The nucleation study on the cationic miniemulsion polymerization of octamethylcyclotetrasiloxane (D4)

The nucleation of the cationic miniemulsion polymerization of octamethylcyclotetrasiloxane (D₄) has been investigated in detail in this work. The particle size was traced by dynamic laser scattering in the polymerization process using different concentration of dodecylbenzenesulfonic acid (DBSA) as both the initiator and surfactant. The results reveal the progressively decreasing particle sizes with the steadily increasing monomer conversion. The descending particle sizes can be explained by the existence of homogeneous nucleation of hydroxyl-terminated polydimethylsiloxane (PDMS) oligomers in addition to the primary droplet nucleation. A linear relationship between the natural logarithm of the average particle diameter (lnd(t)) and the natural logarithm of the monomer conversion (lnf(t)) is then deduced based on the theory, which has been validated by the experimental data. The slope of lnd(t)~lnf(t) line relies on the parameter of K which is the ratio of PDMS oligomers entering water phase to all PDMS oligomers produced. The influence of DBSA concentration on the K and the fraction of homogeneous nucleation (F(H)) has been then obtained. Both of the values of K and F(H) increase with the increasing DBSA concentrations.     

Kinetic model of the evaporation process of benzylbutyl phthalate from plasticized poly(vinyl chloride)

The kinetic model of the physical process of evaporation of plasticizer from plasticized PVC foils was developed from the results of isothermal thermogravimetric investigation of evaporation of benzyl-butyl phthalate in the temperature range 120-150 °C under nitrogen flow. The kinetic parameters were estimated by integral method of analysis. Mathematical modeling of the kinetic of plasticizers evaporation was performed on the basis of function c=f(T,t) and kinetic equation of evaporation −dc/dt=f(T,c₀,c(t)). The developed mathematical model was described by the general kinetic equation . The differential quotients δ(−dc/dt)/δT=f(T,c₀,c(t))=f(T,c₀,t) and δ(−dc/dt)/δc₀=f(T,c(t))=f(T,c₀,t) were performed, and mathematical definition of the changes of the evaporation rate constant with the change of temperature and the change of the initial plasticized concentration were discussed.     

Identification of unknown diffusion coefficient in pure diffusive linear model of chronoamperometry. I. The theory

Coefficient identification problem for diffusion equation u _t (x, t) = (D(x)u _x (x, t)) _x arising in chronoamperometry is studied. The adjoint problem approach is developed for the case when the output measured data is given in the form of left/right flux. Analytical formulas for determination of the values D(0), D(L) at the endpoints x = 0; L, of the unknown coefficient D(x), via the solution v(x, t) of the constant coefficient equation v _t (x, t) = D v _xx (x, t) is obtained. The integral identity relating solutions of the forward and corresponding adjoint problems is derived. This integral identity permits one to prove the monotonicity and invertibility of input-output map, as well as formulate the gradient of the cost functional via the solutions of the direct and adjoint problems.     

Identification of unknown diffusion coefficient in pure diffusive linear model of chronoamperometry. II. Numerical implementation

This article presents numerical implementation of the approach proposed in the previous study (Identification of the unknown diffusion coefficient in ion transport problem. I. The theory, Math. Chem. (2009) (submitted)) for the coefficient inverse problems related to linear diffusion equation in chronoamperometry. The coarse-fine grid algorithm is used for determination of the unknown diffusion coefficient D(x) in the linear parabolic equation u _t  = (D(x)u _x ) _x from the measured output data (left flux). The main distinguished feature of the implemented algorithm is the use of a fine grid for the numerical solution of well-posed forward and backward parabolic problems, and a coarse grid for the interpolation of the unknown diffusion coefficient D(x). The nodal values of the unknown coefficient on the coarse grid are recovered sequentially, solving on each step of the coarse grid iteration algorithm the well-posed forward, and the sequence of backward pababolic problems. This guarantees a compromise between the accuracy and stability of the solution of the considered inverse problem. An efficiency and applicability of the proposed approach is demonstrated on various numerical examples with noisy free and noisy data.     

