Polystyrene Particles In Water Research Articles

Fast and portable fluorescence lifetime analysis for early warning detection of micro- and nanoplastics in water

The presence of plastic fragments in aquatic environments, particularly at the micro- and nano-scale, has become a significant global concern. However, current detection methods are limited in their ability to reveal the presence of such particles in liquid samples. In this study, we propose the use of a fluorescence lifetime analysis system for the detection of micro- and nanoplastics in water. This approach relies on the inherent endogenous fluorescence of plastic materials and involves the collection of single photons emitted by plastic fragments upon exposure to a pulsed laser beam. Briefly, a pulsed laser beam (repetition frequency = 40 MHz) shines onto a sample solution, and the emitted light is filtered, collected, and used to trace the time distributions of the photons with high temporal resolution. Finally, the fluorescence lifetime was measured using fitting procedures and a phasor analysis. Phasor analysis is a fit-free method that allows the measurement of the fluorescence lifetime of a sample without any assumptions or prior knowledge of the sample decay pattern. The developed instrument was tested using fluorescence references and validated using unlabelled micro- and nano-scale particles. Our system successfully detected polystyrene particles in water, achieving a remarkable sensitivity with a detection limit of 0.01 mg/mL, without the need for sample pre-treatment or visual inspection. Although further studies are necessary to enhance the detection limit of the technique and distinguish between different plastic materials, this proof-of-concept study suggests the potential of the fluorescence lifetime-based approach as a rapid, robust, and cost-effective method for early warning detection and identification of plastic contaminants in aquatic environments.

Estimation of the concentration of particles in suspension based on envelope statistics of ultrasound backscattering

This work deals with the development of a methodology to evaluate the concentration in cell or particle suspensions from ultrasound images. The novelty of the method is based on two goals: first, it should be valid when the energy reaching the scatterers is unknown and cannot be measured or calibrated. In addition, it should be robust against echo overlap which may occur due to high scatterer concentration. Both characteristics are especially valuable in quantitative ultrasound analysis in the clinical context. In this regard, the present work considers the ability of envelope statistics models to characterize ultrasound images. Envelope statistical analysis are based on the examination of the physical properties of a medium through the study of the statistical distribution of the backscattered signal envelop. A review of the statistical distributions typically used to characterize scattering mediums was conducted. The main parameters of the distribution were estimated from simulations of signals backscattered by particle suspensions. Then, the ability of these parameters to characterize the suspension concentration was analyzed and the µ parameter from the Homodyned-K distribution resulted as the most suitable parameter for the task. Simulations were also used to study the impact of noise, signal amplitude variability and dispersion of particle sizes on the estimation method. The efficiency of the algorithm on experimental measurements was also evaluated. To this end, two sets of ultrasound images were obtained from suspensions of 7 µm and 12 µm polystyrene particles in water, using a 20 MHz focused transducer. The methodology proved to be efficient to quantify the concentration of particle suspensions in the range between 5 and 3000 particles/µl, achieving similar results for both particle sizes and for different signal-to-noise ratios.

Numerical study of the effect of pressure amplitude and frequency on secondary acoustic radiation force between two polystyrene particles in water

Poly(N-isopropylacrylamide) microgels emulate the behavior of natural platelets, promoting wound healing. Our previous studies suggested that ultrasound stimulation of these synthetic platelets further enhances wound healing, by increasing particle displacement and deformation. It is necessary to understand and model the interaction between ultrasound and these particles. We hypothesize that the acoustic radiation force may play a role. Two types of radiation force are considered: a primary radiation force caused by the external acoustic field, and a secondary radiation force resulting from scattering between particles. We present a parametric numerical study of the interaction between polystyrene beads (similar to the synthetic platelets) and an acoustic field, to investigate the effect of magnitude, frequency and bandwidth of excitation field on particle response. This is done via the numerical modeling of the primary and secondary radiation forces using 2-D and 3-D FEM. The 3-D simulations capture the re-scattering effects between the particles. One particle is placed at the origin of the coordinate system (scatterer) and a second particle (probe) is placed in the nodal and anti-nodal pressure planes. The numerical results show a good agreement with the governing theoretical equations proposed by Silva and Bruus, suggesting the relevance of the radiation force hypothesis.

