Recrystallization of freezable bound water in aqueous solutions of medium concentrations

For aqueous solutions with freezable bound water, vitrification and recrystallization are mingled, which brings difficulty to application and misleads the interpretation of relevant experiments. Here, we report a quantification scheme for the freezable bound water based on the water-content dependence of glass transition temperature, by which also the concentration range for the solutions that may undergo recrystallization finds a clear definition. Furthermore, we find that depending on the amount of the freezable bound water, different temperature protocols should be devised to achieve a complete recrystallization. Our results may be helpful for understanding the dynamics of supercooled aqueous solutions and for improving their manipulation in various industries.     

Evidence of glass transition in thin films of maleic anhydride derivatives: Effect of the surfactant coadsorption

The glass transition temperature of poly (maleic anhydride-alt-1-octadecen) and poly (styreneco-maleic anhydride) cumene-terminated thin films has been measured by mechanical relaxation of Langmuir films of these polymers. The dynamical properties show glass-like features (non-Arrhenius relaxation times and non-Debye mechanical response) interpreted by the coupling model. The glass transition temperature values determined by a mechanical relaxation experiment (step-compression) agree very well with those obtained by surface potential measurements. It is found that the glass transition temperature values in thin films decrease by about 100K as compared with those corresponding to the bulk polymers. The coadsorption of the water-insoluble surfactant DODAB decreases the glass transition temperature.     

Small-angle neutron scattering studies of nonionic surfactant: Effect of sugars

Micellar solution of nonionic surfactantn-dodecyloligo ethyleneoxide surfactant, decaoxyethylene monododecyl ether [CH₃(CH₂)₁₁(OCH₂CH₂)₁₀OH], C₁₂E₁₀ in D₂O solution have been analysed by small-angle neutron scattering (SANS) at different temperatures (30, 45 and 60° C) both in the presence and absence of sugars. The structural parameters like micelle shape and size, aggregation number and micellar density have been determined. It is found that the micellar structure significantly depends on the temperature and concentration of sugars. The micelles are found to be prolate ellipsoids at 30° C and the axial ratio of the micelle increases with the increase in temperature. The presence of lower concentration of sugar reduces the size of micelles and it grows at higher concentration of sugar. The structure of micelles is almost independent of the different types of sugars used.     

Molecular dynamics simulation studies of the miscibility and thermal properties of PMMA/PS polymer blend

This investigation is an attempt to improve our understanding of the thermal properties of PMMA (Polymethyl methacrylate) by using PS(Polystyrene); the miscibility of PMMA/PS polymer blend is studied. Our work aims to study the impact of the percentage of PMMA/PS polymer blend on the simulated values of the glass transition temperature (Tg) using the dilatometric method. Compass was chosen as the force field (second category force field). The results reveal a single value of the glass transition temperature Tg that is found for all the curves of the PMMA/PS blend system (molar ratio: (50:50, 60:40, 54:46 and 80:20)); this could be a good criterion for predicting the miscibility. Additionally, the solubility parameters of PMMA and PS are calculated and used to obtain the Flory–Huggins parameter, and the morphology of our polymer blend is simulated using the dissipative particle dynamics method (DPD). Our results exhibit an increase in the Tg of PMMA whenever PS is added; hence, we can confirm the miscibility of the PMMA/PS polymer system.     

Diffuse ferroelectric phase transitions in cubically sabilized perovskites

Typical examples of ferroelectrics with diffuse phase transitions (relaxor ferroelectrics), like Pb(Mg_1/3Nb_2/3)O₃ are actually non transforming. The paraelectric phase is fully stablized against a ferroelectric phase transition in this case. A phase transition can be induced, however, by an electric field with appropriate orientation below the temperature of the dielectric constant maximum. The analogy with stress-induced martensitic phase transitions in metallic alloys is pointed out. Pecularities of the properties and of the polarization reversal of such systems are demonstrated. Actual diffuse ferroelectric phase transitions in disordered solid solutions and mixed compounds with a partially stabilized parent phase are compared with athermal martensitic transformations. With particular regard to technical ceramics based on PZT, the influence of interfaces between transformed regions and remnants of the parent phase which have to distinguished from domain walls, and of the reduced stability of the ferroelectric phase on the properties of these systems is discussed. Some effects usually explained solely by domain processes may be understood also from this point of view.

