Y. PATEL et al.: INVESTIGATION OF THE HYDROPHOBIC PROPERTIES OF PIEZOELECTRIC NANOCOMPOSITES ...
407–415
INVESTIGATION OF THE HYDROPHOBIC PROPERTIES OF
PIEZOELECTRIC NANOCOMPOSITES AND APPLICATIONS IN
BIOMEDICAL MICRO-HYDRAULIC DEVICES
RAZISKAVA HIDROFOBNIH LASTNOSTI PIEZOELEKTRI^NEGA
KOMPOZITA IN NJEGOVA UPORABA ZA BIOMEDICINSKE
MIKROHIDRAVLI^NE NAPRAVE
Yatinkumar Patel
1
, Giedrius Janu{as
1
, Arvydas Palevi~ius
1
, Andrius Vilkauskas
1
,
Petr Lepsik
2
1
Faculty of Mechanical Engineering and Design, Kaunas University of Technology, Studentu St. 56, Kaunas, Lithuania, LT-51424
2
Faculty of Mechanical Engineering, Technical University of Liberec, Studentska 1402/2, Liberec, Czech Republic, 46117
Prejem rokopisa – received: 2019-10-15; sprejem za objavo – accepted for publication: 2020-02-12
doi:10.17222/mit.2019.249
The main purpose of the paper is to investigate the hydrophobic properties of piezoelectric composites that could be used in
biomedical micro-hydraulic devices. Hydrophobicity plays an important role, and gives less obstruction to the water, which is
the major reason behind the lower efficiency of electrical devices, particularly for piezoelectric polymers. Hydrophobicity is an
important property for the improvement in effectiveness and durability of microhydraulic devices made from PZT composite
materials. To develop the PZT composite material, we began with the lead zirconate titanate (PZT) nanopowder synthesis. The
PZT was additionally blended with three different binding polymers polyvinyl butyral (PVB), polymethyl methacrylate
(PMMA), and polystyrene (PS) in benzyl alcohol to prepare a screen-printing paste. Then, by applying the screen-printing
method, three different PZT coatings were prepared on aluminum and polyethylene terephthalate (PET). The hydrophobicity of
the prepared PZT composite was made using a contact-angle measurement between the drop of water and three PZT composite
materials PZT + PVB, PZT + PMMA, and PZT + PS. Also, the contact-angle measurement made with the drop of glycerin,
spirit, and olive oil on three different PZT composites. Finally, the model of the micro-channel was created using COMSOL
Multiphysics with the PZT + PMMA and simulated by applying the electrical excitation signal on the pattern of electrodes. The
different wave-shaped deformations were achieved from the simulation of the microchannel. The proposed application could be
used for bioparticle transportation.
Keywords: piezoelectric nanocomposite, hydrophobicity, contact angle, microhydraulic systems, microchannel, bioparticles
Avtorji v ~lanku opisujejo raziskavo hidrofobnih lastnosti piezoelektri~nih kompozitov, ki bi se lahko uporabljali v biomedi-
cinskih hidravli~nih napravah. Hidrofobnost je lastnost razli~nih snovi, da odbijajo vodo. Ta je slaba v primeru piezoelektri~nih
polimerov, kar je glavni razlog manj{e u~inkovitosti elektri~nih naprav (sistemov), ki jih vsebujejo. Dobra hidrofobnost je
pomembna lastnost za izbolj{anje u~inkovitosti in trajnosti mikrohidravli~nih naprav, izdelanih iz kompozitnih materialov na
osnovi Pb-Zr-titanatov (PZT). Izhodi{~e za razvoj PZT kompozitnega materiala je svin~ev-cirkonijev titanatni nanoprah.
