Formation of ordered phases of (hydroxypropyl)cellulose in miscible and immiscible isobutyric acid-water mixtures

(Hydroxypropyl)cellulose (HPC) is known to form birefringent liquid-crystalline phases at elevated polymer concentrations in either water or isobutyric acid (IBA). The HPC concentration at which the polymeric phase exhibits birefringence decreases as the IBA content in mixed H₂O/IBA solvents decreases, even though the concentration ?ⁱ_c for the formation of an ordered phase of HPC in water is greater than that in IBA. Water is a spectator component and apparently does not participate in the formation of a birefringent phase when IBA is present. A birefringent phase forms once the concentration of HPC in the solution omitting the H₂O equals the ?ⁱ_c of binary HPC/IBA solutions for temperatures from 23 to 95°C. The strong preferential affinity of HPC for IBA is visually evident as an HPC coagulate separates from dilute solution when the solvent mixture contains as little as 5% IBA. The coagulate dissolves to give a monophasic isotropic solution as the IBA content in the solvent is increased. A heterogeneous system in which a clear supernatant fluid covers a pearly white polymeric phase forms when the solvent mixture is immiscible and the HPC content is less than 50%. At high HPC content, the classical appearance associated with concentrated HPC solutions is seen. The optical and rheological properties of the heterogeneous systems are compared with those of homogeneous solutions at several HPC concentrations.     

Nanofiber formation of hydroxylpropylcellulose (HPC)

The aggregative behaviors of hydroxypropylcellulose (HPC) molecules in aqueous solution and on substrates have been observed by employing laser light scattering (LLS) and, after deposition on a mica surface, atomic force microscopy (AFM). LLS studies showed that the HPC molecules formed large aggregates through self-association when the concentration of the solution was above the critical concentration c(t). AFM measurements revealed that when a dilute aqueous solution of HPC molecules was deposited onto a mica substrate at a temperature below its lower critical solution temperature (LCST) thin nanofibers were formed with a height of 0.9 nm, whereas thick nanofibers were formed when an aqueous solution of HPC molecules was deposited onto a substrate above its LCST. Furthermore, the growth of nanofibers led to the formation of fan structures.     

Phenomenological analysis of elongational flow birefringence in semidilute solutions of hydroxypropylcellulose

The relaxation time of a polymer chain in an elongational flow field was investigated for hydroxypropylcellulose (HPC) semidilute solution systems by two methods: phenomenological analysis of elongational flow-induced birefringence, and dynamic light scattering (DLS) and rheological measurements. To understand the relaxation time of an entangled semiflexible polymer solution in an elongational flow field, scaling analysis of the elongational flow-induced birefringence curve was performed. The results of both temperature and concentration scaling analyses showed that birefringence curves at different temperatures and at several HPC concentrations were described well by a universal birefringence–strain rate curve. This scaling behavior was compared with the "fuzzy cylinder" model. The critical strain rate corresponded to the correlation time of the slow relaxation mode determined by DLS measurement and the relaxation spectrum obtained by dynamic viscoelasticity measurement. The elongational flow-induced birefringence observed in an HPC semidilute solution was concluded to be attributed to the orientation of the HPC segment in the entangled molecular system, because the dominant relaxation mode is found to be the concentration fluctuation of an entangled molecular cluster in a quiescent state.     

Dynamic light scattering in turbid colloidal dispersions: a comparison between the modified flat-cell light-scattering instrument and 3D dynamic light-scattering instrument

