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1.
Curr Probl Diagn Radiol ; 50(6): 784-786, 2021.
Article in English | MEDLINE | ID: mdl-33234341

ABSTRACT

OBJECTIVE: To understand the utilization of the search engine within our hospital system's homepage, stratifying the searches into physician specialty, procedures or therapies, patient conditions, and logistical queries, with a specific focus on radiology-specific terms as a baseline to guide future interventions. METHODS: The top 1000 most searched terms entered into the medical system's homepage between January 1, 2017 and February 28, 2018 were collected. Related or similar terms were combined for analysis. RESULTS: During the study period, there were 121,071 unique searches on the center's website, and the top 1000 most searched terms combined for 65,011 searches. The most searched category was logistical queries (n = 29,667), followed by searches for conditions (n = 14,033), specialties (n = 3083), and procedures or therapies (n = 2252). Within the top 1000 most searched terms, radiology-specific searches accounted for 96 searches. These terms were all mammography-related. CONCLUSION: Radiology as a specialty and radiology-specific terms were not frequently searched for by patients when compared with other specialties. Mammography-related terms were the only radiologic subspecialty items within the top 1000 search terms. Overall, patients searched more for conditions than they did for specialties or therapies. These findings could be a representation of the general public's lack of awareness regarding the specialty.


Subject(s)
Radiology , Search Engine , Forecasting , Hospitals , Humans , Internet
2.
Abdom Radiol (NY) ; 46(1): 387-393, 2021 01.
Article in English | MEDLINE | ID: mdl-32676735

ABSTRACT

PURPOSE: To objectively compare structured and freeform abdominopelvic CT reports based on the number and types of errors as well as report length. METHODS: 90 structured and 89 freeform reports from abdominopelvic CT scans with IV contrast obtained for the indication of abdominal pain were randomly selected for review. Each report was reviewed for errors, which were counted and categorized based on the type of error. The total number of words in each report was tallied. RESULTS: 105 total errors were found in the structured reports, compared to 157 total errors in freeform reports. There were 1.16 errors per structured report and 1.76 errors per freeform report (p < 0.001). 48% of structured reports contained at least one error, while 71% of freeform reports contained at least one error (p = 0.002). When a difference existed between the styles with regard to error categories, more errors were observed in freeform reports, with the exception of the duplicated period error where structured reports had more errors. No difference on the basis of average words per report existed, with 219.2 words per report for each reporting style. CONCLUSION: The use of structured reporting for abdominopelvic CT results in less errors in the report when compared to freeform reporting, potentially reducing clinically significant adverse outcomes in patient care. The report length on the basis of number of words per report is not different between the two reporting styles.


Subject(s)
Tomography, X-Ray Computed , Humans
3.
J Chem Phys ; 150(21): 214702, 2019 Jun 07.
Article in English | MEDLINE | ID: mdl-31176353

ABSTRACT

Molecular dynamics simulations of reactions in Al/Ni layered systems have been carried out under isothermal conditions for a wide range of temperatures and several system sizes. An embedded atom method potential, known to reasonably reproduce the phase behavior of Al/Ni, was employed. Simulations revealed reaction mechanisms involving an initial fast process and much slower more complex longer-time reactions. The initial reaction process consists of diffusion of Ni from the pure solid Ni phase into the molten Al phase, resulting in the formation of an Al-rich Al/Ni liquid. The initial reaction ends when the Al/Ni liquid becomes saturated in Ni and solid Al/Ni phases begin to form at the interfaces between the pure solid Ni phase and the Al/Ni liquid. The growth of these solid phases is intrinsically slow compared to the formation of the liquid and is further slowed by the need for Ni to diffuse through the growing interfacial Al/Ni solid phases. Analysis of the initial Al/Ni liquid forming process indicates Fickian behavior with the Ni diffusion coefficient exhibiting Arrhenius temperature dependence. The longer-time slow reaction process(es) resulting in the growth of Al/Ni solid phases do not lend themselves to detailed numerical analysis because of the complex dependence of the Ni transport on the detailed nature of the interfacial layers.