Structural variation of solid core and thickness of porous shell of 1.7 μm core-shell silica particles on chromatographic performance: narrow bore columns

Chromatographic and mass transfer kinetic properties of three narrow bore columns (2.1 × 50 mm) packed with new core–shell 1.7 μm EIROSHELL™-C₁₈ (EiS-C₁₈) particles have been studied. The particles in each column varied in the solid-core to shell particle size ratio (ρ), of 0.59, 0.71 and 0.82, with a porous silica shell thickness of 350, 250 and 150 nm respectively. Scanning and transmission electron microscopy (SEM and TEM), Coulter counter analysis, gas pycnometry, nitrogen sorption analysis and inverse size exclusion chromatography (ISEC) elucidated the physical properties of these materials. The porosity measurement of the packed HILIC and C₁₈ modified phases provided the means to estimate the phase ratios of the three different shell columns (EiS-150-C₁₈, EiS-250-C₁₈ and EiS-350-C₁₈). The dependence of the chromatographic performance to the volume fraction of the porous shell was observed for all three columns. The naphtho[2,3-a]pyrene retention factor of k′ ∼ 10 on the three EiS-C_18s employed to obtain the height equivalents to theoretical plates (HETPs) data were achieved by varying the mobile phase compositions and applying the Wilke and Chang relationship to obtain a parallel reduced linear velocity. The Knox fit model gave the coefficient of the reduce HETPs for the three EiS-C_18s. The reduced plate height minimum h_min = 1.9 was achieved for the EiS-150-C₁₈ column, and generated an efficiency of over 350,000 N/m and h_min = 2.5 equivalent to an efficiency of 200,000 N/m for the EiS-350-C₁₈ column. The efficiency loss of the EiS-C18 column emanating from the system extra-column volume was discussed with respect to the porous shell thickness.     

Synthèse et caractérisation de fluorbritholites strontiques dopées au néodyme

Strontium fluorbritholites with the general formula Sr_10-xNd_x(PO₄)_6-x(SiO₄)_xF₂ (0 ≤ x ≤ 6), were prepared by solid state reaction at temperatures between 1200 and 1400 °C. The XRD analysis showed that a pure apatitic phase was formed only for x ≤ 2.5. Above this value, there was formation of secondary phases. The variation of the lattice parameters as a function of x indicated that the formed solid solution was discontinuous on both sides of x = 3. The analysis by Raman and IR spectroscopies confirmed the incorporation of SiO₄ groups within the apatite lattice, and showed that this incorporation induced in the structure a disorder that increased with increasing content of Nd³⁺ and SiO₄⁴⁻. Optical absorption measurements showed a wide variation in the local environment of Nd³⁺ ions, corresponding to the existence of new spectroscopic sites, evidenced by a luminescence study.     

A spectroscopic study on medium polarity in fluorous alcohol

The paper describes the polarities of three fluorous (F) aliphatic alcohols: perfluorinated tert-butanol (F-t-BuOH), n-butanol (F-n-BuOH), and n-heptanol (F-n-HepOH). For the purpose, we conducted absorption and fluorescence spectroscopies of coumarin 153 (C153) and 102 (C102) in three F and 13 non-fluorous (non-F) alcohols and determined their maximum energies: ν^a (absorption) and ν^f (fluorescence). We obtained linear relationships between the Stokes shifts of the dyes (i.e., (ν^a − ν^f)) and a medium polarity parameter for 13 non-F alcohols, f(x): f(x) = [(D_s − 1)/(2D_s + 1) − (n² − 1)/(2n² + 1)], where D_s and n were the dielectric constant and refractive index of a solvent, respectively. By comparing the Stokes shifts of the dyes in three F alcohols with those in 13 non-F alcohols (i.e., (ν^a − ν^f) vs. f(x) plot), the D_s values in F-t-BuOH, F-n-BuOH, and F-n-HepOH were evaluated to be 2.7-3.9, 4.3-5.1, and 4.0-5.2, respectively, while those in the relevant non-F alcohols were 12.5, 17.5, and 12.9, respectively. Thus, the present experiments demonstrated that the polarities of these F alcohols were much lower than those of the relevant non-F alcohols.     

