Characterization of microparticles

The morphology of the microparticles was studied using FEI Quanta 3D FEG scanning electron microscope (SEM). The microparticles were loaded into aluminum stubs using double-sided carbon conductive tapes and sputter coated with gold for 25 s before analysis. Low magnification (100×) and high magnification (around 2000×) images were collected to observe the surface morphology of the microparticles. Energy dispersive spectroscopy (EDS) was used to quantify the elemental silicon (Si) along the surface of the microparticles after the calibration of EDS detector with pure Si. Since the size of the microparticles was different for different groups, instead of taking whole microparticle surface, three different regions along the surface of microparticles were selected to quantify the amount of elemental Si. The selection was done with rectangular window and the size of this selection window was kept same to make the quantification surface area constant.

The physico-chemical interaction among the components in microparticle was analyzed using Fourier transform infrared (FTIR) spectrometer (Varian UMA 600 with Ge crystal). The microparticles were grinded into fine powder and the spectrum (700–4000 cm⁻¹) was collected in micro-ATR mode.

The nano-topography of the microparticles was studied using Bruker Multimode 8 atomic force microscope (AFM) with J-scanner. The Nanoscope software was used to set the parameters for scanning and Nanoscope Analysis software was used to analyze the scanned images. The microparticles were fixed into aluminum sample holder using fixative glue and the surface was scanned using silicon nitride probes (SNL-10) in tapping mode. Due to spherical morphology of the microparticles, only the top surface was scanned and imaged to avoid the curvature. Fifteen microparticles from each group were scanned with the scan size of 5 μm and the images collected were analyzed to determine the average roughness (Rq) value.