Interphase interdiffusion

Fig. 7. Different types of interphases. (a) Contact interphases, as produced for example by transcrystalline growth or enhanced adlayer crosslinking in the adhesive phase, (b) Diffusion interphases, as produced by interdigitation or interdiffusion of chains from either or both phases.

The volume of substance in a composite material that exists in a nonequilibrium state due to its proximity to an interface has been termed an interphase [1]. The interphase is a zone of distinct composition and properties formed by chemical or physical processes such as interdiffusion of mutually soluble components or chemical interaction between reactive species. 

Diffusion theory involves the interdiffusion of macromolecules between the adhesive and the substrate across the interface. The original interface becomes an interphase composed of mixtures of the two polymer materials. The chemical composition of the interphase becomes complex due to the development of concentration gradients. Such a macromolecular interdiffusion process is only... 

The adhesion promotion of an organic matrix to an inorganic substrate using a silane has been studied to model the structure of the created interphase [64-66]. The polymer/silane interphase is influenced by the solubility parameter of both the silane coupling agent and the polymer. More interdiffusion occurs when the solubility parameters of the polymer and the silane closely match together. It is believed that this model can be applied to silicone adhesive/solid substrate system. 

When the top coat-coupling agent interphase is formed, some interdiffusion may occur, permitting reaction with functional groups oriented towards the bulk. The reaction is more probable, however, if a significant concentration of reactive groups is present on the surface. 

Hoh et al. [4] used differential scanning calorimetry (DSC), FT-IR, and solid-state 13C-NMR to gain information about the epoxy/silane resin interphase. They used FT-IR to correlate the extent of reaction with the extent of interdiffusion as in the above studies. For both NMR and DSC studies, bulk models were used to study the molecular mobility of interfacial components. 

The characterizations discussed thus far do not involve direct investigation of the actual interphase region although failed surfaces have been analyzed to give indirect evidence for interdiffusion. In other studies, assumptions that the observed properties (extent of reaction, increased solvent resistance, molecular mobility) correlate with the extent of interdiffusion have been made. 

However, the chemical bonding theory cannot account for the increase in adhesion experienced between non-reactive matrices such as polyolefins and inorganic reinforcements in which chemical bonds will not be formed [4], This observation, among others, leads to an alternative proposal that an interphase composed of various constituents forms surrounding the reinforcement. This third phase in the composite is possibly formed through interdiffusion of physisorbed silane and matrix molecules in the interphase and perhaps via preferential adsorption of both matrix components as well as silane coupling agents on the reinforcement surface [5],... 

Another theoretical aspect of adhesion can be optimized with surface treatment. The interdiffusion theory described by Voyutski [6] involves the diffusion of macromolecular chains across a polymer interface. In this case the interface is transformed progressively to a wide interphase. Welding of composites is then the main technique that can enhance this particular aspect. This welding can be performed with ultrasonic, electric induction, or resistance techniques [7]. 

The volume fraction of the interphase layer, (ptp, was estimated in two ways. First, from the DSC data, the fractional interdiffused mass of each component was determined from the fractional decreases in the magnitudes of the corresponding Tg transitions. It was then assumed that the interphase mass fraction and interphase volume fraction are identical (since the densities of each component are similar). Knowing the size of the dispersed phase particles, the interphase thickness can then be calculated. Second, using the PALS data, (pip was estimated independently as follows First, the o-Ps intensity of the fully demixed system can be calculated as... 

Composition profiles generated by interdiffusion in the concentrated regime between polyphenylene oxide-polystyrene blend pairs were experimentally determined by two techniques. Three-point bending moment measurements over a convenient temperature range (dynamic mechanical analysis (DMA)) were used to determine interphase composition profiles. Confocal micro-Raman spectroscopy was also used to measure local compositions along a direction which was perpendicular to the original interface. The study included some limiting cases to test accuracy, precision and flexibility of the DMA method. 4 refs. 

This theory suggests that adhesion is developed through the interdiffusion of molecules in between the adhesive and the adherend. The diffusion theory is primarily applicable when both the adhesive and the adherend are polymers with relatively long-chain molecules capable of movement. The nature of materials and bonding conditions will influence whether and to what extent diffusion takes place. The diffuse interfacial (interphase) layer typically has a thickness in the range of 10-1,000 A (1-100 nm). Solvent cementing or heat welding of thermoplastics is considered to be due to diffusion of molecules. ... 

Interphase Third phase in binary polymer alloys, enhanced by interdiffusion or compatibilization. Thickness of this layer varies with the blend components and compatibilization method from 2 to 60 nm... 

Interphase a nominal third phase in binary polymer alloys, engendered by interdiffusion or compatibilization at the interfaces between the two polymer domains. The interphase thickness A/ varies between 1 and 60 nm depending on polymers miscibility and compatibilization Compatibilization process of modification of the interphase in immiscible polymer blends, resulting in reduction of the interfacial energy, development, and stabilization of a desired morphology, leading to the creation of a polymer alloy with enhanced performance ... 

The material parameter 0 in Eq. 7.124 governs the NDB behavior. It was shown that its value is inversely proportional to the thickness of the interphase, Al, and its viscosity, rii terphase (Bousmina et al. 1999). Theoretically, the same molecular mechanism should be responsible for both factors, viz., better miscibility, better interdiffusion, thus higher Al and tiimerphase- However, the low molecular weight components of the blend, that are forced by the thermodynamics to diffuse to the interphase, may not change much the former parameter, but drastically reduce the latter. For immiscible blends, Al is small, typically 2-6 nm. Thus 0 is large, and interlayer slip takes place. For compatibUized blends, the macromolecules of the two phases interact and interlace, which increases both factors thus, the slip effects are negligible. Measured or calculated values of the interphase viscosity are listed in Table 7.10. 

The compatibilizer may not be directly involved in improving interphase bonding, but rather cause the molecules of each phase to interdiffuse more... 

The temperatures shown in Figure 2.5b are significantly above the glass transition temperatures of polystyrene, 100°C, and poly(methyl methacrylate), 106°C, so polymer chain motion, reptation, and interdiffusion take place. However, polystyrene and poly(methyl methacrylate) are immiscible, inter-diffusing only 20 to 50 A, as determined via neutron reflection techniques (21-23) see Section 12.3.7.Theoretical calculations (see Section 12.3.7.2) yield an interphase thickness of 27 A (3). 

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