Water adsorption behavior of ordered mesoporous silicas modified with an organosilane composed of hydrophobic alkyl chain and hydrophilic polyethylene oxide groups

FSM-type mesoporous silicas with different pore diameters were synthesized and modified with an organosilane composed of hydrophobic alkyl chain and hydrophilic polyethylene oxide (PEO) groups. In the slightly silylated material, both alkyl chains and PEO groups are located on the surfaces of ordered mesopores. In the fully silylated material, it is considered that alkyl chains are present near the silicate frameworks and the residual spaces are filled with PEO groups. Accordingly, inner spaces of ordered mesopores can be designed by the modification. On the basis of the water adsorption–desorption measurements, surface properties of the modified materials was investigated in detail. Although surfaces of ordered mesoporous silicas must be extremely hydrophobic by the presence of surface alkyl chains, the property was largely reduced by the presence of hydrophilic PEO groups and then water molecules can be adsorbed on the modified surfaces and penetrated into PEO moieties even after the organic modification.