Improved diffusing wave spectroscopy based on the automatized determination of the optical transport and absorption mean free path

Diffusing wave spectroscopy (DWS) can be employed as an optical rheology tool with numerous applications for studying the structure, dynamics and linear viscoelastic properties of complex fluids, foams, glasses and gels. To carry out DWS measurements, one first needs to quantify the static optical properties of the sample under investigation, i.e. the transport mean free path l* and the absorption length la. In the absence of absorption this can be done by comparing the diffuse optical transmission to a calibration sample whose l* is known. Performing this comparison however is cumbersome, time consuming, and prone to mistakes by the operator. Moreover, already weak absorption can lead to significant errors. In this paper, we demonstrate the implementation of an automatized approach, based on which the DWS measurement procedure can be simplified significantly. By comparison with a comprehensive set of calibration measurements we cover the entire parameter space relating measured count rates (CRt, CRb) to (l*, la). Based on this approach we can determine l* and la of an unknown sample accurately thus making the additional measurement of a calibration sample obsolete. We illustrate the use of this approach by monitoring the coarsening of a commercially available shaving foam with DWS

Formulation design of complex fluids based products through diffusing wave spectroscopy (DWS)

Complex fluids and soft matter systems are ubiquitous in consumer and cosmetic products and also in products found across many other industrial sectors encompassing foods, paints, coatings, biopharmaceutiucals etc. A critical aspect in the formulation design and optimization of these complex fluids based products is the maintenance of stability and enhancement of the sensory and functional performance. This requires establishing and optimizing the microstructure-property-performance linkages in these complex fluids. Since complex fluids are structured on multiple length scales and undergo dynamics over a wide range of timescales, the establishment of such linkages requires experimental tools that allow access to these length and time scales. Diffusing Wave Spectroscopy has emerged as a versatile experimental technique that allows unique insights into the microstructure/dynamics/rheology of complex fluid based products, allowing the design and optimization of formulations for enhanced performance benefits. This talk reviews a number of different examples and applications of DWS that are relevant for formulation design. This will include sizing, rheology and stability monitoring in emulsions, rheology of polymers to understand short time dynamics and monitoring the effect active/drug release has on the evolution of a micellar system. M. Reufer Journal OF Pharmaceutical Sciences 103:3902–3913, 2014 D. Gaudino et al., PCCP, 19, 2017, 782. LS Instruments Application Note

Transport of light in amorphous photonic materials

Amorphous photonic materials based on dense assemblies of high refractive index spherical particles are presented. Light transmission through these photonic glasses shows a nontrivial wavelength dependence. The transmission spectra can be quantitatively reproduced by modeling the optical properties starting from their building blocks. Our results emphasize the relevance of including short range order correlations and an appropriate effective refractive index in the analysis of light transmission through amorphous photonic materials

Soft Nanotechnology – from Colloid Physics to Nanostructured Functional Materials

We demonstrate how we can tune the size, shape, surface functionality and properties of nanoparticles and use them as ideal model systems for fundamental investigations as well as for materials applications. In particular we describe ways to create functionalized core-shell particles with various degree of anisotropy and interesting magnetic properties. We show how we can use these particles in order to study the equilibrium and non-equilibrium phase behavior of colloidal suspensions with different interaction potentials and summarize our current understanding of the phenomenon of dynamical arrest, i.e. gel and glass formation. While different nanoparticles are vital for fundamental studies of various aspects of soft condensed matter, they also offer fascinating possibilities in materials science. We will demonstrate this with the example of nanocomposites made through an in situ polymerization reaction

