Multiphase immiscible polymer blends

Scanning electron microscopy (SEM) is one of the very useful microscopic methods for the morphological and structural analysis of materials. Larena et al. classified nanopolymers into three groups (1) self-assembled nanostructures (lamellar, lamellar-within-spherical, lamellar-within-cylinder, lamellar-within-lamellar, cylinder within-lamellar, spherical-within-lamellar, and colloidal particles with block copolymers), (2) non-self-assembled nanostructures (dendrimers, hyperbranched polymers, polymer brushes, nanofibers, nanotubes, nanoparticles, nanospheres, nanocapsules, porous materials, and nano-objects), and (3) number of nanoscale dimensions [uD 1 nD (thin films), 2 nD (nanofibers, nanotubes, nanostructures on polymeric surfaces), and 3 nD (nanospheres, nanocapsules, dendrimers, hyperbranched polymers, self-assembled structures, porous materials, nano-objects)] [153]. Most of the polymer blends are immiscible, thermodynamically incompatible, and exhibit multiphase structures depending on the composition and viscosity ratio. They have two types of phase morphology sea-island structure (one phase are dispersed in the matrix in the form of isolated droplets, rods, or platelets) and co-continuous structure (usually formed in dual blends). 

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... 

The reported examples convincingly support that using a purposely tailored diblock copolymer is a powerful tool of generating new, or at least improved, multiphase polymeric materials. Quite interestingly, the interfacial activity of diblock copolymers is not exclusively confined to immiscible polymer blends but it can be fruitfully extended to dispersions of fine solid particles in either a liquid phase or a polymeric matrix, as illustrated hereafter. 

Although immiscible polymer blends and ionomers share a common feature in that both exhibit more than a single phase, a major difference between the two systems involves the dispersed phase size. For blends, this is generally of the order of micrometers and may be detected optically. Ionomers, however, are microphase-separated with domain sizes of the order of nanometers. Thus, blends and ionomers represent two extremes of the subject of multiphase polymers. In this book, the reader will observe similarities as well as differences in the problems... 

The properties of block copolymers, on the other hand, cannot be calculated without additional information concerning the block sizes, and whether or not the different blocks aggregate into domains. The results of calculations using the methods developed in this book can be inserted as input parameters into models for the thermoelastic and transport properties of multiphase polymeric systems such as blends and block copolymers of immiscible polymers, semicrystalline polymers, and polymers containing various types of fillers. A review of the morphologies and properties of multiphase materials, and of some composite models which we have found to be useful in such applications, will be postponed to Chapter 19 and Chapter 20, where the most likely future directions for research on such materials will also be pointed out. 

The Chow equations, which constitute a large set that is too long and complex to reproduce here, are sometimes more accurate. Both of these sets of general-purpose equations (Halpin-Tsai and Chow) are applicable to many types of multiphase systems including composites, blends, immiscible block copolymers, and semicrystalline polymers. Their application to such systems requires the morphology to be described adequately and reasonable values to be available as input parameters for the relevant material properties of the individual phases. 

The rheology of pol5rmer blends is discussed in detail in Chap. 7, Rheology of Pol5rmer Alloys and Blends . Here only an outline will be given. Since the flow of blends is complex, it is useful to refer to a simpler system, e.g., for miscible blends to solutions or a mixture of polymer fractions, for immiscible blends to suspensions or emulsions, and to compatibihzed blends to block copolymers (Utracki 1995 Utracki 2011). It is important to remember that the flow behavior of a multiphase system should be determined at a constant stress, not at a constant deformation rate. 

Interfacial polarization or MaxwelVWagner/SUlars (MWS) polarization (Wagner 1914 SUlars 1937) is a phenomenon that is characteristic for phase-separated or multiphase systems like immiscible polymer blends. Precondition for the observation of a MWS polarization is that the different phases have nonidentical properties. As a result of this, for instance, accumulation of charges takes place at the interfaces of the different phases. Steeman and van Tumhout (2003) published a compilation concerning polymeric materials including polymer blends. 

Block polymers and polymer blends deserve now a great intere because of their multiphase character and their related properties. The thermodynamic immiscibility of the polymeric partners gives rise indeed to a phase separation, the extent of which controls the detailed morphology of the solid and ultimately its mechanical behavior. The advent of thermoplastic elastomers and high impact resins (HIPS or ABS type) illustrates the importance of the industrial developments that this type of materials can provide. In selective solvents, and depending on molecular structure, concentration and temperature, block polymers form micelles which influence the rheological behavior and control the morphology of the material. 

In discussing the elongational flow behavior of polymer blends, the difference between single-phase (homopolymer or miscible blend) and multiphase (antagonistically immiscible PE/PS blend) was demonstrated in Eigures 2.12 and 2.13,... 

However, it is recognized that most polymer blends are both thermodynamically immiscible and technologically incompatible, and hence produce multiphase systems with... 

D IR spectroscopy has been applied extensively to studies of polymeric materials. A recent review of 2D IR spectroscopy cites numerous applications in the study of polymers by this technique [6]. In this section, some representative examples of 2D IR analysis of polymers are presented. We will start our discussion with a simple homogeneous amorphous polymer then move to more complex multiphase systems, such as semicrystalline polymers. Alloys and blends consisting of more than one polymer components are of great scientific and technical importance. Both immiscible and miscible polymer blend systems may be studied by 2D IR spectroscopy. Analysis of microphase-separated block copolymers is also possible. Finally, the possible application of 2D IR spectroscopy to the studies of natural polymers of biological origin is explored. 

---