Hydroxyl end groups influence in vibrational and transport properties in polymer/monomer solutions: the PEO/EG case

A study has been made of vibrational properties in ethylene glycol (EG; H(OCH₂CH₂)OH) and EG monomethyl ether (EGmE; CH₃(OCH₂CH₂)OH) in solution together with poly(ethylene oxide) (PEO; H(OCH₂CH₂)_n,OH) at different concentrations, performed by Fourier transform infrared absorbance (FT-IR) spectroscopy. The results ae compared with previous viscometry and photon correlation spectroscopy (PCS) studies, using EG dimethyl ether (EGdE; CH₃(OCH₂CH₂)OCH₃) as solvent as well. These homologous systems differ from each other in the number of OH end groups, in particular two for EG, one for EgmE and zero for EGdE. Combining analysis of the vibrational and transport properties of EG, EGmE and EGdE in solution with PEO over a wide range of concentration made it possible to check the quality (good theta or poor) of these three different solvents and the role played by the hydrogen bond in the various solute-solvent interaction mechanisms, resulting in the well known de Gennes scaling law.     

Small-angle neutron scattering studies of nonionic surfactant: Effect of sugars

Micellar solution of nonionic surfactantn-dodecyloligo ethyleneoxide surfactant, decaoxyethylene monododecyl ether [CH₃(CH₂)₁₁(OCH₂CH₂)₁₀OH], C₁₂E₁₀ in D₂O solution have been analysed by small-angle neutron scattering (SANS) at different temperatures (30, 45 and 60° C) both in the presence and absence of sugars. The structural parameters like micelle shape and size, aggregation number and micellar density have been determined. It is found that the micellar structure significantly depends on the temperature and concentration of sugars. The micelles are found to be prolate ellipsoids at 30° C and the axial ratio of the micelle increases with the increase in temperature. The presence of lower concentration of sugar reduces the size of micelles and it grows at higher concentration of sugar. The structure of micelles is almost independent of the different types of sugars used.     

Direct synthesis and characterization of highly ordered functional mesoporous silica thin films with high amino-groups content

A series of continuous, crack-free, highly ordered amino-functionalized mesoporous silica thin films have been directly synthesized by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of cationic CH₃(CH₂)₁₅N⁺(CH₃)₃Br⁻ (CTAB), nonionic C₁₆H₃₃(OCH₂CH₂)₁₀OH (Brij-56) or triblock copolymer H(OCH₂CH₂)₂₀(OCH(CH₃)CH₂)₇₀(OCH₂CH₂)₂₀)OH (P123) surfactant species under acidic conditions by sol-gel dip-coating. The molar ration of APTES/(TEOS + APTES) in the starting sol attains a value of 0.4. The effect of the sol aging on the mesostructure of thin films is systematically studied, and the optimal sol aging time is obtained for different surfactant systems. The amino-functionalized mesoporous silica thin films exhibit long-range ordering of 2D hexagonal (p6mm) and 3D cubic (Fm3m) pore arrays of size range from 2.2 to 8.3 nm following surfactants extraction as demonstrated by XRD, TEM and physical adsorption techniques. Based on BET surface area and weight loss, the surface coverage of amino-groups for thin films prepared using different surfactants is calculated to be 3.2 and above amino-groups per nm², which is very useful and promising for incorporating inorganic ions and biomolecules into these mesoporous silica materials.     

Configuration dependence of photon stimulated ion desorption from methyl ester compounds induced by core excitation

Photon stimulated ion desorption (PSID) from methyl ester terminated self-assembled monolayer (MHDA-SAM, HS(CH₂)₁₅COOCH₃) and methyl mercaptoacetate (MA, HSCH₂COOCH₃) on Ag has been investigated using soft X-ray in the C and O K-edge regions. In MHDA-SAM on Ag, site-selective ion desorption has been clearly observed at resonant core excitations of C_1s, O_1s(OCH₃) → σ^∗(OCH₃) and O_1s(OCH₃) → σ^∗(COCH₃). Ion intensity in MA on Ag is obviously reduced for (n = 1-3) at C_1s, O_1s(OCH₃) → σ^∗(OCH₃) excitations, and no site-selective reaction at O_1s(OCH₃) → σ^∗(COCH₃) excitations has been observed. These reactions may be influenced by configurational difference of reactive sites. It is suggested that surface effects on the selective reaction due to positioning methyl ester group near the surface plays an important role.     