Flagellated bacterial motility in polymer solutions

It is widely believed that the swimming speed, $v$, of many flagellated bacteria is a non-monotonic function of the concentration, $c$, of high-molecular-weight linear polymers in aqueous solution, showing peaked $v(c)$ curves. Pores in the polymer solution were suggested as the explanation. Quantifying this picture led to a theory that predicted peaked $v(c)$ curves. Using new, high-throughput methods for characterising motility, we have measured $v$, and the angular frequency of cell-body rotation, $\Omega$, of motile Escherichia coli as a function of polymer concentration in polyvinylpyrrolidone (PVP) and Ficoll solutions of different molecular weights. We find that non-monotonic $v(c)$ curves are typically due to low-molecular weight impurities. After purification by dialysis, the measured $v(c)$ and $\Omega(c)$ relations for all but the highest molecular weight PVP can be described in detail by Newtonian hydrodynamics. There is clear evidence for non-Newtonian effects in the highest molecular weight PVP solution. Calculations suggest that this is due to the fast-rotating flagella `seeing' a lower viscosity than the cell body, so that flagella can be seen as nano-rheometers for probing the non-Newtonian behavior of high polymer solutions on a molecular scale.Comment: 17 page

Inorganic–organic elastomer nanocomposites from integrated ellipsoidal silica-coated hematite nanoparticles as crosslinking agents

We report on the synthesis of nanocomposites with integrated ellipsoidal silica-coated hematite (SCH) spindle type nanoparticles which can act as crosslinking agents within an elastomeric matrix. Influence of the surface chemistry of the hematite, leading either to dispersed particles or crosslinked particles to the elastomer matrix, was studied via swelling, scattering and microscopy experiments. It appeared that without surface modification the SCH particles aggregate and act as defects whereas the surface modified SCH particles increase the crosslinking density and thus reduce the swelling properties of the nanocomposite in good solvent conditions. For the first time, inorganic SCH particles can be easily dispersed into a polymer network avoiding aggregation and enhancing the properties of the resulting inorganic–organic elastomer nanocomposite (IOEN)

Morphology and orientational behavior of silica-coated spindle-type hematite particles in a magnetic field probed by small-angle x-ray scattering

Form factor and magnetic properties of silica-coated spindle-type hematite nanoparticles are determined from SAXS measurements with applied magnetic field and magnetometry measurements. The particle size, polydispersity and porosity are determined using a core−shell model for the form factor. The particles are found to align with their long axis perpendicular to the applied field. The orientational order is determined from the SAXS data and compared to the orientational order obtained from magnetometry. The direct access to both, the orientational order of the particles, and the magnetic moments allow one to determine the magnetic properties of the individual spindle-type hematite particles. We study the influence of the silica coating on the magnetic properties and find a fundamentally different behavior of silica-coated particles. The silica coating reduces the effective magnetic moment of the particles. This effect is enhanced with field strength and can be explained by superparamagnetic relaxation in the highly porous particles

Single step hybrid coating process to enhance the electrosteric stabilization of inorganic particles

We report on a single-step coating process and the resulting colloidal stability of silica-coated spindle-type hematite nanoparticles (NPs) decorated with a layer of poly(acrylic acid) (PAA) polyelectrolyte chains that are partially incorporated into the silica shell. The stability of PAA coated NPs as a function of pH and salt concentration in water was compared to bare hematite particles and simple silica-coated hematite NPs, studying their electrophoretic mobility and the hydrodynamic radius by dynamic light scattering. Particles coated with this method were found to be more stable upon the addition of salt at pH 7, and their aggregation at the pH of the isoelectric point is reversible. The hybrid coating appears to increase the colloidal stability in aqueous media due to the combination of the decrease of the isoelectric point and the electrosteric stabilization. This coating method is not limited to hematite particles but can easily be adapted to any silica-coatable particle

Brushlike interactions between thermoresponsive microgel particles

Using a simplified microstructural picture we show that interactions between thermosensitive microgel particles can be described by a polymer brushlike corona decorating the dense core. The softness of the potential is set by the relative thickness L0 of the compliant corona with respect to the overall size of the swollen particle R. The elastic modulus in quenched solid phases derived from the potential is found to be in excellent agreement with diffusing wave spectroscopy data and mechanical rheometry. Our model thus provides design rules for the microgel architecture and opens a route to tailor rheological properties of pasty materials