Making microgels photo-responsive by complexation with a spiropyran surfactant

We report on triggering of p(NIPAM-AA) microgels' photo-responsiveness by making complexes with a spiropyran (SP) containing surfactant. Being dissolved in water, the SP surfactant in its merocyanine state bears three charges, while irradiation with UV and vis light leads to the partial or comp...

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Published inSoft matter Vol. 19; no. 22; pp. 488 - 498
Main Authors Sharma, Anjali, Gordievskaya, Yulia D, Lomadze, Nino, Bekir, Marek, Jung, Se-Hyeong, Pich, Andrij, Santer, Svetlana
Format Journal Article
LanguageEnglish
Published England Royal Society of Chemistry 07.06.2023
Subjects
Charge density
Complexation
Electromagnetic absorption
Hydrophobicity
Irradiation
Microgels
Phase transitions
Spiropyrans
Surfactants
Transition temperature
Transition temperatures
Ultraviolet radiation
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Summary:We report on triggering of p(NIPAM-AA) microgels' photo-responsiveness by making complexes with a spiropyran (SP) containing surfactant. Being dissolved in water, the SP surfactant in its merocyanine state bears three charges, while irradiation with UV and vis light leads to the partial or complete reversal of the SP state. The complexation of the photo-responsive amphiphile with swollen anionic microgels results in charge compensation within the gel interior and as a consequence its size reduces and the volume phase transition temperature (VPTT) decreases down to 32 °C. Under irradiation the MC form photo-isomerizes to a ring closed SP state generating a more hydrophobic surfactant with one positive charge at the head. The increase in the hydrophobicity of the surfactant and thus of the interior of the gel results in the reversible size change of the microgel. We investigate the photo-responsivity of the microgel as a function of wavelength and irradiation intensity, as well as of surfactant concentration and charge density of the microgel. We show that the change in the size and VPTT of the microgels during irradiation occurs through a combination of two processes: heating of the solution during light absorption by the surfactant (more pronounced in the case of UV irradiation) and the change in the hydrophobicity of the surfactant. We report on triggering of p(NIPAM-AA) microgels' photo-responsiveness by making complexes with a spiropyran (SP) containing surfactant.
Bibliography:c
Fig. S5. UV-Vis absorption spectra of 0.1 mM of MC and SP isomers, along with the values for the rate constants
MC,tot
MC-SP
https://doi.org/10.1039/d3sm00580a
k
in situ
SP-MC
MC
and
Video S1
with respect to time highlighting the values that can be obtained-
addition of the surfactant, Video S2a: photo-response of 5 mol% PAA gels in 2.5 mM SP, Video S2b: photo-response of 5 mol% PAA gels in 5 mM SP. See DOI
Electronic supplementary information (ESI) available: Section 1: Additional experimental details. Fig. S1. VPTT and the size change of 5 mol% microgels dispersed in 0.5 and 1.25 mM surfactant as a function of illumination intensity at 365 nm. Fig. S2. Shift in VPTT of microgels containing different PAA contents under dark and UV light (365 nm) conditions. Fig. S3. Change in the size of the neutral pNIPAM in the presence of 1.25 mM of surfactant under heating, illumination with UV, and combined treatment. Section 2: Kinetic study of photo- and thermo-isomerization. Fig. S4. A graphical representation of the decay of
MC,eq
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ISSN:1744-683X
1744-6848
DOI:10.1039/d3sm00580a