Hypothesis: The sol-gel transition in aqueous suspensions consisting of silica particles and thermosensitive polymer is controlled by inter-particle forces and solution properties of the polymer. Addition of a second non-thermosensitive polymer may affect the transition. The purpose of this work was to characterize the kinetics of the sol-gel transition and to understand the effects of a second non-thermosensitive polymer on the microstructure, using a combination of classical rheology and microrheology. Experiments: Classical rotational rheology as well as two microrheology methods, Multiple Particle Tracking (MPT) and Diffusing Wave Spectroscopy (DWS), were used to investigate the sol-gel transition of a ternary silica-Pluronic F127-starch thermosensitive system. Findings: Classical rheometry and DWS indicated sol-gel transition temperature similar to 25 degrees C at 1 wt% Pluronic, independently of the concentration of the other components. DWS showed a fast gelation process, less than two minutes for all samples, beside a second slow kinetic process. In the gel state, MPT indicated micro-structural and micro-viscoelastic differences compared to rotational rheology. This was explained by formation of an elastic matrix of silica and polymers in combination with assembly of silica particles in large macroporous agglomerates. Presence of starch led to breakdown of the macro porous network, leaving the homogeneous elastic network left.

In this study a systematic investigation of the temperature effect on the interactions between Pluronic F127 and hydroxypropylated oxidised potato starch by surface tension titrations and quartz crystal microbalance (QCM) analysis is presented. The binary mixture examined was subjected to 20 degrees C and 30 degrees C and the results indicated no presence of binary complexes at the lower temperature. However, at elevated temperature, an ability for inclusion complex formation was detected by the here used independent techniques. The formed inclusion complexes at 30 degrees C are presumably a product of hydrophobic interaction between Pluronic F127 and starch, where starch acts as a host molecule and Pluronic F127 due to its increased hydrophobicity is the guest molecule in this complex. (C) 2017 Elsevier Ltd. All rights reserved.

The colloidal stability of a model paper coating dispersion consisting of silica particles, Pluronic F127, starch and glycerol was studied with respect to PF127 temperature responsiveness and its adsorption on the silica surface. Rheological characterization of this system in order to extract structural information for the wet suspension state was accomplished in terms of rotational tests. The analysis, done by Krieger-Dougherty model and the elastic floc model for all flow curves at three different temperatures, 20 degrees C, 25 degrees C and 30 degrees C, and at different particle volume fractions (phi between 0 and 0.31), revealed that the structure of the system changes. Two regions with different behaviour and a plateau region at particle volume fraction of phi similar to 0.16 were observed. At phi <= 0.16 temperature was affecting the suspension structure. By rising the temperature the well dispersed suspension at 20 degrees C transformed to flocculated one, where the higher the temperature was, more open floc structures were detected in terms of degree of flocculation parameter, C-fp, but at the same time with increasing the particle concentration the flocs got denser according to the calculated. At phi >= 0.16, there were not detected major structural differences by changing temperature or particle concentration. At phi similar to 0.16 a plateau in yield stress values was observed. The behaviour of the investigated model coating suspension was discussed in terms of shear stresses and C-fp. 

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, empty set. The results revealed a dense disordered liquid-like state at empty set less than or similar to 0.10, where the strength of attraction between particles increased with increasing particle volume fraction and increasing temperature, a solid-like microcrystalline state at empty set greater than or similar to 0.20, where the temperature did not affect the rheology of the system and a solid-like microcrystalline state were coexisting at empty set similar to 0.16. The structures detected by rheology were related to the dried structures of the corresponding suspensions. At empty set less than or similar to 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.