Synthesis and characterization of cellulose-g-polyoxyethylene (2) hexadecyl ether solid–solid phase change materials

A series of novel solid–solid phase change materials, namely, cellulose-g-polyoxyethylene (2) hexadecyl ether (Cellulose-g-E₂C₁₆) copolymers, were synthesized using toluene 2,4-diisocyanate (TDI) as a coupling reagent in the ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl). The optimum prepolymerization conditions were determined to be 25 °C and 75 min without catalyst, and the optimum reaction conditions of the grafting step were 90 °C, 6 h and 0.1 wt% dibutyltin dilaurate (DBTDL, weight percent of TDI). The successful grafting was confirmed by FTIR and ¹H-NMR. The properties of the Cellulose-g-E₂C₁₆ copolymers were investigated by DSC, TG and XRD. It is shown that the heat storage ability and phase change temperature of Cellulose-g-E₂C₁₆ copolymers depended on the degree of substitution. The crystalline type of the grafted E₂C₁₆ was not affected by the cellulosic backbone. Compared with E₂C₁₆, Cellulose-g-E₂C₁₆ copolymers showed better thermal stability. They are expected to be widely applied in the area of thermal energy storage.     

Synthesis and characterization of alkyl cellulose ω-carboxyesters for amorphous solid dispersion

Poor drug solubility and consequently poor bioavailability are major impediments to new drug innovation, and they limit the performance of many existing drugs. In recent years amorphous solid dispersion (ASD) has emerged as one of the most effective approaches for enhancing drug solution concentration, and thereby bioavailability, including in many marketed drug formulations. Recently efforts have been under way in several laboratories to design new ASD polymers, rather than relying on polymers that are already in FDA-approved formulations, but were not designed as ASD polymers. We describe here the design and synthesis of a new class of polymers, alkyl cellulose ω-carboxyesters, for ASD formulation. We synthesize these polymers by reaction of cellulose alkyl ethers with monoprotected (benzyl ester), monofunctional long chain acid chlorides, followed by protecting group removal using mild hydrogenolysis to form the target alkyl cellulose ω-carboxyalkanoate. These new amphiphilic polymers have high glass transition temperatures (T_g), tunable carboxyl content for controlling release pH and drug-polymer interactions, and certain members of this new group of amphiphilic cellulose ether esters are shown to be successful at forming ASDs with the important model drug ritonavir. These ASDs efficiently release ritonavir at small intestine pH, creating the maximum attainable amorphous solubility (20 μg/mL), and maintaining it for a time period substantially greater than the normal residence time in the absorptive region of the stomach and small intestine. Members of this new class of alkyl cellulose ω-carboxyester amphiphiles show significant potential as ASD polymers for enhancing oral bioavailability of otherwise poorly soluble drugs.     

Measurement and correlation of solid–liquid equilibria of Irganox 1010 with n-hexane

Solid–liquid equilibria (SLE) for the binary mixtures of Irganox 1010 with n-hexane have been measured using a method in which an excess amount of solute was equilibrated with the alkane solution. The liquid concentrations of the Irganox 1010 in the saturated solution were analyzed by UV spectrometry. Activity coefficients for Irganox 1010 have been calculated by means of the Wilson, NRTL and UNIQUAC models and with them were correlated solubility data that were compared with the experimental ones. The best correlation of the solubility data has been obtained by the Wilson model, by which the average root-mean-square deviation of temperature for the system is 0.33 K.     

Bulk physicochemical properties of solid solutions and binary components of the InSb—CdS system

The bulk physicochemical properties (X-ray diffraction, thermographic, and electrophysical) of solid solutions and binary components of the new, not studied earlier, InSb-CdS system are investigated by means of current methods. Solid solutions are obtained in the form of powders and thin films (in a wide range of compositions) by isothermal diffusion of binary components (InSb, CdS) and by discrete thermal deposition on various substrates, respectively. The limited mutual solubility of the components in the InSb-CdS system is found; the interval of the solubility of CdS in InSb is 0-(3–4) mol %. The shortness of the range is related to the energy and geometric factors. The regularities in the behavior of the X-ray diffraction (the lattice parameters and the density), thermographic (the positions and the intensities of endoand exoeffects), electrophysical (the electrical conductivity) properties depending on the composition of the InSb-CdS are revealed. The influence on the physicochemical properties of the system, their behavior, and the interaction between the binary and elemental components is presented.     

