Summary of the thesis: Study the fabrication and photocatalytic, hydrophilic properties of TiO2/SiO2 and TiO2/PEG thin films by sol-gel method

BỘ MINISTRY OF EDUCATION
AND TRAINING

VIETNAM ÂCDEMY OF
SCIENCE AND TECHNOLOGY

GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY

……..….***…………

NGUYEN THI MAI HUONG

Study the fabrication and photocatalytic, hydrophilic
properties of TiO2/SiO2 and TiO2/PEG thin films by
sol-gel method

Major: Solid State Physics
Code: 9 44 01 04

SUMMARY OF THE THESIS

Hà Nội – 2018


The thesis is completed at: Graduate University of Sciences and
Technology, Vietnam Academy of Science and Technology

Supervisors: 1) Dr. Nguyen Trong Tinh
2) Dr. Nghiem Thi Ha Lien

Reviewer 1: …

Reviewer 2: …
Reviewer 3: ….


-1-

A. INTRODUCTION
TiO2 is known as a photocatalytic and hydrophilic
semiconductor material when excited by light. That is why TiO2 is
considered to be a functional material that has the potential to
create self-cleaning materials for practical applications. The
hydrophilic nature of the material surface under optical excitiation
is closely related to the material properties, surface configuration
and stimulus. For this reason, the study on the hydrophilicity of the
material is a very academically attractive subject in studying the
properties as well as physical processes on the surface.
In the world, recent studies show the relationship between the
hydrophilicity of the solid surface and surface energy. Exciation by
light produces a change in surface energy, leading to a change in
hydrophilicity.
The systematic and quantitative study of the changes in
surface energy under the differentiation of TiO2 with different
nano-structures promises to bring further information to the
photocatalytic mechanism and super-hydrophilic effects of TiO2
material.
In Vietnam, there are a few studies related to hydrophilicity or
surface energy of materials, especially hydrophilicity under the
Exciation of the light. Therefore, the objectives of the thesis are
presented as follows:
The objectives of the thesis:

Study on materials fabrication technology; structural photocatalytic properties of TiO2 material, and TiO2 as the
nanostructured variant. On the basis of such material system, the
systematic and quantitative study on hydrophilicity or, in other
words, the study of surface energy of material systems under
Exciation of UV light radiation. Further clarification of the
correlation between photocatalytic activity, self-cleaning and
hydrophobicity of TiO2 nanostructured materials.
Research subjects: The thesis focuses on two structural
systems on the basis of nanostructured and anatse-shaped TiO2: The
complex nano-structure TiO2/SiO2 and Nano-porous TiO2/PEG.


-2-

Main study contents:
Fabrication of TiO2/SiO2, TiO2/PEG material systems and
experimental study on the structural properties as well as the
photocatalytic properties of the two material systems.
The hydrophilicity or surface energy of TiO2/SiO2, TiO2/PEG
nanostructured films is studied by contact angle measurement and
semi-quantitative techniques based on micro-theoretical models of
solid surface under the presence of the stimulus.
The practical and theoretical significance of the thesis
The technology of fabrication of nanostructured TiO2 material
is controlled by sol-gel method. The nanostructures of TiO2 thin
films are controlled. The phase transition is inhibited from the
anatase configure with high photocatalytic activity of Anatase to
Rutile phase into Rutile phase with low photocatalytic activity at
high temperature.
A new methodology is developed for calculation and

quantification of solid phase surface energy quantification based on
micro theory of solid-state physics. Based on this methodology, it
is possible to calculate and quantify the solid surface energy based
on experimental data of measuring the liquid-solid phase contact
angle by contact angle measurement technique.
Quantitative study of surface energy of nanostructured TiO2
photocatalytic film under the Exciation of UV radiation. This
provides empirical evidence about a physical effect: optical
Exciation can change the surface energy of the photocatalyst.
The correlation between the photocatalytic mechanism and
the super-hydrophilic mechanism of the nano-structured TiO2
material system is demonstrated. Quantitative empirical data is
provided, contributing to consolidate the hypothesis of the origin of
the mechanism of super-hydrophilic effect of the TiO2 material
system.
Layout of the thesis: The thesis consists of the introduction,
5 chapters and the conclusion. The results are published in five
journals including 03 international publications and 02 national
publications.


