Nanoscopic templates from domain forming block copolymer

Research area: Nano-fabrication, polymer science
Degree: Honours
Supervisor: Prof Naba Dutta

Description: Polymer chain sequence with different repeating unit with thermodynamic incompatibility between the segments can be chemically linked together through covalent bonds to form block copolymers of unique, ordered nano-phase separated structures. They form meso-domains with size ca. several tens of nanometers.

By controlling appropriately the segment nature and length of each constituent of the block copolymers, a wide variety of meso-domain structures of high degree of richness and complexity (such as lamellar, miceller and vesicular organization) in bulk as well in solution phase is possible.1-3 This structure has significant effect on static, dynamic and other functional properties. Such amphiphilic block copolymers may be optimum nanomaterials, either for their intrinsic properties as self-organised assemblies or for their ability to template other organic, inorganic, semiconductor, metallic or biologically relevant materials.

 Heterogeneity within the specimens due to the presence of micro domain leads to anisotropic nature of the polymer. This micro-phase separation of the copolymers into nanoscopic ordered domains could be harnessed to template the organization of the desired particles into nanoplanes, wires, or spheres within the polymer matrix. This has opened new opportunities for building up functional nanomaterials with potential application in novel biomimetic, photonic and electronic materials.4 The rising cost and complexity associated with lithographically defining structures at nanometer level have opened opportunities for self-assembling physical systems to play a major role in future technological applications.4 

The project will explore the new bottom-up approach to create tightly packed arrays of nanopores, nanodots, and nanowires using amphiphilic block copolymers. The fabrication technique will exploit the block copolymer phase segregation behaviour into a mesoscopic array structure to form well-defined laterally patterned film on smooth surfaces. Different block copolymers will be used to generate different controlled self-assembly structures.

Templating processing parameters will be systematically varied to understand their influence on the self-assembly process. They will be characterized in details using thermal, thermomechanical, atomic force microscopy and micro-thermal analyses. The interfacial curvature and mesostructure of the polymer will be manipulated by using block copolymers of different compositions and with different length of the block. 

The removal of a selective phase of the patterned film by UV/chemical means will create nanoporous film, which will also serve as a compartment for the formation of nanoparticles, deposition of metal nanodots/nano-wire with controlled shape and size. The pore size, shape and separation will be analyzed to quantify the quality of the resulting thin film. Different techniques including physical vapor deposition (PVD) will be employed to deposit metal into the nanopores. The fabrication technique is quite versatile and especially attractive due to its simplicity and control. 

1) Amphiphilic Block Copolymers: Self-Assembly and Applications, Eds. Alexandridis, P. and Lindman B., Elsevier, Amsterdam, 2000 
2) F. S. Bates and G.H. Fredrickson, Physics Today, 52 (1999)32. 
3) Dutta, N.K., Roy Choudhury, N. and Bhowmick, A., Handbook of Thermoplastics, Marcel Dekker
4) Guarini K., Black C.T. and Yeung S.H.I., Advanced Materials, 2002,14,1290 

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