Increasing the Uniformity of Nano-Dispersed SiO2 Distribution in Polymeric Binder of Composite Material

Ultrasonic dispersion of a silica hydrosol is compared with the effects of mechanical activation through the combined action of high shear stresses, ultrasound and cavitation. This action leads to breaking the siloxane bonds and increasing the content of silanol groups. The mechanical activation of binary silica system with acrylate dispersion promotes a chemisorption of oligoacrylate with the formation of Si – O – C and Si – C bonds. The effect of modification of oligoacrylate on the formation of a graft-copolymer and the stiffness of a composite material was evaluated.

Silica Aerogel Monoliths Derived from Silica Hydrosol with Various Surfactants

Owing to their ultra-low thermal conductivity, silica aerogels are promising thermal insulators; however, their extensive application is limited by their high production cost. Thus, scientists have started to explore low-cost and easy preparation processes of silica aerogels. In this work, a low-cost method was proposed to prepare silica aerogels with industrial silica hydrosol and a subsequent ambient pressure drying (APD) process. Various surfactants (cationic, amphoteric, or anionic) were added to avoid solvent exchange and surface modification during the APD process. The effects of various surfactants on the microstructure, thermal conductivity, and thermal stability of the silica aerogels were studied. The results showed that the silica aerogels prepared with a cationic or anionic surfactant have better thermal stability than that prepared with an amphoteric surfactant. After being heated at 600 °C, the silica aerogel prepared with a cationic surfactant showed the highest specific surface area of 131 m2∙g−1 and the lowest thermal conductivity of 0.038 W∙m−1∙K−1. The obtained low-cost silica aerogel with low thermal conductivity could be widely applied as a thermal insulator for building and industrial energy-saving applications.

ANALYSIS OF X-RAY WHISPERING GALLERY WAVES PROPAGATING ALONG LIQUID MENISCUSES

X-ray diffraction and fluorescence of whispering galleries (WGs) which propagate along meniscuses of deionized water or silica hydrosols enriched by CsOH have been analyzed for the first time. The measurements have been performed using the diffractometer with a moving tube-detector system. The X-ray beam rotation angle reached a maximum value of 4° on a silica hydrosol sample. The WG mode propagating near the surface of a concave meniscus as well as the fluorescence intensity have been found from a solution of the respective Helmholtz equations. For analysis of intensities of the X-ray scattering and fluorescence we have used a two-layer model of the liquid with the upper non-uniform corrugated layer in which the concentration of levitating Cs+ ions near the surface has a maximum derived from the experiment in the hydrosol depth of ~ 15 nm for SiO2 particle sizes of ~ 5÷7 nm. In order to determine the fluorescence intensity we have used the approach based on a method of fundamental parameters using the reciprocity theorem.

Thermal properties and water repellency of cotton fabric prepared through sol-gel method

Cotton fabrics were treated by one-step sol-gel method. The pure silica hydrosol and phosphorus-doped hydrosol were prepared with the addition of a hydrophobic hexadecyltrimethoxysilane to decrease the surface energy of cotton fabric. The thermal properties and water repellency of treated cotton fabric were characterized by thermo-gravimetric analysis, micro combustion, limiting oxygen index, and contact angle measurement. The results showed that cotton fabric treated by phosphorus-doped silica hydrosol had excellent flame retardance, and the water repellence was apparently improved with the addition of hexadecyltrimethoxysilane.