A comprehensive study of (CH3)2CHOC(S)SC(O)OCH3 using matrix isolation technique,X‐ray analysis,spectroscopic studies and theoretical calculations

Potassium isopropyl xanthate, (CH₃)₂CHOC(S)SK, reacts with methyl chloroformiate ClC(O)OCH₃ to yield (methoxycarbonyl) (2‐propoxythiocarbonyl) sulfide, (CH₃)₂CHOC(S)SC(O)OCH₃. This novel xanthogen formate was characterized by ¹H and ¹³C{¹H} NMR spectroscopy, mass spectrometry and IR and Raman spectroscopy. The structure of a single crystal of (CH₃)₂CHOC(S)SC(O)OCH₃ was determined by X‐ray diffraction analysis at 173 K. The conformational properties have been studied by liquid IR and Raman spectroscopy, matrix isolation spectroscopy together with photochemical studies and quantum chemical calculations (HF and B3LYP methods with the 6‐31+G* basis set). The analysis of the IR spectrum of liquid (CH₃)₂CHOC(S)SC(O)OCH₃ suggests the presence of two conformers in equilibrium at room temperature. However, in the photochemical matrix study, an equilibrium of three conformers was detected. These forms were further characterized by theoretical calculations. Different photolysis products, such as CH₃OC(O)SCH(CH₃)₂, OCS, CO, CO₂ and CS₂, were identified by matrix spectroscopy. The IR absorptions of CH₃OC(O)SCH(CH₃)₂, for which literature data are scarce, were analysed in the light of the results of appropriate theoretical calculations. Copyright © 2009 John Wiley & Sons, Ltd.     

Computational approach to estimate layer structures of organic derivatives of boehmite

The observed basal spacings of the alkyl derivatives of boehmite, AlO(OH)_1−x(OR)_x, obtained by the reaction of aluminum metal or aluminum alkoxides with alcohols at 250–300 °C was only slightly affected by the population (x) of the alkyl groups (x=0.39−0.21) (Chem. Mater. 12 (2000) 55). In order to clarify the origin of this independency, the molecular mechanics (MM) calculation was carried out, and the effect of the alkyl population upon the basal spacing of the butyl derivative of boehmite, AlO(OH)_1−x(OCH₂CH₂ CH₂CH₃)_x, was examined in a range of x=0.00–0.30. The calculated results clearly suggested that in the range of x from 0.3 to 0.2, the boehmite derivative has the bilayer arrangement of the alkyl groups with essentially all-trans conformation. In this range, the basal spacing was only slightly affected by the population of the alkyl groups because it is determined by the most crowded part of the assembly of the alkyl chains. Since the alkyl chains are fixed to the host layers through the covalent bonding, decrease in the alkyl population does not affect essential feature of the alkyl derivatives of layered inorganics.     

Electrochemical properties and radical anions of carbocycle‐fluorinated quinoxalines and their substituted derivatives

