HYDROPHOBIC-HYDROPHILIC

Report
Seminar on
HYDROPHOBIC AND HYDROPHILIC
MANOJ KUMAR
III Semester
ME
WHAT IS MEANT HYDROPHOBICITY ?
Hydrophobicity comes also from the greek word Hydro(water)
and Phobicity (fear) it refers to the physical property of a
material that repels a mass of water.
•
Some of the common natural
Hydrophobic materials are
waxes, oil and fats.
The evaluation of hydrophobicity
is made through water contact
angle measurements.
A water droplet would be
spherical so the water contact
angle will be significantly high.
Continued….
• At the molecular level, the hydrophobic effect is important in
driving protein folding formation of lipid bilayers and micelles,
insertion of membrane proteins into the nonpolar lipid
environment and protein-small molecule interactions. Substances
for which this effect is observed are known as hydrophobes.
HYDROPHOBIC EFFECT
The hydrophobic effect represents the
tendency of water to exclude non-polar
molecules. The effect originates from
the disruption of highly dynamic
hydrogen bonds between molecules of
liquid water.
SUPER HYDROPHOBIC COATING
The process of coating the surface of a material with hydrophobic
property material in order to avoid sticking of liquids on that surface.
This is absolutely unique way of coating unlike conventional which
shrink continuously during drying to produce low porosity films.
Super hydrophobic technology
makes water bounce, it stops it,
rolls it off the surface.
Young's equation is used to describe the interactions between
the forces of cohesion and adhesion and measure what is
referred to as surface energy.
www.ramehart.com/contactangle.htm
Continued..
• A drop with a contact angle over 90° is hydrophobic.
• This condition is exemplified by poor wetting,
adhesiveness and the solid surface free energy is low.
poor
Hydrophobic interactions
• Hydrophobic interactions describe the relations between water
and hydrophobes (low water-soluble molecules).
• Hydrophobes are nonpolar molecules and usually have a long
chain of carbons that do not interact with water molecules.
• The mixing of fat and water is a good example of this
particular interaction.
• The common misconception is that water and fat doesn’t mix
because the Van der Waals
• forces that are acting upon both water and fat molecules are
too weak.
Causes of Hydrophobic Interactions
• American chemist Walter Kauzmann discovered that nonpolar
substances like fat molecules tend to clump up together rather
that distributing itself in a water medium, because this allow the
fat molecules to have minimal contact with water.
Hydrophobic interactions ChemWiki
Formation of Hydrophobic Interactions
• The mixing hydrophobes and water molecules is not
spontaneous; however, hydrophobic interactions between
hydrophobes are spontaneous.
• When hydropobes come together and interact with each other,
enthalpy increases ( is positive) because some of hydrogen bonds
that form the clathrate cage will be broken.
• Tearing down a portion of the clathrate cage will cause the
entropy to increase ( is positive), since forming it decreases the
entropy.
According to the formula:
ΔG= ΔH-TΔS
ΔH=Small positive value
ΔS=Large positive value
Result :ΔG= Negative
A negative ΔG indicates that hydrophobic interactions are spontaneous
What does the strength of Hydrophobic Interactions depend on?
In order of Effectiveness:
• Temperature
• Number of carbons on the hydrophobes
• The shape of the hydrophobes
APPLICATIONS
• A primary purpose of hydrophobic coatings such as
polytetrafluoroethylene(PTFE) or polyxylylene is to act as a
barrier against water commonly seen in automobiles
• Used in fabrication on metallic nano rod to prevent icing.
• Its is widely used in aerospace industry for providing anti-icing
coating on the surface of the aeroplane .
• Hydrophobic self cleaning glasses are installed in traffic sensor
control unit.
• We induce hydrophobic recovery after plasma treatment, a
physical contact treatment (PCT) .
WHAT IS MEANT HYDROPHILICITY ?
