Phase Transition in Monolayers of Straight Chain and 2-Methyl Branched Alcohols at the Air−Water Interface

Abstract

Monolayers of straight chain and 2-methyl branched chain alcohols with alkyl chain lengths of C10−C18 are experimentally studied by a conventional film balance technique combined with a Brewster angle microscope (BAM). The comparison of the surface pressure (π)−area (A) isotherms with the corresponding BAM images provides information on the phase behavior and the first-order main phase transition of the monolayers. Striking differences in the dependence of the phase transition pressure on temperature of the straight chain and 2-methyl-substituted alcohols are correlated with differences in the molecular ordering. The general conditions for the main phase transition in the corresponding homologous alcohols can be derived. The effect of alkyl chain length and 2-methyl substitution on the general textural features of the condensed phase domains is determined under equilibrium and nonequilibrium conditions. n-Alcohol monolayers form defined and well-shaped condensed phase domains, often with inner texture in equilibrium. The long-range orientational order is strongly reduced in the condensed phase of 2-methyl-alcohols. Therefore, in the two-phase coexistence region of 2-methyl-alcohol monolayers only irregularly shaped domains without any inner structure are formed, which cannot be observed at the medium alkyl chain length C14 because of the low contrast. Model calculations of the two-dimensional lattice structure of the racemic 2-methyl-hexadecanol on the basis of the pg space group are performed and correspond well with the reduced ordering concluded from the experiments.

Strong Headgroup Interactions Drive Highly Directional Growth and Unusual Phase Co-Existence in Self-Assembled Phenolic Films

“…It remains in this phase until film collapse at 20 Å 2 /molecule and 47 mN/m. This collapse area is larger than that of ODG, but not significantly, suggesting that there may be some solubility of LDG in the subphase which has been reported for surfactants with a C12 alkyl chain . AFM measurements of films deposited by the Langmuir–Blodgett method on mica confirm a single phase with a flat, featureless surface (data not shown).…”

“…This collapse area is larger than that of ODG, but not significantly, suggesting that there may be some solubility of LDG in the subphase which has been reported for surfactants with a C12 alkyl chain. 41 AFM measurements of films deposited by the Langmuir−Blodgett method on mica confirm a single phase with a flat, featureless surface (data not shown). As a result, the headgroups should not be in such close proximity as observed with ODG.…”

Autophobing on Liquid Subphases Driven by the Interfacial Transport of Amphiphilic Molecules

“…This packed monolayer on the 63.6 cm 2 surface contains 4.2 × 10 16 molecules, assuming an area/molecule of ∼15 Å 2 /molecule, , and the formation of the monolayer does not remove a significant fraction of the 1.3 × 10 18 molecules in the original drop. Thus, the concentration of the dodecanol before and after spreading is essentially the same, and we may use the surface tension measured for the bulk solution and listed in Table to calculate the spreading coefficient.…”

Self‐Assembled Transparent Conductive Electrodes from Au Nanoparticles in Surfactant Monolayer Templates

“…Alkyl‐coated Au NPs have been previously shown to form diverse 2D nanostructures on water surfaces through co‐deposition of surfactant molecules or lipids 7–9. The two surfactant molecules employed here exhibit important roles: MOH forms condensed monolayer domains (green areas in Figure 1a) 10. Elaidic acid, on the other hand, is capable of solubilizing Au NPs at the air/water interface in the temperature the experiments were carried out 5.…”