Abstract
Hydrophilic fumed silica (FS) and precipitated silica (PS) powders were suspended in mineral oil; increasing the silica volume fraction (φ in the suspension led to the formation of sol, pre-gel, and gel states. Gelation took place at lower φ values in the FS than the PS suspension because of the lower silanol density on the FS surface. The shear stresses and dynamic moduli of the FS and PS suspensions were measured as a function of φ. Plots of the apparent shear viscosity against shear rate depended on φ and the silica powder. The FS suspensions in the gel state exhibited shear thinning, followed by a weak shear thickening or by constant viscosity with an increasing shear rate. In contrast, the PS suspensions in the gel state showed shear thinning, irrespective of φ. The dynamic moduli of the pre-gel and gel states were dependent on the surface silanol density: at a fixed φ, the storage modulus G′ in the linear viscoelasticity region was larger for the FS than for the PS suspension. Beyond the linear region, the G′ of the PS suspensions showed strain hardening and the loss modulus G″ of the FS and PS suspensions exhibited weak strain overshoot.
Highlights
Pristine fumed silica (FS) powders produced by hydrolysis of silicone tetrachloride in a flame, such as hydrophilic or native fumed silica powders, have a low tendency to aggregate and to form agglomerates because of their lower surface density of silanol groups; this results in a lower bulk density compared with precipitated hydrophilic silica (PS) powders, produced by acid precipitation of sodium silicate
The preparation of FS suspensions in PDMS requires lower amounts of powders compared with PS suspensions (1); FS suspensions show a higher bound rubber content, defined as the amount of non-extractable PDMS rubber, than PS suspensions; this suggests that the silica/PDMS interaction is stronger in FS than PS suspensions, with larger adsorbed amounts of PDMS in the former (2); in the case of FS suspensions, the maximum loss modulus was observed at the end of the linear viscoelasticity region, whereas the loss modulus (G”) vs. strain curves of the PS suspensions showed no indications of strain-induced agglomeration (3)
Gelation of the FS suspensions took took place at lower silica concentrations compared with PS suspensions in mineral oil due to the less place at lower silica concentrations compared with PS suspensions in mineral oil due to the less surface surface silanol density and the less compact aggregated microstructures
Summary
Pristine fumed silica (FS) powders produced by hydrolysis of silicone tetrachloride in a flame, such as hydrophilic or native fumed silica powders, have a low tendency to aggregate and to form agglomerates because of their lower surface density of silanol groups; this results in a lower bulk density compared with precipitated hydrophilic silica (PS) powders, produced by acid precipitation of sodium silicate. Yziquel et have studied non-linear viscoelastic of FSthat suspensions in paraffin oil as a function of al They found the reduced storage oil as a function of particle size and silica concentration [16]. Reported the rheological properties of FS when suspensions in mineral oil as a was function of particle sizeetand reported the rheological properties of FS suspensions in mineral oilfound as a function particleviscosities size and silica concentration under steady and oscillatory shear [17]. Only few studies of PShave suspensions in simple liquids, aimed at understanding their stability and rheological properties, been reported, it can be expected that.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