Le-tega so avtorji dodatno me{ali s tremi razli~nimi polimernimi vezivi na osnovi polivinil butirala (PVB), polimetil metakrilata
(PMMA) ter polisterena (PS) v benzil alkoholu in s tem pripravili paste za sitotisk. Nato so, z metodo sitotiska, tri razli~ne paste
kot PZT prevleko nanesli na aluminij in polietilen tereftalat (PET). Hidrofobnost pripravljenih PZT kompozitov so avtorji
ugotavljali z merjenjem kontaktnega kota oz. kota omakanja nastalim med kapljico vode in povr{ino kompozitnih materialov
PZT + PVB, PZT + PMMA in PZT + PS. Prav tako so kot omakanja dolo~ili pri kapljici glicerina, {pirita in olivnega olja,
nastali na povr{ini izdelanih PZT kompozitov. Nazadnje so izdelali {e mikrokanalski model z uporabo programskega orodja
COMSOL Multiphysics na povr{ini PZT + PMMA in izvedli simulacijo z uporabo elektri~nega vzbujanja na vzor~nih
elektrodah. Z mikrokanalsko simulacijo so dosegli razli~ne deformacije v obliki valov. Predlagana aplikacija bi lahko bila
uporabna za prenos biodelcev.
Klju~ne besede: piezoelektri~ni nanokompoziti, mikrohidravli~ni sistemi, kontaktni kot, hidrofobnost, omakanje, mikrokanal,
biodelci
1 INTRODUCTION
Piezoelectric nanocomposites have been the focus of
the development of the microdevices and micro-com-
ponents in the past few decades. Piezoelectric materials
are preferable because of their capability to transform the
biological, chemical or mechanical response to an
electrical signal by using the piezoelectric or piezo-
resistive effect. It has become a new trend in MEMS
devices that are used for medical/medicine purposes
because it promises high performance with a good
accuracy level.
1,2
The use of piezocomposites is reported
to develop microchannels, micropumps, biosensors,
microneedles.
3
Recently, the most important develop-
ment in the field is a micro electromechanical system
(MEMS) and a nano electromechanical systems (NEMS)
in a microfluidic drug-delivery system.
4
Moreover,
piezoceramics are some of the most multifunctional
materials to produce actuators, sensors and transducers.
Hence, piezoceramics are also used in the production of
Materiali in tehnologije / Materials and technology 54 (2020) 3, 407–415 407
UDK 620.1:544.722.1:620.3:537.226.86 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 54(3)407(2020)
*Corresponding author's e-mail:
y.patel@ktu.lt (Yatinkumar Patel)

high-accuracy and precise printer heads, fuel injectors,
ecograms and energy-harvesting devices.
5–8
Hydropho-
bicity is the property of a liquid molecule that is an
intermolecular force from a mass of water. It plays a
significant role in applications in the industrial level as
well as medical. Also, it is an important term in the field
of bioscience, microhydraulic devices and MEMS
(micro-electromechanical systems) development.
9
It has
significance in oil recuperation, grease, fluid covering,
paint enterprises, and printing.
10,11
In recent years there
has been interest in the investigation of surfaces
incorporating superhydrophobic and super hydrophilic.
Because of their possible application in self-cleaning,
nanofluidic, electrowetting and to determine the pro-
perties of the liquid. A study of the wettability and
hydrophobicity involves primary data as the contact
angle study, which is useful to know the degree of
wetting, while the liquid is interacting with solid
surfaces. There will be three possible conditions happen-
ing with small contact angles of less than (<90°), which
indicates high wettability of the hydrophilic surface,
while the angle is larger than (>90°) indicates a low
wettability, which means a hydrophobic surface.
12
The
hydrophobicity gives less obstruction from the water,
which is the main purpose behind the reduced efficiency
of electrical devises, particularly for piezoelectric
polymers. The profoundly hydrophobic surface could
make a natural semiconductor material progressively
steady and lead to broad uses of this material.
13,14
Current
strategies to prepare a hydrophobic surface depend on
the post-adjustment of the surfaces.
15,16
Lately, numerous
hydrophobic materials have been created using different
segments, for example, polypropylene surfaces, poly-
styrene, polyurethane and poly(vinyl chloride), by using
different methods.
17,18
It was discovered that electro-
spinning is a popular method to adjust the wetting
behaviour of a polymer surface.
19,20
A predominant
hydrophobic piezoelectric solid for broad applications
has barely been reported. It is new in the field of nano-
technology, sensors which are working in liquid envi-
ronment studies and nanoscience development because
of the occurrence of many materials in the past few
years. (e.g., graphene, carbon nanotube, boron nitride
nano mash etc.).