Inclusion complexes of lamotrigine and hydroxy propyl β-cyclodextrin: solid state characterization and dissolution studies

Lamotrigine (LMN) is an antiepileptic drug, with poor aqueous solubility, which might lead to erratic bioavailability. The objective of the present work was to improve the dissolution characteristics of the LMN using Hydroxy propyl β-cyclodextrin (HP β-CD), which might offer reliable bioavailability. The phase solubility profile was classified as A _L -type, revealing 1:1 stoichiometric complexation, with a stability constant (Ks) of 573 M^?1. Binary systems of LMN and HP β-CD were prepared in different molar ratios (1:1, 1:2, 1:3 and 1:4) by kneading method. The binary systems were characterized by Fourier Transform Infrared (FT-IR) Spectroscopy, Differential Scanning Calorimetry (DSC) and Powder X-ray Diffraction Analysis (PXRD). Results revealed that in the kneaded products the entire drug was entrapped inside the HP β-CD cavity and reduction in drug crystallinity also took place, which may be responsible for improved dissolution characteristics as compared to that of the pure drug as depicted from the dissolution studies.     

Solid-state electrochemical,X-ray and spectroscopic characterization of substitutional solid solutions of iron–copper hexacyanoferrates

Copper and iron hexacyanoferrate form a continuous series of substitutional solid solutions, which have been studied by solid-state electrochemistry, X-ray powder diffraction, IR and ESR spectroscopy. All methods unambiguously prove the formation of solid solutions. The results show the different capabilities of these techniques to study such systems. Especially in the case of poor crystallinity and strongly magnetically interacting metal ions, voltammetry of immobilized microparticles offers a powerful tool for the determination of the composition and properties of solid solutions.     

Modeling of solid–liquid equilibria in naphthalene,normal-alkane and polyethylene solutions

A solid–liquid equilibrium (SLE) model is developed on the basis of an equation of state referred to as copolymer SAFT. This SLE model is demonstrated for hydrocarbon solutions containing totally and partially crystallizable solutes. Initially regressed and tested on the solubility data for naphthalene, normal-alkane, and polyethylene, this model is used in a sensitivity study to understand the effects of crystallizability, melting temperature, molecular weight, and pressure on solid–liquid and liquid–liquid transitions of polyethylene in subcritical and supercritical propane.     

Sulfated binary and trinary oxide solid superacids

A series of sulfated binary and trinary oxide solid superacids were prepared, and their catalytic activities for n-butane isomerization at low temperature were measured. The incorporation of different metal oxides into ZrO2 may produce a positive or negative effect on the acid strength and catalytic activity of the solid superacids. Sulfated oxides of Cr-Zr, Fe-Cr-Zr and Fe-V-Zr are 2 - 3 times more active than the reported sulfated Fe-Mn-Zr oxide. The enhancement in the superacidity and catalytic activity of these new solid superacids has been discussed on account of the results of various characteriation techniques.     

