Influence of water in the different states on a structure and dielectric properties of microcrystalline cellulose were studied by of X-ray, thermogravimetry, and dielectric spectroscopy. At research of microcrystalline cellulose (MCC) with different content of water, it is shown that the molecules of water are located in the macropores of MCC and in multimolecular hydrated layers. It is shown that at the increase of concentration of water in a hydrated shell, the reorganization of molecules of cellulose in the surface of crystallites takes place, and as a result, their transversal size and crystallinity increase. It is shown that during the concentration of water, more than 13% in a continuous hydrated shell of crystallites appears. Temperature dependences of actual and imaginary parts of complex dielectric permittivity were studied in the interval of temperatures [−180 ÷ 120] °C on frequencies of f = 5, 10, 20, and 50 kHz. A low-temperature relaxation process and high-temperature transition were observed. Low-temperature relaxation process which is related to transition of surface methylol groups of molecules of cellulose conformation from tg to tt is shifted toward low temperatures at the increase of concentration of water in microcrystalline cellulose.
The viscosity, turbidity, and heat capacity of dilute aqueous solutions of hydroxypropyl cellulose have been studied in a concentration interval of 0.047-1.5 g/l and a temperature interval of 20-80 ∘ C. The data obtained testify that, if the temperature does not exceed 40 ∘ C, hydroxypropyl cellulose molecules are prolate spheroidal globules with semiaxis lengths of 7 and 490Å. At temperatures above 70 ∘ C, the hydroxypropyl cellulose solution consists of clusters; every cluster is composed of 11 globules and has a prolate spheroidal form with semiaxes of 41 and 490Å. In the temperature interval from 40 to 70 ∘ C, the solution concerned contains both globules and clusters, with the concentration of the latter increasing, as the temperature grows.K e y w o r d s: hydroxypropyl cellulose, globule, rigid-chain polymer.
The phase equilibrium condition is shown to be strictly satisfied only in the thermodynamic limit. The notion of melting temperature in the thermodynamic limit is introduced. Formulas are obtained that determine the melting conditions and the melting temperature for finite systems including nanocrystals. The validity of those formulas is confirmed, by comparing them with experimental data for organic materials in porous solids.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.