21
In this paper three different types of piezoelectric
composite materials with a polymer composition (PVB,
PS and PMMA) are investigated and display hydro-
phobic properties. hydrophobicity plays an important
role in biosensors, which are working in the viscous
(liquid) environment. The hydrophobicity investigation
was made for PZT composite materials (PVB, PS, and
PMMA) with different liquids (distilled water, glycerin,
spirit, and olive oil). For hydrophobicity, the identifi-
cation of these PZT composite materials simplified the
experimental setup, which has been designed to measure
the contact angle, because a contact-angle measurement
is a convenient method for surface identification, when
either it is hydrophobic or hydrophilic. ImageJ (Drop-
Snake plugins) was used to analyse the images for the
contact angle, which is formed by liquid drops on the
PVB, PS, and PMMA composite surface. Moreover, the
influence of different coating thickness of PZT com-
posite material and different base materials on contact
angle was investigated.
2 EXPERIMENTAL PART
2.1 PZT composite material synthesis
An oxalic acid-water (C
2
H
2
O
4
) based nanopowder of
lead zirconate titanate (Pb (Zrx, Ti1–x) O
3
) with PZT
(58/42) was utilized. The chemical compound of the PZT
(52/48) solution was lead (II) acetate [Pb(NO
3
)
2
],
titanium butoxide [Ti(C
4
H
9
O)
4
], and zirconium butoxide
[Zr(OC
4
H
9
)
4
]. Alternate reagents utilized were oxalic
acid, deionized water, acetic acid, and an ammonia
solution. Lead (II) acetate [Pb(NO
3
)
2
] (8.26 g) was mixed
with 100 mL of water. Then in the same mixture of
liquid acetic acid was poured and the solution of the
mixture was warmed at 50 °C and blended to dissolve.
Thirty-two grams of oxalic acid was diffused in 500 mL
of water, then blended with the titanium butoxide (5.1 g)
and zirconium butoxide (7.65 g) at a combination of
80 %. Thereafter, the solution of lead acetate was com-
bined with the titanium butoxide and zirconium butoxide
solution. The last solution was alkalized with 25 %
ammonia solution to pH 9–10 and mixed for 60 minutes.
The precipitate of the solution was separated in a
vacuum and during filtration, it was washed with water
and acetone. The material was dried at 100 °C for half of
the day after the separation process. The powder was
warmed at 1000 °C for 9 hours. Next, the PZT powder
was grinded and blended with 20 % solution of polyvinyl
butyral in benzyl alcohol blended under defined con-
ditions: 80 % of PZT and 20 % of the binding material.
Finally, the coating of paste was made on a base material
(aluminum and polyethylene terephthalate (PET)) using
a screen-printing technique.
Thus, for the contact-angle measurement the speci-
men was prepared according to the screen-printing tech-
nique for the experimental measurement of the contact
angle, three different PZT composites were produced
with the PZT nanopowder and three different binding
polymers polyvinyl butyral (PVB), polystyrene (PS) and
polymethyl methacrylate (PMMA). The properties of the
binding polymer are presented in Table 1.
Table 1: Properties of binding polymers
Properties PVB PMMA PS
Tensile strength, MPa  20 48–76 32–44
Poisson’s ratio 0.45–0.49 0.35–0.4 0.4–0.41
Density, kg/m
3
1070 1170 1050
Young’s modulus, GPa 0.05 3.1 2.7
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408 Materiali in tehnologije / Materials and technology 54 (2020) 3, 407–415

Using these properties of the binding polymers, the
density of the used composite material was calculated.
The density of different PZT composite materials is
presented in Table 2.
Table 2: Density of composite materials
Sr. no. Composite material Density
1 80 % PZT+ 20 % PVB 6294 kg/m
3
2 80 % PZT+ 20 % PMMA 6314 kg/m
3
3 80 % PZT + 20 % PS 6290 kg/m
3
A modulus of elasticity of 6.3 GPa was obtained for
the PZT nanocomposite with PMMA binding material,
while PS and PVB had lower elasticity moduli of 5.3 and
3.9 GPa, respectively.
22
80 % of the nanocomposite
material was PZT nanoparticles (Young’s modulus 63
GPa), while the portion of binding material was 20 %.
Because of this, the modulus of flexibility was decreased
multiple times.
