Search results for "Gibbs free energy"
showing 10 items of 88 documents
Polymer solutions: Equilibrium clusters versus shear clusters
2021
Abstract Polymer solutions are inhomogeneous on mesoscopic scales as a result of chemical bonds linking their monomeric units. This situation leads to polymer clusters within which the polymer concentration c cluster is only a small fraction of the overall concentration c. The ratio c/ c cluster (overlap parameters Ω ) quantifies the number of clusters that need to overlap to yield c. Equilibrium clusters (minimization of Gibbs energy) and shear clusters (minimization of entropy production) differ fundamentally where Ω equil ≥ Ω shear . Only in the vicinity of the glass transition temperature and at high concentration the opposite is the case. Experimental information on Ω equil as a functi…
On the pyrolytic decomposition of cadmium carbonate
1996
The pyrolytic decomposition of cadmium carbonate was studied by thermogravimetry (TG), derivative thermogravimetry (DTG), differential thermoanalysis (DTA) and exoemission of electrons (EEE).
N-doped carbon networks: alternative materials tracing new routes for activating molecular hydrogen.
2014
The fragmentation of molecular hydrogen on N-doped carbon networks was investigated by using molecular (polyaromatic macrocycles) as well as truncated and periodic (carbon nanotubes) models. The computational study was focused on the ergonicity analysis of the reaction and on the properties of the transition states involved when constellations of three or four pyridinic nitrogen atom defects are present in the carbon network. Calculations show that whenever N-defects are embedded in species characterized by large conjugated π-systems, either in polyaromatic macrocycles or carbon nanotubes, the corresponding H2 bond cleavage is largely exergonic. The fragmentation Gibbs free energy is affect…
Calculation of partition coefficient and hydrophobic moment of the secondary structure of lysozyme
2001
A method that permits a semiquantitative estimate of the partitioning of any solute between any two media is presented. As an example, the partition coefficients and hydrophobic moment of the secondary structure of lysozyme are calculated. Program GSCAP is written as a version of Pascal's solvent-dependent conformational analysis (SCAP) program. The dipole moments calculated for the helices are trebled with respect to that for the sheet. For helices, the main contribution to the water-accessible surface area is the hydrophobic term, while the hydrophilic part dominates in the sheet. Molecular globularity and the three studied partition coefficients differentiate between helices and sheet.
A Molecular Electron Density Theory Study of the Synthesis of Spirobipyrazolines through the Domino Reaction of Nitrilimines with Allenoates
2019
The reaction of diphenyl nitrilimine (NI) with methyl 1-methyl-allenoate yielding a spirobipyrazoline has been studied within molecular electron density theory (MEDT) at the MPWB1K/6-311G(d) computational level in dichloromethane. This reaction is a domino process that comprises two consecutive 32CA reactions with the formation of a pyrazoline intermediate. Analysis of the relative Gibbs free energies indicates that both 32CA reactions are highly regioselective, the first one being also completely chemoselective, in agreement with the experimental outcomes. The geometries of the TSs indicate that they are associated to asynchronous bond formation processes in which the shorter distance invo…
Phase diagrams calculated for sheared ternary polymer blends
1997
Abstract On the basis of the generalized Gibbs energy of mixing G γ (which is the sum of the Gibbs energy for zero shear and the energy the system stores in steady flow) phase diagrams were calculated as a function of shear rate γ for ternary model blends. This modelling uses simple equations for the description of the stagnant systems (Flory-Huggins) and for the contributions resulting from flow. Surface and alignment effects are neglected. A new procedure, which does not require the derivatives of G γ with respect to composition, was used to that end. Choosing typical values for the binary interaction parameters and molar masses, four classes of ternary systems were studied in greater det…
Ab initio simulations of oxygen interaction with surfaces and interfaces in uranium mononitride
2012
Abstract The results of DFT supercell calculations of oxygen behavior upon the UN (0 0 1) and (1 1 0) surfaces as well as at the tilt grain boundary are presented. Oxygen adsorption, migration, incorporation into the surface N vacancies on (0 0 1) and (1 1 0) surfaces have been modeled using 2D slabs of different thicknesses and supercell sizes. The temperature dependences of the N vacancy formation energies and oxygen incorporation energies are calculated. We demonstrate that O atoms easily penetrate into UN surfaces and grain boundaries containing N vacancies, due to negative incorporation energies and a small energy barrier. The Gibbs free energies of N vacancy formation and O atom incor…
Analytical, thermodynamical and kinetic characteristics of photoluminescence immunosensor for the determination of Ochratoxin A
2017
Ochratoxin A (OTA) is one of the most widespread and dangerous food contaminants. Therefore, rapid, label-free and precise detection of low OTA concentrations requires novel sensing elements with advanced bio-analytical properties. In the present paper we report photoluminescence (PL) based immunosensor for the detection of OTA. During the development of immunosensor photoluminescent ZnO nanorods (ZnO-NRs) were deposited on glass substrate. Then the ZnO-NRs were silanized and covalently modified by Protein-A (Glass/ZnO-NRs/Protein-A). The latest structure was modified by antibodies against OTA (Anti-OTA) in order to form OTA-selective layer (Glass/ZnO-NRs/Protein-A/Anti-OTA). In order to im…
Synthesis, characterization and thermal degradation of 8-hydroxyquinoline–guanidine–formaldehyde terpolymer
2007
Abstract Terpolymer (8-HQGF) has been synthesized using the monomers 8-hydroxyquinoline, guanidine, formaldehyde in 1:1:2 molar proportions. The structure of 8-HQGF terpolymer has been elucidated on the basis of elemental analysis and various physicochemical techniques, i.e. UV–Visible, FTIR–ATR and 1 H NMR spectroscopy. Detailed thermal degradation study of the new terpolymer has been carried out to ascertain its thermal stability. Thermal degradation curve is discussed which shows two decomposition steps (265–475 °C and 540–715 °C). Sharp–Wentworth and Freeman–Carroll methods have been used to calculate activation energies and thermal stability. The activation energy ( E a ) calculated by…
Jahn-Teller effect in the phonon properties of defective SrTiO3from first principles
2012
the Jahn–Teller effect occurs, thus reducing the cubic symmetry of a perfect crystal and leading to the appearance of both Raman- and infrared-active vibrational modes. The calculated phonon densities of states and group-theoretical analysis of defect-induced phonon frequencies were used for the interpretation of the relevant experimental data, once defect-induced local modes are identified. The temperature dependence of the Vo formation energy based on the calculated Gibbs free energy was also compared with experiments, and the phonon contribution therein estimated.