The non-linear dependence of 6СНВТ liquid crystal conductivity on the concentration of gold nanoparticles
Within the frequency range 10⁻¹…10⁶ Hz at the temperature 293 K, the effect of gold nanoparticles on the dielectric properties of the planar-oriented nematic liquid crystal 6СНВТ has been studied. The concentration of nanoparticles with the average diameter 3 to 5 nm was chosen as 0.01, 0.02 and 0.1...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2016
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irk-123456789-1216822017-06-16T03:03:04Z The non-linear dependence of 6СНВТ liquid crystal conductivity on the concentration of gold nanoparticles Kovalchuk, O.V. Kopčansky, P. Timko, M. Studenyak, I.P. Kovalchuk, T.M. Within the frequency range 10⁻¹…10⁶ Hz at the temperature 293 K, the effect of gold nanoparticles on the dielectric properties of the planar-oriented nematic liquid crystal 6СНВТ has been studied. The concentration of nanoparticles with the average diameter 3 to 5 nm was chosen as 0.01, 0.02 and 0.1 wt.%. It has been shown that for the frequencies less than 10 Hz, the dielectric properties of the samples can be described with the Debye dispersion. For the samples with the concentration of gold nanoparticles 0.1 wt.%, the time of relaxation has been estimated (4.7±0.5 s). It has been also shown that the conductivity of the liquid crystal depends non-linearly on the concentration of nanoparticles introduced into the liquid crystal. The greatest change in conductivity of the liquid crystal on the concentration of introduced gold nanoparticles has been obtained within the range of 0.01 to 0.02 wt.%. It has been assumed that the conductivity of 6СНВТ that depends non-linearly on the concentration of introduced gold nanoparticles is caused by the competing processes of ion desorption from the gold nanoparticles and of nanoparticle aggregation. 2016 Article The non-linear dependence of 6СНВТ liquid crystal conductivity on the concentration of gold nanoparticles / O.V. Kovalchuk, P. Kopčansky, M. Timko, I.P. Studenyak, T.M. Kovalchuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2016. — Т. 19, № 4. — С. 399-403. — Бібліогр.: 21 назв. — англ. 1560-8034 DOI: 10.15407/spqeo19.04.399 PACS 61.30.Gd, 77.84.Nh http://dspace.nbuv.gov.ua/handle/123456789/121682 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
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English |
| description |
Within the frequency range 10⁻¹…10⁶ Hz at the temperature 293 K, the effect of gold nanoparticles on the dielectric properties of the planar-oriented nematic liquid crystal 6СНВТ has been studied. The concentration of nanoparticles with the average diameter 3 to 5 nm was chosen as 0.01, 0.02 and 0.1 wt.%. It has been shown that for the frequencies less than 10 Hz, the dielectric properties of the samples can be described with the Debye dispersion. For the samples with the concentration of gold nanoparticles 0.1 wt.%, the time of relaxation has been estimated (4.7±0.5 s). It has been also shown that the conductivity of the liquid crystal depends non-linearly on the concentration of nanoparticles introduced into the liquid crystal. The greatest change in conductivity of the liquid crystal on the concentration of introduced gold nanoparticles has been obtained within the range of 0.01 to 0.02 wt.%. It has been assumed that the conductivity of 6СНВТ that depends non-linearly on the concentration of introduced gold nanoparticles is caused by the competing processes of ion desorption from the gold nanoparticles and of nanoparticle aggregation. |
| format |
Article |
| author |
Kovalchuk, O.V. Kopčansky, P. Timko, M. Studenyak, I.P. Kovalchuk, T.M. |
| spellingShingle |
Kovalchuk, O.V. Kopčansky, P. Timko, M. Studenyak, I.P. Kovalchuk, T.M. The non-linear dependence of 6СНВТ liquid crystal conductivity on the concentration of gold nanoparticles Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Kovalchuk, O.V. Kopčansky, P. Timko, M. Studenyak, I.P. Kovalchuk, T.M. |
| author_sort |
Kovalchuk, O.V. |
| title |
The non-linear dependence of 6СНВТ liquid crystal conductivity on the concentration of gold nanoparticles |
| title_short |
The non-linear dependence of 6СНВТ liquid crystal conductivity on the concentration of gold nanoparticles |
| title_full |
The non-linear dependence of 6СНВТ liquid crystal conductivity on the concentration of gold nanoparticles |
| title_fullStr |
The non-linear dependence of 6СНВТ liquid crystal conductivity on the concentration of gold nanoparticles |
| title_full_unstemmed |
The non-linear dependence of 6СНВТ liquid crystal conductivity on the concentration of gold nanoparticles |
| title_sort |
non-linear dependence of 6снвт liquid crystal conductivity on the concentration of gold nanoparticles |
| publisher |
Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
| publishDate |
2016 |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/121682 |
| citation_txt |
The non-linear dependence of 6СНВТ liquid crystal conductivity on the concentration of gold nanoparticles / O.V. Kovalchuk, P. Kopčansky, M. Timko, I.P. Studenyak, T.M. Kovalchuk // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2016. — Т. 19, № 4. — С. 399-403. — Бібліогр.: 21 назв. — англ. |
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Semiconductor Physics Quantum Electronics & Optoelectronics |
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Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 399-403.
