Co-reporter:Hanjong Yoo, Ki Chul Kim, Seung Soon Jang
Computational Materials Science 2017 Volume 126() pp:299-307
Publication Date(Web):January 2017
DOI:10.1016/j.commatsci.2016.10.004
•Coarse-grained models and force field were developed for solar cell simulation.•Coarse-grained molecular dynamics simulations were employed for simulation.•The P3HT-PCBM system was found to attain the best structures among the systems.The interface-to-volume ratio of the structure and the transport property of the charge careers are the two main factors affecting the photovoltaic cell performance. In this study, the blends of poly(3-alkylthiophene) (P3AT) (A denotes H, N, and D for hexyl, nonyl, and dodecyl, respectively) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are investigated to understand the effect of the variation of molecular structure of the thiophene-based polymer in the active layer on the two main factors. First, we develop well-designed coarse-grained models to efficiently describe P3AT-PCBM systems. Next, the coarse-grained molecular dynamics simulations are performed to investigate the structural properties of three coarse-grained active layer systems, P3AT-PCBM. We conclude from our simulated analysis that the P3HT-PCBM system will provide the structurally optimized condition for the best photovoltaic cell performance. This is evidenced by two observations: (1) P3HT exhibits a good contact with PCBM in molecular level and (2) the P3HT-PCBM system forms a well-organized molecular network in each of the electron donor and accepter phases.Figure optionsDownload full-size imageDownload as PowerPoint slide
Co-reporter:Tianyuan Liu;Ki Chul Kim;Byeongyong Lee;Zhongming Chen;Suguru Noda;Seung Woo Lee
Energy & Environmental Science (2008-Present) 2017 vol. 10(Issue 1) pp:205-215
Publication Date(Web):2017/01/18
DOI:10.1039/C6EE02641A
Self-polymerized dopamine is a versatile coating material that has various oxygen and nitrogen functional groups. Here, we demonstrate the redox-active properties of self-polymerized dopamine on the surface of few-walled carbon nanotubes (FWNTs), which can be used as organic cathode materials for both Li- and Na-ion batteries. We reveal the multiple redox reactions between self-polymerized dopamine and electrolyte ions in the high voltage region from 2.5 to 4.1 V vs. Li using both density functional theory (DFT) calculations and electrochemical measurements. Free-standing and flexible hybrid electrodes are assembled using a vacuum filtration method, which have a 3D porous network structure consisting of polydopamine coated FWNTs. The hybrid electrodes exhibit gravimetric capacities of ∼133 mA h g−1 in Li-cells and ∼109 mA h g−1 in Na-cells utilizing double layer capacitance from FWNTs and multiple redox-reactions from polydopamine. The polydopamine itself within the hybrid film can store high gravimetric capacities of ∼235 mA h g−1 in Li-cells and ∼213 mA h g−1 in Na-cells. In addition, the hybrid electrodes show a high rate-performance and excellent cycling stability, suggesting that self-polymerized dopamine is a promising cathode material for organic rechargeable batteries.
Co-reporter:Ki Chul Kim; Eric G. Moschetta; Christopher W. Jones
Journal of the American Chemical Society 2016 Volume 138(Issue 24) pp:7664-7672
Publication Date(Web):May 28, 2016
DOI:10.1021/jacs.6b03309
Molecular dynamics simulations are performed to investigate the cooperatively catalyzed aldol condensation between acetone and 4-nitrobenzaldehyde on alkylamine (or alkylenamine)-grafted silica surfaces, focusing on the mechanism of the catalytic activation of the acetone and 4-nitrobenzaldehyde by the acidic surface silanols followed by the nucleophilic attack of the basic amine functional group toward the activated reactant. From the analysis of the correlations between the catalytically active acid–base sites and reactants, it is concluded that the catalytic cooperativity of the acid–base pair can be affected by two factors: (1) the competition between the silanol and the amine (or enamine) to form a hydrogen bond with a reactant and (2) the flexibility of the alkylamine (or alkylenamine) backbone. Increasing the flexibility of the alkylamine facilitates the nucleophilic attack of the amine on the reactants. From the molecular dynamics simulations, it is found that C3 propylamine and C4 butylamine linkers exhibit the highest probability of reaction, which is consistent with the experimental observation that the activity of the aldol reaction on mesoporous silica depends on the length of alkylamine grafted on the silica surface. This simulation work serves as a pioneering study demonstrating how the molecular simulation approach can be successfully employed to investigate the cooperative catalytic activity of such bifunctional acid–base catalysts.
Co-reporter:Ki Chul Kim; Tianyuan Liu; Seung Woo Lee
Journal of the American Chemical Society 2016 Volume 138(Issue 7) pp:2374-2382
Publication Date(Web):January 29, 2016
DOI:10.1021/jacs.5b13279
The Li-binding thermodynamics and redox potentials of seven different quinone derivatives are investigated to determine their suitability as positive electrode materials for lithium-ion batteries. First, using density functional theory (DFT) calculations on the interactions between the quinone derivatives and Li atoms, we find that the Li atoms primarily bind with the carbonyl groups in the test molecules. Next, we observed that the redox properties of the quinone derivatives can be tuned in the desired direction by systematically modifying their chemical structures using electron-withdrawing functional groups. Further, DFT-based investigations of the redox potentials of the Li-bound quinone derivatives provide insights regarding the changes induced in their redox properties during the discharging process. The redox potential decreases as the number of bound Li atoms is increased. However, we found that the functionalization of the quinone derivatives with carboxylic acids can improve their redox potential as well as their charge capacity. Through this study, we also determined that the cathodic activity of quinone derivatives during the discharging process relies strongly on the solvation effect as well as on the number of carbonyl groups available for further Li binding.