Stabilization of a parent phase against an order-disorder-type phase transition is supposed to be caused by glass-like freezing caused by inelastic cooperative interactions between disordered molecular groups.     

Effect of sugars on liquid-vapour partition of volatile compounds in ready-to-drink coffee beverages

The effect of sugars (sucrose, lactose, glucose, fructose, 10%w/v) on the liquid-vapour partition of selected volatile compounds of coffee beverages has been investigated in espresso coffee and ready-to-drink (RTD) canned coffee prepared and obtained by using the same Arabica roasted coffee beans blend. Aroma composition of coffee beverages has been preliminary investigated by headspace-gas chromatography (HS-GC) and solid phase microextraction-HS-GC-mass spectrometry to characterize the volatile pattern of the systems and to evaluate the effects of sugars on the aroma release/retention. Then, the liquid-vapour partition coefficient (k) of 4 selected key aroma compounds (diacetyl, 2,3-pentanedione, ethylpyrazine, hexanal) was determined in water, sugars solutions as well as RTD coffee brews added with the same sugars (10%w/v). Sugars added in coffee beverages affected the release of the volatiles and thus its aroma profile with differences due to the type of added sugar and coffee brew type. The k values of the selected volatile compounds resulted different depending on the model system composition (water, coffee brew) and sugar type added. In particular, melanoidins as well as other non-volatile components (lipids, acids, carbohydrates) in the RTD coffee brews could be implied in the change of k of the volatile compounds in respect to that observed in water. The effects of the sugar type on the release/retention of the four key coffee aroma compounds were partly explained in terms of 'salting out' especially for the more polar volatile compounds and in the sucrose-added model systems. The change of chemical and physico-chemical properties of the water and brews induced by the sugars as well as the occurrence of interactions between volatile compounds and non-volatile components may be implied in the reduction of the vapour partition of the aroma compounds. Copyright ? 2012 John Wiley & Sons, Ltd.     

Thermo-sensitive N-n-propylacrylamide gels

Thermo-sensitive gels were prepared by irradiating aqueous solutions of poly(N-n-propylacrylamide) (NNPA) and its copolymers with acrylic acid (AA) with γ-rays from a ⁶⁰Co source. The equilibrium swelling volume of the gel in water was determined as a function of temperature. NNPA gel showed a discontinuous and reversible volume phase transition. The transition temperature and the volume change at the transition decreased with irradiation time. The transition temperature was approximately 12°C lower than that of poly(N-isopropylacrylamide) gel. A discontinuous volume transition was also observed in the copolymer gels of NNPA and AA. The dependence of the transition temperature on the concentration of carboxyl groups revealed a marked difference depending on whether they were protonated or dissociated. For gels having side groups of COONa, the transition temperature rose and the volume change at the transition was elevated as the COONa concentration increased. In contrast, an increase in the COOH concentration resulted in a decrease in the transition temperature. These results are discussed in terms of an equation of state constructed based on scaling theory.     

Geometrically-frustrated magnetism on triangular and tetrahedral lattices

The combination of simple, nearest neighbor antiferromagnetic interactions and certain lattice symmetries leads to phenomena known broadly as frustration. In such systems, the formation of a collinear magnetic structure cannot occur at low temperature. The material may undergo a phase transition to an unusual magneticallyordered state, or it may not undergo a conventional transition at all-entering a glass-like state as the temperature is lowered.This paper will review recent work, mostly from neutron scattering studies, on three such magnetic materials. CsMnBr₃ and CsCoBr₃ are XY-like and Ising-like stacked-triangular lattice antiferromagnets, respectively. Both undergo magnetic phase transitions with interesting properties due to the presence of geometricalfrustration within the triangular layers. TD₂Mo₂O₇ is a pyrochlore antiferromagnet, in which the magnetic moments reside on a network of corner-sharing tetrahedra. This material enters a magnetic glass-like state at low temperature.This paper reports on work done in collaboration with D.P. Belanger, A.E. Bunker, M.F. Collins, A. Farkas, J.E. Greedan, C. Kallin, J.Z. Larese, T.E. Mason, R.M. Nicklow, J.N. Reimers, R.B. Rogge, Z. Tun, J. Wang, and Y.S. Yang.     

