Organic foams stabilized by Biphenyl-bridged organosilica particles

Can surface-active particles be designed à la carte just by incorporating functional groups mimicking the structure of the solvent and gas? This is based on the idea that, to achieve good foamability, the particle wettability needs to be finely tuned to adjust the liquid-particle and gas-particle surface tensions. In practice, could particles containing phenyl rings and alkyl chains assemble at the air-liquid interface and stabilize foams based on aromatic solvents?

A library of organosilica particles was prepared by sol-gel synthesis using aromatic organosilane precursors. The particles were characterized by TGA, FTIR and ¹³C/²⁹Si MAS NMR. The foaming properties were studied after hand shaking and high-speed homogenization. The influence of particle wettability and solvent properties on foam formation was systematically investigated. A comparison was carried out between biphenyl-bridged particles and various stabilizers on foamability in benzyl alcohol.

Biphenyl-bridged particles could stabilize foams in aromatic solvents with a high foam volume fraction up to 96% using Ultra-Turrax. The presence of biphenyl rings and short alkyl chains was crucial for foamability. Organic foams were prepared for aromatic solvents with intermediate surface tension (35-44 mN m^-1) and contact angle in the range 32-53°. Biphenyl-bridged particles outperformed polytetrafluoroethylene and fluorinated surfactants in benzyl alcohol.