Multi-Scale Modeling and Rheological Approaches for Understanding the Structure-Property Relationships of Surfactant Solutions.

structure-property relationship;multiscale modeling;rheology;surfactant;Chemical Engineering;Engineering;Chemical Engineering

Tang, XuemingGlotzer, Sharon C. ;

University of Michigan

关键词: structure-property relationship;    multiscale modeling;    rheology;    surfactant;    Chemical Engineering;    Engineering;    Chemical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/111497/xuemtang_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

In this work, we applied multi-scale modeling and rheological measurements to understand the structure-property relationships of surfactant solutions. We used molecular dynamics (MD) and dissipative particle dynamics (DPD) simulations to address behavior extending from the molecular level to the micellar mesoscale, the Cates model to bridge the micellar mesoscale to macroscale rheological behavior, and rheometry to measure rheological behavior and compare it to predictions of the Cates model.Starting with a simple surfactant, sodium dodecyl sulfate, we compared force field effects on micellar properties at various aggregation numbers by MD simulations. We found the parameters that control the shape of large micelles were the Lennard-Jones parameters of Na+ and ionic oxygen atoms, as well as the water model, which controls hydration of Na+ in the presence of surfactants. These parameters control the degree of binding of Na+ to ionic oxygens and head group packing, and resulted in different micellar shapes.We also studied structure-property relationships of a commercial surfactant mixture, polyoxyethylene (PEO) sorbitan oleates, which contains multiple species and were represented as five ;;typical” structures varying the lengths of EO head groups and the number of tails using MD simulations. We found structures with more than one tail, and with shorter EO head group that attaches the tail to the sorbitan ring, pack more efficiently within micelles and at interfaces. This efficient packing leads to lower interfacial tensions at air–water and oil–water interfaces at the same surfactant interfacial density.Finally to assess the behavior of complex body washes containing cylindrical micelles, we studied the effects of salts (NaCl) and perfume raw materials (PRMs) by combining results from rheology, the micellar Cates model, and DPD modeling. We determined the relationship between viscosity and average micelle length, and elasticity and micellar characteristic time. Salts modify viscoelasticities of body washes by condensing Na+ near micellar surface, changing surfactant head groups packing, and maintaining the cross-section radius constant. PRMs modify viscoelasticities of body washes by partitioning into the micelles according to their octanol/water partition coefficients and chemical structures, adjusting surfactant packing at head and/or tail regions, and possibly changing the cross-section radius.