It is also part of presentation of hydrophilic & hydrophobic but it has more details from presentation slide. It will be helped for learning.

1. Bangladesh University of Engineering Technology
Assignment On
Nano Materials for Hydrophilic & Hydrophobic
Surfaces
Subject Of:
Nano-ceramics
Code: GCE6602
Submitted To:
Professor Dr. A. K. M Abdul Hakim
Dept of Glass and Ceramics Engineering
Submitted By:
M. Sc in GCE
Shamsun Nahar
ID: 1017172030
Date of Submission:
03-10-2018

2. Definition of Hydrophilicity:
Hydrophilic is a molecule or other molecular entity that is attracted to water
molecules and tends to be dissolved by water. It refers to having a strong affinity
for water. Something that is hydrophilic is soluble in water and dissolves into
water very easily. Hydrophilic is the opposite of hydrophobic.
Hyrophilic Surface

3. The hydrophilic concept is used in many industries. For example, hydrophilic
membrane filtration is used in several industries to filter various substances such
as:
Bacteria
Viruses
Particulates
Drugs
Contaminates
Hydrophilic coatings are particularly effective in environments of excessive
condensation and to protect the exchanger from the corrosive effect of water.
Hydrophilic coating also exhibits a fine performance in providing protection
against water in high temperature and salty environments.
Since hydrophilic substances attract and hold moisture, it causes a molecular layer
of moisture on the surface, which leads to corrosion. Hydrophilic substances like
chlorides or sulfates promote corrosion by destroying surface film of metal or
alloys. For example, the surface film that usually forms on magnesium alloys, is
exposed to the atmosphere, and gives limited protection from further attack.
Corrosion of magnesium alloys increases with relative humidity and contact with
hydrophilic substances.
Definition of Hydrophobicity:
Hydrophobic molecules are molecules that do not have a charge, meaning they are
non-polar. By lacking a charge, these molecules do not have any charge-to-charge
interactions that will allow them to interact with water. Hydrophobic materials
often do not dissolve in water or in any solution that contains a
largely aqueous (watery) environment. This characteristic of being hydrophobic -
or non-polar - is important for many of the molecules found in nature, in other
organisms, and even within our own bodies.

4. The word hydrophobic comes from the Greek roots hydro- (meaning water) and -
phobia (meaning fearing or hating). The word hydrophobic describes the fact that
nonpolar substances don't combine with water molecules.
Examples of hydrophobic molecules include the alkenes, oils, fats, and greasy
substances in general. Hydrophobic materials are used for oil removal from water,
the management of oil spills, and chemical separation processes to remove non-
polar substances from polar compounds.
Hydrophobic is often used interchangeably with lipophilic, "fat-loving". However,
the two terms are not synonymous. While hydrophobic substances are usually
lipophilic, there are exceptions, such as the silicones and fluorocarbons.
Hydrophilic & Hydrophobic Molecule:
Water is a polar molecule. Polar molecules are molecules that have partial charges
due to uneven bonding. The oxygen atom in a water molecule is highly
electronegative, which means that it will pull the electrons in a bond closer to it.
This, in turn, makes oxygen partially negative and hydrogen partially positive.
Hydrophobic Surface
Hydrophobic Surface

5. Hydrophilic molecules (and portions of molecules) can be contrasted with
hydrophobic molecules (and portions of molecules). In some cases, both
hydrophilic and hydrophobic properties occur in a single molecule. An example of
these amphiphilic molecules is the lipids that comprise the cell membrane. Another
example is soap, which has a hydrophilic head and a hydrophobic tail, allowing it
to dissolve in both water and oil.
Superhydrophilicity & Superhydrophobicity:
Superhydrophilicity refers to the phenomenon of excess hydrophilicity, or
attraction to water; in superhydrophilic materials, the contact angle of water is
equal to zero degrees. This effect was discovered in 1995 by the Research Institute
of Toto Ltd. for titanium dioxide irradiated by sunlight. Under light irradiation,
water dropped onto titanium dioxide forms no contact angle (almost 0 degrees)

