Synthetic hydrogels 2. Polymerization induced phase separation in acrylamide systems

Acrylamide hydrogels were synthesized in the presence of various non-solvents for linear polyacrylamide to examine phase separation during polymerization. The process was found to be dependent upon the segmental volume, the chemical structure, and the concentration of the non-solvent. The concept of conversion-phase diagram for linear polymer is introduced and used qualitatively to understand polymerization induced phase separation (PIPS), and to predict the onset of PIPS during hydrogel synthesis.

Correlation between microstructure and phosphorus segregation in a hypereutectoid Wootz steel

The influence of bands rich in phosphorus on the microstructure of hypereutectoid Wootz steel implement is described. Electron probe micro-analysis is combined with optical microscopy. Phosphorus-rich bands are seen to correspond to regions of internal cracking, carbon depletion, and enhanced frequency of spheroidized cementite in place of pearlite. A rationale for the findings is presented in terms of the influence of phosphorus on the Fe–C phase diagram and on the rate of the eutectoid reaction.

Lithium doped N-methyl-N-ethylpyrrolidiniumbis(trifluoromethanesulfonyl)amide fast-ion conducting plastic crystals

The incorporation of dopant levels of lithium ions (0.5 to 9.3% by mole) in the N-methyl-N-ethylpyrrolidinium bis(trifluoromethanesulfonyl)amide (P₁₂TFSA) plastic crystalline phase results in increases in the solid state ionic conductivity of more than 3 orders of magnitude at 298 K. Conductivities as high as 10^−-4 S cm⁻¹ at 323 K have been measured in these doped plastic crystal phases. These materials can therefore be classified as fast-ion conductors. Higher levels of Li only marginally increase the conductivity, up to around 33 mol%, followed by a slight decrease to 50 mol%. Thermal analysis behaviour has allowed the partial development of the binary phase diagram for the LiTFSA–P₁₂TFSA system between 0–50 mol% LiTFSA, which suggests the presence of a solid solution single phase at concentrations less than 9.3 mol% LiTFSA. There is also strong evidence of eutectic behaviour in this system with a eutectic transition temperature around 308 K at 33 mol% LiTFSA. A model relating ionic conduction to phase behaviour in this system is presented. The increased conductivity upon doping has been associated with lithium ion motion via⁷Li solid state NMR linewidth measurements.

Hydrogen bonded block copolymer systems : from microphase separation in solid state to self-assembly in aqueous solutions

Block copolymer systems with hydrogen bonding interactions have received relatively little attention. Recently, we have investigated the self-assembly and phase separation in such block copolymer systems with an attempt to elucidate the role of hydrogen bonding interactions both theoretically and experimentally [1-4]. In A-b-B/C diblock copolymer/homopolymer systems, the phase behavior was theoretically analyzed according to the random phase approximation and correlated with hydrogen bonding interactions in terms of the difference in inter-association constants (K). To examine how the hydrogen bonding determines the self-assembly and morphological transitions in these systems, we have introduced the K values as a new variable into the phase diagram which we established for the first time (Fig. 1). Multiple vesicular morphologies were formed in aqueous solution of A-b-B/A-b-C diblock copolymer complexes of PS-b-PAA and PS-b-PEO. Interconnected compound vesicles (ICCVs) were observed for the first time as a new morphology (Fig. 2), along with other aggregated nanostructures including vesicles, multilamellar vesicles, thick-walled vesicles and irregular aggregates. Complexation of two amphiphilic diblock copolymers provides a viable approach to vesicles in aqueous media.

Thermomechanical properties of Ni-Ti shape memory wires containing nanoscale precipitates induced by stress-assisted ageing.

This paper systematically examines the thermomechanical properties and phase transformation behaviour of slightly Ni-rich Ni-Ti biomedical shape memory wires containing homogeneously distributed nanoscale precipitates induced by stress-assisted ageing. In contrast to previous studies, particular attention is paid to the role of precipitates in impeding twin boundary movement (TBM) and its underlying mechanisms. The size and volume fraction of precipitates are altered by changing the ageing time. The martensitic transformation temperatures increase with prolonged ageing time, whereas the R-phase transformation temperature remains relatively unchanged. The stress-strain behaviour in different phase regions during both cooling and heating is comprehensively examined, and the underlying mechanisms for the temperature- and thermal-history-dependent behaviour are elucidated with the help of the established stress-temperature phase diagram. The effect of precipitates on TBM is explored by mechanical testing at 133K. It is revealed that the critical stress for TBM (σcr) increases with increasing ageing time. There is a considerable increase of 104MPa in σcr in the sample aged at 773K for 120min under 70MPa compared with the solution-treated sample, owing to the presence of precipitates. The Orowan strengthening model of twinning dislocations is insufficient to account for this increase in σcr. The back stress generation is the predominant mechanism for the interactions between precipitates and twin boundaries during TBM that give rise to the increase in σcr. Such results provide new insights into the thermomechanical properties of precipitate containing Ni-Ti biomedical shape memory wires, which are instructive for developing high-performance biomedical shape memory alloys.

