Aggregation and Layering Transitions in Thin Films of X‐, T‐, and Anchor‐Shaped Bolaamphiphiles at the Air–Water Interface

Abstract

Aggregation in Langmuir films is usually understood as being a disorderly grouping of molecules turning into chaotic three-dimensional aggregates and is considered an unwanted phenomenon causing irreversible changes. In this work we present the studies of 11 compounds from the group of specific surfactants, known as bolaamphiphiles, that exhibit reversible aggregation and, in many cases, transition to well-defined multilayers, which can be considered as a layering transition. These bolaamphiphiles incorporate rigid π-conjugated aromatics as hydrophobic cores, glycerol-based polar groups and hydrophobic lateral chains. Molecules of different shapes (X-, T-, and anchor) were studied and compared. The key property of these compounds is the partial fluorination of the lateral chains linked to the rigid cores of the molecules. The most interesting feature of the compounds is that, depending on their shape and degree of fluorination, they are able to resist aggregation and preserve a monolayer structure up to relatively high surface pressures (T-shaped and some X-shaped molecules), or create well-defined trilayers (X- and anchor-shaped molecules). Experimental studies were performed using Langmuir balance, surface potential and X-ray reflectivity measurements.

Synthesis of an Open‐Cage Structure POSS Containing Various Functional Groups and Their Effect on the Formation and Properties of Langmuir Monolayers

“…Longer intermolecular distances in the perfluorinated OFP‐POSS are a result of the substitution of the silica cage with groups containing strongly electronegative atoms. In this way, fluorination (substitution with strongly electronegative atoms in general) prevents aggregation into 3D forms …”

“…The aggregate lateral dimensions do not exceed 100 nm, protruding typically 2-5 nm above the monolayer. [43] As is well known, the geometry of the surface can have ag reat impact on wettability. [25,42] In addition to that, the PEG-POSS include highly polar groups, which, we concluded, lie on the water surface oriented parallel to each other.I nc lose proximity,d ipolar interactions between them also contribute to repellence of the molecules out of the contact with the water surface.…”

Nanostructures of Nematic Materials of Laterally Branched Molecules

“…[6] Also, it is well-known that bent-shape molecules form smectic clusters, [18][19][20]27] and more complex-shaped molecules, such as dendrimers, [28] T-shaped, X-shaped, H-shaped, and other anisotropic shaped units, [29][30][31][32][33] can self-assemble into complex supramolecular units. [6] Also, it is well-known that bent-shape molecules form smectic clusters, [18][19][20]27] and more complex-shaped molecules, such as dendrimers, [28] T-shaped, X-shaped, H-shaped, and other anisotropic shaped units, [29][30][31][32][33] can self-assemble into complex supramolecular units.…”

Spontaneous self-assembly of partially fluorinated bolaamphiphiles into ordered layered structures

“…reversibility of p(A) isotherms of Langmuir films of fluorinated surfactants when decompression started before the film collapse. 25 In our previous papers 28,29 we reported reversibility and reproducibility of the Langmuir p(A) isotherms of partially fluorinated bolaamphiphiles compressed far beyond the collapse point. Formation of multilayered films due to layering transitions 30 was also proved.…”

“…A similar result was obtained in the case of LB films of X1. 16,29 The thicknesses (around 4.2 nm) were only roughly estimated due to distorted XRR patterns with no well pronounced minima. An attempt to obtain films of L = 3 of X1 via DC onto silicon gave Sm-like monolayers only (d 3 = 2.34 nm).…”