In the current work, a systematic investigation on the thermal behavior of gestodene was carried out to understand temperature induced solid-state transitions between its polymorphs and amorphous phase. The focus was on polymorph identification, thermal stability analysis, and the nature of the phase transitions. These characteristics were compared to the complexity of the phase transitions, studied by differential scanning calorimetry (DSC) and variable temperature X-ray powder diffraction (VT-XRD) techniques. DSC studies indicated that the form II was enantiotropically related to form I, which melted at about 470 K. The temperature of polymorphic transition was 309 K, and form II was the more stable form between room temperature and the transition temperature. A schematic Gibbs free energy-temperature diagram was subsequently constructed to describe the thermal stability of the two forms. Amorphous phase converted exothermically to form I at 368 K on heating and was shown by VT-XRD to be accompanied by diffraction pattern changes. In addition, the crystallization kinetics studied by DSC heating technique followed by analysis using the Kissinger–Akahira–Sunose (KAS) method where values of apparent activation energy (Ea) were estimated as a function of extent of conversion (α). The variations in Ea with α on kinetic analysis from α = 0.10 to 0.88 for the amorphous to form I conversion suggested more complex processes, possibly liquid–solid and solid–solid transformations prior to formation of the form I.

The electric double layer capacitances for a series of titanium dioxide based composite nanotube-arrays (TNTAs, Pt/TNTAs, CdS/TNTAs, CdS/Pt/TNTAs) in aqueous solutions were examined at the polarized potential. As a result, the capacitance increases with a decrease in the ac-frequency, obeying the inverse of the power law of the frequency. The power law is demonstrated to be equivalent to the constant phase element. The intensity of frequency dispersion varies with nanoarrays as to different nano architectonics and materials. The CdS coated TNTAs yield the largest specific capacitance of 2.33 mF cm− 2 at a frequency of 1 Hz, which is about 9 times higher than the capacitance obtained from bare TNTAs at the same condition. The coating of Pt, however, shows less capacitive behavior with more obvious frequency-dispersion.

•The solubility measurements were performed using the dynamic method.•The solubility data increases with rising temperature and initial mole fraction of ethanol.•The modified Apelblat equation is the best correlation model.•The dissolution process of DMHF is endothermic and enthalpy-driven.In the present study, the solubility and dissolution thermodynamics of 4-hydroxy-2,5-dimethyl-3(2H)-furanone (DMHF) in ethanol + water co-solvent mixtures were experimentally measured over the temperature range from 283.15 to 313.15 K under the atmospheric pressure of 0.1 MPa. Measurements were performed using the dynamic method coupled with a laser monitoring system as the observation technique. The onset fusion point temperature and enthalpy of fusion were determined by differential scanning calorimetry (DSC). The effects of temperature and co-solvent composition on the solubility data were discussed. The mole fraction solubility (42.71 × 10− 2 at 313.15 K) of DMHF was observed highest in pure ethanol. However, the lowest mole fraction solubility (0.9112 × 10− 2 at 283.15 K) of DMHF was found in distilled water. The experimental solubilities of DMHF were correlated with the modified Apelblat equation, van't Hoff equation, λh equation and Combined Nearly Ideal Binary Solvent/Redlich–Kister (CNIBS/R–K) model. The used correlation models were all proven to give good agreement with the experimental data and the modified Apelblat equation provided the best correlation results. Dissolution thermodynamic studies indicated that the dissolution process of DMHF was endothermic and enthalpy-driven. Based on the current solubility data, DMHF has been considered as freely soluble in pure ethanol and slightly soluble in distilled water.

•Measurements were performed using the dynamic method.•The solubility data increases with increasing temperature.•The modified Apelblat equation is the best thermodynamic method.•The dissolution process of DMHF is endothermic and enthalpy-driven.The objective of this work was to measure and correlate the solubility of 4-hydroxy-2,5-dimethyl-3(2H)-furanone (DMHF) in six pure solvents, including methanol, ethanol, n-propyl alcohol, n-butyl alcohol, n-hexane and distilled water, over the temperature range from 283.15 K to 313.15 K under atmospheric pressure of 0.10 MPa. Measurements were performed using the dynamic method coupled with a laser monitoring system as the observation technique. The solubility of DMHF in all the selected solvents was found to increase with rising temperature, and methanol has much more dissolving capacity for the DMHF solute. The experimental solubility of DMHF in pure solvents was well correlated with the modified Apelblat equation, van’t Hoff equation and λh equation. The results of the error analysis indicated that the modified Apelblat equation was able to give more accurate and reliable predictions of solubility with the relative average deviation (RAD) and root-mean-square deviation (RMSD) values being observed in the range of 0.21–0.67% and 0.01–0.13%, respectively. The modified Apelblat equation was therefore used to estimate the changes of dissolution enthalpy (ΔdissH°), dissolution entropy (ΔdissS°) and molar Gibbs free energy (ΔG°diss) of DMHF in the solvents investigated. The positive values of the ΔdissH°, ΔdissS° and ΔdissG° revealed the dissolution process of DMHF in the selected solvents was endothermic and enthalpy-driven.

