Surface orientation of a liquid-crystalline polymer studied by polarized reflection spectroscopy

The polarized reflection spectrum was used to evaluate the surface orientation of extruded sheets of liquid-crystalline copolyester consisting of 73 mol % 4-hydroxybenzoic acid units and 27 mol % 2-hydroxy-6-naphthoic acid units. The anisotropy of absorption index was evaluated from the specular reflectance using the Fresnel equation and the Kramers-Kronig relation. An intense absorption and observed in the ultraviolet region was assigned to the π^* ←π transitions of the constituent monomeric units. The observed spectra of the liquidcrystalline polymer were successfully interpreted by use of the spectroscopic data on the monomers. The transition moment directions of the monomeric units were calculated by molecular orbital calculations within the framework of the CNDO/S-Cl approximation. The Surface orientation functions obtained from polarized reflection spectra were compared with the crystal orientation functions in the bulk, which were obtained from the azimuthal intensity distribution of wide-angle x-ray diffraction. The orientation behaviour at the surface of the liquid-crystalline polymer was shown to be equivalent to the orientation behaviour in the bulk at higher draw-down ratio.     

Polarized FT-IR photoacoustic spectroscopy on polymer fibers

The orientation of macromolecular chains in two melt-spun polymer fibers (segmented polyurethane elastomer and melt-modified polyolefine fibers) was studied by photoacoustic spectroscopy (PAS) with polarized light in the mid-infrared range. The PAS orientation functions calculated from the photoacoustic signal intensities of orientation sensitive bands describe the orientation of the different chain segments with respect to the fiber axis. Thus, the orientation of hard and soft segments in the unstressed polyurethane fiber is different and both are similiar to that of the corresponding injection molded bars. With increased spinning velocity an improved orientation of the polyolefine chains along the fiber axis, but only in the amorphous regions of the polymer, were detected. Only a slight reduction of orientation was measured as a result of the subsequent chemical crosslinking in the polyolefines.     

Chain-backbone motion in glassy polycarbonate studied by polarized infrared spectroscopy

Chain-backbone motion in glassy polycarbonate has been investigated both under isothermal stress, and also under zero stress during isothermal annealing of freely contracting film specimens. In both types of experiment, backbone motion was detected by measuring the change in infrared dichroism. The dichroism of absorption bands at 1364 and 2971 cm^?1, which have transition moment vectors directly related to the chain-backbone orientation, was studied. Under tensile stress in the homogeneous region of deformation, changes of up to 2.2° in the mean chain-backbone orientation angle were measured at 23°C. With the onset of cold drawing a total orientation change of some 8° was observed. For the isothermal annealing experiments, a film specimen holder employing conductive heating with radiative losses was employed. It enables infrared measurements to be made while the temperature of the contracting specimen is maintained constant to ± 0.5°C. Oriented specimens were prepared by isothermal stretching of polycarbonate films to strains of the order of 100%. Changes in the mean chain-backbone orientation angle were observed during annealing of these oriented films at temperatures between 80°C and the glass transition (149°C). Chain motion proceeded during annealing, and chain segments were observed to move cooperatively. The temperature at which the polymer is prestretched has a pronounced effect on its subsequent relaxation during annealing: when the sample was stretched at 23°C. motions were detected during annealing at temperatures as low as 81°C, while, if it was stretched at 154°C, no motion was detected at annealing temperatures below 127°C. The data are discussed in comparison with theories of the glassy state that predict the absence of chain-backbone motion at temperatures significantly below the glass transition. A shift in frequency of the ν_a (CH₃) absorption peak in stretched polycarbonate was measured by using polarized radiation. The effect was interpreted in terms of changes in the intermolecular bonding structure of the oriented polymer.     

