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@ARTICLE{Blayo:861706,
author = {Blayo, Camille and Houston, Judith E. and King, Stephen M.
and Evans, Rachel C.},
title = {{U}nlocking {S}tructure–{S}elf-{A}ssembly {R}elationships
in {C}ationic {A}zobenzene {P}hotosurfactants},
journal = {Langmuir},
volume = {34},
number = {34},
issn = {1520-5827},
address = {Washington, DC},
publisher = {ACS Publ.},
reportid = {FZJ-2019-02136},
pages = {10123 - 10134},
year = {2018},
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.},
cin = {JCNS-FRM-II / Neutronenstreuung ; JCNS-1},
ddc = {540},
cid = {I:(DE-Juel1)JCNS-FRM-II-20110218 /
I:(DE-Juel1)JCNS-1-20110106},
pnm = {6G4 - Jülich Centre for Neutron Research (JCNS) (POF3-623)
/ 6G15 - FRM II / MLZ (POF3-6G15)},
pid = {G:(DE-HGF)POF3-6G4 / G:(DE-HGF)POF3-6G15},
experiment = {EXP:(DE-MLZ)External-20140101},
typ = {PUB:(DE-HGF)16},
pubmed = {pmid:30071720},
UT = {WOS:000443524300027},
doi = {10.1021/acs.langmuir.8b02109},
url = {https://juser.fz-juelich.de/record/861706},
}