Fused deposition modeling-based additive manufacturing (3D printing): techniques for polymer material systems

While the developments of additive manufacturing (AM) techniques have been remarkable thus far, they are still significantly limited by the range of printable, functional material systems that meet the requirements of a broad range of industries; including the health care, manufacturing, packaging, aerospace, and automotive industries. Furthermore, with the rising demand for sustainable developments, this review broadly gives the reader a good overview of existing AM techniques; with more focus on the extrusion-based technologies (fused deposition modeling and direct ink writing) due to their scalability, cost efficiency and wider range of material processability. It then goes on to identify the innovative materials and recent research activities that may support the sustainable development of extrusion-based techniques for functional and multifunctional (4D printing) part and product fabrication.     

Structure of short polymers at interfaces: a combined simulation and theoretical study

The structure of polymers confined between surfaces is studied using computer simulation and a density functional approach. The simple model system considers the polymer molecule as a pearl necklace of freely jointed hard spheres, having attractions among the beads, confined between attractive surfaces. This approach uses the universality of the free-energy functional to obtain the self-consistent field required in the single chain simulation. The second-order direct correlation function for the uniform bulk fluid required as input has been calculated from the reference interaction site model integral equation theory using mean spherical approximation. The theoretical results are shown to compare well with the Monte Carlo simulation results for varying densities, chain lengths, and with different attractive interaction parameters. The simulation results on the conformational properties give important indications regarding the behavior of chains as they approach the surfaces.     

A general and convenient method of synthesizing dihydridoplatinum(II) complexes with bulky phosphine ligands

Platinum(II) dihydrides containing bulky phosphine ligands, trans-PtH₂L₂ (L = PCy₃, P-i-Pr₃, P-n-Bu-t-Bu₂, PMe-t-Bu₂), have been prepared conveniently and in excellent yield from the reaction of the corresponding peroxycarbonato complexes with NaBH₄. A similar reduction of the dioxygen platinum(II) complexes also affords the dihydrides but less readily. All these dihydrides react with highly activated acetylenes to form the trans-hydridovinyl complexes.     

Design of Peptides with α,β-Dehydro-Residues: Syntheses and Crystal Structures of (i) N-Tertiarybutyloxycarbonyl-L-Ala-ΔPhe-L-Ala-OCH3 and (ii) N-Tertiarybutyloxycarbonyl-L-Leu-ΔPhe-L-Leu-OCH3

In order to contribute to design rules with α,β-dehydro amino acid residues, two peptides (i) Boc-Ala-ΔPhe-Ala-OCH₃ and (ii) Boc-Leu-ΔPhe-Leu-OCH₃ were synthesized and their crystal structures were determined. Peptide (i) with Ala residues on both sides of ΔPhe adopted a type II β-turn conformation with dihedral angles of two corner residues, φ₁ = ?62.6(4)^°, ψ₁ = 138.9(5)^°, φ₂ = 76.3(4)^° and ψ₂ = 13.1(3)^°, while the peptide (ii) with Leu residues formed an unfolded conformation with dihedral angles, φ₁ = ?81.9(5)^°, ψ₁ = ?28.3(4)^°, φ₂ = 56.7(5)^° and ψ₂ = 42.6(4)^°. The structure of peptide (i) was stabilized by an intramolecular 4→1 hydrogen bond between Ala³ NH and BOC carbonyl oxygen atom, whereas that of peptide (ii) was stabilized by van der Waals forces involving the side chains of two Leu residues.     

Drop Coalescence during Emulsion Formation in a High-Pressure Homogenizer for Tetradecane-in-Water Emulsion Stabilized by Sodium Dodecyl Sulfate

The present study investigates the effects of homogenizer pressure, surfactant concentration, ionic strength, and dispersed phase fraction on the coalescence rate of tetradecane-in-water emulsions during their formation in a high-pressure homogenizer. Experiments were conducted in a recirculating system consisting of a Rannie laboratory-scale single-stage homogenizer and a stirred vessel for tetradecane-in-water emulsions stabilized by sodium dodecyl sulfate (SDS). The initial evolution of the number concentration of droplets in the stirred tank was measured when subjected to a negative stepchange in the homogenizer pressure. The average drop coalescence rate constant in the homogenizer was inferred by fitting the experimental evolution of the number concentration of drops to a simple model accounting for the coalescence in the homogenizer under the assumption of a quasi steady state in the homogenizer. The residence time of the emulsion in the homogenizer was evaluated from the analysis of radial turbulent flow between disks. The step down homogenizer pressure was varied in the range 20.7-48.3 MPa, the drop size in the range 174-209 nm, the dispersed phase fraction in the range 5%-15%, SDS concentration in the range 0.0033-0.25 wt%, and ionic strength in the range 0.01-0.1 M. The coalescence rate constants were found to be in the range from 3.34x10(-17) to 2.43x10(-16) m(3) s(-1). The coalescence rate constant was found to be higher for higher homogenizer pressures, smaller drop sizes, lower dispersed phase fractions, and lower SDS concentrations and was insensitive to variations in ionic strength. Copyright 2001 Academic Press.     

