Fabrication of biomimetic tio2 fdtscotton fabric with special wettability for effective self cleaning application

VIETNAM NATIONAL UNIVERSITY, HANOI
VIETNAM JAPAN UNIVERSITY

NGUYEN THI HONG NHUNG

FABRICATION OF
BIOMIMETIC TiO2-FDTS@COTTON
FABRIC WITH SPECIAL WETTABILITY
FOR EFFECTIVE SELF-CLEANING
APPLICATION

MASTER'S THESIS


VIETNAM NATIONAL UNIVERSITY, HANOI
VIETNAM JAPAN UNIVERSITY

NGUYEN THI HONG NHUNG

FABRICATION OF
BIOMIMETIC TiO2-FDTS@COTTON
FABRIC WITH SPECIAL WETTABILITY
FOR EFFECTIVE SELF-CLEANING
APPLICATION
MAJOR: ENVIRONMENTAL ENGINEERING
CODE: 8520320.01

RESEARCH SUPERVISOR:
Dr. TRAN THI VIET HA

Hanoi, 2021

ACKNOWWLEDGMENTS
First of all, I wish to express my deepest gratitude to Dr. Tran Thi Viet Ha who
is a kindness, esteemed supervisor and other Professors/Lecturers of Master’s Program
in Environment Engineering for their tutelage. I also want to say thank to VNU Vietnam
Japan University (VJU), Hanoi National University – Hanoi University of Science
(HUS); VNU Key Laboratory of Advanced Materials Applied in Green Development
and Laboratory of Master’s Program in Nanotechnology to recognize the invaluable
assistance that you all provided during my study.
In particular, I acknowledge VJU's JICA research fund (period 2021-2023) Principal Investigator Dr. Tran Thi Viet Ha - for financially supporting my thesis
research. With this generous support, my research was favorably conducted on schedule
without any discontinuation.
Finally, I would like to extend my sincere thanks to my classmates and colleagues
who have always been by my side for spiritual support. Specially, I cannot leave La Thi
Ngoc Mai - 4th intake student at Master’s Program in Nanotechnology - without
mentioning, who has spent a lot of time supporting me unconditionally through the
analysis stage.
Hanoi, 2021
Nguyen Thi Hong Nhung


TABLE OF CONTENTS
LIST OF TABLES ..........................................................................................................i
LIST OF FIGURES ...................................................................................................... ii
LIST OF ABBREVIATIONS ......................................................................................iv
CHAPER 1. INTRODUCTION ...................................................................................1
CHAPER 2. LITERATURE REVIEW .......................................................................3
2.1. Theoretical basis .................................................................................................. 3
2.2. Methods to fabricate the superhydrophobic surface ........................................... 5

2.3. Applications of the superhydrophobic material .................................................. 9
2.4. Analysis methodologies .................................................................................... 11
2.4.1. SEM ............................................................................................................11
2.4.2. FTIR ............................................................................................................15
2.4.3. XRD ............................................................................................................16
2.4.4. WCA ...........................................................................................................16
2.5. Superhydrophobic material studies in Viet Nam .............................................. 17
2.6. Oil pollution situation in Vietnam in recent years and treatment methods ....... 18
CHAPTER 3. MATERIALS AND METHODOLOGIES .......................................20
3.1. Materials ............................................................................................................ 20
3.2. Methodologies ................................................................................................... 20
3.2.1. Fabrication produce ....................................................................................20
3.2.2. Material characterization ............................................................................22
3.2.3. Applications of fabricated superhydrophobic fabric ..................................26
3.2.4. Durability test for fabricated superhydrophobic fabric ..............................27
CHAPER 4. RESULTS AND DISCUSSION ............................................................29
4.1. Results ............................................................................................................... 29
4.1.1 Optimization condition for fabrication of superhydrophobic fabric............29
4.1.2. Material characterization results .................................................................32
4.1.3. Applications of fabricated superhydrophobic fabric ..................................36
4.1.4. Durability of fabricated superhydrophobic cotton fabric ...........................40
4.2. Discussion ......................................................................................................... 42


CONCLUSIONS ..........................................................................................................44
REFERENCES ............................................................................................................45