Co-reporter:Chandrani Pramanik, Parveen Sood, Li-na Niu, He Yuan, Sushanta Ghoshal, Walter Henderson, Yaodong Liu, Seung Soon Jang, Satish Kumar, David H. Pashley, Franklin R. Tay
Acta Biomaterialia 2016 Volume 31() pp:339-347
Publication Date(Web):February 2016
DOI:10.1016/j.actbio.2015.12.008
Abstract
Long-term oral and intravenous use of nitrogen-containing bisphosphonates (N-BPs) is associated with osteonecrosis of the jaw. Although N-BPs bind strongly to bone surfaces via non-covalent bonds, it is possible for extrinsic ions to dissociate bound N-BPs from mineralized bone by competitive desorption. Here, we investigate the effects and mechanism of using an ionic cocktail derived from borate bioactive glass for sequestration of heterocyclic N-BPs bound to apatite. By employing solid-state and solution-state analytical techniques, we confirmed that sequestration of N-BPs from bisphosphonate-bound apatite occurs in the presence of the borate-containing ionic cocktail. Simulations by density functional theory computations indicate that magnesium cation and borate anion are well within the extent of the risedronate or zoledronate anion to form precipitate complexes. The sequestration mechanism is due to the borate anion competing with bisphosphonates for similar electron-deficient sites on the apatite surface for binding. Thus, application of the borate-containing ionic cocktail represents a new topical lavage approach for removing apatite-bound heterocyclic N-BPs from exposed necrotic bone in bisphosphonate-related osteonecrosis of the jaw.
Statement of significance
Long-term oral consumption and injections of nitrogen-containing bisphosphonates (N-BPs) may result in death of the jaw bone when there is traumatic injury to the bone tissues. To date, there is no effective treatment for such a condition. This work reported the use of an ionic cocktail derived from water-soluble borate glass microfibers to displace the most potent type of N-BPs that are bound strongly to the mineral component on bone surfaces. The mechanism responsible for such an effect has been identified to be cation-mediated complexation of borate anions with negatively-charged N-BPs, allowing them to be released from the mineral surface. This borate-containing cocktail may be developed into a novel topical rinse for removing mineral-bound N-BPs from exposed dead bone.
Co-reporter:Sang Eun Jee, Jienfeng Zhou, Jianquo Tan, Lorenzo Breschi, Franklin R. Tay, Geneviève Grégoire, David H. Pashley, Seung Soon Jang
Acta Biomaterialia 2016 Volume 36() pp:175-185
Publication Date(Web):May 2016
DOI:10.1016/j.actbio.2016.03.012
Highlights
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Using molecular simulation, ethanol infiltration into the collagen was investigated.
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Ethanol molecules infiltrated into the gap region only.
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Only the third bound water layer was modified by ethanol molecules.
Co-reporter:Byeong Jae Chun, Christina Clare Fisher and Seung Soon Jang
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 8) pp:6284-6290
Publication Date(Web):28 Jan 2016
DOI:10.1039/C5CP07100C
We investigate multicompartment micelles consisting of poly(2-oxazoline)-based triblock copolymers for nanoreactor applications, using the DPD simulation method to characterize the internal structure of the micelles and the distribution of reactant. The DPD simulation parameters are determined from the Flory–Huggins interaction parameter (χFH). From the snapshots of the micellar structures and radial distribution function of polymer blocks, it is clearly presented that the micelle is multicompartmental. In addition, by implementing the DPD simulations in the presence of reactants, it is found that Reac-C4 and Reac-OPh are associate well with the hydrophilic shell of the micelle, whereas the other two reactants, Reac-Ph and Reac-Cl, are not incorporated into the micelle. From our DPD simulations, we confirm that the miscibility (solubility) of reactant with the micelle has a strong correlation with the rate of hydrolysis kinetic resolution. Utilizing accurate methods evaluating accurate χFH parameters for molecular interactions in micelle system, this DPD simulation can have a great potential to predict the structures of micelles consisting of designed multiblock copolymers for useful reactions.
Co-reporter:Giuseppe F. Brunello, Ji Hye Lee, Seung Geol Lee, Ji Il Choi, David Harvey and Seung Soon Jang
RSC Advances 2016 vol. 6(Issue 74) pp:69670-69676
Publication Date(Web):18 Jul 2016
DOI:10.1039/C6RA09274H
In this study, a three-phase interfacial system of a fuel cell is simulated using a multi-scale simulation approach consisting of quantum mechanical density functional theory and molecular dynamics simulations. Through these simulations, the structural and transport properties of the three-phase system are investigated. The molecular interactions among the components of the three-phase interfacial system are examined by density functional theory and parameterized for potential energy functions of force field. First, we investigate the interactions of the Pt clusters with various molecules as a function of distance using the density functional theory method with dispersion correction. Based on the results of these calculations, a non-bonded interaction curve is built for each Pt–molecule pair. Such non-bonded interaction curves are reproduced by potential energy functions with optimized parameters. Based on these investigations, we develop a force field to describe the structures and transport properties of the Nafion–Pt–carbon (graphite) three-phase interfacial system using molecular dynamics simulations.
