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

COMPOSITES

By 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 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

Stirrer

SonicateStir/Titrate

Dry

10

Magnetic Hotplate

Making a Nanocomposite cont’d

Stirrer

Toluene

12345678910

70oC60 oC

Minutes to wait

Changes in Procedure

Initial toluene volume

Cold Mix Mixing mixture at temperature lower than melting

point of polyethylene

“Titration” Adding polyethylene over time

Heat Mix Stirring and leaving the heat on for additional hour

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…)

Measure out the determined amount of polyethylene based on the mass ratio. 5 grams of polyethylene would be needed for a mass

ratio of 10:1

Calculate the volume of polyethylene and multiply it by 3.5. Add that amount of toluene to the silicon carbide.

Picture courtesy of Stancil group and student Charlezetta E. Stokes

Polyethylene (PE)

Silicon Carbide (SiC)

n1

n2

Reflectivity changes with refraction index

S-polarizedS-polarized

P-polarized

Material Refractive Index

Polyethylene 1.5159 - 1.488

Silicon Carbide 2.69026 - 2.55

Carbon Black 1.11-2

Toluene 1.496

Air 1

Polyethylene

SiC

Carbon Black

RESULTS

Kinetics study

Goal: To see how long it took for enough toluene to evaporate before it’s presence was not detected on the FTIR-ATR (Fourier transform infrared spectroscopy – Attenuated Total Reflectance).

What was expected. What was observed.

Importance : Refractive index changes as the components of the nanocomposite changes.

760 810 860 910 96060

65

70

75

80

85

90

95 10:1

Day 1Day 3Day 4Day 5

Cm-1

T%

Increase in Time

Day 5

750 800 850 900 950 10000

5

10

15

20

25

30

1 to 1

Day 1Day 2Day 4Day 5

Cm-1

%T

750 800 850 900 950 100035

40

45

50

55

60

65

70

75

5 to 1

Day 1Day 2Day 3Day 4Day 5

cm-1

%T

750 800 850 900 950 100070

75

80

85

90

15 to 1

Day 1Day 2Day 4Day 5

Cm-1

%T

750 800 850 900 950 100070

75

80

85

90

95

20 to 1

Day 1Day 4Day 5

Cm-1

%T

750 800 850 900 950 10000

10

20

30

40

50

60

70

80

90

100

1 to 15 to 110 to 115 to 120 to 1

Cm-1

%T

Day 5 Averages across all ratios

Increase with decrease in polyethylene

Mixing Challenges Nanoparticles seem to clump together.

This may be caused by the nanoparticles not dispersing fully.

Polyethylene/Nanoparticle mixture becomes too viscous which affects 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. 4 times the volume of polyethylene.

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

VT = volume total

VNP = volume of nanoparticles

X = distance between nanoparticles

Summary

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

Day 5 is dried

Slanting caused by changes in refraction index

Next steps….

To compare the surface phonon-polariton response for one mass ratio with time dependence (Day 1 – Day 5).

To compare the surface phonon-polariton response for different mass ratios on the same day.

Table the SEM determined particle separations versus recipe determined particle separations.

Acknowledgements

I 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)