Miscibility and volume changes of mixing in the polystyrene/poly(2-chlorostyrene) blend system

The specific volume-temperature relationships of polystyrene, poly(2-chlorostyrene), and their polymer blends as well as the volume change of mixing Δv_m of the blends were obtained in the liquid state by dilatometry. The equation of state parameter and the molecular parameter of each homopolymer and blends were determined according to the lattice fluid theory of Sanchez and Lacombe. The experimental Δv_m obtained agreed quite well with that predicted from theory, and the enthalpy of mixing ΔH_m was also predicted using the pair molecular parameter. These two values were negative, indicative of miscibility of polystyrene and poly(2-chlorostyrene) in the liquid state. The absolute values of Δv_m and ΔH_m were about twice those for polystyrene and poly(phenylene oxide) blend, suggesting a specific interaction between the two polymers.     

Rapid Screening of Lipase Inhibitors from Ophiopogonis Radix Using High-Performance Thin Layer Chromatography by Two Step Gradient Elution Combined with Bioautographic Method

In this study, a high-performance thin layer chromatography (HPTLC) method by two step gradient elution with two mobile phases was developed for the simultaneous analysis of seven constituents in Ophiopogonis Radix. The chromatography was performed on silica gel 60 F₂₅₄ plate with dichloromethane-methanol-ethyl acetate-water (70:25:12:3, v/v/v/v) and dichloromethane-methanol (300:1, v/v) as the mobile phase for two step gradient elution. Then, the HPTLC profiles were observed after derivatization with 10% sulfuric acid in ethanol solution. The obtained HPTLC images were further analyzed by chemometric approaches and the samples could be clustered based on regions and/or growth years, which were two important factors affecting the constituents in Ophiopogonis Radix. Furthermore, five compounds including ophiopogonin D, ophiopojaponin C, ophiopogonin D’, ophiopogonin C’ and methylophiopogonanone B were screened as potential lipase inhibitors from Ophiopogonis Radix by the HPTLC-bioautographic method. The binding modes and interactions between the five compounds and lipase were further explored by molecular docking analysis. The developed HPTLC method could be used for quality control of Ophiopogonis Radix and screening of the potential lipase inhibitors.     

Blends of polycarbonate and poly(ϵ‐caprolactone) and the determination of the polymer–polymer interaction parameter of the two polymers

The thermal properties of blends of polycarbonate (PC) and poly(ε‐caprolactone) (PCL) were investigated by differential scanning calorimetry (DSC). From the thermal analysis of PC‐PCL blends, a single glass‐transition temperature (T_g) was observed for all the blend compositions. These results indicate that there is miscibility between the two components. From the modified Lu and Weiss equation, the polymer–polymer interaction parameter (χ₁₂) of the PC‐PCL blends was calculated and found to range from −0.012 to −0.040 with the compositions. The χ₁₂ values calculated from the T_g method decreased with the increase of PC weight fraction. By taking PC‐PCL blend as a model system, the values of χ₁₂ were compared with two different methods, the T_g method and melting point depression method. The two methods are in reasonably good agreement for the χ₁₂ values of the PC‐PCL blends. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2072–2076, 2000     

Calculation of the rotational constants A and C for a slightly perturbed C3v symmetric top molecule

A method that combines basic calculations for the moments of inertia and a computer iteration technique over experimental data was employed to evaluate the constantA _v in an excited vibrational state for a symmetric top molecule. This method has been used to give a good estimate for the constantA _v and provides a reasonable interval of fluctuation, less than 1%, from its average value for computer fitting of experimental microwave data for vibrations up tov _t=4. The angle of bending and the orientation of the molecular system with respect to an axis passing through the center of mass of the system was explored and the results are discussed in this contribution. The method is then extended to thev ₁₀=1 vibration of CH₃CCH with¹³C isotopic species and to thev ₁₀=1,2,3,4 vibrations of CH₃CCH. The results were promising so the method was applied to the¹³C isotopes of CH₃C¹⁵N forv ₈=1 vibrations. The results for each of the molecules are quite good and the calculated values ofA _v were found to be in very good agreement with those deduced from experimental data.     