4.
Clin Transplant ; 31(3)2017 03.
Article in English | MEDLINE | ID: mdl-28075034

ABSTRACT

Morphometric assessments, such as muscle density and body fat distribution, have emerged as strong predictors of cardiovascular risk and postoperative morbidity and mortality. To date, no study has examined morphometric mortality risk prediction among kidney transplant (KT) candidates. KT candidates, waitlisted 2008-2009, were identified (n=96) and followed to the earliest of transplant, death, or administrative end of study. Morphometric measures, including abdominal adipose tissue, paraspinous and psoas muscle composition, and aortic calcification, were measured from CTs. Risk of waitlist mortality was examined using Cox proportional hazard regression. On adjusted analyses, radiologic measures remained independently and significantly associated with lower waitlist mortality; the addition of radiologic measures significantly improved model predictive ability over models containing traditional risk factors alone (net reclassification index: 0.56, 95% CI: 0.31-0.75). Higher psoas muscle attenuation (indicative of leaner muscle) was associated with decreased risk of death (aHR: 0.93, 95% CI: 0.91-0.96, P<.001), and for each unit increase in lean paraspinous volume, there was an associated 2% decreased risk for death (aHR: 0.98, 95% CI: 0.96-0.99, P=.03). Radiologic measures of lean muscle mass, such as psoas muscle attenuation and paraspinous lean volume, may improve waitlist mortality risk prediction and candidate selection.


Subject(s)
Abdominal Fat , Kidney Transplantation/mortality , Muscle Strength , Muscle, Skeletal , Psoas Muscles , Thinness , Waiting Lists/mortality , Adult , Female , Follow-Up Studies , Humans , Male , Middle Aged , Prognosis , Retrospective Studies , Risk Factors , Survival Rate
5.
J Phys Chem B ; 119(7): 3085-96, 2015 Feb 19.
Article in English | MEDLINE | ID: mdl-25592777

ABSTRACT

Molecular dynamics simulations of N-methyl-N-propylpyrrolidinium (pyr13) bis(trifluoromethanesulfonyl)imide (Ntf2) ionic liquid [pyr13][Ntf2] doped with [Li][Ntf2] salt and mixed with acetonitrile (AN) and ethylene carbonate (EC) organic solvents were conducted using polarizable force field. Structural and transport properties of ionic liquid electrolytes (ILEs) with 20 and 40 mol % of organic solvents have been investigated and compared to properties of neat ILEs. Addition of AN and EC solvents to ILEs resulted in the partial displacement of the Ntf2 anions from the Li(+) first coordination shell by EC and AN and shifting the Li-Ntf2 coordination from bidentate to monodentate. The presence of organic solvents in ILE has increased the ion mobility, with the largest effect observed for the Li(+) cation. The Li(+) conductivity has doubled with addition of 40 mol % of AN. The Li(+)-N(Ntf2) residence times were dramatically reduced with addition of solvents, indicating an increasing contribution from structural diffusion of the Li(+) cations.

6.
J Phys Chem B ; 118(19): 5135-43, 2014 May 15.
Article in English | MEDLINE | ID: mdl-24773589

ABSTRACT

The influence of low-molecular-weight poly(ethylene glycol) (PEG, Mw ≈ 550 Da) plasticizers on the rheology and ion-transport properties of fluorosulfonimide-based polyether ionic melt (IM) electrolytes has been investigated experimentally and via molecular dynamics (MD) simulations. Addition of PEG plasticizer to samples of IM electrolytes caused a decrease in electrolyte viscosity coupled to an increase in ionic conductivity. MD simulations revealed that addition of plasticizer increased self-diffusion coefficients for both cations and anions with the plasticizer being the fastest diffusing species. Application of a VTF model to fit variable-temperature conductivity and fluidity data shows that plasticization decreases the apparent activation energy (Ea) and pre-exponential factor A for ion transport and also for viscous flow. Increased ionic conductivity with plasticization is thought to reflect a combination of factors including lower viscosity and faster polyether chain segmental dynamics in the electrolyte, coupled with a change in the ion transport mechanism to favor ion solvation and transport by polyethers derived from the plasticizer. Current interrupt experiments with Li/electrolyte/Li cells revealed evidence for salt concentration polarization in electrolytes containing large amounts of plasticizer but not in electrolytes without added plasticizer.

