甲基乙烯基硅酮在外场作用下的光激发特性研究

采用密度泛函B3P86和组态相互作用方法在6-311++G^**基组水平上计算了甲基乙烯基硅酮分子从基态到前10个激发态的跃迁波长，振子强度，自发辐射系数A_n0和吸收系数B_0n(n＝1—10).同时研究了外电场对甲基乙烯基硅酮分子激发态的影响规律.结果表明，随外电场强度增大，最高占据轨道与最低空轨道能隙变小，激发能随电场增加而急剧减小.因而表明在外电场作用下，分子易于激发和 关键词： 甲基乙烯基硅酮 激发态 外电场     

Synthesis and characterization of siloxane sulfobetaine antimicrobial agents

In this paper, we report a novel antibacterial agent siloxane sulfobetaine (SSB) with reactive siloxane groups, which can be bonded onto the glass surface, rendering excellent antibacterial activity and good durability. Their antibacterial rate against Escherichia Coli and Staphylococcus aureus reach 99.96% and 99.98%, respectively, within the 24 h contact time. Their antibacterial rates of SSB coated glass surface are still beyond 95.0% after 20 washes. Moreover, SSB does not induce a skin reaction and is nontoxic to animals. Therefore, the SSB has great applications in biomaterial applications requiring durable bacteriostasis.     

Electrically induced storage effects in smectic A phase of dyed low molar mass siloxane liquid crystals

A newly synthesized low molar mass liquid crystal having a flexible mesogenic group attached to methylene siloxane exhibiting smectic A phase has been used as a host for 2% (wt./wt.) dichroic dyes. The electro-optic properties of these guest–host mixtures have been studied as a function of temperature, frequency and the applied voltage. At low frequency (≲1 Hz), turbulent scattering texture was induced influenced by conduction mechanism. This texture was transformed to a clear homeotropic state due to dielectric reorientation of the smectic molecules at high frequency (>2 kHz). These materials have shown storage effects similar to monomeric and polymer smectogens. The effects of dichroic dyes on the electro-optic performances have been discussed. These systems are expected to prove functional materials for electronic displays.     

Stability of siloxane couplers on pure and fluorine doped SnO2 (110) surface: A first principles study

Siloxane is a favorable candidate as an anchor group that can be used to bind organic molecules to SnO₂ surfaces, with a wide range of practical applications. Therefore, adsorption geometries and energies of siloxane coupler on the SnO₂ (110) surface have been investigated in this study using quantum-chemical periodic density functional theory (DFT) calculations. We present a comparative study of different siloxane adsorption arrangements on pristine and fluorine doped SnO₂ surface. According to the calculations, the surface doping with fluorine leads to stabilization of the siloxane network at the stannic oxide surface. The trend is analyzed in terms of additional charge provided by F impurities to the chemisorbed oxygen atoms thus increasing the ionicity of their bonding. Implications of the current findings for the design of organic-metal oxide interface with better thermo-stability and improved electronic properties are discussed.     

Surface visco-elastic moduli of a Langmuir film of a polystyrene-polydimethyl siloxane block copolymer at the air-ethyl benzoate interface

Surface quasi-elastic light scattering has been applied to a spread film of a block copolymer of polystyrene and polydimethyl siloxane. The influence of surface concentration (surface pressure) at a fixed surface wave number has been explored. The capillary wave frequency and damping showed a similar dependence on the surface concentration as values obtained earlier, but due to a more appropriate analysis of the correlation functions, surface visco-elastic moduli obtained were distinctly different. By correlating the values obtained with the variations in solvated polystyrene layer thickness from neutron reflectometry, the maximum in dilational modulus was shown to occur at the same nominal surface concentration where the layer begins to stretch and take on brush-like behaviour. This same surface concentration is where the relaxation time of the spread film also has a maximum value, the relaxation time being calculated using the standard linear model of visco-elasticity, which was found to fit the frequency dependence of the surface tension and dilational moduli at the resonant nominal surface concentration of 3.1 mg m^-2. Received 21 August 2001 and Received in final form 11 January 2002     

Two-dimensional solid state NMR characterization of physisorbed siloxane polymer (OV-225) on silica

