The Jozef Stefan Institute focuses on research in physics, engineering, and mathematics. The document discusses working in the Department of Surface Engineering and Optoelectronics on ionized-gas plasmas. The main goals of the project were to gain knowledge about different types of ionized-gas plasmas and how they can be used industrially, and to improve engineering research techniques. The largest part of the summer was spent studying how microwave plasma treatment affects the hydrophobicity of plastics like PLA and PET. Samples were exposed to low-pressure gas plasmas at various powers and times, and contact angle was measured to show changes in hydrophobicity. The results showed that higher plasma powers and pressures of 50 or 80 Pa typically

1. Jozef Stefan Institute
The JSI is a graduate level
institution focused on research in
the fields of physics, engineering,
and mathematics. I worked in the
Department of Surface Engineering
and Optoelectronics alongside Dr.
Miran Mozetic, Dr. Uros Cvelbar,
and several Ph.D. students. All of
the research focused on ionized-gas
plasmas.
Project Goals
There were 2 main goals for this
project:
• to gain knowledge about several types
of ionized-gas plasmas and how each
can be used in a manufacturing setting
• to improve upon research techniques
and practices used in the engineering
field.
Conclusions and Scope
The purpose of altering the hydrophobicity of materials is very broad and
could have many applications. One of these could be increasing the ability to
grow cells using the plastic as a substrate. Thus due to to organic nature of
PLA, it may be possible to grow tissues and organs using the plastic as a
skeleton.
The specific data found during the course of the experiments could have
implications involving the manufacturing and production of hydrophilic
materials. Using minimum power and time would be a large factor in the
engineering design of a production system for these materials.
Main Experiment
The largest portion of my summer was spent studying the effect of
microwave plasma treatment on the hydrophobicity of organic
plastics. Samples of PLA (polylactic acid) and PET (polyethylene
terephthalate) treated with various chemicals were exposed to various
low-pressure gas plasmas for varied amounts of time. Then the water
contact angle (WCA) was measured to show a change in
hydrophobicity. Other methods were used to test effects such as
heating samples pre- and post-plasma exposure.
0
10
20
30
40
50
60
70
80
90
0 10 20 30 40 50 60 70 80 90 100
WCA
Exposure time (s)
Averages (30 Pa)
75 W
100 W
150 W
200 W
250 W
66.35
70.15
61.16666667
72.275
58.125
47.7
66.35
40.95
36.775
25.75 24.875
27.15
66.35
31.6
28
23
24.65
22.75
66.35
40.3
31.775
22.475
24.1 24.66666667
66.35
28.725
24.725
25.875 26.35
0
10
20
30
40
50
60
70
80
0 10 20 30 40 50 60 70 80 90 100
WCA
Exposure time (s)
Averages (50 Pa)
75 W
100 W
150 W
200 W
250 W
0
10
20
30
40
50
60
70
80
90
0 10 20 30 40 50 60 70 80 90 100
WCA
Exposure time (s)
Averages (80 Pa)
75 W
100 W
150 W
200 W
250 W
Results
Below are the WCA results found for PET exposed to NH3 plasma for different lengths of time at five different
plasma powers. The results show that higher-powered plasma typically yields a larger decrease in WCA. Also
pressures of 50 Pa and 80 Pa yield lower WCA than 30 Pa for most scenarios. Also, for these pressures, the
minimum WCA is reached after about 30 seconds of treatment. The smallest WCA achieved in this experiment
was about 20 degrees
Future Plans
For my final Brown Fellows project, I would
like to either work for a company that
produces solar cells, batteries, or electric cars;
or possibly pursue different research interests
more focused on manufacturing and
mechanical engineering aspects of the solar
cell production industry.