Microstructure of Amphiphilic Monodendrons at the Air−Water Interface

Abstract

Grazing incident X-ray diffraction and X-ray reflectivity have been performed on Langmuir monolayers of low generation monodendrons containing a crown-ether polar group, azobenzene spacer, and varying number of peripheral alkyl chains of 1, 2, 4, and 8. We observe that the cross-sectional mismatch between the bulky polar head and the alkyl tails has a profound effect on the local ordering of the alkyl tails. It is found that the alkyl chains in a single-tail molecule are significantly tilted away from the surface normal. The tilt is eliminated in molecules with two or more alkyl chains where the cross-sectional mismatch is in favor of the peripheral tails. The molecule with one tail possesses a supercell orthorhombic packing caused by structural nonequivalency on the neighboring tails. The two- and four-tail molecules form a mixed structure best described by a quasi-hexagonal unit cell, and the eight-tail molecule forms a more stable hexagonal unit cell. Peripheral tails for these molecules are in standing-off orientation. We suggest that the steric constraints cause lower correlations and a staggered packing structure of monolayers from the eight-tail molecule. We suggest that branching alkyl tails off the same phenyl ring and the presence of the phenyl rings in the vicinity of the branching are limiting factors on the chain packing at the air−water interface in monodendrons with multiple peripheral tails. We conclude that a significant portion of the molecules is submerged in the water subphase and possesses a “kink” shape.

Self-Assembled Superhelical Structure of Poly(N-vinylcarbazole)-Based Donor–Acceptor Polymer at the Air–Water Interface

“…This indicates that the morphology of the film formed at the air/water interface is preserved upon the vertical upstroke. 9 As shown in Figure 1, when PVK−AZO− NO 2 solution was spread on the surface of water and barriers were not compressed, a relatively even film with some irregularly dispersed holes, together with a small quantity of fibrillar structures, was observed (more details were given in Figure S4). The height of these films was about 0.6 nm, which is consistent with the size of a PVK chain without the nitroazobenzene side chains.…”

Structural Characterization of Self-Organized Mono- and Multilayers of Poly[bis(2,2,3,3-tetrafluoropropoxy)phosphazene] at the Air/Water Interface

“…This can be illustrated by such particular examples as Langmuir monolayers of different 2D ordered structures from low generation amphiphilic monodendrons containing a crown ether polar group, azobenzene spacer, and varying number of peripheral alkyl chains and reversible crystallization of two-dimensional monolayer of trisilanolbutyl oligomeric polyhedral silsesquioxane under lateral compression at the air/water interface . Especially interesting are monolayers of fluorinated amphiphiles exhibiting specific structures and properties due to the combined hydrophobicity and lipophobicity of chains resulting in microphase separation when fluorinated and hydrogenated amphiphiles are mixed or structurally connected in a copolymer. − The comb-like polymers containing fluorocarbon side chains are attractive representatives of the latter .…”

Structural Transition of Poly(L-lactic acid) Film Induced by Compression at Air/Water Interface

“…cates that the morphology of the film formed at the air/water interface is preserved upon the vertical upstroke. 27 As shown in Fig.2A, when PLLA film was compressed up to 5.0 mN•m -1 at the air/water interface, a relatively even and featureless film with some irregularly dispersed holes was observed. The height of these films based on the defects was about 2.2 nm.…”