doi: https://doi.org/10.15407/spqeo19.04.399
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
399
PACS 61.30.Gd, 77.84.Nh
The non-linear dependence of 6СНВТ liquid crystal conductivity
on the concentration of gold nanoparticles
O.V. Kovalchuk1, P. Kopčansky2, M. Timko2, I.P. Studenyak3, T.M. Kovalchuk4
1Kyiv National University of Technologies and Design
2, Nemirovich-Danchenko str., 01011 Kyiv, Ukraine; e-mail: akoval@knutd.com.ua
2Institute of Experimental Physics, Slovak Academy of Sciences,
47, Watsonova str., 04001 Košice, Slovak Republic
3Uzhhorod National University, Faculty of Physics,
3, Narodna Sq., 88000 Uzhhorod, Ukraine
4V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine,
45, prospect Nauky, 03680 Kyiv, Ukraine
Abstract. Within the frequency range 10–1…106 Hz at the temperature 293 K, the effect
of gold nanoparticles on the dielectric properties of the planar-oriented nematic liquid
crystal 6СНВТ has been studied. The concentration of nanoparticles with the average
diameter 3 to 5 nm was chosen as 0.01, 0.02 and 0.1 wt.%. It has been shown that for the
frequencies less than 10 Hz, the dielectric properties of the samples can be described
with the Debye dispersion. For the samples with the concentration of gold nanoparticles
0.1 wt.%, the time of relaxation has been estimated (4.7±0.5 s). It has been also shown
that the conductivity of the liquid crystal depends non-linearly on the concentration of
nanoparticles introduced into the liquid crystal. The greatest change in conductivity of
the liquid crystal on the concentration of introduced gold nanoparticles has been obtained
within the range of 0.01 to 0.02 wt.%. It has been assumed that the conductivity of
6СНВТ that depends non-linearly on the concentration of introduced gold nanoparticles
is caused by the competing processes of ion desorption from the gold nanoparticles and
of nanoparticle aggregation.
Keywords: planar-oriented nematic liquid crystal, gold nanoparticles, conductivity,
Debye dispersion.
Manuscript received 01.07.16; revised version received 15.09.16; accepted for
publication 16.11.16; published online 05.12.16.
1. Introduction
Despite the chemical “inertness” of bulk gold, Au
nanoparticles (ANP) are catalytically active and can
capture impurities of various types. In the case of
biological objects, these impurities may be, for example,
cancer cells [1, 2]. Subsequently, these cells can be
destroyed by heating the nanoparticles using the plasma
resonance effect. It is clear that in most cases the
concentration of nanoparticles should be sufficiently low
in order to they can be easily excreted from the body due
to immune processes. Therefore, the development of
methods capable to estimate the ANP concentration in
biological fluids has very important practical and
scientific significance.
Since ANP can conduct electricity rather well, they
have to increase the conductivity of body fluids.
Therefore, measurement of fluid conductivity may be
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 399-403.
doi: https://doi.org/10.15407/spqeo19.04.399
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
400
one of the methods to assess the content of a small
amount of ANP. Most of biological fluids are rather
complex systems. To somewhat reduce the number of
problems arising in the course of analyzing the results of
changes in the conductivity of biological systems under
the influence of ANP at the initial stages of the study, it
is purposeful to perform these experiments with simpler
objects possessing the properties to similar to those of
biological systems.
Liquid crystals (LC) can play the role of these
biological objects. Therefore, these crystals were
selected for analysis of the conductivity measurements
in the presence of a small amount of ANP.
