The dioctadecylamine monolayer: Textures, phase transitions, and dendritic growth

Abstract

The phase diagram of dioctadecylamine Langmuir monolayer has been determined from pressurearea isotherms and from direct observations of the monolayer using Brewster angle microscopy. We describe the observed domains, textures, and phase boundaries for the mesophases presented by this system between 5°C and 45°C, at pHϭ3. The phases were named as G, LE, S 1 , and S 2 according to their apparent texture. Contrast between domains of condensed phases is quite low, indicating small tilting of the amine tails. The G -S 1 , G -S 2 , G -LE, and LE-S 1 transitions seem to be of first order; meanwhile, the S 1 -S 2 transition seems to be of second order. We observed how the froths changed when the area density increases at constant pressure, along the G -L, G -S 1 , and G -S 2 phase transitions. In the L -S 1 transition, the shape of the domains of the emerging phase is of sixfold dendrites. The phase diagram obtained is very different from those obtained for single chain amphiphiles. In this system, the extent of the phases depends on the acid used to fix the pH. In addition, all our observations indicate that dioctadecylamine does not form a monolayer above pHϳ3.9.

Structure, photochromic, and electrochemical properties of dioctadecylamine/H3PMo12O40 Langmuir–Blodgett film

“…1 shows π -A isotherms of DOA on pH 4.0 of water and the PMo 12 aqueous subphase (pH 4.0, 3.4 × 10 −6 M). Similar to that described in previous work [24], the isotherm on the water surface exhibits an expanded behavior since DOA molecules could not form stable monolayers. The reason that the π -A isotherm shows low collapsed pressure and a very small molecular area on water is that DOA conglomerates easily and forms a multilayer at the air/water interface.…”

Domain Growth, Pattern Formation, and Morphology Transitions in Langmuir Monolayers. A New Growth Instability

“…Our l is of the same order of DPPC monolayer 34 (114 kJ/mol) at 20°C and of DODA monolayer (89.86 kJ/mol). 20 …”

Interfacial Behavior and Film Patterning of Redox‐Active Cationic Copper(II)‐Containing Surfactants

“…Although self-assembly remains the chief approach for film formation, [11][12][13] isothermal compression [14] allows for greater control over the final morphology. [15,16] This characteristic is fundamental for device nanofabrication, but only in the recent past has the design of amphiphilic precursors departed from lipids to encompass alkylamines, [17] polymers and copolymers, [18] and dendrimers [19] within its subjects. This departure coincides with the availability of surfacededicated techniques, such as Brewster angle microscopy [20,21] (BAM) and fluorescence microscopy [22] that allow for real-time evaluation of the film compression at the air/ water interface.…”

“…Domain morphology can also be influenced by factors such as distinct compression rates, time and temperature changes, and subphase modification. [17,44,47,48] Ongoing work in our labs focuses on these factors. Similarly, to assess the relationship between domain formation and degree of disorder, a detailed study based on atomic-force microscopy and sum frequency generation vibrational spectroscopy is currently underway.…”