Orientation distribution of liquid-crystalline polyester sheets studied by polarized infrared spectroscopy

Polarized infrared spectroscopy was applied to evaluate the orientation distribution in extrusion-molded sheets of a liquid-crystalline copolyester consisting of 73 mol % of 4-hydroxy benzoic acid units and 27 mol % of 2-hydroxy-6-naphthoic acid units. The surface orientation function was evaluated from the polarized attenuated total reflection/Fourier transform infrared spectra and the polarized specular reflection spectra. In the case of the specular reflection method, the absorption and refractive indices were obtained from the specular reflectance using the Kramers–Kronig relation and the Fresnel equation. On the other hand, the microscopic orientation functions inside the sheets were evaluated by Fourier-transform infrared microspectroscopy. The polarized FTIR microspectra of microtomed section of sheets were measured in a microscopic domain as small as 40 μ at various positions from the center of the sheet. The surface orientation function was shown to be higher than the interior orientation function. Orientation functions obtained by the spectroscopic techniques are lower than crystal orientation functions determined by wide-angle x-ray diffraction, implying that the crystal orientation function is higher than the orientation function of noncrystalline molecular chains. The orientation distribution in the sheet is discussed in relation to the morphological structures studied by scanning electron microscopy. © John Wiley & Sons, Inc.     

A polymer double-layer studied by step-scan FTIR photoacoustic spectroscopy

Photoacoustic (PA) magnitude and phase spectra of a polyethylene/polyurethane double-layer are presented. The extension of the Rosencwaig-Gersho theory to a double-layered polymer film introduced by N.C. Fernelius in 1980 is applied to compare the experimental spectra with simulations. A reasonable agreement between experiment and simulation is observed. It is shown that FTIR-PAS in combination with simulation provides an important technique for depth profiling in polymeric laminates.     

Trihalogenomethane - base complexes studied by vibrational spectroscopy in low-temperature matrices

Hydrogen-bonded complexes formed by weak proton donors such as the trihalogenomethanes have received little attention. As a precursor to the study of such complexes, infrared and Raman spectra of trifluoromethane and trichloromethane were examined in argon, nitrogen and other matrices. The spectra of these trihalogenomethanes mixed with water or ammonia in argon or nitrogen matrices showed evidence of complex formation, the complexes with trichloromethane being stronger than those with trifluoromethane.     

Optical anisotropy of a photoreacted side-chain liquid-crystalline polymer induced by linearly polarized UV light

Linearly polarized (LP) UV photoreaction of a photo-crosslinkable side-chain liquid-crystalline polymer (SLCP) containing photoreactive cinnamoyl and biphenyl mesogenic groups ( 1 ) was studied. The optical anisotropy of the polymer film was induced by the LP-UV photoreaction and was investigated by the temperature-controlled polarized UV absorption spectroscopy and polarized FT-IR measurements. The reorientation of the nonreacted mesogenic groups along to the Ê direction of the incident LP-UV light during the photoreaction occurred at the LC temperature range of the polymer, and the induced birefringence Δn was about 0.02. Because of the high-density photo-crosslinking, the LP-UV photoreacted film showed orientational stability up to 160°C. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1521–1526, 1998     

Adsorption of calf thymus DNA on Au(110) studied by reflection anisotropy spectroscopy

Reflection anisotropy spectroscopy (RAS) was used to investigate the adsorption of single-stranded (ss-) and double-stranded (ds-) calf thymus DNA on Au(110) in an electrochemical cell. Both types of DNA form ordered structures for electrode potentials in the range from +0.6 to -0.4 V. Both types of DNA desorb at -0.6 V and may start desorbing at lower negative potentials. When adsorbed at +0.6 V, both forms give rise to a similar RAS signal and adsorb through the phosphate groups. As the potential is reduced, the RAS intensity observed from ss-DNA increases to roughly twice that observed from ds-DNA, a result that is interpreted as due to a change in the adsorption of the ss-DNA from sites involving the phosphate groups to sites involving the bases.     

