Multiple-Particle Tracking (MPT) Measurements of Heterogeneities in Acrylic Thickener Solutions

Abstract

In this study the method of multiple-particle tracking (MPT) is used to quantify the degree of structural and mechanical microheterogeneity of two polymeric thickener solutions finally aiming at a better understanding of the contribution of microheterogeneities, which commonly occur in solutions of many synthetic as well as biopolymers, on bulk rheology. We have chosen the commercial polyacrylate ester Sterocoll FD and Sterocoll D (BASF Aktiengesellshaft) as model systems. For the Sterocoll FD solution the ensemble-averaged mean square displacement (MSD) is almost linear in time, as expected for such a weakly elastic fluid and relatively similar to that observed for a homogeneous aqueous glycerol solution, used as a reference system. However, the MSD distribution is broader than for the glycerol solution and their statistical analysis clearly reveals a heterogeneous structure on the µm length scale. For the Sterocoll D solution, the average MSD exhibits a subdiffusive behavior, typical for highly elastic solutions. Moreover, the displacements of microspheres at different locations within the solution display a wide range of amplitudes and time dependences. The MSDdistribution is very broad/bimodal and the statistical analysis indicates a degree of inhomogeneity slightly higher than for the Sterocoll FD solution.

Tracking errors in 2D multiple particle tracking microrheology

“…Generally, for homogenous materials bulk shear moduli agree very well with the particle tracking determined G′ and G″ [24,25]. This is also true for various other microrheological techniques; in particular for diffusing wave spectroscopy (DWS) or fluorescence correlation spectroscopy (FCS), good agreement between linear viscoelastic moduli of homogenous materials obtained there with and bulk rheological data has been reported for homogeneous model systems [1,22,[26][27][28][29].…”

“…This is also true for various other microrheological techniques; in particular for diffusing wave spectroscopy (DWS) or fluorescence correlation spectroscopy (FCS), good agreement between linear viscoelastic moduli of homogenous materials obtained there with and bulk rheological data has been reported for homogeneous model systems [1,22,[26][27][28][29]. However, significant deviations between results from MPT and bulk mechanical measurements are reported for a variety of fluids [15,25]. This is not surprising for inhomogeneous fluids where the GSE fails, but statistical analysis of individual tracer trajectories still allows for a characterization of local rheological properties on 0.1-1 µm length scale [4,[17][18][19].…”

Micro-rheological properties of lung homogenates correlate with infection severity in a mouse model of Pseudomonas aeruginosa lung infection

“…Additionally, micro-scale inhomogeneity was detected in individual samples, which simultaneously showed diffusive and immobile particles. To quantify the level of inhomogeneity, the MSD distributions at τ = 0.108 s normalized by the ensemble-average MSD (〈MSD at τ = 0.108 s) were plotted 13 . Figure 2 g-i shows three representative MSD/ 〈MSD distribution plots corresponding to the same examples as in Fig.…”

“…We therefore investigated the micro-rheological characteristics of lung homogenates by means of multiple particle tracking (MPT). This technique consists in tracking the Brownian motion of tracer particles dispersed within a complex biological fluid and allows determining the mechanical properties of the material by measuring the displacement of the tracer particles at different time scales 13,14 . To test our hypothesis, we investigated the correlation between CFU counts and the amount of pqsR molecules (PQS and HHQ) determined in the lung homogenates of mice infected with P. aeruginosa NH57388A with the mechanical properties of the same lung homogenates measured by means of MPT micro-rheology.…”

Microstructure, local dynamics, and flow behavior of colloidal suspensions with weak attractive interactions

“…fluorescent tracer particles (a = 105 nm, dragon green) from Bang Laboratories (USA) was added to 100 μL of the colloidal dispersion, which was then vortexed and homogenized for 10 min in an ultrasonic bath. A 20 μL aliquot of this mixture was then injected into a small probing chamber that we constructed 59 and sealed with UV-curing glue. The MPT experiments were performed with an inverted fluorescence microscope (Zeiss Axio Observer D1) equipped with a Fluar 100x, N.A.…”