New insights into the viscosity features of cationic polyacrylamide
microgels in aqueous solutions
Guanghui Li , Xiaoyun Zhao, Qingzhong Chu
Department of Petroleum Engineering, College of Vehicles and Energy in Yanshan University, Qinhuangdao 066004, China
Correspondence to: G. Li (E -mail: email@example.com)
Increasing attention has recently been paid to the rheological behavior of microgel colloids and to the physical forces that
control their behavior. Here, based on a series of cationic microgels that were synthesized by inverse microemulsion polymerization,
the physical forces were explored by viscosity analysis of swollen microgels with different crosslinking densities and cationic contents.
The results indicate that within a wide concentration range, the viscosity curves for these cationic microgels perfectly correspond to
the Krieger–Dougherty model as modified by Tan et al. In particular, the specific volume in this model decreases at the critical over-
lapping concentration and reveals the interaction intensity between neighboring microgels. Furthermore, the viscosity index in the
Herschel–Bulkley equation indicates that the interaction domain among microgels undergoes a transfer from an electroviscous effect
to osmotic deswelling with increasing concentrations.
2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46297.
oil and gas; rheology; viscosity and viscoelasticity
Received 28 September 2017; accepted 15 January 2018
In recent years, the phenomenon of colloidal soft particles has
become an important field of research due to the growing inter-
est in a variety of important systems that are found in the bio-
logical sciences, such as vesicles, membranes, and living cells.
Numerous studies have provided new insights into the rheologi-
cal behavior of microgel colloids and the physical forces that
control their behavior. The aqueous solution viscosity and the
shear thinning behavior of such systems increase dramatically
leading to various commercial applications such as profile con-
trol in petroleum engineering.
This viscosity behavior is
attributed to physical forces such as polymer chain entangle-
ment, electrostatic interactions, and osmotic deswelling among
swollen microgels. For profile control, commonly used micro-
gels were crosslinked by thermolabile and thermostable cross-
linkers. A “popcorn” mechanism of microgels for profile control
has been proposed.
Due to the degradation of thermolabile
crosslinkers under controlled conditions, microgels are largely
swollen to viscosify the work fluid and reduce the permeability
of water-channeling pores by adsorption and a bridging effect.
Given this mechanism, a series of cationic microgels were pre-
pared for profile control to improve the physical forces between
the swollen microgels.
The properties and mechanisms of these microgels have been
The viscosity of microgel solutions plays an
important role in the improvement of conformation by
reducing the mobility ratio of water to oil. The microgels that
were used were classified by several systems according to viscos-
ity ranges at different times and temperatures.
under poor conditions of formation, microgel systems for
profile control become more concentrated,
and some even
exceed the applicable scope (<0.60%) of the empirical viscosity
Here, we report on the preparation of two series of cationic
polyacrylamide microgels with different crosslink densities or
cationic content using inverse microemulsion polymerization.
The Krieger–Dougherty (K–D) model as modified by Krieger
was introduced to describe the viscosity
behavior of microgel solutions at high concentrations. Based on
these findings, the physical forces that control their behavior,
and some new viscosity features, were identified. This research
will provide new insight into microgel systems and can assist in
the selection of viscosity models for simulating microgel seepage
in porous media.
THEORY AND METHODS
The Rheological Theory of Microgels
A microgel solution is actually a type of particle suspension sys-
tem. The relationship between viscosity and particle volume
fraction in a dilute zone was first described by Einstein in
2018 Wiley Periodicals, Inc.
J. APPL. POLYM. SCI. 2018, DOI: 10.1002/APP.46297
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