Carbowax-1000 a conducting polymer was found to give appreciable results in detection of explosive vapours in sensor applications. Coating of Carbowax-1000 over fused silica substrates using solvents such as Acetone, Chloroform, had less temperature stability. So, Carbowax-1000 is being used to form a Polyurethane. As a prelude dielectric parameters change was observed for HTPB-IPDI-PU (Hydroxyl-terminated polybutadiene – Isophorone diisocyanate – Polyurethane) when interacted with Toluene, THF, etc. using SPDR (Split Post Dielectric Resonator). HTPB-IPDI-PU was synthesized and spin coated to obtain thin films of ≈2µm and cured for 5 days at 323 K. Initial frequency and quality factor value (Q) value were measured for bare substrate and polymer film coated substrate. Shift in resonance frequency and Q value was measured after placing Toluene, THF, etc. in µLs over the polymer film. Shift in resonance frequency ranged from 1-100 MHz for different solvents. Considerable Q value changes were also observed.

1. By,
K Hayagreev V Sarma,
IISER-TVM.
24th June,2015.
Resonators based dielectric
parameters change in
Polyurethane as an exordial for
sensor application
At,

2. Abstract
Carbowax-1000 a conducting polymer was found to give appreciable
results in detection of explosive vapours in sensor applications.
Coating of Carbowax-1000 over fused silica substrates using solvents
such as Acetone, Chloroform, had less temperature stability. So,
Carbowax-1000 is being used to form a Polyurethane. As a prelude
dielectric parameters change was observed for HTPB-IPDI-PU
(Hydroxyl-terminated polybutadiene – Isophorone diisocyanate –
Polyurethane) when interacted with Toluene, THF, etc. using SPDR
(Split Post Dielectric Resonator).
HTPB-IPDI-PU was synthesized and spin coated to obtain thin films
of ≈2µm and cured for 5 days at 323 K. Initial frequency and quality
factor value (Q) value were measured for bare substrate and polymer
film coated substrate. Shift in resonance frequency and Q value was
measured after placing Toluene, THF, etc. in µLs over the polymer
film. Shift in resonance frequency ranged from 1-100 MHz for
different solvents. Considerable Q value changes were also observed.

3. Polymer Synthesis
Spin Coating
Dielectric Parameters
Measurement using
SPDR

4. SPDR (Split Post Dielectric
Resonator)
The SPDR provides an accurate
technique for measuring the
complex permittivity of dielectric
and ferrite substrates and thin
films at a single frequency point in
the frequency range of 1 to 20GHz.
Besides the SPDR fixture, a
vector network analyser such as
the PNA or PNA-L and software
package 85071E option 300, are
required for the measurement.
The measurement is automatic and
easy to perform.

5. Advantages:
• superior accuracy compared to other methods
• ability to measure low loss materials.
• convenient, fast, and non-destructive measurement of substrates, printed
circuit boards, and even thin films.
Geometry and
arrangement:

6. Spin Coating:
Fused Silica
Substrates
Spin coating is a procedure used to
deposit uniform thin films to flat
substrates. Usually a small amount of
coating material is applied on the centre
of the substrate, which is either spinning
at low speed or not spinning at all. The
substrate is then rotated at high speed
in order to spread the coating material
by centrifugal force. A machine used for
spin coating is called a spin coater, or
simply spinner.

7. Factors on which thickness of the film
mainly depends:
 Ѡ angular speed(in rpm)
 Viscosity of the Liquid
 Evaporation speed of the liquid.
 Time of Rotation
Substrate
Cleaning:
Ultasonicate
for 5 min in
Acetone
Ultasonicate
for 5 min in 2-
propanol
Ultasonicate
for 5 min in
Distilled water
Blow Nitrogen
Heat for
at least 50 ° C

9. Polyurethane
Polyurethane (PUR or PU) is
a polymer composed of a chain of organic
units joined by carbamate (urethane)
links. While most polyurethanes
are thermosetting polymers that do not
melt when heated, thermoplastic
polyurethanes are also available.
Polyurethane polymers are traditionally
and most commonly formed by reacting a
di- or polyisocyanate with a polyol.

10. Hydroxyl Terminated (poly) butadiene
Isophorone
diisocyanate
Urethane
Functional
group
HTPB-IPDI-PU

11. Polyurethane Synthesis:
 A 3 neck round bottom flask was taken
and HTPB was dissolved in chloroform in
it.
 The middle neck was used for mechanical
stirring and one of the side necks for
nitrogen with the other for adding
reactants.
 IPDI and Catalyst DBTDL was added in
calculated amounts for cyanide alcohol
ratio to be 1.
 Then the mechanical stirring was
continued for 3 hours for optimum
results.
Polymer prepared was then immediately spin coated on
substrates of our choice ( Fused silica substrates).
Polymer coated substrates were cured at 70° C for 5 days.

12. HTPB-
IPDI-PU
Substrat
e No.
RPM on
spin
coater
Trial
1(Angstr
oms)
Trial
2(Angstr
oms)
Trial
3(Angst
roms)
1 1000 17088 17593 --
2 1000 16816 16694 --
3 2000 16644 16696 --
4 2000 22601 20824 --
5 3000 15509 16099 --
6 3000 29261 33360 32380
7 4000 48461 56611 44031
8 5000 38941 42619 --
9 6000 17079 17329 --
Thickness of HTPB-IPDI-PU on Fused Silica
Substrates measured using
Thickness of Each thin film was less than 5 µm
Profilometer

13. Initial
Resonance
Frequency(G
Hz)
Q value
Pure fused
silica
substrate
10.009 10406
Sample 4 10.006 10412
Toluene 2
µL
10.005 10046
Initial
Resonance
Frequency(G Hz)
Q value
Pure fused
silica
substrate
10.006 10616
Sample 7 9.9988 9091.8
THF 2 µL 9.9980 8541.8
Initial
Resonance
Frequency(G
Hz)
Q value
Pure fused
silica
substrate
10.006 10616
Sample 8 10.012 9262
THF 16 µL 9.9828 2006
Initial
Resonance
Frequency(G
Hz)
Q value
Pure fused
silica
substrate
10.009 10406
Sample 9 10.005 9005
TNT in
Acetonitrile
4 µL
9.988 2009
SPDR Measurements for different substances on
Polyurethane

14. Acknowledgments:
• Prof K C James Raju, SoP, UoH. for his valuable suggestions
and support.
• My sincere thanks to Mr E Sivanagi Reddy, Mr Andrews
Joseph, SoP, UoH.
• A very special thanks to Mr Billa Narasimha Rao, ACRHEM,
UoH for his valuable guidance and support for polymer
synthesis.
• Ms Sandhya, Centre of Nanotechnology, UoH.
References:
• Niranjan Sahu, B Parija and S Panigrahi, Indian J. Phys. 83 (4)
493-502 (2009)
• Malkappa, K.; Jana, T. Ind. Eng. Chem. Res., 2013, 52, 12887–
12896.
• Agilent Split Post Dielectric Resonators for Dielectric
Measurements of Substrates Application Note

15. Thank You !!