Charged Microparticles Research Articles

Morphology Engineering of Fullerene (C60) Microstructures Featuring Surface Cracks with Enhanced Photoluminescence and Microscopic Recognition Properties

Surface cracks could improve the optical and photoelectronic properties of crystalline materials as they increase specific surface area, but the controlled self-assembly of fullerene (C60 ) molecules into micro-/nanostructures with surface cracks is still challenging. Herein, we report the morphology engineering of novel C60 microstructures bearing surface cracks for the first time, selecting phenetole and propan-1-ol (NPA) as good and poor solvents, respectively. Our systematic investigations reveal that phenetole molecules initially participate in the formation of the ends of the C60 microstructures, and then NPA molecules are involved in the gradual growth of the sidewalls of the microstructures. Therefore, the surface cracks of C60 microstructures can be finely regulated by adjusting the addition of NPA and the crystallization time. Interestingly, the cracked C60 microstructures show superior photoluminescence properties relative to the smooth microstructures due to the increased specific surface area. In addition, C60 microstructures with wide cracks show preferential recognition of silica particles over C60 particles owing to electrostatic interactions between the negatively charged C60 microstructures and the positively charged silica microparticles. These C60 crystals with surface cracks have potential applications from optoelectronics to biology.

Physical aspects of dust–plasma interactions

AbstractLow‐pressure gas discharge plasmas are known to be strongly affected by the presence of small dust particles. This issue plays a role in the investigations of dust particle‐forming plasmas, where the dust‐induced instabilities may affect the properties of synthesized dust particles. Also, gas discharges with large amounts of microparticles are used in microgravity experiments, where strongly coupled subsystems of charged microparticles represent particle‐resolved models of liquids and solids. In this field, deep understanding of dust–plasma interactions is required to construct the discharge configurations which would be able to model the desired generic condensed matter physics as well as, in the interpretation of experiments, to distinguish the plasma phenomena from the generic condensed matter physics phenomena. In this review, we address only physical aspects of dust–plasma interactions, that is, we always imply constant chemical composition of the plasma as well as constant size of the dust particles. We also restrict the review to two discharge types: dc discharge and capacitively coupled rf discharge. We describe the experimental methods used in the investigations of dust–plasma interactions and show the approaches to numerical modelling of the gas discharge plasmas with large amounts of dust. Starting from the basic physical principles governing the dust–plasma interactions, we discuss the state‐of‐the‐art understanding of such complicated, discharge‐type‐specific phenomena as dust‐induced stratification and transverse instability in a dc discharge or void formation and heartbeat instability in an rf discharge.

The concept of a grid-based instrument for measuring micrometeoroid parameters

The article describes the design of a grid-based device for measuring the parameters of charged microparticles (micrometeoroids). The main attention is paid to the issues of calculating the errors in measuring the charge, mass and velocity of such microparticles. A 3D model of the device was developed and calculated ratios were carried out to calculate the arameters of charged microparticles.

Front Cover: Highly Sensitive Fluorescent pH Microsensors Based on the Ratiometric Dye Pyranine Immobilized on Silica Microparticles (Chem. Eur. J. 53/2021)

Optical fluorescent pH sensors based on positively charged silica microparticles containing anionic pyranine molecules were developed by using a modified Stöber method with a gradual immobilization of ratiometrically pH-sensing pyranine molecules during the growth of silica seed particles and an overall positive charge in a one-step reaction. The overly pH-sensitive nature of pyranine is preserved and long-term stability is ensured by silica shell coating. These cytocompatible ratiometric pH sensors can be used for pH sensing and pH tracking applications where each microparticle can be observed individually due to resolvable size. More information can be found in the Communication by A. Chandra, L. L. del Mercato et al. (DOI: 10.1002/chem.202101568).

