Development of Laser Beam Diffraction Technique for Determination of Thermal Expansion Coefficient of Polymeric Thin Films
Laser beam diffraction by a patterned surface has been investigated theoretically and
experimentally for the determination of the thermalexpansion coefficient (α) of polymeric
materials. By tracking the deviation of the first order diffraction mode from surface-patterned
polymers, expansion coefficients in a range 10
-7
to 10
-4
K
-1
can be measured by temperature
changes less than 100
o
C. A set-up of laser diffraction (SLD) was made, using a He-Ne laser (λ=
632.8 nm) and thin film casting technique. The results of measurements on the SLD system for
polymers like PVK polycarbonate, PDMS, organic complex (chitosan) and conducting polymer
(P3HT) showed that SLD technique can be applied to determine thermal expansion coefficients of
different polymeric materials with a considerably small volume. Especially, the fact that αof
P3HT-composite films was found to be much lower than that of the pure P3HT suggests a
potential application of polymeric composites for organic devices working at elevated temperature,
for organic solar cells (OSC) in particular.