Analysis of publications on the ANP effects on
properties of LC indicates that in most of cases studied
were the optical properties of these mixtures. For
example, in the work [3] it was shown that due to
formation of oriented layers of the LC molecules around
ANP, plasma levels are split. In the works [4, 5], being
based on studies of the optical characteristics inherent to
the mixture of ANP with LC, it was shown that
aggregation of ANP can be reduced if using LC that has
a smectic phase. The change in the optical or electro-
optical properties of ferroelectric LC, when introducing
ANP, was considered in [6-9]. The influence of ANP on
non-linear optical properties of LC was studied in [10].
Studied in the work [11] was aggregation of ANP under
the influence of electric field.
It was shown in [12] that the presence of a small
amount of ANP in nematic LC 6СНВТ affects the
parameters of the Freedericksz transition in crossed
electric and magnetic fields. It was shown that, even at
low concentrations of ANP, there are significant changes
in the magnitude of the voltage of the electric field and
induction of magnetic field for Freedericksz transition.
However, the mechanism of these changes has not been
ascertained.
In addition to nematic and ferroelectric LC, we
investigated the effect of ANP and other types of liquid
crystals. For instance, studied in [13] was formation and
behavior of surface plasmon resonance in thermotropic
calamitic liquid crystals, and in [14] – strain in time of
thermomechanical nematic liquid crystal elastomer. Effect
of ANP on lyotropic liquid crystals similar to the body
fluids was investigated in [15]. It was shown that lyotropic
matrix induces aggregation of nanoparticles, which leads
to a red shift of the surface plasmon resonance.
Performed in the work [16] was the study of
cholesteric liquid-crystalline dispersion formed by
double-stranded nucleic acid molecules of various
families (DNA and poly(I)xpoly(C)). These samples are
in fact already biological fluids. It was shown that
embedding ANP leads to two effects: i) restructuring the
spatial cholesteric structure of particles, ii) formation of
ANP clusters.
From analysis of the above works, it follows that in
none of them the task to determine the content of ANP
distributed in the bulk, being based on the electrical
properties of samples. Therefore, the aim of this study
was to investigate the effect of small amounts of Au
nanoparticles on the dielectric properties of nematic
liquid crystals.
2. Materials and methods of research
In studying the impact of small amounts of ANP
impurities on dielectric properties of LC, its conductivity
is essential. Mixtures of nematic LC that are
advantageously used in display technology have a
relatively high conductivity. Therefore, for our study we
chose a one-component nematic LC 6СНВТ.
As ANP, we used gold nanoparticles functionalized
with dodecanethiol with an average size of 3 to 5 nm
(Sigma-Aldrich Co). In the initial state, ANP were
dispersed in toluene with the concentration 2 wt.%. After
that, ANP in toluene solution was introduced into LC, as
a result of sonication and heating, the solvent was
evaporated and the mixture of gold nanoparticles with
6СНВТ was formed. For studies, except pure 6СНВТ,
we used the mixture of LC with ANP of the
concentrations 0.01, 0.02 and 0.1 wt.%.
We filled the mixture of LC with ANP into cells of
the sandwich type, which consisted of two glass plates
coated with the optical ITO layer consisting of a mixture
of indium and tin oxides, which that is electrically
conductive and transparent in the visible spectral range.
Before filling with the mixture, the cell capacitance was
measured, and in this manner determined was its
thickness. The test samples had the thickness 25 μm. To
provide planar orientation of LC, a polyamide layer was
deposited onto the electrodes (before making the cell).
Further, this layer was mechanically rubbed in a certain
direction. Observations under a polarizing microscope
revealed that a small amount of ANP does not affect the
homogeneity of planar orientation inherent to LC
molecules.
Dielectric properties of the obtained samples were
investigated within the frequency range f = 10–1…106 Hz
by using the oscilloscopic method [17]. The amplitude
of the measuring signal of triangular shape was 0.25 V.
The measurements were performed at 293 K. The
measurement error did not exceed 5%.
3. Experimental results and discussion
Fig. 1 shows the frequency dependence of the real
component of the complex permittivity ε′ of planar
oriented: 6СНВТ (1), 6СНВТ+0.01 wt.% ANP (2),
6СНВТ+0.02 wt.% ANP (3) and 6СНВТ+0.1 wt.%
ANP (4). From the analysis of the data obtained, it
follows that the whole dielectric spectrum can be
separated into three sections: A, B and C. In our
previous studies [18, 19] and in [20], it was shown that
each of these sections characterizes different processes.
