Influence_of_UV_light_intensity_on_dielectric_beha.pdf

Influence of UV light intensity on dielectric behaviours
of pure and dye-doped cholesteric liquid crystals
Gülsüm Kocakülah1
, Mert Yıldırım2
, Oğuz Köysal1,
* , and İsmail Ercan3
1
Department of Physics, Faculty of Arts& Sciences, Düzce University, 81620 Düzce, Turkey
2
Department of Mechatronics, Faculty of Engineering, Düzce University, 81620 Düzce, Turkey
3
Department of Biophysics, Institute for Research and Medical Consultations (IRMC), Imam Abdulrahman Bin Faisal University,
31441 Dammam, Saudi Arabia
Received: 25 August 2020
Accepted: 21 October 2020
Published online:
3 November 2020
Ó Springer Science+Business
Media, LLC, part of Springer
Nature 2020
ABSTRACT
This study aims to explore the ultraviolet (UV) light effects on dielectric prop-
erties of azo dye methyl red (MR)-doped cholesteric liquid crystal (CLC) com-
posite. The CLC composite formed in the study contains 5CB nematic liquid
crystal (LC) and S811 chiral additive. To obtain CLC/MR composite, CLC was
dispersed with 2% wt/wt MR azo dye. Dielectric measurements of the CLC and
CLC/MR samples were performed using dielectric spectroscopy technique in
wide frequency range in the absence of UV light and at various UV light
intensities (30, 60 and 90 mW/cm2
) for 0 and 40 V. It was observed that the
dielectric constant increased with UV light at low-frequency values. Dielectric
loss data were utilized to extract relaxation frequency which was observed to
increase with UV light exposure. Dielectric anisotropy of CLC sample exhibited
typical transition from p-type to n-type, but this behaviour disappears for CLC/
MR composite above 60 mW/cm2
UV light intensity. Cole–Cole plots were used
for extraction of dielectric relaxation data and obtained results showed that CLC
sample shows Debye type relaxation only at 0 V whereas CLC/MR composite
exhibits non-Debye type relaxation both at 0 V and 40 V. Moreover, conduc-
tivity properties of the samples were also investigated, and dc conductivity
values were extracted from experimental ac conductivity values. It was found
that MR incorporation increased dc conductivity, also it was significantly
increased by UV light exposure and thus similar effect was also observed in
current–voltage characteristics of the samples. The results show that azo dye MR
molecules are suitable for CLCs since they lead to some enhancements in
dielectric and electrical properties.
Address correspondence to E-mail: oguzkoysal@gmail.com
https://doi.org/10.1007/s10854-020-04740-6
J Mater Sci: Mater Electron (2020) 31:22385–22397
Content courtesy of Springer Nature, terms of use apply. Rights reserved.

