Tensile Test Specimens with a Circumferential Precrack for Evaluation of Interfacial Toughness of Thermal-Sprayed Coatings

A new testing procedure to evaluate the interfacial toughness of thermal-sprayed coatings has been developed. The newly designed test specimen is a modification of the pin test with an artificially introduced weak interface, which is expected to open up easily under tensile loading and act as a circumferential precrack along the interface between a coating and the substrate. This configuration makes it possible to calculate the stress intensity factor K _Int at the tip of the precrack, which can be expressed as , where σ₀ is the apparent average stress, a the crack length, R the specimen radius, and F _I the geometrical correction function. Finite-element analysis was carried out to calculate the correction function F _I for various values of a/R. In the experiments, the flat surface of a pin was grit-blasted and a ring-shaped area from the periphery was covered with carbon using a pencil and set into a mating dice. SUS316L stainless steel was plasma-sprayed onto the flat surface of the pin and the dice. Then, tensile load was applied to the pin to break the weak interface containing the carbon and finally the unmodified coating-substrate interface. The load required to pull out the pin was measured for various specimen parameters such as a and R. The results indicate that the adhesion of the tested coatings can be represented by interface toughness of 1.9 ± 0.1 MPa m^1/2. As a consequence, this testing procedure can be considered as a viable method to evaluate adhesion of a thermal-sprayed coating on a substrate.     

Multi-step precipitation separation system using mixture of thermosensitive polymers

Summary Multi-step precipitation separation system was developed by using aqueous mixtures of some thermosensitive polymers. The following three polymers were used here; poly(N-n-propylacrylamide), poly(N-isopropylacrylamide), and poly(N-isopropylmethacrylamide). A mixture of the three polymers showed three endothermic peaks, and the peak top temperatures were almost consistent with that of the each polymer solution. The polymers were purified by thermal precipitation to obtain fractions which can respond in narrow temperature ranges prior to use. In the case of the precipitation separation of two polymers mixtures, purities of the obtained precipitate and supernatant fractions became high comparing with the case in which the unpurified polymers were used. Parts of the polymers which were not the precipitation targets were also precipitated by the separation procedures. This was caused not only by insolubilization of the non-targeted polymers due to their phase transitions but also by their non-specific entanglement with the targeted polymers. The purities of the fractions also improved when the difference of the phase transition temperature between two polymers was large enough to avoid the coprecipitation. In the case of the precipitation separation of mixtures of the three polymers, purities of each fraction also improved when the purified polymers were used.     

Small-angle X-ray scattering of long-period structures forming bundles

Small-angle X-ray scattering (SAXS) patterns have been calculated based on a structure model, which consisted of the bundles of long-period structures. The proposed model has produced various scattering patterns of polymers, such as the equatorial, layer line, four-spot, droplet-shaped and triangular scattering. The 0.5th order scattering has arisen when the disorder in or between the long-period structures was large even though the structure did not have the periodicity directly related to the scattering maximum. A slight decrease in the disorder due to slip between the long-period structures has accounted for the sudden change of the SAXS pattern of a poly(ethylene terephthalate) fiber from the four-spot to the layer line scattering which was caused by a slight tensile deformation.     

Effects of preparation conditions on the surface modification and performance of polyethersulfone ultrafiltration membranes

The impact that some membrane preparation steps had on ultrafiltration (UF) membrane characteristics and performance was studied. Polyethersulfone (PES) was employed as base polymer, while N‐methyl pyrrolidone (NMP) was used as a solvent, and polyvinylpyrrolidone (PVP) was used as a nonsolvent pore‐forming additive. The manufacturing variables studied were solvent evaporation time and membrane surface modification, using a fluorine‐based copolymer referred to as surface‐modifying macromolecule (SMM). The flat sheet membranes, prepared via phase inversion, were characterized using solute transport data, X‐ray photoelectron spectroscopy (XPS), and contact angle measurements. Membrane performance was evaluated via filtration test protocol that included a 6‐day filtration of concentrated river water. The flux reduction with time was modeled using single and dual mechanisms of fouling. The pore blockage/cake filtration model described better the behavior of the permeation rate along the experiments. Increasing the solvent evaporation time decreased the size of the pores and the permeation rate. However, it did not significantly affect the removal of the organic compounds naturally present in the river water used as feed. XPS and contact angle measurements proved that the short evaporation periods did not allow enough SMM migration to the surface to provoke a significant effect on the membrane performance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Synthesis of High Density and Transparent Forsterite Ceramics Using Nano-Sized Precursors and Their Dielectric Properties

Forsterite (Mg₂SiO₄) ceramics were prepared using Mg(OH)₂ and SiO₂ as precursors, and the effect of powder characteristics of Mg(OH)₂ on calcination and sintering was investigated. The use of highly dispersed Mg(OH)₂ powder (HD powder) resulted in a lower calcination temperature. Forsterite powder of high homogeneity and small particle size prepared from the HD powder enabled synthesis of high-density forsterite ceramics by ordinary sintering without applying external pressure. Moreover, transparent forsterite ceramics were successfully synthesized through addition of excess Mg to the precursors to compensate for Mg evaporated during the sintering process. Subsequent dielectric measurements revealed that the transparent forsterite ceramics had a very low dielectric loss (tan δ<10⁻⁴).     