Charge of clustered microparticles measured in spatial plasma afterglows follows the smallest enclosing sphere model

The plasma-induced charge of non-spherical microparticles is a crucial parameter in complex plasma physics, aerosol science and astrophysics. Yet, the literature describes this charge by two competing models, neither of which has been experimentally verified or refuted. Here we offer experimental proof that the charge on a two-particle cluster (doublet) in the spatial afterglow of a low-pressure plasma equals the charge that would be obtained by the smallest enclosing sphere and that it should therefore not be based on its geometrical capacitance but rather on the capacitance of its smallest enclosing sphere. To support this conclusion, the size, mass and charge of single particles (singlets) and doublets are measured with high precision. The measured ratio between the plasma-afterglow-induced charges on doublets and singlets is compared to both models and shows perfect agreement with the predicted ratio using the capacitance of the smallest enclosing sphere, while being significantly dissimilar to the predicted ratio based on the particle’s geometrical capacitance.

Determination and control of ion parameters in a complex plasma of a DC discharge

Complex plasmas, comprising a low-pressure DC discharge plasma and charged microparticles, form traps that can accumulate and localize ions. A loss of ions and electrons always occurs on the surfaces of the microparticles, which can lead to a decrease in the ion and electron densities in the plasma bulk. However, in most cases, the collective effect of the interaction between the discharge plasma and the dust cloud leads to an increase in the ion density—both around and inside the dust cloud—in comparison with that in pure plasma at the same discharge currents. Complex plasmas are open dissipative synergetic systems. Feedback between plasma processes allows one to control their properties using the external influences of various physical fields. Such influences thus represent a tool for controlling the dust cloud parameters and the ion density. In this letter, we report a method for determining the ion density inside a dust cloud using an electric field-current diagram (ECD). This method is based on the statement that only a single electric field can relate the particular values of the ion density, the discharge, and the dust cloud parameters. Our method includes a procedure for superimposing the ECD on the ion density-current diagram. To calculate the plasma parameters, a fluid model of a DC discharge with microparticles is employed. The method proposed herein allows us to find the conditions under which the ion density in a plasma with microparticles is less than that in pure plasma without microparticles—or vice versa, increases up to five times.

(Invited) Low Temperature Plasma Electrochemistry with Microscopic Liquid Droplets in Flight

When microscopic-sized liquid droplets travel through a low temperature RF plasma [1] at atmospheric pressure a number of remarkable and unexpected effects have been observed. After a short flight time, ~0.1ms, there is evidence that chemical reactions induced by the plasma and gas flux proceed at a rate that is significantly faster that observed in plasma – bulk liquid studies and many orders of magnitude faster than in standard bulk chemistry.[2] We suspect this is due to the complex interplay between droplet charge, electric fields, both internal and external to the droplet, and high chemical fluxes arriving at the droplet surface.There exists a large potential to develop new plasma-liquid processes for medical, chemical, biological, environmental and materials applications, among others and we can highlight some unique features of the plasma – microdroplet system that may provide opportunities for exploitation, namely: (i) a controlled ambient environment, (ii) a large surface area to volume ratio, (iii) small volume, (iv) low droplet temperature, (v) in-flight chemical synthesis and encapsulation, and (iv) remote delivery. These features offer the possibility of delivering high fluxes of active chemical species and nanoparticles remotely and on demand for applications in, for example, plasma-medicine, agriculture and microreaction while keeping the plasma itself at a safe distance.We have measured reactive oxygen species (ROS) flux variation with distance, up to 150 mm beyond the plasma, along with its effect on bacterial cell viability, DNA and amino acids. We have investigated plasma interactions with single cells, each transported in its own droplet. We have used the individual droplets as chemical microreactors to produce nanoparticles in flight, at rates many orders of magnitude higher that via high energy radiolysis or chemical synthesis. These measurements form the basis for numerical simulation in the gas-plasma and liquid droplet phases. New measurement techniques, based on recently acquired facilities, are being investigated. These include mid-IR absorption studies of droplets and their environment in flight, using tunable supercontinuum and quantum cascade lasers, and freezing plasma-treated droplets in flight for in-situ transfer to XPS surface chemical analysis.Current theories of microparticle charging in a collisional plasma environment are very limited. While in-flight charge measurements represent a significant challenge, the relatively large size of the droplet (10 – 20 μm diameter) and the limited evaporation over the flight time, offer the prospect of using droplets as a spherical probe to develop enhanced collisional probe theories in the regime where the particle size is greater than Debye lengths or mean free paths. In-flight measurements indicate a minimum net charge of ~105 electrons, considerably higher than that obtained by other charging methods. Analytical – numerical and finite element simulations, in tandem with charge measurements, are being developed to better understand the droplet electrical environment and ultimately to link chemistry and charge in a consistent framework.

