The DPPA on KCl subphase lift up earlier than on water. This means that the surface pressure was increased at transition. The expansion show that the presence of K cation Affect the intermolecular force between dppa molecule and help stablize the monolayer.
By Gefei Wang
Foil cover of waste liquid beaker:
One of the major liquid used in lab is ethanol,
which is volatile and inflammable. So it is
important to cover the beaker to prevent ethanol
gas from flowing out. And when you find the foil
has holes or cannot cover the beaker, please
make a new cover, it only takes 1min .
When aspirator fall on the floor, its tip may
touch the dirt on the floor. And the
contaminated tip will affect the experiment
Once you finish using aspirator, please put it
to clean area, like the top of the black box,
or the board.
1,Work in the lab under instruction of Ting
2,Learn basic knowledge about surface lipid interaction
3,Practice technique of measuring surface pressure
What I do this semester
Aerosols play an important role in climate change, so it is necessary to
understand the its property and behavior. The majority of aerosols
come from ocean, and ocean surface is covered by SSML which affect
the formation of aerosols and interact with the aerosol surface. To study
aerosol surface, DPPA is selected as model system.
DPPA (dipalmitoyl-phosphatidic acid):
-has two 16 C chains
-strong intermolecular force
-contains phosphate group
Model system DPPA
• SSML contain plenty
of fatty acid, and the
most abundant is
C16 fatty acid,
• PA is component of
• DPPA itself is
• Study DPPA held
• DPPA contains no
moieties on its
• So it is simple and
easy to study
Langmuir trough: used to compress
monolayers of molecules on the
surface of a given sub phase (usually
During compressing, density of the
monolayer changes. This results in
surface pressure change, which can
be sensed by the tensiometer.
Method: Langmuir-Wilhelmy balance (LWB)
-Used to measure the surface tension
-the compression of barrier changes the distance between
molecule in monolayer
-so the surface pressure change, and is detect by Wilhelmy
𝜋 = 𝛾 𝑤 − 𝛾𝑠
Surface tension of subphase
Surface tension of subphase with monolayer
𝜋 = 𝛾 𝑤 − 𝛾𝑠
𝜋 = −
net force -F width -W, and thickness-T, the contact angle-θ
Assume plate is thin enough, and is completely wetted to ensure a
contact angle of 0°, so cos (0°) = 1
Surface tension: the surface tension of a liquid results from
cohesive forces between surface molecules.
Surface tension is an intensive property.
Surface pressure: the difference between surface tension of
Surface pressure is an extensive property.
Spreading: Spread the solution of surfactant molecule on surface of sub phase dropwise.
1,Clean the trough with deionized water three times
2, Soak the filer paper
3, Clean the barriers with water and ethanol
4, Fill the trough with water and place barriers on trough and hang the paper on hook
5, Test the degree of clean of the trough(<0.1)
6, If trough is clean, calculate the amount of solution of molecule of interest needed
7, Spread the molecule dropwise
8, After all of solvent vaporize, the barriers begin compressing
9, When compression stop, collect data from computer
Skill and procedure
Two dimensional phase change
• molecules in a Langmuir monolayers are very far apart, little intermolecular force.
• closer and stronger lateral interaction
• the liquid-expanded (LE) and liquid-condensed (LC) phase.
• In LE transition, the isotherms display a considerable curvature at liftoff from = 0 mN/m.
• During LC phase, the compressibility of monolayer decreases, and the interaction between
tail part of molecule increases.
• Headgroups of molecule are dehydrate, tail parts are tightly packed. Strong intermolecular
At this point, monolayer cannot be compressed, and further compression will disrupt the film.
DPPA on salt sub phase
-Practice spreading DPPA on salt water to get reproducible data
-Test the DPPA on salt solution with different concentration
-Study DPPA behavior under different pH environment
Langmuir. Digital image. Surface Pressure/molecular Area
Isotherms Measured by the Langmuir Method – a
Nanoscience Approach to Study Films at the Water-air
Interface. Web. <http://nano.uib.no/Langmuir.php>
Notter, Robert H. Lung Surfactants: Basic Science and Clinical
Applications. New York: Marcel Dekker, 2000. Print.
DPPA - Structural Formula Illustration. Digital image. Web.