Measurements of size and absorption coefficient of a single moving particle by using dual burst Doppler signal

Modified LDV method is proposed for measuring the diameter and absorption coefficient of a single moving particle by applying the Lambert–Beer’s law to dual burst Doppler signal. The diameter and absorption coefficient of a particle are determined simultaneously from the time difference and intensity ratio between burst components of reflected and refracted rays in a dual burst Doppler signal, using only a single photodetector. This method can be applied to a particle larger than the cross-sectional area of an illuminating beam. The optimum conditions of an optical system were estimated theoretically. Experiments were performed with polystyrene particles in water, water droplets, and water-black ink droplets to confirm usefulness of the proposed method.

22am2-F5 ダイナミック電子線リソグラフィによる2次元ナノ流体制御

This study proposes the generation method of a nanoscale focused electric field by direct irradiation of electron-beams into dilution, and its application for two-dimensional control of nanofluidics. A negative charges induced by electron-beams irradiation for 100-nm-thick SiN membrane generated a focused electric field around the irradiation point, and the electric field could cause electroosmotic flow, which was large enough to transport 240-nm-diameter polystyrene particles in water. The electron-beam blanking could switch the presence of induced electric field. These results showed that our electron beam lithography system achieved the dynamic control of nanofluidics by fast scanning and blanking of electron beams.

HOW ROBUST IS THE RING STAIN FOR EVAPORATING SUSPENSION DROPLETS?

The ring stain is commonly seen when droplets containing particles, such as coffee, are left to dry on a surface: a pinned contact line leads to outward radial flow, which is enhanced by the diverging evaporative flux at the contact line. As shown by Deegan et al. (1997) particles are swept outwards in this flow and create a ring which grows according to a simple power law with time. The final dried width and height of the ring should also be given by power laws of concentration, with both exponent equal to 0.5 provided all particles are in the ring, and the packing factor and ring profile are constant. We use suspensions of polystyrene particles in water with sizes ranging from 200 to 500 nm and initial concentrations c0 from 0.009% to 1% deposited on glass substrates to investigate these scaling predictions. We vary the drying rate from 0.5 to 5 nl/s using humidity and reduced pressure, use a range of substrates to vary the initial contact angle between 5 ‐ and 35 ‐ , and invert the droplets to change the direction of gravity. We find that for all but the very lowest pressures, the ring height follows the predicted power law, with exponent equal to 0.50 § 0.04 and the ring width having an exponent of 0.33 § 0.05. The discrepancy between the measured and predicted width exponent is accounted for by an observed variation of droplet radius with concentration, and the presence of particles in the center of the droplet. In addition, for low pressures (fast evaporation) the scaling laws no longer hold: the ring is much narrower and there is significant deposition in the center of the droplet, possibly due to reduced particle-enhanced pinning.

Colloidal crystallization by a centrifugation method

Colloidal crystals of high particle concentration were smoothly and continuously fabricated by simple centrifugation of a dispersion of polystyrene particles in water. The larger the applied centrifugal acceleration α at the bottom of the growing crystals (i.e., the interior wall of the container), the higher the growth rates are. The average grain sizes in the crystals increased with decrease in α, and below a critical value of α, we obtained relatively large columnar-shaped grains. The average volume fraction of the obtained colloidal crystals ϕave. increased with an increase in the dispersion’s KCl concentration CKCl: at α=82G, ϕave.=0.57 and 0.61 at CKCl=2×10−3 and 8×10−3molkg−1 water, respectively. The grain size also increased with an increase in CKCl. The maximum grain size in this study was greater than 0.3mm in width and 8mm in length.

Effect of Liquid Properties on Heat Transfer from Miniature Heaters at Different Gravity Conditions

This work presents experiments for the estimation of heat transfer from sub-millimeter spheroidal heaters at varying gravity conditions. Experiments were performed during the 50th Parabolic Flight Campaign of European Space Agency (May 2009). Heat pulses of varying strength were given to a miniature heater submerged in the liquid while its thermal response was registered during heating. Tests were conducted in water and FC-72, two liquids with distinctly different thermophysical properties. Runs were also conducted with packed beds and dense suspensions of two size classes of polystyrene particles in water. The contribution of natural convection in heat transfer was estimated from differences observed when the acceleration varied from 0g to 1.8g. Although the analysis of data is not finished yet, it is evident that natural convection is more profound in FC-72 than water. In addition, closely packed particles suppress entirely natural convection but this is not so for dense particle suspensions.