2.2 Specimen preparation
For the contact-angle measurement the specimen was
prepared with PZT nanopowder and three different
binding polymers polyvinyl butyral (PVB), polystyrene
(PS) and polymethyl methacrylate (PMMA). Moreover,
to observe the influence of different base materials on
the contact angle, two different types of base material
were used Aluminum natural sheet and polyethylene
terephthalate (PET), as shown in Figure 1.
Also, the thickness of the coating for the PZT
binding polymer is different for each base material in
order to examine the influence of the different thickness
of the coating on the contact-angle measurement. Thus,
different base materials are also used to observe the
different base material’s influence on the measurement.
The geometrical dimensions of the specimens are
presented in Table 3.
Table 3: Dimension of specimens
Specimen
Base material
Aluminum, coating
thickness (total), μm
PET, coating
thickness (total), μm
PZT + PVB 20 (310) 50 (140)
PZT + PS 20 (310) 50 (140)
PZT + PMMA 20 (310) 50 (140)
Four different liquids, i.e., water, spirit, glycerin and
olive oil, were used in the experiment in order to
determine the hydrophobic properties of the surface with
different liquids. The properties of the different liquids
are presented in Table 4.
Table 4: Properties of liquids
Sr. no. Liquids
Surface tension,
dyne/cm
Density,
kg/m
3
1 Water 72.8 997
2 Glycerin 64.2 1260
3 Spirit 26.02 793
4 Olive oil 34.76 888.89
2.3 Contact-angle measurements for hydrophobic
analyses of PZT composites
The experiment was performed at the Institute of
Mechatronics and the Department of Mechanical Engi-
neering, Kaunas University of Technology. The purpose
of this experiment was to understand the hydrophobic
properties of different PZT composite materials because
liquid behaviour differs on the various surfaces, so the
easiest way to determine the behavior of the liquid on the
solid surface was by a contact-angle measurement. In
this experiment, the freely available image-analysis soft-
ware platform ImageJ was used for its ever-expanding
flexibility. This software has three plugins to measure the
contact angle, including contact-angle analysis, low bond
axisymmetric drop shape analysis (LB-ADSA) and
DropSnake.
The experimental setup presented in Figure 2 for the
contact-angle measurements of the hydrophobic material
consist of: (1) specimen, (2) adjustable specimen holder,
(3) drop on specimen, (4) double convex lenses, (5)
Guppy F-503 B&W CMOS camera, (6) adjustable
camera holder, (7) computer system with live image of
drop with image-processing software to analyze a cap-
tured image. The optical parts consist of camera (Guppy
F-503 B&W CMOS camera specification of camera:
pixel size: 5,038,848, Resolution: 2592(h) 1944 (v),
sensor size: ½ inch, sensor type: CMOS, connection:
1394A, speed: 7.5 frames/sec with 2592 × 1944 resolu-
tion and 60 frames/sec with 640 × 480 resolution) and
optical lenses with a focal length of 600 mm (holo-
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Materiali in tehnologije / Materials and technology 54 (2020) 3, 407–415 409
Figure 1: Multilayer specimen with: a) aluminum base material and
b) with PET

graphic and optical measurement laboratory, double con-
vex lenses with 50 mm diameter) that is placed between
the camera and the sample. The pipet used for the
dispensing drop for different liquids. The pipet capacity
is 5 mL. Each subdivision is divided into 0.1 mL with a
blue color code scale. The permitted drawing error for
the pipet is ±0.030 mL.
The experiment was performed with an ambient light
source in a dark laboratory room and the light settings
are arranged to make the liquid drop appear black, which
is necessary for measurement accuracy as well as for the
image analysis. The light conditions are fully arranged to
avoid any reflection of the light that spoils the measure-
ment. Also, precautions were taken to prevent the drops
polluted by air impurities such as dust and particles.
An illustration of the critical distance between came-
ra, lenses and the drop of liquid presented in Figure 3,
which is very important during the experiment, to main-
tain the stability of image quality to obtain accurate
results. All the parts are placed on the stable surface
table for an accurate measurement of the contact angle.
Thus, there are two optical lenses placed between the
camera and the specimen for exact focus on the drop.
