Fluorescence-based detection of apparent crystallization pressure in microfluidic channels

We present a fluorescence-based method for estimating apparent crystallization pressure of halite in polydimethylsiloxane (PDMS) microfluidic channels. A fluorescent dye is uniformly embedded within the PDMS matrix, converting stress-induced deformations into local fluorescence intensity changes that are calibrated against known tensile stress. Under controlled imbibitiondrying cycles, real-time monitoring of normalized fluorescence reveals a plateau once the crystal fully fills the channel. By analyzing the intensity corresponding to this plateau with finite element simulations, we determine a conservative lower bound apparent crystallization pressure (including both crystallization pressure and a small capillary contribution) of ∼ 0.14 MPa. Finite element simulations further show stress concentrations that can locally amplify pressure by over an order of magnitude. Together, these findings validate the mechanofluorescent response as a non-invasive, quantitative tool for estimating the apparent crystallization pressure in confined environments.