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 diblock copolymers (FnHm) at the air/water interface were found to display highly elastic behavior. We determined the interfacial viscoelasticity of domain-patterned FnHm Langmuir monolayers by applying periodic shear stresses. Remarkably, we found the formation of two-dimensional gels even at zero surface pressure. These monolayers are predominantly elastic, which is unprecedented for surfactants, exhibiting gelation only at high surface pressures. Systematic variation of the hydrocarbon (n=8; m=14, 16, 18, 20) and fluorocarbon (n=8, 10, 12; m=16) block lengths 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, low-molecular-weight materials.

Influence of Perfluorohexane‐Enriched Atmosphere on Viscoelasticity and Structural Order of Self‐Assembled Semifluorinated Alkanes at the Air‐Water Interface

“…This might explain our results indicating that PFH molecules enriched in the gas phase barely influence the nonlinearity of the response function (THD). This suggests that the self‐assembled domains of FnH 16 m prevent the intercalation of PFH molecules into the fluorocarbon region, which seems to be in line with the formation of 2D gels by these nanodomains at the gas/water interface …”

“…This suggests that the self-assembled domains of FnH16m prevent the intercalation of PFH molecules into the fluorocarbon region, which seems to be in line with the formation of 2D gels by these nanodomains at the gas/water interface. [31]…”

“…Taking the advantage of GISAXS, the capability of full calculation of form and structure factors, we quantitatively determined the influence of the length of the hydrocarbon and fluorocarbon segments on the size and correlation of FnHm domains . Moreover, we found that such films of FnHm at the air/water interface form physical gels even at 0 mN m −1 surface pressure due to the strong dipole repulsion between the CF 3 terminals and the CF 2 −CH 2 junction, which seems promising for the stabilization of fluorocarbon microbubbles …”

“…[25] Moreover, we found that such films of FnHm at the air/water interface form physical gels even at 0 mN m À 1 surface pressure due to the strong dipole repulsion between the CF 3 terminals and the CF 2 À CH 2 junction, which seems promising for the stabilization of fluorocarbon microbubbles. [31] A key question in the context of using semifluorinated alkanes as shell components in fluorocarbon gas-stabilized microbubbles was if the presence of the fluorocarbon gas affects the structure and mechanical properties of the arrays of self-assembled domains of diblocks. It is conceivable that small fluorocarbon molecules can either penetrate into the domains or adsorb to the spaces between domains.…”

Designing the Slide-Ring Polymer Network with both Good Mechanical and Damping Properties via Molecular Dynamics Simulation

“…It is well known that cross-linked polymeric gels have attracted much attention because of their significant practical applications, such as actuators for optics, vehicles for drug delivery and release, and matrices for electronics and tissue engineering [1,2,3,4,5,6]. The polymeric gels are divided into chemical gels [7,8] and physical gels [9], based on covalent and non-covalent bonds such as hydrogen bonds and the hydrophobic interaction [10]. The properties of physical gels are more likely influenced by the high temperature and the solvent, which determine the instability of the non-covalent bonds [11].…”