-3-

B. CONTENTS OF THE THESIS
Chapter 1
OVERVIEW OF TITANIUM DIOXIDE NANOMATERIALS
(TIO2)
1.1. Titanium Dioxide Nanomaterials
1.1.1. Introduction.
In recent years, Nano TiO2 powder in the rutile, anatase, or

mixture of rutile and anatase and brookite mixtures have been
studied for use in the fields of solar cells, manufacturing electronic
device, sensing head, etc. With high photocatalytic activity, TiO2
nano-material are applied in the fields of environmental treatment
such as: decomposition of toxic organic compounds, water
treatment, bactericidal, mildew-proof. Especially, in combination
with hydrophobicity when exposed to light, TiO2 is developed as a
self-cleaning material. With durable and non-toxic structure, TiO2
material is considered to be the most promising material to address
many serious environmental problems and challenges of pollution.
Phase-pure TiO2 nanoparticles:
TiO2 has four forms of formation. In addition to amorphous
form, it has three crystalline forms, including: anatase, rutile and
brookite (Figure 1.1).
Anatase

Rutile

Brookite

Figure 1.1: The Crystal structure of TiO2

Differences in network structure lead to differences in
electronic density between the two rutile and anatase forms of TiO2
and this is the cause of difference in nature between them. The
nature and application of TiO2 is highly dependent on the
crystalline structure of the forms and particle size of such forms.
Among the forms of TiO2, the anatase exhibits higher
photocatalytic activity than the rest.

-4-

Transformation of TiO2 forms: amorphous → anatase →
rutile is significantly affected by synthetic conditions and the
process of form transformation of modified TiO2 material is
different from that of of pure TiO2.
1.1.2.Photocatalytic property of the TiO2 nano-material.
Photocatalytic mechanism of the TiO2 nano-material
TiO2 has an anatase band gap of 3.2eV. Therefore, under the
effect of the photon energy that is greater than 3.2eV, the following
process will occur:


TiO 2  h  eCB
 hVB

When positive holes (h+VB) appear in the water environment,
the *OH radical formation reaction will occur:

hVB
 H 2O  *OH  H 


hVB
 OH  *OH

Figure 1.2: Mechanism of semiconductor photocatalysis.

On the other hand, when electrons appear on the conducting

zone (e-CB) if O2 is present in the water, the *OH radical formation
reaction will occur.
Factors affecting photocatalytic properties.
There are many factors affecting the photocatalytic activity of
the film such as manufacturing method, crystal crystallinity,
heating temperature, effective surface area, catalytic mass,
illumination intensity. However, the two major determinants of
photocatalytic activity of TiO2 films are the effective surface area


-5-

and the crystallinity of the film. In addition, for photocatalytic
reactions to occur in the visible light, it is important to pay attention
to the important factor known as the absorption edge of the right
membrane located within this light zone.
1.1.3. Modified TiO2 nano-material.
TiO2 crystals have a big band gap (3.0-3.2eV), therefore,
photocatalytic sensitivity is located only in ultraviolet light with
wavelengths of less than 380nm, i.e. only 5% of solar energy in the
ultraviolet zone is capable of activating photocatalytic activity.
In order to transfer the photocatalytic reaction into visible
light, where there is 45% of solar energy, the methods are applied
such as TiO2 doping with transitional metal elements to form
intermediate states in the band gap of TiO2; attaching
semiconducting photoresist or organic matter that is capable of
absorbing visible light; forming the TiOx and doping nitrogen,
carbon to replace oxides in TiO2 anatase crystals; forming TiO2
composites with different compounds.
The complex nano-material TiO2/SiO2