Prolonged degradation of end-capped polyelectrolyte multilayer films

Cationic chitosan (CT) and anionic dextran sulfate (Dex) were layer-by-layer (LbL) assembled from aqueous solutions containing 1 M NaCl on a quartz crystal microbalance (QCM) substrate, and the original films ((CT-Dex)₃-CT)) were end-capped with LbL assembly from CT solutions containing 1 M NaCl and Dex solutions without NaCl. The enzymatic degradation of films by chitosanase was quantitatively analyzed by QCM in terms of numbers of end-capping steps. The degradation of films end-capped with (Dex-CT)₃ was considerably prolonged when compared to those end-capped with other end-capping steps. A mechanism for the prolonged degradation was proposed by quantitative QCM data and zeta potential results.     

Alternating copolymer of bithiophene and dialkylbithiazole and its tendency to align on the surfaces

New five-membered ring π-conjugated polymers composed of 2,2′-bithiophene and 4,4′-dialkyl-2,2′-bithiazole units were prepared. The polymers were soluble in 1,2-dichlorobenzene and showed a UV-vis peak at about 490 nm above 120 °C. Cooling the solution led to the appearance of new UV-vis peaks at 550 and 600 nm, which were considered to originate from self-assembled polymer molecules. Powder XRD (X-ray diffraction) data supported a well-stacked solid structure of the polymers and a highly ordered structure of a polymer film formed on a quartz glass substrate. These data revealed a strong tendency of the new polymers to self-assemble and to form an aligned structure on the surface of the substrates.     

Distribution analyses of multi-modal dynamic light scattering data

A method of data analysis for dynamic light scattering is proposed to evaluate the weight fraction, w(R_h), of a small amount of large aggregates in a dilute solution, where R_h is the hydrodynamic radius. We examined the time-correlation function of scattering intensity for model multi-modal systems, i.e., mixtures of latex solutions having different particle sizes and of polystyrene standard solutions having different molecular weights, by properly taking into account the unknown fractions, w(R_h), and scattering intensities of individual components. We derived an equation to evaluate the weight fractions of the components. The validity of this method was verified by successfully reconstructing the observed correlation functions having fast and slow modes. As a demonstration, the fraction of aggregates in a thermosensitive polymer solution in water was evaluated as a function of temperature.     

Efficient preparation of liposomes encapsulating food materials using lecithins by a mechanochemical method

In order to evaluate to the feasibility of using lecithins for nanocapsules including functional food materials, liposomes were prepared from different commercially available lecithins (SLP-WHITE, SLP-PC70 and PL30S) by the Bangham method, and their physicochemical properties were examined by using a confocal laser scanning microscopy (CLSM) and the measurements of trapping efficiency. There was little difference in the trapping efficiency among the three types of liposomes. In all cases, the trapping efficiency clearly increased with an increase of the lecithin concentration up to 10 wt % , and the maximum efficiency reached at approximately 15%. CLSM observation showed the particle size of liposomes prepared from SLP-WHITE is significantly smaller than that prepared from other lecithins. In addition, liposomal solution prepared from SLP-WHITE remained well dispersed for at least 30 days, while two other liposomal solutions showed a phase separation due to aggregation and/or fusion of liposomes. These results indicated that SLP-WHITE is the most appropriate for the preparation of stable liposomes with well dispersed among the lecithins tested. SLP-WHITE liposomes were then prepared by the mechanochemical method using a homogenizer and microfluidizer, aiming at improving the preparation efficiency and liposome stability. The particle size of the prepared SLP-WHITE liposomes decreased with increasing inlet pressure and the number of processed cycles, and reached between 73 and 123 nm based on the measurement using dynamic light scattering. Moreover, freeze-fracture transmission electron microscopy revealed that the prepared liposomes are small unilamellar vesicles (SUV) with a diameter of approximately 100 nm. The extract of Curcuma longa Linn. (Ukon), which contains curcumins as a functional food material, was then subjected to the mechanochemical method with SLP-WHITE to give liposomes including the functional materials. Interestingly, the trapping efficiency of the liposomes for curcumins was found to reach over 85%. From these results, the present mechanochemical method is very likely to allow us to efficiently prepare stable and functional liposomes from the low-cost lecithin. The method may thus have a potential for manufacturing practical nanocapsules, which serves as a novel carrier of functional food materials.     

Cationic copolymerization behavior of a bicyclic orthoester having hydroxy group with glycidyl phenyl ether and volume change on their copolymerization

This article describes cationic ring‐opening copolymerization of a bicyclic orthoester having hydroxy group (BOE‐OH) and glycidyl phenyl ether (GPE), and the volume shrinkage behavior during the copolymerization. THF soluble polyethers [poly(BOE‐OH‐co‐GPE)] were obtained by the copolymerizations at 80–180°C, while crosslinked poly(BOE‐OH‐co‐GPE) was obtained by the copolymerizations at 220–250°C. This crosslinking reaction may originate from the dehydration of methylol groups in the side chain of poly(BOE‐OH‐co‐GPE). The volume shrinkage during the cationic copolymerization reduced as the increase of the BOE‐OH feed ratio. By contrast, the volume shrinkage on the crosslinking polymerization was almost independent on the BOE‐OH feed ratio. Poly(BOE‐OH‐co‐GPE)s with higher BOE‐OH composition showed lower thermal weight loss temperature owing to the release of H₂O by dehydration of methylol groups. The BOE‐OH component in the THF soluble poly(BOE‐OH‐co‐GPE)s lowered the glass transition temperature (T_g), while that in the crosslinked poly(BOE‐OH‐co‐GPE) increased the T_g probably because of the higher crosslinking density. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1356–1361, 2006