LC Determination and Pharmacokinetic Study of Sinomenine in Dog Plasma

A simple HPLC method has been developed for determination of sinomenine in dog plasma and has been used to evaluate the pharmacokinetics of sinomenine tablets in dogs. Chromatographic separation was performed on a reversed-phase column with 0.78% (w/v) NaH₂PO₄-acetonitrile, 88:12 (v/v), as mobile phase, delivered at a flow rate of 1.5 mL min^?1. Detection was performed at 265 nm. The limit of quantification was 5.0 ng mL^?1. The calibration range was from 5.0 to 1000 ng mL^?1. The developed method was applied to pharmacokinetic studies of sinomenine sustained-release tablets (test preparation) and sinomenine conventional tablets (reference preparation) in six dogs. Pharmacokinetic data t _max, C _max, AUC _0-t , AUC _0-∞, and t _1/2 for both preparations were determined from plasma concentration-time profiles. The method was sufficiently sensitive, simple, and repeatable for use in pharmacokinetic studies.     

Aqueous polysaccharide blends based on hydroxypropyl guar gum and carboxymethyl cellulose: synergistic viscosity and thixotropic properties

Aqueous polysaccharide blends, formed from 2.5% (w/v) solution of hydroxypropyl guar gum (HPG) and 2.5% (w/v) solution of carboxymethyl cellulose (CMC) according to different blending ratios, were investigated at 20 °C in terms of their shear-dependent viscosity and thixotropic properties. The Cross viscosity equation was found to fit the shear-dependent viscosity data with reasonable accuracy. When the HPG solution with the mass fraction (f _HPG) of 0.87 was mixed, the zero shear viscosity (η _o) of the corresponding blend was found to be 168.5753 Pa s, while the η _o values of component HPG and CMC solutions were found to be 3.3859 and 98.6525 Pa s, respectively. For the aqueous HPG/CMC blends investigated, the resulting zero shear viscosity was observed to be much greater than the combined zero shear viscosity of the component polysaccharide solutions, showing a synergistic viscosity property. The quantitative determination of the hysteresis loop area, developed during viscometer tests on shear rate–shear stress reverse paths, was used to describe the thixotropic behavior. When compared with aqueous solutions of the component polysaccharides, these polysaccharide blends could afford enhanced thixotropic property. Maximum thixotropy synergism was observed for the HPG/CMC blend with the f _HPG of 0.67.     

Approaches to determine the surface tension of small particles: Equation-of-state considerations

The primary purpose of this paper is a clarification of the question how sensitive five approaches to the determination of solid surface tensions are to the form of the equation of state for interfacial tensions, which is used in the interpretation of the experimental results. The five approaches are (1) adhesion, (2) phagocytosis, (3) sedimentation volumes, (4) solidification front, and (5) contact angles. Three equation-of-state-type relations, i.e., that due to Neumann et al., the unmodified Good equation, and Antonow's rule, are considered. The first three techniques depend on thermodynamic models in a way that requires of the equation of state only symmetry, γ₁₂ = f(γ_1v, γ_2v) = f(γ_2v, γ_1v), and zero as the minimum interfacial tension, γ₁₂ = f(γ_1v, γ_2v) = 0 when γ_1v = γ_2v. All three equations (and many similar ones, which one might consider) satisfy these requirements and hence produce identical results. In other words, the validity of these three techniques and the results which they produce are not sensitive to details of the equation of state used. The last two techniques, the solidification front technique and the contact angle method, present more stringent requirements for the equation-of-state relation used. The solidification front technique eliminates Antonow's rule from further consideration because of this equation's intrinsic inability to predict particle rejection by advancing solidification fronts, a frequent experimental observation. This technique also eliminates those equation-of-state relations which violate the minimum interfacial tension condition. Finally, the contact angle technique is the most discriminating tool with which to study the merit of equation-of-state relations. Of the relations considered here, only that due to Neumann et al. yields, in conjunction with contact angle data, values for the solid surface tension which are in agreement with those obtained from the other techniques.     

