How Detergents Dissolve Polymeric Micelles: Kinetic Pathways of Hybrid Micelle Formation in SDS and Block Copolymer Mixtures.

Synne Myhre,Kenneth D Knudsen,Lutz Willner,Reidar Lund,Matthias Amann

doi:10.1021/acs.langmuir.0c02123

Synne Myhre, Kenneth D Knudsen + Show 3 more

Open Access

PDF Available

https://doi.org/10.1021/acs.langmuir.0c02123

Copy DOI

Export

Save

Cite

Abstract
Highlights/Summary
Full-Text PDF
Similar Papers

Abstract

Listen

Mixtures of amphiphilic polymers and surfactants are used in a wide range of applications, e.g., pharmaceuticals, detergents, cosmetics, and drug delivery systems. Still, many questions remain on how the structure and, in particular, the kinetics of block copolymer micelles are affected in the presence of surfactants and what controls the solubilization kinetics. In this work, we have studied the stability and solubilization kinetics of block copolymer micelles upon the addition of the surfactant sodium dodecyl sulfate (SDS) using small-angle X-ray/neutron scattering. The ability of the surfactant to dissolve polymer micelles or form mixed micelles has been investigated using two types of amphiphilic polymers, poly(ethylene-alt-propylene)–poly(ethylene oxide) (PEP1-PEO20) and n-alkyl-functionalized PEO (C28-PEO5). The exchange kinetics of C28-PEO5 micelles are in the order of hours, while PEP1-PEO20 micelles are known to be frozen on a practical timescale. In this work, we show that the addition of SDS to PEP1-PEO20 provides virtually no solubilization, even after an extended period of time. However, upon adding SDS to C28-PEO5 micelles, we observe micellar dissolution and formation of mixed micelles occurring on the timescale of hours. Using a coexistence model of mixed and neat micelles, the SAXS data were analyzed to provide detailed structural parameters over time. First, we observe a fast fragmentation/fission step followed by a slow reorganization process. The latter process is essentially independent of concentration at low volume fraction but is greatly accelerated at larger concentrations. This might indicate a crossover from a predominance of molecular exchange to fusion/fission processes.

Highlights

The self-assembly of amphiphilic molecules is a highly abundant phenomenon occurring in complex structures like biological membranes as well as commercial systems, such as detergents and food products
The reference average scattering is obtained by measuring the reservoirs at the same concentration separately and adding the intensities, which gives the theoretical scattering if there were no interactions or structural change
The data could be consistently fitted by the mixed micelle model described in Determining the Molecular Exchange Kinetics using time-resolved Small-Angle Neutron Scattering (SANS) (TR-SANS) and indicated that that sodium dodecyl sulfate (SDS) is inserted into the PEP1-PEO20 micelles

Summary

■ INTRODUCTION

The self-assembly of amphiphilic molecules is a highly abundant phenomenon occurring in complex structures like biological membranes as well as commercial systems, such as detergents and food products. To determine whether molecular exchange kinetics is active in the presence of surfactants for the PEP1-PEO20 system, we employed the kinetic zero average contrast (KZAC) SANS technique.[25,46] The method is based on mixing proteated (H) and deuterated (D) micelles in an H2O/D2O mixture that matches the average of the scattering length density of the two micelles and measuring the time-dependent neutron intensity. Evolution of the structural parameters on a logarithmic scale where C28-PEO5 was held constant at 5.00 mg/mL and SDS varied: (a) fraction of SDS in the mixed micelles ( f SDSm) and (b) aggregation number of polymer (Napgg(t)) over time, fitted with the kinetic model.

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES