Controlling micro‐ and nanofibrillar morphology of polymer blends in low‐speed melt spinning process. Part II: Influences of extrusion rate on morphological changes of a PLA/PVA blend through a capillary die

The effects of the extrusion rate on the morphological changes of poly(lactic acid) (PLA)/poly(vinyl alcohol) (PVA) blend through a capillary die were investigated. In this study, the extrusion rate or mass flow rate is altered from 0.5 g min^?1 to 2 g min^?1 with an increment of 0.5 g min^?1. The PLA/PVA blend with a composition of 30/70 (wt %) exhibits a particle matrix morphology with dispersed PLA droplets within the PVA matrix. It is found that, the spherical or ellipsoidal dispersed PLA droplets are elongated and coalesced into rod‐like or longer ellipsoidal droplets when they pass through the capillary die. When the extrusion rate increases, the coalescence between the large PLA droplets occurs more intense. However, the changes of the extrusion rate have no strong effect on the coalescence of small droplets having diameter less than about 150 nm. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44257.     

Molecular characterization of statistical copolymers: 1. Potential and limitations of full adsorption–desorption procedure in separation of statistical copolymers

Dynamic integral desorption isotherms for a series of poly(methyl methacrylate) homopolymers and poly(methyl methacrylate)–polystyrene statistical copolymers were measured. Nonporous silica was the full adsorption–desorption (FAD) column packing and various adsorption‐promoting and desorption‐promoting liquids were used. The aim of this study was to evaluate the applicability of the FAD approach for separation of statistical copolymers. The effects of the adsorbing liquid and desorbing liquid nature were demonstrated on the positions and shapes of desorption isotherms. The desorption isotherms also strongly depended on both (co)polymer molar mass and copolymer chemical composition. This indicates large fractionation potential of the FAD procedure. Simultaneously, the interference of both above parameters prevents the direct use of FAD for fractionation of the copolymers. It is anticipated that the fractionation and/or reconcentration potential of the FAD procedure can be very effectively utilized in combination of FAD with size‐exclusion chromatography and/or with gradient elution liquid adsorption chromatography. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 857–864, 2000     

A role for water molecules in DNA-ligand minor groove recognition

Targeting the minor groove of DNA through binding to a small molecule has long been considered an important molecular-recognition strategy in biology. A wide range of synthetic heterocyclic molecules bind noncovalently in the minor groove of the double helix and are also effective against a number of human and animal diseases. A classic structural concept, the isohelicity principle, has guided much of this work: such heterocyclic molecules require a shape that complements the convex surface of the minor groove. Researchers have used this principle to design molecules that can read DNA sequences. This principle also predicts that molecules that lack the complementary shape requirement would only bind weakly to DNA. Recently, however, researchers have unexpectedly found that some essentially linear compounds, which do not have this feature, can have high DNA affinity. In this Account, we discuss an alternative recognition concept based on these new findings. We demonstrate that highly structured water molecules can play a key role in mediating between the ligand and DNA minor groove without loss of binding affinity. Combined structural and thermodynamic approaches to understanding the behavior of these molecules have shown that there are different categories of bound water in their DNA complexes. For example, application of this water-bridging concept to the phenylamidine platform has resulted in the discovery of molecules with high levels of biological activity and low nonspecific toxicity. Some of these molecules are now in advanced clinical trials.     

Multiscale physical characterization of an outdoor-exposed polymeric coating system

Surface topography and gloss are two related properties affecting the appearance of a polymeric coating system. Upon exposure to ultraviolet (UV) radiation, the surface topography of a coating becomes more pronounced and, correspondingly, its gloss generally decreases. However, the surface factors affecting gloss and appearance are difficult to ascertain. In this article, atomic force microscopy (AFM) and laser scanning confocal microscopy (LSCM) measurements have been performed on an amine-cured epoxy coating system exposed to outdoor environments in Gaithersburg, Maryland. The formation of the protuberances is observed at the early degradation stages, followed by the appearance of circular pits as exposure continues. At long exposure times, the circular features enlarge and deepen, resulting in a rough surface topography and crack formation. Fourier Transform Infrared Spectroscopy (FTIR) study indicates that the oxidation and chain scission reactions are likely the origins of the surface morphological changes. The relationship between changes in surface roughness and gloss has been analyzed. The root mean square (RMS) roughness of the coating is related to nanoscale and microscale morphological changes in the surface of the coating as well as to the gloss retention. A near-linear dependence of RMS roughness with the measurement length scale (L) is found on a double logarithmic scale, i.e., RMS ∼ L ^f. The scaling factor, f, decreases with exposure time. The relationship between surface topography, on nano- to microscales, and the macroscale optical properties such as gloss retention is discussed. Moreover, a recent development in using an angle-resolved light scattering technique for the measurement of the specular and off-specular reflectance of the UV-exposed specimens is also demonstrated, and the optical scattering data are compared to the gloss and the roughness results.

Optimization of the Scratch Test for specific coating designs

The proper design of wear resistant coatings applied to cutting tools comprises the optimization of the mechanical properties (Young's modulus, yield strength, adhesion, intrinsic stresses, fracture, fretting etc.) of the coating-tool system. The goal is to find material and structural solutions which keep the resulting stress-strain field under typical application conditions below the stability limits of the system. Based on nanoindentation measurements obtained from the coating-tool system which should be optimized, a scratch test is dimensioned with respect to load range and indenter geometry. The measured data from this “Physical Scratch Test” are used to simulate spatial stress profiles and to calculate the von Mises stress characteristics and the maximum normal stresses in the scratch direction. In a further step, the simulations are used to suggest scratch parameters for a “Fine Tuned Scratch Test” which increase the sensitivity of the test for specific depth regions in the coating-tool architecture and allow improved and more sensitive investigations of critical interfaces, transition layers and surface-near substrate regions. The tests were performed at PVD coated inserts (nitrides and oxides) and compared with the results obtained from cutting tests.     