It remains a challenge to measure dynamics in dense colloidal systems. Multiple scattering and low light-transmission rates often hinder measurements in such systems. One of the well-established techniques for overcoming the problem of multiple scattering is cross-correlation techniques such as 3D dynamic light scattering (3D-DLS). However, a high degree of multiple scattering, i.e., vanishing single-scattering contribution in the signal, limits the use of the 3D-DLS technique. We present another approach to measure turbid media by way of upgrading our flat-cell light-scattering instrument (FCLSI). This instrument was originally designed for static light-scattering (SLS) experiments and is similar to a Fraunhofer setup, which features a flat sample cell. The thickness of the flat sample cell can be varied from 13 mum to 5 mm. The small thickness increases the transmission, reduces multiple scattering to a negligible amount, and therefore enables the investigation of dense colloidal systems. We upgraded this instrument for DLS measurements by the installation of an optical single-mode fiber detector in the forward scattering regime. We present our instrumentation and subsequently test its limits using a concentration series of a turbid colloidal suspension. We compare the performances of our modified flat-cell light-scattering instrument with that of standard DLS and with that of 3D-DLS. We show that 3D-DLS and FCLSI only have a comparable performance if the length of the light path in the sample using the 3D-DLS is reduced to a minimum. Otherwise, the FCLSI has some advantage.     

Structural investigations of polymer liquid-crystalline solutions: Aromatic polyamides,hydroxy propyl cellulose,and poly(γ-benzyl-L-glutamate)

A comparative structural investigation of the characteristics of polymer liquid-crystalline solutions including Kevlar® (PPD-T)/sulfuric acid, poly(Cl-p-phenylene terephthalamide) (Cl-PPD-T)/sulfuric acid, poly(γ-benzyl-L-glutamate) (PγBLG)/dioxane, and hydroxypropyl cellulose (HPC)/water was undertaken. Experimental procedures included polarized light microscopy, light scattering, absorption spectra, and x-ray diffraction on solutions at various concentrations and temperatures. Both the two-phase region at the onset of liquid-crystal formation and the wholly anisotropic phase were investigated. Each solution exhibited distinctive characteristics. The PPD-T and Cl-PPD-T solutions were nematic, and the PγBLG and HPC solutions were cholesteric. In the two-phase region the PPD-T, Cl-PPD-T, and PγBLG (but apparently not the HPC) exhibited negatively birefringent spherulites and aggregates of spherulites. The HPC solutions only exhibited spherulitic structures in the single-phase anisotropic system. The structures and orientations in the anisotropic phase for the various polymer solutions is considered. The helicoidal structural characteristics of the PγBLG and HPC solutions are contrasted.     

The Christiansen effect of brightly colored colloidal dispersion with an amphiphilic polymer

A novel coloration phenomenon in a colloidal dispersion with an amphiphilic polymer was found. The dispersion consists of tetrahydrofuran (THF), an aqueous solution of sodium thiosulfate (Na(2)S(2)O(3).5H(2)O), and hydroxypropylcellulose (HPC). The dispersion was emulsified by HPC as an amphiphilic polymer, so that the aqueous phase was confined in droplets in the THF matrix. It typically appeared bluish violet at room temperature and turned into blue with increasing temperature. In this system, the refractive indices of the inside and outside of the droplet coincided at a certain wavelength at which the light passes through without scattering, which is called the Christiansen effect. The color observed was successfully simulated by Mie's scattering theory in combination with the Christiansen effect.     

Kinetics of phase separation by spinodal decomposition in a liquid-crystalline polymer solution

Time-resolved light scattering studies have been undertaken for elucidating the dynamics of phase separation in aqueous HPC (hydroxypropyl cellulose) liquid-crystalline solutions. The HPC/water system phase separates during heating and returns to a single phase upon cooling. The phase diagram of thermally induced phase separation was subsequently established on the basis of cloud point measurements. For kinetic studies, T (temperature) jump experiments of 10 per cent aqueous HPC solutions were undertaken. Phase separation occurs in accordance with the spinodal decomposition mechanism. At low T jumps or in reverse quenched experiments, the scattering maximum remains invariant as predicted by the linearized Cahn-Hilliard theory. However, at large T jumps, the SD is dominated by non-linear behaviour in which scattering peaks move to low scattering angles. The latter process has been identified to be a coarsening mechanism associated with the coalescence of phase separated domains driven by a surface tension. A reduced plot has been established with dimensionless variables Q and t. It was found that the scaling law is not valid over the entire spinodal process. The time evolution of the scattering profiles of 10 per cent HPC solutions, following a Tjump to 49°C, is tested with the scaling law of Furukawa. It seems that the kinetics of phase separation at 10 per cent solution resemble the behaviour of off-critical mixture.     