Co-reporter:Juho Lee;Inchan Kwon;Art E. Cho
Journal of Molecular Modeling 2016 Volume 22( Issue 4) pp:
Publication Date(Web):2016 April
DOI:10.1007/s00894-016-2960-x
Neurotoxic plaques composed of 39 to 42 residue-long amyloid beta peptides (Aβs) are copiously present in the brains of patients with Alzheimer’s disease (AD). Erythrosine B (ER), a xanthene food dye, inhibits the formation of Aβ fibrils and Aβ-associated cytotoxicity in vitro. Here, in an attempt to elucidate the inhibition mechanism, we performed molecular dynamics (MD) simulations to demonstrate the conformational change of Aβ40 induced by ER molecules in atomistic detail. During the simulation, the ER bound to the surfaces of both N-terminus and C-terminus regions of Aβ40. Our result shows that ER interacts with the aromatic side chains at the N-terminus region resulting in destabilization of the inter-chain stacking of Aβ40. Moreover, the stablility of the helical structures at the residues from 13 to 16 suggests that ER disturbs conformational transition of Aβ40. At the C-terminus region, the bound ER blocks water molecules and stabilizes the α-helical structure. Regardless of the number of ER molecules used, the interruption of the formation of the salt-bridge between aspartic acid 23 and lysine 28 occurred. To further validate our analysis, binding free energies of ER at each binding site were evaluated. The finding of stronger binding energy at the N-terminus region supports an inhibition mechanism induced by stacking interaction between ER and phenylalanine. These findings could aid present and future treatment studies for AD by clarifying the inhibition mechanism of ER on the conformational transition of Aβ40 at the molecular level.
Co-reporter:Tianyuan Liu, Ki Chul Kim, Reza Kavian, Seung Soon Jang, and Seung Woo Lee
Chemistry of Materials 2015 Volume 27(Issue 9) pp:3291
Publication Date(Web):April 13, 2015
DOI:10.1021/acs.chemmater.5b00314
Reduced graphene oxides are active as positive electrodes for lithium-ion energy storage based on the surface redox reactions between oxygen functional groups and Li ions. For effective Li-ion energy storage within a confined mass and volume, free-standing, high-packing density, and redox-active graphene films were fabricated by a simple two-step compression and vacuum-drying process from a hydrothermally reduced graphene hydrogel. The assembled graphene films showed a folded microstructure with high packing densities up to ∼0.64 g/cm3. Redox-active oxygen functional groups on the graphene oxide were activated and controlled by the hydrothermal reduction temperature. Density functional theory (DFT) calculations revealed that the carbonyl and epoxide groups among various oxygen functional groups on graphene were the main contributors for the high potential redox reactions with Li ions. The folded graphene film electrodes delivered both a high gravimetric energy of ∼419 Wh/kg and a high volumetric energy of ∼239 Wh/L. In addition, the folded graphene film electrodes exhibited an exceptional cycling stability, retaining a gravimetric capacity of ∼160 mAh/g after 50 000 cycles. These results provide significant insights on the effective utilization of surface redox reactions to design graphene-based electrodes for high-performance Li-ion energy storage devices.
Co-reporter:Ji Il Choi, Samuel D. Snow, Jae-Hong Kim, and Seung Soon Jang
Environmental Science & Technology 2015 Volume 49(Issue 3) pp:1529-1536
Publication Date(Web):January 20, 2015
DOI:10.1021/es504614u
The nature of fullerene-water interactions has been the subject of much research and debate. Specifically, the presence of a stabilizing, negative surface potential on colloidal aggregates of C60 in water is unexpected, given the neutral nature of pure carbon, and is not well understood. Previous simulation efforts have focused on the C60-water interaction using molecular dynamics simulations that lacked the ability to account for charge transfer and distribution interactions. In this study, first-principles density functional theory was used to analyze the fundamental electronic interactions to elucidate the polarization and charge transfer between water and C60. Simulations show that charge is inductively transferred to the C60 from water molecules, with subsequent polarization of the C60 molecule. In a case with two neighboring C60 molecules, the charge polarization induces a charge onto the second C60. Simulation suggests that this charge transfer and polarization may contribute at least partly to the observed negative surface potential of fullerene aggregates and, combined with hydrogen bonding network formation around C60, provides a fundamental driving force for aggregate formation in water.
Co-reporter:Samuel D. Snow, Ki Chul Kim, Kyle J. Moor, Seung Soon Jang, and Jae-Hong Kim
Environmental Science & Technology 2015 Volume 49(Issue 4) pp:2147-2155
Publication Date(Web):January 29, 2015
DOI:10.1021/es504735h
The excellent photophysical properties of C60 fullerenes have spurred much research on their application to aqueous systems for biological and environmental applications. Spontaneous aggregation of C60 in water and the consequent diminution of photoactivity present a significant challenge to aqueous applications. The mechanisms driving the reduction of photoactivity in fullerene aggregates and the effects of functionalization on these processes, however, are not well understood. Here, we take a closer look at the molecular phenomena of functionalized fullerene interactions in water utilizing simulation and experimental tools. Molecular dynamic simulations were performed to investigate time-evolved molecular interactions in systems containing fullerenes with water, oxygen, and/or neighboring fullerene molecules, complimented by physical and chemical characterizations of the fullerenes pre- and postaggregation. Aggregates with widely different photoactivities exhibit similar fullerene–water interactions as well as surface and aggregation characteristics. Photoactive fullerene aggregates had weaker fullerene–fullerene and fullerene–O2 interactions, suggesting the importance of molecular interactions in the sensitization route.
Co-reporter:Byeong Jae Chun, Jie Lu, Marcus Weck and Seung Soon Jang
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 43) pp:29161-29170
Publication Date(Web):07 Oct 2015
DOI:10.1039/C5CP03854E
The hydrolytic kinetic resolution (HKR) of epoxides has been performed in a shell-crosslinked micellar (SCM) nanoreactor consisting of amphiphilic triblock copolymers based on poly(2-oxazline)s polymer derivatives with attached Co(III)-salens to the micelle core. To investigate the effect of the molecular interaction of reactant/product molecules with the SCM nanoreactor on the rate of HKR, we calculated the Flory–Huggins interaction parameters (χ) using the molecular dynamics simulation method. For this, the blend systems were constructed with various compositions such as 15, 45, and 70 wt% of the reactant/product molecules with respect to the polymers such as poly(2-methyl-2-oxazoline) (PMOX), poly(2-(3-butinyl)2-oxazoline) (PBOX), and poly(methyl-3-oxazol-2-yl)pentanoate with Co(III)-salen (PSCoX). From the χ parameters, we demonstrate that the miscibility of reactants/products with polymers has a strong correlation with the experimental reaction rate of the HKR: phenyl glycidyl ether (Reac-OPh) > epoxyhexane (Reac-C4) > styrene oxide (Reac-Ph) > epichlorohydrin (Reac-Cl). To validate this finding, we also conducted the potential of mean force analysis using steered molecular dynamics simulation for the molecular displacement of Reac-Cl and Reac-OPh through PMOX and PSCoX, revealing that the free energy reduction was greater when Reac-OPh molecule enters the polymer phase compared to Reac-Cl, which agrees with the findings from the χ parameters calculations.
