Monte Carlo Simulation of Amphiphile Self-Assembly during Dip Coating

Abstract

Fascinating nanostructured porous materials have recently been synthesized by evaporation-driven coassembly of ceramic precursors and amphiphiles. To expand our understanding of this process, we examine the influence of interfaces on self-assembly process using equilibrium lattice-based Monte Carlo simulations of ternary amphiphile-solvent mixtures. The simulations are able to predict the existence of all significant lyotropic mesophases, including lamellae, hexagonal closepacked cylinders, and cubic phases such as the gyroid. In the presence of walls that attract the majority solvent, the amphiphiles are confined to a smaller region of space, and experience a higher local concentration than the bulk concentration. This can lead to early transitions between mesophases. On the other hand, when the surface repels the majority solvent, amphiphiles tend to adsorb at the walls, and the local effective concentration in solution is lower. This can delay mesophase formation. When the amphiphile concentration is high enough that mesophases form in the bulk solution, however, either type of strongly attracting wall will align the mesophase (lamellae or hexagonal channels) parallel to the walls. In contrast, neutral walls (with no preferential interaction with either component) align mesophases perpendicular to themselves, which could be an interesting route to pores aligned normal to a film.

In Situ GISAXS Investigation of Low-Temperature Aging in Oriented Surfactant-Mesostructured Titania Thin Films

“…By analogy with surface chemistry strategies used to orient block copolymer films, − the Rankin group has reported the synthesis of mesoporous titania thin films with o-HCP cylindrical nanopores using EISA with P123 (a triblock copolymer with the composition HO­(CH 2 CH 2 O) x ­(CH 2 CH­(CH 3 )­O) y ­(CH 2 CH 2 O) x H, where, on average, x = 20 and y = 70) as structure directing agent and titanium­(IV) ethoxide as titania precursor. , The hypothesis underlying this approach is that orthogonal alignment of the HCP mesophase can be achieved in a EISA-derived ceramic film by modifying the substrate surface so that it interacts equally with both blocks of the P123 template, making it chemically “neutral” toward the template surfactant. Monte Carlo simulations , have shown that this is the expected outcome for mixtures of surfactants and small molecules, and not just for neat block copolymers . A related epitaxial orientation procedure was demonstrated by Tolbert and co-workers, where HCP film was cast onto a cubic template film to induce orthogonal alignment .…”

“…84,85 The hypothesis underlying this approach is that orthogonal alignment of the HCP mesophase can be achieved in a EISA-derived ceramic film by modifying the substrate surface so that it interacts equally with both blocks of the P123 template, making it chemically "neutral" toward the template surfactant. Monte Carlo simulations 86,87 have shown that this is the expected outcome for mixtures of surfactants and small molecules, and not just for neat block copolymers. 82 A related epitaxial orientation procedure was demonstrated by Tolbert and co-workers, where HCP film was cast onto a cubic template film to induce orthogonal alignment.…”

Highly Ordered Mesoporous Silica Films with Perpendicular Mesochannels by a Simple Stöber‐Solution Growth Approach

“…With the continuous diffusion and re‐assembly of CTAB molecules, newly hydrolyzed silicate oligomers are adsorbed and cross‐linked onto the charged micelle head groups at the solution–silica film interface, leading to a continuous, large‐domain film growth along with the longitudinal direction of cylindrical micelles that are perpendicularly orientated on the substrate (step 4). Previously reported Monte Carlo simulation results also showed that a highly active interface induces a perpendicular alignment in surfactant mesophases 44. After solution assembly and growth, mesoporous silica films with perpendicular channels are subsequently obtained through the removal of surfactants by solvent extraction (step 5).…”

In-Situ X-ray Scattering Study of Continuous Silica−Surfactant Self-Assembly during Steady-State Dip Coating

“…This approach strikes a good balance between molecular detail and the ability to routinely witness spontaneous self-assembly processes on an acceptable computational time scale. 24 The particular implementation here represents the small molecules as a simple lattice gas, single beads occupying single sites. Our surfactants are linear chains (H 2 T 6 ) of 2 headgroup beads and 6 tail group beads, together occupying 8 sites.…”