Thermosetting polymer blends of unsaturated polyester resin and poly(ethylene oxide). I. Miscibility and thermal properties

The miscibility and thermal properties of polyethylene oxide(PEO)/oligoester resin (OER) blends and PEO/crosslinked polyester (PER) blends were studied by differential scanning calorimetry (DSC). The effect of quenching process on the crystallization behavior of PEO for these two systems were investigated and discussed in details. It has been found that a single, composition dependent glass transition temperature (T_g) was observed for all the blends, indicating that the two systems are miscible in the amorphous state at overall compositions. From the melting point depression of PEO, the interaction parameter χ₁₂ for PEO/OER blends and that for PEO/PER blends were found to be −1.29 and −2.01, respectively. The negative values of χ₁₂ confirmed that both PEO/OER blends and PEO/PER blends are miscible in the molten state. Quenching process has a greater hindrance on the crystallization of PEO/OER blends than on that of PEO/PER blends. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3161–3168, 1997     

Raman and Wide-Angle X-Ray Diffraction Studies on Molecular Structure,Crystallinity, and Morphology of Uncompatibilized and Compatibilized Blends of High Molecular Weight Polyethylene/Nylon 12

Molecular structure, crystallinity and morphology of uncompatibilized and compatibilized blends of high molecular weight polyethylene (HMWPE) and Nylon 12 were investigated by using Fourier-transform (FT) Raman spectroscopy, wide-angle x-ray diffraction (WAXD), and scanning electron microscopy (SEM). One of the important purposes of the present study is to compare the present results for HMWPE/Nylon 12 with the previously obtained results for high-density polyethylene (HDPE/Nylon 12). Uncompatibilized and compatibilized blends of HMWPE/Nylon 12 with a Nylon 12 content ranging from 10 to 90 wt% at increments of 10 wt% were prepared. The compatibilized polymer blends were prepared by adding a small amount of maleic anhydride (MAH), and SEM images show that the addition of the small amount of MAH (0.5 wt%) yields a marked improvement of dispersion of HMWPE and Nylon 12. To evaluate the crystallinity of HMWPE from Raman spectra, the relative intensities of bands at 1418 and 1129 cm⁻¹ to the intensity of a band at 1000 cm⁻¹ (I₁₄₁₈/I₁₀₀₀ and I₁₁₂₉/I₁₀₀₀) were estimated for all the uncompatibilized and compatibilized blends of HMWPE/Nylon 12. From the comparison of the relative intensities (I₁₄₁₈/I₁₀₀₀ and I₁₁₂₉/I₁₀₀₀) between the uncompatibilized and compatibilized blends of HMWPE/Nylon 12 it was found that when the Nylon 12 content reaches 40 wt% the crystallinity of HMWPE in the compatibilized blends becomes higher than that of HMWPE in the uncompatibilized blends. The uncompatibilized and compatibilized blends of HMWPE/Nylon 12 (50/50) show quite different x-ray diffraction patterns; the compatibilized blend shows a significantly larger orientational effect in the x-ray pattern of HMWPE. It seems that the increase of interaction of MAH-HMWPE with the Nylon 12 matrix leads to the additional crystallinity.     

The anisotropic van der waals potential for He-N2

We have calculated the spherical v₀ and anisotropic radial components v₂ and v₄ in the usual Legendre expansion for the rigid rotor He-N₂ potential using the method of Tang and Toennies Potential curves covering the range of internuclear distances from 2.5 to 8.0 Å, which includes the minimum region, arc presented and compared with a recent experimental potential derived from differential total cross sections.     

