Search ETDs:
Fabrication of Temperature Responsive Membranes using 248 nanometer Krypton Fluoride Excimer Laser
Tiwari, Ankit

2018, Doctor of Philosophy, University of Akron, Polymer Engineering.
Temperature responsive membranes are widely used in several controlled transport applications such as drug delivery. The transport rate across such membranes is dependent upon the constraints introduced by the grafted network on the travelling solute molecules inside the porous support membranes. The solute flux is also affected by the non-uniformities in pore size, morphology, and the pore size distribution of the support membranes which arise due to fabrication processes. Conventionally, photo-grafting is widely used `grafting-from’ approach to photo-polymerize a temperature responsive monomer inside the pores. This approach is usually slow and often leads to undesirable surface polymerization on the membranes.
To overcome these limitations, we developed a novel dual-step approach for the fabrication of temperature responsive membranes using a 248 nm KrF excimer laser. In the first step, membranes with uniform, ordered, and well-defined pores were fabricated with different pore sizes by masked laser ablation of polyethylene terephthalate (PET) films. Ranges of laser fluence (energy/area) and number of pulses were determined for different PET film thicknesses and mesh sizes to obtain pores in the range of 600 nm to 25 µm.

In the second step, we used the perforated support membranes to polymerize (N-isopropylyacrylamide) (NIPAM) inside the pores using the same KrF excimer laser. Thus, this study also establishes the versatility of 248 nm KrF excimer laser as a tool for combined laser ablation and polymerization during the same manufacturing process. The `bottom-up’ pulsed laser polymerization approach used is extremely fast and it reduces the grafting time considerably from a few minutes to a few seconds. The grafting density of PNIPAM in the pores can be tuned by appropriately selecting the laser parameters resulting in room temperature water permeabilities varying by 6 orders of magnitude. Water permeabilities increased above the lower solution critical temperature (LCST) of PNIPAM as attributed to increase in effective pore size due to network deswelling inside the pores. The hydrogel network gets strongly grafted to the pore walls and remains mechanically stable inside the pores under the applied pressures. Diffusive transport of a small molecule was studied to evaluate membrane performance as temperature responsive barrier for controlled transport of solutes.

Grafting is quantifiable by ATR-FTIR studies and the results can be correlated with chain growth in pulsed laser polymerization. The effects of grafting solution parameters on the grafted PNIPAM network responsivity were also studied. The network growth could be controlled by reducing the monomer and crosslinker concentrations in the grafting solution. Crosslinker concentration had a more pronounced effect on the temperature response of the grafted network across the LCST of PNIPAM. A transition from positive to reverse temperature responsiveness was also observed for highly crosslinked grafted networks. The results establish our method as an efficient, fast, and economical method to fabricate thermo-responsive membranes.
Erol Sancaktar (Advisor)
Sadhan C. Jana (Committee Chair)
Kevin Cavicchi (Committee Member)
Chrys Wesdemiotis (Committee Member)
Bi-min Zhang Newby (Committee Member)
161 p.

Recommended Citations

Hide/Show APA Citation

Tiwari, A. (2018). Fabrication of Temperature Responsive Membranes using 248 nanometer Krypton Fluoride Excimer Laser. (Electronic Thesis or Dissertation). Retrieved from https://etd.ohiolink.edu/

Hide/Show MLA Citation

Tiwari, Ankit. "Fabrication of Temperature Responsive Membranes using 248 nanometer Krypton Fluoride Excimer Laser." Electronic Thesis or Dissertation. University of Akron, 2018. OhioLINK Electronic Theses and Dissertations Center. 19 Sep 2018.

Hide/Show Chicago Citation

Tiwari, Ankit "Fabrication of Temperature Responsive Membranes using 248 nanometer Krypton Fluoride Excimer Laser." Electronic Thesis or Dissertation. University of Akron, 2018. https://etd.ohiolink.edu/

Files

Dissertation_Ankit Tiwari.pdf (4.61 MB) View|Download