Low-temperature heat capacities, and thermodynamic properties of solid–solid phase change material bis(1-octylammonium) tetrachlorocuprate

A new crystalline complex (C₈H₁₇NH₃)₂CuCl₄(s) (abbreviated as C₈Cu(s)) was synthesized by liquid phase reaction. Chemical analysis, elemental analysis, and X-ray crystallography were applied to characterize the composition and crystal structure of the complex. Low-temperature heat capacities of the complex were measured by a precision automatic adiabatic calorimeter over the temperatures ranging from 78 to 395 K, and two solid–solid phase changes appeared in the heat capacity curve. The temperatures, molar enthalpies and entropies of the two phase transitions of the complex were determined to be: T _{trs, 1} = 309.4 ± 0.35 K, Δ_trs H _{m, 1} = 16.55 ± 0.41 kJ mol^?1, and Δ_trs S _{m, 1} = 53.49 ± 1.3 J K^?1 mol^?1 for the first peak; T _{trs, 2} = 338.5 ± 0.63 K, Δ_trs H _{m, 2} = 6.500 ± 0.10 kJ mol^?1, and Δ_trs S _{m, 2} = 19.20 ± 0.28 J K^?1 mol^?1 for the second peak. Two polynomial equations of the heat capacities as a function of the temperature were fitted by least-square method. Smoothed heat capacities and thermodynamic functions of the complex relative to the standard reference temperature of 298.15 K were calculated based on the fitted polynomial equations.     

Supramolecular helix and β-sheet through self-assembly of two isomeric tetrapeptides in crystals and formation of filaments and ribbons in the solid state

Single crystal X-ray diffraction studies show that the β-turn structure of tetrapeptide I, Boc-Gly-Phe-Aib-Leu-OMe (Aib: α-amino isobutyric acid) self-assembles to a supramolecular helix through intermolecular hydrogen bonding along the crystallographic a axis. By contrast the β-turn structure of an isomeric tetrapeptide II, Boc-Gly-Leu-Aib-Phe-OMe self-assembles to a supramolecular β-sheet-like structure via a two-dimensional (a, b axis) intermolecular hydrogen bonding network and π-π interactions. FT-IR studies of the peptides revealed that both of them form intermolecularly hydrogen bonded supramolecular structures in the solid state. Field emission scanning electron micrographs (FE-SEM) of the dried fibrous materials of the peptides show different morphologies, non-twisted filaments in case of peptide I and non-twisted filaments and ribbon-like structures in case of peptide II.     

Dynamics of water and oil at the solid–liquid interface in macroporous media and reservoir rocks

Nuclear magnetic relaxation dispersion experiments at different temperatures, using the magnetic field-cycling method, are reported. These experiments allow the obtaining of original information about water or oil molecular dynamics at solid–liquid interface in porous media, such as grain packing or reservoir rocks. These results on molecular dynamics at the pore surface are of real interest for oil-recovery. The water surface diffusion coefficients are compared to the volume self-diffusion coefficients of water in pores, measured by PGSE method, the latter values being more than an order of magnitude higher than the surface ones.     

Debye–Einstein model and anomalies of heat capacity temperature dependences of solid solutions at low temperatures

An approach is proposed for analysing the deviations of the heat capacity C_p(T) of solid solutions from the Kopp–Neumann rule (KNR) ΔC(T)?=?C_p(T)???C_KNR(T). Temperature dependences of the heat capacity C_p(T) of selected compositions of systems (InP)_x (InAs)_1?x and (GaAs)_x (InAs)_1?x at temperatures of 5–300 K are analysed in the Debye–Einstein approximation. It was established that in the case of substitution of atoms in the cation subsystem (Ga³⁺???In³⁺) with the same subsystem of anions (As^3?), the positive values of ΔC(T) at T?<?100 K are due to the appearance of the low-frequency Einstein mode, whereas the negative values of ΔC(T) at T?>?100 K are the result of a decrease in the fraction of the Debye contribution without changing the upper limit of the oscillation frequency. In the case of substitution in the cation subsystem (P^3????As^3?) with the invariant cation subsystem (In³⁺) to the low-temperature positive contribution of the additional low-frequency Einstein mode, a positive part is added from the modified Debye mode having the characteristic temperature θ_D below the additive value θ_DKNR. The adequacy of this model is confirmed by Raman scattering data.