Solid state ion transport and phase behaviour in composites of N,N-methyl propylpyrrolidinium tetrafluoroborate and amorphous polyethylene oxide

The binary and ternary addition of 2 wt.% LiBF₄ and 2 wt.% amorphous polyethylene oxide (aPEO) respectively to the plastic crystal forming salt P₁₃BF₄ (where P₁₃⁺=methylpropyl pyrrolidinium cation) was investigated with specific focus on the phase behaviour and evaluation of transport characteristics. Differential scanning calorimetry (DSC), optical thermomicroscopy, solid state nuclear magnetic resonance (NMR), and AC impedance spectroscopy were used to develop an understanding of the conduction process in the pure and mixed systems. The morphology of the ternary compound appeared as hexagonal spherulites upon solidification. Multinuclear NMR Pulsed Field Gradient measurements (¹H,¹⁹F,⁷Li) to probe both cation and anion diffusion coefficients are reported. The anion is shown to be the most diffusive (at 320 K:¹⁹F=2.5×10⁻¹¹ m² s⁻¹; 1H: 1.8×10⁻¹¹ m² s⁻¹; ⁷Li: 1.1×10⁻¹¹ m² s⁻¹) in the ternary compound, with enhanced conductivity (2.7×10⁻⁵ S cm⁻¹ at 310 K) just below the melt.

Transport and phase dynamics of poly(vinyl pyrrolidone) doped plastically crystalline N-methyl-N-propylpyrrolidinium tetrafluoroborate

The plastic crystal phase forming N-methyl-N-propylpyrrolidinium tetrafluoroborate organic salt (P₁₃BF₄) was combined with 2, 5 and 10 wt.% poly(vinyl pyrrolidone) (PVP). The ternary 2 wt.% PVP/2 wt.% LiBF₄/P₁₃BF₄ was also investigated. Thermal analysis, conductivity, optical thermomicroscopy, and Nuclear Magnetic Resonance (¹¹B, ¹⁹F, ¹H, ⁷Li) were used to probe the fundamental transport processes. Both the onset of phase I and the final melting temperature were reduced with increasing additions of PVP. Conductivity in phase I was 2.6 × 10^{− 4} S cm^{− 1} 5.2 × 10^{− 4} S cm^{− 1} 1.1 × 10^{− 4} S cm^{− 1} and 3.9 × 10− 5 S cm− 1 for 0, 2, 5 and 10 wt.%PVP/P₁₃BF₄, respectively. Doping with 2 wt.% LiBF₄ increased the conductivity by up to an order of magnitude in phase II. Further additions of 2 wt.% PVP slightly reduced the conductivity, although it remained higher than for pure P₁₃BF₄.

Effect of cooling rate on phase transformations in a high-strength low-alloy steel studied from the liquid phase

The phase transformation and precipitation in a high-strength low-alloy steel have been studied over a large range of cooling rates, and a continuous cooling transformation (CCT) diagram has been produced. These experiments are unique because the measurements were made from samples cooled directly from the melt, rather than in homogenized and re-heated billets. The purpose of this experimental design was to examine conditions pertinent to direct strip casting. At the highest cooling rates which simulate strip casting, the microstructure was fully bainitic with small regions of pearlite. At lower cooling rates, the fraction of polygonal ferrite increased and the pearlite regions became larger. The CCT diagram and the microstructural analysis showed that the precipitation of NbC is suppressed at high cooling rates, and is likely to be incomplete at intermediate cooling rates.

Liquid phase adsorption kinetics and equilibrium of toluene by novel modified-diatomite

The adsorption equilibria of toluene from aqueous solutions on natural and modified diatomite were examined at different operation parameters such as pH, contact time, initial toluene concentration was evaluated and optimum experimental conditions were identified. The surface area and morphology of the nanoparticles were characterized by SEM, BET, XRD, FTIR and EDX analysis. It was found that in order to obtain the highest possible removal of toluene, the experiments can be carried out at pH 6, temperature 25°C, an agitation speed of 200 rpm, an initial toluene concentration of 150 mg/L, a centrifugal rate of 4000 rpm, adsorbent dosage = 0.1 g and a process time of 90 min. The results of this work show that the maximum percentage removal of toluene from aqueous solution in the optimum conditions for NONMD was 96.91% (145.36 mg/g). Furthermore, under same conditions, the maximum adsorption of natural diatomite was 71.45% (107.18 mg/g). Both adsorption kinetic and isotherm experiments were carried out. The experimental data showed that the adsorption follows the Langmuir model and Freundlich model on natural and modified diatomite respectively. The kinetics results were found to conform well to pseudo-second order kinetics model with good correlation. Thus, this study demonstrated that the modified diatomite could be used as potential adsorbent for removal of toluene from aqueous solution.