Domain formation

Siepmann JI and IR McDonald 1993a. Domain Formation and System-size Dependence in Simulatio of Self-assembled Monolayers. Langmuir 9 2351-2355. 

A very special type of ABA block copolymer where A is a thermoplastic (e.g., styrene) and B an elastomer (e.g., butadiene) can have properties at ambient temperatures, such as a crosslinked rubber. Domain formations (which serves as a physical crosslinking and reinforcement sites) impart valuable features to block copolymers. They are thermoplastic, can be eaisly molded, and are soluble in common solvents. A domain structure can be shown as in Fig. 2. 

The frequency-domain format eliminates the manual effort required to isolate the components that make up a time trace. Frequency-domain techniques convert time-domain data into discrete frequency components using a mathematical process called Fast Fourier Transform (FFT). Simply stated, FFT mathematically converts a time-based trace into a series of discrete frequency components (see Figure 43.19). In a frequency-domain plot, the X-axis is frequency and the Y-axis is the amplitude of displacement, velocity, or acceleration. 

Meier D.J., Theory of block copolymers Domain formation in A-B block copolymers, J. Polym. Sci., Part C, 26, 81, 1969. 

Inoue T., Soen T., Hashimoto T., and Kawai, H. Studies on domain formation of the A-B t3fpe block copolymer with polystyrene and polyisoprene. Macromolecules, 13, 87, 1970. 

Spontaneous reflection symmetry breaking in achiral LCs is also well known, driven by specific boundary conditions. A very simple example of this type of chiral domain formation is illustrated in Figure 8.11. Suppose we start with two uniaxial solid substrates, which provide strong azimuthal anchoring ... 

Figure 10. Illustration of influence of domain formation in block copolymers according to the models of Helfand and coworkers. The free energy is shown as a function of the size and separation of the domains of varying composition. (The spontaneous separations may be analogous to the way superstructure is formed in natural polymers of plants and animals.)...

FIG. 65. Antiphase domain formation in polar on nonpolar epitaxy (a) incomplete prelayer coverage, (b) odd step height. (From Ref. 387.)... 

Fig. 7 The two-stage folding scheme for the hammerhead ribozyme, as proposed by Tilley s group [77-80]. The arrow indicates the cleavage site. The scheme consists of two steps to generate the Y- or y-shaped ribozyme/substrate complex. The higher affinity of Mg is related to formation of domain II (structural scaffold non-Watson-Crick pairings between G12-A9, Ais-Gg and A14-U7 forming a coaxial stack between hehces II and III that runs through G12A13A14) and the lower affinity of Mg to formation of domain I (catalytic domain formation by the sequence C3U4G5A6 and the C17 with the rotation of helix I around into the same quadrant as helix II) [78]...

Since the start of modern interpenetrating polymer network (IPN) research in the late sixties, the features of their two-phased morphologies, such as the size, shape, and dual phase continuity have been a central subject. Research in the 1970 s focused on the effect of chemical and physical properties on the morphology, as well as the development of new synthetic techniques. More recently, studies on the detailed processes of domain formation with the aid of new neutron scattering techniques and phase diagram concepts has attracted much attention. The best evidence points to the development first of domains via a nucleation and growth mechanism, followed by a modified spinodal decomposition mechanism. This paper will review recent morphological studies on IPN s and related materials. 

These phenomena cannot be treated Independently, Consequently, the morphology of IPN s is often at a quasi-equlllbrlum state determined by a balance among the several kinetic factors [ l Therefore, in order to understand the domain formation process in IPN s, we should take into consideration the route taken to the final morphology as well as the chemical and physical properties of each constituent. 

In order to understand the domain formation process, an investigation of the Intermediate stages before formation of the final morphology is required. There are several different ways to prepare such intermediate materials [3,A2,A3], see Figure 9. The characteristic domain dimensions of PB/PS IPN s are compared in Figures 10 and 11 [3,12,A1]. 

Initiation of phase domains formation through the presence of heterogeneities [3]. 

Phase behavior of lipid mixtures is a much more difficult problem, due to nonideal mixing of lipid components. Ideal mixing implies like and unlike lipids have the same intermolecular interactions, while nonideal mixing results from differential interactions between lipid types. If the difference is too great, the two components will phase separate. While phase separation and lateral domain formation have been observed in many experiments, we lack a molecular-level physical description of the interactions between specific lipids that cause the macroscopic behavior. The chemical potential of a lipid determines phase separation, as phase coexistence implies the chemical potential of each type of lipid is equal in all phases of the system [3,4],... 

The MARTINI model effectively replaces three to four heavy atoms with a bead, parameterized to reproduce condensed-phase thermodynamic data of small molecules [23]. The MARTINI model has been used to investigate many biological processes, such as lung surfactant collapse [24], nanoparticle permeation in bilayers [25], large domain motion of integral membrane proteins [26], vesicle fusion [27,28], and lateral domain formation in membranes [29]. 

Lipid phase transitions are often slow on the timescale accessible to simulations, such as the gel to liquid-crystalline phase transition. Using the MARTINI model, liquid-crystalline to gel phase transitions and domain formation have been... 

Cholesterol flip-flop is important for general cholesterol trafficking as well as for lateral domain formation. Using methyl-fi-cyclodextrin as a cholesterol acceptor, Steck et al. [83] estimated the halftime for cholesterol flip-flop in a human red cell bilayer to be <1 s. 

Faller, R., Marrink, S.J. Simulation of domain formation in DLPC-DSPC mixed bilayers. Langmuir... 

Figure 9 Typical configuration of the adlayer after adsorption of 0.47 ML NO, showing the onset of c(4 x 2)-2NO domain formation (indicated by the ovals and the zig-zag lines). In addition to the c(4 x 2)-2NO domains also small (2 x 2)-2NO honeycomb domains are present. Two of these domains are highlighted at the left of the figure...

The observation of single channel currents may suggest the successful self-organization of supramolecular channels. This process may require several steps (1) incorporation of the amphiphilic carboxylate-ammonium ion pair into the bilayer lipid membrane (2) molecular recognition of the relatively polar oligoether chain from the surrounding hydrophobic lipid components to induce domain formation of molecular level and (3) interlayer connection of these hydrophilic domains existing in different lipid layers. 

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