Thermal Conductivity of Detonation Nanodiamond Hydrogels and Hydrosols by Direct Heat Flux Measurements

The methodology and results of thermal conductivity measurements by the heat-flow technique for the detonation nanodiamond suspension gels, sols, and powders of several brands in the range of nanoparticle concentrations of 2–100% w/w are discussed. The conditions of assessing the thermal conductivity of the fluids and gels (a FOX 50 heat-flow meter) with the reproducibility (relative standard deviation) of 1% are proposed. The maximum increase of 13% was recorded for the nanodiamond gels (140 mg mL−1 or 4% v/v) of the RDDM brand, at 0.687 ± 0.005 W m−1 K−1. The thermal conductivity of the nanodiamond powders is estimated as 0.26 ± 0.03 and 0.35 ± 0.04 W m−1 K−1 for the RUDDM and RDDM brands, respectively. The thermal conductivity for the aqueous pastes containing 26% v/v RUDDM is 0.85 ± 0.04 W m−1 K−1. The dignities, shortcomings, and limitations of this approach are discussed and compared with the determining of the thermal conductivity with photothermal-lens spectrometry

Insolvency proceedings of a natural person

Bakalaura darba tēma – “Fiziskās personas maksātnespējas process”. Bakalaura darba mērķis ir, pamatojoties uz teorētiskām atziņām un normatīvā regulējuma analīzi, izpētīt fiziskās personas maksātnespējas procesu, un izstrādāt priekšlikumus procesa pilnveidošanai. Autore pēta fiziskās personas maksātnespējas procesa teorētiskos aspektus un norises kārtību, kā arī maksātnespējas ietekmi uz ekonomiku un fizisko personu; maksātnespējas cēloņus. Pētījuma gaitā intervēta persona, kas veiksmīgi uzsākusi un pabeigusi fiziskās personas maksātnespējas procesu, analizēti iegūtie dati. Darba nobeigumā izstrādāti priekšlikumi fiziskās personas maksātnespējas procesa uzlabošanai. Pētniecības darbā izmantotas dažādas metodes, tai skaitā: teorētiskā metode, izmantojot, apkopojot un analizējot informāciju no dažādiem elektroniskajiem avotiem, zinātniskajiem rakstiem, LR likumdošanas u.c., statistiskā pētījumu metode, izmantojot pieejamās statistikas, apkopojot un analizējot tajās ietvertos datus, socioloģisko pētījumu metode un grafiskā metode, ilustratīvi attēloti iegūtie dati un informācija.Bachelor's work theme – “Insolvency proceedings of a natural person”. The aim of the bachelor's thesis is, based on theoretical findings and analysis of the regulatory framework, to study the insolvency process of a natural person, and to develop proposals for the improvement of the process. The author studies the theoretical aspects of the insolvency process of a natural person and the procedure, as well as the impact of insolvency on the economy and a natural person; causes of insolvency. In the course of the research, a person who has successfully started and completed the insolvency process of a natural person was interviewed, and the obtained data were analyzed. At the end of the work, proposals for the improvement of the insolvency process of a natural person have been developed. Various methods have been used in the research, including: theoretical method, using, summarizing and analyzing information from various electronic sources, scientific articles, legislation of the Republic of Latvia, etc., statistical research method, using available statistics, summarizing and analyzing data, sociological research method and graphical method, illustrating the obtained data and information

On a specific state of C60_{60} fullerene in N-methyl-2-pyrrolidone solution: Mass spectrometric study

A solution of fullerene C$_{60}$ in N-methylpyrrolidone (NMP) presents a suitable system for obtaining fullerene's clusters with the tunable size. However, the mechanism of fullerenes interaction with polar NMP molecules is still elusive. Herein, we present the measured laser desorption/ionization mass spectra (LDI MS) of the precipitates produced from C$_{60}$/NMP solutions of different age in comparison with the typical spectra of C$_{60}$ crystallized from toluene and benzene. The distinctive characteristics of the C$_{60}$/NMP mass spectra were identified and carefully examined. The number of characteristic peaks and their relative intensities in the spectra strongly depend on the age of initial C$_{60}$/NMP solutions. This effect was attributed to the specific C$_{60}$-NMP interactions in the solution, namely to the formation of charge-transfer complexes of C$_{60}$ with NMP molecules followed by fullerene cluster formation. The results of additional measurements carried out by means of small-angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR), UV–Vis absorption spectroscopy together with the density functional theory (DFT) calculations are in accord with the proposed hypothesis

Swollen Structures of Brodie Graphite Oxide as Solid Solvates

Swelling of Brodie graphite oxide (B-GO) was studied for a series of normal alcohols from methanol to 1-nonanol. Isopiestic, X-ray diffraction (XRD), thermogravimetric, and differential scanning calorimetry data demonstrated that sorption of polar liquids into GO lamellas formed the set of regular swollen structures, simple binary “solid solvates”, characterized by the distance between the GO planes and the value of sorption. Temperature–composition behavior of the swollen structures was adequately described by conventional binary phase diagrams. Phase transformation of the low-temperature swollen structure of B-GO with 1-nonanol gave a clear example of incongruent melting transition typical for the binary solvates. A discreet set of the interplane distances observed by XRD and the stepwise equilibrium desorption pointed to the layered arrangement of solvent molecules in the swollen structures. The swollen structures with one to five parallel layers were observed for a series of normal alcohols with B-GO. The average volume of one layer, 0.36 ± 0.06 cm3 g–1 B-GO, was almost the same for rather different organic liquids and was possibly restricted by the internal geometry of B-GO. This internal volume available for the sorption of the first layer was reasonably estimated from geometrical parameters of B-GO

Sorption of polar organic solvents and water by graphite oxide : thermodynamic approach