Fig. 2 shows the frequency dependences of ε″ for
6СНВТ (curve 1) and for 6СНВТ with various ANP
concentrations (curves 2 to 4). From the analysis of the
data, it follows that within the frequency range 10 to
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 399-403.
doi: https://doi.org/10.15407/spqeo19.04.399
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
401
103 Hz the ε″ magnitude decreases linearly with
increasing the frequency f. This regularity corresponds to
the condition that the resistance of the sample does not
depend on the frequency and is equal to the resistance of
the sample bulk. If we compare the analyzed section of
the dielectric spectrum in Fig. 2 with the spectrum in
Fig. 1, we see that it corresponds to the section B. For
this section (as seen from Fig. 1), the value ε′ also does
not depend on frequency. Therefore, this ε′ value is
equal to the dielectric permittivity of the samples. As can
be seen from Fig. 1, the ε′ value in LC in the presence of
a small amount of ANP is insignificantly (within
experimental errors) different from ε′ of 6СНВТ.
Therefore, for the section B of the dielectric spectrum,
the dependence of ε″ on the availability and
concentration of ANP was analyzed in more detail. For
this analysis, the AC conductivity σАС is a more
practically used parameter. As it is well known, it is
related to ε″ through the equality
ωεε ′′=σ 0AC , (1)
where ε0 is the electric constant, ω = 2π f – cyclic
frequency.
The dependence of σАС on the ANP concentration is
shown in Fig. 3. It follows from these data that the
conductivity of the test samples depends non-linearly on
the ANP concentration. The greatest changes in the
conductivity are observed within the ANP concentrations
of 0.01 to 0.02 wt.%. It may be caused by the complex
nature of interactions between ions available in LC as well
as ions that are introduced into LC together with ANP. If
one adds to these processes the non-linear adsorption ones
resulting in decreased concentration of nanoparticles in
the sample bulk, it is obvious how it is difficult to describe
this process as a whole. One of the probable mechanisms
of reducing the ANP effect on the dielectric properties of
LC in the concentration range of 0.02 to 0.1 wt.% is
aggregation of nanoparticles.
10-1 100 101 102 103 104 105 106
101
102 CBA
3
4
2
1
ε'
f, Hz
Fig. 1. The frequency dependences of the real part of the
complex dielectric permittivity ε′ of nematic liquid crystal
6СНВТ with different concentrations of gold nanoparticles: 0
(1), 0.01 (2), 0.02 (3), and 0.1 wt% (4). The sample thickness
is 25 μm, temperature – 293 K.
10-1 100 101 102 103
10-1
100
101
102
103
3
4
2
1
ε ''
f, Hz
Fig. 2. The frequency dependences of the imaginary part of the
complex dielectric permittivity ε″ of nematic liquid crystal
6СНВТ with different concentrations of gold nanoparticles: 0
(1), 0.01 (2), 0.02 (3), and 0.1 wt% (4). The sample thickness
is 25 μm, temperature – 293 K.
In this case, according to the data of Fig. 3, the
conductivity does not practically change, which is
caused by formation of ANP aggregates that obstruct
desorption of ions from the surface of nanoparticles in
LC. This aggregation also can occur most likely when
the ANP concentration is less than 0.02, but probably its
effectiveness is considerably lower. A similar non-linear
dependence of the 6СНВТ conductivity on the
concentration of superionic Cu6PS5I nanoparticles was
observed by us in the work [21], and this dependence
was also explained by the complex nature of the
processes of adsorption and desorption of ions on/from
the surface of the nanoparticles.
The obtained by us non-linear dependence of LC
conductivity on the presence of small concentrations of
ANP should be considered when developing the
methods for estimation of nanoparticle concentrations by
using the conductivity change not only in LC, but in
other liquids and particularly in body fluids.
It follows from the analysis of dielectric spectra in
Fig. 1 that in the section A the ε′ value is much higher
than the dielectric permittivity of the sample bulk part,
which was estimated using the analysis of the dielectric
spectrum in the section B. As we have shown in [19], the
reason for this effect is uneven distribution of the
electric field in the sample (at low frequencies the
electric field is mainly applied to the near-electrode layer
with a small thickness). Therefore, changes in the ε′
value for low frequencies characterize the change in the
parameters of the near-electrode layers.
As one of the characteristics of the near-electrode
layer, we can take the ε′ value at the lowest frequency.
The dependence of ε′ on the ANP concentration for the
frequency 10–1 Hz is shown in Fig. 4. It is seen that since
the ANP concentration is close to 0.02 wt.% there
observed a significant (almost 9-fold) change in the ε′
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 399-403.
doi: https://doi.org/10.15407/spqeo19.04.399
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
402
value. The small difference between the ε′ values for
6СНВТ and 6СНВТ+0.01 wt.% ANP as well as for the
mixtures LC+ANP with the concentrations of 0.02 and
0.1 wt.% gives the reason to assume that the parameters
characterizing the near-electrode layer are non-linearly
dependent on the ANP concentration. Thus, not only the
parameters of the bulk part of the sample, but also the
parameters for the near-electrode layer of these samples
are not linearly dependent on the nanoparticle
concentration.