Time-resolved polymer deformation using polarized planar array infrared spectroscopy

Polarized planar array infrared (PA-IR) spectroscopy is shown for the first time to be a powerful approach to study the mechanical deformation of polymers. A dual-beam PA-IR spectrometer was built to enable the simultaneous recording of parallel- and perpendicular-polarized spectra at the same sample spot. The technique provides orientation and structural information during and after fast irreversible deformations with a low-ms (or sub-ms) time resolution and a low data scatter. In proof-of-concept experiments, the possibilities of polarized PA-IR spectroscopy are illustrated by studying the deformation of poly(ethylene terephthalate) thin films.     

Molecular arrangement in a chiral smectic liquid crystal cell studied by polarized infrared spectroscopy

The structure of the chiral smectic C phase (SmC * ) of the mesogen MHP10CBC in a homogeneously aligned thin cell, that exhibits V-shaped-like switching in a certain frequency range, was studied using polarized Fourier-transform infrared spectroscopy and optical microscopy. The molecular orientational distributions were analysed quantitatively in terms of dichroic parameters of the absorbance profiles, by taking into account the orientational properties of the transition moments for several phenyl and carbonyl bands. The polar angles of the transition moments, with respect to the molecular long axis and their azimuthal orientational parameters used in calculations, were determined from the infrared dichroic data for helical and electrically unwound structures in a thicker cell of this material. For a sufficiently thin cell in the SmC * phase at zero electric field, the results on the azimuthal orientational distribution of the director over a ferroelectric liquid crystal cone, with respect to the substrate normal, are in agreement with the model of a partly twisted SmC * structure. The voltage-dependent dichroic parameters in relation to the direction and the degree of the preferable orientation of the molecules in a sample are compared for the SmC * and the SmC * A phases.     

Molecular arrangement in a chiral smectic liquid crystal cell studied by polarized infrared spectroscopy

The structure of the chiral smectic C phase (SmC*) of the mesogen MHP10CBC in a homogeneously aligned thin cell, that exhibits V-shaped-like switching in a certain frequency range, was studied using polarized Fourier-transform infrared spectroscopy and optical microscopy. The molecular orientational distributions were analysed quantitatively in terms of dichroic parameters of the absorbance profiles, by taking into account the orientational properties of the transition moments for several phenyl and carbonyl bands. The polar angles of the transition moments, with respect to the molecular long axis and their azimuthal orientational parameters used in calculations, were determined from the infrared dichroic data for helical and electrically unwound structures in a thicker cell of this material. For a sufficiently thin cell in the SmC* phase at zero electric field, the results on the azimuthal orientational distribution of the director over a ferroelectric liquid crystal cone, with respect to the substrate normal, are in agreement with the model of a partly twisted SmC* structure. The voltage-dependent dichroic parameters in relation to the direction and the degree of the preferable orientation of the molecules in a sample are compared for the SmC* and the SmC* A phases.     

Structure,dynamics and interactions in polymer systems as studied by NMR spectroscopy

The possibilities of NMR spectroscopy in studies of interactions in polymer systems are demonstrated on the example of two types of macromolecular complexes: (i) By measuring ¹H NMR high resolution line intensities, the formation of ordered associated structures of syndiotactic (s) poly(methyl methacrylate)(PMMA) in mixed solvents was quantitatively characterized. The obtained results permit us to assume that the mechanism by which the solvent affects self-association of s-PMMA involves specific interactions of the solvent molecules with PMMA units. Solid state high resolution ¹³C NMR spectra of associated s-PMMA gels were also measured and compared with the spectra of a solid s-PMMA sample. (ii) By using ¹³C solid state NMR spectroscopy, the differences in the structure of the amorphous and crystalline phases in pure poly(ethylene oxide) and its complexes with p-dichlorobenzene or p-nitrophenol were characterized. Prounounced differences also in the dynamic structure of the crystalline phase in these systems are indicated by the relaxation times T₁(C), T_1ρ(C) and T_1ρ(H).     

