Paper Number
FE15
Session
Foams, Emulsions, Surfactants, and Micelles
Title
Factors governing rod formation and growth in polymer micelles
Presentation Date and Time
October 12, 2021 (Tuesday) 9:50
Track / Room
Track 3 / Meeting Room A-B
Authors
- McCauley, Patrick J. (University of Minnesota, Chemical Engineering and Materials Science)
- Kumar, Satish (University of Minnesota, Chemical Engineering and Materials Science)
- Calabrese, Michelle A. (University of Minnesota, Chemical Engineering and Materials Science)
Author and Affiliation Lines
Patrick J. McCauley, Satish Kumar and Michelle A. Calabrese
Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455
Speaker / Presenter
McCauley, Patrick J.
Keywords
experimental methods; micelles; polymer solutions; surfactants
Text of Abstract
Wormlike micelles (WLMs) are elongated, flexible self-assembled structures used in drag reduction and cosmetic applications. While typically studied in small molecule surfactants, WLMs also form in amphiphilic block polymer solutions, where self-assembly can be tuned via block composition and molecular weight. Previous work on polymer WLMs examined limited block polymer compositions or primarily one solution condition like temperature or additive concentration; thus, a holistic picture of the role of these factors on polymer WLM formation and growth is lacking. Here, a series triblock poloxamers with polyethylene oxide (PEO) end blocks and polypropylene oxide (PPO) midblocks are examined comprehensively to determine the role of amphiphile characteristics (molecular weight, block molecular weight, PPO fraction) and solution conditions (temperature, inorganic salt concentration) on WLM formation and growth. In these systems, micelles undergo a sphere-to-rod transition and growth into WLMs with increasing temperature, eventually phase separating at the cloud point temperature. Salt addition reduces these transition temperatures, with most pronounced effects for poloxamers with high PEO molecular weights and PEO fractions. The local micelle structure determined via small-angle neutron scattering (SANS) is then connected with bulk rheological properties. Interestingly, the local microstructure is similar across poloxamers and sodium chloride (NaCl) and sodium fluoride (NaF) content. However, the growth of WLMs varies significantly, where bulk properties such as viscosity and relaxation time increase by orders of magnitude with increasing PPO and decreasing PEO block size. Increasing NaCl content dramatically increases micelle growth whereas NaF content has little impact, attributed to different anion-specific interactions with the micelle. These studies reveal key parameters dictating rod formation and growth in poloxamer micelles, providing a comprehensive dataset for developing or refining computational models.