Narrow Concentration Region Research Articles

Lignin enhances cellulose dissolution in cold alkali

Aqueous sodium hydroxide solutions are extensively used as solvents for lignin in kraft pulping. These are also appealing systems for cellulose dissolution due to their inexpensiveness, ease to recycle and low toxicity. Cellulose dissolution occurs in a narrow concentration region and at low temperatures. Dissolution is often incomplete but additives, such as zinc oxide or urea, have been found to significantly improve cellulose dissolution. In this work, lignin was explored as a possible beneficial additive for cellulose dissolution. Lignin was found to improve cellulose dissolution in cold alkali, extending the NaOH concentration range to lower values. The regenerated cellulose material from the NaOH-lignin solvents was found to have a lower crystallinity and crystallite size than the samples prepared in the neat NaOH and NaOH-urea solvents. Beneficial lignin-cellulose interactions in solution state appear to be preserved under coagulation and regeneration, reducing the tendency of crystallization of cellulose.

What Are ThresholdLess AntiFerroelectric (TLAF) LCs?–Disordered SmC*-Like Phase with qT = 1/2 in a Wide Temperature Range

In the MC881-MC452 binary mixture system developed by MGC, the near-IR Bragg reflection peak is observed in a wide temperature range from 80°C down to room temperature or lower for a narrow concentration region between 54.99 and 57.50 wt.%; the phase responsible for this near-IR Bragg reflection peak can be identified as disordered SmC*-like phase with qT = 1/2 – hereafter designated as SmC*D(1/2) – which has the TLAF property in the bulk. Four intriguing mechanisms are operative: (1) The critical concentration exists, above which the free energy of SmC*A never becomes lower than that of SmC*; (2) The disclination-assisted thermal linkages assure the thermal equilibrium between ferroelectric and antiferroelectric orderings; (3) The long-range interlayer interactions in the quasi-molecular model stabilize the qT=1/2 state in a wide temperature range; and (4) A ferroelectric hexatic phase exists on the low temperature side of SmC*A and the frustration between them stabilizes another qT=1/2 state which may coalesce into the ordinary one in the intermediate concentration region. In this way coalesced SmC*D(1/2) emerges stably. Because of the disclination-assisted thermal linkages, SmC*D(1/2) must be disordered and soft with respect to the tilting directions and senses of the in-layer directors even in the bulk; electric-field-induced switching is expected to occur layer by layer but not cooperatively and hence shows the TLAF property.

Electromechanical and magnetic properties of BiFeO3-LaFeO3-CaTiO3 ceramics near the rhombohedral-orthorhombic phase boundary

BiFeO3-LaFeO3-CaTiO3 ceramics have been studied by X-ray diffraction, magnetization measurements, and piezoresponse force microscopy (PFM). The compositional ranges of the polar, antipolar, and non-polar phases have been estimated. PFM measurements testify gradual decrease of piezoelectric response in Bi0.85−xLa0.15CaxFe1−xTixO3 system with Ca/Ti content increase, except a narrow concentration region near polar-antipolar phase boundary where piezoelectric signal shows maximum value. It is found that increase of dopant concentration leads to apparent decrease of the off-center Bi-O displacement and, consequently, causes a reduction of piezoelectric response. It is concluded that notable remanent magnetization in polar and non-polar structural phases is a result of the Dzyaloshinsky-Moria interaction.

Thermodynamically Stable Vesicle Formation and Vesicle-to-Micelle Transition of Single-Tailed Anionic Surfactant in Water

The aggregation behavior of sodium 3,6,9,12,15-pentaoxa-heptacosanoate (AEC4-Na) in aqueous solution with increase of the concentration at 25 °C was investigated using differential scanning calorimetry, equilibrium surface tension, solubilization of an oil-soluble dye, steady-state fluorescence, dynamic light scattering, and freeze-fractured transmission electron microscopy. Vesicle formation of AEC4-Na preceded micelle formation below the critical micelle concentration (cmc). The vesicle-to-micelle transition was observed through a narrow concentration region above the cmc. The mean diameters of the vesicles and micelles were not affected by the concentration. All solutions over a wide range of concentrations were homogeneously transparent with a low Krafft point below 0 °C. These results indicate that the AEC4-Na vesicles have a thermodynamically stable structure. Vesicle formation may be caused by a pseudobinary mixed surfactant system composed of monomeric AEC4-Na and an acid soap that consists of a dimer complex formed between AEC4-Na and unneutralized AEC4-Na. The thermodynamic stability would then result from the inhibition of close intermolecular aggregation and flexibility of the molecular shape in the vesicles due to the oxyethylene units in AEC4-Na.