Investigation of the molecular mobility of peptin macromolecules using photon-correlation spectroscopy

The pH dependence of the intermolecular interaction coefficient of pepsin in an aqueous solution is obtained by using photon-correlation spectroscopy. The dependence shows a minimum near the isoelectric point (pH 1.6). The dynamic parameters of pepsin macromolecules in solutions containing various metal ions, including potassium, cobalt, lead, cesium, and rubidium are studied. It is shown that the addition of these ions causes a decrease of the translational diffusion coefficients. It is found that an increase in temperature leads to the structural transition of a pure solution of pepsin in water. The activation energy of this transition is calculated using the Arrhenius law.     

氘代聚合物膜靶制备技术与性能研究

 氘代聚合物膜是快点火基础物理实验的一种重要靶型。通过氘代苯乙烯单体的本体自由基聚合反应制备氘代聚苯乙烯，并利用流延法和浇铸法制备出厚度从几十nm到数百μm的膜靶。溶剂挥发过程中的随机扰动对膜厚均匀性造成影响，采用清洁的基片和在涂沫基片或模具外加防护罩可以降低这种影响。采用PVA作脱膜剂有利于获得较薄的聚合物薄膜。DSC分析表明薄膜的玻璃化转变温度与热处理过程有关，缓慢退火有利于提高Ｔ-g和储能模量。     

Use of a modified Drude's equation to investigate the optical rotation property of sugars

Sugar compounds (glucose, xylose, arabinose, and galactose) and their mixed solutions were examined using the optical rotatory dispersion (ORD) measurement technique with a modified Drude's equation. Commonly, spectroscopic methods utilize the observation of absorption bands which are, in the case of sugars, located in the UV-spectral range. However, the polarization method used in this study allows us to investigate sugar samples in a convenient visible spectral range where sugar solutions are relatively transparent. The ORD set-up can be simple and robust as we will demonstrate: the self-constructed apparatus consists of only two linear polarizers, placed one after the other, with the angle between their transmission axes adjusted to 45°. The sugar solution sample in a cuvette was put between the polarizers. The set-up was connected to a sample compartment of a commercial UV–vis spectrophotometer. The method provided us the specific optical rotation and concentration of sugar solutions with a reasonable accuracy. In addition, the optical rotation value for mixed sugars has been found to be the average optical rotation value of individual sugar content. Beside use in the laboratory environment, the method could also have industrial on-site monitoring applications, for example in bio fuel production.     

Thermodynamic analysis and design data for a double-effect absorption heat pump system using four working pairs

Performance analysis of a double-effect absorption heat pump system has been done for water-four working pairs (or mixture) by computer simulation. The coefficient of performance and mass flow ratio are investigated to compare these aqueous solutions [waterLiCl, waterLiBrLiBr waterLiClCaCl₂Zn(NO₃)₂] which was developed for only cooling, with conventional waterLiBr solution, based on mass, material and heat balance equations for each part.From this analysis, it is found that the performances of the new aqueous solutions are better than that of LiBrwater solution not only in cooling systems, but also in heating systems, although the operating temperature ranges of these new aqueous solutions are very narrow in heating. Theoretical thermodynamic performance data can be used and are given here by design data.     

Microstructure of fragile metallic glasses inferred from ultrasound-accelerated crystallization in Pd-based metallic glasses

By utilizing ultrasonic annealing at a temperature below (or near) the glass transition temperature Tg, we revealed a microstructural pattern of a partially crystallized Pd-based metallic glass with a high-resolution electron microscopy. On the basis of the observed microstructure, we inferred a plausible microstructural model of fragile metallic glasses composed of strongly bonded regions surrounded by weakly bonded regions (WBRs). The crystallization in WBRs at such a low temperature under the ultrasonic vibrations is caused by accumulation of atomic jumps associated with the beta relaxation being resonant with the ultrasonic strains. This microstructural model successfully illustrates a marked increase of elasticity after crystallization with a small density change and a correlation between the fragility of the liquid and the Poisson ratio of the solid.     

The changes of holographic characteristics of photopolymer induced by temperature

The changes of holographic characteristics of photopolymer induced by temperature are studied experi-mentally. The results show that the exposure sensitivity increases with the increase of temperature. Themaximum diffraction efficiency and the final maximum diffraction efficiency increase with the increaseof temperature when the temperature is lower than Tg (glass transition temperature), while they decreasewith the increase of temperature when the temperature is higher than Tg. The effect of the change oftemperature on the saturation refractive index modulation is very weak.     