LIST OF TABLES
Table 2.1. The values of the WCA correspond to the solid surface states .................... 5

Table 4.1. WCA of TiO2-FDTS@cotton samples with different number TiO2 coating
...................................................................................................................................... 31
Table 4.2. Optimal conditions in the first layer coating with TiO2 ............................. 32
Table 4.3. Oil recover efficiency ................................................................................. 39

i


LIST OF FIGURES
Figure 2.1. Young theory (Young, 1805) Where, γsv, γsl, γlv are the interfacial tensions
of the solid-vapor, solid-liquid and the liquid-vapor interface, respectively. ................ 3
Figure 2.2. Wenzel and Cassie-Baxter models (Wenzel, 1936),(B D Cassie and Baxter,
n.d.) ................................................................................................................................. 4
Figure 2.3. Wetting state and static water contact angle of the solid surfaces .............. 4
Figure 2.4. Shedding angle ............................................................................................ 4
Figure 2.5. Electron beam and the different types of signals which are generated (T. F.
Scientific, n.d.).............................................................................................................. 12
Figure 2.6. Magnetic lens schematic (T. F. Scientific, n.d.) ....................................... 12
Figure 2.7. Electron beam deflector (a) and lector-static lens (b) (T. F. Scientific, n.d.)
...................................................................................................................................... 13
Figure 2.8. Magnetic lens (T. F. Scientific, n.d.) ........................................................ 13
Figure 2.9. Different kinds of electrostatic lenses: single-aperture positive and negative
lenses (a, b), two-aperture lens (c) and three aperture Einzel lens (d) (T. F. Scientific,
n.d.) ............................................................................................................................... 14
Figure 2.10. Michelson interferometer in configured for FTIR (Petergans, 2017) ..... 15
Figure 2.11. Contact angle measurement (image cut from video) (B. Scientific, n.d.)17
Figure 3.1. Cellulose, TiO2 and FDTS structures ........................................................ 20
Figure 3.2. Experiment process ................................................................................... 21
Figure 3.3. SEM device ............................................................................................... 23
Figure 3.4. FTIR device ............................................................................................... 23

Figure 3.5. XRD device ............................................................................................... 24
Figure 3.6. WCA measurement device (Femtobiomed, 2021) .................................... 25
Figure 3.7. Shedding angle test ................................................................................... 25
Figure 3.8. Self-cleaning test ....................................................................................... 26
Figure 3.9. Oil-water mixture ...................................................................................... 27
Figure 3.10. Preparation for oil-water separation by glass filter holder...................... 27
Figure 4.1. SEM images of TiO2 coated samples (a) pH = 2~3; (b) pH = 3~4; (c) pH =
4~5; (d) pH= 5 ~6; (e) pH= 6~7; (f) pH = 7~8; (g) pH = 8~9; (h) pH = 9~10; (i) pH =
10~11 ............................................................................................................................ 29
Figure 4.2. SEM images of TiO2 coated samples (a) T =100oC; (b) T =120oC; (c) T
=140oC; (d) T =160oC .................................................................................................. 30
Figure 4.3. SEM images of TiO2 coated samples (a) t =2h; (b) t=3h; (c) t=4h; (d) t=5h;
(e) t=6h ......................................................................................................................... 31
Figure 4.4. WCA of 32
Figure 4.5. WCA.......................................................................................................... 33
Figure 4.6. SEM images, EDS spectrum of the cotton (a1, b1) raw cotton, (b1, b2)
TiO2@cotton and (c1, c2) TiO2-FTDS@cotton ........................................................... 34
Figure 4.7. FTIR spectra of the cotton samples........................................................... 35

ii


Figure 4.8. XRD spectra of TiO2-FTDS@cotton ........................................................ 36
Figure 4.9. The water droplets carry dirt (Shrimp sell powder) and roll off the cotton
fabric surface with shedding angle = 7o ....................................................................... 36
Figure 4.10. The water droplets carry dirt (Sand) and roll off the cotton fabric surface
with shedding angle = 7o .............................................................................................. 37
Figure 4.11. Organic solvents removal test. Time sequence of (a-c) toluene dyed red on
water surface, and (d-f) underwater chloroform dyed red with superhydrophobic cotton
pad. ............................................................................................................................... 38

