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

Abstract

The aims of this study are the following two: (1) To show that in Langmuir monolayers (LM) at low supersaturation, domains grow forming fractal structures without an apparent orientational order trough tip splitting dynamics, where doublons are the building blocks producing domains with a seaweed shape. When supersaturation is larger, there is a morphology transition from tip splitting to side branching. Here, structures grow with a pronounced orientational order forming dendrites, which are also fractal. We observed this behavior in different Langmuir monolayers formed by nervonic acid, dioctadecylamine, ethyl stearate, and ethyl palmitate, using Brewster angle microscopy. (2) To present experimental evidence showing an important Marangoni flow during domain growth, where the hydrodynamic transport of amphipiles overwhelms diffusion. We were able to show that the equation that governs the pattern formation in LM is a Laplacian equation in the chemical potential with the appropriate boundary conditions. However, the underlying physics involved in Langmuir monolayers is different from the underlying physics in the Mullins-Sekerka instability; diffusional processes are not involved. We found a new kind of instability that leads to pattern formation, where Marangoni flow is the key factor. We also found that the equations governing pattern formation in LM can be reduced to those used in the theory of morphology diagrams for two-dimensional diffusional growth. Our experiments agree with this diagram.

Lipid Monolayers at the Air–Water Interface

“…On the other hand, different to the cases discussed of equilibrium domain shapes, fast growth leads to out-of-equilibrium shapes, where morphological instability and irregular growth have been described [65,68,96,114,115]. For unequilibrated oversaturated systems, the competition between the rates of phase segregation and molecular migration to the domain (mainly through Marangoni flow [114,115]) determines whether the growth is reaction limited or migration limited.…”

“…For unequilibrated oversaturated systems, the competition between the rates of phase segregation and molecular migration to the domain (mainly through Marangoni flow [114,115]) determines whether the growth is reaction limited or migration limited. Slow phase segregation (low oversaturation) leads to reaction-limited growth and domains with equilibrium shapes, whereas high oversaturation leads to migration-limited growth and fractal domains with branched morphologies, [88,103] which relax to more rounded shapes [68].…”

The many faces (and phases) of ceramide and sphingomyelin II – binary mixtures

“…Copyright 2014 American Chemical Society condensed states of each mixture. In fact, the theory for domain shape equilibrium (McConnell 1990;Gutierrez-Campos et al 2010;Vega Mercado et al 2012) states that the difference in dipole density between the expanded matrix and the overall dipole of the condensed domains determines that flower-like shapes of increased line tension would form, whereas lower dipole density differences among the segregated condensed and expanded phases should lead to round-shaped domains having a lower line tension.…”

Growth and time dependent alignment of KCl crystals in Hemoglobin LB monolayer

“…The FE-SEM images were converted in the black and white 8-bit digitized version (monochrome format) by Microsoft Paint program (v-5.1). The fractal dimensions were calculated using box-counting method implemented within the ImageJ program [44].…”