Also, lenses are kept stable and fixed. The camera fixed
on the adjustable camera holder for adjusting height
respect to the drop. While the specimen fixed on the
adjustable specimen holder for the stable focus on the
drop and to adjust the height of the specimen for
excellent focused and good-quality image.
Firstly, the height of the specimen holder was
adjusted according to parallel camera vision for the
accurate position of the drop image. Then drop of
distilled water 0.02 μl diffused from the pipet to the PVB
surface from the height 15 mm and the quantity of the
diffused drop was kept constant for each drop of
measurement and for all three PZT composite surfaces
for all different liquids. Right after, the stabilization of
the drop image was captured by the camera. Captured
images were analyzed using ImageJ DropSnake plugins
provided by Wayne Rasband (retired from NIH). By
using those plugins, we started to put 7 knots from the
left lower end to the right lower end along the profile of
drop should cover inside all the knots. Then clicking
twice on the image that will demonstrate the rough
estimated value of the angle left-hand and right-hand
side. Then, by adjusting the knots to achieve exact
profile, then click on the fast snake button that will also
show the red profile of drop and angles if it appears
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410 Materiali in tehnologije / Materials and technology 54 (2020) 3, 407–415
Figure 2: Experimental setup for contact-angle measurement
Figure 3: Ilustration of the critical distance between the important parts (camera, lens, and specimen with a drop)

exact to the drop profile, then click on the green play
button for redefining the drop profile and accept it. It
will indicate the exact value of the left- and right-hand
values, as well as the profile of the drop.
A calculation of the confidence level interval for the
error in measurement was made using Equation 1. The
value of Z was taken from the normal distribution 1.96,
because the measured values lie within the range of the
standard deviation of the mean. Also, the standard error
of the mean value was calculated using Equation (2):
Confidance interval =xZ
s
n
± (1)
where, x = average of measurement, Z = 1.960 constant
for accuracy level 95 %, s = standard deviation and n =
number of measurements.
Standard error of mean()  m
=
s
n
(2)
where, s = standard deviation and n = number of
repetition of measurements (i.e., the rate of repetition
was 15).
3 RESULTS AND DISCUSSION
The drop of water tested on three different PZT
polymer multilayer specimens: polyvinyl butyral (PVB),
poly (methyl methacrylate) (PMMA) and polystyrene
(PS). Each sample of drop measurement on polymer was
made using the same parameter a and the images were
analyzed several times. The mean value of the contact
angle ( ) measured for the water drop on the multilayer
specimen of PZT + PVB, PZT + PS, and PZT + PMMA
were 80.71±0.29°, 88.88±0.33°, and 92.94±0.40°, res-
pectively, and graphically presented in Figure 4.
Ilustration of the water drop tested on three polymer
composite materials is presented in Figure 5.
From the measured values of the contact angle ( ) the
maximum angle was observed with PZT + PMMA is
92.94° with an error of ±0.40°. The lowest contact angle
was observed with PZT + PVB is 80.01° with a measure-
ment error of ±0.29°. The measured value of the contact
angle for PZT + PS is 88.8°, with an error of measure-
ment of ±0.33° it falls between the measure value of
PMMA and PVB. So, according to the literature review,
it could be stated that PMMA falls in the range of
hydrophobic material with water.
23,24
PVB and PS show
contact angles less than 90°, so can be considered as a
hydrophilic surface with water.
The measured contact angles for the spirit drop on
different polymer binding material are presented in
Figure 6. The measured values of contact angle for PZT
+ PVB, PZT + PS, and PVB + PMMA are 33.43±0.45°,
38.01±0.48°, and 18.48±0.12°, respectively. From the
results it is possible to state that all three polymer
composite materials are hydrophilic with the spirit.
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Materiali in tehnologije / Materials and technology 54 (2020) 3, 407–415 411
Figure 6: Mean contact angle with different liquids on three different
PZT composite polymer surfaces
Figure 4: Mean contact angle of water droplet on three different PZT
polymer surfaces
Figure 5: Water-drop profile on the PZT composite material surface polynomial fit

For olive oil the different PZT polymer composite
surfaces of PVB, PS, and PMMA are presented in Fig-
ure 6. As seen in the graph the measured values of the
contact angle for PVB, PS, and PMMA are 23.18±0.10°,
25.86±0.29°, and 23.57±0.18°, respectively. There is no
significant statistical difference between the results.
