Influence of DCCAs on Optical Transmittance and Porosity Properties of TMOS Silica Aerogels.

In the present paper, the experimental results on some physical properties of silica aerogels modified by four different drying control chemical additives (DCCAs): (i) oxalic acid (OXA), (ii) glycerol (GLY), (iii) N,N-dimethylformamide (DMF) and (iv) formamide (FA) are reported. The molar ratio of tetramethoxysilane (TMOS), methanol (MeOH), water (H2O) and ammonia (NH4OH) was fixed at 1 : 12 : 4 : 3.6 × 10−3 respectively, throughout our experiments, and the DCCA/TMOS molar ratio was varied accordingly. The DCCA/TMOS molar ratio at around 0.4 was found to be the limiting value for almost all the modified aerogels, above which the cracking probability of the aerogels increased drastically. Further, the DCCA modified aerogels were characterized by optical transmittance and porosity measurements. Physical properties such as bulk density, volume shrinkage and specific surface area were also determined for all the modified aerogels. The pore size distribution (PSD) was found to shift towards smaller pore radii for acidic (OXA) DCCA and larger pore radii for basic (FA, DMF) DCCAs. The results have been supported by particle and pore sizes observed using Scanning Electron Microscopy (SEM) and BET analysis. [ABSTRACT FROM AUTHOR]