Surface%20and%20Interface%20Chemistry - PowerPoint PPT Presentation

View by Category
About This Presentation
Title:

Surface%20and%20Interface%20Chemistry

Description:

Surface and Interface Chemistry Liquid/gas Interface Valentim M. B. Nunes Engineering Unit of IPT 2014 From a technological standpoint, the heterogeneous processes ... – PowerPoint PPT presentation

Number of Views:66
Avg rating:3.0/5.0
Slides: 21
Provided by: INSTIT107
Learn more at: http://www.docentes.ipt.pt
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Surface%20and%20Interface%20Chemistry


1
  • Surface and Interface Chemistry
  • ?
  • Liquid/gas Interface

Valentim M. B. Nunes Engineering Unit of IPT 2014
2
From a technological standpoint, the
heterogeneous processes involve surfaces
precipitation, diffusion, flocculation,
detergents effects, etc.
The concept of phase and interface
Phase ?
Interface, ? Few molecular layers
Phase ?
3
Surface Tension
4
Molecular explanation imbalance in
Intermolecular forces that exists on the surface.
Molecule inside the liquid is subject to
Intermolecular forces, but the resultant is null.
Surface molecule is "pulled" to the interior
5
To increase the surface area is necessary to
perform work against the intermolecular forces of
liquid. The work required to change the surface
area of an infinitesimal quantity ds is given by
The coefficient ? is the surface tension (SI
units J.m-2 or N.m-1). At constant pressure and
temperature dw dG , then
6
Liquids with greater Intermolecular forces are
those that presents larger surface tensions.
?/mN.m-1 (T 293 K) ?/mN.m-1 (T 293 K)
Isopentane 13.72
Ethyl ether 17.10
Hexane 18.43
Ethyl bromide 24.16
Benzene 28.86
Carbon tetrachloride 26.66
Water 72.75
Mercury 472.0
7
There is no fundamental distinction between
surfaces and interfaces, although it is customary
to designate the boundary between two phases in
which one of them is gaseous as surface, and
between two non-gaseous phases as an interface.
At the interface between two liquid's there is
again an imbalance in intermolecular forces in
the interior and along the interface.
Intermolecular forces responsible for surface or
interfacial tension include London dispersion
forces (Universal), hydrogen bonds and metallic
bond.
8
Interfacial tension contact angle
The imbalance of intermolecular forces on the
liquid/gas interface and solid/gas interface are
always bigger than between condensed phases, then
interfacial tensions for two liquids or between
solid and liquid systems are always smaller than
the biggest of the surface tensions. The work of
adhesion between two phases a and ß is expressed
by the equation of Dupré At a solid/liquid
interface it comes
9
Consider the following system
F surface tension of liquid, ?L F
interfacial tension, ?SL F- surface tension of
solid, ?S ? - contact angle
Condition of equilibria (Youngs equation)
And we obtain the Young-Dupré equation
10
(No Transcript)
11
Since WLL is 2 ?L
? 0 ?S ?L WSL WLL Liquid completely wets the solid
0 lt ? lt ?/2 ?S gt ?SL WLL/2ltWSLltWLL Liquid partially wets the solid
?/2lt? lt ? ?S lt ?SL 0 lt WSL lt WLL/2 Solid is difficulty wet by the liquid
? ? ?SL ?L WSL 0 Liquid does not wet the solid
12
As a consequence of surface tension there is a
difference of pressure through any curved
surface consider a drop of liquid Spherically
z
Pe
Pi
a
?
r
13
The existence of surface tension prevents the
liquid to spread across the surface. The outside
pressure (Pe) will be lower than the internal
pressure (Pi). At equilibrium, the resultant of
the forces that are due to the difference in
pressure, Pi-Pe, will be equal to the forces due
to ?, along the zz axis (spherical symmetry)
14
This is the Laplace equation
For non spherically surfaces (two curvature
radii)
Laplace's equation shows that the pressure inside
a curved surface (concave side of the interface)
is greater than the pressure outside (drops,
bubbles,......)
15
Vapor pressure of a pressurized liquid
Pressure of liquid is increased in dP, then dp
represents the change of vapor pressure..
16
This equation shows that the vapor pressure
increases when the pressure exerted over an
condensed phase increases!
Kelvins equation
17
Vapor pressure of water drops with 10-3 mm to
10-6 mm is 1.001 to 2.95 times the vapor pressure
of the water "flat"!, preventing condensation,
and favoring the formation of clouds
18
The surface tension of most liquids decreases
with increasing temperature, being fairly low
near the critical point (except for liquid Cu
and Fe!)
Eötvos equation
Ramsay and Shields k ? 2.1 for normal liquids
(benzene, carbon tetrachloride, S2C, etc)
Katayama
Guggenheim
19
Capillarity
The tendency of fluids to climb in a capillary
tube is a consequence of surface tension and is
called capillarity or capillary rise.
20
(No Transcript)
About PowerShow.com