The experiment was performed on different PZT
polymer composite material (PVB, PS, and PMMA)
with different liquids (water, glycerin, spirit, and olive
oil). The obtained results show that only PMMA has
hydrophobic properties with water. From the plot in
Figure 6 the contact angle for PMMA with water
(92.94°) is only more than 90°. All the other polymer
composite materials show contact angles less than 90°
and the lowest contact angle was found for olive oil
(18.48°) on the surface of PZT + PMMA.
In order to know the influence of the different base
materials on the contact angle the experiment was per-
formed with two different base materials, aluminum and
PET, presented in Figure 7. From the experiment angle
measured for the drop of water on PZT + PVB binding
polymer with aluminum and PET base material is
81.03±0.4° and 80.71±0.42°, respectively. It is only a
difference of 0.4 %. For PZT + PS with aluminum and
PET base material it is 88.47±0.41° and 88.8±0.33°,
respectively. The difference in contact angle is just
0.37 %. PZT + PMMA has the highest contact angle
among the three polymer binding materials. The
observed values are 92.43±0.43° and 92.94±0.4° with
the aluminum and PET base material, respectively. It is
only a difference of 0.55 %. From the results there is no
influence of base material on the water-angle measure-
ment.
In order to understand the environmental effect (tem-
perature, air/impurities) on the contact angle measure-
ment a time dependence study was performed for the
water droplet. To observe the change in WCA (water
contact angle) images were captured for each drop sam-
ple on various polymer composite surfaces at different
time intervals. Images were captured after 10 s, 120 s,
and 240 s for every drop sample. The result are presented
in Figure 8. Initially, after 10 s measured WCA of PZT
+PVB is 80.01°, after 120 s a 1.9° change observed and
it was gradually decreased to 76.96° after 240 s. So, it is
possible to state WCA of PVB has gradually decrement
of 2° after every 120 s. Moreover, a similar effect has
been observed with PS binding polymer initially 88.80°
observed then it decreased to 86.90° and finally, after
240 s, it decreased to 85.64°. For the PMMA binding
polymer it was 92.94° at 10 s, it decreases to 90.73° after
120 s and at last, after 240 s it was observed at 89.44°.
So, for all three polymer binding materials, no signifi-
cant change was observed during first 120 s, but there is
an observable difference in the contact angle between the
initial and final measurement.
To check the possible application of the proposed
PZT composite materials we decided to prepare a micro-
channel with controllable parameters using the thermal
reapplication process. A model of the microchannel is
presented in Figure 9.
The geometrical dimensions of the microchannel
(Figure 9a) are the length (L) = 200 μm, period (P)=20
μm, total thickness (T) = 20 μm, depth of the inner slot
(d) = 10 μm, width of the slot (w) = 10 μm, and thickness
of the two ridge (2r) = 10 μm and radius at the inner
corners are D = 2 μm. The investigation of the micro-
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412 Materiali in tehnologije / Materials and technology 54 (2020) 3, 407–415
Figure 9: a) Dimensions of the finite-element model of the micro-
channel and b) the boundary condition of the finite-element model of
the microchannel
Figure 7: Comparison of WCA on Different base material
Figure 8: Time dependence for WCA

channel was made using the COMSOL Multiphysics 5.4
simulation software.
Just one part of the microchannel was analyzed with
the symmetrical boundary conditions because this is a
periodic system. The boundary conditions (Figure 9b)
were applied to the finite-element model and the left and
right surfaces of the microchannel were kept fixed by
using rollers. The front and back surfaces of the micro-
channel were totally in the fixed condition because these
surfaces are connected to the fluid container. The bottom
surface of the model will be connected to the other ele-
ment of the sensor; therefore, it is also in an unmovable
fixed condition and its serves as an electrical ground.
The top portion of the microchannel is enclosed by elec-
trodes and a high-strength transparent layer. It allows for
a visual inspection of the fluid flow and confirms that the
pressure inside the channel is high.
Then the system of the microchannel is excited by
applying the sinusoidal alternating electrical potential of
20 V. There are three sample tests done for the dynamic
response of the suggested microchannel at a different
frequency.