Figure 4.12. Oil-water separation test ......................................................................... 39
Figure 4.13. Separation efficiency vs no. of cycles representing the durability of
superhydrophobic cotton after several uses. ................................................................. 40
Figure 4.14. Water drop on cotton surface after 10 laundering cycles ....................... 41
Figure 4.15. Water dropt on cotton surface (a) before and (b) after one month in room
condition ....................................................................................................................... 41
Figure 4.16. Water dropt on cotton fabric (a) only TiO2 coated, (b) TiO2-FDTS coated,
(c) only FTDS coated ................................................................................................... 42
Figure 4.17. Mechanism of the attachment TiO2 and FTDS on cotton fiber .............. 43

iii


LIST OF ABBREVIATIONS
BSE: Backscattered electrons
COD: Crystallography open database
EDS: Energy-Dispersive X-Ray Spectrometry
FTDS: 1H,1H,2H,2H-Perfluorodecyltrimethoxysilane
FTIR: Fourier-transform infrared spectroscopy
SA: Shedding angle
SE: Secondary electrons
SEM: Scanning Electron Microscopy
WCA: Water contact angle
XRD: X-Ray Diffraction

iv


CHAPER 1. INTRODUCTION
The self-cleaning materials has been explored and be consider as the materials of

the future in 21st century since the theory was first revealed from 1805 after Thomas
Young's report on the wettability of materials. The natural phenomenon of lotus leaves
is a typical example, inspiring surface studies by its exceptional wetting properties. Until
now, thousands of self-cleaning-material-articles have been published, and these
materials are popularity usage around the world. They are not only for the purpose of
researches, but also have diversity applications in real life, beyond the self-cleaning
feature, and have great contribution to the advance of science and technology.
Although there are several techniques which were reported to develop selfcleaning surface, the consideration of the properties of the substrates and the purposes
of the study make the chosen of appropriate fabrication techniques become extremely
necessary. A substrate can be fabricated by different methods. For instance, on glass,
Haiyan Hi et al.(Ji et al., 2013) was performed the hydrothermal process, while Satish
A. Mahadik et al. making repellent surface by sol-gel route (Mahadik et al., 2010).
Recently, Yi Lin et al.(Lin et al., 2018) Huynh H. Nguyen et al.(Nguyen et al., 2021)
was carried out the laser processing to hydrophobize the surface and have been
successfully obtained the repellent property. A method can be applied on many
different substrate. Thus, each substrate has its own set of optimal conditions. One of
the most popular techniques is sol-gel  which applies to most substrates – has been
show the versatility on several representative are fabric (Yang et al., 2018) copper
(Raimondo et al., 2017), glass (Mahadik et al., 2010), ceramic (Jamalludin et al., 2020),
wood (Jia et al., 2018), paper (Dimitrakellis et al., 2017), etc. Further, the combination
of multiple methods in one study has also is a flexible research plan (Li et al., 2015).
Self-cleaning feature has been successfully built on different substrates.
However, even in recent studies, there are still some limitations such as using toxic
solvents (toluene) or technique that require high energy consumption (plasma etching).
On the other hand, the research and application on this material has not been widely
developed in Vietnam. Superhydrophobic material is one of the economically,

1

effectively oil-water separation method, industrial waste oil recovery, oil spill cleanup
at sea. Although, this technology is also being applied in Vietnam, however it must be
imported from abroad such as Germany, Japan, Taiwan, etc. Hence, this study carried
out to open the development on a material which can use for oil recovery is significant.
Research on self-cleaning materials at low cost and environmental friendly are
rarely conducted so far. Aims to be sustainable and eco-friendly, considering the product
life cycle and the waste generated during process, the hydrothermal combined with dipcoating method was applied to fabricate superhydrophobic cotton fabric. The properties
of fabricated fabric were investigated by several analysis methods such as Scanning
Electron Microscope (SEM), Energy-dispersive X-ray spectroscopy (EDS), FourierTransform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD) and Water contact
angle (WCA) measurement equipment. In addition, potentially applications will be
presented in detailed.