A novel class of organosilicon gemini quaternary ammonium surfactant alkyl-α, ω-bis(diethyl-methyl-dimethoxy-silopropyl ammonium bromide) (α, ω = 1,4; 1,6; 1,8) was synthesized and characterized by 1H-nuclear magnetic resonance (NMR) and elemental analysis. It is found that the quaternization reaction has two steps: first single quaternization and then double quaternization. The effect of solvent on convert ratio has the following sequence: polar aprotic solvents > polar protic solvents > aromatic solvents. The electrical conductivity of aqueous solution was measured at 20, 25, 30 and 35 °C, and the thermodynamic properties of \( \Delta H_{m}^{0} \), \( \Delta G_{m}^{0} \) and \( T\Delta S_{m}^{0} \) were calculated according to the mass action model and Gibbs equation. It is shown that the enthalpy driven and entropy driven are almost equal in the micellization of [SiC3-4-SiC3]Br2 and [SiC3-6-SiC3]Br2, but in the micellization of [SiC3-8-SiC3]Br2, the enthalpic contribution becomes significant and the effect of thermal is greater than the degree of order in the micellization.

To better understand the hydrodynamic behavior of an internally circulating fluidized bed, solids holdup in the down-comer (ɛsD), solids circulation rate (Gs) and gas bypassing fraction (from down-comer to riser γDR, and from riser to down-comer γRD) were experimentally studied. The effects of gas velocities in the riser and in the down-comer (UR and UD), orifice diameter in the draft tube (dor), and draft tube height (HR) were investigated. Experimental results showed that increase of gas velocities led to increase in Gs and γDR, and slight decrease in γRD. Larger orifice diameter on the draft tube led to higher ɛsD, Gs and γDR, but had insignificant influence on γRD. With increasing draft tube height, both Gs and γDR first increased and then decreased, while γRD first decreased and then increased. Proposed correlations for predicting the hydrodynamic parameters agreed reasonably well with experimental values.Graphical abstractHighlights► The internally circulating fluidized bed with a tubular distributor was studied. ► While varying operating conditions, Gs and γDR follow a similar trend, but γRD is opposite to γDR. ► γRD was smaller than 10%, and may be decreased further. ► Correlations were obtained to predict Gs, γRD and γDR.

•The digoxin MIP-sensor was developed.•The device can detect digoxin in the serum samples without pretreatment.•The detection is simple, inexpensive, fast, precise, sensitive and label free.•The linear relationship between the digoxin concentration and the current is 1.28–128 Nm.•A detection limit is 1.28 nM. The detection time is less than 5 min.A novel biosensor (the synthetic receptor sensor) employing the molecular imprinted technology for the digoxin analysis is investigated. The molecularly imprinted polymer (MIP) modified electrode can specifically bind to the analyte in the sample without sample pretreatment. The digoxin analyzed by the MIP sensor was carried out in 1 mM K3Fe(CN)6 solution with the cyclic voltammetry. In the system, the K3Fe(CN)63−/Fe2(CN)64− redox couple was taking place. When the solution contains the digoxin, the MIP on the electrode will bind the digoxin. Further the redox system is interrupted and the peak current is decreased according to the digoxin concentration increasing. Digoxin is a glycosylated steroid-like drug. It is important for the heart disease treatment. However, since the digoxin toxic level is low, the drug remains in the blood sample must be monitored frequently. The device possesses many advantages, such as high specific recognition properties, good chemical and mechanical stability, simplicity and low cost of preparation, sensitive and label free determination. The reproducibility is good (CV < 5). The linear relationship between the digoxin concentration and the current is 1.28–128 nM, and a detection limit of 1.28 nM is achieved. The detection time is less than 5 min.

The solubility of potassium bromide in binary solvents formed by acetone and water was determined in the temperature range between (288.15 and 313.15) K at atmospheric pressure using an isothermal method. The reliability of the measured method used in this study was checked by comparing the experimental data with published data in the literature for the KBr−water system, and the method proved to be accurate. Experimental solubility data were correlated with Sechenov’s equation.

•The solubility data of the two polymorphs (forms I and II) of gestodene were measured.•The metastable zone widths of both forms were determined by FBRM.•Nucleation kinetics parameters were evaluated to understand the nucleation behavior.A systematic investigation of nucleation behavior for the batch cooling crystallization of unseeded gestodene–ethanol solutions was carried out. The solubilities of the two polymorphs (forms I and II) of gestodene in ethanol were gravimetrically measured between 268.15 and 333.15 K under atmospheric pressure of 0.10 MPa. In addition, the metastable zone widths (MSZWs) of the gestodene–ethanol solutions were determined by the polythermal method combined with the focused beam reflectance measurement (FBRM®) technique. Moreover, polymorphic forms of the grown crystals were identified by X-ray powder diffraction (XRD) and optical microscope. Experimental results indicated that the measured MSZWs were dependent on numerous technological parameters, including cooling rate, saturation temperature, and agitation intensity. With variation of the nucleation temperature and cooling rate, forms I, II, and a mixture of the two forms were crystallized from ethanol solution. The nucleation kinetic parameters were estimated from MSZW data using the self-consistent Nývlt-like approach. Due to the high solubility of form I in ethanol at the corresponding temperature range, the stronger solute–solvent interactions confirmed that the nucleation of form I had a greater activation energy than that of form II.