Aerosol OT Quantity Impacts on Calcium Nitrate Self-Healing Microcapsule Properties Used for Sustainable Construction Applications

This paper is a continuation of a previously published paper on this issue that studied the microencapsulation of calcium nitrate in urea-formaldehyde shell using Aerosol OT (AOT) in hexane solution. The aim of this paper is to determine the quantity of AOT that optimizes microcapsule distribution, diameter, and shell thickness. Different quantities of AOT, namely 0.25 g, 0.50 g, 1.5 g, and 2.5 g were dissolved in 180 g of hexane solution to prepare the continuous phase. A Scanning Electron Microscopy (SEM) was used to characterize the distribution and the diameters of the prepared microcapsules. A Transmission Electron Microscopy (TEM) was used to investigate the microcapsule shell thicknesses. The SEM images have shown that using 0.25 g of AOT may be insufficient to totally polymerize the whole quantity of the core materials into fully independent capsules. On the other hand, using 0.50 g of AOT has shown a uniform distribution and almost complete polymerization of the core material components into distinct microcapsules. Higher quantities of AOT (i.e., 1.50 g and 2.5 g) have resulted in agglomerated microcapsules and nonuniform distributions. The results have also demonstrated that the quantity of AOT does not have a significant impact on the microcapsule diameter. Microcapsule average shell thicknesses were found to decrease by increasing AOT amount up to 0.50 g and to increase again due to the agglomeration witnessed for increased AOT quantity. Accordingly, 0.50 g of AOT was recommended for the preparation of calcium nitrate microcapsules in future research work.