About the influence of carbon nanotubes on rheological and viscoelastic properties of polyacrylamide aqueous solutions

This paper presents a comprehensive study on rheological and viscoelastic properties of aquatic solutions of polyacrylamide (PAM) which is modified by single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWVNTs). Research was conducted with a modular rheometer at the temperature of 25 °C. The tested compositions with the base of PAM (0.05 wt. %) exhibit pseudo-plastic behavior and their elastic properties exceed viscous properties in the linear range of shearing strain. It was found that added carbon nanotubes (CNT) result in a considerable change in rheology characteristics. The nanotube concentration growth causes as increase in efficient viscosity, consistency index and reduction in the flow behavior index. The viscoelastic modulus ( G ′ и G ″) increases as well: this demonstrates an almost linear dependency on the CNT content. The study shows a fundamental difference in efficiency of two types of nanotubes. The SWCNT suspension creates a stronger modification impact as compared with the MWCNTs. At the same concentration (0.1 wt. %), the value of consistency index for SWNT solution is by 2.2 times higher, but the elasticity modulus G ′ in by 3.15 times higher that the same PAM water solution modified by MWCNTs. The main reason is a very high aspect ratio for SWNT: this creates a strong percolating network even at lower threshold concentrations. The research demonstrated that addition of carbon nanotubes can be an efficient tool for the control of rheological and viscoelastic properties of PAM water solutions (and modification degree depends on the type and concentration of nanotubes).