The study of the conformation properties of macromolecules is at the heart of polymer science. Essentially all physical properties of polymers are manifestations of the underlying polymer ...conformations or otherwise significantly impacted by the conformation properties. In this Perspective, we review some of the key concepts that we have learned over nearly eight decades of the subject and outline some open questions. The topics include both familiar subjects in polymer physics textbooks and more recent results or not-so-familiar subjects, such as non-Gaussian chain behavior in polymer melts and topological effects in ring polymers. The emphasis is on understanding the key concepts, with both physical reasoning and mathematical analysis, and on the interconnection between the different results and concepts.
We present measurements of pion elliptic flow (ν2) in Au + Au collisions at sNN=200,62.4,39,27and19.6GeV, as a function of event-by-event charge asymmetry (A±), based on data from the STAR experiment ...at RHIC. We find that π−(π+) elliptic flow linearly increases (decreases) with charge asymmetry for most centrality bins and for all the beam energies under study. The slope parameter (r) from ν2(A±) difference between π− and π+ shows a centrality dependency similar to calculations of the Chiral Magnetic Wave. The measurements of charge separation with respect to the reaction plane in search of Local Parity Violation and the Chiral Magnetic Effect are also presented for Au+Au collisions at sNN=200,62.4,39,27,19.6,11.5and7.7GeV, and for U + U collisions at 193 GeV.
The solid-electrolyte interphase (SEI) dictates the performance of most batteries, but the understanding of its chemistry and structure is limited by the lack of in situ experimental tools. In this ...work, we present a dynamic picture of the SEI formation in lithium-ion batteries using in operando liquid secondary ion mass spectrometry in combination with molecular dynamics simulations. We find that before any interphasial chemistry occurs (during the initial charging), an electric double layer forms at the electrode/electrolyte interface due to the self-assembly of solvent molecules. The formation of the double layer is directed by Li
and the electrode surface potential. The structure of this double layer predicts the eventual interphasial chemistry; in particular, the negatively charged electrode surface repels salt anions from the inner layer and results in an inner SEI that is thin, dense and inorganic in nature. It is this dense layer that is responsible for conducting Li
and insulating electrons, the main functions of the SEI. An electrolyte-permeable and organic-rich outer layer appears after the formation of the inner layer. In the presence of a highly concentrated, fluoride-rich electrolyte, the inner SEI layer has an elevated concentration of LiF due to the presence of anions in the double layer. These real-time nanoscale observations will be helpful in engineering better interphases for future batteries.
Integrating multiple mechanisms to maximize photothermal conversion efficiency is a significant strategy but remains challenging to construct therapeutic agents toward photothermal tumor treatment. ...Here, an approach to synthesize asymmetric Bi2Se3/CdSe‐Au hierarchical nanorods with excellent photothermal conversion is reported. Ag wetting‐layer is firstly grown to help overcome the interfacial lattice mismatch and promote the site‐selective growth of AgCdSe onto one end or side surface of Au nanorods. Subsequently, extraction of Ag+ ions out of lattice is observed during cation exchange reaction and epitaxial growth of Bi2Se3 shell. Bi2Se3/CdSe heterojunction with type‐II band alignment is formed and located at the plasmonic hotspots of Au nanorods, which experiences enhanced light absorption and accelerates the charge separation of photo‐excited carriers. Under excitation of near‐infrared 808 nm laser, the matchstick‐like Bi2Se3/CdSe‐Au nanorods show an excellent photothermal conversion, with 4.3 times temperature increment (ΔT) than that of bare Au nanorods. Moreover, in vitro and in vivo experiments verify them as excellent photothermal therapeutic agents.
Controlled growth of type‐II Bi2Se3/CdSe semiconductor heterojunction onto Au nanorods has spatial overlap with plasmonic hotspots. The spectral overlap of longitudinal surface plasmon resonance with near‐infrared excitation leads to optimized photothermal conversion for photothermal therapy.