Co-reporter:Wonsang Koh, Ji Hye Lee, Seung Geol Lee, Ji Il Choi and Seung Soon Jang
RSC Advances 2015 vol. 5(Issue 41) pp:32819-32825
Publication Date(Web):26 Mar 2015
DOI:10.1039/C4RA15619F
In this study, we investigated the mechanisms of Li adsorption on a graphene–C60 nanobud system using density functional theory. Li adsorption on the hybrid system was enhanced compared to those using pure graphene and C60. The Li adsorption energies ranged from −1.784 to −2.346 eV for the adsorption of a single Li atom, and from −1.905 to −2.229 eV for the adsorption of two Li atoms. Furthermore, adsorption energies were similar at most positions throughout the structure. The Li adsorption energy of an 18-Li adsorbed system was calculated to be −1.684 eV, which is significantly lower than Li–Li binding energy (−1.030 eV). These results suggest that Li atoms will be adsorbed preferentially (1) between C60 and C60, (2) between graphene and C60, (3) on graphene, or (4) on C60, rather than form Li clusters. As more Li atoms were adsorbed onto the graphene–C60 nanobud system because of its improved Li adsorption capability, the metallic character of the system was enhanced, which was confirmed via analysis of band structure and electronic density of states.
Co-reporter:Ying Chang, Angela D. Mohanty, Sarah B. Smedley, Khaldoon Abu-Hakmeh, Young Hun Lee, Joel E. Morgan, Michael A. Hickner, Seung Soon Jang, Chang Y. Ryu, and Chulsung Bae
Macromolecules 2015 Volume 48(Issue 19) pp:7117-7126
Publication Date(Web):September 29, 2015
DOI:10.1021/acs.macromol.5b01739
Proton-conducting superacidic polymer membranes with different fluoroalkyl sulfonate pendants attached to aromatic polymer backbones were synthesized via C–H functionalization and Suzuki coupling reactions. Variation in the chemical structures of the pendant acidic sulfonate moieties and their effects on membrane properties including water uptake, ion exchange capacity, morphology, and proton conductivity were systemically investigated. Membranes containing the short −OCF2SO3H pendant (PSU-S5) showed a smaller hydrophilic domain size and lower proton conductivity than those containing the longer pendants −OCF2CF2SO3H (PSU-S1) and −SCF2CF2SO3H (PSU-S4), likely due to the short chain’s less favorable aggregation and lower acidity. Polymer electrolyte membranes with unique branched fluoroalkyl sulfonate pendants (PSU-S6) gave larger ionic domain sizes, more uniform hydrophilic channels, and higher proton conductivity than samples with analogous linear pendant chains (PSU-S1), indicating that branched sulfonate structures may be a key future direction in the field of fuel cell membrane.
Co-reporter:Dr. Wonsang Koh;Hye Sook Moon; Seung Geol Lee;Dr. Ji Ii Choi; Seung Soon Jang
ChemPhysChem 2015 Volume 16( Issue 4) pp:789-795
Publication Date(Web):
DOI:10.1002/cphc.201402675
Abstract
The mechanism of Li adsorption on a graphene–fullerene (graphene–C60) hybrid system has been investigated using density functional theory (DFT). The adsorption energy for Li atoms on the graphene–C60 hybrid system (−2.285 eV) is found to be higher than that on bare graphene (−1.375 eV), indicating that the Li adsorption on the former system is more stable than on the latter. This is attributed to the high affinity of Li atoms to C60 and the charge redistribution that occurs after graphene is mixed with C60. The electronic properties of the graphene–C60 system such as band structure, density of states, and charge distribution have been characterized as a function of the number of Li atoms adsorbed in comparison to those of the pure graphene and C60. Li adsorption is found to preferentially occur on the C60 side due to the high adsorption energy of Li on C60, which imparts a metallic character to the C60 in the graphene–C60 hybrid system.
Co-reporter:Byeong Jae Chun, Seung Geol Lee, Ji Il Choi, Seung Soon Jang
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2015 Volume 474() pp:9-17
Publication Date(Web):5 June 2015
DOI:10.1016/j.colsurfa.2015.03.003
•Adsorption of carboxylates on the hydrophilic calcite surface was simulated.•A new force field was developed to investigate the thermodynamics of the adsorption.•Probable molecular packing of the adsorbed monolayer on the calcite was estimated.•The stability of the adsorbed carboxylates was assessed via steered MD simulation.•Desorption of carboxylate from calcite requires 148 kcal/mol in oil phase.The wettability of the hydrophilic calcium carbonate surface is altered by the adsorption of amphiphilic carboxylate compounds forming an oleophilic layer on the surface. In this study, we characterize the adsorption of carboxylates such as benzoate and stearate on the calcium carbonate (10 1¯ 4) surface using density functional theory (DFT) and molecular dynamics (MD) simulations. From our DFT computations using PBE-D3 method, the binding energy of a carboxylate adsorbed on the calcium carbonate in water phase is calculated to be −29.45 kcal/mol, which is utilized to develop a new set of force field parameters for molecular simulations. The optimal adsorption density of the carboxylates on the carbonate surface is determined using the newly developed force field: the adsorption of benzoate shows two probable adsorption densities at 20.20 Å2/molecule and 40.40 Å2/molecule, while the stearate adsorption has a single optimum at 20.20 Å2/molecule, which is in a good agreement with the experimental results. Lastly, through performing the steered molecular dynamics simulations to characterize the potential of mean force for the desorption of the carboxylate molecules from the calcium carbonate surface, the binding free energy is calculated as −148 kcal/mol in the presence of oil phase. This indicates that due to the stability of the carboxylate monolayer on calcium carbonate, the spontaneous desorption of carboxylate molecule from the calcium carbonate surface in nature is not likely.
