Band texture formation of sheared polymeric liquid crystalline state

The phenomenon of band texture formation of sheared main chain liquid crystalline polymers is reviewed. The bands seen in a polarizing microscope are optical effects. The macromolecular chains are aggregated into zig-zag bent fibrils perpendicular to the bands. The band texture is formed during shear relaxation. The induction period depends on the shear rate applied, the shearing time, solution concentration (lyotropic), solution layer thickness, temperature and the nature of the polymer. There exists a critical shear deformation to bring a multi-domain nematic or cholesteric phase into a monodomain continuous phase, from which the band texture is formed. These two phases show quite different rheological behavior. In certain cases randomly oriented regions of bands can also be formed during quenching of a thermotropic nematic polymer melt or during standing of a lyotropic nematic polymer solution, where the nematic domains in the melt or in the solution have grown to a sufficient size.     

BANDED TEXTURE FORMATION IN NEMATIC SOLUTION OF POLY (1,4-BENZAMIDE) IN SULFURIC ACID

The banded texture in films prepared from nematic poly (1,4-benzamide) (PBA)/H_2SO_4 solution by shearing and without shearing has been studied by using microscopy techniques. The kinetic parameters of banded texture formation γ_c and τ_b were measured for nematic solution of PBA by using parallel-plate shearing apparatus. The banded texture was also observed in randomly packed domains for nematic solution of PBA on standing without shearing. The properties of banded texture show no difference between the two samples with or without shearing.     

MORPHOLOGICAL STUDY ON THE ORIENTED CHITOSAN FILM OBTAINED FROM PRE-SHEARED LIQUID CRYSTALLINE SOLUTION IN DICHLOROACETIC ACID

The oriented chitosan films obtained from pre-sheared liquid crystalline chitosan/dichloroacetic acid (DCA)solutions were studied by means of polarized optical microscopy (POM), scanning electron microscopy (SEM), infra-reddichroism technique and wide angle X-ray diffraction (WAXD). The shear induced band texture in the film was found tocorrespond to the sinusoidal fibrillar microstructure along the shearing direction on the basis of POM and SEM observations.The sinusoidal fibril was found to be lying within the film plane. The model of chitosan molecular orientation in the pre-sheared film with band texture can be established assuming that the main chain orients in the shearing direction and the sidegroup is perpendicular to the shearing direction. The WAXD azimuthal scanning at 2θ= 20° indicates that the (002) planeorients perpendicular to the shearing direction.     

Shear-induced band texture of side group liquid crystalline polymers

The shear-induced band texture of conventional end-on fixed side group liquid crystalline polymers (LCPs) has been investigated by using polarizing optical microscopy (POM), small angle light scattering (SALS) and infra-red dichroism techniques. The band spacing is about 1 μm, which increases very slightly on increasing the temperature of shearing and is independent of shearing rate within the range studied. The band texture is not seen to exhibit an interchange of dark and bright bands on rotation of the sample with respect to the polarizer/analyser, but a typical periodical structure is reflected by the SALS patterns of the band texture. The relaxation behaviour of the bands indicates that the band texture formed here is the result of the orderly aligning of domains exhibiting the focal-conic texture, and this is totally different from the case of main chain LCPs where the band texture is substantially an optical effect of the periodic zigzag or sinusoidal structure of parallel aligned microfibrils. Infra-red dichroism and rotating parallel-plate shearing measurements show that the axes of the backbone of the polymer tend to orient in the shearing direction and the end-on fixed mesogenic side groups tend to align perpendicular to the shearing direction.     