1 Introduction
Liquid crystals (LCs) are materials between the liquid
and solid phases of the matter and have been widely
used in many optoelectronic device applications in
recent years. LCs are known to have both isotropic
properties of liquids and anisotropic properties of
solids [1, 2]. These features play extremely important
role regarding the usage of LCs in liquid crystal
displays (LCDs) [3–7], yet the studies on LC materials
are not solely limited to LCDs. Depending on the
level of order in their molecular structure, LCs are
classified into three groups; nematic, smectic and
cholesteric. Among these, cholesteric liquid crystals
(CLCs) have many different kinds, and their usage in
technological application is quite common [8].
CLCs are obtained by combining chiral additives
and nematic LC [9–11]. The structure of CLCs is
indeed of a special one with a highly indexed spiral
structure in which the nematic LC molecules can be
self-organized to rotate periodically with one step
repeat along a helical axis. For this reason, CLCs can
be considered as one-dimensional photonic band gap
materials [12, 13]. In addition, the photonic band gap
of CLCs can be easily controlled by adjusting the
ratios of LC or chiral materials or by an external effect
such as temperature, pressure, light and electric field
[14–16]. Because CLCs have a helical structure, they
allow selective reflection of circularly polarized inci-
dent light in the same handedness as its helix. The
wavelengths of the Bragg reflection band edges can
be calculated with the formula, Dk Dn p, where p
is the helical pitch value and Dn is the birefringence
of the LC [9, 11]. The orientation of the LC molecules
forming the CLC structure can be also adjusted using
different additives such as polymer [17, 18], dye
[19, 20] and carbon nanotubes [21]. This feature of the
CLC composite structure has led to large number of
studies. For example, Liang et al. [22] created electro-
thermal switchable bistable reverse mode polymer-
stabilized cholesteric texture light shutter. Lee et al.
[23] investigated photosensitivity of reflection notch
tuning and broadening in polymer-stabilized cho-
lesteric liquid crystals. Yeh et al. [12] also studied
colour tuning in thermo-sensitive chiral photonic
liquid crystals based on the pseudo-dielectric heating
effect. In particular, studies on the investigation of
electro-optical and dielectric properties of azo dye-
doped CLC composite structures still continue
widely today.
To the best of our knowledge, no studies have
presented a detailed report about the response of
dielectric properties of azo dye methyl red (MR)-
doped CLC to UV (ultraviolet) light with varying
intensity. For this reason, neat CLC and azo dye MR-
doped CLC composite were investigated in visible
(VIS) and under different UV light intensities using
dielectric spectroscopy technique. Depending on the
different UV light intensities, significant changes
were observed in relaxation time, dielectric aniso-
tropy and ac conductivity values of the samples.
2 Materials and methods
The liquid crystalline material CLC used in this
experiment is a mixture composed of 5CB coded
nematic LC (purchased from Sigma-Aldrich Chemi-
cal Company) and the left-handed chiral dopant S811
(purchased from Daken Chemical Limited). Azo dye
MR was also obtained from Sigma-Aldrich Chemical
Company and used as the dispersal agent. The
molecular structures of the 5CB, S811 and MR are
given in Fig. 1a–c. The 5CB nematic LC is called as
4-pentyl-40
-cyanobiphenyl. Its chemical formula is
known as C18H19N. 5CB nematic LC shows phase
transition from crystal to nematic and then to iso-
tropic at 24 °C and 35 °C, respectively. The refractive
indices ne (at 25 °C) = 1.77 and no (at 25 °C) = 1.58 of
5CB nematic LC, of molecular weight 249.35 g/mol,
are given. The approximately value of the dielectric
anisotropy (De’) is 10 at 1 kHz [24]. The CLC was
prepared with 96% wt/wt 5CB nematic LC and 4%
wt/wt S811 chiral materials. The sufficient weight
percentages were determined so that the helical
structure is achieved. Pitch (p) value of CLC was
calculated as * 2.8 lm using theoretical value of
helical twisting power (HTP) of S811 in
HTP = (p.c)-1
where c is concentration of the chiral
dopant [25]. Initially, CLC was mixed in an ultrasonic
bath for 4 h up to the isotropic temperature of 5CB
LC. After, 2% wt/wt MR was added to the CLC; thus,
CLC/MR composite was obtained. Later, CLC/MR
composite was mixed using an ultrasonic bath for 4 h
at 60 °C for homogeneous distribution of additives.
ITO (Indium Tin Oxide)-coated planar aligned LC
cells were used to perform dielectric spectroscopy
measurements. These LC cells were purchased from
Instec, USA. ITO-coated glass plates were pre-treated
with a polyimide (PI) layer so that planar alignment
22386 J Mater Sci: Mater Electron (2020) 31:22385–22397

