Dynamic thermal gradient-based processes for directed self-assembly of block copolymer (BCP) thin films such as Cold Zone Annealing (CZA) have demonstrated much potential for rapidly fabricating highly ordered patterns of BCP domains with facile orientation control. As a demonstration, hexagonally packed predominantly vertical cylindrical morphology, technologically relevant for applications such as membranes and lithography, was achieved in 1µm thick cylinder-forming PS-b-PMMA (cBCP) films by applying sharp thermal gradients (CZA-Sharp) at optimum sample sweep rates. A thorough understanding of the molecular level mechanisms and pathways of the BCP ordering that occur during this CZA-S process is presented, useful to fully exploit the potential of CZA-S for large-scale BCP-based device fabrication. To that end, we developed a customized CZA-S assembly to probe the dynamic structure evolution and ordering of the PS-b-PMMA cBCP film in-situ as it undergoes the CZA-S process using the Grazing Incidence Small Angle X-ray Scattering (GISAXS) technique. Four distinct regimes of BCP ordering were observed within the gradient that include microphase separation from an 'as cast' unordered state (Regime I), evolution of vertical cylinders under a thermally imposed strain gradient (Regime II), reorientation of a fraction of cylinders due to preferential substrate interactions (Regime III) and finally grain-coarsening on the cooling edge (Regime IV). The ordering pathway in the different regimes is further described within the framework of an energy landscape. A novel aspect of this study is the identification of a graincoarsening regime on the cooling edge of the gradient, previously obscure in zone annealing studies of BCPs. Such insights into the development of highly ordered BCP nanostructures under template-free thermal gradient fields can potentially have important ramifications in the field of BCP directed self-assembly and self-assembling polymer systems more broadly. Graph showing variation of χ within CZA-S gradient, indexing of peaks to hexagonal lattice showing parallel cylinders, surface GISAXS image of post CZA-S sample, example of curve fitting to the 1-dimensional GISAXS integrated intensity profiles to obtain peak widths (fwhm) and orientation correlation lengths, plot of peak widths with respect to CZA-S temperature and time (PDF) AUTHOR INFORMATION

What are cellulose nanomaterialsand why are they of interest?Cellulose nanomaterials (CNM) are naturally occurring nanoparticles present in lignocellulosic biomass (e.g., trees, grasses, municipal waste), bacteria (e.g., acetobacter) and invertebrate sea creatures (e.g., tunicates). Over the past decade, numerous applications for CNM have been developed and investigated worldwide. 1-10Cellulose nanocrystals (CNC) were first isolated in the laboratory by Mukherjee and Woods in 1953, 11 and a commercially scalable process for cellulose nanofiber (CNF) production was invented by ITT Rayonier in 1977. 12,13 Since then, several inventions and techniques have led to the development of pilot-scale production methods which have been implemented across the globe (CelluForce in Canada, American Process, Inc. in the United States of America and Innventia in Sweden to name a few). CNM are an attractive alternative to other high-aspect-ratio nanoparticles, such as carbon nanotubes and silica nanowhiskers, due to their renewable, sustainable origins and expected low toxicity. (Toxicology studies are ongoing but 'powdered cellulose' has recently been placed on the list of Permitted Food Additives in Canada. )Cellulose consists of glucose molecules linked together into polysaccharide chains, which align to form nanocrystalline domains. The hydroxyl substituent groups on each repeat unit form both inter-and intra-chain hydrogen bonds, leading to unique mechanical and thermal properties. 7,15 The nanocrystalline domains are linked together into nanofiber bundles by flexible, amorphous hemicellulose regions. Various processing techniques have been developed to isolate the two general classes of CNM -that is, cellulose nanofibrils and the individual CNC. Isolation of CNC is What do we still need to understand to commercialize cellulose nanomaterials? Davis, Grolman, Karim and Gilman Published with permission by the ICE under the CC-BY license.

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Synthetic topographically patterned films and coatings are typically contoured on one side, yet many of nature's surfaces have distinct textures on different surfaces of the same object. Common examples are the top and bottom sides of the butterfly wing or lotus leaf, onion shells, and the inside versus outside of the stem of a flower. Inspired by nature, we create dual (top and bottom) channel patterned polymer films. To this end, we first develop a novel fabrication method to create ceramic line channel relief structures by converting the oligomeric residue of stamped poly(dimethylsiloxane) (PDMS) nanopatterns on silicon substrates to glass (SiOx, silica) by ultraviolet-ozone (UVO) exposure. These silica patterned substrates are flow coated with polystyrene (PS) films and confined within an identically patterned top confining soft PDMS elastomer film. Annealing of the sandwich structures drives the PS to rapidly mold fill the top PDMS pattern in conjunction with a dewetting tendency of the PS on the silica pattern. Varying the film thickness h, from less than to greater than the pattern height, and varying the relative angle between the top-down and bottom-up patterned confinement surfaces create interesting uniform and nonuniform digitized defects in PS channel patterns, as also a defect-free channel regime. Our dual patterned polymer channels provide a novel fabrication route to topographically imprinted Moiré patterns (whose applications range from security encrypting holograms to sensitive strain gauges), and their basic laser light diffractions properties are illustrated and compared to graphical simulations and 2D-FFT of real-space AFM channel patterns. While traditional "geometrical" and "fringe" Moiré patterns function by superposition of two misaligned optical patterned transmittance gratings, our topographic pattern gratings are quite distinct and may allow for more unique holographic optical characteristics with further development.

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