7.
J Chem Phys ; 139(10): 104503, 2013 Sep 14.
Article in English | MEDLINE | ID: mdl-24050355

ABSTRACT

Molecular dynamics (MD) simulations of mixtures of the room temperature ionic liquids (ILs) 1-butyl-4-methyl imidazolium [BMIM]/dicyanoamide [DCA] and [BMIM][NO3(-)] with HNO3 have been performed utilizing the polarizable, quantum chemistry based APPLE&P(®) potential. Experimentally it has been observed that [BMIM][DCA] exhibits hypergolic behavior when mixed with HNO3 while [BMIM][NO3(-)] does not. The structural, thermodynamic, and transport properties of the IL/HNO3 mixtures have been determined from equilibrium MD simulations over the entire composition range (pure IL to pure HNO3) based on bulk simulations. Additional (non-equilibrium) simulations of the composition profile for IL/HNO3 interfaces as a function of time have been utilized to estimate the composition dependent mutual diffusion coefficients for the mixtures. The latter have been employed in continuum-level simulations in order to examine the nature (composition and width) of the IL/HNO3 interfaces on the millisecond time scale.

8.
J Phys Chem B ; 116(42): 12801-9, 2012 Oct 25.
Article in English | MEDLINE | ID: mdl-22978679

ABSTRACT

Molecular dynamics simulations of N-methyl-N-propylpyrrolidinium (pyr(13)) bis(trifluoromethanesulfonyl)imide (Ntf(2)) ionic liquid [pyr(13)][Ntf(2)] mixed with [Li][Ntf(2)] salt have been conducted using a polarizable force field. Mixture simulations with lithium salt mole fractions between 0% and 33% at 363 and 423 K yield densities, ion self-diffusion coefficients, and ionic conductivities in very good agreement with available experimental data. In all investigated electrolytes, each Li(+) cation was found to be coordinated, on average, by 4.1 oxygen atoms from surrounding anions. At lower concentrations (x ≤ 0.20), the Li(+) cation was found to be, on average, coordinated by slightly more than three Ntf(2) anions with two anions contributing a single oxygen atom and one anion contributing two oxygen atoms to Li(+) coordination. At the highest [Li][Ntf(2)] concentration, however, there were, on average, 3.5 anions coordinating each Li(+) cation, corresponding to fewer bidendate and more monodentate anions in the Li(+) coordination sphere. This trend is due to increased sharing of anions by Li(+) at higher salt concentrations. In the [pyr(13)][Ntf(2)]/[Li][Ntf(2)] electrolytes, the ion diffusivity is significantly smaller than that in organic liquid electrolytes due to not only the greater viscosity of the solvent but also the formation of clusters resulting from sharing of anions by Li(+) cations. The ionic conductivity of the electrolytes was found to decrease with increasing salt concentration, with the effect being greater at the higher temperature. Finally, we found that the contribution of Li(+) to ionic conductivity does not increase proportionally to Li(+) concentration but saturates at higher doping levels.


Subject(s)
Ionic Liquids/chemistry , Lithium/chemistry , Molecular Dynamics Simulation , Electric Conductivity , Models, Molecular , Salts/chemistry , Solubility , Thermodynamics
9.
J Chem Phys ; 136(19): 194506, 2012 May 21.
Article in English | MEDLINE | ID: mdl-22612102

ABSTRACT

Atomistic molecular dynamics simulations were performed on 1-butyl-3-methyl-imidazolium azide [bmim][N(3)], 1-butyl-2,3-dimethylimidazolium azide [bmmim][N(3)], and 1-butynyl-3-methyl-imidazolium azide [bumim][N(3)] ionic liquids. The many-body polarizable APPLE&P force field was augmented with parameters for the azide anion and the bumim cation. Good agreement between the experimentally determined and simulated crystal structure of [bumim][N(3)] as well as the liquid-state density and ionic conductivity of [bmmim][N(3)] were found. Methylation of bmim (yielding bmmim) resulted in dramatic changes in ion structuring in the liquid and slowing of ion motion. Conversely, replacing the butyl group of bmim with the smaller 2-butynyl group resulted in an increase of ion dynamics.

