Modulating dielectric properties of polyimide composite membranes with hydrophobic mesoporous silica via ball milling processing

Abstract

This research work investigated the impact of the ball-milling (BM) process on the dielectric properties of polyimide (PI) composite membranes incorporating hydrophobic mesoporous silica (HMS) particles. Initially, HMS particles were synthesized through base-catalyzed sol-gel reactions among APTES, MTMS, and TEOS, utilizing D-(−)-Fructose as a template. Following synthesis, the HMS particles underwent ball-milling to fine-tune corresponding specific surface area and average particle size. Three distinctive ball-milled HMS variants (referred to as BMS) were thoroughly characterized using FTIR, ¹³C NMR, ²⁹Si-NMR spectra, DLS, BET, CA, TGA, SEM, and TEM techniques. Subsequently, a series of PI composite membranes were fabricated and subjected to characterization via FTIR, EDS, CA, and TGA analyses. It should be noted that the three distinctive BM treated HMS was found to exhibit higher specific surface area and hydrophobicity as compared to non-BM treated HMS based on the data of BET and CA, respectively. Moreover, the surface area and hydrophobicity of ball-milled HMS exhibited the upward trend of BMS1 < BMS2 < BMS3. Subsequently, the dielectric constant (D_k) and dielectric loss (D_f) of PI and its composite membranes containing HMS particles measured at frequency of 10 GHz was found to show the downward trend. For example, the D_k of PI composite membranes: PI/BMS3 (3.34) < PI/BMS2 (3.41) < PI/BMS1 (3.55) < PI/HMS (3.58) < PI (3.66). On the other hand, the D_f of PI composite membranes: PI-BMS3 (0.0113) < PI/BMS2 (0.0114) < PI/BMS1(0.0115) < PI/HMS (0.0121) < PI (0.0123). This resulting decreasing trend of dielectric constant of as-prepared composite membranes may be attributed to the incorporated of HMS particles in PI membrane exhibiting lower moisture absorption (D_k of water = 80) and higher surface area (D_k of air = 1) based on the TGA and CA, respectively.