AgIAg oxysalt high conductivity glasses: a tentative approach to their structure

As a result of electronic microscopy observations the amorphous nature of the high conductivity AgIAg oxysalt electrolytes seems due to a random orientation of structurally ordered microdomains having less than 1 micron size. A tentative approach to the structure of these domains is suggested in order to account for (i) the fast silver ion migration, which would occur along “smooth” passageway tracked by iodide ions, (ii) the critical composition, vis 80 mole% AgI, corresponding to the conductivity maximum found for most of these materials at room temperature, (iii) the low activation energy of the conductivity Arrhenius plots, (iv) the presence of some immobile Ag⁺ which closely surround the oxyanions.     

Effect of compatibilization on the oxygen‐barrier properties of poly(ethylene terephthalate)/poly(m‐xylylene adipamide) blends

The improvement of the oxygen‐barrier properties of poly(ethylene terephthalate) (PET) via blending with an aromatic polyamide [poly(m‐xylylene adipamide) (MXD6)] was studied. The compatibilization of the blends was attempted through the incorporation of small amounts of sodium 5‐sulfoisophthalate (SIPE) into the PET matrix. The possibility of a transamidation reaction between PET and MXD6 was eliminated by ¹³C‐NMR analysis of melt blends with 20 wt % MXD6. An examination of the blend morphology by atomic force microscopy revealed that SIPE effectively compatibilized the blends by reducing the MXD6 particle size. Thermal analysis showed that MXD6 had a nucleating effect on the crystallization of PET, whereas the crystallization of MXD6 was inhibited, especially in compatibilized blends. Blending 10 wt % MXD6 with PET had only a small effect on the oxygen permeability of the unoriented blend when it was measured at 43% relative humidity, as predicted by the Maxwell model. However, biaxially oriented films with 10 wt % MXD6 had significantly reduced oxygen permeability in comparison with PET. The permeability at 43% relative humidity was reduced by a factor of 3 in compatibilized blends. Biaxial orientation transformed spherical MXD6 domains into platelets oriented in the plane of the film. An enhanced barrier arose from the increased tortuosity of the diffusion pathway due to the high aspect ratio of MXD6 platelets. The aspect ratio was calculated from the macroscopic draw ratio and confirmed by atomic force microscopy. The reduction in permeability was satisfactorily described by the Nielsen model. The decrease in the oxygen permeability of biaxially oriented films was also achieved in bottle walls blown from blends of PET with MXD6. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1361–1370, 2005     

Rapid screening test for flame retardation of wood,and its applicability to thermoplastic polymer systems

A rapid screening process was developed to investigate the flame‐retardant properties of new materials and compositions. Wooden tongue depressors (“sticks”) were coated in solutions/suspensions of compositions of interest and tested in a method similar to that of the UL‐94 vertical burn test. The concentration of additives applied to the wooden sticks, as well as the additive application and drying times influenced the burning performance of the sticks, a useful screening method for testing flame retardants applied to wood products. The most promising combination of flame retardants from the wooden stick tests were then compounded into polyolefins, which were tested according to the UL(94) vertical burn protocol. A strong correlation was found between UL(94) results for low density polyethylene, high density polyethylene and polypropylene, and the wooden stick flammability data. This test, therefore, shows promise as a simple, inexpensive, and rapid way to screen new materials and compositions for flammability. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46602.     

Atomic force microscopy (AFM) studies of liquid crystalline polymer (LCP) surfaces

An atomic force microscope (AFM) operating in tapping or contact mode was used to study the surface topography and the molecular organization of Vectra‐A and Vectra‐B films. Large‐scale (15 × 15 μm) AFM images revealed that ribbonlike fibrils with a width/height ≫ 1.0 are the dominant surface features of these liquid crystalline polymers (LCPs). The region of local disorder, surface debris, and interfibrillar debris as well as possible amorphous regions were observed in both LCP samples. Large fibrils, 5.0–10.0 μm in width, can be thought of as formed by smaller microfibrils capable of forming ordered structures. Microfibrils can bend upward, forming raised surface features; bend inward, originating cracks 1–2 μm wide on the film surface; or divide and subdivide into smaller units. Longitudinal and lateral stresses are believed responsible for the variation in fibril size, shape, and orientation. AFM images containing molecular‐scale details showed that microfibrils consists of chains of molecules coiled around a central axis and that they can be only about 2.0 nm wide. These submicron surfaces consist of white spots (representing molecules) that can form ordered structures or that can cluster to form agglomerates distributed in a random manner. Submicron fibrils are believed to represent the LCP basic structural unit. AFM results indicate that the surface topography of Vecta‐B is more ordered and uniform than is the one observed for Vectra‐A. Seemingly, amorphous particles form debris on Vectra‐A surfaces. Short rods oriented crosswise on the fibril surface are instead what increases the Vectra‐B roughness. These LCPs can have a surface topography similar to the one observed in AFM images of a spiderweb. However, the spiderweb fibrils are formed by more uniform microfibrils that are oriented parallel to each other. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2243–2254, 1999     

