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 paracyclophanemolecules 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 COATINGSUROP 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-immobilization of 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, August 22). Streaming Potential Revisited: The Influence of Convection on the Surface Conductivity. Retrieved April 9, 2015, fromhttp://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 pKaPPX-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 Image adopted from Anton Paar (2012)

Figure 3 Image adopted from Barz, D., Garg, A., & Saini, R (2014)

Figure 2

Figure 4Image adopted from Bally and Lahann Laboratory (2013)

Figure 5Functional groups examined circled 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