Simultaneous quantitative determination of resorcinol and 1-Naphthol in haircolor products by high-performance liquid chromatography

Summary A high-performance liquid chromatographic method has been developed for the simultaneous quantitative determination of resorcinol and 1-naphthol in hair tonic and haircolor products. The two compounds could be separated on a μBondapak C₁₈ column by elution with 50∶50 (v/v) methanol-water as mobile phase. The retention times of resorcinol and 1-naphthol were 2.5 and 7.0 min, respectively. Seven dye intermediates could be analyzed within 12 min without any interference with the peaks of resorcinol and 1-naphthol from other cosmetic ingredients present in the haircolor liquid or cream. The results obtained were in good agreement with those obtained by a spectrophotometric method.     

Calculation of the rotational constants A and C for isotopic species of slightly perturbed CH3CN symmetric top molecules

A technique which was employed earlier to calculate the rotational constants of CH₃CCH has been extended to the ground and two vibrational levels in thev ₈ vibration of CH₃CN for several isotopic species. The moments of inertia and a computer iteration technique over experimental data for each isotopic species were employed to evaluate the constantA _v in an excited vibrational state for a symmetric top molecule. This method gave good estimates forA _v for each isotope. The angle of bending and the orientation of each molecular system in reference frames, one fixed on the carbon atom at the -CN site and the other at the center of mass, were explored. These results are discussed in this paper. The method, which was applied by Tam and Roberts to the nv₁₀,n=1, 2, 3, 4, vibrations of CH₃CCH earlier and which was extended to thev ₁₀=1 vibration of CH₃CCH with¹³C isotopic species, has been applied to¹³C isotopic species of CH₃CN and seems to be a useful tool to extract the value ofA ₀. Each of these molecules shows reasonable dependency ofA _v over vibrational levels. Values ofA _v calculated from the geometrical model are in good agreement with those obtained by fitting the terms in the frequency equations, which containedA _v , to the experimental data through an iteration technique in which the value ofA was allowed to vary.     

The relation between relaxed enthalpy and volume during physical aging of amorphous polymers and selenium

This paper reports physical aging results for PMMA, PMMA/PEO blends, PS, PC, PVC and PET (semicrystalline). Also included in this study is amorphous selenium. Temperature down-jumps from equilibrium above T_g to a temperature below T_g were carried out. Relaxed enthalpy, Δh and volume contraction, Δv, were measured. From the aging records, the constant ratio Δh/Δv = K_a was evaluated. For the polymeric samples K_a values of about 2 GPa were observed, thus similar to the inverse value of the isothermal compressibility close to T_g. Similarly for Se the K_a value obtained from Δh and Δv was in fair agreement with its isothermal compressibility.     

Effects of gamma irradiation on poly(vinyl chloride)/polystyrene blends: Investigation of radiolytic stabilization and miscibility of the mixture

Commercial polystyrene (PS) has been studied as a modifier for commercial poly(vinyl chloride) (PVC) when it was submitted to gamma irradiation. PVC/PS blends were prepared with 100/0, 95/05 and 90/10 compositions. Results for gamma-irradiated (⁶⁰Co) blends are reported and changes in viscosity-average molar mass (M_v) were analyzed. The study showed that the addition of PS into PVC decreased by 73% (95/05) and 79% (90/10) the number of scissions/100 eV in the dose range of 25-100 kGy. Viscosity analyses by the Pan et al. criterion and analyses of FT-IR spectra in the C-Cl vibration region showed negligible intermolecular interactions between the components of PVC/PS blends. However when the films of blends were irradiated to 50 kGy, certain intermolecular interactions were observed by the viscosity method. The addition of PS to PVC and the main scission effect induced by gamma irradiation decreased crosslink density of blends causing changes in the elongation of break and Young's modulus.     