The total deformation and X component of the dis-
placement field of the electrically excited microchannel
system at 12 MHz frequency (Figure 10a) shows that the
shape of the channel is deformed and it looks like a
mechanical valve, which means the cross-section area of
the channel is eventually increased or decreased through-
out the length of the microchannel. When the frequency
is increased to 14 MHz, then the cross-section of the
microchannel starts to divide into two segments (Figure
10b) with different concentrations of bioparticles. While
the frequency increased to 18 MHz, the cross-section of
the microchannel actually shows that it is divided into
four segments with different concentrations of bioparti-
cles (Figure 10c). From the simulation and hydropho-
bicity results, it could be possible to state that the
developed material PZT+PMMA could be usable for the
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Materiali in tehnologije / Materials and technology 54 (2020) 3, 407–415 413
Figure 11: Microscope image with water particles in the micro-
channel
Figure 10: a) Surface deformation of microchannel periodically excited at 12 MHz frequency, b) microchannel periodically excited at 14 MHz
and c) microchannel periodically excited at 18 MHz frequency with visualized X component of the displacement field

development of efficient and durable devices in micro-
hydraulic devices. A possible application is presented in
Figure 11.
As shown in Figure 11, the water particles are inside
the microchannel, which is marked inside the orange
circle. the period of the microchannel is 20 μm, chosen
for the simulation. So, from the image it is clear and
possible to state that the proposed material is useful for
the development of microhydraulic devices in biomedi-
cine.
4 CONCLUSIONS
An investigation of the hydrophobic properties of a
PZT composite polymer was performed. Experimental
results showed the contact angles ( ) for the PZT com-
posite material PVB, PS, and PMMA with water are
80.71±0.4°, 88.08±0.33°, and 92.94±0.4°, respectively.
Also, the contact angle was measured with different
liquids, and the results are with glycerin PVB –
73.49±0.5°, PS – 86.92±0.18°, and 72.52±0.29°, with
spirit PVB – 33.43±0.45°, PS – 38.01±0.48°, and
PMMA – 18.48±0.12°, and with olive oil PVB –
23.18±0.10°, PS – 25.86±0.29°, and PMMA –
23.57±0.18°. From the obtained values only the contact
angle of the water drop is noted highest (92.94±0.40°) on
the PZT + PMMA composite surface, which indicates
the PMMA is the only hydrophobic material. Moreover,
PVB, PS would be considered as hydrophilic materials
with water. So, from the results, it is clearly stated that
only the PMMA with PZT composite material surface is
falling in the hydrophobic segment, and the rest of the
surfaces are hydrophilic.
Moreover, it is found that there is no influence of the
different thickness of the coating and the different base
materials on the contact angle. A high Q factor of the
proposed composite materials would permit it to effect-
ively control the microdevice as microchannels.
The presentation of the microchannel simulated by
COMSOL Multiphysics demonstrated that it could work
in three modes: the valve mode that was closed for
bioparticles when half-wavelength oscillation of 12 MHz
frequency was produced; bioparticle designing or trap
mode when a full wavelength oscillation of 14 MHz
recurrence was created; and mode with free go for
bioparticles when no vibrations were produced in the
microchannel.
The experimental setup for the contact-angle
measurement allows us to measure the CA with an
accuracy level of 1.5°. It is possible to capture an
excellent quality image due to the high-speed camera (60
fps) used. Also, the setup could be useful to measure the
dynamic contact angle, time dependence, and advancing
and receding contact angle. The used image-analysis
software is a freely available platform (ImageJ). Drop-
Snake plugins retuned the precise and stable values of
the contact angle in both the relatively high ( = 90°) and
low ( = 40°) regions. Also, it is possible to measure the
contact angle for different solid substrates and liquids.
Acknowledgments
This research was funded by grant S-MIP-17-102
from the Research Council of Lithuania and by grant
CZ.02.1.01/0.0/0.0/16_019/0000843 from the Ministry
of Education, Youth and Sports of the Czech Republic
and the European Union – European Structural and
Investment Funds in the frames of Operational Prog-
ramme Research, Development and Education – project
Hybrid Materials for Hierarchical Structures.
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