In order to increase the hydrophilicity and self-cleaningability
of TiO2 material, SiO2 is doped with TiO2 to increase the acidity of
the surface, which results in stronger water absorption and
reduction in surface contamination.
According to Guan et al., when SiO2 is added into TiO2,
meaning that silicon can enter the titanium network and replace the
position of Ti4+ cations, the number of oxygenatoms associated
with Si and Ti varies, creating an electrical imbalance. The result is
that the acidic center (Lewis center) with a positive charge is
formed on the TiO2/SiO2 complex surface. The acidity of the
surface makes the TiO2/SiO2 absorb more OH-radicals.
Specifically, silicon cations or saying more precisely, Ti-Si bonds
can take OH- of the adsorbed H2O molecules and O2- of the
complex can bind to H+ of the adsorbed water. Therefore, there is a
competition of absorption of compounds in the environment and
water on TiO2/SiO2 complex surface. As the acidity of the surface
increases, the water (OH groups) is more strongly adsorbed and
surface contamination decreases. Hydrophilicactivity causes the


-6-

water to flow all over the surface, absorb into dirt and push it away
from the surface.
Nano porous material TiO2/PEG.
PEG (PolyEthylene Glycol) is an organic polymer with a
chain circuit and when being dissolved in the TiO2 sol, these chains
alternate between TiO2 particles. After the fabrication, the film
undergoes thermal treatment, as a result, the PEG burns and porous
holes are left between the TiO2 particles. Therefore, the addition of

PEG increases the volume and diameter of the porous holes of the
material, leading to the increase in the surface area of the catalyst.
It is hoped that this will increase the hydrophilicity of the material.
1.2. Hydrophilic effects of TiO2.
1.2.1. Hydrophilic mechanism under the light Exciation for the
TiO2 nano-material

Fingre.1.3: Schematic representation of photo-induced hydrophilicity

In the presence of UV light, some electrons and holes
participating in redox reactions with oxygen molecules and water
adsorbed on the TiO2 surface to produce the free oxygen radicals
with strong oxidation and destruction of organic impurities. Other
electrons involved in deoxidizing the Ti4+ catrions into Ti3+
catrions and the hole oxidizes the anions to release the atomic
oxygen and produce oxygen-free locations on the TiO2 surface.
Water in the air will occupy this position and create an OHabsorption group on the TiO2 surface. The OH- absorption groups
form hydrogen bonds with water, therefore, the surface is
hydrophilic (Figure 1.3).


-7-

The hydrophilicity of the material is measured by the contact
angle value of the water drop with the material surface; the smaller
the contact angle is, the greater the hydrophilicity is.
Chapter 2.
FABRICATION TECHNOLOGY, EXPERIMENTAL
PROCESSES AND RESEARCH METHODS
2.1. Fabrivation technology

The thesis selects sol - gel method and centrifugal spin –
coating method for fabrication of materials and thin films on
nanostructured TiO2 base. Fabrication technology is based on two
processes:
Hydrolysis process:

Condensation process:

2.2. Study methods of photocatalytic properties for TiO2
nano-material.
Methods of measuring decomposition of organic pigments
which determine the speed of the photocatalytic reaction.


-8-

The Methylene Blue (MB) solution has an initial
concentration of C0 decomposed on contact with the optically
catalytic active surface due to the UV radiation, resulting in a
discoloration of the solution.
The Ct concentration of the solution is determined at equal
intervals during the measurement from the UV-VIS absorption
spectra. Ln (C0/Ct) = kt, in which k: constant of reaction speed, t:
Reaction time.
Measurement method of bactericidal of photocatalytic
effect.
Photocatalytic materials can destroy biological materials such
as bacteria, viruses and mildew. The germicidal mechanism is
mainly formed by photobiological holes; photobiological electrons
on the catalytic surface will destroy or deform the cell wall, break

down the DNA chain of such biological materials, making them
inoperable or dead.
The principle of the method is to evaluate the number of live
bacteria over time as it comes into contact with the material and
then to evaluate the photocatalytic activity of the material.
Method of measurement of hydrophilic properties by
contact angle technique.
The device includes functional blocks as shown in the figure.

Figure 2.1: Schematic diagram of the contact angle device


-9-

2.3. Technique of hydrophilicity evaluation
Method of evaluation of a hydrophobic, super-hydrophobic,
hydrophobic or super-hydrophobic surface is based on the value of
the contact angle measured by dropping water on it.
Figure 2.2 below is the corresponding exposure/contact angle
value for quantitative evaluation on hydrophilicity of a surface.

