Surface properties block copolymers

One of the most fascinating properties of block copolymers is their ability to self-assemble into ordered nanostructures not only in selective solvent and melts but also at the interface and surface [113]. Self-assembly of amphiphilic or surface-adsorbing block copolymers at the air-water interface can form two dimensional monolayers on the nanometer scale order. 

Block copolymers have gained considerable importance in the last three decades. Their special chemical structure (different A and B chains) yields unusual physical properties. Block copolymers frequently exhibit phase separation one block type in a continuous matrix of the second block type. The fact that block copolymers are able to participate in different types of phases gives them special properties both colloidal and mechanical surface activity, surface elasticity, impact modification. 

Surface-active block copolymer can also be employed to carry a functional group or payload to the surface of a polymer matrix. PS-b-PDMS, wherein the silicone block was terminated with a silane group, was used to create smart surfaces with selective adhesion properties (71). When the block copolymer adsorbed at the surface of PS substrates, the silane group was presented to the surface. Adhesion was observed only toward polymer coatings that could react with the silane group, that is, polymers containing vinyl fimctionality. 

The distinctive properties of densely tethered chains were first noted by Alexander [7] in 1977. His theoretical analysis concerned the end-adsorption of terminally functionalized polymers on a flat surface. Further elaboration by de Gennes [8] and by Cantor [9] stressed the utility of tethered chains to the description of self-assembled block copolymers. The next important step was taken by Daoud and Cotton [10] in 1982 in a model for star polymers. This model generalizes the... 

AB diblock copolymers in the presence of a selective surface can form an adsorbed layer, which is a planar form of aggregation or self-assembly. This is very useful in the manipulation of the surface properties of solid surfaces, especially those that are employed in liquid media. Several situations have been studied both theoretically and experimentally, among them the case of a selective surface but a nonselective solvent [75] which results in swelling of both the anchor and the buoy layers. However, we concentrate on the situation most closely related to the micelle conditions just discussed, namely, adsorption from a selective solvent. Our theoretical discussion is adapted and abbreviated from that of Marques et al. [76], who considered many features not discussed here. They began their analysis from the grand canonical free energy of a block copolymer layer in equilibrium with a reservoir containing soluble block copolymer at chemical potential peK. They also considered the possible effects of micellization in solution on the adsorption process [61]. We assume in this presentation that the anchor layer is in a solvent-free, melt state above Tg. The anchor layer is assumed to be thin and smooth, with a sharp interface between it and the solvent swollen buoy layer. 

In the third part of the chapter the solid state properties of our block copolymer are examined. The surface energies of these materials are characterized by contact angle measurements. The organization of the polymer chains in the solid state phase is investigated by small-angle X-ray scattering (SAXS) and the gas selectivity of porous membranes coated with these block copolymers is characterized by some preliminary permeation measurements. 

Figure 1.6 Top Low-temperature nitrogen adsorption ( ) and desorption (x) isotherms measured on a calcined SBA-15 mesoporous silica solid prepared using an EO20PO70EO20 block copolymer [54]. Bottom Pore size distribution derived from the adsorption isotherm reported at the top [54]. A high surface area (850 m2/g), a uniform distribution of cylindrical nanopores (diameter —90 A), and a large pore volume (1.17 cm3/g) were all estimated from these data. These properties make this material suitable for use as support in the preparation of high-surface-area solid catalysts. (Reproduced with permission from The American Chemical Society.)...

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