Paper Number
CC3 

Session
Confined and Coupled Systems

Title
Rheological behavior of unfilled and filled, uncrosslinked and ionically crosslinked guar solutions

Presentation Date and Time
October 7, 2014 (Tuesday) 10:50

Track / Room
Track 6 / Washington C

Authors (Click on name to view author profile)

1. Barbati, Alexander C. (MIT, Hatsopoulos Microfluids Laboratory)
2. Robisson, Agathe (Schlumberger, Schlumberger-Doll Research Center)
3. McKinley, Gareth H. (Massachusetts Institute of Technology, Department of Mechanical Engineering)

Author and Affiliation Lines (in printed abstract book)
Alexander C. Barbati¹, Agathe Robisson², and Gareth H. McKinley^1
1Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139-4307; ²Schlumberger-Doll Research Center, Schlumberger, Cambridge, MA 02139

Speaker / Presenter 
Barbati, Alexander C.

Text of Abstract
Guar-based materials are used in a variety of foodstuffs and industrial applications. Notably, crosslinked guar solutions are used to support proppant particles for hydraulic fracturing. In this process, solids must remain suspended throughout the flow. Thus, fracture engineering is sensitive to the rheology of the crosslinked guar material. A polysaccharide, guar consists of a mannose backbone with galactose side units in a ratio of approximately 2:1. On the addition of a crosslinker, the galactose side units are bridged creating an entangled ionic network. These physical crosslinks impart increased viscosity and elasticity to the guar solutions, and help sustain suspensions of sand and fibers that build additional structure and load-bearing stresses into this complex highly-filled viscoelastic material. Here, we perform a series of linear and nonlinear measurements to probe the rheological behavior of borate crosslinked and uncrosslinked guar solutions with and without dispersed particles. Small amplitude oscillatory shear (SAOS) tests reveal a rheological response reminiscent of the Green and Tobolsky temporary network model at low frequencies although this model does not capture the moderate and high frequency response. We demonstrate that a fractional Maxwell model with an additional Rouse-like element more accurately captures these data. SAOS data collected at elevated temperature and decreased crosslinker concentration reveal a systematic softening in G’, G’’, and a decrease in the SAOS relaxation (crossover) time of the material. Loading of spherical particles in the crosslinked guar up to 20 wt% appears not to affect the relaxation time, while the loss modulus increases with particle loading. Additionally, we perform steady shear experiments for loaded and unloaded guar and show that the material shear thins for low crosslinker concentrations. As the crosslinker concentration is increased, a pronounced shear thickening region is encountered beyond the initial shear thinning region.