Electrochemical reduction (ECR) and oxidation (ECO) of 5,6,7,8‐tetrafluoroquinoxaline ( 1 ) and its derivatives bearing various substituents R (7‐H ( 2 ), 7,8‐H₂ (3 ), 6‐CF₃ ( 4 ), 6‐Cl ( 5 ), 5,7‐Cl₂ ( 6 ), 5‐NH₂ ( 7 ), 6‐OCH₃ ( 8 ), 6,7‐(OCH₃)₂ ( 9 ), 6,7,8‐(OCH₃)₃ ( 10 ), 5,6,7,8‐(OCH₃)₄ ( 11 ), 6‐OCH₃,7‐N(CH₃)₂ ( 12 ), 6‐N(CH₃)₂ ( 13 ), 6,7‐(N(CH₃)₂)₂ ( 14 ), 5,6,7‐(N(CH₃)₂)₃ ( 15 ), and 7,8‐cyclo‐(=CF‐CF = CF‐CF=) ( 16 )) in the carbocycle have been studied by cyclic voltammetry in MeCN. For 1 – 4 and 7 – 15 , the first reduction peaks have been found to be 1‐electron and reversible, thus corresponding to the formation of their radical anions (RAs), which are long lived at 295 K except those of 4 – 6 and 15 , 16 . Irreversible hydrodechlorination has been observed for 5 and 6 at the first step of their ECR confirmed by EPR detection of corresponding RAs of 2 and 5,7‐H₂ derivative of 1 ( 17 ) at the next steps. Electrochemically generated RAs of 1 – 3 , 7 – 14 , and 17 have been characterized in MeCN by EPR spectroscopy together with DFT calculations at the (U)B3LYP/6‐31 + G(d) level of theory using PCM to describe the solvent. A noticeable alternation of spin density on the –NCCN– moiety of quinoxaline has been observed for all RAs possessing R‐substitution asymmetry. The comparative electron‐accepting ability of 1 – 15 has been analyzed in terms of their experimental reduction peak potentials and the (U)B3LYP/6‐31 + G(d)‐calculated gas‐phase first adiabatic electron affinities (EAs). The differences in electron transfer solvation energies for 1 – 15 have been evaluated on the basis of ECR peaks' potentials and calculated gas‐phase EAs. The ECO of 1 – 5 and 7 – 14 has been found to be irreversible.     

Differential friction force spectroscopy of micropatterned organosilane self-assembled monolayers

Frictional properties of organosilane self-assembled monolayers (SAMs) and hydrated silicon oxide (SiOH) surfaces on a single sample substrate were studied; the frictional force difference between the surfaces was measured by employing one as a standard. Using a lateral force microscope (LFM), differential frictional force microscopic data were obtained by measuring the difference in the friction forces of the two surfaces with respect to the vertical load force applied to the LFM probe. The SAMs were prepared from n-octadecyltrimethoxysilane [ODS, H₃C(CH₂)₁₇Si(OCH₃)₃], n-(6-aminohexyl) aminopropyltrimethoxysilane [AHAPS, H₂N(CH₂)₆NH(CH₂)₃Si(OCH₃)₃], 3,3,3-trifluoropropyltrimethoxysilane [FAS3, F₃C(CH₂)₂Si(OCH₃)₃] and heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane [FAS17, F₃C(CF₂)₇(CH₂)₂Si(OCH₃)₃] by chemical vapor deposition. In the vertical force range of 0 to 600 nN, the SAMs showed no damage at all, and frictional force on the SAM surfaces increased linearly with the vertical force. The order of the frictional force magnitudes determined with the SiOH-terminated probe was SiOH > AHAPS > FAS3 > FAS17 > ODS. In addition, the frictional force difference did not become zero even at a vertical force of 0 nN, that is, the frictional differences could even be imaged by LFM through probe-sample adhesion.     

Selective resonance population in high resolution electron energy loss spectroscopy of 4-ethylbenzenethiol self-assembled monolayers on Au(1 1 1)

We have investigated the vibrational frequencies and excitation cross-section of self-assembled monolayers (SAMs) of 4-ethylbenzenethiol (CH₃CH₂(C₆H₄)SH) on Au(1 1 1) by high resolution electron energy loss spectroscopy (HREELS). Negative ion resonances were observed in the energy loss intensities as a function of the incident electron energy. Analysis of the C–H stretching modes indicates resonances of different energies are localised in both the ethyl and phenyl functional groups of the SAM molecules, which regulate the observed vibrational lineshape.     