of LC molecules was achieved and unidirectionally
rubbed with a spacer of 7.7 lm. Neat CLC and CLC/
MR composites were injected into LC cells with the
help of capillary action by using temperature to
reduce viscosities. Later, dielectric measurements of
the samples were performed with a computer con-
trolled Novocontrol Alpha-A Dielectric/Impedance
Analyser in the bias range of 0 V and 40 V while the
sample was applied with ac signal of Vrms = 0.1 V in
the frequency range of 1 kHz-10 MHz. Current–
Voltage (I–V) measurements of CLC and CLC/MR
composites were performed using a Keithley 2400
source metre in the bias range of 0–40 V. UV illumi-
nation was achieved using Omron ZUV-C20H UV
light source with a 365 nm wavelength. UV light was
directly sent on the LC cell with an active area of
1 cm2
, and the experimental data were taken at dif-
ferent power intensity levels from 0 to 90 mW/cm2
.
Therefore, measurements were repeated for VIS light
condition (0 mW/cm2
) and UV light conditions (30,
60 and 90 mW/cm2
) while the samples were kept at
room temperature.
3 Results and discussions
The schematic representation of the MR-doped CLC
composite is given in Fig. 2a–c. The orientation of the
LC and MR materials in the composite structure in
the planar alignment LC cell is shown in Fig. 2a. It is
seen in the schematic representation that LC mole-
cules form a spiral/helical structure inside the cell.
Figure 2b and c shows the surface cross section of
CLC/MR composite for the case of no UV light, i.e.
visible light case, and for the case of UV light,
respectively. MR used in this study is an azo dye and
has a strong light absorption feature. As MR absorbs
the light, the shape of its molecules changes, and this
is called trans–cis photo-isomerization. In the case of
VIS state, the LC and MR molecules are oriented
parallel to the plates of LC cell and have smooth
orientation. On the other hand, the orientations of
both LC and MR molecules change under UV light.
The main reason for this change is that MR azo dye
shows trans–cis photo-isomerization feature with UV
light exposure in which the absorbance of light by
dye molecules causes these molecules to become V
shaped with 120°. This spatial change of dye mole-
cules reinforces the molecular orientation of neigh-
bour LC molecules by frictional forces. This change is
thought to significantly alter both electro-optical and
dielectric properties.
The dielectric response of LCs varies significantly
depending on the frequency. When analysing the
dielectric properties of these structures, complex
dielectric constant is the basic parameter that is uti-
lized. It consists of two parts: real and imaginary, and
is expressed by the following equation [21, 26, 27]:
Fig. 1 Molecular structures of
a 5CB, b S811 and c MR
materials
J Mater Sci: Mater Electron (2020) 31:22385–22397 22387

e
¼ e0
ie00
: ð1Þ
In this equation, the real part of complex dielectric
constant, e0
, is called as dielectric constant which is
related to the energy stored in the material and is
given by [26, 27],
e0
¼
C
Co
¼
Cd
eoA
; ð2Þ
where C is capacitance, Co is the capacitance of the
empty cell; thus, d is the cell thickness and A is the
ITO covered area of the LC cell, eo is the permittivity
of free space (eo ¼ 8:85 1014
F/cm).
As to the imaginary part, e00
, it is dielectric loss
which is related to the energy losses in the material
and is expressed as follows [26, 27]:
e00
¼
G
xCo
¼
Gd
xeoA
; ð3Þ
where x is the angular frequency (x = 2pf) and G is
the conductance.
Figure 3a–d shows the frequency-dependent e0
values of the samples for various UV light intensities.
It is seen in the figures that datasets for neat CLC and
CLC/MR are available for both 0 V and 40 V. The
state of 0 V corresponds to the situation where LC
and MR molecules orient parallel to the plates of LC
cell; hence, it is referred as planar state. On the other
hand, the 40 V state indicates the homeotropic state
where the LC and MR molecules are perpendicular to
the plates of the LC cell. When neat CLC sample is
focused, it is seen in Fig. 3 that e0
value of the sample
increases depending on the voltage. The reason for
this behaviour is that the LC molecules in the com-
posites orient with the direction of the electric field;
thus, polarization of the liquid crystalline medium is
increased. On the other hand, the change in e0
value
of neat CLC sample is quite small as the UV light
intensity is increased.
In the case of CLC/MR composite, it is seen that
the e0
value varies both with increasing voltage and
increasing UV light intensity. Also, when compared
to the pure CLC structure, it is seen that the e0
value
of the CLC/MR composite structure is slightly lower
for 40 V and slightly higher for 0 V. The difference
between the values of e0
of 40 V and 0 V is not sig-
nificantly changed for CLC in the low and interme-
diate frequencies; however, this difference for CLC/
MR disappears as the UV light intensity is increased.
MR azo dye shows trans–cis photo-isomerization
feature with UV light exposure, and it is believed that
this hinders the orientation of dipoles although there
is a significant increase in electric field. The trans–cis
photo-isomerization is even so strong that the plot of
e0
for 40 V almost overlaps that for 0 V for CLC/MR
composite. Another interesting result is observed for
the data of 90 mW/cm2
for low-frequency region. It is
observed that the e0
value at 1 kHz frequency is
almost tripled and doubled at 90 mW/cm2
UV light
intensity compared to the VIS state when it is biased
with 0 V and 40 V, respectively. This stems from e0
of
Fig. 2 Schematic diagram of
CLC/MR composite in LC
cell: a Lateral cross section of
LC cell showing planar
alignment of the molecules.
Surface cross section of LC
cell for b VIS light and c UV
light

