Polymer-blend thin films phase-separation process

In the last decade, there has been great interest in the imdeistanding of the phase-separation process in the production of the thin films of immiscible polymer blends. This curiosity is as a direct consequence of the particular surface structures found in polymer blends that will define their final surface properties. Due to the extensive literature concerning both theoretical [9,17-21], and experimental [22] studies this part will be limited in order to briefly present the main concepts on polymer blends thin films. 

Phase separation of polymer blends and block copolymers. Confining polymer blends and block copolymers between surfaces may influence the phase separation process, as a consequence of the preferential affinity of one of the components for the interface. Since the pioneer works of Reich and Cohen [26] and later by Nesterov et al. [27], Ball and Essery [28], and Jones [29] amongst others much work has been done to understand the mechanisms of phase separation in polymer thin films. The presence of substrate-film and/or film-air interfaces introduces an additional complexity compared to bulk phase separation processes [30-35]. Complex structures can be produced by slight differences on parameters... 

When polymers undergo phase separation in thin films, the kinetic and thermodynamic effects are expected to be pronounced. The phase separation process can be controlled to effect desired morphologies. Under suitable conditions a film deposition process can lead to pattern replication. Demixing of polymer blends can lead to structure formation. The phase separation process can be characterized by the binodal and spinodal curves. UCST is the upper critical solution temperature, which is the temperature above which the blend constituents are completely miscible in each other in all proportions. LUST behavior is not found as often in systems other than among polymers. LUST is the lower critical solution temperature. This is the... 

Phase separation can emerge spontaneously in thin films of polymer blend, and it is this thermodynamically driven phase-separation process that produces the patterning of thin polymer blend films. It can be induced by several parameters, each with critical values, including (i) the ratio between the components [10,22] (ii) the demixing temperature [12] and (iii) the chemical nature of the solvent. 

As discussed in Section 2.23.1.2, one of the advantages of AFM over electron miaoscopy is that it enables 3D imaging of untreated samples in a physically relevant environment. Given the surface nature of the technique, initial AFM studies of phase separation processes in polymer mixtures have been primarily focused on thin or ultrathin films. " " The confinement in a film and component segregation to the interfaces have been shown to have a profound effect in both spinodal decomposition, and nucleation and growth processes of the phase separation. The spectrum of AFM applications has been extended to bulk phase separation of polymer mixtures using conventional and oblique microtoming of polymer blend films. 

In addition to particle breakup, the coalescence process may be affected as well. It has been speculated that exfoliated clay platelets or well-dispersed nanoparticles may hinder particle coalescence by acting as physical barriers [19,22]. Furthermore, it has been suggested that an immobilized layer, consisting of the inorganic nanoparticles and bound polymer, forms around the droplets of the dispersed phase [50]. The reduced mobility of the confined polymer chains that are bound to the fillers likely causes a decrease in the drainage rate of the thin film separating two droplets [44]. If this is the case, this phenomenon should be dependent on filler concentration this is shown in Figure 2.8, which shows the effect of nanoclay fillers on the dispersed particle size of a 70/30 maleated EPR/PP blend [19]. 

The properties of the external surface can significantly alter phase separation in a thin polymer film. In extensive experimental investigations of the phase separation of polymer blends directed by patterned substrates [1,56,58,60,80-88] it was observed that the domain size evolved in a power law relation with time. The composition wave was normal to, and propagates inward from, the functionalized substrate. Likewise, processing parameters such as pattern size in the substrate were seen to affect refinement of the morphology. 

Much of the preceding discussion has included semicrystalline thermoplastics and blends that were used as examples for discussions of structure and process. A brief literature review of impact modified thermoplastics follows. Reich and Cohen [339] studied the phase separation of polymer blends in thin films and compared... 

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