Theory of dynamic light scattering by polymers and gels

It is shown under very general conditions that the intermediate scattering function for the generalized Rouse—Zimm model always takes the simple form G(K, t) α exp[?K²(k_BT/f)t], when the scattering vector K becomes sufficiently large. (Here k_B is Boltzmann's constant, T is the absolute temperature and f is the individual bead friction factor.) A microscopic formulation for the bulk modulus and friction factor density of a gel network is incorporated into the viscoelastic continuum model of Tanaka et al. The resulting expression for the apparent long-wavelength diffusion coefficient of the gel is D_G = (k_BT/f)2(1 - 2/Φ), where Φ is the network functionality.     

CdSe quantum dots capped PAMAM dendrimer nanocomposites for sensing nitroaromatic compounds

The detection of nitroaromatic compounds, best known as raw materials in explosives preparations, is important in many fields including environmental science, public security and forensics. CdSe quantum dots capped with PAMAM-G₄ dendrimer were synthetized in water and used for the detection of trace amounts of three nitroaromatic compounds: 4-methoxy-2-nitrophenol (MNP), 2-amine-5-chloro-1,3-dinitrobenzene (ACNB) and 3-methoxy-4-nitrobenzoic acid (MNB). To increase the apparent water solubility of these compounds α-cyclodextrin (α-CD) was used to promote the formation of inclusion complexes. The studied nitroaromatic compounds (plus α-CD) significantly quenched the fluorescence intensity of the nanocomposite with linear Stern-Volmer plots. The Stern-Volmer constants (standard deviation in parenthesis) were: MNB, K_SV = 65(5) × 10⁴ M⁻¹; ACNB, K_SV = 19(2) × 10⁴ M⁻¹; and, MNP, K_SV = 33(1) × 10² M⁻¹. These constants suggest the formation of a ground state complex between the nitroaromatric compounds and the sensor which confers a relatively high analytical sensitivity. The detection sensibilities are about 0.01 mg L⁻¹ for MNB and ACNB and about 0.1 mg L⁻¹ for MNP. No interferences or small interferences are observed for trinitrotoluene [K_SV = 10(2) × 10² × M⁻¹], 2,4-dinitrotoluene [K_SV = 20(3) × 10 M⁻¹], 2,6-dinitrotoluene [K_SV = 11(4) × 10 M⁻¹] and nitrobenzene [K_SV = 2(1) × 10³ × M⁻¹].     

High temperature and highly selective stationary phases of ionic liquid bonded polysiloxanes for gas chromatography

Due to the special performance of “dual nature” and synthetic flexibility, ionic liquids (ILs) have been an attractive research subject of stationary phases for gas chromatography (GC). In this work, a novel ionic liquid (IL) bonded polysiloxane ([PSOMIM][NTf₂]) with anion of bis-trifluoromethanesulfonylimide (NTf₂⁻) was synthesized, and another one with chloride anion ([PSOMIM][Cl]) was also prepared for the purpose of comparison. The thermo-stability of the product was evaluated by thermogravimetric (TG) test and the result indicated that [PSOMIM][NTf₂] did not decompose slightly until 380 °C. Then the solvation behaviors of the ILs were characterized using solvation parameter model. Subsequently, [PSOMIM][NTf₂] and [PSOMIM][Cl] were used as stationary phases to prepare capillary columns for GC, respectively. The column efficiency of [PSOMIM][NTf₂] column was 4776 plates/m (k = 3.64 ± 0.08, naphthalene), and that of the other one was 3170 plates/m (k = 2.84 ± 0.11, naphthalene). The selectivity of the novel stationary phases for analytes, including Grob reagent, aromatic positional isomers was further evaluated. Furthermore, the chromatograms of n-alkanes and polycyclic aromatic hydrocarbons (PAHs) on [PSOMIM][NTf₂] column were compared with that on [PSOMIM][Cl] column. [PSOMIM][NTf₂] stationary phase also exerted good selectivity for fatty acid methyl esters (FAMEs), polychlorinated biphenyls (PCBs) and aromatic amines.     