Molecular dynamics of amorphous/crystalline polymer blends studied by broadband dielectric spectroscopy

The molecular dynamics of poly(vinyl acetate), PVAc, and poly(hydroxy butyrate), PHB, as an amorphous/crystalline polymer blend has been investigated using broadband dielectric spectroscopy over wide ranges of frequency (10⁻² to 10⁵ Hz), temperature, and blend composition. Two dielectric relaxation processes were detected for pure PHB at high and low frequency ranges at a given constant temperature above the T_g. These two relaxation peaks are related to the α and α′ of the amorphous and rigid amorphous regions in the sample, respectively. The α′-relaxation process was found to be temperature and composition dependent and related to the constrained amorphous region located between adjacent lamellae inside the lamellar stacks. In addition, the α′-relaxation process behaves as a typical glass relaxation process, i.e., originated from the micro-Brownian cooperative reorientation of highly constraints polymeric segments. The α-relaxation process is related to the amorphous regions located between the lamellar crystals stacks. In the PHB/PVAc blends, only one α-relaxation process has been observed for all measured blends located in the temperature ranges between the T_g’s of the pure components. This last finding suggested that the relaxation processes of the two components are coupled together due to the small difference in the T_g’s (ΔT_g = 35 °C) and the favorable thermodynamics interaction between the two polymer components and consequently less dynamic heterogeneity in the blends. The T_g’s of the blends measured by DSC were followed a linear behavior with composition indicating that the two components are miscible over the entire range of composition. The α′-relaxation process was also observed in the blends of rich PHB content up to 30 wt% PHB. The molecular dynamics of α and α′-relaxation processes were found to be greatly influenced by blending, i.e., the dielectric strength, the peak broadness, and the dielectric loss peak maximum were found to be composition dependent. The dielectric measurements also confirmed the slowing down of the crystallization process of PHB in the blends.     

Effect of thermooxidation on tinuvin 783 in LDPE films: Characterization by UV and ftir spectroscopy

The effect of thermooxidation on Tinuvin 783 which is a hindered amine light stabilizer in LDPE films has been investigated by UV and FTIR spectroscopy. Initially, a standard curve describing the variation of the concentration of Tinuvin 783 in LDPE films was plotted using the method of integration of the band area. The relation obtained was: band area = 19.6249 × [Tinuvin 783]. This equation was then applied to measure the variation of the concentration of Tinuvin 783 in the 0.2%_wt stabilized samples which have undergone thermooxidation at 90°C for 98 days. The results showed a considerable decrease in the concentration of Tinuvin 783 by 35% during the first 30 days due to probably the formation of nitroxyl radicals. After this, the concentration was observed to be unchanged and may correspond to the phase of nitroxyl radical regeneration. On the other hand, no chemical change in the stabilized LDPE films was observed by FTIR spectroscopy at 90°C during 98 days while the band characteristic of ketone groups (1720 cm⁻¹) was detected for the unstabilized samples after only 11 days. (LDPE: low density polyethylene; HALS: hindered amine light stabilizer)     

Dynamics of water in partially crystallized polymer/water mixtures studied by dielectric spectroscopy

The dielectric relaxation process of water was investigated for polymer/water mixtures containing poly(vinyl methyl ether), poly(ethyleneimine), poly(vinyl alcohol), and poly(vinylpyrrolidone) with a polymer concentration of up to 40 wt % at frequencies between 10 MHz and 10 GHz in subzero temperatures down to -55 degrees C. These polymer/water mixtures have a crystallization temperature TC of water at -10 to -2 degrees C. Below TC, part of the water crystallized and another part of the water, uncrystallized water (UCW), remained in a liquid state with the polymer in an uncrystallized phase. The dielectric relaxation process of UCW was observed, and reliable dielectric relaxation parameters of UCW were obtained at temperatures of -26 to -2 degrees C. At TC, the relaxation strength, relaxation time, and relaxation time distribution change abruptly, and their subsequent changes with decreasing temperature are larger than those above TC. The relaxation strength of UCW decreases, and the relaxation time and dynamic heterogeneity (distribution of relaxation time) increase with decreasing temperature. These large temperature dependences below TC can be explained by the increase in polymer concentration in the uncrystallized phase C(p,UCP) with decreasing temperature. C(p,UCP) is independent of the initial polymer concentration. In contrast to the relaxation times above TC, which vary with the chemical structure of the polymer and its concentration, the relaxation times of UCW are independent of both of them. This indicates that the factor determining whether the water forms ice crystals or stays as UCW is the mobility of the water molecules.     

