Effect of Ionic Repulsion among Hydrophilic Groups on Aggregation Structure of Fatty Acid Monolayer on the Water Surface

Abstract

The effect of ionic repulsion among hydrophilic groups of arachidic acid molecules on the aggregation structure of the arachidic acid monolayer on the water surface was investigated on the basis of surface pressure-surface area (π-A) isotherm measurements, Fourier transform infrared spectroscopic (FT-IR) measurements, and transmission electron microscopic (TEM) observations. π-A isotherm and FT-IR measurements revealed that the degree of ionic dissociation of hydrophilic groups in the monolayer drastically changed in a pH range of 10-12. The arachidic acid monolayer in a slightly dissociated state of hydrophilic groups (pH ) 5.8) did not exhibit the phase transition from an amorphous state to a crystalline one during compression. On the other hand, the monolayer in a highly dissociated state (pH ) 12.6) showed the phase transition from an amorphous state to a crystalline one by surface compression at the subphase temperature, T sp, below the melting temperature, Tm, of the monolayer, and also, the monolayer was still in an amorphous state without the phase transition to a crystalline state at Tsp above Tm. The aggregation structure of the monolayers on the water surface was systematically classified into "the crystalline monolayer", "the amorphous monolayer", and "the compressing crystallized monolayer" with respect to the thermal and chemical (intermolecular repulsive) factors.

Monolayers of mixture of alkylaminomethyl rutin and lecithin at the air/water interface

“…The value of A limt (46.04 Å 2 / molecule at 15°C) is higher than that for quercetin-3-O-palmitate (43 Å 2 /molecule at 10°C) [3] and is not in agreement with that for single fatty acid (22.0 Å 2 /molecule at 20°C) in the neutral subphase (pH 6.0) [25][26][27]. This result indicates that rutin moiety as the hydrophilic head group contributes prominently to the sur- face-occupied area per molecule.…”

Langmuir monolayers and Langmuir–Blodgett films of 1-acyl-1,2,4-triazoles

“…from C15 to C21 [6,[18][19][20][21][22][23], or more than 18 carbon atoms, e.g. from C20 to C24 [5][6][7]10,13,[24][25][26] have been investigated. Several publications study the collapse mechanism for stearic acid.…”

Molecular layers of hydroxamic acids in copper corrosion inhibition

“…There are publications about the effect of temperature and additives in the subphase on the morphology of fatty acid monolayers [17][18][19][20], and about the influence of the pH values on the monolayer stability [21][22][23][24][25][26][27][28][29]. With increasing temperature the monolayer stability decreases.…”