Brownian Motion In Liquid Research Articles

Nanoparticle sizing by focused-beam dynamic ultrasound scattering method

When nanoparticles in Brownian motion in liquid are irradiated with ultrasonic waves in the megahertz frequency range, scattering from the particles occurs, albeit at a very low intensity. The diffusion coefficient and the corresponding particle size can be calculated by analyzing the time correlation function of the ultrasound pulses. Since ultrasonic waves with long wavelengths in comparison with the particle size are unfavorable for detecting such small particles, increasing the energy of the ultrasonic waves is a primary solution. Increasing the energy, conversely, causes an unexpected acoustic flow. Consequently, a method using a strong ultrasound pulse while suppressing this acoustic flow field is required. In this study, we apply (1) a focused transducer with high ultrasonic energy, (2) a high-frequency sensor enhancing scattering performance, and (3) a short pulse repetition time to achieve high-speed and high-precision nanoparticle measurement while confining the sample in a narrow space to eliminate the acoustic flow. This enables direct tracking of nanoparticle motion by observing diffusive motion without perturbation particle dynamics. We specifically investigated a suspension of silica particles with a hydrodynamic radius of 15 nm and also achieved particle size discrimination in mixtures. The time correlation analysis using megahertz ultrasound pulses also takes advantage of ultrasonic waves’ inherent advantages, such as high-speed, high-precision particle size analysis in the submicron range beyond the wavelength of visible light.

Dynamics of gold nanoparticle clusters observed with liquid-phase electron microscopy

The dynamics of processes of nanoparticles such as diffusion, attraction and repulsion, and self-assembly of structures of nanoparticles at the solid-liquid interfaces differ significantly from those occurring for bulk conditions and their fundamental physical rules are still unknown. Here, we used liquid phase scanning transmission electron microscopy (LP-STEM) to study several aspects of nanoparticle dynamics of colloidal chitosan coated gold nanoparticle (TCHIT-AuNP) clusters in a liquid layer enclosed between two SiN membranes. We found that upon beam irradiation using an electron flux of 0.9 e−/sÅ2, the AuNPs assembled in clusters that shifted and rotated with time. The newly formed clusters could join and form larger clusters via a mechanism of oriented attachment. By increasing the electron flux to 6.2 e−/sÅ2, we observed the fragmentation of some of the clusters and TCHIT-AuNPs were exchanged between clusters. At the highest electron flux studied 25 e−/sÅ2, we observed AuNPs moving at a very slow speed compared to Brownian motion in liquid even though they were not directly attached or pinned to the liquid-enclosing membrane. Experiments using branched polyethylenimine (BPEI) coated AuNPs were carried out for comparison.

A Microfluidic Chip and Dark-Field Imaging System for Size Measurement of Metal Wear Particles in Oil

We present a dark-field video microscopy setup and microfluidic sample cell to detect suspended particles and measure their size. The microfluidic chip was fabricated by etching of shallow chambers in silicon and bonding with glass, thus achieving robust devices with low background signal for dark-field microscopy. The system is suitable for measuring particles in liquid media, such as metallic wear particles originating from lubricated tribocontacts in oil. Here, sample wear particles were generated in the laboratory by sliding a piston ring section against a cylinder liner section with a reciprocating tribometer using base oil (PAO8) as lubricant. Individual microparticles and nanoparticles are visualized by means of their scattered light, and sizes are determined by tracking of the diffusive Brownian motion in liquid. By heating the oil sample, the viscosity is reduced, which increases the extent of Brownian motion and facilitates tracking-based size calculations. The height of the microfluidic chamber was matched with the focal depth of the optical system, so that particles stay in focus during the whole measurement time. The resulting particle size distributions were monomodal and displayed a peak diameter of 230 nm, as confirmed by reference measurements with dynamic light scattering. Our approach represents a straightforward way to determine the size of microparticles and nanoparticles and has the potential for a continuous online operation. Compared with the state-of-the-art particle counters used in condition monitoring of industrial machinery, it is possible to detect much smaller particles and, therefore, allow early detection of wear before severe failure events take place.

