Reorientational and vibrational relaxation in liquid trichloracetonitrile

The first- and second-order reorientational correlation functions were determined from i.r. and Raman bandshapes of ν_s(CN)in liquid trichloracetonitrile and discussed in terms of the J-diffusion model. A consistent fit for G_1r(t) and G_2r(t) was possible for short times only (0–1.5 ps). The vibrational correlation functions, determined from Raman studies of the ν_s(CN) and ν_s(CC) bandshapes, are discussed in terms of recent theories of vibrational dephasing.     

Infrared dispersion of liquid sym-collidine

The optical constants of liquid sym-collidine were determined in the 12 500–600 cm⁻¹ range using a thin film transmission technique. The complete spectrum of both components of the complex electric permittivity in the near-infrared and infrared regions and the related high-frequency dielectric properties of the liquid were determined and discussed.     

Infrared spectroscopy of acetone-hexane liquid mixtures

Acetone and hexane mixtures covering the whole solubility range were studied by Fourier transform infrared attenuated total reflectance spectroscopy. Factor analysis separates the spectra into four principal factor spectra and multiplying factors. Those containing negative factors are abstract, but the spectra are real. A statistical distribution model of the molecules in the solutions rendered the factors real. From these we define the intermediate species that occur in a 1:2 molar ratio of acetone in hexane, present principally in the low acetone concentration regions, and in a 2:1 molar ratio of acetone in hexane, present principally in the higher acetone concentration region. However, except at the concentration range limits where only pure acetone and pure hexane are present, the four species are present over the whole solubility range. The IR spectra of the species indicated very little displacement of the CH stretch bands, HCH deformation bands, and CC stretch bands, although there are some small intensity variations. Most of the modifications are observed on the acetone C=O stretch band. From the gas phase position, a strong bathochromic shift of 19 cm(-1) of the pure liquid is assigned to dipole-dipole interactions. In the 2:1 groupings, the shift that decreases to 15 cm(-1) is due to the diminished dipole-dipole interactions. In the 1:2 groupings, no dipole-dipole interaction can exist, and the bathochromic displacement of 9 cm(-1) is attributed to van der Waals interactions. In the one acetone to two hexanes grouping, no dipole-dipole interaction can exist, and the bathochromic displacement of 9 cm(-1) is attributed to van der Waals interactions. From the statistical distribution of the molecules, we determine that mixtures of hexane and acetone form a random organization with no preferred association or complex.     

Infrared study of 1-octanol liquid structure

A detailed analysis of the temperature behavior of the OH stretching bands in infrared (IR) and near infrared (NIR) spectra has been performed for neat liquid 1-octanol. Spectral features have been interpreted using a three-state model, based on different typologies of OH oscillator. The H-bond energy dispersion has been calculated from IR data. Structural properties such as self-association degrees and H-bonding enthalpy formations have been reported. Results have been compared with recent Molecular Dynamic simulation studies. From temperature induced intensity variations the average H-bonding cooperative energy is evaluated. For the 1-octanol liquid system a break point temperature is detected around 50 °C. The existence of two temperature domains connected with self-association properties is in agreement with the behavior of relaxation processes evidenced in previous light scattering studies. These results evidence the correlation existing among structural and dynamical properties in complex self-associating liquid systems.     

Infrared spectra of DCl in liquid alkanes

Preliminary results are reported on the effect of solute-solvent interactions on the form of the DCl fundamental infrared absorption band. It is found that the band shape varies as a function of alkane chain length and isomerism. The results are interpreted in terms of the correlation function for DCl reorientation.     

Microtubule particle dispersion in liquid crystal hosts

Microtubule particles and metal-coated microtubules were dispersed in various host liquid crystal mixtures. Dispersion effects were evaluated as a function of liquid crystal type, viscosity, dielectric anisotropy and surface interaction. Experimental results indicated that all the types of liquid crystals studied were aligned perpendicular to the microtubule surfaces, regardless of liquid crystal composition or various surface coatings used on the metal-coated microtubules. Low concentrations of the metal-coated microtubules in nematic liquid crystal hosts were aligned by flow or cell surface alignment conditions, and could be modulated by electric or magnetic fields. We observed better microtubules dispersion uniformity in high viscosity liquid crystal host mixtures and in liquid crystal-monomers than in isotropic fluids. Microtubules particles dispersed in ROTN-404 liquid crystal mixture had a much higher birefringence in the microwave region than dispersion in a paraffin oil.     