Figure 2.2: Hydrophilic and hydrophobic surfaces.

However, to have more quantitative results on the
hydrophilicity of the surface, we should carry out studies on the
surface tension and the free surface of the material. Specifically, the
approaches through micro-physics models of the liquid and solid's
surface interaction should be used.
Chapter 3.
SURFACE ENERGY OF THE SOLID AND CONTACT

ANGLE OF SOLID-LIQUID PHASE MODEL OF SURFACE
ENERGY CALCULATION FOR TIO2 MATERIAL
Chapter 3 presents an overview of some approaches to the
micro interaction model in solid-liquid transition related to the
contact angle. On this basis, a specific approach and calculation
method will be developed for TiO2 surface free energy in this
thesis.
3.1. Free surface energy of the solids and its relationship

with liquid drop contact angle on the solid surface.


- 10 -

Surface free energy and surface tension of the solids.
Surface energy is the energy to create a unit of material surface
area in equilibrium with the surrounding vacuum. Another opinion of
surface energy is that it is related to the effort for cutting a sample
block in order to create new surfaces in an area unit. Therefore, the
unit of surface energy in the SI is J/ m2.
Surface Tension of liquid.
Surface tension is the tensile force among surfaces in a
tangential direction of the surface in equilibrium with the
environment where the surface is formed.
Surface energy = Energy/Area = J/m2 = (Nx m)/m2 = N/m =
Force/length = Surface tension.
Relationship between solid-liquid phase contact angle and
surface energy.
Young's equation.
In 1805, Thomas Young reported on the relationship between

contact angle and surface energy. The contact surface of a liquid
drop on a solid surface is determined by the mechanical equilibrium
of the water falling under the surface of the energy of the three
phases, the solid-liquid energy  sl , the solid-vapor energy  sv , and
the liquid-vapor energy  lv described in Figure 3.1 below.

Figure3.1:Diagram showing the relationship for the three surface
tensions (surface free energies) for a droplet of liquid resting on a solid
substrate at the three-phase point

 sv   sl   lv cos
3.2. The thesis's methodology of TiO2 photocatalytic surface
energy calculation.


- 11 -

From the hypothesis of the TiO2 surface under the effect of
UV radiation upon contact with water, to separate the different
physicochemical interaction components on the surface, the fairly
complex chemical experiments are requested. In fact, the empirical
data of the thesis mainly include:
- The contact angle of various liquids such as H2O, alcohol,
Triton X, Ethylene Glycol, Glycerol, etc. on TiO2 membrane
surface is experimentally measured.
- The structure of TiO2 film form is made by different method
(photocatalytic properties depends on TiO2 membrane
configuration).
- TiO2 film is stimulated by UV radiation over illumination
time and recovery time to their initial state (State dynamics under

Exciation and recovery of the TiO2 photocatalytic film).
In order to calculate the surface energy of the TiO2
photocatalytic film, the thesis will use the semi-empirical approach
as follows:
- Assuming that the surface energy of the TiO2 photocatalytic
film is the sum of the components involving in the interaction at
the solid-liquid contact;
- Using the Young's equation, considering the modification of
dynamic interaction coefficient due to the contact among the three
phases solid - liquid - vapor at the location of contact point
calculation. This approach was used by Good for calculating
surface energy from contact angle data:

 sl   lv   sv  2  lv  sv
Developing Li's approach on the basis of Good Fowkes'
theory of transforming the interaction coefficient Φ into the
expanel dynamic coefficient (e-exponential function) that contains
the parameters γLV, γSV and the experimental ratio β depending on
the solid.

 sl   lv   sv  2  lv  sv e   (

lv  sv ) 2

With this approach, Li leads to the contact angle dependence
on the surface energy quantities in Young type as follows:


- 12 -

cos  1  2

 sv   (
e
 lv

lv  sv )

2

In case of using different liquids (with known surface tension
value γlv), we have set the dependent function Cosθ in the γlv with
the different liquids. In this case, γsv and β will be constants in the
above equation.
By using the approximation method with a parameter γlv
going from at least 4 points (4 different types of liquis), we can
calculate the constants β and γsv of the solid surface (TiO2). The
Matlab tool is used in the approximation method.
After calculating the γsv of the TiO2 surface, Young's
equation can be used to calculate the solid-liquid transition energy
γsl of TiO2 and water.