2


CHAPER 2. LITERATURE REVIEW
2.1. Theoretical basis
In 1805, Thomas Young reported for the first time about contact angle between
liquid and homogeneous solid surface, and explained the relationship between water
contact angle (WCA) and surface energies for a liquid and a solid surface based on
mechanical theories (Young, 1805). After that, in the mid-20th century, Wenzel and
Cassie-Baxter further modified and developed the principle of contact angle changes
based on surface roughness (Wenzel, 1936),(B D Cassie and Baxter, n.d.). Until now,
wettability of the materials’ surface still attracts much attention in researches and
practical applications.
When water drop is dropped onto a solid surface, the angle between the liquid and solid
surface called contact angle (). The Young’s equation can be applied only to a
homogeneous solid surface (Figure 2.1).

Figure 2.1. Young theory (Young, 1805). Where, γsv, γsl, γlv are the interfacial tensions

of the solid-vapor, solid-liquid and the liquid-vapor interface, respectively.

3


Heterogeneous surface is more complex and it was explained by Wenzel and
Cassie-Baxter. Wenzel reported a model when the liquid might completely penetrate
into the rough surface. In Cassie-Baxter model, because of the roughness, it is
considered that the grooves under the water droplets are filled by air-trapped which
pushed water up prevents water contact the surface.

Figure 2.2. Wenzel and Cassie-Baxter models (Wenzel, 1936),(B D Cassie and Baxter,
n.d.)
The term of superhydrophobic and superhydrophilic surface first appeared when
Onda et al. published two papers on the wettability of rough surface in 1996 (Shibuichi
et al., 1996). Since then, numerous studies on the water permeability of the material
have been published. A surface is considered as superhydrophobic when it reaches two
conditions that (i) static WCA equal or greater than 150o (Figure 2.3) and (ii) dynamic
contact angle is lower than 10o (Figure 2.4).

Superhydrophilic

Superhydrophobic

Figure 2.3. Wetting state and static water
contact angle of the solid surfaces

Figure 2.4. Shedding angle

4

Table 2.1. The values of the WCA correspond to the solid surface states
States

Water contact angle (WCA)

Superhydrophilic

 < 5o in 5 seconds

Hydrophilic

5o ≤  < 90o

Hydrophobic

90o ≤  < 150o

Superhydrophobic

  150o

2.2. Methods to fabricate the superhydrophobic surface
In order to obtain the superhydrophobicity, a variety of methods have been
adopted to modify the substrate structure. There are two main methods TOP-DOWN is
create nanoparticles from bigger particles, and BOTTOM-UP is forming nanoparticles
from atoms or ions. Both two approach is also combine to have superhydrophobic
surface. The combination of two-way approach often follow step by step which is first
using top-down method, then added bottom-up restructure. However, the other

combinations order has applied as well. These techniques have the purpose of creating
roughness for the surface by attaching nanoparticles with crystalline structure, thereby
reducing the contact area of water with the solid surface and achieving a high contact
angle.
Top-down approach which restructure the surface in process by carving,
molding, machining materials with the supporting of lasers or other tool. The top-down
methods used for create superhydrophobic surfaces such as electro-spinning, plasma
etching, chemical etching, electrochemical deposition, etc.
(i)

Electro-spinning
Electro-spinning is a technique for manufacturing electro-spun fibers based on

electrostatic driven process. It can create the fibers has diameter ranges between tens of
nanometers to a few micrometers. The versatility processing to create fibers with
multiple arrangements and morphological structures is one of the remarkable advantages
of the technique. Thereby, Electro-spinning has paved the way for the development of

5


many technologies such as tissue engineering, regenerative medicine, encapsulation of
bioactive molecules, to emerge and evolve over recent years. For instance, Malvika
Nagrath et al. (Nagrath et al., 2019) were combined sol-gel and electro-spinning to
fabricate the bioactive glass fiber application in the biomedical field, support for the
treatment and recovery process which usually been used towards osteogenesis and other
potential use as hemostats; Nguyen Thuy Ba Linh et al. (Linh et al., 2011) were prepared
successfully PVA-TiO2 composite polymer membranes for filtration applications; ThiHiep Nguyen et al. (Nguyen et al., 2010) were synthesis the PVA nano-fibers which
contains Ag NPs had strong antibacterial by combination of microwave irradiation and
electro-spinning technique.

