Papers by Keyword: Phase Separation

Abstract: We report formation of complex responsive fibers consisting of a low molecular weight liquid crystal (LC) core surrounded by a polymer sheath using simple airbrush or jet spraying techniques. The fibers are formed using a solution of LC and polymer dissolved in a common solvent. With proper control of the solution composition and formation conditions the fibers self‐assemble. The diameter of the resulting fibers can be adjusted over a range spanning from one to tens of microns. The core of the fiber retains all of the responsive properties associated with low molecular weight LCs. A nematic LC core's director aligns along the long axis of the fiber making them highly birefringent. An electric field applied across the fiber changes both the director alignment and the optical properties of the fiber. Alternatively, thermochromic fibers are formed using a cholesteric LC in the core. Unlike similar electrospun fibers, the airbrushed fibers can be sprayed as continuous mats on virtually any surface or woven into textiles. The resulting fabrics can be made into displays, thermochromic temperature sensors, or for detection of chemical or biological agents. They offer numerous opportunities for wearable textiles that respond optically to a variety of stimuli.

Abstract: A control and utilizability of spatial fluctuations in polymer capacitors using immiscible binary mixtures are described. The spatial fluctuations for the device elements are of particular important for bioinspired multielemental network devices that is composed of elements with distributed electric property. Here we first report that spatial distribution of dielectric properties can be enhanced on the fabrication of SDDE using thermal processing that changes the morphology of immiscible PLLA/PCL binary mixture.

Abstract: Polymer blend consist of epoxy and polymethylmethacrylate (PMMA) was prepared via two different blending methods. Conventional blending method which required solvent to obtain polymer blend of PMMA and epoxy. However, due to the high consumption of solvent and environmental issue, a new approaching method: direct mixing method was used to prepare the polymer blend without the usage of solvent. The PMMA pellets are grinded and sieved into fine powders and incorporated into epoxy. Comparison between the conventional and new method was done through the investigation based on the morphology and mechanical behaviour, with different PMMA content (0, 10, 20, 30, 40 and 50 vol.%) between two blending methods. In overall, the polymer blend system prepared via direct mixing methods exhibited better mechanical properties as compared to conventional solvent dissolution method. Improvement on fracture toughness was observed in direct mixing method.

Abstract: The absorption behavior of water in poly (ethylene terephthalate)-poly (ethylene glycol) (PETG) block copolymers was investigated using the time-resolved FTIR-ATR (Fourier Transform Infrared Attenuated Total Reflection) spectra. The data was analyzed by two-dimensional correlation spectra (2D-COS), which provided relevant and complementary information on the absorption mechanism and the molecular interactions formed (H-bonding). It was found that there were two kinds of water molecules, named bound water and free water in absorption process. The delicate relationship between dynamic water absorption behavior and the morphology resulting from phase separation was also discussed. Furthermore, two-dimensional correlation analyses revealed that in the absorption process, water first diffuses into the continuous soft-rich PEG phase and then into the hard-rich PET domains, forming hydrogen bonds with-O-groups prior to that of free volume.

Abstract: B₂O₃- or P₂O₅-doped Li₂O-MgO-Al₂O₃-SiO₂ (LMAS) glass-ceramics were prepared by solid state method using Li₂CO₃, MgO, Al₂O₃ and SiO₂ as the raw materials, B₂O₃ or P₂O₅ as the additives. The effects of adding B₂O₃ and P₂O₅ on the phase separation, crystallization and thermal expansion coefficient were investigated by means of X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM) and thermal dilatometer, respectively. The results showed that B₂O₃ or P₂O₅ addition could promoted phase separation of glass and increased the size of spherical phase separation droplet. With the addition of B₂O₃ or P₂O₅, the crystallization temperatures (Tc) of LMAS system decreased from 764 ^oC to 726 ^oC and 764 ^oC to 750 ^oC, respectively. However, the crystalline phase compositions did not changed, and β-quartz solid solution (s.s) (Li₂Al₂Si₃O₁₀) was still the main crystalline phase, and lithium silicate (Li₂SiO₃) and forsterite (Mg₂SiO₄) were the minor phases. The thermal expansion coefficient (α) of B₂O₃-doped and P₂O₅-doped LMAS glass-ceramics in the temperature range 20-600 ^oC were 5.215×10^-6/ ^oC and 5.008×10^-6/ ^oC, respectively, which were higher than that of LMAS glass-ceramics (α=3.790×10^-6/ ^oC).

