Dynamic Performance of Duolayers at the Air/Water Interface. 1. Experimental Analysis

Abstract

Understanding, and improving, the behavior of thin surface films under exposure to externally applied forces is important for applications such as mimicking biological membranes, water evaporation mitigation, and recovery of oil spills. This paper demonstrates that the incorporation of a water-soluble polymer into the surface film composition, i.e., formation of a three-duolayer system, shows improved performance under an applied dynamic stress, with an evaporation saving of 84% observed after 16 h, compared to 74% for the insoluble three-monolayer alone. Canal viscometry and spreading rate experiments, performed using the same conditions, demonstrated an increased surface viscosity and faster spreading rate for the three-duolayer system, likely contributing to the observed improvement in dynamic performance. Brewster angle microscopy and dye-tagged polymers were used to visualize the system and demonstrated that the duolayer and monolayer system both form a homogeneous film of uniform, single-molecule thickness, with the excess material compacting into small floating reservoirs on the surface. It was also observed that both components have to be applied to the water surface together in order to achieve improved performance under dynamic conditions. These findings have important implications for the use of surface films in various applications where resistance to external disturbance is required.

Structure-Dependent Interfacial Properties of Chaplin F from Streptomyces coelicolor

“…The morphology and homogeneity of Chp F Langmuir films at pH 3.0 or 10.0 at the air/water interface was visualized using a Brewster angle microscope (BAM, KSV NIMA, Biolin Scientific, Västra Frölunda, Sweden) mounted on a Langmuir trough (KN 2003, KSV NIMA). The BAM was equipped with a 50 mW laser emitting p-polarized light with a wavelength of 658 nm, which was reflected off the air/water interface at the Brewster angle (~53°) [ 40 ]. The lateral resolution of the microscope was 2 μm.…”

Dynamic Performance of Duolayers at the Air/Water Interface. 2. Mechanistic Insights from All-Atom Simulations

“…Interestingly, canal viscometry experiments have shown that the duolayer has a greater surface viscosity than the monolayer, 19 which suggested it may be more stable under wind. This two-part (1 and 2) publication series aims to examine the dynamic performance of the duolayer systems experimentally (part 1) 20 and elucidate the molecular mechanisms of its behavior theoretically using all-atom NEMD simulations, presented herein (part 2). The experimental data on the dynamic performance of the three-monolayer and three-duolayer systems presented in part 1 of this two-part series 20 show that, under wind conditions, not only does the duolayer outperform the monolayer as an evaporation suppressant, but it also outperforms itself under stationary conditions.…”

“…This two-part (1 and 2) publication series aims to examine the dynamic performance of the duolayer systems experimentally (part 1) 20 and elucidate the molecular mechanisms of its behavior theoretically using all-atom NEMD simulations, presented herein (part 2). The experimental data on the dynamic performance of the three-monolayer and three-duolayer systems presented in part 1 of this two-part series 20 show that, under wind conditions, not only does the duolayer outperform the monolayer as an evaporation suppressant, but it also outperforms itself under stationary conditions. Here, we use classical molecular dynamics techniques to compare the interfacial properties of the monolayer and duolayer systems under equilibrium and applied force conditions.…”

“…However, the main water surface is covered only by one monolayer or one duolayer, as shown by Brewster angle microscopy. 20 Therefore, in the molecular simulations, only one monolayer or one duolayer is used, as only a small time frame (50 ns) and surface area (1640 Å 2 ) are examined, without any change in surface area during simulation. The starting monolayer chain configurations were taken from previously modeled liquid-condensed states of the aliphatic chains, characterized by a tightly packed chain arrangement, typical of equilibrium surface pressure.…”

“…We employed the NVT ensemble to sustain the C18E1 packing density, as this best mimics the experimental conditions, where the equilibrium area per molecule was maintained throughout the experiment. 20 Trajectories were generated by saving atomic coordinates in 10 ps time intervals. The Eq-Monolayer and Eq-Duolayer systems were simulated for a total time of 50 ns, and considered equilibrated when the standard deviation of the total energy was within 1% of the average, the monolayer tilt reached a steady value, and for the duolayer systems when the PVP center of mass reached a steady z-position at the interface.…”