Influence of rhamnolipids, anionic surfactants, and <scp>Al₂O₃</scp> nanoparticles on the viscosity of distilled water‐based fluids: A comparative experimental study

Abstract This experimental study examines the effect of different surfactants—sodium lauryl sulfate (SLS), sodium dodecyl sulfate (SDS), and bio‐surfactant rhamnolipids (RHL)—on the viscosity of distilled water (DW) with varying concentrations of aluminium oxide (Al 2 O₃) nanoparticles (NPs). Al 2 O₃ NPs were used in concentrations ranging from 0.02 to 0.5 wt%, while surfactant concentrations ranged from 2000 to 4000 ppm for SDS and SLS and from 200 to 600 ppm for RHL. Viscometric experiments revealed that the type and concentration of surfactants, along with the NP loading, influenced the viscosity of nanofluids (NFs). NFs without surfactant exhibited consistently higher viscosities compared with DW with surfactant alone. At 0.5 wt% Al 2 O 3 , NF viscosity was 17% higher than SDS and RHL and 9% higher than SLS. Interestingly, in DW with both surfactant and NPs, viscosity initially decreased with increasing Al 2 O 3 concentration, followed by a rapid increase after 0.1 wt%. These results offer insights into the interaction between surfactants and NPs, relevant for industries requiring precise viscosity control, such as pharmaceuticals, cosmetics, and environmental applications.