6. Superhydrophilic material has various advantages. For example, it can defog glass,
and it can also enable oil spots to be swept away easily with water. Such materials
are already commercialized as door mirrors for cars, coatings for buildings, self-
cleaning glass, etc.
Several mechanisms of this superhydrophilicity have been proposed by
researchers. One is the change of the surface structure to a metastable structure,
and another is cleaning the surface by the photodecomposition of dirt such
as organic compounds adsorbed on the surface, after either of which water
molecules can absorb to the surface.
Superhydrophobic surfaces are highly hydrophobic, i.e., extremely difficult
to wet. The contact angles of a water droplet on an ultra hydrophobic material
exceed 150°. This is also referred to as the lotus effect, after the superhydrophobic
leaves of the lotus plant. A droplet striking these kinds of surfaces can fully
rebound like an elastic ball or pancake.
Superhydrophilic surface
Superhydrophobic Surface

7. Frank Schellenberger and his colleagues from the Max Planck Institute for
Polymer Research in Germany have performed the first microscopic imaging of
how a contact line advances on a rough superhydrophobic surface [3]. The team
found that commonly used definitions of superhydrophobicity based on the
advancing contact angle are unreliable. Instead, they propose using the receding
contact angle, which gives consistent values between macroscopic and microscopic
techniques. This redefinition could be embraced by designers looking for more
efficient superhydrophobic materials.
Condition of Superhydrophilic & Superhydrophobic
Surfaces:
Young’s Equation for superhydrophilicity:
The shape of a liquid–vapor interface is determined by the Young–Laplace
equation, with the contact angle playing the role of a boundary condition via
the Young equation.
The theoretical description of contact arises from the consideration of
a thermodynamic equilibrium between the three phases: the liquid phase (L),
the solid phase (S), and the gas or vapor phase (G) (which could be a mixture of
ambient atmosphere and an equilibrium concentration of the liquid vapor). (The
"gaseous" phase could be replaced by another immiscible liquid phase.) If the
solid–vapor interfacial energy is denoted by the solid–liquid interfacial energy
by , and the liquid–vapor interfacial energy (i.e. the surface tension) by then
Superhydrophobic Surface

8. the equilibrium contact angle is determined from these quantities by the Young
equation:
- - = 0
The contact angle can also be related to the work of adhesion via the Young–Dupré
equation:
=
Where is the solid – liquid adhesion energy per unit area when in the medium
V.
Diagram for superhydrophilicity conditions equation
Dynamic contact of droplet with superhydrophobic surface in
conditions favors icing:
Flight like droplet impact with superhydrophobic substrate in conditions favor
icing is discussed in this work. Test stand with fast camera and equipment
eligible to obtain temperatures and humidity at different ranges, lead to results
which can prove, that superhydrophobic surface might be good ice repellent
substrate. The influence of air humidity on droplet freezing was confirmed.

9. Various studies have shown that as well as having ultra water repellency the
surfaces have reduced ice adhesion and can delay water freezing. However, the
structure or texture (roughness) of the superhydrophobic surface is subject to
degradation during the thermo cycling or wetting process. This degradation can
impair the superhydrophobicity and the icephobicity of those coatings. In this
review, a brief overview of the process of droplet freezing on superhydrophobic
coatings is presented with respect to their potential in anti-icing applications. To
support this discussion, new data is presented about the condensation of water onto
physically decorated substrates, and the associated freezing process which impacts
on the freezing of macroscopic droplets on the surface.
Case Study for Superhydrophilic: Photocatalytic
ActivityTiO2 and Photo-Hydrophilic function
TiO2 containing visible-light-active nano-sized heterostructures based on coupled
oxides generally exploit oxide semiconductors with band gap energy lower than
that of TiO2 and with a more negative redox potential of conduction band (CB)
electrons in order to absorb visible light and inject photo-generated electrons in
TiO2 CB. Under these conditions, the CB electrons in TiO2 can initiate the photo-
reduction processes responsible for pollutant removal. In particular, the TiO2/WO3
couple has received much attention for improving the Photocatalytic properties of
TiO2 under visible light irradiation, since WO3 can be regarded as an electron
accepting species. Indeed, both valence and conduction band of WO3 lie below
those of TiO2. In addition, WO3 has a narrow band gap (~2.8 eV). Therefore,
under visible light, photo-generated electrons can be excited from the valence band
(VB) to the CB of WOx and the holes in the VB of WOx can be transferred to
TiO2 or remain in the VB of WOx.