Enantiomeric resolution of (±)-licarin A by high-performance liquid-chromatography using a chiral stationary phase

(±)-Licarin A (1), a neolignan obtained by the oxidative coupling reaction of isoeugenol, had in this study its enantiomers resolved. A novel, quick and efficient enantiomeric resolution of 1 was directly performed by chiral high-performance liquid chromatography (HPLC-PDA) protocol (CHIRALPACK^® AD column; 9:1 (v/v) n-hexane:2-propanol; 1.0 mL/min). This method provided a chromatogram profile with a well-resolved peak separation. After isolation of each enantiomer with ee > 99.9%, they were analysed in a polarimeter. Compound 2, which showed a retention time (t_r) of 12.13 min, was the (+)-enantiomer and compound 3 (t_r = 18.90 min) was the (−)-enantiomer.     

Identification of unknown diffusion and convection coefficients in ion transport problems from flux data: an analytical approach

This article presents an analytical approach for identification problems related to ion transport problems. In the first part of the study, relationship between the flux j_L : = (D(x)u_x(0, t)_x=0{\varphi_L := (D(x)u_x(0, t)_{x=0}} and the current response I(t){{\mathcal I}(t)} is analyzed for various models. It is shown that in pure diffusive linear model case the flux is proportional to the classical Cottrelian I_C(t){{\mathcal I}_C(t)}. Similar relationship is derived in the case of nonlinear model including diffusion and migration. These results suggest acceptability of the flux data as a measured output data in ion transport problems, instead of nonlocal additional condition in the form an integral of concentration function. In pure diffusive and diffusive-convective linear models cases, explicit analytical formulas between inputs (diffusion or/and convection coefficients) and output (measured flux data) are derived. The proposed analytical approach permits one to determine the unknown diffusion coefficient from a single flux data given at a fixed time t ₁ > 0, and unknown convection coefficient from a single flux data given at a fixed time t ₂ > t ₁ > 0. Linearized model of the nonlinear ion transport problem with variable diffusion and convection coefficients is analyzed. It is shown that the measured output (flux) data can not be given arbitrarily.     

Determination of imipramine and trimipramine by capillary electrophoresis with electrochemiluminescence detection

The tricyclic antidepressants (TCA) imipramine (Imi) and trimipramine (Tri) were successfully analyzed by capillary electrophoresis (CE) coupling with Tris(2,2-bipyridyl) ruthenium(II)-based (Ru(bpy)₃²⁺) end-column electrochemiluminescence (ECL) detection. The addition of β-CD to the running buffer was found to enable baseline separation of the two analytes and the addition of acetonitrile (ACN) as an organic additive to improve the repeatability and sensitivity of the CE method. Under the optimized separation and detection conditions (50 mM PBS (pH = 7.0) and 2 mM Ru(bpy)₃²⁺ in the ECL detection cell, 20 mM Tris (pH = 2.0), 0.2 mM β-CD and 20% ACN (v/v) as running buffer), wide linear ranges of 0.1-5 μM and 0.1-5 μM were achieved, with the correlation coefficients of 0.9990 (n = 8) and 0.9980 (n = 8) for Imi and Tri, respectively. Detection limits 5 nM and 1 nM (S/N = 3) were obtained for Imi and Tri, respectively. The method was also successfully applied for the determination of Imi in pharmaceutical dosage form.     