Influence of boron concentration on growth characteristic and electro-catalytic performance of boron-doped diamond electrodes prepared by direct current plasma chemical vapor deposition

A series of boron-doped diamond (BDD) electrodes were prepared by direct current plasma chemical vapor deposition (DC-PCVD) with different compositions of CH₄/H₂/B(OCH₃)₃ gas mixture. A maximum growth rate of 0.65 mg cm⁻² h⁻¹ was obtained with CH₄/H₂/B(OCH₃)₃ radio of 4/190/10 and this growth condition was also a turning point for discharge plasma stability which arose from the addition of B(OCH₃)₃ that changed electron energy distribution and influenced the plasma reaction. The surface coating structure and electro-catalytic performance of the BDD electrodes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Hall test, and electrochemical measurement and electro-catalytic oxidation in phenol solution. It is suggested that the boron doping level and the thermal stress in the films are the main factors affecting the electro-catalytic characteristics of the electrodes. Low boron doping level with CH₄/H₂/B(OCH₃)₃ ratio of 4/199/1 decreased the films electrical conductivity and its electro-catalytic activity. When the carrier concentration in the films reached around 10²⁰ cm⁻³ with CH₄/H₂/B(OCH₃)₃ ratio over a range of 4/195/5-4/185/15, the thermal stress in the films was the key reason that influenced the electro-catalytic activity of the electrodes for its effect on diamond lattice expansion. Therefore, the BDD electrode with modest CH₄/H₂/B(OCH₃)₃ ratio of 4/190/10 possessed the best phenol removal efficiency.     

The interaction between vapor-deposited Al atoms and methylester-terminated self-assembled monolayers studied by time-of-flight secondary ion mass spectrometry,X-ray photoelectron spectroscopy and infrared reflectance spectroscopy

The deposition of 2 Å of Al metal onto a monolayer of methylester-terminated alkanethiolate (HS(CH₂)₁₅CO₂CH₃) self-assembled on polycrystalline Au(111) was studied using time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS) and infrared reflectance spectroscopy (IRS). The deposited Al was found to be highly reactive with the oxygen atoms in the self-assembled monolayer terminal functional group. No reactivity between Al and the methylene backbone of the monolayer was observed, nor was any Al observed at the monolayer/Au interface. However, the deposition of Al does induce some chain disordering.     

乙醚团簇的激光电离质谱及从头计算

应用激光多光子电离质谱与超声脉冲分子束技术研究了乙醚团簇，实验中观测到乙醚的碎片离子以及强度较小的(E)H⁺，(E)^＋₂和(E)₂H⁺(E代表CH₃CH₂OCH₂CH₃)，没有发现更大尺寸的团簇离子.结合从头计算理论，在B3LYP/6-311++G(d,p 关键词： 乙醚团簇 偶极-偶极相互作用 从头计算     

Adsorption behaviors of V2O5 nanowires on binary mixed self-assembled monolayers

The adsorption behaviors of V₂O₅ nanowires on binary mixed self-assembled monolayers (SAMs) were investigated with variation of the mixing ratio of two differently terminated thiolates on Au. Hydroxyl-covered V₂O₅ nanowires showed a preferential adsorption on amine (NH₂)-terminated thiolates over methyl (CH₃)-terminated ones. However, on the binary mixed SAM of NH₂- and CH₃-terminated thiols, the adsorption behavior did not follow a simple expectation based upon the electrostatic interaction. The total number of adsorbed V₂O₅ nanowires increased with the mole fraction of NH₂-terminated thiolates up to χNH₂∼0.5, then it decreased with further increase of χNH₂. The height distribution of adsorbed nanowires showed that the relative portion of the agglomerated wires thicker than 3.5 nm to individual wires thinner than 3.5 nm increased up to χNH₂∼0.75 and then it decreased with further increase of χNH₂. The dispersion of molecules with polar-functional groups as well as the molecular ordering of mixed SAMs is attributed to such adsorption behaviors of V₂O₅ nanowires.     

