Isomerically-featured aggregate images of phenol-formaldehyde monolayers by BAM and SMM

Abstract

Brewster angle microscopy (BAM) and scanning Maxwell-stress microscopy (SMM) were applied to investigate the characteristic aggregate patterns of reactive phenolic resin monolayers. For the two-dimensional condensation reaction in the monolayer at the air-water interface, amphiphilic phenols of structural isomers, o -, m - and p -hexadecoxyphenol ( o -, m - and p -HP), were synthesized by the reaction of catechol, resorcinol, and hydroquinone, respectively, with 1-iodohexadecane. Monolayers of the HPs were spread on aqueous 1% formaldehyde subphases. The surface pressure-area isotherms revealed characteristic monolayer phases and collapse pressures according to the structural isomers at the air-water interface. The optical images of the HP-formaldehyde monolayers were monitored by BAM. The noticeable image was not observed until the monolayer collapse began. The images similar to dots, entangled threads, and blood vessels were respectively produced from o -, m -, and p - HP-formaldehyde monolayers after monolayer collapse. The HP-formaldehyde monolayers were transferred onto silicon wafers, and the morphologies of LB monolayers were observed by SMM. The SMM images have also supported the characteristic aggregate patterns of isomeric HP-formaldehyde monolayers.