Self-Assembly into Strands in Amphiphilic Polymer Brushes

Abstract

The self-assembly of amphiphilic macromolecules end-grafted to a plane surface is studied using mean-field theory and computer simulations. Chain backbones are built from hydrophobic groups, whereas side groups are hydrophilic. The brush is immersed in a solvent, which can be good or poor, but on average is not far from θ conditions. It is demonstrated that the strong amphiphilicity of macromolecules at a monomer unit level leads to their self-assembly into a system of strands with a 2D hexagonal order in a cross-section parallel to the grafting plane. The structure period is determined by the length of side groups. In theory, this effect is explained by the orientation of strongly amphiphilic monomer units at a strand/solvent boundary that leads to an effective negative contribution to the surface tension. Computer simulations with molecular dynamics (MD) are used for a detailed study of the local brush structure. The aggregation number of strands grows with the increase of the grafting density and side group length.

Self-assembly in densely grafted macromolecules with amphiphilic monomer units: diagram of states

“…Side B groups create the outer periphery. 41 At a higher value of |e BB | some of the strands are merged into prolonged clusters which could be considered as short lamellae. The short lamellae form a few domains and coexist with the strands (Fig.…”

“…Computer modeling and analytical theory of end-grafted macromolecules with (A-graft-B) monomer units reveal that in brushes, the type of mesophase structure depends crucially on the solvent selectivity towards backbone A or side B groups. 40,41 In a solvent poor for the polymer A backbone, dense brushes could form a system of strands from a few (up to 5) intertwined macromolecules. These strands are perpendicular to the surface, and can be only observed in the case of rather strong AB incompatibility.…”

“…These strands are perpendicular to the surface, and can be only observed in the case of rather strong AB incompatibility. 41 In the opposite case of the solvent being poor for the side B groups and in the absence of AB energetic interaction, the macromolecules join into clusters starting from relatively low grafting density and form ultra-thin and nearly flat micelles on the surface. The thickness of the micelles is about double the size of a monomer unit or twice larger and their shapes change with an increase in the grafting density as follows: circular micelles-prolonged micelles-inverse micelles-continuous bilayer.…”

Lamellae—Parking Garage Structure—Lamellae Transition in Densely Grafted Layers of Amphiphilic Homopolymers: Impact of Polymerization Degree

“…29 Domains oriented perpendicularly to the substrate are observed in densely grafted amphiphilic homopolymers. 30,31 Depending on the solvent selectivity, they can be strands of few macromolecules, 30,31 lamellae with different periods, and parking garage structures, 31 joining lamellae with different periods by screw ramps.…”

Simultaneous Alcoholic and Malolactic Fermentations by Saccharomyces cerevisiae and Oenococcus oeni Cells Co-immobilized in Alginate Beads

“…In recent years, it is increasing the interest in using immobilized cells for fermentation processes, such as beer production (Masschelein et al, 1994 ), cider production (Nedovic et al, 2000 ), sparkling wine fermentation (Yokotsuka et al, 1997 ). Compared to the conventional free cell system, these strategies offer numerous technical and economic advantages (Nedović et al, 2011 ).…”