Gas–Liquid Slug Flow Studies in Microreactors: Effect of Nanoparticle Addition on Flow Pattern and Pressure Drop

Colloidal suspensions of nanoparticles (e.g., metals and oxides) have been considered as a promising working fluid in microreactors for achieving significant process intensification. Existing examples include their uses in microflow as catalysts for enhancing the reaction efficiency, or as additives to mix with the base fluid (i.e., to form the so-called nanofluids) for heat/mass transfer intensification. Thus, hydrodynamic characterization of such suspension flow in microreactors is of high importance for a rational design and operation of the system. In this work, experiments have been conducted to investigate the flow pattern and pressure drop characteristics under slug flow between N2 gas and colloidal suspensions in the presence of TiO2 or Al2O3 nanoparticles through polytetrafluoroethylene (PTFE) capillary microreactors. The base fluid consisted of water or its mixture with ethylene glycol. The slug flow pattern with nanoparticle addition was characterized by the presence of a lubricating liquid film around N2 bubbles, in contrast to the absence of liquid film in the case of N2-water slug flow. This shows that the addition of nanoparticles has changed the wall wetting property to be more hydrophilic. Furthermore, the measured pressure drop under N2-nanoparticle suspension slug flow is well described by the model of Kreutzer et al. (AIChE J 51(9):2428–2440, 2005) at the mixture Reynolds numbers ca. above 100 and is better predicted by the model of Warnier et al. (Microfluidics and Nanofluidics 8(1):33–45, 2010) at lower Reynolds numbers given a better consideration of the effect of film thickness and bubble velocity under such conditions in the latter model. Therefore, the employed nanoparticle suspension can be considered as a stable and pseudo single phase with proper fluid properties (e.g., viscosity and density) when it comes to the pressure drop estimation.

In-situ Characterization of Crystallization and Melting of Soft, Thermoresponsive Microgels by Small-Angle X-ray Scattering

Depending on the volume fraction and interparticle interactions, colloidal suspensions can form different phases, ranging from fluids, crystals, and glasses to gels. For soft microgels that are made from thermoresponsive...

Antibacterial Effect of Colloidal Suspensions Varying in Silver Nanoparticles and Ions Concentrations

A lot of effort has been dedicated recently to provide a better insight into the mechanism of the antibacterial activity of silver nanoparticles (AgNPs) colloidal suspensions and their released silver ionic counterparts. However, there is no consistency regarding whether the antibacterial effect displayed at cellular level originates from the AgNPs or their ionic constitutes. To address this issue, three colloidal suspensions exhibiting different ratios of AgNPs/silver ions were synthesized by a wet chemistry method in conjunction with tangential flow filtration, and were characterized and evaluated for their antimicrobial properties against two gram-negative, Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa), and two gram-positive, Staphylococcus aureus (S. aureus) and Staphylococcus epidermidis (S. epidermidis), bacterial strains. The produced samples contained 25% AgNPs and 75% Ag ions (AgNP_25), 50% AgNPs and 50% Ag ions (AgNP_50), and 100% AgNPs (AgNP_100). The sample AgNP_100 demonstrated the lowest minimum inhibitory concentration values ranging from 4.6 to 15.6 ppm for all four bacterial strains, while all three samples indicated minimum bactericidal concentration (MBC) values ranging from 16.6 ppm to 62.5 ppm against all strains. An increase in silver ions content results in higher bactericidal activity. All three samples were found to lead to a significant morphological damage by disruption of the bacterial cell membranes as analyzed by means of scanning electron microscopy (SEM). The growth kinetics demonstrated that all three samples were able to reduce the bacterial population at a concentration of 3.1 ppm. SEM and growth kinetic data underline that S. epidermidis is the most sensitive among all strains against the investigated samples. Our results showed that all three AgNPs colloidal suspensions exhibited strong antibacterial properties and, thus, they can be applied in medical devices and antimicrobial control systems.

Nanocrystals- A substantial platform for drug delivery applications.