Adsorption of nanoparticles on the electrode
surface can be considered as one of the main reasons for
changes in the parameters of near-electrode layers in the
presence of a small amount of ANP. Therefore, being
based on the data obtained, it can be assumed that the
concentration of ANP adsorbed on the electrode surface
is a non-linear function of their concentration.
The dielectric spectrum in the section A is caused by
the relaxation process of a certain type. To establish the
mechanism of this process, the dependence ε″(ε′) (Cole–
Cole diagram) was analyzed. For all the samples, except
6СНВТ+0.1 wt.% ANP, the experimental values form
only a small section of the arc, from which it was difficult
to plot the whole Cole–Cole diagram. Therefore, the detail
analysis of the Cole–Cole diagram was performed only
for the samples 6СНВТ+0.1 wt.% ANP.
0.00 0.02 0.04 0.06 0.08 0.10
2.0x10-9
4.0x10-9
6.0x10-9
σ,
O
hm
-1
m
-1
C, wt.%
Fig. 3. The dependence of the conductivity of the liquid crystal
6СНВТ of the concentration of gold nanoparticles.
0.00 0.02 0.04 0.06 0.08 0.10
100
200
300
400
500
600
ε'
C, wt.%
Fig. 4. The dependence of the dielectric permittivity of the
liquid crystal 6СНВТ on the concentration of gold
nanoparticles at the frequency 10–1 Hz.
It follows from these data that the dependence
ε″(ε′) for the sample 6СНВТ+0.1 wt.% ANP can be
approximated by a semi-circle with a small error.
According to the theory [20], the relaxation process of
this type is described by the Debye equation:
ωτ+
ε−ε
+ε=ε ∞
∞ i
s
1
* , (2)
where ε* is the complex dielectric permittivity, ε∞ and εs
are the values of the dielectric permittivity at the
frequencies f = ∞, and f = 0 Hz, respectively, τ is the
dielectric relaxation time.
From the parameters in the equation (2), the most
informative is the time of dielectric relaxation. We have
estimated its value as 4.7±0.5 s.
In the section C of dielectric spectrum, changes in
the parameters of dielectric processes under the
influence of nanoparticles were significantly lower than
those in the sections A and B. That’s why they have not
been analyzed in detail in this paper. The relaxation
process that occurs in this frequency range is
characteristic for any polar liquids and is caused by the
transition from the dipole and electron polarization (at
lower frequencies) to the purely electron polarization (at
higher frequencies). The reason for this effect is that the
molecules (and, hence, their dipole moments) have no
time to oscillate under the field action for the period
close to that of alternating electric field.
4. Conclusions
It has been experimentally shown that the presence of
gold nanoparticles with the concentrations of 0.01 to
0.1 wt.% in nematic liquid crystal 6СНВТ leads to
changes in the parameters of near-electrode layers and
bulk part of the sample, which considerably exceed the
error of measuring these parameters.
In general, the presence of nanoparticles in LC
leads to increasing the conductivity value. However, this
dependence (as well as that of the near-electrode layer
parameters) on the concentration of nanoparticles is non-
linear. In the presence of 0.1 wt.% ANP, the
conductivity of the mixture of liquid crystal and ANP is
increased almost by 4 times. Moreover, the maximum
changes in the value of conductivity occur within the
concentration range of 0.01 to 0.02 wt.% ANP.
One reason of the non-linear dependence of the
parameters of near-electrode and bulk properties of the
sample on the nanoparticle concentration may be
aggregation of nanoparticles, the efficiency of which
considerably increases beginning from the ANP
concentrations higher than 0.02 wt.%.
The non-linear dependence of the conductivity on
the concentration of gold nanoparticles revealed in the
mixture of liquid crystal and ANP can be characteristic
for biological objects. Therefore, when developing the
methods to control nanoparticles in biological systems,
which are based on conductivity measurements, one
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2016. V. 19, N 4. P. 399-403.
doi: https://doi.org/10.15407/spqeo19.04.399
© 2016, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
403
should take into account that, even at low concentrations
of nanoparticles, the conductivity can be a non-linear
function of the concentration typical to introduced
impurities.
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