By Jesse L. Gray, III Mentors: Dr. Kimani A. Stancil Dr. James S. Hammonds

EXPLORING THERMAL TRANSFER VIA SURFACE PHONON-POLARITONS IN TUNABLE SILICON CARBIDE BULK

COMPOSITESBy

Jesse L. Gray, III

Mentors:Dr. Kimani A. Stancil

Dr. James S. Hammonds

Overview Goal and Importance What are Surface Phonon-Polaritons? Making of Nanocomposite Analysis Preliminary Results Discussion Next Steps

Goal – To make tunable bulk nanocomposite comprised of Silicon Carbide & Polyethylene that exhibits Surface Phonon-Polariton coupling.

Importance – The results will be used to give the capability to tune and dictate the thermal conductance of a material based on nanoparticle spacing.

What are Surface Phonon-Polaritons?

Electromagnetic waves that propagate along the interfaces of polar dielectrics.

Results from an evanescent wave’s electric field coupling of infrared photons and optical phonons like two coupled oscillators with the same frequency.

They can enhance fields near the interfaces at infrared frequencies.

Magnetic Hotplate

Making a Nanocomposite

Silicon Carbide

Nanoparticles Polye

thyle

ne

StirrerToluene

Making a Nanocomposite cont’d

Preparation Measure out a predetermined ratio of silicon

carbide nanoparticles to polyethylene. .5 grams of nanoparticles is a base reference for

all mass ratios (1:1, 5:1, 10:1, etc…)

Magnetic Hotplate

Making a Nanocomposite cont’d

Stirrer

Mix Heat / Stir Dry

AnalysisSmall samples from dried composite are analyzed

using an FTIR (Fourier transform infrared spectroscopy)-ATR (Attenuated Total Reflectance) machine.

Picture courtesy of Stancil group and student Charlezetta E. Stokes

Preliminary Results Mixing Challenges

Nanoparticles seem to clump together. This may be caused by the nanoparticles not dispersing fully.

Proper mixing will have nanoparticles ~70nm apart.

Polyethylene/Nanoparticle mixture becomes too viscous which effects the mixing of additional polyethylene. Idea: Toluene is evaporating too fast. Improvement: Starting out with a greater amount of

Toluene may solve the predicament. Use toluene volume that is approx. 3 times the volume of polyethylene.

SEM of 15:1 SiC/PE

SiC Nanoparticles Polyethylene

Picture courtesy of Cory Davis

Ratio 15:1

Ratios 1:1, 5:1, 10:1, 20:1

Picture courtesy of Cory Davis

Figure of a SiC particle of diameter, D, enclosed by a rectangularrepresentation of polyethylene of length = height = D+X

Early Discussion Ratios 10:1 and lower cracked up when

force was applied to them for FTIR measurement resulting in sloping graphs.

Nanoparticles did not mix well in ratios 5:1 and below.

Phonon-Polariton activity happens between the wavelengths of 766-969 nanometers.

Next steps…. To use a titration method for mixing

polyethylene and silicon carbide.

Limit toluene evaporation using a lid.

Stir with heat over longer time periods.

AcknowledgementsI would like to thank

Dr. Kimani A. Stancil, Dr. James S. HammondsCory Davis, Josh Brown

Howard University Physics & Astronomy

National Science Foundation (funding the HU Physics REU)

Virginia Union University (and Dr. Francis Mensah)