Friction reduction in a nanochannel with grafted poly(N-isopropylacrylamide) oligomers: A molecular dynamics study

Superhydrophobic surfaces have been used for reducing friction in micro- and nanochannels. In the present work, water flow between two carbon walls with nanostructures made of poly(N-isopropylacrylamide) via the molecular dynamics method has been studied. The structure of this polymer can change based on the temperature of the environment, so that by increasing the temperature the structure becomes hydrophobic. This property has been studied and the effect of multiple factors on the slip length is presented. The effects of the number of monomers in the polymer, the distance between the polymers, and the temperature on the flow field are investigated. The results reveal that the slip length and the flow rate increase with the temperature but both have a maximum with respect to the distance between the polymers and the number of monomers. For different temperatures considered in the study, the minimum friction occurs when the number of monomers and the distance are equal to 30 and 80, respectively. In this condition, the slip length increases by 180% and the flow rate rises by 200%. We also study the effect of air fraction in the fluid. The results indicate that by increasing the air fraction to 30%, the slip length and the flow rate increase by 250% and 310%, respectively.