Selective synthesis of poly(p‐oxybenzoyl) by fractional polycondensation: Enhancement of selectivity by shearing

The influence of shear flow, especially the timing for the application of shearing, was examined to enhance the selectivity for the preparation of poly(p‐oxybenzoyl) (Pp‐OB) by using hydrodynamically induced phase separation during polymerization of 4‐(4‐acetoxybenzoyloxy)benzoic acid (p‐ABAD) and m‐acetoxybenzoic acid (m‐ABA). The polymers containing few m‐oxybenzoyl (m‐OB) moieties were obtained as precipitates even at high content of m‐OB moiety in feed (χ_f) under shear flow. The content of m‐OB moiety in the precipitates (χ_p) prepared under shearing throughout the polymerization at the shear rate (γ) of 489 s^?1 was 6.3 mol % even at χ_f of 60 mol %. Especially, the Pp‐OB was obtained as the precipitates at χ_f of less than 50 mol %. The timing of the application of the shearing influenced the selectivity significantly, and the shearing just after the precipitation of the oligomers started was quite efficient to enhance the selectivity more. The χ_p of the precipitates prepared with shearing at γ of 489 s^?1 just after the precipitation was only 3.9 mol % even at χ_f of 60 mol %. The shear flow reduced the difference in the reactivity between p‐ABAD and m‐ABA, resulting in the decrease in the selectivity with regard to the formation of p‐oxybenzoyl homo‐oligomer. However, the shear flow enhanced the difference in the miscibility between homo‐oligomers and co‐oligomers. This change in the miscibility by shear flow brought about the more rapid precipitation of homo‐oligomers, leading to the enhancement of the selectivity. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Volumetric rheology of polymers

A novel dilatometer has been used to measure the evolution of specific volume at different cooling rates and at elevated pressures under quiescent conditions and under shear for a series of commercial iPP homopolymers and polypropylene–ethylene random copolymers. Significant influences of cooling rates, pressures, and shear flow on the transition temperature T _tr related to molecular weight and polydispersity and of course the temperature at which shearing was applied could be found for the iPP homopolymers. In the copolymers, the composition defined by the ethylene content determined the position of the transition temperature T _tr.     

Recovery of thick shear bands in atactic polystyrene

The DSC thermograms of the shear band material cut out by a diamond saw to include some undeformed material revealed two T_g's clearly separated by about 10°C. The first T_g was at the same temperature as the T_g of the undeformed material. The second T_g, which was at a higher temperature than the first T_g, appeared shortly after the shear strain recovery during the heating of the shear band material in the DSC. When the shear strain in the shear band was partially reversed by mechanical means before taking the DSC thermogram, the ΔT between the two T_g's decreased and when the shear strain was mechanically reversed to almost zero, the second T_g disappeared. The stored energy of shear band material was found to be similar to that of the bulk compressed material for large strains. Dimensional recovery during heating of specimens with thick and fine bands was similar, both taking place above T_g.     

Raman study of structural defects in SiO2 aerogels

The structure of the silica aerogels was studied by Raman spectroscopy. The spectra of the solid network resembles that of bulk silica with additional bands related to organic groups and a large amount of OH groups.The typical bands due to ring breathing also called defect bands D ₁ and D ₂ located at 490 and 610 cm^–1 are present. However, the evolution of the D ₂ band compared to that of OH band (980 cm^–1) seems apparently, in contradiction with the results previously reported in the literature. During heat treatments between 25 and 300°C the D ₂ and the OH bands increase simultaneously. Generally, in silica glass the defect band D ₂ grows at the expense of the OH groups.This result is explained by the oxidation of the organic compounds which, in this temperature range, leads to the formation of the both species (OH) and those related to siloxane rings. ²⁹Si MAS NMR results are in agreement with the Raman study.     

Asymptotic relations between shear stresses and normal stresses in general incompressible fluids

It is shown that in the general theory of incompressible simple fluids with fading memory there are, for several types of nonsteady shearing motions, simple universal asymptotic relations between the shear stress S₁₂ and the first normal stress difference N₁ = S₂₂ – S₁₁. The kinematical situations considered include initiation of steady shearing, rest after steady shearing, and sinusoidal oscillation. In, for example, relaxation following cessation of a steady shearing flow with rate of shear κ, there holds, to within an error O(κ⁴): This and the other derived universal relations between N₁ and S₁₂ are either consequences of, or are closely related to a general asymptotic formula [B. D. Coleman and W. Noll, Revs. Mod. Phys., 33 , 239 (1961), eq. (6.15)] expressing N₁ as an integral of the product of the shear relaxation modulus and the square of the history of the relative shear strain.     