Poor solubility of a drug is one of the major concerns in drug delivery. Many strategies have been employed for solving this problem, but there are still some deficiencies with current strategies, such as low drug loading, high toxicity, poor stability, potential drug loss during storage and complex manufacturing method. By formulating nanocrystals, problems associated with the delivery of drugs with low water or lipid solubility can be addressed. Unlike polymeric nanoparticles and lipidic nanoparticles, they are not a reservoir or matrix system. Nanocrystals are colloidal suspensions of nanosized particles stabilized by polymeric or electrostatic stabilization. They can be prepared by Top-down or Bottom-up approaches. Some of the methods for the preparation of nanocrystals are nanoprecipitation, media milling, high-pressure homogenization, emulsions and microemulsions as templates, supercritical fluid technology and co-grinding. They can be used for oral, intravenous, ocular, inhalation, intramuscular drug delivery and drug targeting.

SONOLUMINESCENCE SPECTROSCOPY OF COLLOIDAL SUSPENSIONS: MOLECULAR, IONIC AND ATOMIC LUMINESCENCE DURING SONOCHEMICAL DECOMPOSITION OF SILICON DIOXIDE NANOPARTICLES CONTAINING RUTHENIUM AND COPPER COMPOUNDS

The article is devoted to an example of the sonoluminescence spectroscopy use, which was previously known as a method for analyzing substances from the characteristic spectra of their sonoluminescence only in true solutions, for carrying out a similar analysis of substances contained in insoluble nanoparticles in colloidal suspensions. The solutions sonolysis, that is, their irradiation with ultrasound, is accompanied by the formation of cavitation bubbles that vibrate radially at the frequency of the ultrasonic field. Volatile components of the solution enter the bubbles, evaporating from the liquid-gas interface; nonvolatile components can penetrate into the bubble as a result of the injection of solution nanodroplets into the gas phase, which occurs during intense bubble movements accompanied by their deformation. In a nonequilibrium plasma periodically forming in cavitation bubbles, destruction occurs, as well as collisional excitation of these components, followed by luminescence. It has been shown that this mechanism of sonoluminescence also operates in colloidal suspensions, where substances are present in the form of nanoparticles with sizes less than 50 nm. Such nanoparticles penetrate into moving cavitation bubbles, without destroying them, as part of nanodroplets, and then undergo decomposition in bubble plasma with the excited particles generation as emitters of characteristic sonoluminescence. In this work, we synthesized colloidal suspensions in dodecane of porous SiO2 nanoparticles containing adsorbed Ru(bpy)3Cl2 and CuSO4 salts. During moving single-bubble sonolysis for these suspensions, characteristic emission spectra of Ru and Cu atoms, SiO molecules, and Ru(bpy)3 ions suitable for sonoluminescence spectroscopic analysis were recorded. By comparing the experimental and calculated (at different temperatures) luminescence spectra of Ru atoms, we estimated the electron temperature attained upon acoustic compression of single bubble in colloidal suspension in dodecane: Te = 7000 K.

Influence of Inorganic Metal (Ag, Cu) Nanoparticles on Biological Activity and Biochemical Properties of Brassica napus Rhizosphere Soil

Two separate forms of application of silver and copper nanoparticles (AgNP and CuNP in a nanocolloidal suspension) to winter oilseed rape seeds were used: (1) seed soaking (S) for 1 h at 20 °C in a NP suspension and (2) additional seed soaking and spraying plants 21-day-old seedlings (SP) with NP. The AgNP and CuNP colloidal suspensions in sterile distilled water were applied in three different NP concentrations (50, 100, 150 mg L−1). However, the changes in the biology and biochemistry of the Brassica napus rhizospheric soil after the application of CuNPs and AgNPs are not considerable, although mostly statistically significant, and the application of CuNPs is more beneficial for this activity than the application of AgNPs. The number of CFUs (colony–forming units) of the tested groups of culturable microorganisms (fungi and copiotrophic, oligotrophic, and siderophore-producing bacteria) indicates the following trend: the abundance of all the tested groups was slightly positively correlated with CuNPs and clearly negatively correlated with AgNPs in each version of application. The soil pH value and tested biochemical soil parameters (IAA: indole-3-acetic acid, PhC: phenolic compounds, FeCC: Fe–chelating compounds) were negatively correlated with AgNPs applied to the seeds (S) at all the tested concentrations and to the seeds and plants (SP) at the concentration of 50 mg L−1. In turn, these parameters were strongly positively correlated with CuNPs applied to the S and SP groups at the concentration of 50 mg L−1 as well as Ag applied to SP at 100 mg L−1. Decrease in dehydrogenase activity (DHA) was lower after the application of CuNPs and AgNPs in S than in the SP way, and the DHA activity was equal to the activity in the control sample after the CuNP application in 100 and 150 mg L−1 concentrations.