Area-Creep Measurements for Crystalline Monolayer of Stearic Acid on the Water Surface

Abstract

Abstract The area-creep mechanism for the crystalline monolayer of stearic acid on the water surface was discussed on the basis of area-creep measurements and transmission electron microscopic observations. The area-creep behaviors of the crystalline monolayer at a high surface pressure region (≥ 15 mN m−1) was apparently different from those at a low one (≤ 10 mN m−1). At a high surface pressure region, the area-creep behavior of the monolayer was mainly classified into the two processes in shorter and longer creep time regions with respect to around 1 × 102 s. The area strain in a short creep time region was small and increased linearly with the creep time, that might be attributed to rearrangement of molecules in the crystalline monolayer during the area-creep (molecular creep). On the other hand, the area strain in a long creep time region increased remarkably owing to collapse of the monolayer (geometrical aggregation creep). Also at a low surface pressure region, the area strain was small and became almost constant at around 1 × 104 s after the area-creep experiment started. In the case of the area-creep of the crystalline monolayer at a low surface pressure, rearrangement of molecules in the crystalline monolayer and/or filling in vacancies of molecular level in the interfacial regions among the crystalline monolayer domains were proceeded with a creep time, and then, the crystallographical regularity in the monolayer was increased owing to molecular rearrangement and/or sintering at an interfacial region among crystalline monolayer domains (molecular creep).