Effect of the Janus Amphiphilic Wall on the Viscosity Behavior of Aqueous Surfactant Solutions

Abstract

The effects of the chemical nature of an interface are one of the key parameters which can affect self-assembly and rheological behavior. To date, several studies have reported selfassembled structures and rheological behaviors in the development of various functional materials. In this study, we investigated the self-assembly and viscosity behavior of aqueous surfactant solutions confined in three types of Janus amphiphilic nanotubes (JANTs), which have two, four, and eight sequential domains, respectively, using molecular simulation. We found that the viscosity behavior depends on the surfactant concentration and the chemical nature of the wall surface. For instance, although the concentration levels of the surfactants are the same (c = 10%), completely different viscosity behaviors were observed in the two sequential domains (Newtonian-like) and the four and eight sequential domains (strong shear-thinning) of the JANTs. Our simulations demonstrated how the rheological properties of aqueous surfactant solutions, including viscosity and velocity profiles, can be controlled by the chemical nature of the JANT wall surface, effect of confinement, and their self-assembly structures. Considering the foregoing, we hope that our study offers new knowledge on nanofluid systems.

Molecular Insight into the Possible Mechanism of Drag Reduction of Surfactant Aqueous Solution in Pipe Flow

“…The inner surface of the cylindrical tube was treated as smooth, in agreement with our previous studies [ 43 , 48 , 50 , 51 ]. The potential function of the smooth wall was built by summing the DPD force between every solution particle and the wall particles [ 54 ].…”

“…Figure 2 shows the frictional coefficient of the pipe as a function of . The volumetric flow rate, Q , is estimated by applying the cylindrical shell method to a velocity profile [ 50 , 51 , 58 ] and a generalized Reynolds number is used [ 59 , 60 ], as we focus on the onset point of the transition to turbulence. Here, the power-law parameter, n , is obtained from the relation between the wall shear rate, , and the wall shear stress, , in the steady state (see Figure S2 in the Supplementary Materials ).…”

“…As the repulsive parameters increase between hydrophilic head groups, the hydration radius may also be estimated to be larger. The same values of interaction parameters were adopted in many studies [ 43 , 47 , 48 , 49 , 50 , 51 ]. We also examined that our previous bulk simulation of CTAB containing a NaSal solution [ 47 ] produced the same results as those in a previous examination that Yamamoto and Hyodo performed [ 46 ].…”

“…The noise amplitude and friction coefficient were set to be 3.0 and 4.5, respectively. The temperature was set at a constant value, i.e., 1.0 k B T. The inner surface of the cylindrical tube was treated as smooth, in agreement with our previous studies [43,48,50,51]. The potential function of the smooth wall was built by summing the DPD force between every solution particle and the wall particles [54].…”

Self-Assembly Behaviors and Flow Properties of Amphiphiles by Mesoscale Simulations with Hydrodynamic Interactions

“…These results indicate that the viscosity be-havior of the surfactant solution in nanofluidic devices can be altered by steering the chemical patterns on the nanochannel surface. Additionally, DPD simulations were conducted to investigate the phase diagrams 44) and viscosity behavior 45) of the surfactant aqueous solutions confined in Janus amphiphilic NTs, based on recent advances in the available experimental techniques to synthesize NTs comprising both hydrophobic and hydrophilic surfaces. 46)…”