title: Slow relaxation dynamics of water in hydroxypropyl cellulose-water mixture traces its phase transition pathway: a spectroscopic investigation.
abstract: In this study, we have explored the slow (of the order of several hundreds of picoseconds) relaxation dynamics of water associated with the hydration shell of a biocompatible polymer, hydroxypropyl cellulose (HPC)-water mixture as a function of HPC concentration using time-resolved fluorescence spectroscopy. The relaxation dynamics slows down with a progressive increase in HPC content indicating restriction of the relaxation pathway of water molecules specially beyond a cellulose concentration of 20% wherein an isotropic to liquid crystalline cholesteric microscopic phase separation sets in. The activation energy calculated from the temperature dependent solvation dynamics studies also shows a similar trend. The nucleophilic activity of water molecules in these mixtures is determined by measuring the reaction kinetics of solvolysis of benzoyl chloride, and the reaction rate exhibits a marked decrease as the phase separation sets in. The observed results are correlated with a transition between the 'bulk' and 'bound' type of water molecules present in the system.
authors.affiliation: Unit for Nano Science & Technology, Department of Chemical Biological and Macromolecular Sciences, S.N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700098, India.
authors.forename: Animesh
authors.initials: A
authors.lastname: Patra
authors.forename: Pramod Kumar
authors.initials: PK
authors.lastname: Verma
authors.forename: Rajib Kumar
authors.initials: RK
authors.lastname: Mitra
mesh_terms: D002482:Cellulose / Q000031:analogs & derivatives* / Q000737:chemistry; D008958:Models, Molecular; D044367:Phase Transition; D013050:Spectrometry, Fluorescence; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D002482:Cellulose; C008079:hydroxypropylcellulose