Near-wall velocities of particles suspended in shear flow and a streamwise electric field

Particles with a diameter of ∼0.5 µm in a dilute (volume fractions φ_∞ < 4 × 10⁻³) suspension assemble into highly elongated structures called “bands” under certain conditions in combined Poiseuille and electroosmotic flows in opposite directions through microchannels at particle-based Reynolds numbers Re_p < < 1. The particles are first concentrated near, then form “bands” within ∼6 µm of, the channel wall. The experiments described here examine the near-wall dynamics of individual “tracer” particles during the initial concentration, or accumulation, of particles, and the steady-state stage when the particles have formed relatively stable bands at different near-wall shear rates and electric field magnitudes. Surprisingly, the near-wall upstream particle velocities are found to be consistently greater in magnitude than the expected values based on the particles being convected by the superposition of both flows and subject to electrophoresis, which is in the same direction as the Poiseuille flow. However, the particle velocities scale linearly with the change in electric field magnitude, suggesting that the particle dynamics are dominated by linear electrokinetic phenomena. If this discrepancy with theory is only due to changes in particle electrophoresis, electrophoresis is significantly reduced to values as small as 20%–50% of the Smoluchowski relation, or well below previous model predictions, even for high particle potentials.     

MULTIPLE CHROMOPHORE SPECIES IN PHYTOCHROME*,†,‡

Abstract— Buffered aqueous solutions of pure phytochrome, when irradiated at 730 nm, had a main absorption band at about 660 nm and a shoulder or secondary band at 580–600 nm. When irradiated at 660 nm, these absorption bands bleached and a pair of bands at 670 and 725–730 nm appeared. When 660 nm irradiated samples were placed in the dark the 730 nm absorption slowly bleached and the 670 nm absorption band shifted to 660 nm. The kinetics of the bleaching indicated that two populations of P_FR existed initially. These two populations decayed by first order kinetics with k's of 4.8 × 10^-4 sec^-1 and 3.1 × 10^--⁵ sec^-1at 25°. While the bleaching of P_FR was occumng, the appearance of the 660 nm and 580–600 nm absorption bands characteristic of P_R took place. The kinetics of the increase in the 580 and 660 nm absorption bands indicated that it was arising from two populations of reactants by two first order reactions with k's of 6.4 × 10^-4 sec^-1 and 3.1 × 10^-5sec^-1 at 25°. When the sodium chloride concentration of the solvent was changed the proportions of the kinetically different populations were altered. In some conditions, especially in the presence of air. reversible but non-reciprocal changes in the four absorption bands were observed. These effects were evident after the lapse of many hours in the dark. When native phytochrome was treated with sodium dodecyl sulfate all absorption bands but the 580–600 nm absorption band were bleached and photoreversibility was lost. When native phytochrome was treated with glutaraldehyde, the 730 nm absorption band was bleached but photoreversibility was retained. It was concluded that at least four species of chromophore exist in phytochrome with absorption maxima at 580, 660 , 670 and 730 nm. Each chromophore is capable of being bleached by appropriate irradiation or in the dark by chemical reactions rather than photochemical reactions. The reactions are probably coupled redox reactions between the 580–660 nm pair and the 670–730 pair of chromophores. Discrepancies observed in the reciprocity of the absorption changes in these paired bands are probably due to various degrees of uncoupling and secondarily to the redox potential of the solvent when such uncoupling occurs.     

