A two-dimensional network of phenol–formaldehyde monolayers by the Langmuir–Blodgett technique

Abstract

A monolayer network film of a phenolic resin was produced through the Langmuir–Blodgett (LB) technique. Amphiphilic phenols, o-, m- and p-hexadecoxyphenol ( o-, m- and p-HP), were synthesized by the reactions of catechol, resorcinol, and hydroquinone, respectively, with 1-iodohexadecane. Monolayers of the HPs were spread on aqueous subphases with different pHs and on aqueous 1% formaldehyde subphase. The surface pressure–area isotherms revealed characteristic monolayer behaviors according to the structural isomers at the air–water interface. Spontaneous increase of the surface pressure by the reaction of the phenol moiety with formaldehyde at the air–water interface was found on the aqueous formaldehyde subphase. The p-HP monolayer was transferred onto calcium fluoride substrate as Y-type and the molecular structure was determined by the Fourier transform infrared spectroscopy (FTIR). Acid and following heat treatments were applied for the enhancement of network formation. The network film showed resistance toward organic solvents. The mechanical stability of the network film was indirectly evaluated by the scanning electron microscopy (SEM) observation of the LB film morphology covered over the porous substrate and less than eight layers were enough to cover the pores of 0.1 μm diameter.