Hydrophilicity, also comes from the Greek word Hydro (water)
and Philicity (friendship) it refers to a physical property of a
material that can transiently bond with water (H2O) through
hydrogen bonding. Furthermore it allows the liquid to enter the
pores of a material and totally wet it.
• Almost all natural materials are
hydrophilic in nature.
The evaluation of hydrophilicity is
made through water contact angle
measurements. A water droplet
would occupy as long surface of the
hydrophilic material as possible. So
the water contact angle will be
significantly low.
Continued…
• This is thermodynamically favorable, and makes these
molecules soluble not only in water but also in other polar
solvents. There are hydrophilic and hydrophobic parts of the
cell membrane.
• A hydrophilic molecule or portion of a molecule is one that is
typically charge-polarized and capable of hydrogen bonding,
enabling it to dissolve more readily in water than in oil or
other hydrophobic solvents.
HYDROPHILIC COATING
Hydrophilic coatings wet the surface
very easily, and maintain the wetness for
longer time. Thus, using hydrophilic
coatings eliminates the need for
additional lubricants.
Here ,also we use same figure of young’s equation to explain
hydrophilicity
A drop with a small contact angle
is hydrophilic.
This condition reflects better
wetting, better adhesiveness, and
higher surface energy.
Hydrophilic Interactions
Interactions between water and other molecules such that the
other molecules are attracted to water are called hydrophilic
interactions.
Molecules that have charged parts to them are attracted to the
charges within the water molecule.
This is an important reason why water is such a good solvent
Continued….
Glucose molecules have polar hydroxyl(OH) groups in them and
these attract the water to them. When sugar is in a crystal the
molecules are attracted to the water and go into solution.
Once in solution the molecules stay in solution at least in part
because they become surrounded by water molecules. This layer of
water molecules surrounding another molecule is called a hydration
shell.
What does the strength of Hydrophilic Interactions depend on?
• Inhibitory effect mainly depended on their concentration and to a
lesser extent on the ion charge and hydrated ion radii.
• Stepwise regression analysis proved that the strength of
interaction depends on the polarity parameters of amino acids
and is independent of their chemical structure.
APPLICATIONS
• Spray Painting
• Film coating
• Bio-Medical
Wenzel and Cassie States of Wetting
Here are two natural parameter:
 A first natural and simple effect arising from the presence of
microstructures is an increase of the surface area of the material.
r =1+2πbh/p2
we can define two levels; namely, the top of the posts and the ground
on which they sit.
 A second natural parameter is the ratio ϕS between the top and
bottom surface areas, which is also the post density.
ϕS = πb2/p2
Quéré D , Reyssat M Phil.
Trans. R. Soc.
A 2008;366:1539-1556
When depositing a water drop on a such solid .It can adopt at
least two type of configurationconforming to the solid surface (Wenzel situation)
Sitting on the top of the posts((Cassie or fakir state)
www.me.umn.edu/~lixxx099/EFRI_CAES/Research/texturing.htm
Wenzel state
The Second and simplest picture is the so-called Wenzel state
(figure the drop just follows the structures on the material
(Wenzel 1936).
This will affect both the wetting (the value of the equilibrium
angle, that is the one which minimizes the surface energy of the
drop) and the adhesion (characterized here by the value of the
contact angle hysteresis).
cosθ*=r cosθ
Cassie state-Fakir state
Third fig. implies the creation of a liquid–vapour interface below the
drop, on a fraction of surface of the order of 1−ϕS, considering these
interfaces as flat (the drop is large compared with the pillars,
implying a negligible curvature of the liquid–vapour interface at the
scale of pillars). (Cassie & Baxter 1944)
The cosine of the apparent contact angle is then an average between
the cosine of the Young angle and the cosine of 180°, the angle of a
water drop on air, where the weights for the average are, respectively,
ϕS and 1−ϕS.
cosθ*= -1 + Φs(1+cosθ)
THANKS

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