10.
J Phys Chem A ; 116(11): 2978-85, 2012 Mar 22.
Article in English | MEDLINE | ID: mdl-22352952

ABSTRACT

We have conducted quantum chemistry calculations and gas- and solution-phase reactive molecular dynamics simulation studies of reactions involving the ethylene carbonate (EC) radical anion EC(-) using the reactive force field ReaxFF. Our studies reveal that the substantial barrier for transition from the closed (cyclic) form, denoted c-EC(-), of the radical anion to the linear (open) form, denoted o-EC(-), results in a relatively long lifetime of the c-EC(-) allowing this compound to react with other singly reduced alkyl carbonates. Using ReaxFF, we systematically investigate the fate of both c-EC(-) and o-EC(-) in the gas phase and EC solution. In the gas phase and EC solutions with a relatively low concentration of Li(+)/x-EC(-) (where x = o or c), radical termination reactions between radical pairs to form either dilithium butylene dicarbonate (CH(2)CH(2)OCO(2)Li)(2) (by reacting two Li(+)/o-EC(-)) or ester-carbonate compound (by reacting Li(+)/o-EC(-) with Li(+)/c-EC(-)) are observed. At higher concentrations of Li(+)/x-EC(-) in solution, we observe the formation of diradicals which subsequently lead to formation of longer alkyl carbonates oligomers through reaction with other radicals or, in some cases, formation of (CH(2)OCO(2)Li)(2) through elimination of C(2)H(4). We conclude that the local ionic concentration is important in determining the fate of x-EC(-) and that the reaction of c-EC(-) with o-EC(-) may compete with the formation of various alkyl carbonates from o-EC(-)/o-EC(-) reactions.

11.
J Phys Chem Lett ; 3(9): 1124-9, 2012 May 03.
Article in English | MEDLINE | ID: mdl-26288046

ABSTRACT

Electrostatic double-layer capacitors (EDLCs) with room-temperature ionic liquids (RTILs) as electrolytes are among the most promising energy storage technologies. Utilizing atomistic molecular dynamics simulations, we demonstrate that the capacitance and energy density stored within the electric double layers (EDLs) formed at the electrode-RTIL electrolyte interface can be significantly improved by tuning the nanopatterning of the electrode surface. Significantly increased values and complex dependence of differential capacitance on applied potential were observed for surface patterns having dimensions similar to the ions' dimensions. Electrode surfaces patterned with rough edges promote ion separation in the EDL at lower potentials and therefore result in increased capacitance. The observed trends, which are not accounted for by the current basic EDL theories, provide a potentially new route for optimizing electrode structure for specific electrolytes.

12.
Eur Polym J ; 47(10): 2022-2027, 2011 Oct 01.
Article in English | MEDLINE | ID: mdl-22021933

ABSTRACT

Rheological evidence is provided demonstrating that covalent grafting of monodisperse isotactic poly(L-leucine) branches onto linear hyaluronan (HA) polysaccharide chains yields comb-branched HA chains that self-assemble into long-lived physical networks in aqueous solutions driven by hydrophobic interactions between poly(L-leucine) chains. This is in stark contrast to native (unmodified) HA solutions which exhibit no tendency to form long-lived physical networks.