- 13 -

Chapter 4.
FINDINGS ON MANUFACTURING TECHNOLOGY,
STRUCTURAL PROPERTIES AND PHOTOCATALYTIC
PROPERTIES OF TIO2/SIO2 AND TIO2/PEG MATERIALS
4.1. The complex nano-material TiO2/SiO2.

4.1.1. Result of TiO2/SiO2 material fabrication

Figure 4.1: Sol TiO2/SiO2(0-50%) fabrication process.

4.1.2. Crystalline phase structure of TiO2/SiO2 material.
The findings on the crystalline phase structure gives a very
important comment that when SiO2 is introduced, the crystalline
phase structure of the TiO2 material is not transferred to the Rutile
phase when the material is sintered at high temperature.


- 14 -

X-ray diffraction spectra of
TiO2/SiO2(0÷50%) sintered at 500oC.

X-ray diffraction spectra of
TiO2/SiO2 (0÷50%) sintered 800oC

4.1.3.Structure of TiO2/SiO2thin film.

TiO2 /SiO2 (0%)
500oC.15->25nm

TiO2 /SiO2 (0%)
600oC.15->30nm

TiO2 /SiO2 (0%)
700oC.30->60nm

TiO2 /SiO2 (0%)
TiO2 /SiO2 (10%)
TiO2 /SiO2 (40%)
o
o
800 C.40->90nm
800 C.15->30nm
800oC.15->30nm
According to the findings on the film surface form and
particle size, the particle size of pure TiO2 gradually increases with
the annealing temperature. However, when the annealing
temperature increases to 8000C, the particle size does not increase.


- 15 -

4.1.4. Findings on photocatalytic properties based on the
results of methylene blue (MB) decomposition

Figure 4.2: MB concentration
by time of illumination.

Figure 4.3: The MB decay rate
constant depends on the SiO2

Figure: 4.3 demonstrates the decomposition rate constants of
TiO2/SiO2 film samples (0 ÷ 50%), showing the effect of % SiO2 on
the decomposition rate. The TiO2/SiO2 sample (40%) has the fastest
MB decomposition rate.

- 16 -

4.2. Nano porous TiO2/PEG.
4.2.1.Results of material fabrication

Figure 4.4: TiO2/PEG fabrication process

4.2.2.Crystalline phase structure of TiO2/PEG material

(a)

(b)

(c)

Hình 4.5: X-ray diffraction spectra of TiO2/PEG (0÷50%)
sintered at 5000C (a), 6500C (b) và 8000C (c)

Thus, the percentage of introduced PEG affects the phase
transition from anatase to rutile when the sample is sintered at high


- 17 -

temperature (6500C). However, when the sintering temperature is
raised to 8000C for TiO2/PEG samples (0%, 30% and 50%) (Figure
4.5), the whole crystalline phase structure has been transformed
into a rutile form. This is an undesirable phase for TiO2
photocatalyst.

4.2.3. Structure of TiO2 / PEG film surface form
0%

10%

20%

30%

40%

50%

Hình 4.6: SEM image of TiO2/PEG (0÷50%) thin films
Surface area of nano porous material TiO2/PEG.
Sample
TiO2 - 0%PEG
TiO2- 10%PEG
TiO2- 20%PEG
TiO2- 30%PEG
TiO2- 40%PEG
TiO2 - 50%PEG

Surface area(m2/g)
41,5
47,1
63,2
68,5
86,7
54,3

Table4.1: Surface area of TiO2/PEG (0÷50%)
According to the result of the surface form structure and
surface area measurement, when PEG is added to TiO2 solution,


- 18 -

resulting in a change in film porosity and the optimum level at the
percentage of PEG in the sol of about 40%.
4.2.4. The findings on photocatalytic properties of nano porous
material TiO2/PEG.

