Thermo sensitive behavior of cellulose derivatives in dilute aqueous solutions: from macroscopic to mesoscopic scale.

Thermal behaviors of thermo sensitive hydroxypropyl cellulose (HPC), methyl cellulose (MC) and methyl hydroxypropyl cellulose (MHPC) solutions have been investigated in dilute regime of concentration (C<C*) by means of optical density (OD), Quasi Elastic Light Scattering (QELS) and Pyrene Fluorescence Spectroscopy (PyFS) measurements. The importance of controlling the rate of a temperature sweep regarding to the kinetic of association has been demonstrated. MHPC copolymer exhibits only one thermal transition at macroscopic scale (OD and QELS) but two distinct thermal transitions have been evidenced at mesoscopic scale (PyFS) suggesting a double association step for each thermo associative group (i.e. hydroxypropyl and methyl). In HPC/MC mixture, HPC undergoes its own thermal transition. The presence of MC leads to a shift of the temperature of HPC precipitation toward higher temperature even in dilute regime.