Co-reporter:Byeong Jae Chun, Ji Il Choi, Seung Soon Jang
Colloids and Surfaces A: Physicochemical and Engineering Aspects 2015 Volume 474() pp:36-43
Publication Date(Web):5 June 2015
DOI:10.1016/j.colsurfa.2015.03.002
•SDS micelle was simulated for 20 ns using all-atom MD simulation.•SDS conformations are mostly bent in micelle.•Free volume in SDS micelle is ∼0.35% of the micelle volume.•Free energy change for water penetration through SDS micelle is ∼10 kcal/mol.•Dissociation of a single SDS molecule from the micelle requires ∼13 kcal/mol.We investigate a micelle consisting of 60 sodium dodecyl sulfate (SDS) molecules in water phase using molecular dynamics simulation method. The dimension of the micelle is evaluated as ∼16 Å and ∼21 Å for the radius of gyration and geometric radius, respectively, which are well agreed with the previous studies. By calculating the formation energy, it is found that the stability of micelle is driven by the interaction of the micelle with water phase. Via Connolly surface analysis, it was found that ∼58% of the micelle surface is occupied by the hydrophobic alkyl tails. The conformation analysis shows that the individual SDS molecules are bent within the micelle and are not aligned radially from the center-of-mass of the micelle. However, it turns out that the micelle is well packed with a small free volume (0.35% of the micelle volume) which does not allow the diffusion-in of water molecules. The PMF required to drag a water molecule from water phase to the center-of-mass of micelle is calculated as ∼10 kcal/mol while the PMF for a SDS molecule to be dissociated from the micelle is ∼13 kcal/mol, both of which demonstrate that the micellization is driven by minimizing unfavorable interaction of hydrophobic alkyl tail of SDS molecule with water phase.
Co-reporter:Soonchul Kwon, Ji Il Choi, Seung Geol Lee, Seung Soon Jang
Computational Materials Science 2014 Volume 95() pp:181-186
Publication Date(Web):December 2014
DOI:10.1016/j.commatsci.2014.07.042
•Multiple CO2 adsorption mechanisms on MgO and MgSi2O4 surface.•The adsorption energy of CO2 on Mg2SiO4 is 1.9–2.7 times higher than MgO.•The surface coverage (θ) of CO2 on Mg2SiO4 is four times higher than MgO.•The charge redistribution occurs more readily in the Mg2SiO4 than in the MgO.In this study, we investigated the adsorption of multiple CO2 on Mg-rich minerals such as magnesium oxide (MgO) and olivine (MgSi2O4) surface in order to understand the adsorption mechanism of CO2 using density functional theory (DFT) approach. It is found that the energy required for the adsorption of CO2 onto Mg2SiO4 surface is 2.5 times (−1.30 eV) and 2.7 times (−0.70 eV) higher than that onto MgO surface for single and multiple CO2 chemisorption, respectively. The surface coverage (θ) of Mg2SiO4 surface is 1, which is four times higher than that of MgO surface. By analyzing the charge distribution of each atom of the MgO and Mg2SiO4 surfaces before and after the adsorption of CO2 molecules, we observed that charge redistribution occurs more readily in CO2–Mg2SiO4 than in CO2–MgO.Graphical abstract
Co-reporter:Kyung Won Han ; Kwan Ho Ko ; Khaldoon Abu-Hakmeh ; Chulsung Bae ; Young Jun Sohn
The Journal of Physical Chemistry C 2014 Volume 118(Issue 24) pp:12577-12587
Publication Date(Web):May 22, 2014
DOI:10.1021/jp412473j
We investigate two types of polysulfone-based membranes (quaternary ammonium-functionalized anion exchange membrane and sulfonated proton exchange membrane) using molecular dynamics simulations to compare their nanophase-segregated structures and transport properties. Although the distribution of ionic groups on the polymer backbone is similar for both types, the quaternary ammonium groups and hydroxide ions in the anion exchange membrane are more solvated by water compared to the sulfonate groups and hydronium ions in the proton exchange membrane. Correspondingly, such better solvation of the ammonium groups and hydroxide ions leads the internal structure to a less matured hydrogen bonding network in the water phase, especially at low water content conditions. Through analysis of the nanophase segregation of the membranes, it is found that the characteristic correlation length has a similar value for both membranes, whereas the concentration contrast between the polymer domain and water phase is more distinct in the anion exchange membrane relative to the proton exchange membrane. Within such nanophase-segregated structures, it is found that the diffusion of hydroxide is ∼6% and ∼11% of that of hydronium at 10 and 20 wt % of water content, respectively, which might be due to the strong correlation at ∼4 Å among the hydroxide in the anion exchange membrane.
