Novel Approaches to Manufacturing Membranes with Controlled Selectivity
Sadeghi, Ilin.
2018
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Abstract: Membrane
separation processes are energy-efficient, green and easy to implement. They are used in
a wide array of applications from waste water treatment to pharmaceuticals to food
industries. However, these established applications are mostly constrained to
separations based on a size sieving mechanism. Moreover, there are only a handful of
membrane chemistries on the market, further ... read morelimiting their applications. In this
dissertation, these two problems are addressed by utilizing new approaches. First,
chemoselective membranes are fabricated by self-assembly of random copolymer micelles, a
simple and scalable method. This copolymer self-assembles during coating to form a
structure with interconnected 1-2 nm nanochannels, lined with functional groups. The
nanoconfinement along with chemical functionality leads to high separation efficiency of
small organic molecules. In addition, the high porosity of the membrane selective layer
leads to high permeability. Initially, this approach was used to prepare membranes to
separate a mixture of two solute with similar size, but different charge in both
diffusion and pressure-driven filtration experiments. The membranes exhibited
unprecedented charge-based selectivity for small molecules that was further enhanced in
competitive experiments. This effect is similar to that observed in biological pores
such as ion channels, implying novel selective transport mechanisms. Next, these
membranes were modified to address a more complex separation of small molecules based on
their aromaticity. A simple and straightforward conjugation chemistry was used to
convert the carboxylate groups in the pores to aromatic groups. The permeation
selectivity of these membranes for separation of two steroid hormones of similar size
and charge was examined. Selectivity was linked with the interactions of these solutes
with functional groups on the membrane surface, measured using quartz crystal
microbalance with dissipation (QCM-D), which provides a significant insight into
separation mechanism. The functionalized membrane showed exceptionally high selectivity
for the aromatic solute in competitive diffusion experiments. This, in combination with
additional results, imply a hopping transport mechanism. In another direction, a novel
method to fabricate of membranes with a wide range of monomer chemistries in a simple
and scalable manner, interfacially initiated free radical polymerization (IIFRP), is
presented. We developed this method and exploited the applicability of this method for
fabrication of ultrathin hydrogel selective layers and its application for protein
purification. Membrane performance can be tuned by experimental parameters such as UV
irradiation time, monomer concentration, and the addition of porogen or functional
comonomers. The results illustrate successful fabrication of uniform, defect-free and
ultrathin hydrogel layers whose dry thickness varies by UV irradiation time. The
hydrogel membranes are efficient and stable with excellent antifouling properties, and
suitable for protein purification. Overall, the results presented in this dissertation
illustrate simple, robust and scalable approaches for fabrication of selective membranes
for various targeted separations. Both methods can have a broad impact in various areas
from pharmaceuticals, drug delivery, sensors, barrier materials to water filtration or
gas purification.
Thesis (Ph.D.)--Tufts University, 2018.
Submitted to the Dept. of Chemical and Biological Engineering.
Advisor: Ayse Asatekin.
Committee: Hyunmin Yi, Iryna Zenyuk, and William Phillip.
Keywords: Polymer chemistry, Nanoscience, and Materials Science.read less - ID:
- bg257s19w
- Component ID:
- tufts:25076
- To Cite:
- TARC Citation Guide EndNote