Preparation of sodium dimolybdate by the pyrolysis of sodium oxomolybdenum (VI) oxalate

Thermal studies on various oxalato complexes have been of immense interest as they yield finely divided, highly reactive oxides which are usually obtained at a much lower temperature than that required in the conventional method of preparation, i.e., heating a mixture of two or more constituents [1]. A survey of the literature reveals that the compounds having the general formula A₂[Mo₂O₅(C₂O₄)₂(H₂O)₂], where A = K⁺, NH⁺₄[2] and A = Cs⁺ [3], have been prepared and their thermal decomposition is studied, but no such information is available regarding the preparation and characterisation of Na₂[Mo₂O₅(C₂O₄)₂(H₂O)₂] (SMO), which forms the subject of study of this paper. Sodium dimolybdate (Na₂Mo₂O₇), the decomposition product of SMO, is obtained at 280°C, a temperature much lower than that required in the conventional method of preparation of heating a mixture of Na₂MoO₄ and MoO₃ [4].     

Thermodynamics and heat transfer study of a circular tube embedded with novel perforated angular-cut alternate segmental baffles

Journal of Thermal Analysis and Calorimetry - Baffles are used for heat transfer enhancement in heat exchanger tubes. However, they also increase the friction factor in the flow channel....     

Development and Validation of Highly Sensitive LC–ESI-MS/MS Method for Bortezomib and Its Applications for Plasma Levels and Drug Content of Branded and Generic Formulations in India

In the present study, a highly sensitive and reproducible bio-analytical method was developed using LC–ESI-MS/MS to assess the lower plasma levels of bortezomib in multiple myeloma patients. The gradient elution was optimized using reverse-phase C18 column with mobile phases consisting of water and acetonitrile in 0.1% formic acid. Multiple reaction monitoring mode was used for quantification using precursor-to-product ion transition for bortezomib and sulfadiamethoxine was used as internal standard. This method was validated with a linearity range of 0.195–25 ng mL^?1. Intra-day and inter-day accuracy was 99.17–101.89% and 95.01–102.92% with precision of?<?9.87% and?<?8.77%, respectively. Bortezomib was stable in plasma samples stored at ? 80 °C for up to 10 months. The lower limit of quantification was found to be 0.195 ng mL^?1. This method was also found to be capable of quantifying bortezomib trough levels (ranging 0.19–0.7 ng mL^?1) in plasma of multiple myeloma patients post-cycle 1–6. Bortezomib content in the commonly prescribed generic formulations was also studied. The concentration in all formulations was within the 90–110% of the innovator, as prescribed by the USFDA, ruling out their role blood level variation. The study supports the use of this method for trough level estimation and therapeutic drug monitoring of bortezomib in multiple myeloma patients.

     

Synthesis, structural characterisation and biological activity of novel N-(ferrocenylmethyl)benzene-carboxamide derivatives

A series of N-(ferrocenylmethyl)benzene-carboxamide derivatives (4a-f) have been synthesised by coupling ferrocenylmethyl amine 3 with benzoic acid and various substituted fluorobenzoic acids using the standard 1,3-dicyclohexylcarbodiimide (DCC), 1-hydroxybenzotriazole (HOBt) protocol. All compounds were fully characterised using a combination of ¹H NMR, ¹³C NMR, ¹⁹F NMR, DEPT-135, ¹H-¹H COSY and ¹H-¹³C COSY (HMQC) spectroscopy and electrospray ionisation mass spectrometry (ESI-MS). The compounds 4a, 4d, 4e and 4f exhibited cytotoxic effects on the MDA-MB-435-S-F breast cancer cell line. Single crystal X-ray crystallographic data for 4d is also presented.     

Structure of spherical electric double layers: a density functional approach

A density functional theory is presented for the structure of spherical electric double layers within the restricted primitive model, where the macroion is considered as a hard sphere having uniform surface charge density, the small ions as charged hard spheres, and the solvent is taken as a dielectric continuum. The theory is partially perturbative as the hard-sphere contribution to the one-particle correlation function is evaluated using suitably averaged weighted density and the ionic part is obtained through a second-order functional Taylor expansion around the uniform fluid. The theory is in quantitative agreement with Monte Carlo simulation for the density profiles and the zeta potentials over a wide range of macroion sizes and electrolyte concentrations. The theory is able to provide interesting insights about the layering and the charge inversion phenomena occurring at the interface.