Welcome to my webpage.  This page summarizes my experience doing research throughout summer 2011 in the physics department at Kansas State University.  I looked at gold nanoparticles to study the Marangoni Effect and at cadmium selenide nanoparticles to study the Soret Effect. I would like to thank Dr. Bruce Law and Dr. Chris Sorensen for their guidance throughout the project as well as Dr. Haeng Sub Wi for teaching me how to use all of the instruments. I would also like to thank Dr. Kristan Corwin and Dr. Larry Weaver for supporting the project and the National Science Foundation for funding the project.

Project Goal: The goal of my project was to study gold nanoparticles ligated with dodecanethiol (Au@DDT) in octadecane and cadmium selenide nanoparticles ligated with trioctylphosphine oxide (CdSe@TOPO) in octadecane to observe the Marangoni effect and the Soret effect.

Nanoparticles: Nanoparticles are important to study because they behave differently than both atoms and larger sized particles. This could be due to the fact that they have a larger surface area to mass ratio than larger sized particles causing them to be more reactive. Nanoparticles are being used it many fields and for many reasons including to identify cancerous tumors, to deliver drugs into the body, to increase battery power and reduce recharge time of lithium-ion batteries, to clean polluted ground water, to make odor-resistant or stain-proof clothing, and to make tennis rackets stronger. In a nanoparticle solution if the surface energy of the nanoparticles is lower than that of the solvent then the nanoparticles will remain on the surface of the solution in order to lower the overall surface energy. When the nanoparticles’ surface energy is lower than that of the solvent then the nanoparticles will stay in the bulk of the solution so as to not raise the surface energy.

Marangoni Effect: This phenomenon was first identified in 1855 by James Thomson, an engineer and physicist from the United Kingdom. However, it is named after the Italian physicist Carlo Marangoni who studied the effect for his doctoral dissertation and published the results in 1865. The Marangoni effect occurs when there is a difference in surface energy between two substances. An example of these two substances is a scenario in which a solution is applied across a temperature gradient so that half of the solution is liquid and half is solid. The temperature Marangoni effect occurs because surface energy is dependent upon temperature. A colder solution has a higher surface energy than a warmer solution. Surface energy is also a force meaning that when a solution is applied across a temperature gradient the larger force, on the colder side, overcomes the lesser force, on the warmer side, and pulls the liquid toward the solid side. The liquid solution then freezes while the force from the solid side continues to pull the liquid side until the entire solution has solidified. The liquid solidifies near the interface and forms a solid “mountain.” The temperature Marangoni effect is strong, but even stronger is the particle Marangoni effect. The particle Marangoni effect occurs then there are nanoparticles located on the surface of a solution. Nanoparticles located on the surface of the solution lower the overall surface energy of the solution. When this solution is applied across a temperature gradient and the solid side freezes, the nanoparticles freeze out before the octadecane. This results in a higher surface energy in the solid half because the surface is now pure octadecane. The force on the solid side pulls even stronger on the liquid side until all the liquid moves over, solidifies, and forms a “mountain.”

Soret Effect: This effect in liquid mixtures was first observed and reported by the German physician and physiologist Carl Ludwig in 1856 and then further understood by the Swiss physicist and chemist Charles Soret in 1879. The Soret effect is a thermodynamic phenomenon occurring in the bulk solvent when mobile particles are placed across a temperature gradient. The positive Soret effect occurs when the larger/heavier particles move to a colder region and the smaller/lighter particles move toward a warmer area, whereas the reverse effect is called the negative Soret effect. The positive Soret effect could be modeled by a nanoparticle solution applied across a temperature gradient in which the solvent moves to the colder side and the nanoparticles move toward the warmer region. The Soret effect is distinguishable from the Marangoni effect by the lack of mountain building activity. Although the Soret effect is not very well understood microscopically, it is still a useful tool in separating a mixed solution or in preventing the mixing of a separated solution.

Project Summary: It was known that a solution of gold Au@DDT in octadecane formed a mountain when a temperature gradient was applied across the solution in which half was liquid and half was solid. This was due to the particle Marangoni effect because the nanoparticles were on the surface of the octadecane solvent, as discovered by measuring the surface energy. Pure octadecane also formed a mountain when a temperature gradient was applied due to the temperature Marangoni effect. A solution of CdSe@TOPO in octadecane was thought to follow the Soret effect. This was because the measured surface energy was the same as pure octadecane indicating that the nanoparticles were in the bulk solvent instead of on the surface. However, it was found that the CdSe@TOPO in octadecane solution did not follow the Soret effect, but rather the temperature Marangoni effect like the pure octadecane. This implied that the bulk solvent had no affect on the observed trend. The only thing that mattered in determining whether the Marangoni effect or Soret effect was observed was the surface composition.

Pictures:

Pure Octadecane at Time = 0 hours

Pure Octadecane at Time = 8 hours

Au@DDT in Octadecane at Time = 0 hours

Au@DDT in Octadecane at Time = 8 hours

CdSe@TOPO in Octadecane at Time = 0 hours

CdSe@TOPO in Octadecane at Time = 8 hours

Final Presentation:  To see my final presentation in click here.

Final Report: To see my final written report click here.

About Me:  I grew up near Kansas City, Kansas and now attend Kalamazoo College located in Michigan. I will be graduating in 2013 with a double major in chemistry and physics. I had never taken a physics class until college when I found myself pre-registered for Introductory Physics I and had nothing better to take. Ever since then I have been taking and enjoying physics classes. Outside of class I enjoy playing sports, making tie-dye, playing cards, travelling the world, and cheering on the KC Royals and the KU Jayhawks.

This program is funded by the National Science Foundation through grant number PHY-0851599.