CLC/MR which suddenly increases from few kHz to
1 kHz. Such increase is particularly observed when
CLC/MR is exposed to UV light. It is believed that
extra polarization is yielded for low-frequency region
due to trans–cis photo-isomerization such that life-
time of MR molecules only allows them to follow ac
signal until its frequency reaches 10 kHz.
Figure 4a–d depicts the frequency-dependent e00
For CLC sample, e00
slightly decreases with increasing
frequency and then increase and yield a peak
between couple 100 kHz and 1 MHz. Similar beha-
viour was observed for CLC/MR composite; how-
ever, the decrease in e00
values with increasing
frequency is much more prominent as a result of high
e00
values in low-frequency range of 1 kHz and
10 kHz. In this region, e00
gets even higher values as
the UV light intensity is increased so it can be said
that CLC/MR composite would have higher dc
conductivity (rdc) compared to CLC, and higher rdc
values would be yielded as a result of UV light
exposure. In addition, the increase in e00
of CLC/MR
composite for 60 mW/cm2
and 90 mW/cm2
UV light
intensities at low frequencies can be associated with
increased ionic charge density due to the impurity
ions in the composite structure as a result of UV light
exposure. Similar to the case of e0
plots, the dispersion
in e00
plots of CLC/MR for 0 V and 40 V also disap-
pears as the UV light intensity is increased and
almost overlap for 90 mW/cm2
UV light intensity.
Moreover, information about molecular relaxation
mechanisms of composites can be achieved from
frequency-dependent e00
graphs. The relaxation fre-
quency (fR) values of the samples are obtained from
Fig. 3 e0
-f graphs of CLC composites under a 0 mW/cm2
, b 30 mW/cm2
, c 60 mW/cm2
, and d 90 mW/cm2
UV light

the peak position of e00
-f graphs. The values of fR for
various UV light intensities are depicted in Fig. 5. In
the absence of the bias voltage, the value of fR
appears to have higher values particularly for CLC
sample. On the other hand, CLC/MR composite has
lower fR values as a result of MR molecules’ hinder-
ing molecular orientation. When the samples are
applied with bias voltage, e00
peaks in general shifted
towards lower frequencies compared to the peaks in
the case of zero bias. Also, UV light intensity caused
an increase in fR values indicating that less time is
needed for the molecules’ alignment with the electric
field formed by the applied voltage. Therefore, CLC
sample is expected to have lower relaxation time
particularly in the absence of bias. The situation
changes when the samples are biased and CLC/MR
composite is expected to have larger relaxation time
whose intensity is decreased with increased intensity
of UV light.
The dielectric anisotropy (De0
) values of samples
were calculated using the following formula [28, 29]:
De0
¼ e0
k e0
?; ð4Þ
Fig. 4 e00
, b 30 mW/cm2
, c 60 mW/cm2
and d 90 mW/cm2
UV light
Fig. 5 Relaxation frequency values of CLC composites
depending on the UV light intensity

where e0
k is the parallel components of the real part of
complex dielectric constant which corresponds to
high forward bias voltage (at 40 V), and e0
? is per-
pendicular components of the real part of complex
dielectric constant which corresponds to low forward
bias voltage (at 0 V). According to this equation,
composites have positive dielectric anisotropy (p-
type) when e0
k takes higher value than e0
? (De0
[ 0), or
negative dielectric anisotropy (n-type) where e0
k takes
smaller value than e0
? (De0
0).
Figure 6a–d depicts the frequency-dependent De0
It is seen that De0
gets lower values for CLC/MR
composite as the UV illumination intensity is
increased since UV light induced trans–cis photo-
isomerization caused a decrease in order parameter
[30].
In VIS state, De0
value appears to decrease in CLC/
MR composite compared to pure CLC. The reason for
this decrease is the agglomerations formed in the
composite structure as a result of the MR addition to
the CLC. The decrease of De0
value of CLC/MR
composite structure with increasing UV light inten-
sity can be interpreted as disruption of the molecular
orientation of LC molecules in the composite struc-
ture as a result of trans–cis photo-isomerization of
MR molecules.
Also, the crossover frequency (fc) values of the
samples were extracted from the De0
-f graphs. This
frequency value is defined as the frequency at which
is passes from p-type De0
to n-type De0
. UV light-de-
pendent fc values of CLC composites are given in
Fig. 7. It is seen that fc values are increased with the
effect of UV light however there is not an increasing
trend with increasing light intensity which can be
associated with exposure time of the samples during
Fig. 6 De0
, b 30 mW/cm2
, c 60 mW/cm2
and d 90 mW/cm2
UV light