13.
J Phys Chem A ; 115(47): 13896-905, 2011 Dec 01.
Article in English | MEDLINE | ID: mdl-22004044

ABSTRACT

The oxidative decomposition mechanism of the lithium battery electrolyte solvent propylene carbonate (PC) with and without PF(6)(-) and ClO(4)(-) anions has been investigated using the density functional theory at the B3LYP/6-311++G(d) level. Calculations were performed in the gas phase (dielectric constant ε = 1) and employing the polarized continuum model with a dielectric constant ε = 20.5 to implicitly account for solvent effects. It has been found that the presence of PF(6)(-) and ClO(4)(-) anions significantly reduces PC oxidation stability, stabilizes the PC-anion oxidation decomposition products, and changes the order of the oxidation decomposition paths. The primary oxidative decomposition products of PC-PF(6)(-) and PC-ClO(4)(-) were CO(2) and acetone radical. Formation of HF and PF(5) was observed upon the initial step of PC-PF(6)(-) oxidation while HClO(4) formed during initial oxidation of PC-ClO(4)(-). The products from the less likely reaction paths included propanal, a polymer with fluorine and fluoro-alkanols for PC-PF(6)(-) decomposition, while acetic acid, carboxylic acid anhydrides, and Cl(-) were found among the decomposition products of PC-ClO(4)(-). The decomposition pathways with the lowest barrier for the oxidized PC-PF(6)(-) and PC-ClO(4)(-) complexes did not result in the incorporation of the fluorine from PF(6)(-) or ClO(4)(-) into the most probable reaction products despite anions and HF being involved in the decomposition mechanism; however, the pathway with the second lowest barrier for the PC-PF(6)(-) oxidative ring-opening resulted in a formation of fluoro-organic compounds, suggesting that these toxic compounds could form at elevated temperatures under oxidizing conditions.


Subject(s)
Propane/analogs & derivatives , Quantum Theory , Anions/chemistry , Oxidation-Reduction , Propane/chemistry
14.
J Phys Chem B ; 115(12): 3073-84, 2011 Mar 31.
Article in English | MEDLINE | ID: mdl-21384838

ABSTRACT

Molecular dynamics simulations were performed on N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (pyr(13)FSI) room temperature ionic liquid (RTIL) confined between graphite electrodes as a function of applied potential at 393 and 453 K using an accurate force field developed in this work. The electric double layer (EDL) structure and differential capacitance (DC) of pyr(13)FSI was compared with the results of the previous study of a similar RTIL pyr(13)bis(trifluoromethanesulfonyl)imide (pyr(13)TFSI) with a significantly larger anion [ Vatamanu, J.; Borodin, O.; Smith, G. D. J. Am. Chem. Soc. 2010, 132, 14825]. Intriguingly, the smaller size of the FSI anion compared to TFSI did not result in a significant increase of the DC on the positive electrode. Instead, a 30% higher DC was observed on the negative electrode for pyr(13)FSI compared to pyr(13)TFSI. The larger DC observed on the negative electrode for pyr(13)FSI compared to pyr(13)TFSI was associated with two structural features of the EDL: (a) a closer approach of FSI compared to TFSI to the electrode surface and (b) a faster rate (vs potential decrease) of anion desorption from the electrode surface for FSI compared to TFSI. Additionally, the limiting behavior of DC at large applied potentials was investigated. Finally, we show that constant potential simulations indicate time scales of hundreds of picoseconds required for electrode charge/discharge and EDL formation.

15.
J Chem Theory Comput ; 7(6): 1902-15, 2011 Jun 14.
Article in English | MEDLINE | ID: mdl-26596451

ABSTRACT

We have developed a quantum chemistry-based polarizable potential for poly(ethylene oxide) (PEO) in aqueous solution based on the APPLE&P polarizable ether and the SWM4-DP polarizable water models. Ether-water interactions were parametrized to reproduce the binding energy of water with 1,2-dimethoxyethane (DME) determined from high-level quantum chemistry calculations. Simulations of DME-water and PEO-water solutions at room temperature using the new polarizable potentials yielded thermodynamic properties in good agreement with experimental results. The predicted miscibility of PEO and water as a function of the temperature was found to be strongly correlated with the predicted free energy of solvation of DME. The developed nonbonded force field parameters were found to be transferrable to poly(propylene oxide) (PPO), as confirmed by capturing, at least qualitatively, the miscibility of PPO in water as a function of the molecular weight.

