*2.1. Chemicals*

Azobenzene derived molecules possess two stable geometric isomers: an energetically stable *trans* form and a meta-stable *cis* form. For most azobenzenes, molecules can be optically isomerized from *trans* to *cis* using light in the near UV and Visible: upon absorption of a photon with a wavelength in the near UV (around 330 nm), molecules convert, with high efficiency, from the *trans* isomer into the *cis* isomer. A second photon with a wavelength in the visible range (around 440 nm) can induce the back-conversion. UV illumination can also enable conversion of azobenzene molecules from a *cis* form to a *trans* form as photons of UV light have higher energy than visible light, which is sufficient to induce *cis* to *trans* isomerization. Azobenzene photo-isomerization is completely reversible and both forward and reverse photoisomerizations typically exhibit picosecond timescales. The *trans* isomer is thermodynamically more stable than the *cis* isomer, by approximately 50–100 kJ/mol and the energy barrier for thermal isomerization is in the order of 100–150 kJ/mol. Hence, in the dark, the *cis* isomer thermally relaxes back to the *trans* isomer on a timescale ranging from milliseconds to hours, or even days, depending on the substitution pattern around the azobenzene group and the local environment of the molecules.

We synthesized a new fluorinated azobenzene derivative surfactant polymer, named in this study KryAz600. It consists of a triblock copolymer surfactant, composed of a perfluoro-polyether (PFPE) hydrophobic chain, linked to a polyethylene-glycol (PEG-600) hydrophilic chain (Sigma-Aldrich, Saint-Quentin Fallavier, France) through an azobenzene group, as shown in Figure 2. The PFPE hydrophobic chain was derived from a commercially available carboxy-terminated fluorinated polymer, namely Krytox 157-FSH (Dupont) and linked to the azobenzene group following a similar procedure as described in detail by Lee et al. [25], see also supporting information at (S1) for details.
