Diblock structure, modifications

The properties of the hybrid diblock structures can be altered drastically by simply taking advantage of the high terminal functionality of the dendritic block. For example unusual diblock structures useful for the modification of surfaces have been prepared by ATRP of polystyrene (PS) initiated from the benzylic halide focal point of Frechet-type dendrons with terminal isophthalate ester groups [9b], Well-defined copolymers with narrow molecular weight distributions were obtained and excellent agreement was observed between calculated... 

Figure 34 Template-directed synthesis of metal oxide nanowires by using PFSi7-/hP2VPi7o diblock copolymer cylindrical micelles with various functional and structural modifications. Reproduced with permission from Wang, H. Patil, A. J. Liu, K. etal. Adv. Mater. 2009,21,1805-1808. ...

PS-fc-PI diblock copolymers [65], poly(fumarate)s or poly(acrylate)s [131], lamellar structures are found in nearly all cases if the number of m is not too small. The backbone and its flexibility seem to have only marginal influence. In simple terms, the strong phase separation into areas with fluorinated segments and areas with the nonfluorinated rest seems to be the first principle in structure formation. Whereas in sf alkanes besides lamellar structures also hexagonally packed cylinder structures are possible [128], the attachment of the. segments as side chain onto the polymer backbone prevents structure modifications with other symmetries. 

In order to improve the tribological properties of molecular films, molecular surface modification is the first choice to make an approach. A Diblock polymer polystyrene-poly(ethylene)oxide (PS-PEO) thin-films were studied in our previous research because of its interesting structure (one... 

The formation of nanopattemed functional surfaces is a recent topic in nanotechnology. As is widely known, diblock copolymers, which consist of two different types of polymer chains cormected by a chemical bond, have a wide variety of microphase separation structures, such as spheres, cylinders, and lamellae, on the nanoscale, and are expected to be new functional materials with nanostructures. Further modification of the nanostructures is also useful for obtaining new functional materials. In addition, utilization of nanopartides of an organic dye is also a topic of interest in nanotechnology. 

Laser ablation of polymer films has been extensively investigated, both for application to their surface modification and thin-film deposition and for elucidation of the mechanism [15]. Dopant-induced laser ablation of polymer films has also been investigated [16]. In this technique ablation is induced by excitation not of the target polymer film itself but of a small amount of the photosensitizer doped in the polymer film. When dye molecules are doped site-selectively into the nanoscale microdomain structures of diblock copolymer films, dopant-induced laser ablation is expected to create a change in the morphology of nanoscale structures on the polymer surface. 

Further modification of the above nanostructures is useful for obtaining new functional materials. Thirdly, we apply the dopant-induced laser ablation technique to site-selectively doped thin diblock copolymer films with spheres (sea-island), cylinders (hole-network), and wormlike structures on the nanoscale [19, 20]. When the dye-doped component parts are ablated away by laser light, the films are modified selectively. Concerning the laser ablation of diblock copolymer films, Lengl et al. carried out the excimer laser ablation of diblock copolymer monolayer films, forming spherical micelles loaded with an Au salt to obtain metallic Au nanodots [21]. They used the laser ablation to remove the polymer matrix. In our experiment, however, the laser ablation is used to remove one component of block copolymers. Thereby, we can expect to obtain new functional materials with novel nanostmctures. 

As aforementioned, diblock copolymer films have a wide variety of nanosized microphase separation structures such as spheres, cylinders, and lamellae. As described in the above subsection, photofunctional chromophores were able to be doped site-selectively into the nanoscale microdomain structures of the diblock copolymer films, resulting in nanoscale surface morphological change of the doped films. The further modification of the nanostructures is useful for obtaining new functional materials. Hence, in order to create further surface morphological change of the nanoscale microdomain structures, dopant-induced laser ablation is applied to the site-selectively doped diblock polymer films. 

Taking into account all of the results presented above, we can conclude that in order to be sure that homogenous nucleation is indeed present (even when first-order crystallization kinetics is encountered), the crystallization rate must exhibit a dependence on the volume of the droplets or on the cube of the particle diameter. Additionally, even in extremely small droplets comparable to only a few chains in size, the nucleation still occurs within the interior of the droplets. Furthermore, the homogeneous nucleation event is independent of the molecular weight and of the molecular architecture (at least when comparing homopolymers and diblock copolymers). The homogeneous nucleation temperature is a function of the particle size. In certain cases, when the droplets size is nanometric, modifications of the crystal structure of the polymer as compared with that usually observed in the bulk have been reported. The effects of superficial nucleation are important and should be taken into consideration. 

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