Approaching the hard sphere limit in colloids suitable for confocal microscopy – the end of a decade lasting quest

Abstract

PMMA-PHSA particles serve as the hard sphere model system since the 1980s. We investigate the fluid structure of fluorescent ones in three different solvents by laser scanning confocal microscopy: a...

Structure and short-time diffusion of concentrated suspensions consisting of silicone-stabilised PMMA particles: a quantitative analysis taking polydispersity effects into account

“…4. In accordance to the de Gennes relation [eqn (10)], D eff (Q) and S M (Q) show an alternating progression: The collective diffusion is decelerated on length scales with stable configurations, precisely where the local maxima of the structure factor occur.…”

“…The hard-sphere model is of special interest, as it describes, despite its simplicity, the most fundamental properties of dense, simple liquids with a dominating repulsive interaction potential. 1,2 Initiated by the pioneering work of Pusey and van Megen, 3,4 suspensions of sterically stabilised poly(methyl methacrylate) (PMMA) particles in non-polar solvents are the most commonly used colloidal model systems for experimental studies of hard spheres, which encompass investigations of the bulk phase behaviour, 3,5 the fluid structure, both in reciprocal space via scattering experiments 6,7 and in real space via microscopy, [8][9][10] structure-dynamics relations, [11][12][13][14] crystalline 15,16 and glass-like [17][18][19][20][21][22] structures as well as the study of non-equilibrium phenomena such as sedimentation under gravity 23 or rheological properties. 24,25 Synthesis via dispersion polymerisation 26 yields particles which are composed of a solid PMMA core, surrounded by a shell of stabiliser molecules, whose steric hindrance prevents the aggregation of particles upon close contact, leading to steep repulsive forces.…”

Temporal Evolution of Interparticle Potentials of PMMA Colloids in CHB/Decalin

“…The initial value compares well to recent data reported for a similar system (the particles in this case were labeled with a cationic dye) where Z = 15 e μm −2 to Z = 30 e μm −2 was found. 26 In this publication, the authors report a strong dependence of Z on the volume fraction ϕ in a range of 0.1 < ϕ < 0.49. While our experiments were done in highly diluted dispersions with ϕ ≈ 8 • 10 −7 one might speculate that contacts between particles and between particles and the chamber surfaces contribute to the discharging of the particles.…”

“…This reasoning was motivated by previous report of similar variations in parameters like Debye lengths and effective charges for different samples despite their careful preparation. 19,26 Sorting the same data as a function of time after sample preparation, however, shows that the observed variations are not caused by irregularities in the sample preparation, but are rather much due to a change of the samples as a function of time after preparation (cf. Figure 3b).…”

“…This demonstrates a reasonable reproducibility of our data with added TBAB that has been reported to be difficult in earlier studies. 26 The remaining differences between measurements might be due to the previously observed phenomenon of fluctuating charges on colloids. 49−51 In addition, variations in particle charges could also result from different degrees of the covalent binding of the steric stabilizer, that is known to strongly influence the surface charge.…”