16.
J Am Chem Soc ; 132(42): 14825-33, 2010 Oct 27.
Article in English | MEDLINE | ID: mdl-20925318

ABSTRACT

Molecular dynamics simulation studies of the structure and the differential capacitance (DC) for the ionic liquid (IL) N-methyl-N-propylpyrrolidinium bis(trifluoromethane)sulfonyl imide ([pyr(13)][TFSI]) near a graphite electrode have been performed as a function temperature and electrode potential. The IL exhibits a multilayer structure that extends 20-30 Å from the electrode surface. The composition and ion orientation in the innermost layer were found to be strongly dependent on the electrode potential. While at potentials near the potential of zero charge (PZC), both cations and anions adjacent to the surface are oriented primarily perpendicular to the surface, the counterions in first layer orient increasingly parallel to the surface with increasing electrode potential. A minimum in DC observed around -1 V(RPZC) (potential relative to the PZC) corresponds to the point of highest density of perpendicularly aligned TFSI near the electrode. Maxima in the DC observed around +1.5 and -2.5 V(RPZC) are associated with the onset of "saturation", or crowding, of the interfacial layer. The asymmetry of DC versus electrode polarity is the result of strong interactions between the fluorine of TFSI and the surface, the relatively large footprint of TFSI compared to pyr(13), and the tendency of the propyl tails of pyr(13) to remain adsorbed on the surface even at high positive potentials. Finally, an observed decreased DC and the disappearance of the minimum in DC near the PZC with increasing temperature are likely due to the increasing importance of entropic/excluded volume effects (interfacial crowding) with increasing temperature.

17.
Phys Chem Chem Phys ; 12(26): 7064-76, 2010 Jul 14.
Article in English | MEDLINE | ID: mdl-20485804

ABSTRACT

Molecular dynamics simulations of fluoroalkyl-derivatized imidazolium:bis(trifluoromethylsulfonyl)imide (TFSI) room temperature ionic liquids (FADI-RTILs) with cations of the structure 1-F(CF(2))(n)(CH(2))(2)-3-methyl imidazolium have been performed and compared with simulations of alkyl-derivatized 1-H(CH(2))(n+2)-3-methyl imidazolium analogs (ADI-RTILs). Simulations yield RTIL densities, viscosities and ionic conductivities for the FADI-RTILs and ADI-RTILs in reasonably good agreement with experimental data. Partial fluorination results in a larger increase in density than would be anticipated based upon the density difference between perfluoralkane and alkane melts. Similarly, the slowing down in dynamics upon partial fluorination is greater than would be expected based upon the increase in cation volume. Examination of cation-cation, anion-anion and cation-anion centers-of-mass radial distribution functions reveal remarkably little influence of partial fluorination on the spherically averaged intermolecular structure of the RTILs. Similarly, simulations reveal little change in tail conformations and the extent of tail-tail aggregation upon partial fluorination. The interaction of the TFSI anion with the positively charged imidazolium ring hydrogen and nitrogen atoms is also little influenced by partial fluorination. However, the partially fluorinated alkyl tail exhibits increased interaction with the TFSI anion due to the electron withdrawing character of the fluorinated groups. We believe this strong tail-anion electrostatic interaction largely accounts for the higher than expected density and slower than expected dynamics in the FADI-RTILs.

