Dynamics of Concentrated Colloidal Suspensions

1989 ◽  
Vol 177 ◽  
Author(s):  
D. A. Weitz ◽  
L. Ye ◽  
Ping Sheng ◽  
J. S. Huang ◽  
D. J. Pine ◽  
...  
Keyword(s):  
Light Scattering ◽  
Acoustic Waves ◽  
Volume Fraction ◽  
Brillouin Scattering ◽  
Particle Diameter ◽  
Colloidal Suspensions ◽  
Colloid System ◽  
Wide Range ◽  
Diffusive Modes ◽  
Pmma Particles

ABSTRACTWe study the dynamics of concentrated colloidal suspensions by measuring the frequency dependent structure factor, S(q,w), using light scattering techniques. We introduce Diffusing Wave Spectroscopy, which extends dynamic light scattering to the multiple scattering regime, allowing us to study the lower frequency, diffusive modes of S(q,w), which reflect the Brownian motion of the particles. We study the behavior of the higher-frequency, propagating modes of S(q,w), which reflect acoustic waves, using Brillouin scattering. To study S(q,w) at low qa, where q is the scattering vector and a the particle diameter, we use inverted micelles, and find that the interactions between the micelles has a dramatic impact on the speed of sound as the volume fraction of micelles increases. To study S(q,w) at large qa, we use index matched PMMA particles, allowing us to measure the dispersion curve of phonons in a hard sphere colloid system. Together, these results provide a measure of S(q, w) over a wide range of q and of w.

scholarly journals Time-domain Brillouin Scattering as a Local Temperature Probe in Liquids

MRS Advances ◽  
2019 ◽  
Vol 4 (1) ◽  
pp. 9-14
Author(s):  
Ievgeniia Chaban ◽  
Hyun D. Shin ◽  
Christoph Klieber ◽  
Rémi Busselez ◽  
Vitaly Gusev ◽  
...  
Keyword(s):  
Light Scattering ◽  
Frequency Shift ◽  
Time Domain ◽  
Acoustic Waves ◽  
Brillouin Scattering ◽  
Local Temperature ◽  
Pump Probe ◽  
Probe Technique ◽  
Temperature Probe

ABSTRACTWe present results of time-domain Brillouin scattering (TDBS) to determine the local temperature of liquids. TDBS is based on an ultrafast pump-probe technique to determine the light scattering frequency shift caused by the propagation of coherent acoustic waves in a sample. Since the temperature influences the Brillouin scattering frequency shift, the TDBS signal probes the local temperature of the liquid. Results for the extracted Brillouin scattering frequencies recorded at different liquid temperatures and at different laser powers are shown to demonstrate the usefulness of TDBS as a temperature probe.

Colloidal Dynamics from Forced Rayleigh Scattering

1991 ◽  
Vol 248 ◽  
Author(s):  
C. Gochanour ◽  
S. Mazur ◽  
M.S. Wolfe
Keyword(s):  
Rayleigh Scattering ◽  
Volume Fraction ◽  
Translational Motion ◽  
Colloidal Suspensions ◽  
High Volume ◽  
Close Packing ◽  
Correlation Spectroscopy ◽  
Molecular Fluids ◽  
Characteristic Features ◽  
Diffusive Modes

AbstractColloidal suspensions are remarkable analogues of molecular fluids. In particular, at high volume fraction (Φv) they share two characteristic features with super-cooled molecular liquids: the appearance of two distinct modes of translational motion (fast and slow diffusive modes), and a critical retardation of the latter as Φv approaches random close packing (a colloidal “glass transition”). These phenomena have been studied extensively by photon correlation spectroscopy (PCS) [1-4] and are the subject of many theoretical analyses [5-12]. This paper concerns the use of forced Rayleigh scattering (FRS) to address questions not resolved by existing data or theory. We report: 1) properties of a hydrophobic silica colloid bearing photoactive azo-dye groups suitable for FRS studies, and 2) preliminary results from FRS measurements which reveal some unanticipated features regarding the transition from short-time to long-time self-diffusion at small k.

scholarly journals Volume Fraction Measurement of Soft (Dairy) Microgels by Standard Addition and Static Light Scattering

