Phase Homogenization Research Articles

The effect of physical interactions on melt-phase homogenization of mixtures of poly( m-xylene adipamide) with aliphatic polyamides induced by interchange reactions

Poly( m-xylene adipamide) (MXD6) was melt mixed at 290°C in a Brabender with the aliphatic polyamides: nylon-6,6, nylon-6,9, nylon-6,10, nylon-6,12 and nylon-12,12. MXD6 was found to be physically immiscible with each nylon- x, y; however, owing to interchange reactions during melt mixing, the mixtures eventually became one-phase. The time required for this reaction-induced phase homogenization was followed visually and by differential scanning calorimetry (loss of ability to crystallize and change in glass transition behaviour) and was found to increase significantly as the ratio of methylene to amide units, CH 2 NHCO ratio, in the aliphatic polyamide increased. The extent of reaction at the point of phase homogenization was determined by 1H nuclear magnetic resonance, and this, too, increased with the CH 2 NHCO ratio but not as much as the melt mixing time required for phase homogenization. These effects are attributed to the more unfavourable polymer-polymer interaction energy between MXD6 and nylon- x, y as the CH 2 NHCO ratio increases. This physical parameter is believed to influence the initial interfacial area (through the interfacial tension), the initial interfacial thickness and the length of the critical copolymer segment length for conversion of a microphase-separated block copolymer to a single-phase melt. All these factors influence the melt mixing time required for phase homogenization.

Toughening of phase-homogenized mixtures of nylon-6 and poly( m-xylene adipamide) with a functionalized block copolymer

Mixtures of nylon-6 and poly( m-xylene adipamide) (MXD6) undergo sufficient interchange reactions when melt blended at 290°C to give a homogeneous melt phase and a material with a single T g. However, the extent of reaction is sufficiently low that the product retains a high level of ability to crystallize. These phase-homogenized mixtures become supertough when blended with a maleic anhydride (MA) grafted elastomeric styrene-(ethylene/butene)-styrene (SEBS) triblock copolymer, i.e. SEBS- g-MA. Pure nylon-6, pure MXD6, or mixtures of the two prepared under low-temperature extrusion conditions (260°C) that do not lead to phase homogenization are not similarly supertoughened by blending with SEBS- g-MA. The reasons appear to relate to differences in elastomer particle morphology and inherent ductility for the various matrices. SEBS- gMA blends with nylon-6 are not supertough because the rubber particles are too small. Addition of MXD6 causes the particles to become larger and of optimum size for toughening, but it is postulated that MXD6 is difficult to toughen because of low inherent ductility. The polyamide mixtures that were not phase homogenized are also inherently incompatible. The differences in rubber particle geometry are explained in terms of the functionality of the two polyamides towards reactions with anhydride groups.

Effect of polyamide functionality on the morphology and toughness of blends with a functionalized block copolymer

Previous work has shown that blends of a maleic anhydride functionalized triblock copolymer (with an ethylene/butene mid-block and styrene end-blocks, or SEBS- g-MA) with nylon-6,6 gives super-tough materials with complex-shaped rubber particles that are just below the upper critical particle size for toughening. Similar blends of SEBS- g-MA with nylon-6 are not toughened because the rubber particles are evidently too small, i.e. below a proposed lower critical size for toughening. It was further proposed that this difference in morphology stems from the difunctional (nylon-6,6) versus monofunctional (nylon-6) character of these polyamides for reaction with anhydrides. This proposal is supported here by the observation that blends of SEBS- g-MA with nylon-12,12 give large complex rubber particles like those in nylon-6,6 while nylon-11 and nylon-12 give smaller particles like nylon-6. Further support of this notion is provided by blending nylon-6 with other polyamides in an attempt to produce a chemically modified matrix. Addition of 10% nylon-6,6, poly( m-xyle adipamide) (MXD6) and nylon-12,12 to the nylon-6 matrix (under conditions that cause phase homogenization by interchange reactions) leads to rubber particle enlargement and toughening, while addition of nylon-11 or nylon-12 does not lead to either particle enlargement or toughening. Possible effects of rheological factors, extent of interchange reactions, interfacial tension and end-group contents are discussed.