Physisorbed cyanopropyl-methyl-phenyl-methyl-siloxane polymer on a silica surface was characterized by one- and two-dimensional solid state NMR techniques including heteronuclear proton-silicon correlation spectroscopy. Spin-lattice relaxations of protons of the siloxane polymer exhibited only small changes upon anchoring to the silica surface indicating somewhat altered molecular dynamics of proton moieties that contribute to the relaxation process. However, the same relaxation rates of the siloxane polymer’s silica atoms were reduced due to restricted mobility of the polymer. Proton-silicon heteronuclear correlation spectroscopy (HETCOR) revealed strong correlations of silanol protons with both Q³ and Q⁴ sites of the silica surface. In addition, a correlation between methyl protons and the Q³ site of the silica surface was observed when HETCOR experiments with very small mixing time (5 ms) were performed. The presence of these correlations is indicative of the coherent magnetization transfer mainly through dipolar mechanisms. Since magnetization transfer through the dipolar mechanism is 1/r³ dependent, methyl protons must lie in close proximity to the silica surface. Hydrogen bonding of the silica surface’s hydroxyl protons with the bridging oxygen of the siloxane polymer is most likely responsible for positioning the methyl protons closer to the surface. Additional correlations between ²⁹Si nuclei and methylene protons next to cyano group was also observed with mixing time indicating the closer proximity of these protons to the silica surface as well. This juxtaposition of methylene protons is most likely due to hydrogen bonding of the siloxane polymer through the cyano moiety. Furthermore, the hydrogen bonding through the cyano group is most likely to be in parallel orientation to the surface. Finally, the aromatic protons exhibited weak correlations only with Q³ sites, indicating that these protons must also lie in close proximity of the silica surface.     

Dependence of the structure of siloxane urethane elastomer on the conditions of synthesis

The morphology and thermal and mechanical properties of siloxane urethane block copolymers based on oligosiloxane- and oligoalkylene diols are investigated. The dependence of morphology on the conditions of synthesis is studied via atomic force microscopy and scanning electron microscopy.     

Adsorption behavior of protein onto siloxane microspheres

The siloxane microspheres with core-shell structure (PMMA/PMPS) (MMA, methyl methacrylate; MPS, 3-methacryloxypropyl-trimethoxysilane) have been prepared by dispersion polymerization as described in our previous work. In this paper, the developed poly(MMA-MPS) microspheres, as a carrier, are used to investigate the adsorption behavior of bovine serum albumin (BSA) on them. The Langmuir and Freundlich models have been applied to describe the adsorption behavior. The experimental results indicated that the presence of PMPS evidently increases the adsorption rate and the amount of protein, and it also influences the interaction of BSA molecules. The adsorption of BSA on the poly(MMA-MPS) microspheres seems to be sensitive to pH and ionic strength. The fittings curves from Langmuir and Freundlich models showed that the adsorption was actually more complicated than ideal situation because one or more interactions were involved in the process. For understanding the electronic contribution, the Zeta potential was used to measure the reactive system before and after protein adsorption.     

Small-angle neutron scattering study of the mesostructure of bioactive coatings for stone materials based on nanodiamond-modified epoxy siloxane sols

The structure formation of sol-gel-derived epoxy siloxane compositions with different ratios of the main precursors (R _{TEOS/EPONEX 1510} = 16/38, 27/27, 38/16 wt %) and with different concentrations of detonation synthesis nanodiamonds (c _DND = 0.05, 0.10, 0.20 wt %) has been investigated using small-angle neutron scattering (SANS). Based on the SANS data, it has been revealed that the synthesized epoxy siloxane xerogels are systems with a two-level fractal structure, in the formation of which the siloxane component plays a dominant role. It has been found that the fractal dimension D _m2 and the radius of gyration R _g2 of clusters in the epoxy siloxane compositions decrease with an increase in the content of the siloxane component. It has been established that the introduction of small additions of detonation synthesis nanodiamonds (less than 1 wt %) into the epoxy siloxane composition with an equal ratio of the main precursors R _{TEOS/EPONEX 1510} = 27/27 wt % leads to a transition from the two-level to three-level structure organization and affects the fractal dimension D _m and the radius of gyration R _g of the formed clusters.     

A new class of photo-induced phenomena in siloxane films

The light induced atomic desorption effect, known as LIAD, is observed whenever Pyrex cells, coated with siloxane films and containing alkali atoms, are illuminated. LIAD is a non-thermal phenomenon and it can be observed even with very weak light intensities. We show that the simultaneous contribution to the photo-emission of atoms adsorbed both at the film surface and within the film must be taken into account in order to fit the experimental data. We demonstrate that both the desorption efficiency and the diffusion coefficient of the alkali atoms embedded in the dielectric film depend on the desorbing light intensity. These features characterize a new class of photo-induced phenomena whose analysis gives new insights in the comprehension of the atom-surface interaction and of the atom-bulk diffusion and opens interesting perspectives for applications. Received 27 April 2000 and Received in final form 15 September 2000     

Vibrational study of tin-containing siloxane ring compounds

By a condensation reaction of (t-Bu)₂Si(OH)₂ (L) with tin tetrachloride (SnCl₄), two different compounds were obtained: a condensation product between two molecules of L and a tin-containing siloxane bicycloheptane ring compound formed by a subsequent reaction between partially hydrolysed SnCl₄ and L. The latter was identified by x-ray diffraction. The Raman spectra of both isolated compounds were recorded and confirmed the structure obtained for the ring compound. © 1997 John Wiley & Sons, Ltd.     

