15:00-15:45

Photo-triggered assemblies of amphiphilic copolymers with and with no surfactants: experimental studies and model predicting the response to light

Amphiphilic copolymers form in aqueous solutions co-assemblies, for instance with micelles of surfactants, lipids. They also form self-assemblies upon transferring a fraction of their hydrophobic groups from water into apolar clusters. The energy balance between attractive hydrophobic binding and intra/inter chain repulsions controls these assemblies, that are used since decades to tailor properties of complex fluids, for instance emulsions, physical gels, dispersion of cargoe-particles for drug delivery, etc… In practice, the hydrophobic drive toward (self-)assembly can be modulated at the microscopic level upon variation of control parameters (pH, temperature, or exposure to stimuli: e.g. light), which in turn provide remote control of macroscopic properties. We tailor azobenzene-modified copolymers to achieve marked photo-switch in such assemblies. Experimental illustrations include mixed micellization with surfactants⁽¹⁾, and photo-triggered permeabilization of lipid and plasma membrane of mammal cells⁽²⁾. To analyze experimental data on the degree of hydrophobic binding of polymer chains, we propose a model based solely on one parameter: a critical hydrophobicity of a (bound) polymer segment⁽³⁾. This model is shown to reproduce the measured fractions of micelle-bound hydrophobes (here azobenzene) as a function of density of hydrophobic groups per chain. Non-monotonic variation of LCST are also predicted and experimentally evidenced. The model enables us to discuss a bottom up approach to the design of systems having optimal responses to light.

References

(1) J. Ruchman, S. Fouilloux, C. Tribet, Soft Matter, 2008, 4, 2098-2108.

(2) S. Sebai et al., Angewandte Chem. Int. Ed., 2012, DOI. 10.1002/anie.201106777

(3) J. Ruchman, S. Sebai, C. Tribet, Macromolecules, 2011, 44, 604-611.

Speaker

Dr. Christophe Tribet, Department of Chemistry, The École normale supérieure (ENS), France

Chair

Prof. Francoise Winnik, MANA Satellite PI, NIMS