Area-temperature ( A-T) isobars of monolayers of octadecylureas at the air/water interface

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Vol. 102; pp. 69 - 73
• Main Authors: Shimizu, Masaru, Yoshida, Masaaki, Iimura, Ken-ichi, Suzuki, Noboru, Kato, Teiji
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 13-09-1995; Elsevier
• Subjects: Air/water interface; Area-temperature isobars; Chemistry; Exact sciences and technology; Gas-liquid interface and liquid-liquid interface; General and physical chemistry; Monolayers; Octadecylureas; Surface physical chemistry; Area-temperature isobars; Octadecylureas; Air/water interface; Monolayers; Gas liquid interface; Monolayer; Phase transformation; Ethanol; Isobar; Benzene; Temperature effect; Surface pressure; Air water interface; Surface area; Experimental study; Lattice structure
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/0927-7757(95)03240-E

A-T isobars of octadecylurea and
N-methyl-
N-octadecylurea monolayers were measured. The former material shows a phase transition from a condensed state (β) to another condensed state (α), with an accompanying area contraction, under a constant surface pressure with increasing temperature. Two-dimensional thermal expansivity of the β phase was very small but negative. These characteristic properties of octadecylurea monolayers can be explained by formation of the hydrogen-bond network among the urea head-groups. In contrast, the latter material exhibits only a phase transition from a condensed state to an expanded state with increasing temperature. These facts suggest that the hydrogen atom attached to the same nitrogen atom to the octadecyl group plays an important role in the formation of the hydrogen-bond network in the monolayer.