Physicochemical Studies on the Interfacial and Bulk Behaviors of Sodium N-Dodecanoyl Sarcosinate (SDDS)

Sodium N-dodecanoyl sarcosinate (SDDS), a novel amino-acid based surfactant, has immense biological and industrial importance. Although it is being used in a number of cosmetic formulations, systematic analysis of the bulk and interfacial properties of the surfactant is scarce in the literature. In this study, effects of salt, temperature, and pH on the self-association and related properties of SDDS have been examined in detail using methods such as tensiometry, conductometry, fluorimetry, pH-metry, spectrophotometry, calorimetry, and circular dichroism. The nature of amphiphilic packing and the aggregation numbers of the assemblies have been deciphered. Properties of the acid form of the surfactant have also been explored. The results have been conceptually rationalized and systematically presented together with associated energetics of the interfacial adsorption and self-aggregation of the surfactant in the bulk.

Experimental evidence of concurrent compositional and structural instabilities leading to ω precipitation in titanium-molybdenum alloys

The ω phase is commonly observed in many commercial β or near-β titanium alloys on rapidly cooling from the single β phase field and also during subsequent isothermal annealing. However, the crystallographic formation mechanism for the ω particles is hitherto unclear/under discussion. The present study primarily focuses on ω precipitation within the β (body-centered cubic (bcc)) matrix of simple model binary titanium-molybdenum (Ti-Mo) alloys. It provides direct experimental evidence of the formation of ω-like embryos from competing compositional and structural instabilities arising in the bcc lattice of Ti-Mo alloys during rapid cooling from the high-temperature single β phase field. The displacive partial collapse of the {1 1 1} planes of the parent bcc structure within compositionally phase-separated regions containing several at.% less of Mo, forming ω-like embryos, has been conclusively shown by coupling aberration-corrected high-resolution scanning transmission electron microscopy with atom probe tomography observations. Growth and coarsening of these ω-like embryos take place during subsequent isothermal annealing, accompanied with both a completion of the collapse of the {1 1 1} β planes leading to a fully developed ω structure as well as rejection of Mo from these precipitates, resulting in near-equilibrium compositions.     

Effect of specimen thickness on the creep response of a Ni-based single-crystal superalloy

Creep tests on Ni-based single-crystal superalloy sheet specimens typically show greater creep strain rates and/or reduced strain or time to creep rupture for thinner specimens than predicted by current theories, which predict a size-independent creep strain rate and creep rupture strain. This size-dependent creep response is termed the thickness debit effect. To investigate the mechanism of the thickness debit effect, isothermal, constant nominal stress creep tests were performed on uncoated PWA1484 Ni-based single-crystal superalloy sheet specimens of thicknesses 3.18 and 0.51 mm under two test conditions: 760 °C/758 MPa and 982 °C/248 MPa. The specimens contained initial microvoids formed during the solidification and homogenization processes. The dependence of the creep response on specimen thickness differed under the two test conditions: at 760 °C/758 MPa there was a reduction in the creep strain and the time to rupture with decreasing section thickness, whereas at 982 °C/248 MPa a decreased thickness resulted in an increased creep rate even at low strain levels and a decreased time to rupture but with no systematic dependence of the creep strain to rupture on specimen thickness. For the specimens tested at 760 °C/758 MPa microscopic analyses revealed that the thick specimens exhibited a mixed failure mode of void growth and cleavage-like fracture while the predominant failure mode for the thin specimens was cleavage-like fracture. The creep specimens tested at 982 °C/248 MPa in air showed the development of surface oxides and a near-surface precipitate-free zone. Finite-element analysis revealed that the presence of the alumina layer at the free surface imposes a constraint that locally increases the stress triaxiality and changes the value of the Lode parameter (a measure of the third stress invariant). The surface cracks formed in the oxide scale were arrested by further oxidation; for a thickness of 3.18 mm the failure mode was void nucleation, growth and coalescence, whereas for a thickness of 0.51 mm there was a mixed mode of ductile and cleavage-like fracture.     

Modeling of heat transfer in rotational molding

Rotational molding is a process for manufacturing hollow or open‐sided plastic products using a rotating mold subjected to heating and then cooling. The process is attractive for the production of stress‐free objects at a competitive cost. In this article, a modified model for heat transfer in rotational molding is proposed, which assumes that the heat transfer at the mold‐powder interface is because of convection, whereas the powder particles are heated up by conduction. Heat transfer through the mold–air contact is also included. A source‐based formulation is used for modeling the layer‐by‐layer nonisothermal deposition of plastic. The reduced heat transfer due to warpage is calculated by using a modified heat transfer coefficient. Good overall agreement is found between the cycle times as predicted by the model and the experimental data. The model is then used for calculating the cycle time for particulate composites, based on their effective properties. A reduction in the cycle time is observed in the case of reinforced composites. This is attributed to the increase in thermal conductivity of the particulate composites and the reduced mass fraction of the polymer. Numerical calculations of the cycle time for the glass‐bead reinforced composites are found to be in good agreement with the experimental results. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

An XPS Study with Depth Profiling for the Surface Oxide Layer Formed on Aluminides Produced on Superalloy 690 Substrates