Methods for measuring refractive index and absorption coefficient of a moving particle using polarized-type phase-Doppler technique

Two methods are proposed for measuring the refractive index or the absorption coefficient simultaneously with the diameter and velocity of a moving spherical particle by using a polarized-type phase Doppler method. A particle refractive index is determined from phases of reflected and refracted rays detected individually by using different polarization angles of scattered light, whereas an absorption coefficient is obtained by applying the Lambert–Beer law to intensity of a dual-burst Doppler signal generated by the reflected and refracted rays. The optimum conditions of an optical system were estimated theoretically. Experiments were performed with polystyrene particles in water, water droplets, and water-black ink droplets to confirm usefulness of the proposed methods.

Simple and Precise Size-Separation of Microparticles by a Nano-Gap Method

A simple and precise size measurement device of microparticles in liquid has been developed by using a narrow gap between a cylindrical lens and a flat glass wall, in which the distance of the gap is precisely determined by the diffraction Moiré pattern of irradiated light. Two different methods to transfer the particles toward the center line of the lens, a hydrodynamic flow mode and an electrophoretic mode, have been established. By using these methods, simultaneous size-determination and size-separation of small amounts of micrometer and sub-micrometer sized polystyrene particles in water have been attained with high precision. Novel advantages of the cylindrical nano-gap method were demonstrated for different surface types of polystyrene particles.

Towards VCSEL-based integrated optical traps for biomedical applications

A new concept to miniaturise optical trapping and manipulation systems is presented. Integrated optical traps based on top-emitting vertical-cavity surface-emitting lasers (VCSELs) with near-infrared emission in combination with photoresist microlenses were fabricated, characterised and demonstrated. Elevation and trapping of 10 µm-sized polystyrene particles in water is achieved at optical output powers as small as 9 mW.

Particle sizing and flow measurement using self-mixing interferometry with a laser diode

New applications are presented for self-mixing interferometry, based on optical scattering, feedback and self-mixing in laser diodes. The self-mixing interferometry method has been developed for the determination of sub-micron particle sizes and for the measurement of flows in narrow diameter tubes. The rate equations for laser diodes subjected to frequency-shifted feedback are reviewed and extended to include a normalized frequency distribution to be characterized by the backscattered light spectrum. Experimental investigations are presented for (a) particle sizing using polystyrene particles in water from 0.02 to 0.20 mu m in diameter and (b) for transverse velocity profile determination using a 1.4 mm diameter tube with flow rates ranging between 10 and 100 ml h(-1). The observed frequency band increases for smaller particles when observing Brownian motion and for higher flow rates when observing flowing liquids. This experimental technique is inherently simple and low cost. Further potential applications of this technique include blood flow measurement in medicine, electrophoresis investigations in biology and particle characterization in process engineering and chemistry.

Effects of particle size on near-wall depletion in mono-dispersed colloidal suspensions

In this work we investigate the change in particle concentration near a solid boundary for colloidal dispersions in pressure driven flow, commonly referred to as wall depletion. In particular we determine the effect of Peclet number on the strength and spatial extent of the depleted layer. The change in concentration near the solid boundary is measured with attenuated total reflection infrared (ATR-IR) spectroscopy described previously (P.J.A. Hartman Kok et al., J. Rheol. 46 (2002) 481). The method is capable of measuring the concentration of particles at distances ranging from 0.2 to 1.0 mum from the boundary. The suspensions investigated consisted of mono-dispersed polystyrene particles in water. Particles of four different sizes were used, with radius, a, of 30, 54, 105, and 197 nm. (The ratio H/a was in the range 2500-17,000 with H being the height of the flow cell.) This enabled us to measure the wall depletion effect over a wide range of Peclet numbers, ranging from 0.01 to 45. We found that wall depletion was not significant for Peclet numbers smaller than unity. Estimates of the wall slip layer thickness obtained from rheological experiments were consistent with the results obtained by ATR-IR spectroscopy.

Forces between Polystyrene Particles in Water Using the AFM: Pull-Off Force vs Particle Size

Adhesion between polystyrene particles in high purity water has been measured for a wide range of particle sizes. The results are compared with predictions based on the JKR model using literature values of the solid−vapor surface energy. When the surface roughness of the particles is accounted for, the JKR adhesion is still too large. An optimum value of the surface energy is calculated for one tip particle size and used for predicting the pull-off force for all of the substrate particle sizes, and it was found that this produces much closer agreement between theory and experiment although the scatter in the data is large. The mean pull-off force for all of the particle−particle measurements studied here is of the order of a few nanonewtons. Because of the large scatter in the pull-off force data, no clear trend in the pull-off force for different particle sizes has been observed. It is suggested that the effect of surface roughness on the pull-off force is significant.

