Electrophoretic microrheology of a dilute lamellar phase: Relaxation mechanisms in frequency-dependent mobility of nanometer-sized particles between soft membranes

Abstract

Viscoelastic properties of complex fluids in the microscopic scale can be studied by measuring the transport properties of small, embedded probe particles. We have measured the complex electrophoretic mobility micro*(omega) of nanometer-sized particles dispersed in a lyotropic lamellar phase, which shows two relaxation processes at approximately 1 kHz (high frequency relaxation, HF) and 1 Hz (low frequency relaxation, LF). It is shown quantitatively that these processes are caused by the trapping of particles within two local structures of characteristic size in the lamellar phase: the interbilayer distance and the persistence length. The origin of observed relaxations is further investigated and augmented in this study with data obtained by two other complementary methods, dielectric spectroscopy and the direct observation of fluorescently labelled probe particles under an optical microscope. It is shown that the local distortion field of the lamellar phase is induced by the extra steric interaction involving the collision of a colloidal particle with the membrane. The resulting distortion field hinders the Brownian motion of colloidal particles parallel to the membranes (not vertical), and causes the observed HF relaxation. On the other hand, the origin of LF relaxation is presumably a result of the defects in the lamellar structure. Since the results of this study show that the transport property is strongly influenced by microscopic environments, this method is referred to as electrophoretic microrheology.

Simulations of complex particle transport in heterogeneous active liquids

“…Trapping regimes are 54.5 to 68 s long and the convective regimes are 4 to 8 s long. The resulting trajectories were similar to data that has been experimentally obtained by us (unpublished data) and others Mizuno et al 2004;Suh et al 2004). Standard analysis of the entire trajectories in Fig.…”

Brownian motion near an elastic cell membrane: A theoretical study

“…Further theoretical investigations have been recently carried out by Salez and collaborators via thin-film soft lubrication theory [110][111][112]. Experimentally, particle motion near elastic cell membranes has been investigated using optical traps [113][114][115][116], magnetic particle actuation [117] and quasi-elastic light scattering [118][119][120] where a significant decrease in the mobility normal to the cell membrane has been observed in line with theoretical predictions. Additionally, near-membrane dynamics has been used in interfacial microrheological experiments as an efficient and reliable way to extract membrane unknown moduli [115,121].…”

Small-world rheology: an introduction to probe-based active microrheology

“…Cappallo and co-workers 79 applied non-linear OcAM to a non-biological system, where they used nanowire probes to investigate the rheology of worm-like micellar solutions. Using a slightly different technique (electrophoresis), Mizuno 80 and colleagues used light scattering and fluorescent particle tracking to measure the electrophoretic mobility of small (a E 25 nm) particles in a lamellar phase of a surfactant.…”