Itinerant-electron metamagnetism in Y(Co 1 −xNi x) 5

The magnetization processes of the Y(Co 1 −x Ni x ) 5 system were measured at 4.2 K in pulsed high magnetic fields up to 40 T. The spontaneous magnetization decreases linearly with increasing Ni concentration up to x=0.4. In the narrow concentration region 0.5⩽ x⩽0.6, the magnetization rapidly decreases, but weak ferromagnetism persists up to x=0.8. On the other hand, the high-field susceptibility exhibits a maximum at x=0.55. These results show that the magnetic state of Y(Co 1− x Ni x ) 5 changes from the high- to the low-moment state at the critical concentration x=0.55. In the vicinity of this concentration, the magnetization was measured at high pressures up to 1 GPa. The compound Y(Co 0 .5 Ni 0 .5 ) 5 shows a very large pressure effect, indicating that it is very close to the critical concentration.

Phase diagram studies in the systems La2O3–SrO–Ga2O3 and La2O3–MgO–Ga2O3 at 1400°C in air

The ternary systems La2O3–SrO–Ga2O3 and La2O3–MgO–Ga2O3 were studied at 1400°C in air with emphasis on LaGaO3. The compound exhibits a small solid solubility of Sr substituting for La, and Mg substituting for Ga, respectively. In the system La2O3–SrO–Ga2O3 the compound is stable within a very narrow concentration region. In the system La2O3–MgO–Ga2O3 it is in equilibrium with most of the phases of the system present at 1400°C.

Phase Diagram Studies in the Systems La2O3–SrO–Ga2O3, La2O3–MgO–Ga2O3, and SrO–MgO–Ga2O3 at 1400°C in Air

The ternary systems La2O3–SrO–Ga2O3, La2O3–MgO–Ga2O3, and SrO–MgO–Ga2O3 were studied at 1400°C in air, with emphasis on LaGaO3. The compound exhibited a small solid solubility of strontium substituting for lanthanum and also of magnesium substituting for gallium. In the system La2O3–SrO–Ga2O3, LaGaO3 existed only within a very narrow concentration region, whereas in the system La2O3–MgO–Ga2O3, LaGaO3 was in equilibrium with most of the phases of the system. The system SrO–MgO–Ga2O3 at 1400°C in air was characterized by an extended liquid phase at ∼1185°C.

Phase equilibria in an athermal solution of platelike particles

A molecular frame lattice theory of athermal solutions of platelike particles is presented. Steric repulsion between the particles is assumed to be the sole interaction present in the system (the athermal limit). The theory is developed for flat rectangular parallelepipeds, and examined in detail for two opposite shape anisotropy limits: rods and square boards. Numerical calculations show that in a pure system of either long rods or square boards, a nematic phase is formed once the shape anisotropy exceeds some critical value: for rods the critical aspect ratio x(crit)(r) is 8. 019, and for boards x(crit)(d) is 3.742. For higher values of the ratio, a narrow concentration region of coexistence for the nematic and isotropic phases, which separates the isotropic (low concentration) from the nematic (high concentration) solution, is found on dilution of each system.

