1. Surface charge can influence protein adsorption as well as the
diffusion behavior of adsorbed molecules, and is hence a critical
property in characterizing biomedical polymer coatings. The
Lahann lab employs chemical vapor deposition polymerization, a
solvent-free, pinhole-free, room temperature process, to create
polymer coatings of desired thickness and chemical functionality
on a substrate of choice. The monomer units are paracyclophane
molecules to which pendant functional groups such as alkyne,
chlorine, bromoisobutyrate, hydroxyl, amine, carboxyl and
aldehyde groups can be attached, facilitating bio-orthogonal
conjugation to proteins or peptides bearing complementary
reactive groups. The charge characteristics of these polymer
coatings as a function of chemical functionality has not been
studied yet. Here we present a comparison of the isoelectric
points of each of these surfaces, as determined by zeta potential
measurements.
Use techniques and procedures involved in surface initiated
polymerization and characterization of polymer coatings skills, in
order to research and determine the isoelectric point (IEP) of
CVD monomers.
The zeta potential is a potential difference between the surface
of a solid and liquid boundary. It indicates the formation of a
charge. The surface of the solid will behave similar to a weak acid
or base, when interacting with the solution. Therefore, the
surface charge is dependent on the pH of the solution. Typically,
as the pH of the solution becomes more acidic, the charge tends
to decrease (Figure 2). The movement of the solution through
the capillary is known as a streaming potential. The Helmholtz-
Smoluchowski equation relates the streaming and zeta potential:
ISOELECTRIC POINT DETERMINATION OF FUNCTIONALIZED CVD COATINGS
UROP Sponsor: Joerg Lahann
Project Sponsor and Manager: Ramya Kumar
Chemical Engineering Department
UROP Student: Aymen Maktari
Chemical Vapor Deposition (CVD)
• Precursor (monomer) navigated to the sublimation where the
temperature is 120 degrees Celsius.
• Then, monomers travel to the furnace, where temperature is 660
degrees Celsius.
• Finally, monomers enter deposition center, where the temperature is
15 degrees Celsius. A rotating platform is present, which contains the
gold substrates and polystyrene plates.
• Argon gas is flowing at a rate of 20 sccm and pressure maintained at
approximately 0.08 Torr.
Fourier transform Infrared Spectroscopy
• Gold samples bombarded with various wavelengths; the wavelengths
absorbed dictate the structure of the compound.
Streaming Potential Measurements
• Samples placed in clamping cell rinsed with a conductive solution
(Potassium Chloride).
• Solution titrated by hydrochloric acid (0.1 Molar), with increments of
0.3.
• Nitrogen gas used to purge the solution from carbon dioxide.
Upon conclusion of my research, the surface charge of the polymer
coatings follow pKa. However, this is not too obvious, since the
poly(paraxylene) backbone is highly electronegative). Furthermore,
the isoelectric points of each monomer are distinguishable from
each other. For example, when comparing the two versions of PPX-
CHO, both possess different IEP value, since one oxidized promptly
when exposed to air. When comparing the thickness of PPX-
Aminomethyl, it was interesting to note that the thicker layer
required a more protic surrounding, in order to exhibit no charge. In
any event, one can witness and state that the functional groups
influence the isoelectric point.
Bally, F., Cheng, K., Nandivada, H., Deng, X., Ross, A., Panades, A., & Lahann, J. (2013). Co-
immobilizationof Biomolecules on Ultrathin Reactive Chemical Vapor Deposition Coatings Using
Multiple Click Chemistry Strategies. ACS Applied Materials & Interfaces, 9262-9268.
Barz, D., Garg, A., & Saini, R. (2014, August22). Streaming Potential Revisited: The Influence of
Convection on the Surface Conductivity. Retrieved April 9, 2015, from
http://pubs.acs.org/doi/abs/10.1021/la501426c
Gleason, K. (2015). Multifuctiontal Reactive Polymer Coatings. In CVD Polymers: Fabrication of
organic surfaces and devices (p. 200). Weinheim: Wiley-VCH.
SurPASS Operation Procedures. (2012). Graz: Anton Paar.
-4
-2
0
2
4
6
8
10
12
0 2 4 6 8 10 12 14
Mv
pH
Polymer Coating pH pKa
PPX-Alcohol (Green) 3.80 16.0
PPX-Aldehyde (Vacuum) (Red) 3.82 17.0
PPX-Aldehyde (Non-Vacuum) (Grey) 3.629 17.0
PPX-Alkyne (Black) 4.0 26.0
PPX-Aminomethyl (Thick) (Yellow) 4.285 36.0
PPX-Aminomethyl (Thin) (Blue) 4.7 36.0
PPX-Trifluoride (Purple) 3.78 7.52
PPX-Dichloro (Brown) 3.42 3.13
Figure 1
Imageadopted from Anton Paar (2012)
Figure 3
Imageadopted from Barz, D., Garg, A., & Saini, R (2014)
Figure 2
Figure 4
Imageadopted from Bally and Lahann Laboratory
(2013)
Figure 5
Functional groups examinedcircled in red (Gleason, 2015)
Figure 6
and Table
-100
-80
-60
-40
-20
0
20
40
60
80
100
2.5 3.5 4.5 5.5 6.5
Mv
pH
ABSTRACT
BACKGROUND
OBJECTIVE
METHODS RESULTS
CONCLUSION
REFERENCES