10. Synthesized WO3/TiO2 by a sol-gel process using solutions of Ti(OBu)4 and
solutions of ammonium tungstate. Subsequently, the product was activated in a
single-step thermal treatment in a vacuum to enhance the Photocatalytic activity in
the visible region. Recently, prepared TiO2/WO3 composites with different
contents of tungsten oxide by a microwave-assisted hydrothermal method, an
environmentally friendly and novel process. Specifically, they have prepared
TiO2/WO3 from TiCl4 and Na2WO4 without using any organic species [35].
Furthermore, a promising strategy to enhance the visible-light Photocatalytic
performance is to combine Bi2WO6 with TiO2. The photo catalyst based on the
TiO2/Bi2WO6 hetero-junction has been synthesized by a simple and practical
liquid phase method. The hybrid nanocrystals are characterized by a special
morphology with the TiO2 particles coating the surface of the flower-like Bi2WO6
microspheres. The obtained hetero-structure has demonstrated improved light
harvesting efficiency and effective electron/hole pair separation, which results in
improved photo activity. Also, BiFeO3/TiO2 and ZnFeO4/TiO2 are favorable
materials to develop a high-efficiency photo catalyst active in the visible region
[1]. Core-shell structured BiFeO3/TiO2 nanocomposites have been synthesized by
a hydrothermal process, followed by hydrolysis precipitation of tetra butyl titanate
(TBOT). The results indicate that BiFeO3/TiO2 nanocomposites have good
visible-light absorption properties, which should be induced by Fe or Bi/Ti inter-
diffusion in the interfaces. ZnFeO4/TiO2-coupled semiconductors have been
successfully fabricated by a two-step process of anodization and a vacuum-assisted
impregnation method, followed by annealing. In this case, the ZnFe2O4
sensitization enhances the probability of photo-induced charge separation and
extends the range of the photo-response of TiO2 nano-tube arrays from the UV to
the visible region.
Case Study for Superhydrophobic: manganese oxide
polystyrene for superhydrophobic surfaces
Superhydrophobic transparent thin films using Mn doped zinc oxide (Mn/ZnO)
and polystyrene (PS) composites have been synthesized successfully by chemical
solution method. The nanocomposites thin films were fabricated by using Mn/ZnO
and PS mixture in toluene, followed by film casting on glass substrate. For a
comparison ZnO nanoparticles thin film was also prepared with PS. Mn/ZnO
nanostructures have been synthesized by hydrothermal method using
hexamethylenetetramine (HMTA) as a capping agent. The XRD analysis shows
that the development of hexagonal wurtzite structure of Mn/ZnO with preferred
(101) orientation. SEM analysis shows that Mn/ZnO nanorods have been

11. uniformly dispersed in the PS matrix. Water contact angle (WCA) was found as
107° and 151° for the ZnO/PS and Mn doped ZnO/PS thin film, respectively. The
transparency of the Mn doped ZnO/PS films are also large (∼90%) as compared to
ZnO/PS film (∼80%) which is attributed to enhanced energy band gap of ZnO
after Mn doping. The larger contact angle (WCA ∼151°) in the Mn/ZnO/PS thin
film has been recognized to the rough surface of PS thin film due to the presence
of Mn/ZnO nanorods. The present process is very simple and embraces ability for
extensive applications for making super hydrophobic transparent surfaces.
Lotus Effect or Self-cleaning by Superhydrophobic
Surfaces
Some plant leaves just can’t get wet or dirty! Lotus plants have superhydrophobic
surfaces. Water drops that fall onto them bead up and roll off. These leaves not
only stay dry, but the droplets pick up small particles of dirt as they roll, so that the
lotus leaves are even self-cleaning.

12. Figure: Lotus Effect
How Does It Stay Dry?
The lotus leaves have nano-structures on their surfaces. These nanostructures are
coated with hydrophobic wax crystals approximately 1 nm in diameter. This makes
the surface at the nanoscale quite rough. This rough surface is more hydrophobic
than a smooth surface would be.
Figure: self-cleaning

13. Application of Hydrophilic Surfaces:
1. Self-cleaning glass
2. Anti-fogging glass
3. Waste water treatment
4. anti-icing: Low surface energy or liquid-infused
5. Oil and Gas Applications
6. Anti-frosting glass
7. Anti-fouling coating
Application of Hydrophobic Surfaces:
 self-cleaning surface
 anti-icing surfaces
 drag reduction
 enhanced heat transfer
 a thin air layer that reduces attractive interactions between the solid surface
and the liquid
 Water proof circuit
 Solar Panels.
 Dirt cleaning
Biomedical Application:
 to control protein adsorption
 cellular interaction
 bacterial growth
 drug delivery devices
 diagnostic tools