Preparation of superhydrophobic films on titanium as effective corrosion barriers

Stable superhydrophobic films were prepared on the electrochemical oxidized titania/titanium substrate by a simple immersion technique into a methanol solution of hydrolyzed 1H,1H,2H,2H-perfluorooctyltriethoxysilane [CF₃(CF₂)₅(CH₂)₂Si(OCH₂CH₃)₃, PTES] for 1 h at room temperature followed by a short annealing at 140 °C in air for 1 h. The surface morphologies and chemical composition of the film were characterized by means of water contact angle (CA), field emission scanning electron microscopy (FESEM), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). The water contact angle on the surface of this film was measured to be as high as 160°. SEM images showed that the resulting surfaces exhibited special hierarchical structure. The special hierarchical structure along with the low surface energy leads to the high surface superhydrophobicity. The corrosion resistance ability and durance property of the superhydrophobic film in 3.5 wt.% NaCl solution was evaluated by the electrochemical impedance spectroscopy (EIS). The anticorrosion properties of the superhydrophobic film are compared to those of unmodified pure titanium and titania/titanium substrates. The results showed that the superhydrophobic film provides an effective corrosion resistant coating for the titanium metal even with immersion periods up to 90 d in the 3.5 wt.% NaCl solution, pointing to promising future applications.     

The Influence on NMR Parameters of Silicon Penta Coordination in Silatranes

¹H, ¹³C, ¹⁹F and ²⁹Si NMR chemical shifts and coupling constants for Si-substituted silatranes, XSi(OCH₂CH₂)₃N, and triethoxysilanes, XSi(OCH₂CH₃)₃, where X = H, CH₃, and F have been studied. Expansion of the coordination numbers of silicon and tin leads to similar changes in the NMR parameters.     

Static ToF-SIMS analysis of plasma chemically deposited ethylene/allyl alcohol co-polymer films

A plasma co-polymerization of ethylene as a “chain extending” monomer and allyl alcohol as a carrier monomer for hydroxyl groups was studied. The composition of the feed gas was systematically varied and the plasma co-polymers were analyzed in terms of their relative concentrations of OH functional groups by static Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) immediately after their preparation without any air contact, i.e., under so called “in situ” conditions.The relative OH group concentration involved in the -CH₂-OH groups was derived from the normalized yields of the CH₃O⁺ secondary fragment ion. The density of functional groups in the plasma co-polymers was found to vary non-linearly with respect to the mole percentage of the monomers in the feed gas.Co-polymerization phenomena, i.e. chemical interactions and recombination reactions taking place between monomer molecules in the plasma and/or during the deposition process, become evident in ToF-SIMS spectra.     

Formation pathways of HO2 and OH changing as a function of temperature in photolytically initiated oxidation of dimethyl ether

The time resolved product formation in oxidation of dimethyl ether (DME) has been studied between 298-625 K and 20-90 torr total pressure. Near-infrared frequency modulation spectroscopy (FMS) with Herriott type multi pass optics and UV absorption spectroscopy (UV) were conducted in the same cell. The reaction was initiated by pulsed photolysis in a mixture of Cl₂, O₂, and DME via CH₃OCH₂ radical formation. The reaction process was investigated through FMS measurement of HO₂ and OH, and UV measurement of CH₃OCH₂O₂. The yields of HO₂ and OH are obtained by comparison with reference mixtures, Cl₂, O₂, and CH₃OH for HO₂, and Cl₂, O₂, CH₃OH, and NO for OH, which convert 100% of initial Cl to HO₂ and OH. The CH₃OCH₂O₂ yield is also obtained. It was found that the HO₂ yield increases sharply over 500 K mainly with a longer time constant than that of R + O₂ reaction, while a prompt component exists throughout the temperature range at a few percent yield. OH was found to be produced promptly at a yield considerably larger than that known for the simplest alkanes. The CH₃OCH₂O₂ profile has a prompt rise followed by a gradual decay whose rate is consistent with the slow HO₂ formation. The species profiles were successfully predicted with a model constructed by modifying the existing one to suit the reduced pressure condition. After modification, it was inferred that the HO₂ formation over 500 K is secondary from HCHO + OH and HCO + O₂ and a part of HCO is formed directly from the O₂ adduct, whereas the HO₂ formation below 500 K is governed by CH₃OCH₂O₂ chemistry. The HCO forming pathway via isomerization-decomposition of the O₂ adduct, which was not included in the former models, was supported by our quantum-chemical calculations.     