On the relaxation of volume and shear viscosities in vegetable oils

Longitudinal and shear ultrasonic measurements were performed on castor, tung, soyabean and cottonseed oils in the frequency ranges 50 kHz–30 MHz and 10–150 MHz using reverberation, pulse and impedance techniques respectively. In castor and tung oils relaxation spectra for both volume and shear viscosities are broad and identical in shape. In soyabean and cottonseed oils both volume and shear viscosities undergo single relaxation but the volume relaxation time is about 10 times larger than the shear. It is suggested that shear relaxation results from molecular orientation and volume relaxation from rearrangement of molecular packing.     

甲基苯基乙烯基硅橡胶电离总剂量效应

甲基苯基乙烯硅橡胶具有耐高低温、防震等独特优势,在航天器的减震、密封等领域具有广泛应用前景。研究了甲基苯基乙烯基硅橡胶的电离总剂量效应。结果表明,随着辐射剂量的增加,甲基苯基乙烯基硅橡胶的力学性能出现了不同程度的退化。拉伸强度和撕裂强度变化规律以1×106 Gy(Si)剂量点为分界点。低于该剂量,拉伸和撕裂随剂量增加快速下降;高于该剂量时,随辐照剂量增加,拉伸强度出现一定程度反弹,呈现出宽"U"形,而撕裂强度则是先增加后下降。拉断伸长率和邵氏硬度A随辐照剂量增加分别出现快速下降和增加,最终接近饱和。最后,从辐射交联和裂解方面讨论了甲基苯基乙烯基硅橡胶电离总剂量效应的潜在物理机制。     

Atomic composition and stability of Langmuir–Blodgett monolayers based on siloxane dimer of quaterthiophene on the surface of polycrystalline gold

Physics of the Solid State - Atomic composition of monolayers based on siloxane dimer of quaterthiophene deposited by Langmuir–Blodgett technique on a silicon dioxide surface partially...     

Quantitative and high mass ToF-SIMS studies of siloxane segregation in hydrogel polymers using cryogenic sample handling techniques

This paper examines the capabilities of cryogenic sample handling to examine composition and structure of hydrogel materials where siloxane components are central to the analysis. XPS analysis of multicomponent polymers with cryogenic sample handling following exposure to aqueous environments has revealed the composition and kinetics of near surface reorganization for siloxane and fluorocarbon containing polymers. In this study we report results from a ToF-SIMS protocol for cryogenic sample handling applied to the analysis of surface changes upon hydration/dehydration of hydrogel polymers. Comparison of results from angle dependent XPS and ToF-SIMS are discussed for a range of commercial soft contact lens materials. Both methods detected changes in surface chemistry between the hydrated (frozen) and dehydrated surfaces. Analysis of the hydrated surfaces detected polymer components indicative of the commercial formulation as well as ice clusters. Analysis of the dehydrated materials detected changes in surface chemistry relative to the hydrated surface in addition to loss of water due to sample dehydration. A quantitative standard additions method for ToF-SIMS data was used to determine submonolayer amounts of PDMS impurities at the surface of the hydrogels. ToF-SIMS analysis of a series of seven poly (allyl methacrylate-g-dimethylsiloxane), AMA-g-DMS, graft copolymers in the hydrated state revealed high mass oligomeric ion distributions for systems with bulk PDMS content greater than 25 wt.%. This marks the first time that detection of high mass oligomeric ion distributions from hydrated (frozen) surfaces has been reported. Analysis of the dehydrated surface detected formation of high mass oligomeric ion distributions for systems with PDMS bulk content greater than 15 wt.%, but only detected these ion distributions in wet (frozen) samples when the bulk concentration was greater than 25 wt.%.     