Formation of Myoglobin Corona at Polymer Microparticles

Adsorption of myoglobin molecules at negatively charged polystyrene microparticles was studied using the dynamic light scattering (DLS), electrophoresis (LDV) and the solution depletion method involving atomic force microscopy (AFM). The measurements were carried out at pH 3.5 and NaCl concentration of 10−2 and 0.15 M. Initially, the stability of myoglobin solutions and the particle suspensions as a function of pH were determined. Afterward, the formation of myoglobin molecule corona was investigated via the direct electrophoretic mobility measurements, which were converted to the zeta potential. The experimental results were quantitatively interpreted in terms of the general electrokinetic model. This approach yielded the myoglobin corona coverage under in situ conditions. The maximum hard corona coverage was determined using the AFM concentration depletion method. It was equal to 0.9 mg m−2 for the NaCl concentration in the range 0.01 to 0.15 M and pH 3.5. The electrokinetic properties of the corona were investigated using the electrophoretic mobility measurements for a broad pH range. The obtained results confirmed that thorough physicochemical characteristics of myoglobin molecules can be acquired using nM amounts of the protein. It was also argued that this method can be used for performing electrokinetic characteristics of other proteins such as the SARS-Cov-2 spike protein exhibiting, analogously to myoglobin, a positive charge at acidic pHs.

A physicochemical, structural, microbiological and kinetic study of hen egg white lysozyme in complexes with alginate and chitosan

Complexes of hen egg white lysozyme (HEWL) with alginate (ALG) and chitosan (CS) (natural biodegradable polysaccharides) are important as antimicrobial agents in oral, intranasal and buccal administration. The HEWL–ALG, HEWL–ALG–Ca, [HEWL–ALG]–CS, and [HEWL–ALG–Ca]–CS complexes have been investigated using a combination of physicochemical methods (fluorescent spectroscopy, circular dichroism, microscopy, turbidimetry, microbiology, in vitro cytotoxicity assay). The complexes obtained were non-toxic negatively charged microparticles with high HEWL entrapment efficiency. The [HEWL–ALG]–CS and [HEWL–ALG–Ca]–CS complexes were found to have the altered tertiary structure of HEWL (and/or changes in the polarity of the microenvironment of Trp residues in HEWL molecules). The HEWL entrapment in all studied complexes was carried out with retention of the HEWL activity. Under the long–term storage conditions (1.5 years at 4 °C), Ca++ cations and CS stabilized HEWL. Under physiological conditions, the [HEWL–ALG]–CS and [HEWL–ALG–Ca]–CS complexes demonstrated sustained release of HEWL and resistance to protease action. The [HEWL–ALG]–CS and [HEWL–ALG–Ca]–CS complexes were highly active against Gram-negative Escherichia coli cells. The data obtained are important in the development of antibacterial drugs based on lytic enzymes.

Effect of long-range Coulomb repulsion on adhesive particle agglomeration in homogeneous isotropic turbulence

Abstract

Vortex Formation and Separation from the Surface of a Charged Dielectric Microparticle in a Strong Electric Field

—The motion of a charged dielectric microparticle in an electric field is first studied over a wide parameter range on the base of the numerical solution of the system of Nernst–Planck–Poisson–Stokes equations. As the most important result, the formation of microvortices on the rear side of the particle is revealed. The microvortices lose their steadiness with increase in the electric field strength and separate periodically from the particle surface. Separation becomes chaotic with further increase in the electric field strength. The phenomenon strongly resembles the formation of the Karman street but it has another physical mechanism by virtue of almost zero Reynolds numbers of micro- and nanoparticle flow. The asymptotic analysis is carried out and the mechanism of microvortex formation and separation is theoretically substantiated at small Debye numbers.