Observation of Brownian Motion in Liquids at Short Times: Instantaneous Velocity and Memory Loss

Measurement of the instantaneous velocity of Brownian motion of suspended particles in liquid probes the microscopic foundations of statistical mechanics in soft condensed matter. However, instantaneous velocity has eluded experimental observation for more than a century since Einstein's prediction of the small length and time scales involved. We report shot-noise-limited, high-bandwidth measurements of Brownian motion of micrometer-sized beads suspended in water and acetone by an optical tweezer. We observe the hydrodynamic instantaneous velocity of Brownian motion in a liquid, which follows a modified energy equipartition theorem that accounts for the kinetic energy of the fluid displaced by the moving bead. We also observe an anticorrelated thermal force, which is conventionally assumed to be uncorrelated.

The liquid–glass transition – is it a fourth order phase transition?

The liquid–glass transition is analyzed using a theory of Brownian motion in liquids recently developed by the author. It is shown that if a liquid could be cooled in quasi-static process and still avoids crystallization it would transform into a stable non-crystalline solid, which would be a normal thermodynamic phase. This hypothetical phase transition is neither first nor second order. At equilibrium transition temperature the free energy of the system and its first, second and third derivatives are all continuous functions, but its fourth derivative with respect to temperature is discontinuous. Therefore, the equilibrium liquid to non-crystalline solid transition may be considered a fourth order phase transition. The temperature of this phase transition, T K, which coincides approximately with the Kauzmann temperature, is below the standard glass transition temperature T g. (When the temperature decreases below T g, the viscosity increases above 10 13 dPa s.) When the temperature decreases below T K, the system becomes an ideal solid because the molecular mobility becomes zero and the viscosity becomes infinite if we neglect vacancy-like mechanisms of mobility. This hypothetical quasi-static transition is physically unobservable because the real liquid–glass transition must be done at a cooling rate high enough to suppress the growth of nanocrystals, which makes the liquid–glass transformation a non-equilibrium complicated phenomenon. Understanding this ideal phase transition is a first step towards describing the real liquid–glass transition from first principles.

Fractal analysis of brownian trajectories in fluids

Fractal analysis of molecular brownian motion in liquids was carried out in two and three dimensions. It was observed that the trajectories are self-affine and can be characterized by a differential fractal dimension, which varies with the trajectory length. The analysis of the brownian motion by different kinds of coverings, and the comparison of this motion with diffusion-limited processes, allows us to deduce that the ensemble of all trajectories has a multifractal structure. Finally, the brownian motion in disordered media was studied. Significant differences were found depending on the euclidean dimension in which the motions were performed.

Rotational Brownian motion in liquid and plastic crystalline CBr4 from far infrared induced absorptions

The far infrared induced absorption bands of CBr4 in the liquid and plastic single crystalline states have been measured in order to study the changes in rotational dynamics brought about by the increased translational constraint and packing symmetry of the solid. Analysis of the band-shapes in terms of rotational Brownian type dynamics suggests that the barrier to such motion is slightly increased on going from the plastic crystal to the liquid a few degrees above the melting point, thus making the change of phase energetically desirable. The integrated intensity per molecule is greater in the liquid, although the macroscopic density is less, which suggests that the spatial disposition of the electrostatic (long range) part of the intermolecular potentials is important in determining the magnitude of the molecular induced dipole moment.The dipole cross-correlation function corresponding to these bands is compared with that of octopole-induced dipole absorption of a two molecule collision of spherical tops, and with the auto-correlation function for a Maxwellian ensemble of freely rotating molecules of this symmetry. It is found that the mean torque is greater initially in the condensed phases, thereafter, rotational motion is correlated.

Activation Energies of Brownian Motion in Liquid Determinated by Luminescence Methods

AbstractThe activation energies for rotation and translation of fluorescein molecules in glycerin determined in this paper are different. These activation energies decreases with increasing concentration of fluorescence quenching molecules (KI).

On the Mechanism of Brownian Motion in Liquids

On the Mechanism of Brownian Motion in Liquids