Microtubule particle dispersion in liquid crystal hosts

Abstract

Microtubule particles and metal-coated microtubules were dispersed in various host liquid crystal mixtures. Dispersion effects were evaluated as a function of liquid crystal type, viscosity, dielectric anisotropy and surface interaction. Experimental results indicated that all the types of liquid crystals studied were aligned perpendicular to the microtubule surfaces, regardless of liquid crystal composition or various surface coatings used on the metal-coated microtubules. Low concentrations of the metal-coated microtubules in nematic liquid crystal hosts were aligned by flow or cell surface alignment conditions, and could be modulated by electric or magnetic fields. We observed better microtubules dispersion uniformity in high viscosity liquid crystal host mixtures and in liquid crystal-monomers than in isotropic fluids. Microtubules particles dispersed in ROTN-404 liquid crystal mixture had a much higher birefringence in the microwave region than dispersion in a paraffin oil.     

High-pressure liquid dispersion and fragmentation of flame-made silica agglomerates

The influence of primary particle diameter and the degree of agglomeration of flame-made silica agglomerate suspensions in aqueous solutions is studied by high-pressure dispersion (up to 1500 bar) through a nozzle with a 125 microm inner diameter. These particles were produced (4-15 g/h) by oxidation of hexamethyldisiloxane (HMDSO) in a coflow diffusion flame reactor. Their average primary particle size (10-50 nm) and degree of agglomeration were controlled by varying the oxygen and precursor flow rates. The particles were characterized by nitrogen adsorption, electron microscopy, and small-angle X-ray scattering. Hydrodynamic stresses break up soft agglomerates and yield hard agglomerate sizes in the range of 100-180 nm, as characterized by dynamic light scattering. Soft agglomerates exhibited decreasing light scattering diameters with increasing dispersion pressure, while hard agglomerates were insensitive.     

Boundary conditions of liquid phase reactors with axial dispersion

Numerical calculations of concentration profiles in axially dispersed flow reactors with different properties from section to section show that the conversion may depend considerably on the kind of boundary conditions applied at the boundary surfaces between sections. The jump condition of Danckwerts and the non-jump condition of Wehner and Wilhelm yield different concentration profiles. An experimental study of an isothermal liquid phase reactor divided into sections with different properties reveals that no back effect can be found as would be predicted by the application of Wehner and Wilhelm's boundary conditions. This result and earlier experimental findings in the literature lead to the conclusion that the mechanism of effective turbulent diffusivity in liquids does not provide any back transport of mass. Therefore the application of the boundary conditions of Wehner and Wilhelm for flow reactors is not justified if mass dispersion is caused predominantly by effective turbulent diffusivity. From a macroscopic point of view, the jump condition of Danckwerts appears to be more appropriate as it predicts conversion profiles which agree well with experimental results.     

Infrared dispersion of H-bonded systems. The dielectric function for weak complexes

The spectrum of the complex electric permittivity was obtained in the ν_s(OH) region for several weakly H-bonded systems. The molar atomic polarizations and atomic polarizabilities related to this vibration were determined and are discussed.     

Infrared dispersion studies: Part 12: infrared dispersion of dichloro-, dibromo- and diiodomethane and their deuterated analogues

Absorption spectra and dispersion curves have been obtained for dichloro-, dibromo- and diiodomethane in the liquid phase between 500 and 20 cm^?1 using interferometric and Fourier spectroscopic techniques. The refractive index data extend existing information on these molecules to include all infrared active fundamental modes. Dispersion curves have also been obtained for deuterated dichloro- and dibromomethane, in the liquid phase, between 5000 and 450 cm^?1.The refractive indices have been used to calculate absolute band intensities, dipole moment derivatives and vibrational polarizations.     

Infrared absorption study of hexapentyloxytriphenylene A discotic liquid crystal

Abstract

Fourier transform infrared absorption (FTIR) spectroscopy has been used to study a discotic liquid crystal. IR spectra are reported as a function of temperature for hexapentyloxytriphenylene (H5T). The order parameter S has been determined using unpolarized radiation and by comparing the spectra of the discotic phase with that of the isotropic phase. Variations in frequency for some of the most significant bands are presented as a function of temperature.     

Infrared study of phase transitions in thermotropic liquid crystal polyesters

Three samples of semiflexible thermotropic liquid-crystalline polyesters based on mesogenic aromatic triads and a decamethylene spacer have been investigated by IR spectroscopy at various temperatures between room temperature and 290°C. The crystal-to-liquid crystal (either nematic or smectic) phase transition was accompanied by fairly strong spectral variations, whereas slight, but significant, changes in the IR profiles were detected at the liquid crystal-to-isotropic transition. By comparing the results obtained with the spectral behavior recorded for corresponding structural analogs of low molar mass, it was possible to attribute the spectral variations observed in the polymer samples to a decrease in intermolecular interactions rather than to conformational changes. The thermal transitions indicated by IR spectra were in good agreement with the analogous data obtained by calorimetric or optical microscopy techniques.     

