Understanding, tuning and using the collapse transition of thermoresponsive polymer brushes

Abstract

This work focuses on the properties of surfaces grafted by responsive polymer brushes. Responsive polymer brushes are an assembly of macromolecules densely grafted from a surface, capable to respond to an external stimulus. They adapt their configuration according to external stimuli including temperature, pH or light. Responsive polymer brushes undergo dramatic variations of properties during the so-called collapse transition. In this work, the thermocollapse transition of polymer brushes from the well-swollen to the collapsed state was investigated in details, in order to describe finely the transition and exploit its specificities in a range of applications. The measurements reveal that the collapse mechanism consists first of the progressive collapse of the bulk of the brush occurring over a wide temperature range, followed by a sharp collapse of the surface occurring at a higher temperature. Reactive and carboxylic acid units were introduced along the backbone of the thermoresponsive polymer chains in order to tune the temperature of the collapse by other stimuli than temperature, such as pH or light. For instance, reactive and thermoresponsive polymer brushes were used as platforms to anchor photochromic trigger molecules in order to induce by light changes in the swelling of the polymer brushes. Furthermore, the coupling of an antibacterial peptide to a reactive and thermoresponsive polymer brush combined to the deeper knowledge of the details of the mechanism of the thermocollapse transition attained in this thesis, finally led to the fabrication of smart surfaces switching from antibacterial at room temperature to antifouling at physiological temperatures, for applications in medicine.(FSA 3) -- UCL, 201