Figure 4.7: MB concentration Figure 4.8: The MB decay rate
by time of illumination.
constant depends on the PEG

Figure 4.8 demonstrated the decomposition rate of TiO2/PEG
film samples (0 ÷ 50%), showing the effect of PEG percentage on
the decomposition rate. Of which, the TiO2/PEG sample (40%) has
the fastest MB decomposition rate.
Chapter 5
FINDINGS ON HYDROPHIBILITY AND SURFACE
ENERGY OF TWO PHOTOCATALYTIC MATERIAL
SYSTEMS TIO2/SIO2, TIO2/PEG
There are many applications in life directly related to wetting
such as the industries of printing, painting, detergents, weaving,
dyeing, self-cleaning materials, textiles and so on. The biomedical
sector also has applications related to the wetting such as ability of
absorption of protein, interaction on the cell surface, etc.

Therefore, the study on the wetting (hydrophilicity,
hydrophobicity) or, in other words, the study on surface energy is
very useful and of big concern.


- 19 -

In a normal way, surface energy is denoted by γ, but there is
rarely an absolutely ideal surface, in fact the contact surface is
always between two different phases or two different substances.
It is very important to determine the interface energy of two
solid-vapor (γsv) phases and two solid-liquid (γsl) phases in pure
science and in application. Direct measurement of energy among
phases is very difficult. At present, there is a series of indirect
approaches to obtain these values. Determination of the surface
energy through the contact angle from the Young’s equation
(  sl   sv   lv .cos  ) is one of the simplest methods since the contact
angle is a value that can be easily determined by experiment.
In order to change the surface energy, physicochemical agents
have been used such as changing the coating with surfactants or
mechanical-physical-thermal effects, as well as fabrication
technology, changing the position of atoms, molecules in structure,
etc. However, recently, there are other methods. In this thesis, we
use experiment to prove that it is possible to use light Exciation to
change surface energy of TiO2 photocatalyst. And we have also
started to study the properties and rules of photocatalytic effects
that affect surface energy. This is a kind of physically pure agent,
which is different from known physicochemical agents.
5.1. Hydrophilicity and surface energy of complex nanomaterial TiO2/SiO2.
5.1.1. Hydrophilicity of of complex nano-material TiO2/SiO2.

TiO2/SiO2 thin films (0 ÷ 50%) are applied to the sintered
glass substrate at a temperature of 5000C. The film is UV-irradiated
(365 nm wavelength), the light intensity measured on the sample
surface is 1mW/cm2.
The graph demonstrates the contact angle of the TiO2/SiO2
samples at illumination time shown in Figure 5.1. In all samples,
the contact angles of the water drop decrease with the illumination,
reaching a saturation value.


- 20 -

Hình 5.1: Contact angle by the time
illumination of the TiO2/SiO2
(0÷50%) thin films

Hình 5.2:Saturation angle of
TiO2/SiO2(0÷50%) thin films

It can be commented that the wetting increases (ie, the
wetting angle decreases) when the ratio of SiO2 increases, however,
when the ratio of SiO2 is up to 50%, the wetting decreases. The
optimum ratio of SiO2 is at about 40%.
This changing law is in line with the changing law of
photocatalytic properties discussed in Chapter 4. It can be deduced
that photocatalytic activity and the wetting are created by the same
origin.

Hình 5.3: contact angle is restored
_ TiO2/SiO2 (0÷50%)

Surface acidity produces surface hydroxyl groups. Such stable
hydroxyl groups are beneficial for maintaining hydrophilicity. This
explains why the contact angle of water slowly increases and
remains at low value for a long time in the dark for complex films.
5.1.2. Energy surface of TiO2/SiO2 thin films.
When a liquid drop is placed on the surface of a solid, it is
easy to determine the contact angle through the measurement.


- 21 -

However, the important thing is that the contact angle holds
important information about the surface energy of the solid γsl and
interface energy of the liquid γsl through the Young's equation:
 sv   sl   lv cos 
Surface energy (γsv) value of TiO2/SiO2 film.