Vibrational phase relaxation of O–H stretch in bulk water: Role of large amplitude angular jumps and negative cross-correlations among the forces on the O–H bond

The ultrafast vibrational phase relaxation of O–H stretch in bulk water is investigated in molecular dynamics simulations. The dephasing time (T₂) of the O–H stretch in bulk water calculated from the frequency fluctuation time correlation function (C_ω(t)) is in the range of 70–80 femtosecond (fs), which is comparable to the characteristic timescale obtained from the vibrational echo peak shift measurements using infrared photon echo [W.P. de Boeij, M.S. Pshenichnikov, D.A. Wiersma, Ann. Rev. Phys. Chem. 49 (1998) 99]. The ultrafast decay of C_ω(t) is found to be responsible for the ultrashort T₂ in bulk water. Careful analysis reveals the following two interesting reasons for the ultrafast decay of C_ω(t). (A) The large amplitude angular jumps of water molecules (within 30–40 fs time duration) provide a large scale contribution to the mean square vibrational frequency fluctuation and gives rise to the rapid spectral diffusion on 100 fs time scale. (B) The projected force, due to all the atoms of the solvent molecules on the oxygen (F_O(t)) and hydrogen (F_H(t)) atom of the O–H bond exhibit a large negative cross-correlation (NCC). We further find that this NCC is partly responsible for a weak, non-Arrhenius temperature dependence of the dephasing rate.     

The effect of titanium alkoxides in the synthesis of heterobimetallic complexes by titanocene(III) alkoxide-induced metal-metal bond cleavage of metal carbonyl dimers

A series of titanocene(III) alkoxides L₂Ti(III)OR where L = Cp, R = Et(1b), ^tBu(1a), 2,6-Me₂C₆H₃(1c), 2,6-^tBu₂-4-Me-C₆H₂(1d), or L = Cp*, R = Me(2e), ^tBu(2a), Ph(2f) was synthesized and subjected to reaction with [CpM(CO)₃]₂ [M = Mo, W], [CpRu(CO)₂]₂, and Co₂(CO)₈. The Ti(III) precursors 1a, 1c, 2a, 2e, and 2f reacted with [CpM(CO)₃]₂ [M = Mo, W] to form heterobimetallic complexes L₂Ti(OR)(μ-OC)(CO)₂MCp [M = Mo, W], of which Ti and M are linked by an isocarbonyl bridge. Reactions of these Ti(III) complexes with Co₂(CO)₈ resulted in formation of Ti-Co₁ heterobimetallic complexes, from 2a, 2e, or 2f, or Ti-Co₃ tetrametallic complexes, Cp₂Ti(O^tBu)(μ-OC)Co₃(CO)₉ from 1a, 1b, or 1c. The products were characterized by NMR, IR, and X-ray crystallography. Reaction mechanisms were proposed from these results, in particular, from steric/electronic effects of titanium alkoxides.     

Kinetics of the CH3 + HCl/DCl → CH4/CH3D + Cl and CD3 + HCl/DCl → CD3H/CD4 + Cl reactions: An experimental H atom tunneling investigation

The kinetics of the radical reactions of CH₃ with HCl or DCl and CD₃ with HCl or DCl have been investigated in a temperature controlled tubular reactor coupled to a photoionization mass spectrometer. The CH₃ (or CD₃) radical, R, was produced homogeneously in the reactor by a pulsed 193 nm exciplex laser photolysis of CH₃COCH₃ (or CD₃COCD₃). The decay of CH₃/CD₃ was monitored as a function of HCl/DCl concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature, typically from 188 to 500 K. The rate constants of the CH₃ and CD₃ reactions with HCl had strong non-Arrhenius behavior at low temperatures. The rate constants were fitted to a modified Arrhenius expression k = QA exp (−E_a/RT) (error limits stated are 1σ + Students t values, units in cm³ molecule⁻¹ s⁻¹): k(CH₃ + HCl) = [1.004 + 85.64 exp (−0.02438 × T/K)] × (3.3 ± 1.3) × 10⁻¹³ exp [−(4.8 ± 0.6) kJ mol⁻¹/RT] and k(CD₃ + HCl) = [1.002 + 73.31 exp (−0.02505 × T/K)] × (2.7 ± 1.2) × 10⁻¹³ exp [−(3.5 ± 0.5) kJ mol⁻¹/RT]. The radical reactions with DCl were studied separately over a wide ranges of temperatures and in these temperature ranges the rate constants determined were fitted to a conventional Arrhenius expression k = A exp (−E_a/RT) (error limits stated are 1σ + Students t values, units in cm³ molecule⁻¹ s⁻¹): k(CH₃ + DCl) = (2.4 ± 1.6) × 10⁻¹³ exp [−(7.8 ± 1.4) kJ mol⁻¹/RT] and k(CD₃ + DCl) = (1.2 ± 0.4) × 10⁻¹³ exp [−(5.2 ± 0.2) kJ mol⁻¹/RT] cm³ molecule⁻¹ s⁻¹.     

