Understanding Lithium-ion Transport in Sulfolane- and Tetraglyme-Based Electrolytes Using Very Low-Frequency Impedance Spectroscopy

With the increasing interest in highly concentrated electrolyte systems,correct determination of the cation transference number is important.Pulsed-field gradient NMR technique,which measures self-diffusion coefficients,is often applied on liquid electrolytes because of the wide accessibility and simple sample preparation.However,since the assumptions of this technique,that is,complete salt dissociation,all ions participating in motion,and all of them moving independently,no longer hold true in concentrated solutions,the transference numbers,thus obtained are often over-estimated.In the present work,impedance spectroscopy at a frequency range of 1 MHz to 0.1 mHz was used to examine the concentration effect on lithium-ion transference number under anion-blocking conditions T abc Liþfor two electrolytes:lithium bis(fluorosulfonyl)imide(LiFSI)in sulfolane(SL)and lithium bis(trifluorosulfonyl)imide(LiTFSI)in tetraglyme(G4).The T abc Liþof the former was almost an order of magnitude higher than that of the latter.It also appeared to increase with increasing concentration while the latter followed an opposite trend.The faster Li^(+)transport in the SL system is attributed to the formation of a liquid structure consisting of extended chains/bridges of SL molecules and the anions,which facilitate a cation-hopping/ligand-exchanged-typed diffusion mechanism by partially decoupling the cations from the anions and solvent molecules.The G4 system,in contrast,is dominated by the formation of long-lived,stable[Li(G4)]+solvation cages that results in a sluggish Li+transport.The difference between the two transport mechanisms is discussed via comparison of the bulk ionic conductivity,viscosity,ion self-diffusion coefficients,and the Onsager transport coefficients.

Classifying Electrolyte Solutions by Comparing Charge and Mass Transport

The conventional classification of electrolyte solutions as“strong”or“weak”accounts for their charge transport properties,but neglects their mass transport properties,and is not readily applicable to highly concentrated solutions.Here,we use the Onsager transport formalism in combination with linear response theory to attain a more general classification taking into account both charge and mass transport properties.To this end,we define a molar mass transport coefficientΛ_(mass),which is related to equilibrium center-of-mass fluctuations of the mobile ions and which is the masstransport analogue of the molar ionic conductivityΛ_(charge).Three classes of electrolyte solution are then distinguished:(i)“Strong electrolytes”with 4Λ_(mass)≈Λ_(charge);(ii)“weak charge transport electrolytes”withΛ_(charge)≪4Λ_(mass);and(iii)“weak mass transport electrolytes”with 4Λ_(mass)≪Λ_(charge).While classes(i)and(ii)encompass the classical“strong”and“weak”electrolytes,respectively,many highly concentrated electrolytes fall into class(iii)and thus exhibit transport properties clearly distinct from classical strong and weak electrolytes.

Study of ss-DNA Adsorption and Nano-mechanical Properties on Mica Substrate with Surface Forces Apparatus

Many DNA?based devices need to build stable and controllable DNA films on surfaces. However, the most com?monly used method of film characterization, namely, the probe?like microscopes which may destroy the sample and substrate. Surface Forces Apparatus(SFA) technique, specializing in surface interaction studies, is introduced to investigate the e ects of DNA concentration on the formation of single?stranded DNA(ss?DNA) film. The result demonstrates that 50 ng/μL is the lowest concentration that ss?DNA construct a dense layer on mica. Besides, it is also indicated that at di erent DNA concentrations, ss?DNA exhibit diverse morphology: lying flat on surface at 50 ng/μL while forming bilayer or cross?link at 100 ng/μL, and these ss?DNA structures are stable enough due to the repeatabil?ity even under the load of 15 mN/m. At the same time, an obvious adhesion force is measured:/m at 100 ng/μL, respectively, which is attributed to the ion?correlation e ect. M-6.5 mN/m at 50 ng/μL and-5.3 mNoreover, the atomic force microscopy(AFM) images reveal the entire surface is covered with wormlike ss?DNA and the measured surface roughness(1.8±0.2 nm) also matches well with the film thickness by SFA. The desorption behaviors of ss?DNA layer from mica surface occur by adding sodium salt into gap bu er, which is mainly ascribed to the decreased ion?ion cor?relation force. This paper employing SFA and AFM techniques to characterize the DNA film with flexibility and stable mechanical ability achieved by ion bridging method, is helpful to fabricate the DNA?based devices in nanoscale.

Multiplicity fluctuation and correlation of mesons and baryons in ultra-relativistic heavy-ion collisions at the LHC

We study the multiplicity fluctuation and correlation of identified mesons and baryons formed at hadronization by the quark combination mechanism in the context of ultra-relativistic heavy-ion collisions. Based on the statistical method of free quark combination, we derive the two-hadron multiplicity correlations, including meson-meson and meson-baryon correlations, and take the effects of quark number fluctuation at hadronization into account by a Taylor expansion method. After including the decay contributions, we calculate the dynamical fluctuation observable ν_（dyn） for Kπ, pπ and Kp pairs and discuss what underlying physics can be obtained by comparing with data from Pb-Pb collisions at sNN^（1/2）=2.76 Te V and simulations from the HIJING and AMPT event generators.

A brief review of continuous models for ionic solutions: the Poisson–Boltzmann and related theories

The Poisson–Boltzmann(PB)theory is one of the most important theoretical models describing charged systems continuously.However,it suffers from neglecting ion correlations,which hinders its applicability to more general charged systems other than extremely dilute ones.Therefore,some modified versions of the PB theory are developed to effectively include ion correlations.Focused on their applications to ionic solutions,the original PB theory and its variances,including the field-theoretic approach,the correlation-enhanced PB model,the Outhwaite–Bhuiyan modified PB theory and the mean field theories,are briefly reviewed in this paper with the diagnosis of their advantages and limitations.