Temperature measurement of the reaction zone during polyamide film formation by interfacial polymerization

Composite membranes used for water purification are formed by interfacial polymerization (IP), where choices of chemistry, formulation and reaction conditions conspire to dictate the final membrane performance. Here, we report in-situ visualization experiments of IP, performed using a microfluidic platform, under several representative conditions. Calibrated, temperature-sensitive fluorescence intensity enabled mapping of microscopic fluorescent images into temperature fields. Specifically, the temperature at the interface was monitored and illustrated a two-stage time-evolution, increasing rapidly at early times and then tapering. Polymerization appears to proceed so long as monomers are supplied, suggesting that the process may not be truly self-limiting. Results further show that under conditions promoting fast mass transfer and supply of monomers, temperatures at the interface may reach the boiling point of some solvents. Such interfacial boiling or release of dissolved gasses may be responsible for the formation of voids recently shown to exist in polyamide thin films. Curiously, the morphologies formed in the microfluidic experiments resemble commercial membranes despite the disparate length-scales involved, suggesting a possible spatial similitude. Ultimately, extensions beyond our current device, adding the capability to measure transport properties of the film formed within the device, can lead to a microfluidic-based platform to be used for rapid prototyping of materials, using small samples and short time scales, and provide insight for better informed membrane design.