Superalloy 690 substrates containing mainly Cr and Ni aluminides on the uppermost surface, formed by atmospheric plasma spraying and heat treatment, were oxidized at 1273 K in air for 2 h. Quantitative X-ray photoelectron spectroscopy (XPS) analyses indicated that the outermost surface layer formed on aluminides is composed of ~ 21.0 at.% Al⁺³ (as Al₂O₃), 17.0 at.% Al⁰ (elemental aluminium), 1.4 at.% Cr⁺³ (as Cr₂O₃) and 60.5 at.% O (in Al₂O₃ and Cr₂O₃ and also includes oxygen contaminant). Surface sputtering for 5 min exhibited splitting of Cr2p_3/2 peak into a doublet comprising Cr⁺³ (0.9 at.%) and Cr⁰ (0.4 at.%) with the presence of 1.15 at.% Ni⁰ in the surface layer that mainly contained ~ 37.3 at.% Al⁺³, 7.3 at.% Al⁰ and 52.9 at.% O. Surface sputtering for 15 min indicated surface composition similar to surface sputtered for 5 min but with a marked reduction in ratio of Al⁺³/Al⁰ (32.2 at.% Al⁺³/11.90 at.% Al⁰) in the surface layer.     

Short jute fiber‐reinforced polypropylene composites: Dynamic mechanical study

Short jute fiber‐reinforced polypropylene (PP) composites were prepared using a high‐speed thermokinetic mixer. A compatibilizer was used to improve the molecular interaction between jute and PP. Both the percent weight fraction of the jute fiber and compatibilizer were varied to study the dynamic mechanical thermal (DMT) properties. Dynamic parameters such as storage flexural modulus (E′), loss flexural modulus (E″), storage shear modulus (G′), loss shear modulus (G″), and loss factor or damping efficiency (tan δ) were determined in a resonant frequency mode. The transition peak nature, amplitude, and temperature of E′, E″, G′, G″, and tan δ of different compositions were shown to indicate possible improvements of molecular interaction in the presence of a compatibilizer. The modulus retention term, a plot of the reduced modulus with the weight fraction of the jute fiber, also indicate its improvement. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 531–539, 1999     

Photograft copolymerization of methyl methacrylate on silk fiber using titanium(III) chloride–potassium persulphate redox initiator in a limited aqueous system. I

Graft copolymerization of methyl methacrylate (MMA) onto mulberry silk fibers has been investigated in a limited aqueous system employing titanium(III) chloride–K₂S₂O₈ as the redox initiator under a photoactive condition with visible light. Polymerization in the presence of light at 32 ± 1°C has been found to be more pronounced than in the dark under identical conditions. The percentage of grafting, the percentage of total conversion, and the percentage of grafting efficiency have been studied by varying the reaction time, concentration of monomer, initiator concentration, solvent composition, and pH of the medium. A high percentage of grafting (∼ 93%), high grafting efficiency (∼ 97%), and the percentage of total conversion (∼ 25%) have been obtained with little homopolymer formation. Characterization of the grafted fibers has been investigated by Fourier transform infrared spectroscopy and scanning electron microscopy. Finally, the reaction mechanism has been discussed by considering hydrogen bonding. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2187–2193, 1999     

Synthesis of nanocrystalline hydroxyapatite using surfactant template systems: Role of templates in controlling morphology

Hydroxyapatite (HA) nanopowder was synthesized by reverse microemulsion technique using calcium nitrate and phosphoric acid as starting materials in aqueous phase. Cyclohexane, hexane, and isooctane were used as organic solvents, and Dioctyl sulfosuccinate sodium salt (AOT), dodecyl phosphate (DP), NP5 (poly(oxyethylene)₅ nonylphenol ether), and NP12 (poly(oxyethylene)₁₂ nonylphenol ether) as surfactants to make the emulsion. Effect of synthesis parameters, such as type of surfactant, aqueous to organic ratio (A/O), pH and temperature on powder characteristics were studied. It was found that the surfactant templates played a significant role in regulating the morphology of the nanoparticle. Hydroxyapatite nanoparticle of different morphologies such as spherical, needle shape or rod-like were obtained by adjusting the conditions of the emulsion system. Synthesized powder was characterized using X-ray diffraction (XRD), BET surface area and transmission electron microscopy (TEM). Phase pure HA nanopowder with highest surface area of 121 m²/g were prepared by this technique using NP5 as a surfactant. Densification studies showed that this nanoparticle can give about 98% of their theoretical density. In vitro bioactivity of the dense HA compacts was confirmed by excellent apatite layer formation after 21 days in SBF solution. Cell material interaction study showed good cell attachment and after 5 days cells were proliferated on HA compacts in OPC1 cell culture medium. The results imply this to be a versatile approach for making hydroxyapatite nanocrystals with controlled morphology and excellent biocompatibility.     

Growth of nano-particles of Al2O3, AlN and iron oxide with different crystalline phases in a thermal plasma reactor

The paper presents the experimental results showing that the crystalline phase of the nano-particles, synthesized in a DC transferred arc thermal plasma reactor, critically depend on the operating pressure in the reaction zone. The paper reports about the changes in crystalline phases of three different compounds namely: aluminium oxide (Al₂O₃), aluminium nitride (AlN) and iron oxide (Fe_xO_y) synthesized at 760 Torr and 500 Torr of operating pressures. The major outcome of the present work is that the phases having higher defect densities are more probable to form at the sub-atmospheric operating pressures. The variations in the crystalline structures are discussed on the basis of the change in the temperature during the nucleation process, prevailing at the boundary of the plasma, on account of the ambient pressures. The as-synthesized nano-particles were examined by X-ray diffraction analysis and transmission electron microscopy. In addition, the confirmatory analysis of the crystalline phases of iron oxides was carried out with the help of Mössbauer spectroscopy.