Interfacial melting

We have surveyed the most recent progress and presented a new molecular level understanding of melt flow instabilities and wall slip. This article can at best be regarded as a partial review because it advocates the molecular pictures emerging from our own work over the past few years [27-29,57,62,69]. Several results from many previous and current workers have been discussed to help illustrate, formulate and verify our own viewpoints. In our opinion, the emerging explicit molecular mechanisms have for the first time provided a unified and satisfactory understanding of the two major classes of interfacial melt flow instability phenomena (a) sharkskin-like extrudate distortion and (b) stick-slip (flow discontinuity) transition and oscillating flow. 

Previous studies about dynamics of water near interfaces by quasi-elastic neutron scattering involved measurements of the mobility of water on the surface of Nafion membranes [63,64], the diffusive motions and the density of states of water in silica gels [65], and the interfacial melting of ice in graphite and talc pow-... 

The review by Dash et al. also discusses interfacial melting of ice in contact with other substances and the many environmental consequences of ice premelting, including frost action and thunderstorms. 

Several surface-specific structural phase transitions are observed in ice. We will focus here on complementary aspects of the basic phenomena of interfacial melting, surface roughening, and molecular kinetics and their application to the equilibrium and growth structures of ice crystals. A central issue is how the interfacial structure at ice/vapor, ice/gaseous-atmosphere and ice/water interfaces influences the adsorption potential, the growth shapes and surface transport properties. The environmental relevance concerns die fact that ice dominates the crystal growth phenomena we observe... 

As discussed in section 2.3, both surface melting and interfacial melting are treated as wetting phenomena at the interface between a solid and its vapor phase, or a wall of a different material, at temperatures below the bulk freezing point Tm- The melting... 

The experiment clearly demonstrates the phenomenon of interfacial melting, the viscous nature of the premelted liquid and its dynamical consequences. Initially the observed relative lack of membrane deformation at lower temperatures was thought to be due to an abrupt jump to 0. Such an interpretation is consistent with an interfacial free energy that decreases monotonically with d at long range, but which possesses a local minimum at shorter range. The theory has allowed us to show that the... 

Interlayer adhesion between a polycarbonate (PC) layer and a PC-ABS blend layer, in 3-layer films made by melt coextrusion in a multi-manifold die, was analyzed using nonlinear viscoelastic (NLVE) die-flow simulations with POLYFLOW. These simulations showed significant extensional stresses in the interface vicinity where the two melt layers come into contact for the first time. A Viscosity Normalized Nonlinearity Ratio parameter was defined to correlate the simulated interfacial melt stresses and the observed adhesion behavior. Larger deviation of this parameter from a value of 1.0 (large disparities in melt extensional configuration across the interface) corresponded to poorer observed peel strength. 

Molten naphthalene at its melting point of 82°C has the same density as does water at this temperature. Suggest two methods that might be used to determine the naphthalene-water interfacial tension. Discuss your suggestions sufficiently to show that the methods will be reasonably easy to cany out and should give results good to 1% or better. 

Neumann and co-workers have used the term engulfrnent to describe what can happen when a foreign particle is overtaken by an advancing interface such as that between a freezing solid and its melt. This effect arises in floatation processes described in Section Xni-4A. Experiments studying engulfrnent have been useful to test semiempirical theories for interfacial tensions [25-27] and have been used to estimate the surface tension of cells [28] and the interfacial tension between ice and water [29]. 

Many of the fiindamental physical and chemical processes at surfaces and interfaces occur on extremely fast time scales. For example, atomic and molecular motions take place on time scales as short as 100 fs, while surface electronic states may have lifetimes as short as 10 fs. With the dramatic recent advances in laser tecluiology, however, such time scales have become increasingly accessible. Surface nonlinear optics provides an attractive approach to capture such events directly in the time domain. Some examples of application of the method include probing the dynamics of melting on the time scale of phonon vibrations [82], photoisomerization of molecules [88], molecular dynamics of adsorbates [89, 90], interfacial solvent dynamics [91], transient band-flattening in semiconductors [92] and laser-induced desorption [93]. A review article discussing such time-resolved studies in metals can be found in... 

Acid chlorides are generally more reactive than the parent acids, so polyester formation via reaction 5 in Table 5.3 can be carried out in solution and at lower temperatures, in contrast with the bulk reactions of the melt as described above. Again, the by-product molecules must be eliminated either by distillation or precipitation. The method of interfacial condensation, described in the next section, can be applied to this type of reaction. 

Most elastomers that are used for nylon modification contain a small amount of maleic anhydride (0.3 to 2%). In the melt blending process, these elastomers react with the primary amine end groups in nylon, giving rise to nylon grafted elastomers. These grafts reduce the interfacial tension between the phases and provide steric stabili2ation for the dispersed mbber phase. Typically, thermally stable, saturated mbbers such as EPR, EPDM, and styrene—ethylene/butylene—styrene (SEBS) are used. 

Bisphenol A Polycarbonate Resins. These resins are manufactured by interfacial polymerization (84,85). A small amount of resin is produced by melt-polymerization of bisphenol with diphenyl carbonate in Russia and the People s RepubHc of China. Melt technology continues to be developmental in Japan and the West, but no commercial activities have started-up to date, although some were active in the late 1960s. No reports of solvent-based PC manufacture have been received. 

Polyphosphonates are well-known flame-retardant materials [110] and are generally prepared by melt [111,112], interfacial [113-115] and solution polycondensation methods [116]. A typical example of synthesis is the polycondensation of bifunctional organophosphorus compounds, such as dichlorophenylphosphine oxide, with bisphenols [117,118]. 

Polyphosphates are also an important class of organophosphorus polymers. In addition to their flame-retardant characteristics, they possess attractive plasticizing properties and can be used as polymeric additives to other polymers [123-128]. In general, polyphosphates can be prepared by interfacial [119,129], melt [130], or solution polycondensation [131,132a,b]. Kricheldorf and Koziel [133] prepared polyphosphates from silylated bisphenols. 

TPEs from blends of rubber and plastics constitute an important category of TPEs. These can be prepared either by the melt mixing of plastics and rubbers in an internal mixer or by solvent casting from a suitable solvent. The commonly used plastics and rubbers include polypropylene (PP), polyethylene (PE), polystyrene (PS), nylon, ethylene propylene diene monomer rubber (EPDM), natural rubber (NR), butyl rubber, nitrile rubber, etc. TPEs from blends of rubbers and plastics have certain typical advantages over the other TPEs. In this case, the required properties can easily be achieved by the proper selection of rubbers and plastics and by the proper change in their ratios. The overall performance of the resultant TPEs can be improved by changing the phase structure and crystallinity of plastics and also by the proper incorporation of suitable fillers, crosslinkers, and interfacial agents. 

The graft polymer formed during melt mixing results in good interfacial adhesion between the phases. The... 

Fig. 2 Segregation of Cu and Mg at the SiC-series 2000 Al interface. The melting point of the interfacial region is expected to be reduced as a result of such segregation (data from Ref. [7]).

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