Journal Article

FZJ-2019-02136

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Unlocking Structure–Self-Assembly Relationships in Cationic Azobenzene Photosurfactants

Blayo, C. ; Houston, J. E.FZJ* ; King, S. M. ; Evans, R. C. (Corresponding author)

2018
ACS Publ. Washington, DC

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Please use a persistent id in citations: doi:10.1021/acs.langmuir.8b02109

Abstract: Azobenzene photosurfactants are light-responsive amphiphiles that have garnered significant attention for diverse applications including delivery and sorting systems, phase transfer catalysis, and foam drainage. The azobenzene chromophore changes both its polarity and conformation (trans–cis isomerization) in response to UV light, while the amphiphilic structure drives self-assembly. Detailed understanding of the inherent relationship between the molecular structure, physicochemical behavior, and micellar arrangement of azobenzene photosurfactants is critical to their usefulness. Here, we investigate the key structure–function–assembly relationships in the popular cationic alkylazobenzene trimethylammonium bromide (AzoTAB) family of photosurfactants. We show that subtle changes in the surfactant structure (alkyl tail, spacer length) can lead to large variations in the critical micelle concentration, particularly in response to light, as determined by surface tensiometry and dynamic light scattering. Small-angle neutron scattering studies also reveal the formation of more diverse micellar aggregate structures (ellipsoids, cylinders, spheres) than predicted based on simple packing parameters. The results suggest that whereas the azobenzene core resides in the effective hydrophobic segment in the trans-isomer, it forms part of the effective hydrophilic segment in the cis-isomer because of the dramatic conformational and polarity changes induced by photoisomerization. The extent of this shift in the hydrophobic–hydrophilic balance is determined by the separation between the azobenzene core and the polar head group in the molecular structure. Our findings show that judicious design of the AzoTAB structure enables selective tailoring of the surfactant properties in response to light, such that they can be exploited and controlled in a reliable fashion.

Keyword(s): Polymers, Soft Nano Particles and Proteins (1st) ; Soft Condensed Matter (2nd)

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Contributing Institute(s):

1. JCNS-FRM-II (JCNS-FRM-II)
2. Neutronenstreuung (Neutronenstreuung ; JCNS-1)

Research Program(s):

1. 6G4 - Jülich Centre for Neutron Research (JCNS) (POF3-623) (POF3-623)
2. 6G15 - FRM II / MLZ (POF3-6G15) (POF3-6G15)

Experiment(s):

1. Measurement at external facility

Appears in the scientific report 2019

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Database coverage:
; Clarivate Analytics Master Journal List ; Current Contents - Physical, Chemical and Earth Sciences ; Ebsco Academic Search ; IF < 5 ; JCR ; NCBI Molecular Biology Database ; Nationallizenz ; SCOPUS ; Science Citation Index ; Science Citation Index Expanded ; Web of Science Core Collection

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