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.

A cellulose liquid crystal motor: a steam engine of the second kind

“…These micro-fibrils, in turn, associate to form supermolecular rod-like fragments, resulting in a network of rigid rod-like fragments joined together by flexible polymer linkages. As the polymer concentration is increased, the increasingly densely packed rodlike fragments become parallel, and liquid crystal mesophases are formed5.…”

Solvent dynamics in a reverse micellar water-pool: a spectroscopic investigation of DDAB–cyclohexane–water systems

“…Steady-state and time resolved fluorescence measurements have been carried out using Coumarin 500 (C-500), which has extensively been used as a fluorophore to study the relaxation dynamics of water in confined systems. 31,[64][65][66][67] The absorption spectrum of C-500 in Cy has a peak at B360 nm along with a shoulder at B380 nm. C-500 is sparingly soluble in water and produces a peak at B390 nm.…”

“…Such temperature induced transition could be correlated with an Arrhenius type of transition in the following manner. It has been established in earlier studies 31,32,66,67,75,76 that the transition of water molecules at the RM and other microheterogeneous assemblies follows an Arrhenius type barrier crossing model given as:…”

Thermal inverse phase transition of azobenzene hydroxypropylcellulose in aqueous solutions

“…Due to nontoxicity, biodegradability and biocompatibility, it has been generally recognized safe by the U.S. Food and Drug Administration for application in many fields as pharmaceutical, food, biomedical, thickener, and binder (Gong et al 2012;Patra et al 2012). It has attracted much research attention because it resonates with the concept of green chemistry and sustainable material world (Lott et al 2013b).…”