Abstract: TiO₂ photocatalyst plays an important role in the degradation of sewage and cleaning the air. nanoporous TiO₂ fibers have excellent photocatalytic properties due to their high porosity and specific surface area. Based on DMF and alcohol as solvent, nanoporous TiO₂ fibers were produced by electrospinning with phase separation. The spinning dope advance rate, DMF/alcohol ratio and calcination temperature were investigated on the influence of micro-structure, porous structure, phase composition and photocatalytic performance of the nanoporous TiO₂ fibers. It showed that nanoporous anatase TiO₂ fibers had surface pores at 20nm by 550°C calcination. And when the proportion of DMF and alcohol was 1:3, the BET Surface Area of nanoporous TiO₂ fibers was 40.75m²/g. They get photocatalytic degradation rate of 85.2% to 20mg·L^-1 methyl orange solution after 35 min.

Abstract: Glassy solid electrolytes are important integral components for all-solid-state devices for energy storage and conversion. The use of multiple network formers is an important part of their design strategy for specific applications. In many glass systems the interaction between the different network formers results in strongly non-linear variations in physical properties (network former mixing (NFM) effects), requiring a detailed understanding on a structural basis.The issues to be addressed involve both the structural organization and connectivities within the framework, the local environments and spatial distributions of the mobile ions, and the dynamical aspects of ion transport, to be discussed in relation to possible phase separation or nano-segregation effects. Besides Raman and X-ray photoelectron spectroscopies, solid state nuclear magnetic resonance (NMR) methods are particularly useful for providing detailed answers to such issues. The present review introduces the basic principles of modern solid state NMR methods and their applications to glass structure, with a particular focus on the characterization of network-former mixing effects in the most common lithium and sodium conducting oxide and chalcogenide glass systems. Based on the current state of the literature reviewed in the present work, some emerging general principles governing structure/property correlations are identified, to be tested by further experimenteation in the future.

Abstract: This paper describes the use of microcrystalline cellulose (MCC) as hydrophilic filler in two types of natural rubber latexes which are high ammonia natural rubber (HA) and epoxidised natural rubber latex (ENR). Light microscopy (LM), Scanning electron microscopy (SEM) and tensile strength measurements were then conducted on the resulting films. The light microscopy analysis revealed that more MCC particles appeared at the air–facing (AF) surfaces relative to the substrate-facing (SF) surfaces of the HA films with increasing MCC content. In contrary, the ENR25 films showed more or less similar MCC particles appearing at both air-facing surfaces and substrate-facing surfaces. Further SEM cryo-fracture analysis at the cross sections of the MCC filled ENR25 films indicated that the MCC particles were randomly dispersed in the rubber matrix. It can be suggested that the phase separation of MCC particles to the films surfaces occurred due to the incompatibility of MCC with the rubber matrix. Thus, it can be inferred that the occurrence of phase separation is minimised in the MCC filled ENR films in comparison to the MCC filled HA films.

Abstract: In this paper, the kinetics of precipitate growth in metastable binary solid solutions is analyzed considering two mechanisms: (i) diffusion of the one component from the bulk of composition matrix and its incorporation in the precipitate, and (ii) emission and outdiffusion of the second component from the interface of precipitate with surrounding matrix. A kinetic model is proposed that enables a description of these both mechanisms in a unique way. Using this model, the mechanism of oxygen emission and outdiffusion from the interface of Si precipitates with the silicon oxide surrounding is confirmed to determine the phase separation kinetics upon high temperature annealing nonstoichiometric silicon oxide films.

Abstract: Phase Change Material (PCM) is a material that uses the phase transition properties as latent heat storage for certain application. Salt hydrate CaCl₂.6H₂O (melting temperature, T_m = 29°C, and melting entalphy, DH = 190 kJ/kg) is a common inorganic PCM that can be used for regulating the air temperature of the room, in order to reduce the electrical energy consumption for energy conservation. General problems of inorganic PCM, in particular during the crystallization or latent heat release, are the subcooling and phase separation effects. It is worth mentioning that understanding the crystallization of PCM is important to keep its performance for application. In this research we choose two types additive materials as nucleator to CaCl₂.6H₂O to overcome those two negative effects, namely Ba₂CO₃ and K₂CO₃. We also study the amount of additives needed for effective reduction of subcooling and its phase stability by performing the cycling process. The average temperature and maximum temperature of the subcooling will be determined from temperature vs time recording.