Microphase Separation in Polymers

Krause [13] reviewed empirical evidence of the activity of microdomains in block copolymer membranes such as those used for reverse osmosis and ion exchange processes. Depending on whether they are dispersed or continuous, the microphases may either sequester compatible solutes or serve as channels for their transport through the membrane. Partitioning of solutes into the microdomains was found to be a complex function of solute structure and microdomain structure and composition and could not easily be predicted quantitatively. 

Even in the solid state, microphase separation resulting in a dispersed-phase structure has been shown to occur in block copolymers [14]. Thus the dispersed-phase structure is clearly the preferred configuration for these polymers in a network. Networks prepared as cast films from block copolymer 

---

Microphase separation in polymer blends critical micelle concentration... 

These techniques allow visions of the microphase separation in polymers. As one can say that eye is the mirror of the soul, microphase is the mirror of the polymer structure. Remember the well known Alexander Pope s quote a few hundreds of years ago where he was asking why has not man a microscopic eye " Certainly if he had been a scientist nowadays and if he had had access to these techniques, he woudn t have stated that man has not a microscopic eye for the plain reason he is not a fly . 

Alexei R. Khokhlov s main research interests are polymer science, statistical physics of macromolecules, physical chemistry of polyelectrolytes and ionomers, microphase separation in polymer systems, polymer liquid crystals, polyelectrolyte responsive gels, topological restrictions in polymer systems, dynamics of concentrated polymer solutions and melts, coil-globule transitions, associating polymers, computer simulation of polymer systems, biomimetic polymers, and proton-conducting polymer membranes. 

Each of these categories has been the subject of extensive experimental and theoretical investigations over the last decades. It would be an unrealistic task to cover in one article all applications of meso-thermodynamics. In particular, we do not consider such important topics as the thermodynamics of adsorption, wetting transitions, microphase separation in polymers, gels, or phase equilibria in confined fluids. Nor do we discuss the increasingly informative simulations of meso-scale systems (see, for example, refs 8, 22 and 23). Instead, in this Chapter we demonstrate only a few characteristic applications of meso-thermodynamics to each category, while emphasizing universality rather than specific details of the phenomena. 

Block (Star) Arrangement. The known star polymers, like their linear counterparts, exhibit microphase separation. In general, they exhibit higher viscosities in the melt than their analogous linear materials. Their rheological behavior is reminiscent of network materials rather than linear block copolymers (58). Although they have been used as compatibiUzers in polymer blends, they are not as effective at property enhancements as linear diblocks... 

We are currently initiating three research projects that include (1) the synthesis of reflective liquid crystal/polymer composite films, (2) a study of microphase separation in hyperbranched block copolymers, and (3) the design and synthesis of polar organic thin films, which is the subject of this proposal. (47 words aim for 41 words)... 

Marko (1993) has considered microphase separation in cyclic block copolymers, and found that the spinodal is shifted to higher for a given copolymer composition compared to a diblock. This is due to the suppression of composition fluctuations because of the closed topology of the ring polymer. 

Confinement Effects on the Microphase Separation and Polymer-Solvent Interactions in Swollen Films... 

MSI) that uses the same time-dependent Ginzburg Landau kinetic equation as CDS, but starts from (arbitrary) bead models for polymer chains. The methods have been summarized elsewhere. Examples of recent applications include LB simulations of viscoelastic effects in complex fluids under oscillatory shear,DPD simulations of microphase separation in block copoly-mers ° and mesophase formation in amphiphiles, and cell dynamics simulations applied to block copolymers under shear. - DPD is able to reproduce many features of analytical mean field theory but in addition it is possible to study effects such as hydrodynamic interactions. The use of cell dynamics simulations to model non-linear rheology (especially the effect of large amplitude oscillatory shear) in block copolymer miscrostructures is currently being investigated. ... 

