TITLE:
Clusters: Viscosity Cause?
AUTHORS:
V. P. Malyshev, A. M. Makasheva
KEYWORDS:
Dynamic Viscosity, Cluster, Associate, Temperature, Fluidity, Activation Energy
JOURNAL NAME:
Open Journal of Physical Chemistry,
Vol.9 No.3,
July
22,
2019
ABSTRACT: The significance of the work is determined by the need to develop a
cluster theory of the liquid state of a substance in order to more deeply
substantiate the viscosity, which is still expressed by empirical parameters
within the framework of ideal ideas about the stratified flow of a liquid.
According to the reference data on the dynamic viscosity of the melts for
chlorides of the first group of the Periodic System, the approximating
dependences in the form of cluster-associate and Frenkel’s models were
constructed at various temperatures. The first model is based on taking into
account the share of particles that cannot overcome the thermal melting barrier
and thus serve to form virtual clusters and associates while preserving the
structural motifs of the solid phase. In the framework of the cluster-associate
viscosity model developed by the authors, these formations determine the melt
viscosity and serve as flow units to which the energy of fluid motion is
applied. The Frenkel’s model allows us to
estimate the activation energy of fluidity. Calculations show that by comparing
this energy with the degree of cluster association obtained in the framework of
the cluster-associate model, a fairly close linear correlation is obtained, and
the proportionality coefficient has the meaning of the activation energy per
cluster. This energy does not go beyond the van der Waals energy of the
unsaturated intermolecular bond characteristic of the interaction of particles
in a liquid. This confirms the earlier established by the authors a similar
pattern for melts of simple substances, based on the understanding of fluidity
as a consequence of the destruction of cluster associates while preserving the
clusters themselves.