2021 ◽  
Author(s):  
Anisa Heck ◽  
Stefan Nöbel ◽  
Bernd Hitzmann ◽  
Jörg Hinrichs
Keyword(s):  
Light Scattering ◽  
Apparent Viscosity ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Standard Addition ◽  
Static Light Scattering ◽  
Soft Particle ◽  
Size Distributions ◽  
Functional Relationships ◽  
Wide Range

AbstractThe volume fraction of the dispersed phase in concentrated soft (dairy) microgels, such as fresh cheese, is directly related to structure and rheology. Measurement or modeling of volume fraction for soft and mechanically sensitive microgel dispersions is problematic, since responsiveness and rheological changes upon mechanical input for these systems limits application of typical functional relationships, i.e., using apparent viscosity. In this paper, we propose a method to measure volume fraction for soft (dairy) microgel dispersions by standard addition and volume-weighted particle size distributions obtained by static light scattering. Relative particle volumes are converted to soft particle volume fraction, based on spiked standard particle volumes. Volume fractions for two example microgel dispersions, namely, differently produced fresh cheeses, were evaluated before and after post-treatments of tempering and mechanical processing. By selecting the size of standard particles based on size ratios and the levels of the mixing ratios/relative fractions, the method could be applied robustly within a wide range of particle sizes (1 to 500 μm) and multimodal size distributions (up to quadmodal). Tempering increased the volume fraction for both example microgel dispersions (P < 0.05). Subsequent mechanical treatment reduced the volume fraction back to the starting value before tempering (P < 0.05). Furthermore, it was shown that the increase and successive decrease in apparent viscosity with tempering and mechanical post-treatments is not exclusively due to particle aggregation and breakdown, but to volume changes of each particle. For environmentally responsive soft matter, the proposed method is promising for measurement of volume fraction.

Electrokinetic instabilities of non-dilute colloidal suspensions

2009 ◽  
Vol 619 ◽  
pp. 331-365 ◽  
Author(s):  
GURU NAVANEETHAM ◽  
JONATHAN D. POSNER
Keyword(s):  
Electrical Conductivity ◽  
Electric Fields ◽  
Colloidal Particles ◽  
Volume Fraction ◽  
Flow Instability ◽  
Colloidal Suspensions ◽  
Critical Conditions ◽  
Scaling Analysis ◽  
Average Particle ◽  
Wide Range

An experimental investigation of electrokinetic instabilities (EKIs) of non-dilute colloidal suspensions in microchannels is presented. The addition of charged colloidal particles to a solution can alter the solution's electrical conductivity and permittivity as well as the average particle electrophoretic mobility. In this work, a colloidal (500 nm polystyrene) volume fraction gradient is achieved at the intersection of a Y-shaped polydimethylsiloxane (PDMS) microchannel. The flow becomes unstable when the electroviscous stretching and folding of the conductivity and permittivity interfaces exceed the dissipative effects of viscous forces and particle diffusion. The suspension conductivity as a function of the particle volume fraction is presented. The critical conditions required for flow instability are measured along with a scaling analysis which shows that the flow becomes unstable due to a coupling of applied electric fields and the electrical conductivity and permittivity gradients in the flow. The flow becomes unstable at a critical electric Rayleigh number of Rae = 1.8 × 105 for a wide range of applied electric fields spanning three orders of magnitude and colloid volume fractions varying two orders of magnitude. EKIs of non-dilute colloidal suspensions may be important for applications such as the electrophoretic deposition of micropatterned colloidal assemblies, electrorheological devices and on-chip electrokinetic (EK) manipulation of colloids.

scholarly journals Dense granular flow rheology in turbulent bedload transport

2016 ◽  
Vol 804 ◽  
pp. 490-512 ◽  
Author(s):  
Raphael Maurin ◽  
Julien Chauchat ◽  
Philippe Frey
Keyword(s):  
Granular Flow ◽  
Large Scale ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Particle Diameter ◽  
Bedload Transport ◽  
Spherical Particles ◽  
Granular Rheology ◽  
Wide Range ◽  
Dense Granular Flow