18.
J Phys Chem B ; 114(20): 6786-98, 2010 May 27.
Article in English | MEDLINE | ID: mdl-20433203

ABSTRACT

The pulsed-field-gradient spin-echo NMR measurements have been performed on 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([emim][FSI]) and 1-ethyl-3-methylimidazolium [bis[(trifluoromethyl)sulfonyl]imide] ([emim][TFSI]) over a wide temperature range from 233 to 400 K. Molecular dynamics (MD) simulations have been performed on [emim][FSI], [emim][TFSI], [N-methyl-N-propylpyrrolidinium][FSI] ([pyr(13)][FSI]), and [pyr(13)][TFSI] utilizing a many-body polarizable force field. An excellent agreement between the ion self-diffusion coefficients from MD simulations and pfg-NMR experiments has been observed for [emim][FSI] and [emim][TFSI] ILs. The structure factor of [pyr(13)][FSI], [pyr(14)][TFSI], and [emim][TFSI] agreed well with the previously reported X-ray diffraction data performed by Umebayashi group. Ion packing in the liquid state is compared with packing in the corresponding ionic crystal. Faster transport found in the FSI-based ILs compared to that in TFSI-based ILs is associated with the smaller size of FSI(-) anion and lower cation-anion binding energies. A significant artificial increase of the barriers (by 3 kcal/mol) for the FSI(-) anion conformational transitions did not result in slowing down of ion transport, indicating that the ion dynamics is insensitive to the FSI(-) anion torsional energetic, while the same increase of the TFSI(-) anion barriers in [emim][TFSI] and [pyr(13)][TFSI] ILs resulted in slowing down of the cation and anion transport by 40-50%. Details of ion rotational and translational motion, coupling of the rotational and translational relaxation are also discussed.

19.
J Phys Chem B ; 114(15): 4984-97, 2010 Apr 22.
Article in English | MEDLINE | ID: mdl-20337454

ABSTRACT

Utilizing the transferable, quantum-chemistry-based, Atomistic Polarizable Potential for Liquids, Electrolytes, & Polymers (APPLE&P) force field, we have systematically investigated the influence of polarization effects on the accuracy of properties predicted from molecular dynamics simulations of various room temperature ionic liquids (ILs). Simulations of ILs in which the atom-based polarizability was set to zero for all atoms (nonpolarizable APPLE&P potential) resulted in changes in thermodynamic and dynamic properties from those predicted by the polarizable APPLE&P potential that are qualitatively different from changes observed for nonionic liquids. Investigation of structural and dynamical correlations using both the polarizable and nonpolarizable versions of APPLE&P allowed us to obtain a mechanistic understanding of the influence of polarization on dynamics in the ILs investigated. Additionally, the Force Matching (FM) approach was employed to systematically obtain nonpolarizable two-body force fields for several ILs that reproduce as accurately as possible intermolecular forces predicted by the polarizable model. Unlike water, for which the FM approach was found to yield an accurate representation of the liquid phase structure predicted by a polarizable model, the FM approach does not result in a two-body potential that accurately reproduces either structure or dynamics predicted by the polarizable IL model.


Subject(s)
Ionic Liquids/chemistry , Electrolytes/chemistry , Molecular Dynamics Simulation , Polymers/chemistry , Temperature , Thermodynamics
20.
Phys Chem Chem Phys ; 12(1): 170-82, 2010 Jan 07.
Article in English | MEDLINE | ID: mdl-20024457

ABSTRACT

The electric double layer (EDL) structure and capacitance have been studied for atomically flat and nanoporous conductive electrodes with a molten LiCl electrolyte using an electroactive interface molecular dynamics simulation methodology. For the atomically flat electrodes the electrolyte was observed to form a multilayer structure near the electrode described by exponentially decaying sinusoidal oscillations in ion and charge densities perpendicular to the electrode/electrolyte interface. The differential EDL capacitance vs. electrode potential was found to exhibit "U-shaped" behavior while the EDL capacitance exhibited complex dependence on electrode potential including regions of negative capacitance near zero electrode potential. Increased capacitance and an enhanced degree of electrode-electrolyte interface structure were observed with decreasing temperature. For nanoporous electrodes with both slit and cylindrical pore geometries, the electrolyte was observed to form highly structured alternating charged layers within the electrode nanopores. A maximum in the normalized (per unit electrode area) EDL capacitance was found for pore widths that accommodate several charged layers inside the pores. The observed dependence of capacitance on pore size appears to be a compromise between increasing structure/charge imbalance and decreasing ion density with decreasing pore width/diameter.

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