Zoning and genesis of the Darwin Pb-Zn-Ag skarn deposit, California; a reinterpretation based on new data

The > 1-million-metric-ton Darwin Pb-Zn-Ag-W skarn deposit has been previously described as a group of sulfide replacement bodies zoned away from the Darwin quartz monzonite pluton and formed from magmatic fluids at 325oC. Detailed surface mapping and available radiometric data, however, indicate that the Pb-Zn skarn sulfide bodies are appreciably (>20 Ma) younger than the Darwin pluton, and underground mapping and core logging indicate there are several skarn sulfide pipes with strong concentric zoning. One of the pipes is zoned around a deep granite porphyry plug. The pipes exhibit outward zoning in wt percent Pb/Zn and oz/ton Ag/wt percent Pb (both ratios 1.0 margin). The pipes show mineralogical zoning, with a core defined by higher sphalerite-galena, higher chalcopyrite, darker sphalerite, more abundant pyrite inclusions in sphalerite, and evidence for multiple sulfide depositional events. In contrast, both graphite in marble and pyrrhotite in sulfide ores are zoned around the Darwin pluton, which suggests that pyrrhotite stability is influenced by prePb-Zn skarn (Darwin pluton related?) bleaching of marble beds. Garnet zoning is highly complex, with four generations identified by petrographic and compositional relations; younger garnet types are more abundant in upper and lateral parts of the pipe. Retrograde alteration of garnet is concentrated in the upper and laterally distal parts of the skarn, but garnet in apparent equilibrium with sulfide is present throughout the vertical extent of skarn. Systematic mineral compositional patterns include outward increase in hedenbergite + johannsenite components in clinopyroxene ( 20 outward), increase in Sb -I- Bi contents of galena, initial increase followed by decrease in Mn contents of sphalerite (range from 1% Mn), and an initial increase followed by outward variable increase and decrease in FeS contents of sphalerite (range of 20% FeS). Previously published sulfur isotope data are compatible with a decrease in sulfur isotope ratios outward around the pipe core. Published isotopic data combined with temperature estimates from phase homogenization and arsenopyrite-sphalerite geothermometry show a systematic decrease in temperature from the skarn sulfide pipe center (>425oC) to the margin (<300oC). Comparison of stope maps to isotherm cross sections indicates that the bulk of mined sulfides were from areas surrounding the pipe core, in which temperatures declined from approximately 375 o to 300oC (gradient of loC/m). Combined mineral composition and assemblage and sulfur isotope systematics indicate that as the ore fluids flowed outward they underwent progressive decrease in oxidation state (''1 log unit) and increase in pH (2-3 units); upwardmoving fluids underwent initial decrease in oxidation state and increase in pH followed by a reversal to higher oxidation state and lower pH. The process of ore deposition was chemically complex and may have involved remobilization of earlier deposited sulfides. Realistic ore depositional models at Darwin require simultaneous changes in (at least) temperature, pH, and oxidation state.

Phase homogenization of mixtures of poly( m-xylene adipamide) and nylon 6 by interchange reactions

Melt blends of poly( m-xylene adipamide) and nylon 6 prepared by extrusion at 260°C have two glass transitions and are opaque, whereas similar preparation at 290°C yields transparent melts and materials with a single glass transition. This phase homogenization has been shown by thermal, dynamic mechanical, and nuclear magnetic resonance analyses to be the result of interchange reactions. A single phase develops after as few as five interchange reactions per molecule. This segmented block structure explains the high level of crystallinity that is retained after phase homogenization. Such behaviour is possible when the unreacted components have an unfavourable but small interaction energy density, i.e. near miscibility, as argued using thermodynamic theories. Retention of crystallinity is useful for certain property considerations.