Thermal inverse phase transition of azobenzene hydroxypropylcellulose in aqueous solutions

Water soluble 2-azobenzenoxy-ethoxy-hydroxpropylcelluloses (azo-EHPC) were synthesized by etherification reaction of bromoethoxy-azobenzene (BEA) with hydroxypropylcellulose (HPC) to study their phase transition behavior in aq. solution. The degree of substitution (DS) of the water soluble azo-EHPCs was less than 0.066. Their chemical structure and thermal property were characterized by proton nuclear magnetic resonance (¹H-NMR), fourier transform infrared spectroscopy (FT-IR), and differential scanning calorimetry. The azo-EHPC showed a reversible sol–gel transition behavior in its aq. solution, i.e. a clear azo-EHPC aq. solution became turbid when the solution temperature surpassed a lower critical solution temperature (LCST). The sol–gel transition phenomenon was investigated by optical microscopy and turbidimetric measurement. It was found that the LCST was related to the cis-/trans- conformation of the azobenzene side group, the type of cyclodextrin (CD), concentration of azo-EHPC, and NaCl concentration. The LCST of azo-EHPC was lower than that of HPC (36.6 °C) by at most 13.6 °C, and the LCST of trans-azo-EHPC was less than that of cis-azo-EHPC by ca. 3 °C. Additionally, the presence of CD in solutions displayed a positive effect on the LCST, i.e. increasing the LCST by 3–5 °C. And this impact was more profound on the azo-EHPC with higher DS values. The thermoreversible phase transition mechanism was discussed. We proposed that the effect of DS, conformation of azobenzene group, azo-EHPC concentration, salt concentration, and CD on the LCST of azo-EHPCs was a rearrangement of the hydrophilic/hydrophobic interaction between side azobenzene groups and water molecules.     

Interactions between sodium dodecyl sulphate and non-ionic cellulose derivatives studied by size exclusion chromatography with online multi-angle light scattering and refractometric detection

The novel approach described allows to characterise the surfactant-polymer interaction under several sodium dodecyl sulphate (SDS) concentrations (0-20 mM) using size exclusion chromatography (SEC) with online multi-angle light scattering (MALS) and refractometric (RI) detection. Three different cellulose derivatives, hydroxypropyl cellulose (HPC), hydroxypropyl methyl cellulose (HPMC) and hydroxyethyl cellulose (HEC), have been studied in solution containing 10 mM NaCl and various concentrations of sodium dodecyl sulphate. It is shown that this approach is well suited for successful application of both Hummel-Dreyer and multi-component light scattering principles and yields reliable molecular masses of both the polymer complex and the polymer itself within the complex, the amount of surfactant bound into the complex as well as appropriate values of the refractive index increment (dn/dc)micro, of both the complex and the polymer in question. The more hydrophobic derivatives HPC and HPMC adsorbed significantly more SDS than HEC. The inter-chain interactions close to critical aggregation concentration (cac) were clearly seen for HPC and HPMC as an almost two-fold average increase in polymer molecular mass contained in the complex.     

新型卟啉-酞菁二元分子内光物理过程的研究

合成了以哌嗪连接的含卟啉－酞菁的双发色团分子，测定了它的吸收光谱，荧光光谱和荧光寿命。并计算了在不同溶剂中两发色团之间的能量传递效率ΦＥｎＴ和电子转移效率ΦＥＴ。结果表明：在非极性溶剂苯中，两发色团之间的光物理过程以激发态单线态能量传递为主（ΦＥｎＴ８０％）。而在极性溶剂ＤＭＦ中，则以电子转移为主（ΦＥＴ６９．８％）。该二元化合物在ＤＭＦ中，哌嗪以船式构象存在，我们以前合成的以氧或柔性链连接的二元     

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.     

