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 limiting 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.