We report a uniform and low-defect synthesis of bilayer graphene on evaporated polycrystalline nickel films. We used atmospheric pressure chemical vapor deposition with ultra-fast substrate cooling after exposure to methane at 1,000°C. The optimized process parameters, i.e., growth time, annealing profile and flow rates of various gases, are reported. By using Raman spectroscopy mapping, the ratio of 2D to G peak intensities (I2D/IG) is in the range of 0.9 to 1.6 over 96% of the 200 μm × 200 μm area. Moreover, the average ratio of D to G peak intensities (ID/IG) is about 0.1.

This work aims to elucidate how the branching effect of macromonomer influences the polymerization, structural features, and solution properties of AB n long-subchain hyperbranched polymers (LHPs). Our result reveals that compared with linear AB2 macromonomers, star AB3 macromonomers result in the suppression of chain extension, and the enhancement of macromonomer self-cyclization during the preparation of LHPs by “click” polymerization, due to the branching-enhanced steric hindrance effect. The combined triple-detection SEC and stand-alone LLS studies of unfractionated and fractionated AB3 LHPs unambiguously demonstrate their statistically fractal nature. Namely, the intrinsic viscosity ([η]) and radius of gyration (R g) are scaled to the macromonomer molar mass (M macro) and the total molar mass (M hyper) as [η] = K η ,AB3 M hyper νM macro μ (ν ≃ 0.39, μ ≃ 0, and K η ,AB3 ≃ 0.29 mL/g) and R g = H R ,AB3 M hyper α M macro β (α ≃ 0.47, β ≃ 0, and H R ,AB3 ≃ 3.6 × 10–2 nm). Surprisingly, [η] and R g are both almost independent of M macro (μ ≃ 0 ≃ β), indicating a similar draining property and local segment density for LHPs with different subchain lengths, which is different from the classic AB2 systems (μ ≃ 0.3 and β ≃ 0.1). A comparison of results for AB n LHPs (n = 2, 3) and short-subchain hyperbranched systems indicates that the fractal dimensions (f) for LHPs are generally smaller than short-subchain systems, whereas f is not sensitive to the local segment density or branching pattern. A combination of experimental observation and Langevin dynamics simulation of AB n dendrimers and LHPs further reveals (i) the segment back-folding phenomenon is prominent only for AB n (n ≥ 3) LHPs systems because it is mainly dominated by the macromonomer branching effect, rather than the internal subchain length, and (ii) the trend for segment interpenetration increases remarkably as M macro increases for both dendrimers and LHPs. The result also indicates that the unique synergistic effect of segment back-folding and segment interpenetration in AB3 system is the most probable reason for the observed M macro independent solution properties. Specifically, because of the unique synergistic effect, small macromonomer/oligomer chains can interpenetrate more easily into hyperbranched oligomer chains composed of longer subchains and subsequently “click” couple with the back-folded segments in the interior space of LHPs, which eventually could lead to a similar draining property and local segment density for AB3 LHPs with different subchain lengths.

This work aims to experimentally clarify how the single chain conformation evolves as a function of grafting density for model comb-like chains in dilute solution in the whole density regime. Via a combination of rational design, precise synthesis and accurate characterization, we obtained four sets of PPA Nb-g-PS30-σ comb-like samples with well-defined architectures and accurately extracted their molecular parameters by triple detection size exclusion chromatography (TD-SEC). With these samples in hand, we quantified how the excluded volume interaction and chain conformation evolve with the grafting density (σ) in the whole density regime. Three main findings are reported: (i) the graft–graft excluded volume interaction is not ignorable even in the low σ-regime; (ii) contrary to theoretical predictions, both the excluded volume interaction and the chain conformation are found to be N b-dependent; (iii) both R g ∼ σ1/3 and [η] ∼ σ0 are experimentally confirmed for comb-like chains from different σ and N b, signifying a unique 3D mass-size growth pattern and a quasi-3D fractal feature. The obtained results help clarify some long-existed controversial issues in the field.

This work aims to explore the feasibility for utilizing the “coil-to-stretch” transition for polymer separation/fractionation/characterization during a “dead-end” ultrafiltration process from both theoretical and experimental perspectives. Theoretically, advantages/disadvantages of “dead-end” ultrafiltration and some other popular polymer separation/fractionation techniques (PSFTs) are compared and thoroughly discussed on the basis of key requirements for any technique to qualify as mature PSFTs. Experimentally, a home-designed ultrafiltration apparatus was developed and successfully applied to execute various separation/fractionation tasks for mixed solutions of polymer chains with varied topologies and sizes at laboratory scale. Based on theoretical modeling and experimental examination, the “dead-end” ultrafiltration system containing a detection module that can complement the prevailing PSFTs is found to be a powerful PSFT with the merits of low cost, high efficiency, high accessibility, easy handling, and universal applicability.

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