The synthesis of allyl ether functionalized siloxane monomers under ultrasonic irradiation at ambient conditions

The novel class of cationic UV-curable allyl ether functionalized siloxane monomers type CH₂=CH---CH₂---O---R---O---Si(CH₃)₃ and type CH₂=CH---CH₂---O---R---O---Si(CH₃)₂---O---R---CH₂---CH=CH₂ have been synthesized in excellent yields in short times at ambient temperature conditions in the absence of any added catalyst by the classical silylation reactions of homoallyloxyalcohols with chlorosilanes under ultrasonic irradiation.     

Preparation and characterization of core/shell particles with siloxane in the shell

The core/shell particles consisting of polystyrene core and 3-(methacryloxypropyl)-trimethoxysilane (MPS) shell were prepared in the present study by successive seeding polymerization under kinetically controlled conditions and were characterized by particle size analyser, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM image indicated that the particles containing organic siloxane presented an evident core/shell structure. Additionally, the study of XPS also revealed that MPS could be grafted onto the surface of polystyrene microspheres and the atomic ratio of C/Si on the surface of the core/shell particles (MPS-40) was very close to the ratio of C/Si in the molecule of MPS. The surface properties of the films produced from the core/shell particles were also investigated by the static contact angle method. Compared with the homopolymer of PS, the core/shell particles were more effective to create hydrophobic surface, so, the introduction of MPS was capable of obvious increase in water repellency.     

Influence of Particle Morphology and Flow Conditions on the Dispersion Behavior of Fumed Silica in Silicone Polymers

The dispersion behavior of agglomerates of several grades of fumed silica in poly(dimethyl siloxane) liquids has been studied as a function of particle morphology and applied flow conditions. The effects of primary particle size and aggregate density and structure on cohesivity were probed through tensile and shear strength tests on particle compacts. These cohesivity tests indicated that the shear strength of particle compacts was two orders of magnitude higher than the tensile strength at the same overall packing density. Experiments carried out in both steady and time‐varying simple‐shear flows indicate that dispersion occurs through tensile failure. In the steady‐shear experiments,enhanced dispersion was obtained at higher levels of applied stress and, at comparable levels of applied stress, dispersion was found to proceed faster at higher shear rates. Experiments conducted in time‐varying flows further corroborated the results obtained in tensile cohesivity tests. Experiments in which the mean and maximum stresses in the time‐varying flows were matched to the stresses produced in steady shear flows highlight the influence of flow dynamics on dispersion behavior.     

A siloxane polymer lightwave circuit on ceramic substrate applicable to ultrafast optoelectronic multi-chip-modules

Technique for integrating optical waveguide circuits on electrical circuits is developed toward the application to opto-electronic multi-chip modules (O/E-MCM), which enables one to handle ultrafast lightwave pulses and electrical signals on a common circuit board. We use ceramic material as the substrate of O/E-MCM having a multi-layer structure. A siloxane polymer is utilized to form low loss optical waveguides on ceramic substrates by low temperature processes. The waveguide has shown high transparency around 1310 nm. The group velocity dispersion has been measured and shown to become almost zero at wavelength of 1310 nm and about 0.4 fs/cm nm at 1550 nm. An optical circuit has been formed on simple electrical circuit consisting of a thermometer film resistance layer. A Mach–Zehnder interferometer optical switch exhibiting the waveguide extinction ratio of 30 dB, control power of 5 mW, and switching speed of 6 ms has been demonstrated. Thermal management characteristics also have been demonstrated successfully. This single-mode optical waveguide can thus be formed readily on ceramic substrates involving electrical circuit layers; this result confirms its applicability to O/E-MCM.     

Segmental dynamics of poly(methyl phenyl siloxane) confined to nanoporous glasses

The effect of a nanometer confinement on the molecular dynamics of poly(methyl phenyl siloxane) (PMPS) was studied by dielectric spectroscopy (DS), temperature modulated DSC (TMDSC) and neutron scattering (NS). Nanoporous glasses with pore sizes of 2.5–20 nm have been used. DS and TMDSC experiments show that for PMPS in 7.5 nm pores the molecular dynamics is faster than in the bulk which originates from an inherent length scale of the underlying molecular motions. For high temperatures the temperature dependence of the relaxation rates for confined PMPS crosses that of the bulk state. Besides finite states effects also the thermodynamic state of nano-confined PMPS is different from that of the bulk. At a pore size of 5 nm the temperature dependence of the relaxation times changes from a Vogel/Fulcher/Tammann like to an Arrhenius behavior where the activation energy depends on pore size. This is in agreement with the results obtained by NS. The increment of the specific heat capacity at the glass transition depends strongly on pore size and vanishes at a finite length scale between 3 and 5 nm which can be regarded as minimal length scale for glass transition to appear in PMPS.