Fluid inclusion study of greisens associated with the Nicholson Granite Complex, Murphy Inlier, Northern Territory

The Early Proterozoic Nicholson Granite Complex contains Sn‐W‐bearing quartz‐muscovite greisens as irregular pods and as tabular veins with both interstitial and vug‐filled cassiterite and minor wolframite. Within the greisens, alteration to muscovite varies with the intensity of alteration from iron‐poor non‐pleochroic through iron‐rich pleochroic to iron‐bearing pleochroic fibrous varieties. Because of accompanying silicification, a typical greisen contains about 20% muscovite and 75% quartz; other minerals include pyrite, chalcopyrite, hematite, fluorite, topaz and phlogopite. Six kinds of fluid inclusions are present in vein quartz within the greisens: Type A (liquid + <10% vapour); Type B (liquid + 10–30% vapour); Type C (vapour only or liquid + >80% vapour); Type D (liquid + halite + <10% vapour); Type E (liquid + halite) and Type F (liquid only). Early ‘primary’ inclusions represented by Types B and C have higher temperatures (range: 190–400°C, mean = 300°C) and lower salinities (range: 0.3–12 wt% eq. NaCl, mean=6 wt% eq. NaCl) than the late pseudosecondary inclusions represented by Types A, D and E (temperature range: 90–330°C, average 165°C, salinity range: 0.5–40 wt% eq. NaCl, mean = 24 wt% eq. NaCl). Co‐existing vapour and liquid + vapour inclusions in most samples indicate that solutions were boiling, which is substantiated by vapour phase homogenization of many inclusions. The late high salinity‐low temperature fluids were probably caused by extensive boiling. In the early high temperature‐low salinity fluids, tin was predominantly transported as a stannous hydroxide complex and precipitation caused by an increase in oxidation and decrease in temperature, both of which are attributed to boiling. The late low temperature‐high salinity fluids carried tin predominantly as stannic hydroxide and precipitation was essentially due to lowering temperature. Comparisons with other tin‐bearing granites suggest a crustal source for the Nicholson Granite Complex and associated tin greisens.

Microstructure of Pb-modified Bi-Ca-Sr-Cu-O superconductor

The microstructure of samples with and without Pb addition has been characterized by transmission electron microscopy. An amorphous Pb-rich grain boundary phase has been found in Pb-doped samples. It is suggested that a Pb-rich liquid phase assists sintering and homogenization of the composition of the superconducting phase to attain the higher zero Tc. In both samples, Ca replacement by Bi has been found. The implications of such a replacement are briefly discussed.

Role of current oscillations in ac-dc interference effects inNbSe3

We investigate the relation between rf-induced Shapiro steps and current oscillations in the charge-density-wave (CDW) state of ${\mathrm{NbSe}}_{3}$. The Shapiro step magnitude is independent of the oscillation amplitude, and a rich spectrum of harmonic and subharmonic steps is observed. These results provide evidence for phase homogenization or excitation of internal modes of the CDW condensate.

Scattering of visible light by glasses undergoing phase separation and homogenization

A kinematic theory of light scattering and modern concepts of phase-separation theory were used to examine the most typical experimental results obtained from the study of light scattering by glasses. The examination was made by taking into account the positions of figurative points in the immiscibility diagram. It has been shown that the anomalous phenomena (the predominant light scattering into the backward semi-sphere and the spectral dependence of intensity of type λ ⇔ p , where p > 4) arise in four cases: at the stage of decomposition when the figurative point lies in both the binodal and spinodal regions; after the completion of the decomposition stage when interparticle interference is essential; and in the one-phase region when the concentration fluctuations tend to a higher equilibrium level of development. In each case these phenomena are due to the sign-changed behavior of the dielectric constant and to the existence of a range of negative values in the correlation function. The processes of complete or partial homogenization of the glass are characterized by either the gradual disappearance of anomalous phenomena or the appearance of normal scattering due to the increase in space extension of the inhomogeneity regions at their dissolution.