     

Hydrothermal processing and characterization of Ce1−xPbxO2−δ solid solutions

Nanocrystals of Ce_1?xPb_xO_2?δ (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, and 0.35) were prepared by a hydrothermal reaction route. During the formation reaction, buffer solutions were explored as an effective additive to retain the initial molar ratio. With increasing the Pb²⁺ content, the average crystallite size was slightly retarded. Morphologies observed by transmission electron microscope indicated that the particles were spherical-like and highly uniformed. Pb²⁺ ions are homogenously distributed in the solid solutions. Analyses using X-ray diffraction, Raman and UV spectroscopies showed that the solid solubility limit of Pb²⁺ in CeO₂ was about x = 0.20. For x < 0.20, with increasing the Pb²⁺ content, the bulk conductivity increased, and the oxygen storage capacity was enhanced as followed by a decrease in reduction temperature.     

Crystal structure and electrical conductivity of the “one-dimensional solid electrolyteN,N-dimethylmorpholinium pentaiodotetraargentate

The new solid electrolyteN, N-dimethylmorpholinium pentaiodotetraargentate, [(CH₃)N(CH₂)₂-(CH₂)₂O]Ag₄I₅ (DMMAg₄I₅), has a crystal structure which allows the Ag⁺ ions to move effectively in only one dimension. The channels for this motion result from the sharing of opposite faces of icosahedra, having iodides at their centers, forming infinite chains of icosahedra along thea axis. The joining of the icosahedra forms three more face-sharing tetrahedra at each junction, or a total of 23 tetrahedra per eight Ag⁺ ions, which are distributed non-uniformly over the tetrahedral sites. The limited number of pathways for the Ag⁺ ion diffusion leads to a low average conductivity, 1 × 10⁻⁴ Ω⁻¹ cm⁻¹ and a high activation enthalpy, 0.35 eV. Crystals of DMMAg₄I₅ belong to space groupP2₁2₁2₁ (D⁴₂) witha = 13.167(4), b = 23.437(3), c = 12.758(3)A˚; the unit cell contains eight formula units. The structure of dimethylmorpholinium iodide (DMMI) confirms the chair model for the DMM⁺ ion. Crystals of DMMI belong to space groupP2₁m(C²_2h), witha = 8.861(4), b = 8.020(2), c = 6.685(2)A˚, β = 101.07(3)°; each unit cell contains two formula units.     

Measurement of mixing time and holdup of solids in gas–solid fluidized bed using radiotracer technique

Mixing times and holdup of solids were measured in a gas–solid fluidized bed using radiotracer technique. Sand and air were used as solid and gas phase, respectively in the fluidized bed. Gold-198 labeled sand particles were used as radiotracer for mixing time measurement at different operating conditions and ¹³⁷Cs sealed source was used for holdup measurement at different axial and radial positions. The experiments were conducted at different operating conditions. The measured mixing times ranged from 1.4 to 21 s at different conditions. It was observed that at a particular bed height, the mixing time initially decreases with increasing gas velocity and tend to become constant at higher gas velocities. However, mixing time increases with increasing bed height. The holdup fraction of solid was found to be more towards the wall compared to the centre of the column. The study provided inputs to improve the existing design, design of a new system and scale-up of the process.     

Study on the microstructure and liquid–solid correlation of Al–Mg alloys

Based on the available structural models and theories of electrical resistivity (ER) of liquid alloys, the structure and the liquid–solid correlation of Al _(100-x) Mg_x (x = 0, 10, 20, 30, 40, 50) alloys have been qualitatively studied by measuring the ER during the heating/cooling process using the direct-current (DC) four-probe method, as well as by characterizing the solidification morphology and testing the hardness. The result shows that the ER of Al–Mg alloys increases with the increasing temperature and the Mg content; thermal state and history have an effect on the solidification structure and properties: the ER of Al–Mg alloys exhibits a lag phenomenon of structure change during the heating/cooling process. A higher heating/cooling rate contributes to the more obvious relaxation effect of ER and the more uniform structure. Furthermore, higher pouring temperature (PT) leads the melts and solidification structure to be more homogeneous, which increases the hardness.