Controlling the orientation of nanostructured thin films of block copolymers (BCPs) is essential for next-generation lithography using BCPs. According to conventional wisdom, the orientation of BCP thin films is mainly determined by molecular interactions (enthalpy-driven orientation). Here, we show that the entropic effect can be used to control the orientation of BCP thin films. Specifically, we used the architecture of star-block copolymers consisting of polystyrene (PS) and poly­(dimethylsiloxane) (PDMS) blocks to regulate the entropic contribution to the self-assembled nanostructures. The study unequivocally demonstrate that for star-block copolymers with the same volume fractions of PS and PDMS, perpendicularly oriented BCP nanostructures could be induced via an entropic effect regulated by the number of arms. Also, the feasibility of using the star-block copolymer thin films for practical applications is demonstrated by using the thin film as a mask for nanolithography or as a template for the fabrication of nanoporous monolith.

The formation of well-oriented cylinders with perpendicular morphology for polystyrene-b-polydimethylsiloxane (PS-PDMS) thin films was achieved by spin coating. The self-assembled PS-PDMS nanostructured thin films were used as templates for nanopatterning; the PDMS blocks can be oxidized as silicon oxy carbide microdomains, whereas the PS blocks were degenerated by a simple oxygen plasma treatment for one-step oxidization. As a result, freestanding silicon oxy carbide thin films with hexagonally packed nanochannels were directly fabricated and used as masks for pattern transfer to underlying polymeric materials by oxygen reaction ion etching (RIE) to generate topographic nanopatterns. By taking advantage of robust property and high etching selectivity of the SiOC thin films under oxygen RIE, this nanoporous thin film can be used as an etch-resistant and reusable mask for pattern transfer to various polymeric materials. This approach demonstrates a simple, convenient, and cost-effective nanofabrication technique to create the topographic nanopatterns of polymeric materials.

A simple method to create a variety of nanostructures via the self-assembly of a single composition silicon-containing block copolymer (BCP) is developed. By using selective solvents for the self-assembly of polystyreneblock-poly(dimethylsiloxane) (PS−PDMS), the phase behavior of intrinsic BCP can be enriched due to the strong segregation of the PS−PDMS enabling the diversity of the phase behavior of PS−PDMS/solvent mixtures and clear-cut phase transitions upon solvent evaporation. The solution-state phase behaviors of the strong segregation BCP system in different solvents are systematically studied using temperature-resolved and time-resolved SAXS experiments. A variety of phases, such as sphere, cylinder, gyroid, lamellar phases and even inverted phases, can be acquired by simply tuning the selectivity of solvent for casting. Meanwhile, owing to the high etching contrast of the silicon-containing block versus the PS block, various nanostructured SiOC can be fabricated by using one-step oxidation. This approach suggests an easy way to create inorganic oxide nanostructures for various applications.

Controlling the orientation of nanostructured block copolymer (BCP) thin films is essential for next-generation lithography. However, obtaining BCP with perpendicular orientation remains a challenge because of the surface selectivity to the different blocks. This challenge is especially severe for silicon-containing BCPs which is notorious for its high surface energy difference between constituted blocks. Here, we demonstrate a new approach to achieve perpendicular orientation with high aspect ratio using a combination of architecture effect (entropy effect) and surface air plasma treatment (enthalpy effect). Specifically, perpendicular cylinders of star-block copolymers composed of polystyrene and poly­(dimethylsiloxane) blocks can be formed from the bottom substrate to the top surface of the thin film.

A new technique for the modification of lamellar domain sizes in polymeric ionic liquid block copolymers has been proposed. Anion exchange in polymeric ionic liquids opens new ways to modify the sizes of lamella domains without modifying the ratio between the two different blocks of the neat copolymer. This study focuses on the influence of quaternization of poly(2-vinylpyridine) in poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) and the effect of anion exchange in the nanostructured phases for thin films. The resulting materials obtained from the quaternization modification technique of the block copolymers and the anion exchange of the polymeric ionic liquid were characterized with Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and nuclear magnetic resonance (NMR). Furthermore, morphological characterization of the initial block polymer and several polymeric ionic liquid block copolymers has been carried out by atomic force microscopy (AFM) in order to analyze the influence of the anion in the nanostructures of these block copolymers.

Three grades of PolyActive block copolymers are investigated for CO2 separation from light gases. The polymers are composed of 23 wt % poly(butylene terephthalate) (PBT) and 77 wt % poly(ethylene glycol terephthalate) (PEGT) having the poly(ethylene glycol) segments of 1500, 3000, and 4000 g/mol, respectively. A commercial PEG POSS (poly(ethylene glycol) functionalized polyoctahedral oligomeric silsesquioxanes) is used as a nanofiller for these polymers to prepare nanocomposites via a solvent casting method. Single gas permeabilities of N2, H2, CH4, and CO2 are measured via the time-lag method in the temperature range from 30 to 70 °C. The thermal transitions of the prepared membranes are studied by differential scanning calorimetry (DSC). It is found that the length of PEG segment has a pronounced influence on the thermal transition of the polymers that regulates the gas separation performance of the membranes. The stability of the nanocomposites is also correlated with the thermal transition of the polyether blocks of the polymer matrices.

Well-defined linear (n = 1, 2) and star (n = 3, 4) architecture (PS-b-PDMS)n block copolymers were synthesized by anionic polymerization in combination with chlorosilane chemistry. The self-assembly is significantly influenced by entropy constraints for the star samples due to overcrowding.

a b s t r a c tTailor-made block copolymer nanocomposite membranes are prepared by incorporation of 40 wt% methoxy poly(ethylene glycol) (PEG) functionalized polyoctahedral oligomeric silsesquioxanes (POSS) nanoparticles in commercial thermoplastic elastomer multiblock copolymer PEBAX s MH 1657. Atomic force microscopy was used to find out the location of the nanoparticles in the block copolymer matrix. Separation of CO 2 from N 2 and H 2 is studied by measurements of single gas transport properties of nanocomposite materials using the time-lag method in the temperature range 30-70 1C. PEG functionalized POSS nanoparticles increase the CO 2 permeability of the nanocomposite membranes without loss of CO 2 /N 2 and CO 2 /H 2 selectivity. Thermal properties of the nanocomposite membranes are studied by differential scanning calorimetry (DSC) to assess the stability of the nanocomposite membranes upon melting of polyether and polyamide blocks.