Influence of membrane character on suppression of coffee-ring effect

Abstract

The evaporation process of deposited solution drop is likely to form ring-like structure on solid surfaces. In this study, we studied the effect of coffee-ring observed on two different polymeric membrane with understanding of membrane’s morphology. Characterization of both nitrocellulose and polyvinylidene (PVDF) membranes were performed with water contact angle (WCA) test, Fourier transform infrared (FTIR), Scanning Electron Microscopy (SEM) and Atomic Force Microscope (AFM) before performing porosity test and measuring pore size. The characterized membranes were then spotted with IgG from bovine serum. The dried spots were stained using Ponceau S dye before being scanned using scanner and undergo pre-analysis using online software, ImageJ for quantitative measurements. Different type of ring-like structure were observed in the respective membrane referring to the reliance of stain formation within the parameter that had been characterized. Between the membranes, PVDF shows higher porosity despite lower mean pore size compared to nitrocellulose but lower distribution of pore size. As the protein solution immobilized on the surfaces, the side profiles shows that the ring-like effect are visible in both condition. However nitrocellulose membrane are able to reduce the effect compared to PVDF as the pore size distribution are much smaller in even manner alongside with the surface roughness that leads to smaller contact angle. This contribute to faster evaporation rate in nitrocellulose as these factors enhanced the capillary flow, driving the particles to the contact line. In suppressing the coffee-ring effect, it is suggested to further investigate the interaction of solution with the membrane for a better result.