Existence of Two‐Dimensional Physical Gels even at Zero Surface Pressure at the Air/Water Interface: Rheology of Self‐Assembled Domains of Small Molecules

Abstract

Films of mesoscopic domains self-assembled from fluorocarbon/hydrocarbon diblockcopolymers (FnHm) at the air/water interface were found to displayh ighly elastic behavior.W ed etermined the interfacial viscoelasticity of domain-patterned FnHm Langmuir monolayers by applying periodic shear stresses.Remarkably,wefound the formation of two-dimensional gels even at zero surface pressure.T hese monolayers are predominantly elastic, whichisunprecedented for surfactants,e xhibiting gelation only at high surface pressures.S ystematic variation of the hydrocarbon (n = 8; m = 14, 16, 18, 20) and fluorocarbon (n = 8, 10, 12;m= 16) blockl engths demonstrated that subtle changes in the block length ratio significantly alter the mechanics of two-dimensional gels across one order of magnitude.These findings open perspectives for the fabrication of two-dimensional gels with tuneable viscoelasticity via self-assembly of mesoscale,l owmolecular-weight materials.

Nonlinear Viscoelasticity of Highly Ordered, Two-Dimensional Assemblies of Metal Nanoparticles Confined at the Air/Water Interface

“…However, to date, little has been understood about how surface chemical functions and core metals modulate the lateral correlation and thus the mechanical properties of colloidal assemblies of metal nanoparticles at the interface. Recently, we studied the linear viscoelasticity of self-assembled domains of fluorinated surfactants by interface shear stress rheology 19 and dilational rheology. 20 The latter is especially useful in the case the film has high viscoelastic moduli near or beyond the instrumental limitation of shear stress rheology.…”

Langmuir Nanoarchitectonics from Basic to Frontier

“…Krafft, Tanaka, and co-workers found the existence of twodimensional physical gels on water even at zero surface pressure. 54 The observed phase was significantly affected by subtle changes in the polymer structure such as the block length ratio, which can be useful for stabilizing microbubbles, emulsions, and gels.…”

Long‐Range Lateral Correlation between Self‐Assembled Domains of Fluorocarbon‐Hydrocarbon Tetrablocks by Quantitative GISAXS

“…Such strong correlations between FnHm domains suggested that the repulsive inter‐domain interactions would make the interface highly elastic. In fact, our recent interfacial stress rheometry study demonstrated that FnHm monolayers form two‐dimensional gels even at zero surface pressure …”

“…In fact, our recent interfacial stress rheometry study demonstrated that FnHm monolayers form two-dimensional gels even at zero surface pressure. [26] We extended the strategy to study "tetrablock" molecules ( Figure 1a) possessing two fluorocarbon and two hydrocarbon chains in one molecule; di(FnHm) ((C n F 2n + 1 CH 2 )(C m-2 H 2m-3 )CHÀ CH (C n F 2n + 1 CH 2 )(C m-2 H 2m-3 ). [27] Similar to the diblocks, all tetrablocks formed monolayers at the air/water interface.…”