Solvent mediated inclusion of metal oxide into block copolymer nanopatterns: mechanism of oxide formation under UV-Ozone treatment

Uniform, periodic and ordered iron oxide nanopatterns can be generated by selective metal ion inclusion into microphase separated polystyrene-b-poly(ethylene oxide) (PS-b-PEO) block copolymer (BCP) thin films. After solvent mediated metal ion inclusion into the PEO block, an ultraviolet-ozone (UVO) treatment was used to remove the polymer and oxidize the metallic ions to their oxides. This paper provides an in-depth study of the UVO processing steps as a function of exposure time. Surface wettability, topography, morphology, compositional and interfacial changes were analysed by contact angle measurement, microscopic and spectroscopic techniques through the UVO treatment. It was found that the UVO treatment initially cross-links the polymer network followed by oxidation and removal of the polymer simultaneously. It was also found that if short UVO exposure times are used, a post calcination treatment can be used to generate similar patterns. The iron oxide nanopatterns created due to strong coordination bond between metallic ions and free electron pairs of O atoms in the PEO and these interactions are responsible for the final pattern mimicking the original self-assembled BCP morphology. The film thicknesses, surface roughness, the size/shape of the iron oxides and patterns, the amount of residual polymers were also investigated regarding the UVO exposure time

Quantitative principles of cis-translational control by general mRNA sequence features in eukaryotes.

BackgroundGeneral translational cis-elements are present in the mRNAs of all genes and affect the recruitment, assembly, and progress of preinitiation complexes and the ribosome under many physiological states. These elements include mRNA folding, upstream open reading frames, specific nucleotides flanking the initiating AUG codon, protein coding sequence length, and codon usage. The quantitative contributions of these sequence features and how and why they coordinate to control translation rates are not well understood.ResultsHere, we show that these sequence features specify 42-81% of the variance in translation rates in Saccharomyces cerevisiae, Schizosaccharomyces pombe, Arabidopsis thaliana, Mus musculus, and Homo sapiens. We establish that control by RNA secondary structure is chiefly mediated by highly folded 25-60 nucleotide segments within mRNA 5' regions, that changes in tri-nucleotide frequencies between highly and poorly translated 5' regions are correlated between all species, and that control by distinct biochemical processes is extensively correlated as is regulation by a single process acting in different parts of the same mRNA.ConclusionsOur work shows that general features control a much larger fraction of the variance in translation rates than previously realized. We provide a more detailed and accurate understanding of the aspects of RNA structure that directs translation in diverse eukaryotes. In addition, we note that the strongly correlated regulation between and within cis-control features will cause more even densities of translational complexes along each mRNA and therefore more efficient use of the translation machinery by the cell

Microphase separation of highly amphiphilic, low N polymers by photoinduced copper-mediated polymerization, achieving sub-2 nm domains at half-pitch

The lower limit of domain size resolution using microphase separation of short poly(acrylic acid) homopolymers equipped with a short fluorinated tail, posing as an antagonist 'A block' in pseudo AB block copolymers has been investigated. An alkyl halide initiator with a fluorocarbon chain was utilized as a first 'A block' in the synthesis of low molecular weight polymers (1400-4300 g mol -1) using photoinduced Cu(ii)-mediated polymerization allowing for very narrow dispersity. Poly(tert-butyl acrylate) was synthesized and subsequently deprotected to give very low degrees of polymerization (N), amphiphilic polymers with low dispersity (D = 1.06-1.13). By exploiting the high driving force for demixing and the well-defined 'block' sizes, we are able to control the nanostructure in terms of domain size (down to 3.4 nm full-pitch) and morphology. This work demonstrates the simple and highly controlled synthesis of polymers to push the boundaries of the smallest achievable domain sizes obtained from polymer self-assembly

Poly(cyclohexylethylene)-<i>block</i>-poly(ethylene oxide) Block Polymers for Metal Oxide Templating