Wetting and Interfacial Transitions in Dilute Solutions of Trisiloxane Surfactants

Wetting behavior on apolar solid and fluid substrates of nonionic trisiloxane surfactants BE-n (B = (Me3SiO)2Si(Me)(CH2)3, hydrophobic moiety, the same for surfactants studied, n = 6, 8, and 12, ethoxy group number) aqueous solutions was studied in a wide surfactant concentration range. BE-6 and BE-8 form vesicles at the critical aggregation concentration (CAC) while BE-12 forms micelles. It was found that three different regions can be observed in wetting behavior dependence on surfactant concentration. Below the CAC, the cosine of the contact angle grows almost linearly with surfactant concentration increase. At a certain surfactant concentration, higher than the CAC, the transition from partial wetting with low but measurable contact angle to complete wetting has been observed. The critical wetting concentration (CWC) was found to be independent of subphase surface energy for the substrates studied. The CWC values increase while ethoxy chain length grows. In the intermediate region, CAC < C < CWC, the surface pressure πsl on |1 − C/CWC|dependence at the subphase−solution interface can be described by a critical scaling equation with critical exponent β = 0.3−0.4. The transition from partial to complete wetting corresponds to stepwise decrease of the equilibrium interfacial tension. At the same narrow concentration region, the equilibrium spreading coefficient for solution/tetradecane becomes positive and a transition from a lens to a rapidly spreading unstable thick film was observed for these solutions on tetradecane. The adsorption of BE-12 on Graphon study has shown that the wetting transition was related to a transition from a plateau region to a significant increase of surfactant adsorption on solid substrate. The mechanism of observed wetting behavior was discussed on the basis of modern conceptions of interfacial transition and surfactant thin-film properties. The applicability of Cahn's concept of critical wetting transition to the observed wetting behavior is also discussed.

Phase structure, morphology and phase boundary diagram in an aromatic polyimide (BPDA–PFMB)/m‐cresol system

AbstractAn organo‐soluble aromatic polyimide has been synthesized from 3,3′, 4,4′‐bis(phenyltetracarboxylic) dianhydride (BPDA) and 2,2′‐bis (trifluoromethyl)‐4,4′‐diaminobiphenyl (PFMB) via a one‐step polymerization in m‐cresol. The phase boundary diagram for this system has been established by differential scanning calorimetry, polarized light microscopy (PLM) and wide angle X‐ray diffraction (WAXD) experiments. A crystallosolvate form I has been found over the entire concentration region at low temperatures. When the temperature is increased, an isotropic phase has been observed below concentrations of about 40%. In the relatively high concentration region between 45 and 95%, a transition from the crystallosolvate from I to a crystallosolvate form II has been observed. Form II exhibits a different WAXD pattern. In a narrow concentration region between the isotropic and the crystallosolvate form II (40–45%), a biphase behavior has been found. The birefringence of this region may be an indication of a liquid crystalline phase. The BPDA–PFMB polymer crystal has been found in the very high concentration region (&gt;95%) for temperatures &gt;250°C. The morphologies of these phases have been investigated via PLM and transmission electron microscopy. Above the gel/sol transition temperature, the form I shows negative birefringent spherulites consisting of thin lamellae. The form II exhibits a tendency of positive birefringent spherulites. Possible mechanisms of the formation of the metastable phase morphology and their associations with the mechanical gel/sol transition are also discussed.

Development of system for measuring bubble coalescence time by using a laser.

A new system to measure very short bubble coalescence time was developed using a laser. The system’s reliability was confirmed by comparing the system output with photographic observation by high-speed video camera. The result for aqueous solutions of n-alcohol was in good agreement with the previous data. The system was applied to various kinds of aqueous solutions more dilute than those in previous work where the value of bubble coalescence time was expected to be less than 2 ms. It was revealed that the bubble coalescence time reported in previous work was composed of two parts. The first part was the time length of the contacting period of two bubbles and the second was the time length of the initial stage of a film rupture between the bubbles. The former decreased considerably, even to an undetectably small value, with decrease in concentration, but the latter was constantly at about 0.3 ms regardless of concentration. Effects of bubble age and bubble approach velocity were examined. It was also found that the bubble coalescence time in surfactant solution was significantly influenced in a narrow concentration region as low as ppb order and that the bubbles did not coalesce in solution of higher concentration.

Transverse Young modulus of a composite with nonregular structure

This paper considers the transverse Young modulus of specially constructed ‘‘plane’’ composites for various volume fractions of filler. It was determined that the sharp increase of composite elastic stiffness in a narrow concentration region relates to the material’s percolation peculiarities.