Cholesteric hydroxypropylcellulose solutions: Microscopy and small-angle light scattering

Polarized optical microscopy and small-angle light scattering (SALS) are used to investigate the cholesteric phase of aqueous hydroxypropylcellulose (HPC) solutions. The results suggest a polygonal focal conic rather than the recently proposed parabolic focal conic morphology. Measurements of the polygonal domain size show it to decrease with increasing HPC concentration. Depolarized SALS gives clover-leaf patterns, whose maximum of intensity at 45° is related to the domain size.     

S-shaped deformation profiles in sheared liquid-crystalline polymers

A tracer particle technique has been used to investigate the deformation profiles of a liquid-crystalline polymer under shear between parallel plates. The system was an aqueous solution of hydroxypropylcellulose (HPC), the good transparency of which allows for optical observations over thicknesses of the order of millimetres, as used here. The results indicate that the deformation profile deviated considerably from linearity, whereas a linear profile was confirmed for isotropic liquids, including polymeric ones. For the HPC liquid-crystalline solution most of the deformation was concentrated close to the walls.     

Kinetics of phase separation by spinodal decomposition in a liquid-crystalline polymer solution

Abstract

Time-resolved light scattering studies have been undertaken for elucidating the dynamics of phase separation in aqueous HPC (hydroxypropyl cellulose) liquid-crystalline solutions. The HPC/water system phase separates during heating and returns to a single phase upon cooling. The phase diagram of thermally induced phase separation was subsequently established on the basis of cloud point measurements. For kinetic studies, T (temperature) jump experiments of 10 per cent aqueous HPC solutions were undertaken. Phase separation occurs in accordance with the spinodal decomposition mechanism. At low T jumps or in reverse quenched experiments, the scattering maximum remains invariant as predicted by the linearized Cahn-Hilliard theory. However, at large T jumps, the SD is dominated by non-linear behaviour in which scattering peaks move to low scattering angles. The latter process has been identified to be a coarsening mechanism associated with the coalescence of phase separated domains driven by a surface tension. A reduced plot has been established with dimensionless variables Q and t. It was found that the scaling law is not valid over the entire spinodal process. The time evolution of the scattering profiles of 10 per cent HPC solutions, following a Tjump to 49°C, is tested with the scaling law of Furukawa. It seems that the kinetics of phase separation at 10 per cent solution resemble the behaviour of off-critical mixture.     

Electron transfer in a radical ion pair: quantum calculations of the solvent reorganization energy

Results are presented for an investigation of intermolecular electron transfer (ET) in solution by means of quantum calculations. The two molecules that are involved in the ET reaction form a solvent-separated radical ion pair. The solvent plays an important role in the ET between the two molecules. In particular, it can give rise to specific solute-solvent interactions with the solutes. An example of specific interactions is the formation of a hydrogen bond between a protic solvent and one of the molecules involved in the ET. We address the study of this system by means of quantum calculations on the solutes immersed in a continuum solvent. However, when the solvent can give rise to hydrogen bond formation with the negatively charged ion after ET, we explicitly consider solvent molecules in the solute cavity, determining the hydrogen bond energetic contribution to the overall interaction energy. Solute-solvent pair distribution functions, showing the different arrangement of solvent molecules before and after ET in the first solvation shell, are reported. We provide results of the solvent reorganization energy from quantum calculations for both the two isolated fragments and the ion pair in solution. Results are in agreement with available experimental data.     

Tunable thermal lens spectrometry utilizing microchannel-assisted thermal lens spectrometry

A tunable thermal lens spectrometry system was developed for microchip analysis. The system utilized a Xe lamp as an excitation source, instead of a laser. The system can measure the absorption spectrum of a turbid solution without disturbance of the light scattering background.     

