Molecular Studies of Phase Transitions in Soft Matter: The Lower Critical Solution Temperature Transition Études moléculaires de transitions de phases dans la matière molle: LCST

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In this 5-year research program, we want to exploit the powerful multi-scale approach to study a topic of great scientific and technological interest: Lower Critical Solution Temperature (LCST) in thermoresponsive polymers. Above the LCST, thermoresponsive polymers in aqueous solution show a decrease in their solubility, resulting in phase separation. Due to its particular technological and biomedical interests, such phenomenon has been increasingly scrutinized over the past two decades. Despite numerous studies, many fundamental questions remain not fully understood such as the transition from coil-to-globule (CTG), the aggregate formation and their stability, the co-monomer and the cononsolvency effects. Conceptually, a phase transition is a collective phenomenon. Evaluating a cooperativity length, through an accurate depiction of atomic interactions, and a fortiori molecular arrangement, will make the description of phase transition invaluable, and allow unveiling molecular changes. The universal character, inherent to thermodynamics, or to the mean-field model, of a phase transition must be considered as a limit. The proposed research program is thus aimed at addressing such important and fundamental questions by exploiting the multi-scale approach. This study is part of a longer and ambitious research program: molecular study of phase transitions. This captivating research domain exposes the fact that well-established thermodynamic transitions are not well understood on the molecular level. Significant issues exist and need to be considered: discreteness versus continuity; finite to infinite size consideration of statistics with Avogadro number of molecules; reductionism versus emergence; specific interactions/fluctuations versus mean-field. Many important problems of complexity are related in one way or another with the presence of phase transition phenomena. Cancer can be considered as the onset of phase transition.