Nanoscale hydrogel films and polymer brushes grafted onto nanocapillary array membranes for externally controllable size-selective molecular transport

Grafting membrane surfaces with polymers having tunable properties is an effective route to obtain environmentally-responsive composite membranes in controlling transport of molecular and macromolecular species through nanochannels. Such polymer grafted nanocapillary array membranes (NCAMs), composed of discrete parallel cylindrical nanopores, can be employed as interconnects to establish controllable fluidic communication between micrometer-scale channels operating in vertically separated planes, thereby making possible three-dimensional integration of fluidic microstructures.; This thesis investigates the swelling behaviors of two types of nanoscale polymer films, poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogels and poly(N-isopropylacrylamide) (PNIPAAm) brushes, in response to voltage and temperature variations, respectively, and the use of PNIPAAm grafted NCAMs as temperature-controlled size-selective molecular transport regulators. A self-assembled monolayer of 11-mercaptoundecanoic acid (MUA) on a planar Au surface is reacted with 2-aminoethylmethacrylate (AEM) to produce a methacrylate terminated surface layer, which readily polymerizes to graft a thin film of pHEMA by photopolymerization. These nanofilms show thickness changes as large as 50% with applied voltages in the range | Vappl| ≤ 600 mV in NaCl electrolyte solution. The film thickness and the swelling extent can be optimized by varying the monomer and crosslinker concentration, solvent composition, and the monomer irradiation time.; In a second generation of environmentally-responsive devices, thermally switchable NCAMs were prepared by grafting nanoscale PNIPAAm polymer brushes onto the exterior surface of a Au coated NCAMs through surface-initiated atom transfer radical polymerization (ATRP). Thermal evaporation of Au onto the native NCAM yields smooth membrane surface and a monodisperse pore size distribution, which are key in obtaining reproducible size-selecting molecular switching. These surface modified membranes show continuous and tunable molecular transport properties ideal for an actively controlled size-selective filtration devices.; The reactions used to achieve both types of composite membranes were characterized by external reflection mode Fourier-transformed infra-red (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), while SPR measurements were used to characterize both the synthesis of the hydrogel, as well as to characterize potential-induced volume changes on planar Au surfaces. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to elucidate the surface morphology and the Au plating rates on NCAMs. Molecular transport through the PNIPAAm polymer brush-modified NCAMs was investigated by real-time fluorescence measurements using fluorescein isothiocyanate (FITC) labeled dextrans.