(ii)

Plasma etching
In room temperature, the elements in material etched react with the reactive

species generated by the plasma. As the result, the atoms of the element stick themselves
at the surface of the object, therefore the physical properties of the substrates being
modify. The plasma source or as known as etch species, could be the charged (ions) or
neutral (atoms and radicals). This technique is quite complicated, but its advantage is
created a uniform surface structure, thereby it is still appear for many recent studies
(Hou et al., 2020), (Nguyen-Tri et al., 2019).
(iii)

Chemical etching
Chemical etching is a process using highly acidic or basic solutions, in which the

surface elements are made to react by wet method. This technique can perform under
simple equipment, high etching rate, selectivity and save-time produce. Also, its
manufacture process is ecofriendly and provides corrosion resistant product. Beside,
along with advantages, chemical etching leads the contamination of the substrates, poor
process control and high amount of etchant chemicals are needed. Despite these
difficulties, numerous studies that exploit the strengths of this method have done (Yao
et al., 2018), (Huang et al., 2015).
Bottom-down approach is the process of adding or self-assembly material in nano
or micro scale on initial surfaces. Which includes some typical techniques as follow.

6


(iv)

Electrochemical Deposition
Electrochemical Deposition is a process that assembles solid materials from

molecules, ions or complexes in a solution. In which, a specific pattern produces one
metal masking on top of another metal, electrical energy can press a chemical process
that changes ions into atoms. Usually created a nano-scale thin layer of zinc, copper,
platinum, gold, etc. Plenty of studies on this method has proven effective in creating a
thin metal film with high durability. M.J. Zheng et al. has fabricated nanowire based on
alumina membrane (Zheng et al., 2002), Yan Song et al. (Song et al., 2010) were
successfully deposited Au-Pt on an indium tin oxide surface by direct electrochemical
method, possibly be used as electrocatalysts and sensors, and many more studies.
(v)

Hydrothermal synthesis
Hydrothermal method is a technique for synthesis of superhydrophobic coating

by produce the crystalline substances. First, crystals are grown in an autoclave, then at
high pressure and temperature create the roughness on the surface of substrate. Although
it has inability to monitor crystals growth process of growth, but simple carry out
process, high quality of crystals. However, the crystal structures are adjustable by
varying the experimental conditions such as temperature, reaction time, etc. This
technique requires initial equipment investment. Many published papers have
demonstrated the effectiveness and popularity of this technique when applied to a wide
variety of chemicals and substrates. Shuhui Li et al (Li et al., 2015) were fabricated
flower-like hierarchical TiO2 micro/nanoparticles onto cotton fabric that exhibits a
superior anti-wetting and self-cleaning property with WCA lager than 160° and a sliding
angle lower than 5°; Ruan Bing Hu et al (Hu et al., 2013) created superhydrophobic
glass surface by combined two-step method. The glass first coated with composite of
carbon/silica. Following, carbon nanoparticles were coated on glass by hydrothermal

route.

The

surface

structure

was

further

modified

by

1H,1H,2H,2H-

perfluordecyltrimethoxysilane to increase the WCA; Chunmei Xiao et al (Xiao et al.,
2014) has successfully developed superhydrophobic ZnO micro/nanocrystals using onepot hydrothermal process, they were obtained the largest static CA for water is 167 o;
Yanjing Tuo et al (Tuo et al., 2018) were created superhydrophobic surface on
aluminum foil which have great self-cleaning property, and plenty other researches.

7


(vi)

Solution Immersion method
Also known as dip coating method, Dip coating technique is a simple, low cost,

and facile process. A substrate is immersed into a solution which contains coating agent.
After a certain period of dipping time, it will be pulled up. Then, the solvent is
evaporated to deposit a coating on the surface. This method does not require any
complicated equipment. Moreover, it has various advantages such has simultaneous
coating both two side of substrate, applicable for all kind of materials, uniform structure,
highly durable, and stable coating layer. Several studies use dip coating technique. For
example, Changyu Liu et al (Liu et al., 2011) were fabricated superhydrophobic wood
from potassium methyl siliconate; Chun-Wei Yao et al (Yao et al., 2018) have achieved
the artificial superhydrophobic copper surfaces with wet chemical etching and an
immersion method for anti-corrosion application; Thirumalaisamy Suryaprabha and
Mathur Gopalakrishnan Sethuraman (Raimondo et al., 2017) were carried out the
solution immersion experiment using green-based flame retardants – silver nitrate and
octadecyltriethoxysilane – to get flame-retardant superhydrophobic cotton.
(vii)