Pulse radiolysis study on the initial processes of radiation-induced cationic polymerization of styrene and α-methylstyrene

Initial processes of radiation-induced cationic polymerization of styrene and α-methylstyrene have been studied by means of microsecond pulse radiolysis. For styrene, absorption bands caused by the monomer cation radical St⁺? appear at 630 and 350 nm in a mixture of isopentane and n-butyl chloride at about ?165°C. In parallel with the decay of St⁺?, three absorption bands appear in the near-infrared (IR) region, and at 600 and 450 nm. The IR and 600 nm bands are assigned to the associated dimer cation radical St₂⁺?, and the 450 nm band to the bonded dimer cation radical St-St⁺?. The kinetic behavior of these species shows that reaction of St⁺? with styrene monomer forms both St₂⁺? and St-St⁺?. With the decay of St-St⁺?, another absorption band appears at 340 nm, and the lifetime of this band is relatively long. The 340 nm band may be due to carbonium ions of the growing polystyrene. For α-methylstyrene, the monomer cation radical (at 690 and 350 nm), the associated dimer cation radical (in the near-IR region and at 620 nm) and the bonded dimer cation radical (at 480 nm) behave in a manner similar to that of the corresponding styrene species. The absorption band caused by carbonium ions of growing poly(α-methylstyrene) appears at 340 nm.     

Shear-dependent rheological properties of starch/bentonite composite gels

 Rheological properties of starch/bentonite gels (5.3–8.2% solids, 0–100% starch) were investigated at shear rates 0.0083–0.33 s^-1 (Brookfield viscometer). Prior to these measurements the strain introduced during preparation of the gel was kept as low as possible. Under these conditions six different types of structural units could be identified in the gel: bentonite particles associated in a band-type structure; bands coated with starch polymers; bundles of bands interlaced and enveloped by starch polymers (strands); individual bentonite platelets dispersed in a polymer matrix; starch polymer networks; and swollen granules. A power-law model was fitted to the experimental viscosity data: μ_app= Kγ ^n-1 . In all cases n was found to be less than 0.5. Its value decreased with the ability of the structural components to reorient under applied shear. K was found to be proportional to the compaction and/or entanglement of the structural units. These trends in K and n were further confirmed by the index of thixotropy (IT) and complex modulus of shear elasticity (G ^* ) measurements. Received: 12 August 1996 Accepted: 7 January 1997     

A Raman spectroscopic study of the mono-hydrogen phosphate mineral dorfmanite Na2(PO3OH)·2H2O and in comparison with brushite

Aspects of the molecular structure of the mineral dorfmanite Na₂(PO₃OH)·2H₂O were determined by Raman spectroscopy. The mineral originated from the Kedykverpakhk Mt., Lovozero, Kola Peninsula, Russia. Raman bands are assigned to the hydrogen phosphate units. The intense Raman band at 949 cm⁻¹ and the less intense band at 866 cm⁻¹ are assigned to the PO₃ and POH stretching vibrations. Bands at 991, 1066 and 1141 cm⁻¹ are assigned to the ν₃ antisymmetric stretching modes. Raman bands at 393, 413 and 448 cm⁻¹ and 514, 541 and 570 cm⁻¹ are attributed to the ν₂ and ν₄ bending modes of the HPO₄ units, respectively. Raman bands at 3373, 3443 and 3492 cm⁻¹ are assigned to water stretching vibrations. POH stretching vibrations are identified by bands at 2904, 3080 and 3134 cm⁻¹. Raman spectroscopy has proven very useful for the study of the structure of the mineral dorfmanite.     

