulsed Nd:YAG laser to irradiate the NPs, a piezoelectric detector mounted to a 1 cm pathlength cuvette, and a 1 GHz digital oscilloscope for signal processing, a simple, custom-built, and adaptable photoacoustic cell and measurement technique was developed to measure the acoustic pressure signal produced by nanoparticles. The dependence of the photoacoustic signal strength upon laser energy and nanoparticle concentration has been tested, revealing a linear dependence upon each within limits of optical density and laser energy. Preliminary efforts have been made to calculate the heat flux and temperature changes that produced the photoacoustic signal.