A parametric study of layer-by-layer deposition of CaCO3 on glass surfaces towards fabricating carbonate reservoirs on microfluidic chips

Abstract

Recently, geomaterial-functionalized microfluidic chips have been receiving increased attention as they facilitate material representation to mimic surface mineralogy in addition to direct visualization and quantification of multiphase flow and transport processes in a porous media. In particular, calcite-coated glass surfaces have been used to mimic the solid-fluid interactions involved in carbonate reservoirs. The coating procedure usually involves the deposition of calcium carbonate layers on a functionalized glass surface. Depending upon experimental conditions, the deposited calcium carbonate could be one or more of the three polymorphs: calcite, vaterite, and aragonite. Hence, it is essential to analyze and control the formation of the desired calcium carbonate polymorph. In this study, we transformed glass surfaces into carbonate surfaces by growing calcium carbonate particles in-situ using a layer-by-layer deposition procedure. The influences of process parameters involved in the deposition procedure on the formation of calcium carbonate polymorphs were analyzed. The parameters evaluated were: initial glass surface cleaning phase – DI water, plasma, piranha and NaOH as substrate cleaners; surface functionalization phase – DI water and chloroform as silane solvents; and calcite crystals growth phase – effect of number of coating cycles and concentration of CaCl2 and Na2CO3 solutions on the coating. After CaCO3 deposition, strategies to transform kinetically favorable vaterite to thermodynamically stable calcite are discussed. Coating uniformity, morphology, elemental atomic percentage of coating, and the CaCO3 polymorphs were examined by optical microscopy, Scanning Electron Microscopy (SEM), SEM Energy Dispersive X-Ray Spectroscopy (SEM EDS), and Raman spectroscopy, respectively.