Phase Behavior of PS-(PS-b-P2VP)(3) Miktoarm Star Copolymer

We synthesized polystyrene-[polystyrene-b-poly(2-vinylpyridine)](3) miktoarm star copolymer [PSL-(PSS-b-P2VP)(3)], where PSL and PSS are long and short PS chains, respectively, by the combination of anionic polymerization, atom transfer radical polymerization (ATRP), and click reaction. We changed the volume fraction of the PS block (f(PS)) and the chain asymmetry of the PS chain t = f(PS,L)/(f(PS, L) + f(PS,S)). Phase behavior of PS-(PS-b-P2VP)(3) was investigated by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). Inverted gyroids consisting of PS chains were formed at f(PS) = 0.64 and tau = 0.65, while asymmetric lamellae were observed at f(PS) = 0.81 and tau = 0.79. Because a long PS chain (PSL) and three short PSS-b-P2VP copolymer chains are linked at a single junction point, a huge configurational entropy penalty was expected, resulting in distorting the original phase boundaries observed for conventional AB diblock copolymer. PSS-b-P2VP chains are mainly located at the interface between PS and P2VP microdomains, whereas PSL chains fill the regions far from the interface, which causes a radial distribution to form interfacial curvature. Interestingly, the phase behavior was greatly affected by tau at a fixed f(PS). For instance, at a fixed f(PS) (0.64), an inverted gyroid structure was formed at tau = 0.65, while a lamellar structure was observed at tau = 0.46. With the decrease in tau (or the difference of molecular weight between PSL and PSS becomes smaller), the interfacial curvature is not expected because all PSS-b-P2VP chains have no need to be arranged in the same direction. The experimental results are consistent with the predictions based on self-consistent field theory (SCFT).11Nsciescopu

Draft genome sequence of the extremely halophilic Halorubrum sp. SAH-A6 isolated from rock salts of the Danakil depression, Ethiopia

The draft genome sequence of Halorubrum sp. SAH-A6, isolated from commercial rock salts of the Danakil depression, Ethiopia. The genome comprised 3,325,770 bp, with the G + C content of 68.0%. The strain has many genes which are responsible for secondary metabolites biosynthesis, transport and catabolism as compared to other Halorubrum archaea members. Abundant genes responsible for numerous transport systems, solute accumulation, and aromatic/sulfur decomposition were detected. The first genomic analysis encourages further research on comparative genomics, and biotechnological applications. The NCBI accession number for this genome is SAMN04278861 and ID: 4278861 and strain deposited with accession number KCTC 43215

High-Density Packing of Spherical Microdomains from A(AB₃)₃ Dendron-like Miktoarm Star Copolymer

An A(AB3)3 dendron-like miktoarm star copolymer consisting of polystyrene (PS, A) and poly(2-vinylpyridine) (P2VP, B) was synthesized using a series of anionic polymerization, atom-transfer radical polymerization (ATRP), and click reaction. The morphology of A(AB3)3 changed greatly depending on the volume fraction of A and the chain asymmetry. Interestingly, a body-centered cubic spherical phase was found even at fA = 0.51 because the chain architecture of A(AB3)3 stabilizes the large interfacial curvature toward A domains. On the other hand, when the length difference between the end and middle A blocks decreased, a hexagonally packed cylindrical phase was formed at fA = 0.50. This is attributed to the fact that the middle A chains are arranged in a more relaxed way, resulting in a milder interfacial curvature toward A domains. The experimental observations are well-consistent with the predictions based on self-consistent-field theory