Physics
Research Experience for Undergraduates 2010
This program is funded by the National Science Foundation through
grant number
PHY-0851599.
Langmuir-Blodgett Film Low
and High Pressure Study of Trioctylphosphine oxide (TOPO), Dipalmitoylphosphatidylcholine
(DPPC) and Colloidal Gold Nanoparticles coated in Dodecanethiol (DDT)
Sam Stites
(supervisor: Bret
Flanders)
This summer I am working with Langmuir-Blodgett methods to produce
and study single-molecule thick layers. These layers can be suspended between
two liquids or, as in my case, between a liquid and an air surface. In essence
these layers only consist of two dimensions and the layers produced will
exhibit gas-like, liquid-like and solid-like states. I intend to study these
layers by looking at the relations between surface tension and area of surface,
look at what happens when two different molecules are combined into a single
layer and look into just how rigorously the ideal gas law applies to these
monolayers. These films are used to make glasses anti-reflective and have
possible applications in molecular electronics, applied optics, mechanical
filters, sensors and more.
On the Langmuir-Blodgett method
The Langmuir-Blodgett
method centers around the use of a trough which contains compressible barriers
which allow the manual manipulation of area (in the units of cm2 or
Ĺ2) and a Wilhelmy plate which will allow for
the measure of surface pressure (or tension – measured in mN/m). The molecule
of choice is mixed in a solution of chloroform which has a high evaporation
rate and, after the solution is placed on the surface of the deionized water,
will evaporate from the surface -homogeneously distributing the surfactant on
the water. The trough is also equipped with a dipping
mechanism which allows a sample of the monolayer to be put onto a slide and
observed under the florescence microscopy. The barriers can be configured in
such a way that they will then compress to a desired pressure and maintain this
pressure as the dipper raises a slide from the surface of the water with the
surfactant distributed evenly upon it. Although the Langmuir-Blodgett field is
the study of monolayers and contains many more aspects, I will be using these
specified methods in my project.
Goal
The goals of this
project are to look at the interactions of mixed DPPC and TOPO layers and to
compare DPPC’s “gas” state to that of a metallic gold nanoparticle. If the latter
part of this goal goes well and the trend of a metallic nanoparticle and a
phospholipid is comparable to that of the ideal gas law, then it can be assumed
that the ideal gas law is comparable and applicable for all molecules in a
monolayer at this phase.
Strategy
First I will look at
pure DPPC and TOPO layers’ pressure-area isotherms and mix them in 75%, 65%,
50%, 35% and 25% differences by volume to make sure that the layers are
behaving as desired. To look at the layer’s interaction at these mixed solutions
I will fluoresce the DPPC and observe these layers under an inversion
microscope with florescence capabilities. Finally I will analyze the layers
between the pressures of 0 and .5 mN/m by plotting them against a theoretical
model for a “gaseous” DPPC molecule and a “gaseous” colloidal gold
nanoparticle.
Progress
I have recorded a day-by-day summary which can
be found here
About me
This summer I am a
rising junior at