Light-responsive and self-healing behavior of azobenzene-based supramolecular hydrogels

Martina Salzano de Luna; Valentina Marturano; Marina Manganelli; Chiara Santillo; Veronica Ambrogi; Giovanni Filippone; Pierfrancesco Cerruti

doi:10.1016/j.jcis.2020.02.038

Light-responsive and self-healing behavior of azobenzene-based supramolecular hydrogels

J Colloid Interface Sci. 2020 May 15:568:16-24. doi: 10.1016/j.jcis.2020.02.038. Epub 2020 Feb 12.

Authors

Martina Salzano de Luna¹, Valentina Marturano², Marina Manganelli³, Chiara Santillo⁴, Veronica Ambrogi², Giovanni Filippone⁵, Pierfrancesco Cerruti⁶

Affiliations

¹ Department of Chemical, Materials and Production Engineering (INSTM Consortium - UdR Naples), University of Naples Federico II, P.le Tecchio 80, 80125 Naples, Italy; Institute for Polymers, Composites and Biomaterials, National Research Council of Italy, P.le E. Fermi 1, 80055 Portici, Italy.
² Department of Chemical, Materials and Production Engineering (INSTM Consortium - UdR Naples), University of Naples Federico II, P.le Tecchio 80, 80125 Naples, Italy; Institute for Polymers, Composites and Biomaterials, National Research Council of Italy, Via Campi Flegrei 34, 80078 Pozzuoli, Italy.
³ Department of Chemical, Materials and Production Engineering (INSTM Consortium - UdR Naples), University of Naples Federico II, P.le Tecchio 80, 80125 Naples, Italy.
⁴ Institute for Polymers, Composites and Biomaterials, National Research Council of Italy, P.le E. Fermi 1, 80055 Portici, Italy.
⁵ Department of Chemical, Materials and Production Engineering (INSTM Consortium - UdR Naples), University of Naples Federico II, P.le Tecchio 80, 80125 Naples, Italy; Institute for Polymers, Composites and Biomaterials, National Research Council of Italy, P.le E. Fermi 1, 80055 Portici, Italy. Electronic address: gfilippo@unina.it.
⁶ Institute for Polymers, Composites and Biomaterials, National Research Council of Italy, Via Campi Flegrei 34, 80078 Pozzuoli, Italy.

PMID: 32070851
DOI: 10.1016/j.jcis.2020.02.038

Abstract

Hypothesis: Multi-component supramolecular hydrogels are gaining increasing interest as stimuli-responsive materials. To fully understand and possibly exploit the potential of such complex systems, the hierarchical structure of the gel network needs in-depth investigations across multiple length scales. We show that a thorough structural and rheological study represents a crucial pillar for the exploitation of this class of functional materials.

Experiments: Supramolecular hydrogels are prepared by self-assembly of hexadecyltrimethylammonium bromide (CTAB) and azobenzene-4,4'-dicarboxylic acid (AZO) in alkaline aqueous solution. The CTAB/AZO concentration was varied from ϕ = 0.25 to 4 wt% keeping the CTAB:AZO molar ratio fixed at 2:1. The systems were thoroughly studied through a combination of X-ray scattering, microscopy, rheological and spectroscopic analyses.

Findings: The CTAB/AZO solutions form a self-supporting gel with nanofibrillar structure below ~30 °C. The critical gelation concentration is ϕ_c = 0.45 wt%. Above this threshold, the gel elasticity and strength increase with CTAB/AZO content as ~(ϕ-ϕ_c)¹. The hydrogels exhibit self-healing ability when left at rest after a stress-induced damage. Moreover, the light-induced isomerization of the AZO moieties provides the gel with light-responsiveness. Overall, the multi-stimuli responsiveness of the studied CTAB/AZO hydrogels makes them a solid starting point for the development of sensors for mechanical vibrations and UV/visible light exposure.

Keywords: Photorheological fluid; Rheology; Self-assembly; Self-healing; Stimuli-responsive; Supramolecular gel.