Co-reporter:Jung-Il Hong, Jiil Choi, Seung Soon Jang, Jiyeong Gu, Yangling Chang, Gregory Wortman, Robert L. Snyder, and Zhong Lin Wang
Nano Letters 2012 Volume 12(Issue 2) pp:576-581
Publication Date(Web):January 3, 2012
DOI:10.1021/nl203033h
It is known that bulk ZnO is a nonmagnetic material. However, the electronic band structure of ZnO is severely distorted when the ZnO is in the shape of a very thin plate with its dimension along the c-axis reduced to a few nanometers while keeping the bulk scale sizes in the other two dimensions. We found that the chemically synthesized ZnO nanoplates exhibit magnetism even at room temperature. First-principles calculations show a growing asymmetry in the spin distribution within the distorted bands formed from Zn (3d) and O (2p) orbitals with the reduction of thickness of the ZnO nanoplates, which is suggested to be responsible for the observed magnetism. In contrast, reducing the dimension along the a- or b-axes of a ZnO crystal does not yield any magnetism for ZnO nanowires that grow along c-axis, suggesting that the internal electric field produced by the large {0001} polar surfaces of the nanoplates may be responsible for the distorted electronic band structures of thin ZnO nanoplates.
Co-reporter:Seung Geol Lee, Tod A. Pascal, Wonsang Koh, Giuseppe F. Brunello, William A. Goddard, III, and Seung Soon Jang
The Journal of Physical Chemistry C 2012 Volume 116(Issue 30) pp:15974-15985
Publication Date(Web):July 11, 2012
DOI:10.1021/jp301610b
Technologies ranging from solvent extraction and drug delivery to tissue engineering are beginning to benefit from the unique ability of “smart polymers” to undergo controllable structural changes in response to external stimuli. The prototype is poly(N-isopropylacrylamide) (P(NIPAAm)) which exhibits an abrupt and reversible hydrophilic to hydrophobic transition above its lower critical solution temperature (LCST) of ∼305 K. We report here molecular dynamics simulations to show the deswelling mechanisms of the hydrated surface-grafted P(NIPAAm) brush at various temperatures such as 275, 290, 320, 345, and 370 K. The deswelling of the P(NIPAAm) brush is clearly observed above the lower critical solution temperature below which the P(NIPAAm) brush is associated with water molecules stably. By simulating the poly(acrylamide) brush as a reference system having the upper critical solution temperature (UCST) behavior with the same conditions employed in the P(NIPAAm) brush simulations, we confirmed that the deswelling of P(NIPAAm) brush does not take place at a given range of temperatures, which validates our simulation procedure. By analyzing the pair correlation functions and the coordination numbers, we found that the dissociation of water from the P(NIPAAm) brush occurs mainly around the isopropyl group of the P(NIPAAm) above the LCST because of its hydrophobicity. We also found that the NH of the amide group in NIPAAm does not actively participate in the hydrogen bonding with water molecules because of the steric hindrance caused by the attached isopropyl group, and thereby the hydrogen bonding interactions between amide groups and water molecules are significantly weakened with increasing temperature, leading to deswelling of the hydrated P(NIPAAm) brush above the LCST through favorable entropic change. These results explain the experimental observations in terms of a simple molecular mechanism for polymer function.
Co-reporter:Wonsang Koh, Ji Il Choi, Kevin Donaher, Seung Geol Lee, and Seung Soon Jang
ACS Applied Materials & Interfaces 2011 Volume 3(Issue 4) pp:1186
Publication Date(Web):March 28, 2011
DOI:10.1021/am200018w
The lithium (Li) adsorption mechanism on the metallic (5,5) single wall carbon nanotube (SWCNT)-fullerene (C60) hybrid material system is investigated using first-principles method. It is found that the Li adsorption energy (−2.649 eV) on the CNT-C60 hybrid system is lower than that on the peapod system (−1.837 eV) and the bare CNT (−1.720 eV), indicating that the Li adsorption on the CNT-C60 hybrid system is more stable than on the peapod or bare CNT system. This is due to the C60 of high electron affinity and the charge redistribution after mixing CNT with C60. In order to estimate how efficiently Li can utilize the vast surface area of the hybrid system for increasing energy density, the Li adsorption energy is calculated as a function of the adsorption positions around the CNT-C60 hybrid system. It turns out that Li preferably occupies the mid-space between C60 and CNT and then wraps up the C60 side and subsequently the CNT side. It is also found that the electronic properties of the CNT-C60 system, such as band structure, molecular orbital, and charge distribution, are influenced by the Li adsorption as a function of the number of Li atoms. From the results, it is expected that the CNT-C60 hybrid system has enhanced the charge transport properties in addition to the Li adsorption, compared to both CNT and C60.Keywords: carbon nanotubes; density functional theory; fullerenes; hybrid carbon material; Li adsorption mechanism
Co-reporter:Wonsang Koh, Ji I. Choi, Seung G. Lee, Wang R. Lee, Seung Soon Jang
Carbon 2011 Volume 49(Issue 1) pp:286-293
Publication Date(Web):January 2011
DOI:10.1016/j.carbon.2010.09.022
A carbon hybrid material system consisting of single wall carbon nanotubes (SWCNTs) and fullerene (C60) has been investigated using the first-principles methods. Through combining metallic SWCNTs with C60 of high electron affinity, the lithium adsorption energy on this CNT-C60 hybrid system (−2.110 eV) is found to be larger than that of the pure SWCNTs (−1.720 eV). By characterizing the electronic properties of the CNT-C60 system such as band structure, density of states and charge distribution as a function of the Li adsorption in comparison with SWCNT or C60, it is also found that the Li adsorption takes place on the C60 side preferably due to the large adsorption energy, which imparts metallic character to the C60 in the CNT-C60 hybrid system. Investigating various adsorption sites on the CNT-C60 system in order to understand the adsorption mechanism of Li, it is found that Li atoms are preferably adsorbed at every other hexagonal or pentagonal site (next nearest neighboring sites) rather than every site (nearest neighboring sites) on the hybrid system. The possibility of Li cluster formation in this CNT-C60 system does not seem to be high since the Li–Li binding is less favorable than the Li adsorption on the CNT-C60 system.A new carbon hybrid material system is made combining metallic single-walled carbon nanotubes and fullerene. This new carbon hybrid system has enhanced Li adsorption energy. Such enhanced adsorption energy is due to the high electron affinity of fullerene facilitating charge transfer from Li to the carbon hybrid system.
