Polymer blends interface

Cho D et al. (2000) Segregation dynamics of block copolymers to immiscible polymer blend interfaces. Macromolecules 33( 14) 5245—5251... 

M. Sprenger, S. Walheim, A. Budkowski, U. Steiner, Hierarchic structure formation in binary and ternary polymer blends. Interface Science 11 (2(X)3) 225-235. 

One approach to obtain the energy to break single chains involves placing them across a polymer blend interface. Polymer interfaces between two polymers, however well annealed, are often weak see Chapter 12. One way to strengthen an interface is to put small quantities of block copolymers at the interface. Usually the two blocks are identical to or at least soluble in their... 

Helfand and Tagami (10) derived thermodynamically based equations for the interfacial tension at a polymer blend interface. 

Figure 12.18 The density profile of a polymer blend interface goes through a minimum if the polymers are immiscible. The quantity is a function of the compressibility.

Rgure 12.35 (1) summarizes the state of the art of polymeric and multi-component polymer materials from the point of view of the role of surfaces and interfaces. The three main types of surfaces and interfaces are (a) free surfaces, (b) polymer blend interfaces, and (c) polymer composite interfaces. While the dilute solution-colloid interfaces are noifree in the ordinary sense, the fluid phase exhibits a low viscosity allowing rapid diffusion similar in some ways to the free air surface, and is classified as such for the present purposes. The concepts of polymer blends and composites will be further developed in Chapter 13. 

There are specific structural and spatial problems in whieh Raman spectroscopy plays a dominant and important role based on higher sensitivity (due to resonance enhancement) and higher spatial resolution than FTIR. Specifically, micro-Raman spectroscopy has been applied in the analysis of (glass) fibres and their surface treatments, fibre composites, multilayer plastic films, foils and coatings, polymer blends, interfaces in eomposites, contaminant and paints/pigments [488]. 

Hu et al. [48] studied the addition of PS-h-PDMS diblock copolymer to the PS/PDMS blend. A maximum interfacial tension reduction of 82% was achieved at a critical concentration of 0.002% diblock added to the PDMS phase. At a fixed PS homopolymer molecular weight, the reduction in interfacial tension increases with increasing the molecular weight of PDMS homopolymer. Moreover, the degree of interfacial tension reduction was found to depend on the homopolymer the diblock is mixed with when the copolymer was mixed into the PS phase, the interfacial tension reduction was much less than that when the copolymer was blended into the PDMS phase. This behavior suggested that the polymer blend interface may act as a kinetic trap that limits the attainment of global equilibrium in these systems. 

The concept of co-continuous polymer blends with carbon black preferentially located in one of the continuous polymer phases or at the polymer-blend interface has been studied for more than a decade with an aim to reduce the percolation threshold. Examples of this kind are the work by Geuskens et al. in as early as 1987 [31], which shows that for the same carbon loading, the resistivity of the co-continuous polymer/rubber blends is several orders of magnitude smaller than that of the single polymer/carbon black composites. Recent works on polymer/elastomer combinations [32,33] and on polymer/polymer systems [34- 1] have also shown that the... 

The last part of this chapter briefly deals with the general aspects of polymer blend interface and its characterization. 

Copolymers as Emulsifying Agents in Polymer Blends 4.1 Copolymer Localization at the Polymer Blend Interface... 

Figure B3.6.2. Local mterface position in a binary polymer blend. After averaging the interfacial profile over small lateral patches, the interface can be described by a single-valued function u r. (Monge representation). Thennal fluctuations of the local interface position are clearly visible. From Wemer et al [49].

Inoue, T. and Marechal, P. (1997) Reactive processing of polymer blends polymer-polymer interface aspects, in Processing of Polymers, ed. Meijer, H.F..H. Materials. Science and Technology, A Comprehensive Treatment, eds. Cahn, R.W., Haasen, P. and Kramer, E.J. (VCH, Weinheim) p. 429. 

Characterization and control of interfaces in the incompatible polymer blends were reported by Fayt et al. [23]. They used techniques such as electron microscopy, thermal transition analysis, and nonradiative energy transfer (NRET), etc. They have illustrated the exciting potentialities offered by diblock copolymers in high-performance polymer blends. 

Fig. la —c. Schematic drawing of some specific examples of polymer molecules at an interface (a) the free surface of a homopolymer, (b) the surface enrichment of one component in a miscible polymer blend, and (c) the interface between polymers of different molecular weight and/or chemical composition... 

Thus, for the investigation of buried polymer interfaces, several techniques with molecular resolution are also available. Recently NMR spin diffusion experiments [92] have also been applied to the analysis of a transition zone in polymer blends or crystals and even the diffusion and mobility of chains within this layer may be analyzed. There are still several other techniques used, such as radioactive tracer detection, forced Rayleigh scattering or fluorescence quenching, which also yield valuable information on specific aspects of buried interfaces. They all depend very critically on sample preparation and quality, and we will discuss this important aspect in the next section. 

When dealing with polymer blends or blockcopolymers, surface enrichment or microstructures may be observed as already discussed in Sect. 3.1. Quite similar effects may be expected for buried interfaces e.g. between polymer and substrate where one component may be preferentially enriched. In a system of PS, PVP and diblock copolymer PS-6-PVP it has been shown by FRS that the copolymer enrichment is strongly concentration dependent [158]. In a mixed film of PS(D) and end-functionalized PS on a silicon wafer the end-functionalized chains will be attached to the silicon interface and can be detected by NR [159],... 

Usually polymeric substances of appropriate chemical structure and morphology which promote the miscibility of incompatible materials. Block copolymers are especially useful surfactants at the polymer/polymer interface because the two blocks can be made up from molecules of the individual polymers to be mixed. Typical compatibilisers in polymer blends are LDPE-g-PS in PE/PS CPE in PE/PVC acrylic- -PE, -PP, -EPDM in polyolefin/PA and maleic-g-PE, -PP, -EPDM, -SEBS in polyolefin/polyesters. 

The data of Zink et al. (1998) illustrate the measurement by NRA of near-surface composition profiles in isotopically labelled polymer blends. If a mixture of polymers is adjacent to a phase interface (e.g. a solid or an air surface), often one of the components is preferentially attracted to the surface and will segregate to it, and this phenomenon will influence the tribological behaviour the interface (lubrication, wear and adhesion). 

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