The local granular rheology is investigated numerically in turbulent bedload transport. Considering spherical particles, steady uniform configurations are simulated using a coupled fluid–discrete-element model. The stress tensor is computed as a function of the depth for a series of simulations varying the Shields number, the specific density and the particle diameter. The results are analysed in the framework of the $\unicode[STIX]{x1D707}(I)$ rheology and exhibit a collapse of both the shear to normal stress ratio and the solid volume fraction over a wide range of inertial numbers. Contrary to expectations, the effect of the interstitial fluid on the granular rheology is shown to be negligible, supporting recent work suggesting the absence of a clear transition between the free-fall and turbulent regimes. In addition, data collapse is observed up to unexpectedly high inertial numbers $I\sim 2$, challenging the existing conceptions and parametrisation of the $\unicode[STIX]{x1D707}(I)$ rheology. Focusing upon bedload transport modelling, the results are pragmatically analysed in the $\unicode[STIX]{x1D707}(I)$ framework in order to propose a granular rheology for bedload transport. The proposed rheology is tested using a 1D volume-averaged two-phase continuous model, and is shown to accurately reproduce the dense granular flow profiles and the sediment transport rate over a wide range of Shields numbers. The present contribution represents a step in the upscaling process from particle-scale simulations towards large-scale applications involving complex flow geometry.

Brillouin light scattering from surface acoustic waves in photonic microwires

2014 ◽  
Author(s):  
Jean-Charles Beugnot ◽  
Sylvie Lebrun ◽  
Gilles Pauliat ◽  
Vincent Laude ◽  
Thibaut Sylvestre
Keyword(s):  
Light Scattering ◽  
Acoustic Waves ◽  
Surface Acoustic Waves ◽  
Brillouin Light Scattering

scholarly journals Experimental demonstration of negative refraction with 3D locally resonant acoustic metafluids

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Benoit Tallon ◽  
Artem Kovalenko ◽  
Olivier Poncelet ◽  
Christophe Aristégui ◽  
Olivier Mondain-Monval ◽  
...  
Keyword(s):  
Experimental Data ◽  
Yield Stress ◽  
Multiple Scattering ◽  
Silicone Rubber ◽  
Acoustic Waves ◽  
Scattering Theory ◽  
Negative Refraction ◽  
Volume Fraction ◽  
Experimental Demonstration ◽  
Acoustic Beam

AbstractNegative refraction of acoustic waves is demonstrated through underwater experiments conducted at ultrasonic frequencies on a 3D locally resonant acoustic metafluid made of soft porous silicone-rubber micro-beads suspended in a yield-stress fluid. By measuring the refracted angle of the acoustic beam transmitted through this metafluid shaped as a prism, we determine the acoustic index to water according to Snell’s law. These experimental data are then compared with an excellent agreement to calculations performed in the framework of Multiple Scattering Theory showing that the emergence of negative refraction depends on the volume fraction $$\Phi$$ Φ of the resonant micro-beads. For diluted metafluid ($$\Phi =3\%$$ Φ = 3 % ), only positive refraction occurs whereas negative refraction is demonstrated over a broad frequency band with concentrated metafluid ($$\Phi =17\%$$ Φ = 17 % ).

scholarly journals Factors Affecting Acoustic Properties of Natural-Fiber-Based Materials and Composites: A Review

Textiles ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 55-85
Author(s):  
Tufail Hassan ◽  
Hafsa Jamshaid ◽  
Rajesh Mishra ◽  
Muhammad Qamar Khan ◽  
Michal Petru ◽  
...  
Keyword(s):  
Sound Absorption ◽  
Natural Fiber ◽  
Volume Fraction ◽  
Fiber Type ◽  
Alkali Treatment ◽  
Acoustic Properties ◽  
Synthetic Fiber ◽  
Sound Insulation ◽  
Factors Affecting ◽  
Wide Range

Recently, very rapid growth has been observed in the innovations and use of natural-fiber-based materials and composites for acoustic applications due to their environmentally friendly nature, low cost, and good acoustic absorption capability. However, there are still challenges for researchers to improve the mechanical and acoustic properties of natural fiber composites. In contrast, synthetic fiber-based composites have good mechanical properties and can be used in a wide range of structural and automotive applications. This review aims to provide a short overview of the different factors that affect the acoustic properties of natural-fiber-based materials and composites. The various factors that influence acoustic performance are fiber type, fineness, length, orientation, density, volume fraction in the composite, thickness, level of compression, and design. The details of various factors affecting the acoustic behavior of the fiber-based composites are described. Natural-fiber-based composites exhibit relatively good sound absorption capability due to their porous structure. Surface modification by alkali treatment can enhance the sound absorption performance. These materials can be used in buildings and interiors for efficient sound insulation.

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