Sorption of polar organic solvents CH3OH, C4H8O (THF), CH3CN, C3H7NO (DMF), C2H6OS (DMSO), C5H9NO (NMP) and water was quantitatively evaluated for Hummers (H-GO) and Brodie (B-GO) graphite oxides at T = 298K and at melting temperature (Tm) of the solvents. H-GO showed stronger sorption compared to B-GO for all studied solvents and the increase of sorption upon lowering temperature was observed for both H-GO and B-GO. Thermodynamic equations allowed to explain earlier reported "maximums" of swelling/sorption in the binary systems H-GO – solvent at Tm. The specific relation between the values of enthalpies of sorption and melting leads to the change of sign in enthalpies of sorption at Tm and causes maximal swelling/sorption. The same thermodynamic explanation was given for the "maximum" on the swelling vs. pressure dependence in B-GO and H-GO – H2O systems earlier reported at pressure of phase transition "liquid water-ice VI". Notably higher sorption of H2O was observed for H-GO compared to H-GO membrane (H-GOm) at high relative humidity (RH), RH > 0.75. Experimental sorption isotherm of H-GOm was used to simulate permeation rates of water through H-GOm and to estimate effective diffusion coefficient of water through the membrane

Swelling of graphene oxide membranes in alcohols : effects of molecule size and air ageing

Swelling of Hummers graphene oxide (HGO) membranes in a set of progressively longer liquid alcohols (methanol to 1-nonanol) was studied using synchrotron radiation XRD after air ageing over prolonged periods of time. Both precursor graphite oxides and freshly prepared HGO membranes were found to swell in the whole set of nine liquid alcohols with an increase of interlayer spacing from approximate to 7 angstrom (solvent free) up to approximate to 26 angstrom (in 1-nonanol). A pronounced effect of ageing on swelling in alcohols was found for HGO membranes stored in air. The HGO membranes aged for 0.5-1.5 years show progressively slower swelling kinetics, a non-monotonic decrease of saturated swelling in some alcohols and complete disappearance of swelling for alcohol molecules larger than hexanol. Moreover, the HGO membranes stored under ambient conditions for 5 years showed a nearly complete absence of swelling in all alcohols but preserved swelling in water. In contrast, precursor graphite oxide powder showed unmodified swelling in alcohols even after 4 years of ageing. Since the swelling defines the size of permeation channels, the ageing effect is one of the important parameters which could explain the strong variation in reported filtration/separation properties of GO membranes. The time and conditions of air storage require standardization for better reproducibility of results related to performance of GO membranes in various applications. The ageing of GO membranes can be considered not only as a hindrance/degradation for certain applications, but also as a method to tune the swelling properties of HGO membranes for better selectivity in sorption of solvents and for achieving better selective permeability

Vapor Composition and Vaporization Thermodynamics of 1-Ethyl-3-methylimidazolium Hexafluorophosphate Ionic Liquid

The processes of the sublimation and thermal decomposition of the 1-ethyl-3-methylimidazolium hexafluorophosphate ionic liquid (EMImPF6) were studied by a complex approach including Knudsen effusion mass spectrometry, IR and NMR spectroscopy, and quantum chemical calculations. It was established that the vapor over the liquid phase primarily consists of decomposition products under equilibrium conditions. Otherwise, the neutral ion pairs are the only vapor components under Langmuir conditions. To identify the nature of the decomposition products, an experiment on the distillation of the ionic liquid was performed and the collected distillate was analyzed. It was revealed by the IR and NMR spectroscopy that EMImPF6 decomposes to substituted imidazole-2-ylidene (C6N2H10PF5) and HF. The measured vapor pressure of C6N2H10PF5 reveals a very low activity of the decomposition products (−4) in the liquid phase. The absence of a significant accumulation of decomposition products in the condensed phase makes it possible to determine the enthalpy of sublimation of the ionic liquid assuming its unchanged activity. The thermodynamics of the EMImPF6 sublimation was studied by Knudsen effusion mass spectrometry. The formation enthalpy of EMImPF6 in the ideal gas state was found from a combination of the sublimation enthalpy and formation enthalpy of the ionic liquid in the condensed state. The obtained value is in good agreement with those calculated by quantum chemical methods

Approach to the Assessment of Size-Dependent Thermal Properties of Disperse Solutions: Time-Resolved Photothermal Lensing of Aqueous Pristine Fullerenes C₆₀ and C₇₀

An approach is proposed for assessment of the thermal properties of aqueous pristine fullerene C₆₀ and C₇₀ dispersions (AFDs) at the level of 10^–7–10^–5 mol L^–1 by photothermal (thermal-lens) spectroscopy for their application in medicine and technology. Along with relevant size-characterization techniquesdifferential scanning calorimetry (DSC) with the Gibbs–Kelvin equation and dynamic light scattering (DLS) techniquesthis approach provides an estimation of the size-dependent thermal properties of disperse solutionsthermal diffusivity, thermal effusivity [thermal inertia], and thermal conductivity. The values for AFDs under the conditions of the attained thermal equilibrium show good precision, and the cluster size estimations agree with the reference methods. The reconstruction of the thermal-lens characteristic time over the course of the blooming of the thermal-lens effect reveals a short increase in the apparent thermal diffusivity. This is accounted for by nonequilibrium heat transfer within fullerene clusters upon initial laser heating, which is supported by the independent estimations from widespread methods like high-resolution transmission electron microscopy, DLS, and DSC. Thermophysical parameters of the disperse phase estimated from transient thermal lensing are as follows: thermal diffusivity, 1.6–2.0 × 10^–7 m² s^–1 depending on fullerene concentration and up to 3.5 × 10^–7 m² s^–1, more than 2-fold higher than for water; thermal effusivity, 6.7 × 10² J m^–2 K^–1 s^–1/2, three times lower than for water