乙基醋酸纤维素液晶态条带织构的形成机理

本文应用平行板移动式和转动式二种剪切装置研究了乙基醋酸纤维素的二氯乙酸体系液晶态受剪过程形成条带织构的临界剪切速率,条带织构的形成机理以及所形成的条带织构在升降温过程中的变化。结果表明,高分子液晶态受剪过程条带织构不是在受剪时产生,而是在受剪停止后的弛豫过程中形成的。可以观察到条带织构出现的诱导时间(t_b),其值的大小与溶液的浓度、剪切速率等因素有关。最后提出一模型来解释高分子液晶态受剪切过程条带织构的形成机理。     

Organosilicon Amidophosphates and Their Eu and Er Complexes in Solutions and Films: Spectral and Luminescence Properties

Fluorescence and fluorescence excitation spectra of phosphorus-containing organosilicon ligands O = PX₂NHR (X = NMe₂, OPh; R = CH₂CH₂CH₂Si(Oet)₃ and their Eu(III) complexes in acetonitrile solutions and in films are studied. In UV region (285–420 nm), bis(dimethylamido)triethoxysilylpropylamidophosphate (X = NMe₂) and diphenyltriethoxysilylpropylamidophosphate (X = OPh) exhibit two emission bands, whose position and intensity depend on the nature of substituents at the phosphorus atom. The Eu complexes show the ligand and the cation luminescence. The emission bands of coordinated ligands are shifted to long-wave region. The cation luminescence appears as three or four bands due to f-f transitions from the excited ⁵ D ₀ level to the lower ⁷ F _1–4 levels. The most intense transition is ⁵ D ₀ → ⁷ F ₂. The emission band in a region of 420 nm appears in solutions and films prepared from both pure ligands and their Eu(III) complexes. This band is due to luminescence of spatially crosslinked nanoparticles of sesquioxane structure. The intensity ratio of the Eu³⁺ emission bands changes when going from solutions to films, the emission intensity increases in a range of 420 nm. Films containing incorporated Er complexes with amidophosphates show intense luminescence of a matrix at 430 nm and a series of weak narrow bands due to the Er³⁺ cation at 550–700 nm.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 7, 2005, pp. 550–558.Original Russian Text Copyright © 2005 by Semenov, Cherepennikova, Klapshina, B. Bushuk, S. Bushuk, Douglas.     

Raman spectra in the libration region of concentrated aqueous solutions of lithium-6 and lithium-7 halides. Evidence for tetrahedral Li(OH2) 4 +

The Raman spectra of saturated solutions of⁶LiCl and⁷LiCl have been decomposed into Gaussian components, one of which is a polarized band that occurs at 360 cm^–1 when the ion is⁶Li⁺ and shifts to 335 cm^–1 when the ion is⁷Li⁺. Equivalent bands occur in the spectra of saturated solutions of⁶LiBr and⁷LiBr at 343 and 320 cm^–1, respectively. These bands are assigned to solvent-separated ion aggregates. The Raman spectra of 8.0 and 3.5 m solutions of the isotopic lithium chlorides have been decomposed into five Gaussian components, three of which are assigned to water librations. In addition, there is a polarized band at 440 cm^–1 independent of the lithium isotope used, and a depolarized band which occurs at 385 cm^–1 in the⁶LiCl solutions and 360 cm^–1 in the⁷LiCl solutions. We interpret these two additional bands as theA ₁ andF ₂ stretching modes of Li⁺ tetrahedrally solvated by water molecules.     

Effect of shear history on the steady shear flow behavior of a thermotropic liquid-crystalline polymer