repeated measurements [31]. On the other hand, an
interesting behaviour is observed that transition from
p-type De0
to n-type De0
disappears above 60 mW/
cm2
UV light intensity. Sign reversal of De0
does not
take place as if fc goes to infinity. Thus, the CLC/MR
composite no longer exhibits dual-frequency liquid
crystal feature as a result of increased number of MR
molecules at cis-state with increased UV light
intensity.
The complex dielectric constant of the samples was
also analysed using Cole–Cole equation [32–34]:
e
¼ e0
1 þ
e0
s e0
1
1 þ ixs
ð Þ1a
: ð5Þ
The e0
and e00
value of the composites were also
given in terms of Cole–Cole equation take the fol-
lowing form after utilizing Eq. 1 [34]:
e0
¼ e0
1 þ e0
s e0
1
1 þ xs
ð Þn
cos np
2

1 þ 2 xs
ð Þn
cos np
2

þ xs
ð Þ2n
; ð5aÞ
e00
¼ e0
s e0
1
xs
ð Þn
sin np
2

1 þ 2 xs
ð Þn
cos np
2

þ xs
ð Þ2n
: ð5bÞ
In this equations, e0
s and e0
1 are the real parts of
complex dielectric constant values in the low- and
high-frequency limits, respectively, s is relaxation
time, a is relaxation distribution parameter which
ranges from 0 to 1 and n = 1 - a. The Cole–Cole
equation is a comprehensive function such that the
case of a = 0 for Cole–Cole function corresponds to
the Debye model. In this case, the centre of the
semicircle is on the e0
-axis, and the system has a
single relaxation time. However, when a takes the
non-zero value (a = 0), the relaxation behaviour is
referred as non-Debye model where the centre of the
semicircle is located below the e0
-axis and there exists
a distribution of relaxation times for the investigated
relaxation mechanism in the system. Also, the e0
s e0
1
value in the equation is defined as the dielectric
strength, de0
, of composite materials. The de0
param-
eter is described by the value against the voltage
before the breakdown occurs [35].
Cole–Cole graphs of the samples in VIS and under
different UV light intensities are given in Fig. 8a–d. It
is seen that the dielectric data almost form half circle
for CLC sample indicate mostly Debye type relax-
ation for the sample. However, the situation is
changed for CLC/MR sample particularly for high
UV light intensities. Nonlinear curve fit was applied
for the experimental data and dielectric relaxation
parameters such as s, a and de0
were determined so
that Cole–Cole fit curves were drawn (dashed-line
curves in Fig. 8). These curves match with the
experimental data quite well. Thus, obtained relax-
ation parameters are given in Fig. 9a–c. As seen in
Fig. 9a, s is increased both increased voltage and MR
contribution to the CLC composite. When the CLC
material is dispersed with MR, dielectric frictions
occur in the composite due to molecular interactions
between LC and MR materials and these frictions
increase the relaxation time. On the other hand, it is
seen that s value decreases significantly at home-
otropic state with increasing UV light intensity in
CLC/MR composite. This result suggests that MR-
doped CLC composite requires less time to reach
equilibrium under UV light due to their new form in
cis-state which assumably weakens dielectric friction.
Figure 9b shows that CLC has Debye behaviour
under zero voltage regardless of UV light intensity.
However, this sample exhibits non-Debye behaviour
with an increase in voltage yet its a value gets
smaller. On the other hand, CLC/MR composite
shows non-Debye behaviour independent of voltage;
however, a values in general increase with increased
UV light intensity particularly in the homeotropic
state with an exception for 90 mW/cm2
UV light
intensity. The value of de0
for CLC sample does not
change significantly with UV light intensity both for
planar and homeotropic states (Fig. 9c). However, the
value of de0
for both samples is increased when the
samples are applied with voltage particularly in VIS
Fig. 7 Crossover frequency values of CLC composites depending
on the UV light intensity

