Abstract
Suspensions of silica nanoparticles showed shear-thickening profiles under steady shear conditions up on addition of a small amount of poly(ethylene oxide) (PEO). The suspensions turned into gels upon shaking and their fluidity was recovered several minutes after resting. We studied the rheological properties of these shake gels with small amounts of sodium chloride (NaCl). Gelation occurred at lower shear rates upon addition of small amounts of NaCl. In addition, the time taken by the gelated samples to recover their original viscosity increased with the increasing NaCl content. The weakened repulsive interactions between the silica particles upon NaCl addition lead to particles in closer proximity, and three-dimensional networks of PEO chains are easily formed as the electric double layer of the particles becomes thinner.
Highlights
When considering suspensions of fine particles in polymer solutions, the polymer chains can adsorb to different particles, binding them together and creating polymer bridges [1] [2] [3] [4]
The weakened repulsive interactions between the silica particles upon NaCl addition lead to particles in closer proximity, and three-dimensional networks of poly(ethylene oxide) (PEO) chains are formed as the electric double layer of the particles becomes thinner
The shear rate is reduced upon gelation due to weakening of the repulsive interactions between silica particles
Summary
When considering suspensions of fine particles in polymer solutions, the polymer chains can adsorb to different particles, binding them together and creating polymer bridges [1] [2] [3] [4]. In order to bridge large particles, several polymer chains must attach to the surface of the particles. In this scenario, each polymer molecule binds the particles at multiple positions of the chain and it is hard to break all those points of attachments imultaneously. For small particles of diameter
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