Development of curcumin loaded core-shell zein microparticles stabilized by cellulose nanocrystals and whey protein microgels through interparticle interactions.

Novel multilayered core-shell microparticles were developed to deliver curcumin using positively charged zein microparticles coated with negatively charged cellulose nanocrystals (CNCs) and positively charged whey protein microgels (WPMs) at pH 4. Different levels of WPMs (0.10%-1.50%, w/v) were utilized to regulate the structure, stability, and in vitro digestion of curcumin loaded zein-CNC core-shell microparticles. The size of zein-CNC-WPM core-shell microparticles ranged from 2087.7 to 2928.2 nm. The electrostatic attraction and hydrogen bonding were mainly involved in the assembly of the core-shell microparticles through particle-particle interactions. The microstructure of the core-shell microparticles was dependent on the level of the WPM. When its appropriate level was adopted (0.50%-1.00%, w/v), the WPM formed a protective shell for zein-CNC-WPM core-shell microparticles. The retention rate of curcumin in the core-shell microparticles increased by 47.56% and 32.79% during light and thermal treatment, respectively. Excess microgels facilitated the bridging aggregation and formation of a network structure on the particle surface, which further reduced their stability and greatly restricted the curcumin release. The potential of nanosized protein microgels was explored to stabilize and modulate the physicochemical properties of multilayered core-shell microparticles through interparticle interactions.

Recovery of dust particles trajectories in modeling physical processes in the near-surface exosphere of the moon

This study demonstrates the visualization and recovery of the 3D dynamic trajectories of charged microparticles in electric field conditions. The main aim of this work is to simulate plasma-dust processes above the surfaces of the Moon and other Solar system bodies without atmospheres. The experimental setup includes two parts: a vacuum chamber, in which microparticles imitate lunar dust dynamics under electrostatic field conditions, and a stereo camera system for image registration combined with laser and optics for illuminating the investigation volume. Image processing techniques for estimating the 3D particle trajectory were developed. Examples of processing results and their prospective application are discussed.

Structural and Double Layer Forces between Silica Surfaces in Suspensions of Negatively Charged Nanoparticles.

Direct force measurements between negatively charged silica microparticles are carried out in suspensions of like-charged nanoparticles with atomic force microscopy (AFM). In agreement with previous studies, oscillatory force profiles are observed at larger separation distances. At smaller distances, however, soft and strongly repulsive forces are present. These forces are caused by double layer repulsion between the like-charged surfaces and can be quantitatively interpreted with the Poisson-Boltzmann (PB) model. However, the PB model must be adapted to a strongly asymmetric electrolyte to capture the nonexponential nature of these forces. Thereby, the nanoparticles are modeled as highly charged co-ions, while the counter ions are monovalent. This model permits extraction of the effective charge of the nanoparticles, which is well comparable to the one obtained from electrophoresis. The PB model also explains the presence of a particle-free layer close to the interface.

Microparticle Deposition on Human Serum Albumin Layers: Unraveling Anomalous Adsorption Mechanism