New details in the polarized spectrum of naphthalene by means of linear dichroism studies in oriented polymer matrices

Linear dichroism (LD) spectra are presented for naphthalene oriented in stretched polyethylene and polypropylene matrices at 77 K and 296 K. From the calculated spectrum LD(λ)/A(λ), where A(λ) is the corrected absorbance spectrum of the sample by unpolarized light, orientational parameters are calculated and component spectra, 235–315 nm, are resolved corresponding to polarization parallel to the long (B_3u = x) and the short (B_2u = y) axes in the molecular plane (D_2h). The orientational parameters indicate different orientational mechanisms in polyethylene and polypropylene, but the resolving procedure yields mainly identical component spectra. It is suggested that the polarization (B_3u) predominating in the 245–275 nm region isdue to a B_1g vibronic perturbation of the ¹B_2u state.     

烷基磷(膦)酸萃取剂钠盐及其微乳液的NMR,FTIR光谱研究

制备了五种皂化度大于97%的无水烷基磷(膦)酸钠盐,用NMR 谱测定了其微乳体系的H化学位移,测定了酸性萃取剂原液,其固体钠盐以及微乳液的FTIR光谱,观察到微乳液中钠盐阴.阳离子都有水化效应,讨论了水合配位与阴离子结构的关系.     

Molecular orientation of azobenzene chromophores in ultrathin polymer nanosheets studied by attenuated total reflection spectroscopy

This paper describes characterization of molecular orientation for azobenzene moieties in a polymer nanosheet. Copolymers of N-[4-(phenylazo)phenyl] acrylamide (PAZoA) with tert-pentyl acrylamide (tPA) were synthesized and the monolayers deposited on tapered quartz waveguides by Langmuir–Blodgett (LB) technique. Spectroscopic properties of the copolymer (p(tPA/PAZoA)) monolayers were monitored by integrated optical waveguide technique on the molecular level. Molecular orientation of the azobenzene was precisely determined by polarized absorption spectra. It was found that the azobenzene groups took a horizontal orientation and distributed uniformly in the p(tPA/PAZoA) monolayer without significant PAZoA aggregation. Photoisomerization process from trans to cis form was also investigated. More than half of the trans form (60–70%) was photoisomerized under unpolarized light irradiation, and the photoisomerization rate was independent on the PAZoA contents. This implies that the microenvironment of PAZoA moieties was almost the same in three different p(tPA/PAZoA) monolayers.     

Furanized rubber studied by NMR spectroscopy

The double bonds of natural rubber latex (stabilized by a nonionic surfactant) were reacted with an approximately equimolar amount of performic acid at room temperature with a limited amount of formic acid present. Product analysis by ¹H-NMR during the course of the reaction showed that 69–90% epoxidation occurred before the advent of ring opening and ring expansion to produce furanized rubber; hence the rate of epoxidation was greater than the rate of furanization. Indeed, at lower concentrations of formic acid and rubber latex, epoxidation occurred to 90% and furanization was prevented; it was subsequently brought about by the addition of a catalytic amount of orthophosphoric acid. Increased formic acid concentration caused early coagulation of the modified rubber latex. By ¹H- and ¹³C-NMR, it was found that the furanized rubber probably consisted of tetrahydrofuran rings linked together by C? C bonds at positions adjacent to the hetero atom and contained a terminal hydroxy group. The number average sequence length was 2–9, but only the sample with an average sequence length of 9 was effective as a cation binder.