Sol-gel method
Sol-gel technique is the most common method in material science to fabricate

superhydrophobic surfaces. In process, the monomer be convert to colloidal solution
(sol) which leading the formation for a linked network (gel) of polymers or particles.
The colloidal particles sizes range is from 1 to 100nm. Despite the contraction that
occurs during process, long processing time, fine pores, and residual hydroxyl or carbon
groups, the benefits of using this method is significant. Sol-gel route can produce a thin
coating layer but still ensure the durability, simply performance at low temperature,
economical and high purity product in output. The composition is highly controllable,
can be applied to any type of surface with homogenous coating as well. Hence, sol-gel
method is being used widely. Hooda et al (Hooda et al., 2018) were synthesized
Triethoxyoctylsilane-nanosilica on glass substrate via sol-gel method, they obtained the
static WCA of 162 ± 2° and shedding angle (SA) of 3 ± 1°, the transparent

superhydrophobic surface has application on self-cleaning and cover glass of solar
panels; Raimondo et al (Raimondo et al., 2017) were deposited a alumina nanoparticles
on copper via two different preparation routes based on either an alcoholic and an

8


aqueous Al2O3 sol-gel in order to compare the wettability, measurement results showed
that the alcoholic sol gave values of WCA nearly 180°, while hydrophobic state
exhibited coating are obtained with the aqueous sol; Czyzyk et al (Czyzyk et al., 2020)
were examined thermal, radiation, and dual curing processes whether to obtain enhanced
interfacial adhesion between the silica NPs, the sol-gel matrix and the substrate, result
is all three curing processes exhibited highly transparent SHCs with WCA > 150° and
SA < 5°; most recent, Nurul Pratiwi et al. (Pratiwi et al., 2020) were fabricate a
transparent superhydrophobic glass based TiO2 film using octadecyltrichlorosilane
(OTS), they obtained static WCA is 158 ± 2° and sliding angle of 4 ± 1°, the
superhydrophobic glass be able to maintain good performance after UV irradiation,
chemical immersion, and physical abrasion. And many more other papers have given
good results and the applicability of objects fabricated through sol-gel technique.
Moreover, many other methods can be applied to fabricate superhydrophobic
materials such as Casting method, Phase separation method, Chemical vapor deposition,
Self-Assembly, Lithography technique, etc. based on the purpose of application, the
properties of the substrate and the permissible experimental conditions.
2.3. Applications of the superhydrophobic material
The diversity of substrate give rise to a variety of applications. Additionally,
modifiable of the materials wettability shows great potential in the production of
superhydrophobic materials, going beyond simple effects of self-cleaning in nature, they
have applications in life, industry, the environment and even medical treatment. Some
prominent applications of superhydrophobic materials are presented below.
(i)

Anti-icing
Icephobicity is a property which able to prevent icing of water. For instance, if

ice is formed in fridge, the adhesion between ice and surface would become weak for
easy removal; Ice adhesion or formation might modify to shape of the aircrafts which
leading the changes the aerodynamic properties of air flow. Thus, anti-icing surface
ensure the reliability of aircrafts. Moreover, a surface with superhydrophobicity and
icephobicity can be applied in ships, wind turbines, and air-conditioners, etc. (Boinovich
et al., 2013).