Corrosion of Cr2AlC in Ar/1%SO2 Gas Between 900 and 1200?��C

Cr₂AlC compounds were synthesized by a powder metallurgical route and corrosion tested at 900, 1000, 1100 and 1200 °C for up to 150 h under an Ar/1% SO₂ gas atmosphere. The compounds were resistant to corrosion because a thin ??-Al₂O₃ barrier layer quickly formed on the surface which suppressed sulfidation. Virtually no sulfur was detected inside the scale except during the initial corrosion stage. The superior corrosion resistance of Cr₂AlC originated from the high affinity of Al for oxygen to form the thermodynamically stable Al₂O₃. Unlike Al, Cr was not active because Cr was strongly bound to carbon as Cr₂C layers in Cr₂AlC. The small amount of Cr₂O₃ that had formed was dissolved in the Al₂O₃ layer. The corrosion of Cr₂AlC resulted in the formation of an ??-Al₂O₃ layer and an underlying Cr₇C₃ layer.     

Heat transfer and solidification microstructure evolution of continuously cast steel by non-steady physical simulation

The heat transfer and solidification microstructure evolution during continuous casting were experimentally studied in this work. A new approach to physically simulate the steel solidification behavior during continuous casting was developed. Six steel grades with different solidification mode were introduced to elucidate the carbon equivalent dependent mold heat flux, prior austenite grain size and secondary dendrite arm spacing. It is found that the non-steady mold heat fluxes in the experiment against time for all steel grades are comparative to that versus distance in practical continuous casting. Due to the occurrence of L→L+δ→δ+γ→γ transformation with the largest amount of volume contraction in hypo-peritectic steel, it shows the lowest mold heat flux among these six steel grades. It is also demonstrated from the solidification microstructure results that the prior austenite grain size and secondary dendrite arm spacing in the physical simulation are in good agreement with those in continuously cast strand. In addition, the steel with a higher temperature for the onset of δ→γ transformation reveals the larger prior austenite grains resulted from the higher grains growth rate in the post solidification process.     

Enhanced corrosion performance of magnesium phosphate conversion coating on AZ31 magnesium alloy

Magnesium phosphate conversion coating (MPCC) was fabricated on AZ31 magnesium alloy for corrosion protection by immersion treatment in a simple MPCC solution containing Mg²⁺ and PO^3?₄ ions. The MPCC on AZ31 Mg alloy showed micro-cracks structure and a uniform thickness with the thickness of about 2.5 µm after 20 min of phosphating treatment. The composition analyzed by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed that the coating consisted of magnesium phosphate and magnesium hydroxide/oxide compounds. The MPCC showed a significant protective effect on AZ31 Mg alloy. The corrosion current of MPCC was reduced to about 3% of that of the uncoated surface and the time for the deterioration process during immersion in 0.5 mol/L NaCl solution improved from about 10 min to about 24 h.     

Oxidation of ZC63 Mg alloys reinforced with SiC particles between 390 °C and 500 °C in air

The ZC63 magnesium alloys reinforced with 10 wt.% of SiC particles with an average particle size of 50 μm were cast. The fabricated SiC_p/ZC63 composite consisted of an α-Mg matrix, unreacted α-SiC particles, and an intergranularly formed CuMgZn compound. It was oxidized at 390 °C to 500 °C up to 5 h in air. The oxide scales were thin and compact below 430 °C, but became porous and loose above 450 °C. They consisted primarily of MgO and a small amount of Mg₃N₂. SiC particles were stable over the temperature range explored.     

Adsorption of gold(III) from waste rinse water of semiconductor manufacturing industries using Amberlite XAD-7HP resin

Advanced hydrometallurgical separation processes are gaining significant importance for the recovery of gold from the aqueous solutions viz. leach liquor of waste electronics, plating material solutions, and waste wash water from electronic industries. In the present investigation, gold adsorption from the waste rinse water of semiconductor manufacturing industries is reported using Amberlite XAD-7HP. For experimental purposes, chloride waste rinse water that contained primarily Au (281 mg/ L) with trace amounts of Cu, Ni, Zn, Sn etc was used. Batch studies were carried out to optimize various process parameters, including contact time, acidity of solution, and resin dosage for the adsorption of gold from the above waste effluent. Adsorption of 92.25% gold was found from the waste solution within a contact time of 30 minutes at an aqueous to resin (A/R) ratio of 25 mL/g and an equilibrium pH of 0.63. In optimal conditions, the loading capacity of resin for gold was observed to be 58.82 mg of gold/g of resin. The gold adsorption phenomena were confirmed by the comparative FT-IR spectroscopic characterization studies of fresh resin and gold loaded resin. Elution tests were carried out for the elution of gold from the gold loaded resin using various ratio mixtures of acetone and 1.0 M HCl. An elution efficiency of 96.96% gold was achieved at an acetone-to-acid ratio of 9. In this condition, gold-enriched solution containing 7,240 mg gold/ L was obtained. The maximum elution of gold was found to be 99.33% using pure acetone in a contact time of 30 minutes. The data obtained will be useful to simulate the continuous gold adsorption process within a column.