Spinodal decomposition phenomena

For spin-coated ultrathin films, nucleation occurs by a spinodal decomposition phenomena or by airborne particles falling on the surface of the film. Spinodal decomposition proceeds by amplification of surface disturbances on the free surface of the film due to thermal fluctuations or mechanical vibrations. Conjoining forces overwhelm the tendency for surface tension to level the film, thus driving the growth of the surface modulations until they reach the substrate to nucleate a hole. 

Polymer Blends and Phase Separation the spinodal decomposition phenomena d(J / Ct... 

Fig. 42. (a c) The anomalous peak effect on the magnetization curves of Nsingle crystals subjected to different post-growth heat-treatment, and (d) its possible relationship with a spinodal decomposition phenomenon (M. Nakamura et al. 1996d). values in all cases were measured to be high (about 95 K). 

Polymer-polymer systems exhibit phase behavior similar to other mixtures, such that an initially uniform system separates into two or more phases as a result of small change in thermodynamic variable. Two mechanisms can be envisioned to explain this phenomenon nucleation and growth (NG), and spinodal decomposition (SD). 

In Fig. 1.14, the dotted lines for each curve show the activity of the coexisting phases at chemical equilibrium. Similarly in Fig. 1.16 the dotted line BDF shows the activity of the coexisting phases (5 = 0.185 and 0.815). The coexisting phases, which have the same structure, differ in the concentration of vacancies. This phenomenon is generally called phase separation or spinodal decomposition (it is observed not only in the solid phases but also in the liquid phases), and originates from the sign of the interaction energy... 

Immiscibility of polymers in the melt is a common phenomenon, typically leading to a two-phase random morphology. If the phase separation occurs by a spinodal decomposition process, it is possible to control the kinetics in a manner that leads to multiphase polymeric materials with a variety of co-continuous structures. Common morphologies of polymer blends include droplet, fiber, lamellar (layered) and co-continuous microstructures. The distinguishing feature of co-continuous morphologies is the mutual interpenetration of the two phases and an image analysis technique using TEM has been described for co-continuous evaluation.25... 

Now, we turn our attention to late stages of spinodal decomposition. Since the phase separation in binary mixture is intrinsically a nonlinear phenomenon, a number of nonlinear theories have been put forward on the basis of statistical consideration, notably the LBM (Danger, Baron k Miller) (H) and BS (Binder k Stauffer) (12) theories. Both theories predicted the power law scheme rather than the exponential growth of the structure... 

We observed that the phase separation in the 107. aqueous UPC solutions is the spinodal decomposition. The linearized theory of Cahn-Hilliard predicts many of the qualitative features of the SD in the present system, but is not adequate in the quantitative comparison. The phenomenon of SD is non-linear in nature dominated by the late stage of SD. The growth mechanism has been identified to be the coarsening process driven by surface tension. The kinetics of phase separation at the 107. aqueous HPC resembles the behavior of off-critical mixtures. 

Another peculiar phenomenon is double phase separation in which each of the two phases formed during spinodal decomposition of a mixture of A and B becomes unstable to a second phase separation, in which droplets of B-rich phase appear in the A-rich domain and droplets of A-rich phase appear within the B-rich domains (Tanaka 1994b). This phenomenon is thought to occur when the capillary coarsening process (in which the domain size grows as a oc t) outruns the diffusion process and the A-rich domains are left with a small excess concentration of B over that allowed at bulk equilibrium. This excess of B cannot diffuse to the interface with the A-rich phase as fast as that interface moves away by capillary coarsening. The excess B therefore nucleates into droplets of B-rich phase within the coarsened A domains. The converse occurs in the A-rich domains. 

Surface-directed spinodal decomposition was first observed in an isotopic polymer blend (Jones et al. 1991) thin films of a mixture of poly(ethylene-propylene) and its deuterated analogue were annealed below the upper critical solution temperature and the depth profiles measured using forward recoil spectrometry, to reveal oscillatory profiles similar to those sketched in figure 5.30. Similar results have now been obtained for a number of other polymer blends, including polystyrene with partially brominated polyst)u-ene (Bruder and Brenn 1992), polystyrene with poly(a-methyl styrene) (Geoghegan et al. 1995) and polystyrene with tetramethylbisphenol-A polycarbonate (Kim et al. 1994), suggesting that the phenomenon is rather general. 

Time evolution of phase-separating morphology (or concentration fluctuations, in general) in binary mixtures has been extensively studied as a research theme on nonlinear and nonequilibrium phenomenon in various fields of science [1]. Especially, a lot of work has been devoted to the spinodal decomposition process (SD) [2], a phase-separation process for the mixtures with thermodynamic instability. Experimental studies, especially time-resolved... 

Our results suggest that the above dynamics can be viewed as an evolution in a stochastic potential whose qualitative aspect depends on time at the beginning it is similar to the deterministic potential, but subsequently it deforms (the deformation depending on the volume and initial conditions) and develops a second minimum. This minimum is responsible for the transient "stabilization" of the maximum of P(X,t) before the inflexion point. As the tunneling towards the other minimum on the stable attractor goes on, the first minimum disapears and the asymptotic form of the stochastic potential, determining the stationary properties of P(X,t), reduces again to the deterministic one. This phenomenon of "phase transition in time" is somewhat reminiscent of spinodal decomposition. 

The second group of interactions affecting diffusion involves solute olvent interactions. In Section 6.3, we explore the extremely large solute-solvent interactions which occur near the spinodal limit, where phase separation is incipient. Diffusion in these regions leads to the phenomenon of spinodal decomposition, which is also discussed in Section 6.3. 

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