Microphase separation in the melts of diblock copolymers composed of linear and amphiphilic blocks

Computer-aided simulation performed via two independent methods (the Monte Carlo method and method of dissipative particle dynamics) is performed for studying the effect of microphase separation in concentrated solutions of diblock copolymers composed of linear blocks A and amphiphilic blocks A-graft-B. The type of microstructures generated by strong incompatibility between units A and B is shown to be controlled by the ratio of block lengths. For example, in the case of short amphiphilic blocks, elongated micelles with correlated mutual alignment are formed. In the case of longer amphiphilic blocks, lamellar structures are produced; with an increase in the length of this block, these structures are transformed into sequences of lamellas containing parallel layers, lamellas with intersecting layers, and perforated lamellas. When the system contains long amphiphilic blocks, bicontinuous structures arise.     

Secondary globular structure of copolymers containing amphiphilic and hydrophilic units: Computer simulation analysis

The coil-globule transition in copolymers composed of amphiphilic and hydrophilic monomer units has been studied by the computer simulation technique. It has been shown that the structure of globules formed in such systems substantially depends on the rate at which the solvent quality worsens. The globule resulting from slow cooling is cylindrical, and its core contains a large amount of hydrophilic groups. The globule formed upon rapid cooling takes the helical conformation, in which all hydrophilic groups are displaced to the periphery. One helix turn of such globules contains 3–5 units. In both cases, the backbone of the polymer chain forms a typical zigzag-shaped structure with an average angle between neighboring bond vectors of about 60°. This fact implies that globules of copolymers consisting of amphiphilic and hydrophilic units comprise secondary structure components.     

Helix-coil transition in DNA in the presence of a denaturating agent

A theory of the helix-coil transition in solutions containing a denaturing agent is proposed. It is shown that, if the transition is induced by an increase in the concentration of the denaturant, the range of the conformational transition narrows with a growing activity of the agent. In contrast, if the transition is induced by temperature variation, addition of a denaturant makes the transition broader, the more so for a higher activity of the agent. The results of the computation agree with published experimental data.     

Void Microstructuring in Lamellar Phase of Amphiphilic Macromolecules

The free volume (voids) distribution in the lamellae of the conventional symmetric and amphiphilic diblock copolymers is studied via Monte–Carlo simulation based on the standard bond fluctuation model. Both in the conventional and amphiphilic block copolymers the voids are found to concentrate on the interfaces between the incompatible units, the magnitude of the effect being unexpectedly significant. A crystalline‐like ordering of voids with increase of the incompatibility between the different repeated units in amphiphilic copolymers is first reported and implications of this peculiarity for the morphology and mechanical properties of the amphiphilic copolymers are discussed.

     

Ferromagnetic resonance in a uniaxial magnetic film subjected to magnetic biasing along its hard axis

The precession dynamics of the magnetization of a film with an in-plane uniaxial anisotropy is analyzed in the spectrum of ferromagnetic resonance corresponding to magnetic biasing along the hard axis of the film. An additional resonance peak is revealed near magnetic anisotropy field H _u . This peak is related to the appearance of angular bistability due to the presence of two symmetric angular equilibrium positions in field H < H _u .     

Features of ZnO Nanocrystal Size Distribution in a Polymer Matrix

Physics of the Solid State - X-ray diffraction patterns of a photocurable epoxy acryl-based polymer composite with addition of ZnO nanocrystals are analyzed. We recover the size distribution...