Calculations of thermal functions of group-III nitrides

The change of thermal functions (ΔH ⁰(T), ΔS ⁰(T), ΔG ⁰(T)) and formation functions (ΔH _f⁰(T), ΔG _f⁰(T), K _f(T)) with temperature for gallium nitride and indium nitride have been formulated based on the reliable experimental data obtained by the use the same equipment in one laboratory.     

The use of hydrogenated Schiff base ligands in the synthesis of multi-metallic compounds II

Tris(2-hydroxybenzylaminoethyl)amine (H₃L) complexes of nickel, copper and zinc are investigated as potential metallo-ligands ([(H_xL)M]; x = 0, 1: M = Ni, Cu, Zn). The homometallic complexes formed are dimetallic ([{(HL)Ni}Ni(OAc)₂] and [{(L)Zn}ZnCl]), tetrametallic ([{(L)Cu}Cu]₂²⁺) and hexametallic ([{(L)Ni}Ni₂(μ-OH)₂(OEt)(OH₂)]₂). Hetero-dimetallic complexes can be formed with [(HL)Ni] and copper chloride ([{(HL)Ni}CuCl₂]) or zinc bromide ([{(HL)Ni}ZnBr₂]). The metallo-ligand acts as a chelating agent using phenolate pairs. The remaining phenolate either does not coordinate or can be used to increase the number of metals included in the scaffold from two to four or six. Not all combinations are possible and [(HL)Cu]⁺ produces a charge separated species with zinc chloride rather than a complex. An exchange reaction is observed to take place when [(HL)Zn]⁺ is treated with the halides of nickel or copper producing [(HL)M]⁺ (M = Ni, Cu, respectively).     

Cascades of energy among the vibrational levels of diatomic molecules trapped in a rare gas matrix: With application to 12C16O(ν) in Ar

Energy stored in vibrational level ν = 1 of several individual dipolar diatomic molecules AB which are trapped in a rare gas matrix M is automatically accumulated in a higher level ν > 1 of a single molecule AB. This remarkable cascade of energy upwards competes with a cascade of energy downwards. the radiative decay. The interplay of both cascades, first observed by Dubost and Charneau, is explained a simple model. The model incorporates three processes into a master equation for the relative populations P_ν(t) of levels ν: (a) migration of single quanta by resonance energy transfer, AB(1) + AB(0) ? AB(0) + AB(1); (b) phonon assisted excitation of upper levels, AB(1) + AB(ν) → AB(0) + AB(ν+1); and (c) radiative decay, AB(ν) → AB(ν-1). The model assumes that there is only one isotopic species AB which has a small but nonzero vibrational anharmonicity, that the temperature is low, T → 0 K, the concentration ratio ?_M/?_AB is large and that, initially, at time t = 0, a small fraction p₁ of molecules AB is excited to level ν = 1. The master equation has only two parameters, the radiative lifetime t_rad and k  2/[?_AB?₁k(1,1 → 0,2)t_rad], where k(1,1 → 0,2) is the reference rate constant of process (b). The master equation is solved in closed form for the Pν(t). For t_rad = 14 ms and k = 0.2, very satisfactory qualitative agreement is found for the theoretical P_ν(t) and the experimental time evolution of the relative population of vibrational levels of ¹²C¹⁶O in an argon matrix, for ?_M/?_AB = 2000 at T = 9 K. In agreement with experimental results it is concluded that the risetime of the fluorescence signals decreases whereas population inversion increases for decreasing values of ?_M/?AB. At long times, t > t_rad, any population inversion should disappear.