Effect of cellulose beads on shear-thickening behavior in concentrated polymer dispersions

Tuning rheological performance of silica concentrated shear thickening fluid by using boric acid as additive

Shear thickening fluid (STF) are non-Newtonian fluids that usually behave as liquid in normal condition however under sudden impact, they transformed into a solid like structure with abrupt rise in viscosity. The rheological properties of these fluids play a significant role in energy dissipation. In the present work, effect of boric acid (BA) as an additive for the fine tuning of shear thickening (ST) behavior of colloidal silica-based shear thickening fluids (STFs) was investigated. STFs were synthesized with silica particles (600 nm) in liquid polyethylene glycol (PEG-200). Both the steady state and dynamic rheological studies of STFs were carried out to compare ST behavior of BA based STFs with only silica-based STFs. In steady state rheology, it was observed that max. viscosity increases four time compared to only silica based STF. In dynamic rheology, it was observed that the maximum G′ and G″ of the STF composition (69% + 1.2% BA) at a frequency of 70 rad/s has increased by ∼41 times and ∼14 times, respectively, when the deforming strain reaches at 100% strain. Both the steady state and dynamic rheological analyses have confirmed that boric acid based STFs exhibited higher shear/strain thickening behavior, as well as higher energy absorption property.

Rheological and Technological Aspects in Designing the Properties of Shear Thickening Fluids

This work focuses on shear thickening fluids (STFs) as ceramic-polymer composites with outstanding protective properties. The investigation aims to determine the influence of raw material parameters on the functional properties of STFs. The following analyses were used to characterize both the raw materials and the STFs: scanning electron microscopy, dynamic light scattering, matrix-assisted laser desorption/ionization time-of-flight, chemical sorption analysis, rheological analysis, and kinetic energy dissipation tests. It was confirmed that the morphology of the solid particles plays a key role in designing the rheological and protective properties of STFs. In the case of irregular silica, shear thickening properties can be obtained from a solid content of 12.5 vol.%. For spherical silica, the limit for achieving shear thickening behavior is 40 vol.%. The viscosity curve analysis allowed for the introduction of a new parameter defining the functional properties of STFs: the technological critical shear rate. The ability of STFs to dissipate kinetic energy was determined using a unique device that allows pure fluids to be tested without prior encapsulation. Because of this, it was possible to observe even slight differences in the protective properties between different STFs, which has not been possible so far. During tests with an energy of 50 J, the dissipation factor was over 96%.

Impact of particle flocculation on the dissolution and bioavailability of injectable suspensions

Injectable suspensions occasionally exhibit variations in dissolution and bioavailability, which may impact the clinical outcome of the drug product. Here, variation in the injection method (i.e., applied shear) for triamcinolone acetonide (TA) injectable suspension (40 mg/mL) altered the flocculation state of the particles and subsequently their dissolution. Notably, TA suspensions contained primary particles of approximately 2 µm and secondary flocculates of tens of microns. The conversion between flocculated and deflocculated particles was rapid, reversible and highly shear dependent. As such, changing shear rates during laser diffraction (LD) measurement like stirring rate, sonication, and sample introduction method (micropipette vs 25-gauge needle) may result in variability in particle size distributions (PSD) that have the potential to alter drug dissolution. Furthermore, a non-sink, discriminatory in vitro release testing (IVRT) method was developed, which combined in-situ fiber optic UV with LD to simultaneously monitor the dissolution and changing PSD of the suspension. The simultaneously measured dissolution and PSD data showed that flocculated and deflocculated particles followed different dissolution pathways. Importantly, deflocculated particles dissolved up to six times faster than the flocculated particles. Similar shear-induced changes during injection could occur in a clinical setting and have implications for drug bioavailability.