Co-reporter:Ying Chang, Giuseppe F. Brunello, Jeffrey Fuller, Marilyn Hawley, Yu Seung Kim, Melanie Disabb-Miller, Michael A. Hickner, Seung Soon Jang, and Chulsung Bae
Macromolecules 2011 Volume 44(Issue 21) pp:8458-8469
Publication Date(Web):October 11, 2011
DOI:10.1021/ma201759z
A novel sulfonation method that involves iridium-catalyzed aromatic C–H activation/borylation and subsequent Suzuki–Miyaura coupling with sulfonated phenyl bromides was developed for the preparation of aromatic ionomers. Superacidic fluoroalkyl sulfonic acid and less acidic aryl and alkyl sulfonic acids were efficiently incorporated into the aromatic ring of model polystyrene, and the resulting sulfonated ionomers were characterized for their properties as proton-conducting membranes. The membrane properties of ionomers containing sulfonic acid groups with different acidity strengths were compared to study the effect of acidity on the water properties, proton conductivity, and morphology. The superacidic fluoroalkyl sulfonated ionomer (sPS-S1) exhibited a significantly higher proton conductivity than that of the less acidic aryl and alkyl sulfonated ionomers (sPS-S2 and sPS-S3, respectively) at low relative humidity, despite a lower ion exchange capacity and lower water uptake. Hydration behaviors of the ionomers as a function of relative humidity were studied to correlate the acid strength of the sulfonates and water uptake properties. Morphology studies of the sulfonated ionomers show that sPS-S1 has a larger hydrophilic domain than that of sPS-S3. Molecular dynamic simulations were performed to understand the origin of the improved proton conductivity of the superacidic ionomer at the molecular level. These simulations suggest that the enhanced proton conductivity of sPS-S1 is due to the cumulative effect of higher acidity of the sulfonate, which leads to increased dissociation to hydronium ions and a higher degree of ionic character in the sulfonate, and better solvation of the sulfonate with water molecules.
Co-reporter:In-Yup Jeon, Ji Il Choi, Seung Geol Lee, Han Gi Chae, Seung Soon Jang, Satish Kumar and Jong-Beom Baek
The Journal of Physical Chemistry C 2010 Volume 114(Issue 35) pp:14868-14875
Publication Date(Web):August 19, 2010
DOI:10.1021/jp105918a
Few-walled carbon nanotube (FWCNT) was functionalized with two different natures of functional groups in a mild poly(phosphoric acid) (PPA)/phosphorus pentoxide (P2O5). The one is less polar 4-ethylbenzoyl-functionalized FWCNT (EB-FWCNT) and the other is more polar 4-(aminomethyl)benzoyl-functionalized FWCNT (AB-FWCNT). The degrees of their functionalities were estimated by thermogravimetric analysis (TGA) and they had one functional group per average 17.7 and 25.3 carbon atoms, respectively. Contrary to expectation, the amount of bound water in the EB-FWCNT was 96.6 wt % and it is higher than that for AB-FWCNT (82.3 wt %). The unusual sponge behavior of EB-FWCNT is attributed to higher hydration energy as determined based on molecular simulation studies. The electrochemical behaviors are also greatly different between the EB- and AB-FWCNT.
Co-reporter:Hyungjun Kim, Wei-Qiao Deng and William A. Goddard, III, Seung Soon Jang, Mark E. Davis, Yushan Yan
The Journal of Physical Chemistry C 2009 Volume 113(Issue 3) pp:819-826
Publication Date(Web):2017-2-22
DOI:10.1021/jp804873s
To investigate the effect of hydration on the diffusion of sodium ions through the aluminum-doped zeolite BEA system (Si/Al = 30), we used the grand canonical Monte Carlo (GCMC) method to predict the water absorption into aluminosilicate zeolite structure under various conditions of vapor pressure and temperature, followed by molecular dynamics (MD) simulations to investigate how the sodium diffusion depends on the concentration of water molecules. The predicted absorption isotherm shows first-order-like transition, which is commonly observed in hydrophobic porous systems. The MD trajectories indicate that the sodium ions diffuse through zeolite porous structures via hopping mechanism, as previously discussed for similar solid electrolyte systems. These results show that above 15 wt % hydration (good solvation regime) the formation of the solvation cage dramatically increases sodium diffusion by reducing the hopping energy barrier by 25% from the value of 3.8 kcal/mol observed in the poor solvation regime.
Co-reporter:Hyungjun Kim, William A. Goddard III, Seung Soon Jang, William R. Dichtel, James R. Heath and J. Fraser Stoddart
The Journal of Physical Chemistry A 2009 Volume 113(Issue 10) pp:2136-2143
Publication Date(Web):February 18, 2009
DOI:10.1021/jp809213m
Donor−acceptor binding of the π-electron-poor cyclophane cyclobis(paraquat-p-phenylene) (CBPQT4+) with the π-electron-rich tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) stations provides the basis for electrochemically switchable, bistable [2]rotaxanes, which have been incorporated and operated within solid-state devices to form ultradense memory circuits ( ChemPhysChem 2002, 3, 519−525; Nature 2007, 445, 414−417) and nanoelectromechanical systems. The rate of CBPQT4+ shuttling at each oxidation state of the [2]rotaxane dictates critical write-and-retention time parameters within the devices, which can be tuned through chemical synthesis. To validate how well computational chemistry methods can estimate these rates for use in designing new devices, we used molecular dynamics simulations to calculate the free energy barrier for the shuttling of the CBPQT4+ ring between the TTF and the DNP. The approach used here was to calculate the potential of mean force along the switching pathway, from which we calculated free energy barriers. These calculations find a turn-on time after the rotaxane is doubly oxidized of ∼10−7 s (suggesting that the much longer experimental turn-on time is determined by the time scale of oxidization). The return barrier from the DNP to the TTF leads to a predicted lifetime of 2.1 s, which is compatible with experiments.