Attenuation of sound in concentrated suspensions: theory and experiments

Ensemble-averaged equations are derived for small-amplitude acoustic wave propagation through non-dilute suspensions. The equations are closed by introducing effective properties of the suspension such as the compressibility, density, viscoelasticity, heat capacity, and conductivity. These effective properties are estimated as a function of frequency, particle volume fraction, and physical properties of the individual phases using a self-consistent, effective-medium approximation. The theory is shown to be in excellent agreement with various rigorous analytical results accounting for multiparticle interactions. The theory is also shown to agree well with the experimental data on concentrated suspensions of small polystyrene particles in water obtained by Allegra & Hawley and for glass particles in water obtained in the present study.

Operating Characteristics of Acoustically Driven Filtration Processes for Particulate Suspensions

Operating characteristics for an ultrasonically assisted filtration technique applicable to micron to millimeter-sized particles suspended in liquid have been studied. The technique uses a highly porous filtration medium having pores up to two orders of magnitude larger than the particles being collected. When a resonant ultrasonic standing wave field is applied to the medium, the particles become trapped on the elements comprising the porous medium or within its pores. The test suspension consisted of 325-mesh polystyrene particles in water. The porous medium was a polyester mesh containing 30 pores per inch (the nominal pore size is 847 μm). Filtration efficiencies ranging from 60 to 85% have been observed. The effect of flow configuration on filtration efficiency and two approaches for cleaning of the mesh have been examined.

Experimental and Theoretical Study of the Field Induced Phase Separation in Electro- and Magnetorheological Suspensions

We present here the study of field induced phase separation in E.R. and M.R. fluids. Two thermodynamic models — one for the formation of chais of particles and the other for phase separation are presented and compared with experimental results obtained with two kinds of suspensions. One was made of silica particles in silicone oil and the other was made of magnetic polystyrene particles in water. In the presence of a flow the phase separation occurs with the dense phase forming a regular pattern of stripes. The dependence of the period of these stripes on the intensity of the magnetic field is well reproduced by the same kind of thermodynamic model if we add the effect of normal stresses induced by the shear flow.

The Hamaker and the Lifshitz approaches for the Van der Waals interaction between particles of composite materials dispersed in a medium

Based on the superpositional principle of the classical Hamaker–De Boer approach to the Van der Waals interaction, an equation for the interaction energy between two identical composite particles in a medium has been developed. The particles are supposed to be composed of an arbitrary number of components that are intimately mixed to avoid appreciable scattering of interacting EM waves. A discussion is presented on how intimately the components have to be mixed for the theory to be applicable. As an example, the main theoretical result is applied to porous polystyrene particles in water, while the pores are not filled with water (‘non-wetting surface’). Numerical results for composite particles are evaluated, using interaction parameters as obtained by various methods that are based on either the Hamaker–de Boer or the Lifshitz approach.

Highly anisotropic light emission from laser breakdown of microparticles in water

LASER breakdown, in which a substance is transformed explosively to a plasma by a focused pulsed laser beam, has been much studied1–8. Light emission from the plasma formed by breakdown of liquid media or suspended microparticles is generally observed lateral to the laser beam, and can be used for spectrochemical analysis4,8,9. Here we report the observation of highly anisotropic emission of hydrogen Balmer-α (Hα) radiation from the laser breakdown of polystyrene particles in water. The emission was strong and spectrally narrow in the forward and backward directions (with respect to the beam), and weak and broad in others. The incorporation of a single-mirror cavity in the optical arrangement and the observed nonlinear dependence of intensity on the focal length of the focusing lens suggest that the plasma may induce gain in the emitted radiation. The exact mechanism of the anisotropic emission is not yet known.

Imaging by polystyrene latex particles

Imaging by particles of polystyrene (PS) latexes has been investigated under drying and in water by means of a microscope. When a few drops of a dilute aqueous solution of the purified PS latexes were dried on a cover glass below the minimum film-forming temperature, the close-packed structure of PS particles in a layer was easily formed extending over a wide range. The arranged PS particles all within a sweep of a microscope imaged an object like a compound eye. The interesting phenomenon that the PS particles in water execute Brownian movement while carrying an imaged object shape with them was also observed.