分散聚合法制备液相芯片聚苯乙烯磁性复合微球的研究

本文将丙烯酸基磁流体均匀分散到苯乙烯单体中,采用分散聚合法制备出了适于构建液相芯片微球载体的单分散性微米级磁性微球.考察了丙烯酸基磁流体预处理时间、加料顺序和单体量对微球形貌和粒径分布的影响及其条件优化.扫描电镜(SEM)显示磁性微球平均粒径为7.77 μm,具有良好的单分散性(多分散指数PDI为1.03),并且表面光滑致密;用超导量子干涉磁强计测量了Fe3O4纳米粒子的磁化曲线;用红外光谱(FT-IR)和热失重(TG)方法表征了磁性微球的化学结构及Fe3O4含量.     

Spatial dispersion in chiral liquid crystals. Effects of higher orders

Abstract

Spatial dispersion effects in chiral liquid crystals are reviewed. New spatial dispersion phenomena are observed in the vicinity of the Bragg reflection wavelength–an anomaly of the refractive index and an optical anisotropy of the cubic blue phases. These effects can be explained by taking into account the spatial dispersion correction of the dielectric tensor of the medium of higher orders in the ratio of the light wave vector to the structural wave vector of chiral phases.     

Optical rotatory dispersion from liquid crystalline solutions and films of hydroxypropylcellulose

The chiroptical properties of (hydroxypropyl)cellulose (HPC) in methanol are measured by optical rotatory dispersion (ORD), both in isotropic solution and in the cholesteric liquid crystalline phase. The ORD spectra of HPC films cast from lyotropic solution are also examined. Isotropic solutions of HPC in methanol provide no ORD evidence for the presence of a helical conformation, or for concentration-induced changes in conformation. The ORD curve of HPC in methanol, when expressed as specific rotation, is independent of polymer concentration for isotropic solutions containing between 1 and 43 per cent polymer by weight. From the slope of Drude plots, the Cotton effect responsible for the observed ORD curve occurs at 175-180 nm. However a 45 per cent liquid crystal-line solution exhibits plain positive dispersion, and the magnitude of the specific rotation is also much greater than that found for solutions containing less than 43 per cent polymer. Results for more concentrated solutions confirm that ORD spectra of lyotropic liquid crystals of HPC in methanol contain a significant positive component that is not accounted for by the de Vries equation for cholesteric reflection. ORD measurements in other solvents and on dry films show that this contribution to the optical activity vanishes when the solvent is removed or when hydrogen bonding is disrupted. The effect is tentatively ascribed to a hydrogen bonded structure that contributes strongly to the optical rotation.     

Infrared spectroscopy of acetone-water liquid mixtures. II. Molecular model

In aqueous acetone solutions, the strong bathochromic shifts observed on the OH and CO stretch infrared (IR) bands are due to hydrogen bonds between these groups. These shifts were evaluated by factor analysis (FA) that separated the band components from which five water and five acetone principal factors were retrieved [J. Chem. Phys. 119, 5632 (2003)]. However, these factors were abstract making them difficult to interpret. To render them real an organization model of molecules is here developed whose abundances are compared to the experimental ones. The model considers that the molecules are randomly organized limited by the hydrogen bond network formed between the water hydrogen atoms and the acetone or water oxygen atoms, indifferently. Because the oxygen of water has two covalent hydrogen atoms which are hydrogen-bonded and may receive up to two hydrogen atoms from neighbor molecules hydrogen-bonded to it, three types of water molecules are found: OH2, OH3, and OH4 (covalent and hydrogen bonds). In the OH stretch region these molecules generate three absorption regimes composed of nu3, nu1, and their satellites. The strength of the H-bond given increases with the number of H-bonds accepted by the oxygen atom of the water H-bond donor, producing nine water situations. Since FA cannot separate those species that evolve concomitantly the nine water situations are regrouped into five factors, the abundance of which compared exactly to that retrieved by FA. From the factors' real spectra the OH stretch absorption are simulated to, respectively, give for the nu3 and nu1 components the mean values for OH2, 3608, 3508; OH3, 3473, 3282 and OH4, 3391, 3223 cm(-1). The mean separations from the gas-phase position which are respectively about 150, 330, and 400 cm(-1) are related to the vacancy of the oxygen electron doublets: two, one, and zero, respectively. No acetone hydrate that sequesters water molecules is formed. Similarly, acetone produces ten species, two of which evolve concomitantly. Spectral similarities further reduce these to five principal IR factors, the abundance of which compared adequately to the experimental results obtained from FA. The band assignment of the five-acetone spectra is given.