Suppression of multiple scattering by photon cross-correlation techniques

The effectiveness of cross-correlation schemes for suppressing multiple scattering in light scattering measurements has been demonstrated convincingly. Thus, measurements on turbid samples can be analysed as though the samples were transparent, i.e. exhibiting only single scattering. The methods are now being used for new research, particularly in the study of concentrated colloidal dispersions. This article reviews the current state of the field with emphasis on the two-colour and three-dimensional dynamic light scattering techniques. Although these methods were originally designed to suppress multiple scattering in dynamic light scattering, it has recently been recognised that they are also effective in static light scattering. The cross-correlation schemes are compared briefly with other light-scattering methods for studying turbid and opaque samples such as fibre-optic probes and diffusing wave spectroscopy.     

Solid-state characterization of the structure and deformation behavior of water-soluble hydroxypropylcellulose

A modus operandi is developed for determining the molecular structure of hydroxypropylcellulose (HPC), and characterizing, in quantitative terms, the morphological changes occurring when a water-cast film of the polymer is deformed. This involves the application of the following eleven different physical measurements: wide-angle x-ray diffraction, differential scanning calorimetry, density, melt rheometry, infrared spectroscopy, refractive index, birefringence, sonic modulus, small-angle light scattering, optical and electron microscopy. In addition, a computer was utilized as a mathematical diffractometer. Morphologically, water-cast HPC was observed to have structure at all levels, from the molecular to the supermolecular. The HPC molecule has a backbone of anhydroglucose units twisted into an irregular 3₁ helix. Intramolecular hydrogen bonding of the poly(propylene oxide) side chains leads to a stiff, rodlike molecule. The molecules are packed into microfibrillar crystallites 470 Å long and 34 Å in diameter. The microfibrils in turn, associate into supermolecular rodlike structures. The structural rearrangements that occur at each morphological level during deformation of HPC film are quantitatively examined and described.     

Oriented and low‐density tin dioxide film by sol–gel mineralizing tin‐contained hydroxypropyl cellulose lyotropic liquid crystal for laser‐induced extreme ultraviolet emission

A series of tin‐doped hydroxypropyl cellulose (HPC) lyotropic liquid crystal (LC) was synthesized using a simple process and their properties were characterized using selective reflection, wide‐angle X‐ray diffraction (WAXD), and the band texture observed under polarized optical microscope. The present preparation is applicable for mass production using large substrate with low cost HPC. A cholesteric lyotropic LC phase was observed for the hybrid solution with higher than 40 wt % HPC. After sol–gel condensation, the HPC‐Sn hybrid LC films were calcined at 400 °C and the as‐prepared product was determined to obtain tin dioxide (SnO₂) which was characterized using WAXD. The iridescent color and ～2 nm structure seen after the condensation disappeared in the as‐prepared SnO₂. Scanning electronic microscope images of the SnO₂ showed that the HPC content in the HPC‐Sn hybrid played an important role in controlling the SnO₂ morphology. A spectrum of relatively monochromatic extreme ultraviolet (13.5 nm) emission was measured in the as‐prepared SnO₂ in comparison with bulk tin and inverse opal SnO₂. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4566–4576, 2009     

Microfluidic light scattering as a tool to study the structure of aqueous polymer solutions

A small-angle light scattering (SALS) apparatus, coupled with a specially designed microfluidic device is shown to monitor the formation and subsequent size distribution of giant multilamellar vesicles of a diblock copolymer in aqueous solution. The closed-face design, fabricated between glass slides using a UV-curable optical adhesive, incorporates multiple inlets, a mixing system, and a viewing window to perform on-line SALS. The mixing of each component is tested using polystyrene latex microspheres. Vesicles of the block copolymer, EO6BO11 in aqueous solution are formed on the SALS chip and the pair distance distribution function determined using an inverse Fourier transformation of the scattered intensity to quantify the population and distribution for a range of vesicle sizes. These experiments provide demonstrations of how SALS on a microfluidic device can be used as a rapid screening tool to optimize processing conditions for a range of polymer solutions.