The steady shear stress (σ) and first normal stress difference (N₁) of a thermotropic liquid-crystalline polyester, poly[(phenylsulfonyl)-p-phenylene 1,10-decamethylene-bis(4-oxybenzoate)] (PSHQ10), in both the isotropic and nematic regions were measured as a function of shear rate (γ), using a cone-and-plate rheometer. For the study, PSHQ10 was synthesized via solution polymerization in our laboratory. The PSHQ10 was found to have (a) the weight-average molecular weight of 45,000 relative to polystyrene standards and a polydispersity index of 2, (b) a glass transition temperature of 88°C, (c) a melting point of 115°C, and (d) a nematic-to-isotropic transition temperature of 175°C. For the measurements of σ and N₁ in the nematic region of PSHQ10, its initial conditions for the startup of shear flow was controlled by (a) first heating an as-cast specimen to 190°C, (b) shearing there at γ = 0.085 s^?1 for about 5 min, and then (c) cooling slowly down to a predetermined temperature (130, 140, 150, 160, or 171°C) in the nematic region. For each γ chosen, after start-up of shear flow, we waited for a sufficiently long time until both the shear stress and first normal stress difference leveled off, giving rise to steady-state values of σ and N₁. Emphasis was placed on investigating the effect of shear history on σ and N₁ of PSHQ10 in the nematic region. For this, the following experiments were conducted: (a) a fresh specimen was sheared continuously by increasing the γ stepwise, and (b) a presheared specimen was further sheared continuously by increasing the γ stepwise. We have found that fresh specimens exhibited ‘shear-thinning’ behavior over the entire range of γ (0.008?0.27 s^?1) tested, whereas the presheared specimens exhibited both zero-shear viscosities and shear-thinning behavior. When using fresh specimens, we found that N₁ was positive over the entire range of γ (0.008–0.27 s^?1) tested. However, when using presheared specimens we found that (a) at very low γ, N₁ initially was negative and then became positive as shearing continued, and (b) at higher γ, N₁ was positive over the entire duration of shearing. © 1994 John Wiley & Sons, Inc.     

Solvent effects on the ultraviolet absorption spectrum of mercury atom

Absorption spectrum of mercury dissolved in hexane and heptane in the region 280–180 nm was found to consist of three bands. These bands were assigned to the ¹S₀ → ¹P₁ transition (A band, λ = 254 nm), to the ¹S₀ → ³P₂ transition (B band, λ = 226 nm) and to the ¹S₀ → ¹P₁ transition (C band, λ = 190 nm) of a mercury atom placed into a liquid cell. The B and C absorption bands of mercury in liquid solutions were observed for the first time. It was found that the A band and the C band have, respectively, distinct doublet and triplet structure, while the doublet structure of the B band is only slightly seen. The oscillator strengths of all three bands of mercury in solutions were estimated. The structure of the C, A and B bands of mercury in solutions most probably results from the removal of the degeneracy of the excited states ¹P₁, ³P₁ and ³P₂ of a mercury atom, placed into a cell of low symmetry.     

Vibrational spectroscopic study of the arsenate mineral strashimirite Cu8(AsO4)4(OH)4·5H2O—Relationship to other basic copper arsenates

The basic copper arsenate mineral strashimirite Cu₈(AsO₄)₄(OH)₄·5H₂O from two different localities has been studied by Raman spectroscopy and complemented by infrared spectroscopy. Two strashimirite mineral samples were obtained from the Czech (sample A) and Slovak (sample B) Republics. Two Raman bands for sample A are identified at 839 and 856 cm⁻¹ and for sample B at 843 and 891 cm⁻¹ are assigned to the ν₁ (AsO₄³⁻) symmetric and the ν₃ (AsO₄³⁻) antisymmetric stretching modes, respectively. The broad band for sample A centred upon 500 cm⁻¹, resolved into component bands at 467, 497, 526 and 554 cm⁻¹ and for sample B at 507 and 560 cm⁻¹ include bands which are attributable to the ν₄ (AsO₄³⁻) bending mode. In the Raman spectra, two bands (sample A) at 337 and 393 cm⁻¹ and at 343 and 374 cm⁻¹ for sample B are attributed to the ν₂ (AsO₄³⁻) bending mode. The Raman spectrum of strashimirite sample A shows three resolved bands at 3450, 3488 and 3585 cm⁻¹. The first two bands are attributed to water stretching vibrations whereas the band at 3585 cm⁻¹ to OH stretching vibrations of the hydroxyl units. Two bands (3497 and 3444 cm⁻¹) are observed in the Raman spectrum of B. A comparison is made of the Raman spectrum of strashimirite with the Raman spectra of other selected basic copper arsenates including olivenite, cornwallite, cornubite and clinoclase.