L. Leibler (1980) Theory of microphase separation in block co-polymers. 

These five sets of observations, plus knowledge of the phenomenon of microphase separation in block copolymers leads to a model of reverse osmosis or ion exchange membranes in which the hydrophobic portions of the polymer chains have come together to form one more or less continuous microphase, while the hydrophilic portions of the polymer chains (ionic groups, -OH groups, -NH2 or > NH groups) have "dissolved" in a small amount of water to form another more or less continuous microphase when the meni>rane is swollen in water. The hydrophilic groups, in most cases, probably form clusters but not continuous microphases in the dried membranes. 

Sofia P, Fiilber C, Demco DE, Bliimlich B, Spiess FTW (1996) Effect of residual dipolar interactions on the NMR relaxation in cross-linked elastomers. Macromolecules 29 6222-6230 Suzuki M, Hirasa O (1993) An approach to artificial muscle using polymer gels formed by microphase separation. Adv Polym Sci 110 241-261 Tanaka T, Fillmore DJ (1979) Kinetics of swelling of gels. J Chem Phys 70 1214—1218 Tanaka T, Hooker LO, Benedek GB (1973) Spectrum of light scattered from a viscoelastic gel. J Chem Phys 59 5151-5159... 

AYD Aydin, S., Erdogan, T., Sakar, D., Hizal, G., Cankurtaran, O., Tunca, U., and Karaman, F., Detection of microphase separation in poly(tert-butyl acrylate-Z>-methyl methacrylate) synthesized via atom transfer radical polymerization by inverse gas chromatography, Eur. Polym. J., 44, 2115, 2008. 

LC-BCPs provide theorists with novel model systems for developing new theories of polymer behavior [41]. Consider the process of microphase separation in LC-BCPs starting from the disordered BCP structure (or isotropic solution) (Scheme 1). As the temperature decreases, the system will undergo microphase separation to form ordered microdomain structures. As temperature falls past the LC clearing transition temperature (Jj) the LC block will shift from the isotropic phase to a LC phase. If this temperature is lower than the Tg of the other... 

A remarkable property of polymer melts is their ability to self-assemble, driven by thermodynamic incompatibilities of the different monomers. A brief introduction to the thermodynamic theory of macrophase separation in homopolymer blends and microphase separation in diblock copolymer melts is given. In particular, the effect of controllable parameters, including the monomer interactions, the block composition. 

In the absence of strong interactions such as H-bonding and electrostatic interactions, different polymers do not mix. Most block copolymers undergo block segregation or microphase separation in the sofid state [51]. If the block copolymers have narrow molecular weight distributions and homogenous composition, highly periodic structures are formed. For ABC triblock copolymers, there are compositions at which periodic B-C shell-core cylinders are... 

Nowadays, all the main problems of physics and physic-chemistry of polymers became closely intertwined when studying block-copolymers the nature of ordering in polymers, the features of phase separation in polymers and the infiuence of general molecular parameters on it, the stability of phases at exposing to temperature and power impacts, the features of physical and mechanical properties of microphases and the role of their conjugation. 

The notoriously poor polymer crystals described in Chap. 5 and their typical microphase and nanophase separations in polymer systems have forced a rethit ing of the application of thermodynamics of phases. Equilibrium thermodynamics remains important for the description of the limiting (but for polymers often not attainable) equilibrium states. Thermal analysis, with its methods described in Chap. 4, is quite often neglected in physical chemistry, but unites thermodynamics with irreversible thermodynamics and kinetics as introduced in Chap. 2, and used as an important tool in description of polymeric materials in Chaps. 6 and 7. 

The interest in the phase behaviour of block copolymer melts stems from microphase separation of polymers that leads to nanoscale ordered morphologies. This subject has been reviewed extensively [1 ]. The identification of the structure of bicontinuous phases has only recently been confirmed, and this together with major advances in the theoretical understanding of block copolymers, means that the most up-to-date reviews should be consulted [1,3]. The dynamics of block copolymer melts, in particular rheological behaviour and studies of chain diffusion via light scattering and NMR techniques have also been the focus of several reviews [1,5,6]. 

---