In this article, we study the doubly heavy baryon states and pentaquark states with the QCD sum rules by carrying out the operator product expansion up to the vacuum condensates of dimension 7 and 13 ...respectively in a consistent way. In calculations, we separate the contributions of the negative parity and positive parity hadron states unambiguously, and study the masses and pole residues of the doubly heavy baryon states and pentaquark states in details. The present predictions can be confronted to the experimental data in the future.
Molecular weight distribution of polymers, termed dispersity (Đ), is a fundamental parameter for determining polymer material properties. This paper reports a novel approach for controlling Đ by ...exploiting a temperature‐selective radical generation in organocatalyzed living radical polymerization. The polymers with tailored Đ were synthesized in a batch system without the assistance of an external pump. A unique aspect of this approach is that Đ was tuneable from 1.11 to 1.50 in any segment in diblock, triblock, and multiblock copolymers and in any form of star and brush polymer without segmental or topological restriction. This approach is amenable to various monomers and free from metals and thus attractive for applications. The approach also generated polymer brushes on surfaces with tailored Đ. An interesting finding was that the polymer brushes exhibited unique interaction with external molecules, depending on the Đ value.
Brush up: A novel approach for modulating polymer dispersity was developed. It is based on temperature‐selective organocatalyzed living radical polymerization and enabled dispersity modulation in any segment in linear and branched block copolymers as well as polymer brushes. A dispersity‐dependent size‐exclusion effect to external molecules was observed for the polymer brushes.
One‐step C2H4 purification from ternary C2H6/C2H4/C2H2 mixtures by a single adsorbent is of great industrial significance, but few adsorbents achieve this separation. Herein, we report a robust ...metal–organic framework (MOF) that possesses methyl‐decorated nonpolar pores and shows one‐step C2H4 purification (purity >99.9 %) from binary C2H6/C2H4 mixtures and ternary C2H6/C2H4/C2H2 mixtures. The methyl groups in pores provide a suitable pore environment to simultaneously enhance the adsorption capacity for C2H2 and C2H6 compared to C2H4. Simulations revealed the multiple interactions between C2H6 or C2H2 molecules and the pore wall, while the interactions with C2H4 molecules are weak and also unfavorable due to the repulsion from methyl groups in pores. The MOF displays high C2H6 and C2H2 uptakes and benchmark C2H6/C2H4 selectivity (2.2), surpassing all of the reported MOFs for one‐step C2H4 purification from ternary C2H6/C2H4/C2H2 mixtures.
The combination of nonpolar pore environment and accessible active sites in a metal–organic framework affords benchmark C2H6/C2H4 selectivity and realizes one‐step C2H4 purification from ternary C2H6/C2H4/C2H2 mixtures.
Single-degree-of-freedom lumped parameter model, conventional finite element method, and distributed parameter model have been developed to design, analyze, and predict the performance of ...piezoelectric energy harvesters with reasonable accuracy. In this article, a spectral finite element method for bimorph piezoelectric beam energy harvesters is developed based on the Timoshenko beam theory and the Euler–Bernoulli beam theory. Linear piezoelectric constitutive and linear elastic stress/strain models are assumed. Both beam theories are considered in order to examine the validation and applicability of each beam theory for a range of harvester sizes. Using spectral finite element method, a minimum number of elements is required because accurate shape functions are derived using the coupled electromechanical governing equations. Numerical simulations are conducted and validated using existing experimental data from the literature. In addition, parametric studies are carried out to predict the performance of a range of harvester sizes using each beam theory. It is concluded that the Euler–Bernoulli beam theory is sufficient enough to predict the performance of slender piezoelectric beams (slenderness ratio > 20, that is, length over thickness ratio > 20). In contrast, the Timoshenko beam theory, including the effects of shear deformation and rotary inertia, must be used for short piezoelectric beams (slenderness ratio < 5).
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