Role Of Phase Separation Research Articles

The nature of phase separation in binary oxide melts and glasses. II. Selective solution mechanism

A comprehensive review of structural data in binary silicate systems indicates that the tetrahedral critical radius (87.2 pm) of binary silicate melts (or glasses) is associated with the silicon tetrahedral network that defines the structure of the melt. In a binary system, most of the cages present in the melt are made of six and five-membered rings of silicon tetrahedra. Cages bounded by six or more-membered rings can host cations of all sizes. However, cations that enter in cages made of five-membered rings are discriminated by their ionic radius. Cations with ionic radii larger than about 87.2 pm (network modifiers) cannot enter in pentagonal apertures; cations with radii smaller than 87.2 pm (amphoteric cations) can. Cages bounded by pentagonal rings play a key role in phase separation by selecting which cations can fit in them, adopt a four-fold coordination, and reduce the size of miscibility gaps, i.e. the cages permit explaining why some cations are amphoteric. This result is important because it shows that a structural control is exerted by the solvent (here SiO 2) upon immiscibility which creates a selective solution mechanism that affects small (<87.2 pm) cations in binary silica-rich melts.

Role of water structure on phase separation in polyelectrolyte–polyethyleneglycol based aqueous two-phase systems

Partitioning of proteins in aqueous two-phase systems (ATPS) has emerged as one of the important downstream processing techniques in bioprocess technology. The phase separation behavior of polyelectrolyte–polyethyleneglycol (PEG) based ATPS have been studied to elucidate the mechanism controlling phase behavior. The effect of various inorganic salt additives revealed the importance of water structure as a major factor controlling phase separation in these systems. Nitrate and potassium (water structure breaking ions) elevated the binodial line while sulphate, phosphate and sodium (water structure making ions) depressed the binodial line in both polyacrylic acid–PEG as well as polyethylenimine–PEG based ATPS. The effect of increase in concentration of either of the constituent polymers in both systems (at constant salt concentration) always led to a greater propensity towards phase separation. These results point to a mechanism in which salt-assisted polymer-modified water structure interactions play a central role in phase separation in ATPS.

A study of the microhardness of ethylene glycol dimethacrylate (EGDM)/Poly (methyl methacrylate) (PMMA) network polymer

The application of the network formed from ethylene glycol dimethacrylate and poly (methyl methacrylate) (PMMA) in dentistry and orthopaedics has generated interest among material scientists in the study of its mechanical behaviour. This paper reports the preparation of the network polymer with varying concentrations of PMMA in the network and its effect on the Vickers microhardness (H v ) of the specimens at different loads ranging from 80 to 160 g. The increasing and decreasing trend in values of H v have been observed with varying concentrations of PMMA in the network. The observed behaviour has been attributed to the effect of localized plastic deformation and cross-linking density. The role of phase separation has also been envisaged.

Investigation of interaction of polyester-polyurethanes and their zwitterionomers by solid-state nuclear magnetic resonance

High-resolution 1H and 13C nuclear magnetic resonance spectra are used to investigate the intermolecular interaction of polyester-polyurethanes with different contents of hard segments and different degrees of ionization. Because there are several kinds of hydrogen bonds, the hydrogen bonds play an important role in phase separation and physical properties. The higher the percentage of intermolecular hydrogen bonds, the greater are the tensile strength and strength at definite elongation. The interaction between 4,4′-methylene diphenyl diisocyanate and N-methyldiethanolamine is weak for the ES-33.4 series. Ionization does not change the percentage of intermolecular hydrogen bonds for the ES-33.4 series and ES-41 series, and ionization does not improve the physical properties and phase separation.