Speeds of sound and isentropic compressibilities of (2-ethoxyethanol + ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol) binary mixtures at 298.15 K

The speed of sound (u) has been obtained at a frequency of 8.3 MHz in {CH₃CH₂OCH₂CH₂OH + HOCH₂CH₂(OCH₂CH₂)_nOH}for n = 0, 1, 2, and 3 over the whole composition range of studied binary liquid mixtures, at T = 298.15 K. The speed of sound values were combined with those of our previous results for densities and viscosities to obtain isentropic compressibility (κ_s), free volume (V_f), and intermolecular free length (L_f). From all these data excess isentropic compressibility (κ_s^E), excess free volume (V_f^E) and excess intermolecular free length (L_f^E) as well as the deviations of the speed of sound (Δu) were obtained. The results are interpreted in terms of molecular interactions occurring in the solutions.     

Atmospheric oxidation chemistry of 1–methoxy 2–propyl acetate initiated by OH radicals: kinetics and mechanisms

Kinetics and mechanism of the gas-phase reaction of CH₃C(O)OCH(CH₃)CH₂OCH₃ (MPA) with OH radicals in the presence of O₂ and NO have been investigated theoretically by performing a high and reliable level of theory, viz., CCSD(T)/6-311?+?G(d,p)//BH&HLYP/6-311++G(d,p)?+?0.9335×ZPE. The calculations predict that the H-abstraction from the ?CH₂?O? position of MPA is the most facile channel, which leads to the formation of the corresponding alkoxy radicals CH₃C(O)OCH(CH₃)C(O ?)HOCH₃ under atmospheric conditions. This activated radicals CH₃C(O)OCH(CH₃)C(O ?)HOCH₃ will undergo further rearrangement, fragmentation and oxidative reactions and predominantly leads to the formation of various products (methyl formate HC(O)OCH₃ and acetic anhydride CH₃C(O)OC(O)CH₃). In the presence of water, acetic anhydride can convert into acetic acid CH₃C(O)OH via the hydrolysis reaction. The calculated total rate constants over the temperature range 263–372?K are used to derive a negative activation energy (E_a= ?5.88 kJ/mol) and an pre-exponential factor (A?=?1.78×10^?12 cm³ molecule^?1 s^?1). The obtained Arrhenius parameters presented here are in strong agreement with the experimental values. Moreover, the temperature dependence of the total rate constant over a temperature range of 263?1000?K can be described by k?=?5.60 × 10^?14×(T/298?K)^3.4×exp(1725.7?K/T) cm³ molecule^?1 s^?1.     

Anilinium Ions: Relations Between pK, σ and Intensity of the UV Transition

Spectroscopists have often assumed, based only on the UV spectrum of the anilinium ion (φNH₃ ⁺), that ammonium groups cannot bring a “mesomeric” effect upon π systems. This assumption^(1–3) which could be justified for the anilinium ion itself, whose OO band of the secondary transition (towards 260 nm) is very weak, has been unduly extended to all the ammonium groups. Actually, the interaction between a π system and (NX_aX_bX_c)⁺ groups has been studied by several authors^(4–8) and we have shown that contrary to what had been assumed by spectroscopists, such an interaction induces strong effects on the UV spectrum of the benzene chromophore^(9–11). Using the MNDO and the CNDO methods, we have studied the quantum factors which play a part in the long range interaction, between: an ω group X on the one hand, N on the other hand, and then φ, in φNH₂ ⁺CH₂X, φNH⁺ (CH₂X_a) CH₂X_b and φNH⁺ (C₂H₄)₂X.