Human serum albumin (HSA) layers are adsorbed on mica under controlled diffusion transport at pH 3.5 and various ionic strengths. The surface concentration of HSA is directly determined by AFM imaging of single molecules. It is shown that the adsorption kinetics derived in this way is quantitatively described using the random sequential (RSA) adsorption model. The electrokinetic characteristics of the HSA layers at various pHs comprising their zeta potential are acquired in situ while using the streaming potential method. It is shown that at pH 3.5 the zeta potential of mica becomes positive for HSA concentrations above 3000 μm−2. At larger pHs, HSA layers exhibit negative zeta potential for the entire range of coverage. Thorough characteristics of these monolayers at various pHs were performed applying the colloid deposition method involving negatively charged polystyrene microparticles. The kinetics of their deposition and their maximum coverage are determined as a function of the HSA layer surface concentration, pH, and ionic strength. An anomalous deposition of microparticles on substrates also exhibiting a negative zeta potential is observed, which contradicts the Derjaguin, Landau, Vervey, Overbeek (DLVO) theory. This effect is interpreted in terms of heterogeneous charge distribution that results from molecule concentration fluctuations. It is also shown that the maximum concentration of microparticles abruptly decreases with the electric double-layer thickness that is regulated by changing ionic strength, which indicates that their deposition is governed by electrostatic interactions. One can argue that the results obtained in this work can be exploited as useful reference data for the analysis of deposition phenomena of bioparticles on protein layers.

Mechanistic Investigation of Charge Separation in Electrospray Ionization using Microparticles to Record Droplet Charge State.

The mechanism of charge separation and droplet breakup during electrospray has been investigated using both biological and nonbiological microparticles as probes to preserve and record the charge state of droplets in the micron size range. Charged droplets and/or microparticles were observed using two-stage image charge detection after entering a differentially pumped, atmospheric pressure inlet. Microparticle probes allowed observation of not only droplets that did not fully evaporate but also product droplets small enough to fully evaporate, as well as the ability to distinguish between these two types of droplets. In both positive- and negative-mode electrospray ionization of aqueous suspensions, we observed roughly 20% of particles carrying charges opposite to the biased voltage on the capillary. Both positive and negative modes yielded distributions of charge states with maxima in the expected polarity but with tails extending into the opposite polarity of charge. Both polarities produced similar fractions of particles with opposite charge, with no preference for either polarity. This result is consistent with electric-field-induced charge separation and droplet breakup within the high-field region between the capillary and the counter electrode. These results suggest that electric-field-induced charge separation may be the dominant mechanism, at least in the micron size range and under the present experimental conditions, in which primary charged droplets of either polarity split into smaller progeny with a range of charges spanning both polarities. Implications for electrospray ionization mass spectrometry are discussed.

Wave‐like excitations in the system of a charged long filament interacting with the microparticles in the linear Paul trap

AbstractIn this paper, we experimentally and numerically studied the wave‐like excitations in the system comprised by a charged nylon filament (macroobject) and charged microparticles levitating in a linear quadrupole electrodynamic trap. It has been found out that a filament with sufficient sag forms a rotating standing‐like wave, while the particles due to the Coulomb repulsion are localized in its antinodes. Numerical simulation shows that this dynamic collective motion can be excited at high enough voltages on the electrodes, when the energy losses due to air viscosity can be compensated by the energy contribution of the altering electric fields of the trap.

Preparation and Properties of Hydrogel Microparticles Based on Chitosan

Positively charged (zeta potential 22-31 mV) hydrogel microparticles based on low and high molecular weight chitosan were synthesized. The effect of the crosslinking agent on their physicochemical characteristics was studied. It was established, that among obtained hydrogel particles, the ones based on low molecular weight chitosan crosslinked with citrate anions, followed by additional treatment with glutaraldehyde, are the most promising as carriers of growth regulators or plant protection products.

Nondestructive microparticle analysis method

We present a study of the nonlinear dynamics of charged microparticles in a linear electrodynamic trap at normal pressure and temperature. In this work, will be considered a mathematical modeling of the nonlinear dynamics of a microparticle under viscous friction conditions, as well as experimental confirmation of theoretical results. Based on theoretical and experimental findings, we propose an innovative method for determining charge, mass and size of a certain microparticle localized in the linear electrodynamic trap.

Coulomb crystal splitting effect in a linear electrodynamic trap

We consider a simple model of charged microparticles trapped in an electrodynamic field and interacting according to Coulomb forces. We reveal a bifurcation of the stable equilibrium point depending on the system parameters. Mathematical modelling of charged particles localization in a linear electrodynamic trap was implemented and effective potential splitting was demonstrated. The obtained splitting of Coulomb crystal corresponds to the experimental results.