The liquids are selected as in Table 5.1.
Table5.1: Surface energy (γsv) value of liquids.
Liquids

 lv (mJ.m-2)

Liquids

 lv (mJ.m-2)

Ethanol
TritonX

PEG 600

22,39
33
44,5

Ethyleneglycol
Glycerol
Nước

47,3
63,4
72,29

From the results of the contact angle of different solutions on
the TiO2/SiO2 film (0 ÷ 50%) according to the illumination time
by UV light (365nm). The illumination intensity at the sample
surface is 1mW/cm2. Apply the surface energy calculation model
with TiO2 material presented in Chapter 3:

cos    1  2

 sv   ( 
e
 lv

lv

  sv ) 2

We can calculate the surface energy value γsv of TiO2/SiO2 films (0
÷ 50%).
Bảng 5.2: Surface energy value γsv of TiO2/SiO2 (0÷50%) thin films
at times0, 30, 60, 90,120 minute
TiO2/SiO2
(0÷50%)
0%
10%
20%
30%
40%
50%

γsv(mJ.m-2)
0 minute 30 minute 60 minute 90 minute 120 minute
43,5
51,0
59,9
60,7
60,8
42,6
59,8
60,6
60,8
60,9
46,5
60,3
61,1
61,3
61,6

44,8
60,2
61,5
61,4
61,6
48,6
61,2
62
62,1
62,1
45,7
59,3
60,2
60,9
61,5


- 22 -

Illumination time (Minute)

Hình 5.4: Surface energy γsvof TiO2/SiO2(0÷50%) thin films by time of
illumination.

Figure 5.4 demonstrates the dependence of the surface energy
γsv of the TiO2/SiO2 film (0 ÷ 50%) by the illumination time. We
have comment that the γsv of the samples increases according to the
illumination time to the saturation value.
The magnitude of the change in energy value γsv from the
moment of non- illumination to the saturation value is about 20%.

The saturated energy values among samples with different
SiO2 ratios are different but insignificant. Of which, the TiO2/SiO2
sample (40%) had the highest saturation value γsv.
Value of the interface energy (γsl) between water and TiO2/SiO2
film.
With the γsv of each kind of TiO2/SiO2 film (0 ÷ 50%), by
substituting the value γsv in the Young’s equation

 sv   sl   lv cos  ,

for each value of the contact angle θ


- 23 -

changing at the illumination time, it is possible to calculate the
interface energy between water and thin films.

 sl   sv   lv cos
Table 5.3: Contact angle θ of the water, the surface energy γsv and the
interface energy between water and TiO2/SiO2(0÷50%) thin films
illumination
time
(minute)
0
30
60
90
120
illumination

time
(minute)
0
30
60
90
120
illumination
time
(minute)
0
30
60
90
120

TiO2/SiO2 (0%)

TiO2/SiO2 (10%)

θ

γsv

γsl

θ

γsv

γsl

33,7
25,2
17,4
16,3
17,4

43,5
51
59,9
60,7
60,8

-16,7
-14,4
-9,1
-8,7
-8,2

29,3
22,3
13,8
13,1
14,6

42,6
59,8
60,6
60,8

60,9

-20,5
-7,1
-9,6
-9,6
-9,1

TiO2/SiO2 (20%)

TiO2/SiO2 (30%)

θ

γsv

γsl

θ

γsv

γsl

28,3
20,6
12,1
11,2
13,2

46,5
60,3
61,1
61,3
61,6

-17,2
-7,4
-9,6
-9,6
-8,8

26,9
19,2
9
7,6
8,2

44,8
60,2
61,5
61,4
61,6

-19,7
-8,1
-9,9
-10,3
-10,0

TiO2/SiO2 (40%)

TiO2/SiO2 (50%)

θ

γsv

γsl

θ

γsv

γsl

24,7
15,6
5,1
4,8
3,9

48,6
61,2
62
62,1
62,1

-17,1
-8,4

-10,0
-9,9
-10,0

30,5
21,1
14,5
12
13,1

45,7
59,3
60,2
60,9
61,5

-16,6
-8,1
-9,8
-9,8
-8,9

Figure 5.5 demonstrates the dependence of the interface
energy value between the TiO2/SiO2 film surface (0 ÷ 50%) and
water γsl at the illumination time.