9


(ii)

Anti-fogging
Fog is a phenomenon of particles dispersed in the air when temperature is

changes in high humidity condition. They interfering driving vision, causing discomfort
to people wearing glasses, and other inconveniences. An anti-fogging surfaces has
ability in increasing evaporation rate due to larger surface area compare to conventional
materials in order to reduce the fog formation. Anti-fogging surfaces can be
superhydrophobic and superhydrophilic as well. For example, Lai et al. were created the
superhydrophobic/superhydrophilic layers (with zero WCA) in glass which has
promising applications in eyewear, windshield, mirrors and other industrial fields (Lai
et al., 2012).
(iii)

Self-cleaning surfaces

Researches on fabrication of superhydrophobic surfaces on fibers have paved the

way for the industry to manufacture waterproof shoes, clothing, for everyday use or as
protective clothing. Moreover, self-cleaning surfaces can keep solar panels clean due to
their dust removal behavior, which ensure the efficiency of cell panels.
(iv)

Biomedical applications
Superhydrophobic materials are also introduced into biomedical applications that

help to prevent the stick between platelets and artificial implants, and it is a functional
to help the transplant process of artificial organs and artificial blood vessels successfully
which Sun et al. research (Sun et al., 2005) was an example.
(v)

Oil-water separation
In environmental treatment, superhydrophobic materials have the ability to

separate oil-water, organic solvents-water, therefore they are used to clean up waste oil
at in the sea, collect the excess oil and organic solvents in industry as well. For instance,
Shuhui Li et al. (Li et al., 2015) were fabricated the hierarchical TiO2
micro/nanoparticles onto cotton fabric which allows versatility for self-cleaning and oilwater separation effectively. They obtained WCA of 163° and a SA lower than 5°; Tudu
et al. (Tudu et al., 2020) were prepared superhydrophobic cotton fabric shows
superhydrophobicity with a static WCA of 169.3 ± 2.1° and SA of 6.3 ± 2.0°, their
superhydrophobic cotton able to separate oil-water effectively in 140 cycles; Recently,

10


Aliasghar Parsaie et al. (Parsaie et al., 2020) were successful fabricated a robust

superhydrophobic/superoleophilic polyurethane sponge which has potential treating in
large-scale of oil spills; Dheeraj Ahuja et al. (Ahuja et al., 2021) were developed
superhydrophobic sponge for absorbed motor oil and diesel oil in over 10 cycles; and
many other studies were carried out give good results on the ability to filter oil and water
on different substrates.
2.4. Analysis methodologies
2.4.1. SEM
Principles of Scanning Electron Microscopy
Inside the SEM device, a scan beam of electrons over the surface to signify a
magnified image of a specimen. In the time electrons from the beam whop the surface
of the specimen and bounce up, a detector registers these reflected beam and transfers
them into an image with a resolution to the nanometer scale. The beam is focused on the
sample surface is started from lenses place in the electron column. The SEM produce
must operate under vacuum conditions in order to avoid collisions between electrons
and gas molecules.
The main parts inside SEM directly involved in the process presented bellow
(i)

Electrons
There are two types of electrons are detected: backscattered electrons (BSE) and

secondary electrons (SE). Backscattered electrons are reflected back after elastic
interactions between the beam and the surface of object. While secondary electrons
came from the atoms of the sample which is the result of the inelastic interactions
between the electron beam and the object. Because of their origin, BSE and SE bring
different types of information. BSE has the origin of deeper regions of the object,
thereby, the images of BSE has high sensitivity due to differences in atomic number: the
higher the atomic number, the brighter the material appears in the image. While SE
imaging can provide more detailed surface information due to SE originated from
surface position.

11


Figure 2.5. Electron beam and the different types of signals which are generated (T. F.
Scientific, n.d.)
(ii)

Electron column
The electron column containing the source of electron and a collection of lenses.

The electrons are gathered into a beam by the condenser lenses and then hit on the
sample surface by the objective lens or as known as the final lens as shown in Figure
2.6.

Figure 2.6. Magnetic lens schematic (T. F. Scientific, n.d.)

12


(iii)

Deflectors

In order to control the direction of the electrons flow, the deflectors are necessary.
Electrons carry negatively charged particles and go through the electron column at high
energy and high speed. The electron is deflected at an angle when it travels through an
electron column under the effect of the electric filed which depends on the electron
energy, the electric field applied in between the plates at potential +U and -U, and the
length of the plates as in Figure 2.7.

