Microdomain Dynamics

In order to account for the real 3D structure of cylindrical microdomains, we denote the configurations in Fig. 22a, e and c, g as cylinder-phase defects (cyl-dislocation and +1/2 cyl-disclination), and the configurations in Fig. 22b,f and d,h as matrix defects (m-dislocation and m-disclination). In our systems, cyl-dislocations generally develop during the early stages of film annealing when the overall defect density is high. In well-equilibrated films, cyl-dislocations are less frequent as compared to m-dislocations. 

The rich phase behavior of cylinder-forming block copolymers is reflected in the modification of classical defects by incorporation of elements of non-bulk structures such as +1/2 disclination with incorporated PL ring (Fig. 23a, d) or white dot (b, e) and —1/2 disclination with incorporated PL domain (Fig. 23c, f). Defects Fig. 23a and b are topologically equivalent, but functionally different. Their 

Detailed analysis of defect configurations in the cylinder phase and of their evolution allowed us to conclude that representative defect configurations provide connectivity of the minority phase in the form of dislocations with a closed cylinder end or of classical disclinations with incorporated alternative, non-bulk structures with planar symmetry. Further, block copolymers show a strong correlation between the defect structure and chain mobility on both short- and long-term time scales. 

We note that earlier research focused on the similarities of defect interaction and their motion in block copolymers and thermotropic nematics or smectics [181, 182], Thermotropic liquid crystals, however, are one-component homogeneous systems and are characterized by a non-conserved orientational order parameter. In contrast, in block copolymers the local concentration difference between two components is essentially conserved. In this respect, the microphase-separated structures in block copolymers are anticipated to have close similarities to lyotropic systems, which are composed of a polar medium (water) and a non-polar medium (surfactant structure). The phases of the lyotropic systems (such as lamella, cylinder, or micellar phases) are determined by the surfactant concentration. Similarly to lyotropic phases, the morphology in block copolymers is ascertained by the volume fraction of the components and their interaction. Therefore, in lyotropic systems and in block copolymers, the dynamics and annihilation of structural defects require a change in the local concentration difference between components as well as a change in the orientational order. Consequently, if single defect transformations could be monitored in real time and space, block copolymers could be considered as suitable model systems for studying transport mechanisms and phase transitions in 2D fluid materials such as membranes [183], lyotropic liquid crystals [184], and microemulsions [185], 

2 Phase Transitions and Defect Evolution in Dynamic SFM Measurements and DDFT Simulations 

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Of particular importance are in situ SFM measurements, which allow real-time data collection during structure evolution [111, 112, 117, 133-135], Both concentrated block copolymer solutions [117, 136, 137] and block copolymer melts [111, 112] have been imaged in situ to access the microdomain dynamics. Figure 3... 

While thin polymer films may be very smooth and homogeneous, the chain conformation may be largely distorted due to the influence of the interfaces. Since the size of the polymer molecules is comparable to the film thickness those effects may play a significant role with ultra-thin polymer films. Several recent theoretical treatments are available [136-144,127,128] based on Monte Carlo [137-141,127, 128], molecular dynamics [142], variable density [143], cooperative motion [144], and bond fluctuation [136] model calculations. The distortion of the chain conformation near the interface, the segment orientation distribution, end distribution etc. are calculated as a function of film thickness and distance from the surface. In the limit of two-dimensional systems chains segregate and specific power laws are predicted [136, 137]. In 2D-blends of polymers a particular microdomain morphology may be expected [139]. Experiments on polymers in this area are presently, however, not available on a molecular level. Indications of order on an... 

Bhat, R. A., Miklis, M., Schmelzer, E., Schulze-Lefert, P. and Panstruga, R. (2005). Recruitment and interaction dynamics of plant penetration resistance components in a plasma membrane microdomain. Proc. Natl. Acad. Sci. USA 102, 3135 40. 

Babiychuk EB, Draeger A 2000 Annexins in cell membrane dynamics. Ca2+-regulated association of lipid microdomains. J Cell Biol 150 1113-1124 Ber DM 2001 Excitation-contraction coupling and cardiac contractile force, 2nd edn. Kluwer Academic Publishers, Dordrecht/Boston/London Blaustein MP, Golovina VA 2001 Structural complexity and functional diversity of endoplasmic reticulum Ca2+ stores. Trends Neurosci 24 602—608 Flynn ER, Bradley KN, Muir TC, McCarron JG 2001 Functionally separate intracellular Ca2+ stores in smooth muscle. J Biol Chem 276 36411-36418 Fry CH, WuCl 997 Initiation of contraction in detrusor smooth muscle. Scand J Urol Nephrol Suppl 184 7-14... 

Harder, T. and Simons, K., 1997, Caveolae, DlGs, and the dynamics of sphingobpid-cholesterol microdomains. Curr. Opin. Cell. Biol. 9 534-542. 

Harder T, Simons K. Caveolae, DIGs, and the dynamics of sphingolipid-cholesterol microdomains. Curr Opin Cell Biol 1997 9 534-542. 

Microemulsions are dynamic systems in which droplets continually collide, coalesce, and reform in the nanosecond to millisecond time scale. These droplet interactions result in a continuous exchange of solubilizates. The composition of the microemulsion phase determines the exchange rate through its effect on the elasticity of the surfactant film surrounding the aqueous microdomains. Compared with nonionic surfactant-based microemulsions, AOT reverse micelles have a more rigid... 

The high temporal resolution of SFM imaging uncovered elementary dynamic processes of structural rearrangements. We observed short-term interfacial undulations [111], fast repetitive transitions between distinct defect configurations [112], their spatio-temporal correlations on a length scale of several microdomains [112], and unexpected defect annihilation pathways via formation of temporal excited states [51, 111]. 

Much experimental work has appeared in the literature concerning the microphase separation of miktoarm star polymers. The issue of interest is the influence of the branched architectures on the microdomain morphology and on the static and dynamic characteristics of the order-disorder transition, the ultimate goal being the understanding of the structure-properties relation for these complex materials in order to design polymers for special applications. 

Henis Yl, Rotblat B, Kloog Y. FRAP beam-size analysis to measure palmitoylation-dependent membrane association dynamics and microdomain partitioning of Ras proteins. Methods 2006 40 ... 

The Singer-Nicolson model of the membrane played a very important role in understanding membrane structure and function. However, many properties of biomembranes are not consistent with this model. In recent years, a growing consensus points at more complex membrane structure, which can be characterized as dynamically structured fluid mosaic. Compared with the original fluid mosaic model, the emphasis has shifted from fluidity to mosaicity. Experimental observations have led to the membrane microdomain concept that describes compartmen-talization/organization of membrane components into stable or transient domains. 

Apart of forming the bilayer, membrane lipids exhibit dynamic structures within the lamellas, forming microdomains with specific functionalities. The so called membrane rafts are sphingolipid-cholesterol domains that contribute to signal transduction, as well as to lipid and protein sorting and transport [18]. 

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