Thermosensitive Silica-Pluronic-Starch model coating dispersion-Part II: The relationship between rheology and microstructure

Abstract

The colloidal interaction between the components in coating dispersions play a key role in the structural organization on a micro level, which has influence upon the macroscopic properties of the material. The viscoelastic properties of a model coating suspension, consisting of colloidal silica particles, a temperature-responsive triblock copolymer Pluronic F127 and starch were studied and related to the corresponding dried structures. Pluronic F127 was used in order to produce a temperature-sensitive starch system and to simulate the drying of a paper coating at a low shear rates. The gelation process was investigated by the change in storage modulus upon heating and the change in particle volume fraction, ϕ. The results revealed a dense disordered liquid–like state at ϕ≲0.10, where the strength of attraction between particles increased with increasing particle volume fraction and increasing temperature, a solid-like microcrystalline state at ϕ≳0.20, where the temperature did not affect the rheology of the system and a solid-like microcrystalline state were coexisting at ϕ∼0.16. The structures detected by rheology were related to the dried structures of the corresponding suspensions. At ϕ≲0.10 and elevated temperatures, a controlled formation of self-supporting floc structure was performed, which could be used to promote the even distribution of starch within the composite material.