Probing the stability of sterically stabilized polystyrene particles by centrifugal sedimentation

Abstract

The stability and sedimentation behaviour of sterically-stabilized temperature-sensitive colloidal particles has been investigated as a function of temperature and electrolyte concentration via an analytical centrifugation technique, the LUMiSizer®. The technique builds a steady particle bed at low centrifugal acceleration (~145 g), that is subsequently assessed in terms of network strength as the centrifugal field is increased up to~2325 g. Stable particle dispersions produce a smooth constant profile irrespective of applied force, whilst aggregated dispersions show a stepwise compression profile with increasing force. The extent of bed compression, which correlates to 10 the degree of particle aggregation, is more prominent at high electrolyte concentrations and temperatures. This is due to the dehydration of the steric stabilising layer and/or electrical double layer screening effects, which induce greater instability in the particles. Equilibrium compressive yield stress, P y (ø eq ), has been used to characterise the bed compression responses. P y (ø eq ) shows a power-law dependency on the particle volume fraction, with a denser bed produced at lower electrolyte concentrations at a given centrifugal force. P y (ø eq ) analysis has also assisted in describing the differences in particle structure as a function of thermal stability of the colloidal particles (i.e. 15'sterically-repulsive solvated polymeric shell or 'attractive' collapsed polymeric shell).

Wetting and Drying of Aqueous Droplets Containing Nonionic Surfactants CnEm

“…For SDS solutions, the concentrations were 5, 10, and 20 mM. For experiments on internal flows during the evaporation of a picoliter droplet, 0.04−0.05 vol % polystyrene (PS) particles were added as tracers (median diameter 997 nm, steric stabilized by polyethylene glycol methacrylate (PEGMA); 39 University of Leeds, U.K.).…”

Correction of wall adhesion effects in the centrifugal compression of strong colloidal gels

“…The centrifuge method has been used recently to examine the effect of temperature on the stability of incipiently flocculated polystyrene latices 37 , but without taking the possibility of adhesion into account. It has been used also to measure the compressibility of microgels 38 , albeit using inclined rather than horizontal or swingout rotors which adds complication to the analysis.…”

Amphiphilic Thermoresponsive Poly(Hydroxyaminoethers) as Effective Emulsifiers for Preparation of Waterborne Epoxy Resins

“…Every 10 s, light transmission profiles were captured at 𝜆 = 865 nm throughout the cell to quantify the sedimentation velocity of particles. [28][29][30] The sedimentation velocity under normal gravity was estimated by extrapolation of the measured sedimentation velocity at high relative centrifugation forces (RCF) to 1 g. Corrosion tests were performed by coating polymer emulsion on steel plates (70 × 150 mm 2 ) followed by treatment with ASTM B117 standard in a salt spray cabinet. [31,32] Figure 2.…”

“…The sedimentation velocities of the particles were estimated from the light transmission profiles as functions of time and position over the entire samples under various centrifugal forces. [26][27][28] The sedimentation velocities were then plotted against the RCF as shown in Figure S6, Supporting Information, and the velocity under normal gravity was determined by extrapolation to a gravity of 1 g. As shown in Table 2, the sedimentation velocities of the emulsions range from 0.03 to 0.12 mm/day, that is, an overall movement distance less than 7.2 mm after 2 months. These results imply that the epoxy resins emulsified by the amphiphilic PHAEs are rather stable at room temperature.…”