light and low-intensity UV light. Since the applied
voltage is high enough to overcome threshold volt-
age, de0
gets quite larger compared to the case of 0 V
[36].
The ac conductivity, rac, of the samples was
obtained using the equation below [37, 38], and rac–
f graphs of CLC composites in VIS and under dif-
ferent UV light intensities are given in Fig. 10a–d.
rac ¼ eoxe00
: ð6Þ
It is seen in Fig. 10 that rac increases with increas-
ing frequency for all samples. rac values of planar
and homeotropic states differ particularly in the
intermediate frequency region. There is not signifi-
cant difference between rac values of CLC and CLC/
MR composite at VIS light. However, rac of CLC/MR
becomes larger compared to that of CLC sample in
the low-frequency region. On the other hand, the
situation is reversed after certain frequency, which is
below 10 kHz and gets higher value with increasing
UV light intensity.
Low-frequency region rac values were utilized to
extract dc conductivity, rdc, of the samples. The
equation for the value of rdc with respect to rac was
given below [39]:
rac ¼ rdc þ
1
s
drac
d ln x
; ð7Þ
where s is defined as a constant of the frequency
dependence of the conductivity. Figure 11 depicts rdc
values of the samples. This figure clearly shows that
MR addition into CLC increases the dc conductivity
of the sample significantly. It is believed that incor-
poration of MR enable hopping of charge carriers.
Moreover, rdc gets even higher with increasing UV
Fig. 8 Cole–Cole graphs of CLC composites under a 0 mW/cm2
, b 30 mW/cm2
, c 60 mW/cm2
and d 90 mW/cm2
UV light

light intensity values. The reason for such increment
is due to the increased number of free ions in the
composite structure owing to high charge density in
the cis-state thanks to UV light.
Figure 12a–d shows current–voltage (I–V) charac-
teristics of the CLC composites in VIS and under
different UV light intensities. In consistency with rdc
values, prominent increase in current is observed as a
result of MR incorporation such that the current
value at 40 V is increased 14, 19, 18 and 24 times
thanks to MR for 0, 30, 60 and 90 mW/cm2
UV light
intensities, respectively. It is also seen that current is
increased with increasing UV light intensity since the
illumination causes creation of electron–hole pairs
and these carriers are swept due to voltage. I–V
characteristics of 60 mW/cm2
UV light intensity yield
higher current values compared to those of 90 mW/
cm2
UV light intensity. This result is believed to be
due to the increased recombination of carriers due to
increased number of cis-state MR molecules.
4 Conclusions
In this study, frequency-dependent dielectric prop-
erties of the CLC and CLC/MR composites were
investigated in VIS and under different UV light
intensities. Higher values were obtained for the
dielectric constant in the low-frequency region due to
the increasing UV light intensity in the CLC/MR
composite structure. The highest increase in CLC/
MR sample was observed in 90 mW/cm2
UV light
intensity. Similarly, the highest fR value for CLC/MR
composite structure is obtained at 90 mW/cm2
UV
light intensity in the presence of voltage. This result
indicates forming a composite material of CLC can
help altering relaxation behaviour of the CLC when
Fig. 9 a Relaxation time, b relaxation distribution parameter and c dielectric strength parameter values of CLC composites depending on
the UV light intensity

illuminated with UV light. In addition, De0
is
decreased with MR incorporation, and it is decreased
further with increasing UV light intensity. Exposure
to UV light also caused an increase in fc value for
CLC samples. However, dual-frequency liquid crys-
tal behaviour of CLC/MR composite structure dis-
appeared after 60 mW/cm2
UV light intensity, and it
was associated with trans–cis photo-isomerization of
MR molecules. The s values at 40 V obtained from
Cole–Cole graphs in general decrease with increasing
UV light intensity whereas those at 0 V exhibit
opposite behaviour. Moreover, a value increased
significantly for CLC/MR composite structure with
the exposure to UV light intensity, whereas its value
for CLC sample at 0 V is zero; thus, the sample
exhibits Debye behaviour. Furthermore, conductivity
of the samples is also improved after UV light
exposure. It was found that dc conductivity of the
CLC is significantly improved as a result of MR
incorporation. The effect of this improvement was
also observed for I–V characteristics of the samples.
Obtained results suggest that MR incorporation
enhances the dielectric and electrical properties of
CLC composite.
Fig. 10 rac-f graphs of CLC composites under a 0 mW/cm2
, b 30 mW/cm2
, c 60 mW/cm2
and d 90 mW/cm2
UV light
Fig. 11 DC conductivity values of CLC composites depending on
the UV light intensity

Acknowledgements
This work was supported financially by Düzce
University Scientific Research Project (Project No:
2020.05.02.1103).
Compliance with ethical standards
Conflict of interest The authors declare that they
have no conflict of interest.
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