Sample Preparation Method to Observe Transport in Membrane Adsorbers Using Single Molecule Spectroscopy | AIChE

Sample Preparation Method to Observe Transport in Membrane Adsorbers Using Single Molecule Spectroscopy

Authors 

Schmidt, S. - Presenter, Case Western Reserve University
Monge Neria, R., Case Western Reserve University
Kisley, L., Case Western Reserve University
Duval, C., Case Western Reserve University
Membrane separations have significantly increased in popularity for industrial applications over the past few decades. As affinity separations, they offer a high degree of selectivity by purifying desired species on the basis of attractive interactions with the separating substrate. Using membranes as this substrate offers optimal column geometry for industrial separations as they have ultrathin bed height and large surface area, reducing the required operating pressure while increasing throughput. The increased interest in membrane adsorbers has produced a range of substrates and selective layers for numerous separations. Traditionally, mass transport in these systems is modeled at the continuum level using classical fluid mechanics and bulk measurements; however, there remains the fundamental problem in the lack of empirical understanding of particle diffusion at the membrane surface and within the functional polymer brushes of the selective layer. High resolution spectroscopy methods, such as single molecule spectroscopy (SMS), can be used to address this problem by allowing for the visualization of diffusion through a membrane adsorber’s selective layer at the molecular scale.

The authors aim to develop a platform with which molecular transport across functionalized membrane surfaces can be studied with SMS. Samples prepared for SMS must be thin, optically transparent, and affixed to a glass coverslip. Polymer solutions were prepared by dissolving between 10 and 30 wt% of two different molecular weight polyvinylidene fluorides (PVDF) in dimethyl formamide (DMF) or dimethyl sulfoxide (DMSO). By drying these different casting solutions at conditions ranging from ambient to 100°C under vacuum, it was found the optimal casting solution was 10 wt% PVDF in DMF dried at 100°C and atmospheric pressure. When cast at 30 or 50 microns using a micrometer-adjustable doctor blade, this solution yielded optically clear films with no yellowing or cloudiness. Film thickness and uniformity were measured using optical profilometry. Samples were mounted in the fluorescent microscope for background measurements and to confirm the films do not auto-fluoresce. This method is laying the groundwork to use SMS to study the nonequilibrium processes that occur within the polymer brushes of membrane adsorbers during dynamic binding experiments. Results of this research will better inform the design of future functional membranes.