Multidimensional gas chromatography for the characterization of permanent gases and light hydrocarbons in catalytic cracking process

An integrated gas chromatographic system has been successfully developed and implemented for the measurement of oxygen, nitrogen, carbon monoxide, carbon dioxide and light hydrocarbons in one single analysis. These analytes are frequently encountered in critical industrial petrochemical and chemical processes like catalytic cracking of naphtha or diesel fuel to lighter components used in gasoline. The system employs a practical, effective configuration consisting of two three-port planar microfluidic devices in series with each other, having built-in fluidic gates, and a mid-point pressure source. The use of planar microfluidic devices offers intangible advantages like in-oven switching with no mechanical moving parts, an inert sample flow path, and a leak-free operation even with multiple thermal cycles. In this way, necessary features such as selectivity enhancement, column isolation, column back-flushing, and improved system cleanliness were realized. Porous layer open tubular capillary columns were employed for the separation of hydrocarbons followed by flame ionization detection. After separation has occurred, carbon monoxide and carbon dioxide were converted to methane with the use of a nickel-based methanizer for detection with flame ionization. Flow modulated thermal conductivity detection was employed to measure oxygen and nitrogen. Separation of all the target analytes was achieved in one single analysis of less than 12 min. Reproducibility of retention times for all compounds were found to be less than 0.1% (n = 20). Reproducibility of area counts at two levels, namely 100 ppm_v and 1000 ppm_v over a period of two days were found to be less than 5.5% (n = 20). Oxygen and nitrogen were found to be linear over a range from 20 ppm_v to 10,000 ppm_v with correlation coefficients of at least 0.998 and detection limits of less than 10 ppm_v. Hydrocarbons of interest were found to be linear over a range from 200 ppb_v to 1000 ppm_v with correlation coefficients of greater than 0.999 and detection limits of less than 100 ppb_v.     

Unexpected frequency shifts and linewidth changes for rovibrational lines in the infrared emission spectra of CO2 excited by active nitrogen

Fourier transform emission spectra from flowing CO₂ excited by active nitrogen have been recorded in the 4.5 μm region, with a resolution of 0.0054 cm⁻¹, for different time intervals between the mixing of the two gases and observation of the emission. Significant frequency shifts (reaching 30 times the absolute uncertainty of the experimental frequencies) and linewidth changes are observed depending on the time interval and the value of the quantum number v₃, for thousands of rovibrational lines belonging to v₁v¹₂v₃ → v₁v¹₂(v₃-1) vibrational transitions.     

Determination of Biodiesel and Triacylglycerols in Diesel Fuel by LC

A high performance liquid chromatographic method was developed for quantifying blends of biodiesel (simple alkyl esters of fatty acids) in petrodiesel. The method uses a silica column with an isocratic mobile phase consisting of hexane and methyl t-butyl ether. Separated components were quantitated using either an evaporative light scattering detector (ELSD) or UV detector. Precision of injection and linearity of response of the ELSD and UV detectors over a range of biodiesel-petrodiesel blends [1–30 v/v %] were established by use of standards. The method also can be used for quantitating similar levels of oils or fats (triacylglycerols) in petrodiesel.     

Single-Step Preparative Extraction of Artemisinin from Artemisia annua by Charcoal Column Chromatography

Activated charcoal column chromatography was successfully applied for preparative extraction of artemisinin with high-purity from Artemisia annua L. in one single run for the first time in this study. The adsorption kinetics study showed that powdery activated charcoal had high adsorption speed for artemisinin. The experimental adsorption data fitted well using the Langmuir adsorption model. The optimal parameters for the extraction of artemisinin were obtained using a column packed with activated charcoal: the loading amount, 1 g extract/5 g activated charcoal; the elution mode, CH₂Cl₂?CMeOH (2:5, v/v) for 5 BV (bed volume) after the removal of some impurities with CH₂Cl₂?CMeOH (1:10, v/v). With this optimized condition, artemisinin was finally obtained with purity at 95.2% and the recovery at 72.3%. The developed technique would provide a feasible large-scale method for the extraction of artemisinin in pharmaceutical industry.     

H-bonds of imidazole crystals. I. Measurements of polarized light IR spectra

This article is the first of a series on the v_s bands of imidazole crystals. It deals with experimental results on fully protonated and N—D deuterated species. We first describe the experimental conditions which enable us to obtain polarized spectra of monocrystals of imidazole which are sufficiently thin (≈1 μm) to give non-saturated v_s bands, so that we can measure with good precision the first moments of the v_s bands of these two species at various temperatures ranging from 10 to 300 K.