A series of poly­(cyclohexylethylene)-<i>block</i>-poly­(ethylene oxide) (CEO) diblock copolymers were synthesized through tandem anionic polymerizations and heterogeneous catalytic hydrogenation. Solvent-annealed CEO diblock films were used to template dense arrays of inorganic oxide nanodots via simple spin coating of an inorganic precursor solution atop the ordered film. The substantial chemical dissimilarity of the two blocks enables (i) selective inclusion of the inorganic precursor within the PEO domain and (ii) the formation of exceptionally small feature sizes due to a relatively large interaction parameter estimated from mean-field analysis of the order–disorder transition temperatures of compositionally symmetric samples. UV/ozone treatment following incorporation produces an ordered arrangement of oxide nanodots and simultaneously removes the block polymer template. Herein, we report the smallest particles (6 ± 1 nm) templated from a selective precursor insertion method to date using a block polymer scaffold

Structural Transitions in Asymmetric Poly(styrene)-block-Poly(lactide) Thin Films Induced by Solvent Vapor Exposure

International audienceSuccessive structural transitions in thin films of asymmetric poly(styrene)-block-poly(lactide) (PS-PLA) block copolymer samples upon exposure to tetrahydrofuran (THF) vapors have been monitored using atomic force microscopy (AFM) and both in situ and ex situ grazing incidence small-angle X-ray scattering (GISAXS). A direct link was established between the structure in the swollen state and the morphology formed in the dried state post solvent evaporation. This was related to the high incompatibility between the constituting blocks of the copolymer that thwarted the system from reaching the homogeneous disordered state in the swollen state under the specific conditions utilized in this study. Upon rapid solvent removal, the morphologies formed in the swollen state were trapped due the fast evaporation kinetics. This work provides a better understanding of the mechanisms associated with block copolymer thin film morphology changes induced by solvent vapor annealing

Modification of poly(styrene) thin films and enhancement of cryogenic plasma etching resistance by ruthenium tetroxide vapor staining

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High aspect ratio etched sub-micron structures in silicon obtained by cryogenic plasma deep-etching through perforated polymer thin films

Cryogenic plasma deep-etching for silicon sub-micron structures was studied with the use of modified poly(styrene) (PS) perforated masks obtained from laterally phase separated PS and poly (lactic acid) PLA blend thin films. PS mask was stained by heavy metal (ruthenium) or transferred to an intermediate hard mask (silicon oxide). For the stained mask, optimization of standard STiGer cryogenic plasma etching process led to etched Si cavities with minimal defects at rate of 0.8 μm/min but within a limited depth (~1.4 μm). For intermediate hard mask, optimized STiGer etching process was used in order to improve the reproducibility and to obtain the deeply etched features up to 10 μm depth with minimal defects. A higher etch rate of around 1.2 μm/min was achieved. Keywords: Polymer mask, STiGer process, Cryogenic etching, Sub-micron hole etchin

Diurnal Oscillations in Liver Mass and Cell Size Accompany Ribosome Assembly Cycles.

The liver plays a pivotal role in metabolism and xenobiotic detoxification, processes that must be particularly efficient when animals are active and feed. A major question is how the liver adapts to these diurnal changes in physiology. Here, we show that, in mice, liver mass, hepatocyte size, and protein levels follow a daily rhythm, whose amplitude depends on both feeding-fasting and light-dark cycles. Correlative evidence suggests that the daily oscillation in global protein accumulation depends on a similar fluctuation in ribosome number. Whereas rRNA genes are transcribed at similar rates throughout the day, some newly synthesized rRNAs are polyadenylated and degraded in the nucleus in a robustly diurnal fashion with a phase opposite to that of ribosomal protein synthesis. Based on studies with cultured fibroblasts, we propose that rRNAs not packaged into complete ribosomal subunits are polyadenylated by the poly(A) polymerase PAPD5 and degraded by the nuclear exosome