Paper Number
SF14
Session
Surfactants, Foams and Emulsions
Title
Drainage via stratification in freestanding films made with polymer-surfactant complexes
Presentation Date and Time
October 11, 2022 (Tuesday) 1:50
Track / Room
Track 7 / Ontario
Authors
- Xu, Chenxian (University of Illinois Chicago, Department of Chemical Engineering)
- Martinez, Carina (University of Illinois Chicago, Department of Chemical Engineering)
- Sharma, Vivek (University of Illinois Chicago, Department of Chemical Engineering)
Author and Affiliation Lines
Chenxian Xu, Carina Martinez and Vivek Sharma
Department of Chemical Engineering, University of Illinois Chicago, Chicago, IL
Speaker / Presenter
Xu, Chenxian
Keywords
foams; polymer solutions; surfactants
Text of Abstract
Freestanding films of soft matter exhibit stratification due to confinement-induced structuring and layering of supramolecular structures like micelles. In many cosmetics, foods, pharmaceuticals, and petrochemical applications, often polymers are added to surfactant solutions as rheology modifiers. Interaction between neutral polymers like PEO and monomers and micelles of anionic surfactants like SDS results in the formation of polymer-surfactant complexes and changes both interfacial properties and bulk shear rheology response. The influence of such polymer-surfactant complexes on foam formation, stability, drainage, and lifetime is not well-understood and motivates this study. In this contribution, we show foams formed with PEO-SDS mixtures exhibit three features of stratification: step-wise thinning, co-existence of thick thin regions, and formation of nanoscopic topological features like nanoridges and mesas. The nanoscopic thickness variations and transitions in foam films are characterized using interferometry, digital imaging, and optical microscopy (IDIOM) protocols, with unprecedented high spatial (thickness < 10 nm, lateral ~500 nm) and temporal resolution (< 1 ms). We characterize the variation in surface tension, shear viscosity, and extensional relaxation time as a function of surfactant concentration at fixed polymer concentration. By complementing with tensiometry and rheometry measurements, we seek an understanding of the influence of added polymer on forces, flows, and fluxes that drive drainage via stratification, and model drainage via thin-film equation amended with thickness-dependent disjoining pressure.