Sonochemistry of volatile and non-volatile solutes in aqueous solutions: e.p.r. and spin trapping studies

Recent spin trapping studies of the free radical intermediates generated by the sonolysis of aqueous solutions are reviewed. Studies of rare gas saturated solutions of volatile solutes (e.g., methanol and ethanol) and of non-volatile solutes (acetate, amino acids, sugars, pyrimidines, nucleotides and surfactants) are consistent with the theory of three reaction zones in aqueous sonochemistry. The very high temperatures and pressures induced by acoustic cavitation in collapsing gas bubbles in aqueous solutions lead to the thermal dissociation of water vapour into hydrogen atoms and hydroxyl radicals. Reactions take place in the gas phase (pyrolysis reactions), in the region of the gas-liquid interface, and in the bulk of the solution at ambient temperature (similar to radiation chemistry reactions). By use of the rare gases with different thermal conductivities, the contributions of individual reaction steps with widely different energies of activation can be evaluated.     

Viscometric Study of the Gelatin Solutions Ranging from Dilute to Extremely Dilute Concentrations

The viscosity of gelatin solutions with concentrations between 10^?4 and 10^?5 g/cm³, covering the extremely dilute zones, was studied via a photoelectric viscometer, and the effects of the electrolyte, pH, surfactant, urea, and temperature were discussed. The results showed that the reduced viscosity (η_sp/C) of gelatin exhibited a drastic increase with dilution in the extremely dilute aqueous solutions, this being a typical polyelectrolyte effect. The reduced viscosity of gelatin underwent several oscillations with varying pH; the minimum value of the viscosity was at pH = 5.0, corresponding to its isoelectric point, where gelatin exhibited antipolyelectrolyte behavior. The reduced viscosity of gelatin decreased with increasing temperature, which was due to the helix–coil transition in the gelatin solution. The temperature of the helix–coil transition was 30.0°C in gelatin aqueous solution; however the temperature of helix–coil transition decreased to 20.0°C in urea. Upon cooling, the gelatin molecules in aqueous solution underwent a coil–helix transition. Hydrophobic interactions caused chain folding in the presence of the surfactant sodium dodecylsulphate.     

Temperature dependence of the slip length in polymer melts at attractive surfaces

Using Couette and Poiseuille flows, we extract the temperature dependence of the slip length, delta, from molecular dynamics simulations of a coarse-grained polymer model in contact with an attractive surface. delta is dictated by the ratio of bulk viscosity and surface mobility. At weakly attractive surfaces, lubrication layers form; delta is large and increases upon cooling. Close to the glass transition temperature Tg, very large slip lengths are observed. At a more attractive surface, a sticky surface layer is built up, giving rise to small slip lengths. Upon cooling, delta decreases at high temperatures, passes through a minimum, and grows for T-->Tg. At strongly attractive surfaces, the Navier-slip condition fails to describe Couette and Poiseuille flows simultaneously. The simulations are corroborated by a schematic, two-layer model suggesting that the observations do not depend on details of the computational model.     

Temperature and concentration dependence of SANS spectra of aqueous solutions of short-chain amphiphiles

The small-angle neutron scattering (SANS) of some aqueous solutions of short-chain amphiphiles (glycols, diglycols, diols) has been measured as a function of concentration and temperature. The analysis of the spectra in terms of the Teubner-Strey phenomelogical formula indicates that, on increasing the concentration of the amphiphile, the structure of all these systems evolves in a similar way, i.e. a transition from disordered structures toward correlated aggregates (microstructures). The transition is depressed by increasing the temperature.     

Experimental evidence for a new parameter to control the glass transition of confined polymers

Polymer nanocomposites can be used to study confinement effects on the polymer glass transition temperature (Tg) in a controlled manner by varying interparticle spacing. Using gold nanoparticles in polymethylmethacrylate, we show how the polymer Tg can be tuned by variation of the nanoparticle-polymer interface width (sigma), keeping interparticle spacing fixed. We report the first experimental observation of a crossover in the sign of Tg deviation for confined polymers by variation of sigma and propose a model to explain the dependence of crossover width on the spatial extent of cooperatively rearranging regions.