Multilayered confinement of iPP/TPOSS and nylon 6/APOSS blends

A series of isotactic polypropylene and nylon 6 blends with silsesquioxane (POSS) additives were produced, then layered to nanometer thicknesses to test the effects of confinement upon polymer property modification. POSS is shown to be a poor filler, lacking solubility and favorable interaction with the polymer matrices. It was initially hypothesized that under extreme confinement and orientation, such as in melt-spun fibers, or confined within 2D nanoscale layers, that POSS would undergo forced-assembly into elongated, rebar-like reinforcement structures, or even act as crosslinking molecules for the polymer chains. The current results, however, show POSS existing as large, phase separated aggregates, in order to minimize interactions with the polymer matrix; the aggregates behave as debonded hard particles upon tensile deformation. POSS has been previously shown to enhance the properties of polymer matrices in which the POSS molecules have been grafted to, or copolymerized within the chain, but this is not the case for these POSS blends. In comparison to results from the iPP/DBS/TPOSS system, in which POSS is unable to directly interact with the polymer matrix, and the nylon 6/APOSS system, in which POSS can potentially form hydrogen bonds with the polymer matrix, the results are similar and reveal that POSS blends are largely incompatible with the polymer matrix. Small improvements in blend properties can be made via functionalization of the POSS cage, in order to enhance interactions, but these improvements are quite limited.     

Effect of linear comonomers on the rate of crystallization of copolyesters

Small amounts of dimethyl‐4,4′‐biphenyldicarboxylate, 2,7‐dimethyl‐4,5,9,10‐tetrahydropyrenedicarboxylate, and dimethyl‐2,7‐pyrenedicarboxylate have been copolymerized into poly(ethylene) terephthalate (PET). The thermal transitions of the copolymers have been characterized, and the crystallization rates have been measured isothermally. Avrami analysis indicates that all the copolymers crystallized at a slower rate than that of the PET homopolymer. Addition of perylene to the copolymers containing pyrene enhanced the rate of crystallization, which could be the consequence of stacked arene assemblies serving as templates for crystal formation. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2696–2704, 2001     

Fibers from polypropylene/nano carbon fiber composites

Fibers from polypropylene and polypropylene/vapor grown nano carbon fiber composite have been spun using conventional melt spinning equipment. At 5 wt% nano carbon fiber loading, modulus and compressive strength of polypropylene increased by 50 and 100%, respectively, and the nano carbon fibers exhibited good dispersion in the polypropylene matrix as observed by scanning electron microscopy.     

Atomic force microscopy (AFM) study of poly(ethylene terephthalate-co-4,4′-bibenzoate): A polymer of intermediate structure

An atomic force microscope (AFM) operating in both tapping and contact modes was used to study the surface topography and the molecular organization of a molded flexural test bar prepared from a poly(ethylene terephthalate-co-4,4'-bibenzoate) copolymer containing a terephthalate:4,4′-bibenzoate molar ratio of 45:55 (PETBB-55). Micrometer-scale (15 × 15 μm) contact-mode AFM images revealed that the PETBB surface contains a deep indentation that forms trenches that extend over the entire surface examined. In addition, the surface may appear as an overlay of fibrils having different orientation. At greater magnification (1 × 1 μm), it is possible to observe the existence of micropores. These results were also observed in images obtained while operating the AFM in the tapping mode. The side of the part is more homogeneous and ordered than is its top surface. It has the appearance of a stacked lamellar structure in which missing fibrils can originate cracks ∼0.5-μm wide. Fine surface details were observed in nanometer-scale images, showing the presence of chains of white spots that could represent molecules or a cluster of molecules. These chains can form domains in which they are almost parallel to each other and have a preferred orientation; this structural organization was generated without any orientation other than that produced during a mold flow. Alternatively, chain lengths are interrupted and white spots form, distorted by easily recognizable hexagonal arrangements. The degree of lamellar order observed in the side of the bar, the area of greatest flow orientation in the part, was not been observed for the PET homopolymer in the past and bears some resemblance to previously imaged liquid crystalline polyester (LCP) structures. Combined with some previously reported LCP-like mechanical properties, we propose that this PETBB copolymer is, in fact, a “frustrated LCP,” one that with some driving force could be converted to liquid crystallinity. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2616–2623, 2001