Ústav fyzikální a spotřební chemie

Browse

Recent Submissions

Now showing 1 - 5 of 114
  • Thumbnail Image
    Item
    Effect of shear-thinning on pressure-swirl atomization
    (2026-02-01) Jedelský, Jan; Cejpek, Ondřej; Malý, Milan; Kadlec, Martin; Smilek, Jiří; Strmiska, Pavel; Hájek, Ondřej
    Atomization of non-Newtonian liquids is an underexplored topic despite their numerous spray applications. Key spray characteristics in such processes are mean droplet size and size distribution. Several studies demonstrate that non-Newtonian shear-thinning liquids can narrow the droplet size distribution compared to Newtonian liquids, reducing the number of excessively small or large droplets. Various spray applications benefit from minimized occurrence of droplets outside the desired size range. This applies to atomizers in spray towers or agricultural sprays where too-small droplets are blown away while those too large are ineffectively used. In this study, several non-Newtonian dilute aqueous solutions with different degrees of shear-thinning were prepared by mixing Xanthan Gum or Sodium carboxymethyl cellulose with deionized water. Their performance was compared with Newtonian sprays (water and water-glycerol solution) of comparable shear viscosity at defined shear rates. A common pressure-swirl atomizer was used, and a range of operational pressures along with varying viscosities allowed for examining the spraying process across a wide spectrum of Reynolds and Weber numbers. Velocity and size of droplets in the spray were measured simultaneously using a 1D phase Doppler anemometer. High-speed visualization was employed to track spray morphology and the breakup process. Calculations of the flow parameters inside the atomizer complemented these outcomes. Results show that varying viscosity and shear-thinning behaviour influence the flow dynamics from the liquid entry into the atomizer to the fully developed spray. Viscoelasticity complicates these processes further. The discharge occurs near the infinite-shear rate viscosity plateau, and its character depends, primarily on the flow conditions near the exit orifice. The shear-thinning and elasticity slightly affects liquid breakup, with production of more frequent and longer-lasting ligaments. Droplet size reduces with increasing pressure as expected, and this effect is more pronounced for non-Newtonians, the impact on the Relative span factor is inconsistent. Downstream droplet size increases for all liquids due to coalescive droplet collisions, with the secondary breakup and evaporation being ineffective.
  • Thumbnail Image
    Item
    Impact of Microwave Plasma Torch on the Yeast Candida glabrata
    (MDPI, 2020-08-11) Trebulová, Kristína; Krčma, František; Kozáková, Zdenka; Skoumalová, Petra
    Recently, various cold plasma sources have been tested for their bactericidal and fungicidal effects with respect to their application in medicine and agriculture. The purpose of this work is to study the effects of a 2.45 GHz microwave generated plasma torch on a model yeast example Candida glabrata. The microwave plasma was generated by a surfatron resonator, and pure argon at a constant flow rate of 5 Slm was used as a working gas. Thanks to a high number of active particles generated in low-temperature plasma, this type of plasma has become highly popular, especially thanks to its bactericidal effects. However, its antimycotic effects and mechanisms of fungal inactivation are still not fully understood. Therefore, this study focuses on the antifungal effects of the microwave discharge on Candida glabrata. The main focus is on the measurement and evaluation of changes in inactivation effects caused by varying initial concentration of Candida glabrata cells, applied microwave power and exposure time. The discharge was applied on freshly inoculated colonies of Candida glabrata spread on the agar plates and its inhibitory effects were observed in the form of inhibition zones formed after the subsequent cultivation.
  • Thumbnail Image
    Item
    Determination of Critical Parameters of Drug Substance Influencing Dissolution: A Case Study
    (Hindawi Publishing Corporation, 2014-09-15) Bojňanská, Erika; Kalina, Michal; Pařízek, Ladislav; Bartoníčková, Eva; Opravil, Tomáš; Veselý, Michal; Pekař, Miloslav; Jampílek, Josef
    The purpose of this study was to specify critical parameters (physicochemical characteristics) of drug substance that can affect dissolution profile/dissolution rate of the final drug product manufactured by validated procedure from various batches of the same drug substance received from different suppliers.The target was to design a sufficiently robust drug substance specification allowing to obtain a satisfactory drug product. For this reason, five batches of the drug substance and five samples of the final peroral drug products were analysed with the use of solid state analysis methods on the bulk level. Besides polymorphism, particle size distribution, surface area, zeta potential, and water content were identified as important parameters, and the zeta potential and the particle size distribution of the drug substance seem to be critical quality attributes affecting the dissolution rate of the drug substance released from the final peroral drug formulation.
  • Thumbnail Image
    Item
    High-Resolution Ultrasonic Spectroscopy: Looking at the Interpolyelectrolyte Neutralization from a Different Perspective
    (American Chemical Society, 2023-02-14) Klačić, Tin; Jugl, Adam; Pekař, Miloslav; Kovačević, Davor
    In this study, the high-resolution ultrasonic spectroscopy (HR-US) technique was applied to examine interpolyelectrolyte neutralization. The mentioned method was tested on the example of complexation between poly(allylammonium) cations and poly(acrylate) anions in aqueous solutions at pH = 7. It was confirmed by HR-US that the type of titration (stepwise or abrupt), the direction of titration, and the type of background salt affect the outcome of interpolyelectrolyte neutralization. The obtained results were explained on the basis of ultrasonic velocity and attenuation changes in the context of suspension compressibility, a parameter that is extremely sensitive to molecular organization and intermolecular interactions. Moreover, the results of HR-US measurements proved to be consistent with previous results obtained by more traditional methods such as dynamic light scattering, microcalorimetry, and electrokinetics. This research demonstrates that HR-US is a convenient and reliable method that can be employed for the investigation of interpolyelectrolyte neutralization and polyelectrolyte-related processes.
  • Thumbnail Image
    Item
    Polarity-Based Sequential Extraction as a Simple Tool to Reveal the Structural Complexity of Humic Acids
    (MDPI, 2021-03-19) Enev, Vojtěch; Sedláček, Petr; Kubíková, Leona; Bačovská, Šárka; Doskočil, Leoš; Klučáková, Martina; Pekař, Miloslav
    A sequential chemical extraction with a defined series of eluotropic organic solvents with an increasing polarity (trichloromethane < ethyl acetate < acetone < acetonitrile < n-propanol < methanol) was performed on peat-bog humic acid. Six organic fractions were obtained and subjected to a physicochemical characterization utilizing methods of structural and compositional analysis. Advanced spectroscopic techniques such as Attenuated Total Reflectance (ATR-FTIR), total luminescence, and liquid-state 13C NMR spectrometry were combined with elemental analysis of the organic fractions. In total, the procedure extracted about 57% (wt.) of the initial material; the individual fractions amounted from 1.1% to 19.7%. As expected, the apolar solvents preferentially released lipid-like components, while polar solvents provided organic fractions rich in oxygen-containing polar groups with structural parameters closer to the original humic material. The fraction extracted with acetonitrile shows distinct structural features with its lower aromaticity and high content of protein-like structural motifs. The last two—alcohol extracted—fractions show the higher content of carbohydrate residues and their specific (V-type) fluorescence suggests the presence of plant pigment residues. The extraction procedure is suggested for further studies as a simple but effective way to decrease the structural complexity of a humic material enabling its detail and more conclusive compositional characterization.