Figure 2.7. Electron beam deflector (a) and lector-static lens (b) (T. F. Scientific, n.d.)
(iv)

Lenses

Figure 2.8. Magnetic lens (T. F. Scientific, n.d.)
Electrostatic lenses and magnetic lenses are the types have used in SEM device.
Magnetic lens has a metallic body as known as the ferromagnetic with two pole pieces
at the end. Magnetic lenses work based on the Lorentz force, this force in charge of
modify velocity in order to deflect electrons. A coil at the top of the ferromagnetic circuit
generate the magnetic field, as shown in Figure 2.8. Changing the distance of the pole

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pieces and electric flow in to the coils is the way of making the changing the strength of
the lens.

Figure 2.9. Different kinds of electrostatic lenses: single-aperture positive and
negative lenses (a, b), two-aperture lens (c) and three aperture Einzel lens (d) (T. F.
Scientific, n.d.)
Electrostatic lenses have the metallic plates connected to high voltage where the
electron beam travels through. Single-aperture lenses contain only one metallic plate.
The single-aperture lenses could eventuate a beam converges if the lens is positive
(Figure 2.9(a)) and beam diverges if the lens negative (Figure 2.9(b)). Two-aperture
lens has two metallic plates at different position and apertures was aligned (Figure
2.9(c)). The electric field in between the two plates always heading up. This is a positive
lens and the beam is hit the second plate at below. A three-aperture lens (Figure 2.9(d))
has three plates with apertures was aligned. They can either have the same or different

diameter. The triple lenses consist the first and the third plate bring positive charge,
when the electric field flow head towards the plates while the second plate carry negative
charge. Final lens has positive charge and the beam hit below the third plane.
Among them, the magnetic lens is most commonly used type due to their stability
of the structure which generate the magnetic field.

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2.4.2. FTIR

Figure 2.10. Michelson interferometer in configured for FTIR (Petergans, 2017)
The bonds between elements absorbs light in different frequencies. Thus FTIR is
able to detect the functional groups in surface of object by premiered the infrared
radiation (IR) in order to measures the infrared region of the electromagnetic radiation
spectrum, which has a longer and shorter wavelength than visible light.
First, Infrared light from the source travel through a Michelson interferometer.
The Michelson interferometer consist a beam splitter, mobile mirror, and fixed mirror.
The light beam be split into two by the beam splitter of two mirrors reflection, then
recombined by the beam splitter. The mobile mirror moves along the optical path to
make difference of the phase changes with time. The light beams are collected in the
Michelson interferometer which produces the output of an infrared spectrum. Which
showing in graph of infrared light absorbance of the substance on the vertical axis and
the wavelength on the horizontal axis (PerkinElmer, 2009).
Operate the FTIR process is quite simple. First, place the object in the FTIR
spectrometer. The beams directly hit at the surface of object and measures how much
and at which frequencies the object absorbs the infrared light. The sample should be thin
enough for the infrared light could travel through. Then, a mathematical technique call
Fourier transformation be applied in order to decode the signal. Final, the spectra

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database references help to recognize substances on samples. Interestingly, particular
molecular identities can be determined.
2.4.3. XRD
X-ray diffraction (XRD) is a technique used as a tool to determine the
crystallographic structure of a solid material. XRD principle is irradiating an incident
X-rays to the sample the measure the intensities and scattering angles of the X-rays that
reflect the sample.
Inside the XRD device, crystal atoms on sample scatter the incident X-rays based
on the interaction with the atoms’ electrons leading an elastic scattering phenomenon in
which the electron is the scatterer. Due to regular array of crystals, they create a regular
array of spherical waves. These waves cancel each other out through destructive
interference in almost directions. However, some of them disperse constructively in a
few specific directions, as determined by Bragg’s law:
2dsinθ = nλ
Where d is the distance between diffracting planes, θ {theta} is the incident angle,
n is an integer, and λ is the wavelength of incident ray. The results of reflections from
these waves called diffraction which appear as spots on diffraction pattern. In
conjunction with Crystallography open database (COD) we able to identify chemical
compositions in objects. The reason X-rays are used to generate the diffraction pattern
because their wavelength, λ, is often the same order of magnitude as the distance, d,
between the crystal planes (1-100 angstroms).
2.4.4. WCA
Contact angle measurement is one of the most used measurement method to
evaluate the surface properties. Static WCA is measured under conditions where all
three phases’ solid, liquid and gas are not moving.

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