SAMPE Journal - May/June 2021 - 40

FEATURE / SOL AR RADIATION

Figure 4. Thermal properties of spectrum
selective ZnO/LDPE films. The DSC curves of a).
Pure LDPE film; b). 4% film; c). 5% film; and d).
6% film.

of 4%, 5%, and 6%, show that the ZnO NPs were
reasonably well dispersed in the films. Figure 3 a2,
d2, and c2 show that the diameters of NPs followed
Normal distribution with the peaks of 90 nm for 4%
and 6% films or 110 nm for 5% film that seemed to
have certain degree of agglomeration. This could
greatly influence the light scattering behavior of
the films.

of the films created by different NP concentrations
should mainly come from the NPs induced
scattering.

Thermal Properties of Spectrum Selective
Films
The thermal properties of pure LDPE, 4%, 5%,
and 6% of the spectrum selective ZnO/LDPE films
were shown in Figure 4. Curves in gray, red, green,
and blue displayed the first cycle of temperature
change (increasing from -80 to 300°C and then
decreasing from 300 to -80°C) at 10°C/min. The
crystallinity of pure LDPE film was 3.2%. The
corresponding crystallinities were virtually the
same for the three samples, namely 37.3%, 37.8%,
and 37.9%, respectively. The NP composite films
have NPs, crystalline and amorphous phases of
LDPE, resulting in plenty of boundary surfaces.
When incident lights hit the films, only small
amount of light reflected on the film surface, while
most of the lights were reflected and refracted
when encountering the boundary surfaces,
due to refractive index change of the different
phases. However, if the crystallinities of the films
are rather similar, the effect of crystallinity on
shielding performance should also be similar for all
composite films regardless the NP concentration.
Therefore, the difference in shielding performance

	

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SAMPE JOURNAL

May June 2021 Journal.indd 40

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M AY/J U N E 2 0 2 1

Scattering Effect of Spectrum Selective Films
The fractional distribution of an incident
electromagnetic spectrum on a translucent film
can be expressed as follows:
	 	

a+r+t=1 		

[2]

where a is the fraction of absorbance which is
the amount of the light absorbed into the film;
r is the reflectance representing the part of the
incident spectrum reflected from the film; and
t is the transmittance, which is the light passes
through the film. This means that the extinction
part of the incident light is either reflected or
absorbed by the film. The transmissivities,
absorptivities, and reflectivities of the three
spectrum selective films and the pure LDPE film
were shown in Figure 5. Compared with the pure
LDPE film, the transmittances of the NP doped
films were substantially decreased, especially in
the two regions of incident light (200 - 400 nm
and 2200 - 2500 nm) where the transmissivities
were sharply reduced (shown in Figure 5 a). The
absorptivities of the doped films were lower than
3% in region of 200 to 2500 nm (shown in Figure
5 b and c). The reflectivity curves of the three NP
composite films had the opposite trend to those of
the transmittivity curves. Obviously, the extinction
part of the incident beam was mainly shielded by

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SAMPE Journal - May/June 2021

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