Co-reporter:Seung Geol Lee, Giuseppe F. Brunello, Seung Soon Jang, J. Hannah Lee and David G. Bucknall
The Journal of Physical Chemistry B 2009 Volume 113(Issue 19) pp:6604-6612
Publication Date(Web):April 9, 2009
DOI:10.1021/jp8058867
We have used molecular modeling of both random and blocky hydrogel networks of poly (N-vinyl-2-pyrrolidone-co-2-hydroxyethyl methacrylate) with VP:HEMA = 37:13 composition to investigate the effect of the monomeric sequence on the mechanical properties. The degrees of monomer sequence randomness for the random and the blocky copolymers were 1.170 and 0.104, respectively, and the degree of polymerization was set as 50. The equilibrated density of the dry gel network was 0.968 ± 0.007 and 0.911 ± 0.007 g/cm3 for the random and the blocky sequences, respectively. In the partially hydrated state with 10 wt % water content, the effect of the monomeric sequence causes more distinct differences in density of 1.004 ± 0.007 and 0.916 ± 0.009 g/cm3 for the random and the blocky copolymer network, respectively. We observed that in such networks, the water molecules are associated more closely with the N-vinyl-2-pyrrolidone than with the hydroxyethyl methacrylate moieties, which is consistent with results from quantum mechanical solvation free energy calculations. By simulating a compressive deformation of the dry gels up to 80% strain, we found that the random sequence network develops higher stress levels than the blocky network. We also found that stress reduction occurs in the random sequence network due to the hydration, which is not evident in the blocky sequence network. This difference in stress reduction between the random and the blocky sequence networks is due to the difference in the structural rearrangement of monomers in the presence of water during deformation. The random sequence network is able to undergo much more efficient rearrangement of HEMA units than in the blocky sequence network.
Co-reporter:
Science 1920 Vol 51(1308) pp:85
Publication Date(Web):23 Jan 1920
DOI:10.1126/science.51.1308.85
Co-reporter:Chas. D. Woods
Science 1920 Vol 52(1355) pp:584-585
Publication Date(Web):17 Dec 1920
DOI:10.1126/science.52.1355.584
Co-reporter:Seung Geol Lee, Ji Il Choi, Wonsang Koh, Seung Soon Jang
Applied Clay Science (January 2013) Volume 71() pp:
Publication Date(Web):1 January 2013
DOI:10.1016/j.clay.2012.11.002
In this study, we investigate the kaolinite surfaces and their interaction with β-d-glucose and cellobiose using density functional theory calculations. We found that their molecular adsorption energy on kaolinite depends on i) the characteristics of the kaolinite surfaces such as the hydroxylated (001) surface or the siloxane 001¯ surface and ii) a molecular orientation of the monomer on the surface. The adsorption energy of the β-d-glucose and the cellobiose on the hydroxylated (001) surface are significantly greater (almost 200%) than that on the siloxane 001¯ surface since the hydroxyl group can form hydrogen bond more efficiently than the oxygen in siloxane group. Through Mulliken population analysis, we found that the hydrogen bond formation induces charge redistribution of the kaolinite surfaces. Therefore, the hydroxylated (001) surface undergoes more significant charge redistribution due to more hydrogen bond formation with adsorbate molecules in comparison to the siloxane 001¯ surface.Download full-size imageHighlights► We model the adsorption of β-D-glucose and cellobiose on kaolinite surface using DFT. ► Their adsorption energies are greater on the hydroxylated (001) surface in comparison to the siloxane 001¯ surface due to the hydrogen bond. ► The hydroxylated (001) surface undergoes more significant charge redistribution through the hydrogen bond formation.
Co-reporter:Byeong Jae Chun, Christina Clare Fisher and Seung Soon Jang
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 8) pp:NaN6290-6290
Publication Date(Web):2016/01/28
DOI:10.1039/C5CP07100C
We investigate multicompartment micelles consisting of poly(2-oxazoline)-based triblock copolymers for nanoreactor applications, using the DPD simulation method to characterize the internal structure of the micelles and the distribution of reactant. The DPD simulation parameters are determined from the Flory–Huggins interaction parameter (χFH). From the snapshots of the micellar structures and radial distribution function of polymer blocks, it is clearly presented that the micelle is multicompartmental. In addition, by implementing the DPD simulations in the presence of reactants, it is found that Reac-C4 and Reac-OPh are associate well with the hydrophilic shell of the micelle, whereas the other two reactants, Reac-Ph and Reac-Cl, are not incorporated into the micelle. From our DPD simulations, we confirm that the miscibility (solubility) of reactant with the micelle has a strong correlation with the rate of hydrolysis kinetic resolution. Utilizing accurate methods evaluating accurate χFH parameters for molecular interactions in micelle system, this DPD simulation can have a great potential to predict the structures of micelles consisting of designed multiblock copolymers for useful reactions.
Co-reporter:Byeong Jae Chun, Jie Lu, Marcus Weck and Seung Soon Jang
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 43) pp:NaN29170-29170
Publication Date(Web):2015/10/07
DOI:10.1039/C5CP03854E
The hydrolytic kinetic resolution (HKR) of epoxides has been performed in a shell-crosslinked micellar (SCM) nanoreactor consisting of amphiphilic triblock copolymers based on poly(2-oxazline)s polymer derivatives with attached Co(III)-salens to the micelle core. To investigate the effect of the molecular interaction of reactant/product molecules with the SCM nanoreactor on the rate of HKR, we calculated the Flory–Huggins interaction parameters (χ) using the molecular dynamics simulation method. For this, the blend systems were constructed with various compositions such as 15, 45, and 70 wt% of the reactant/product molecules with respect to the polymers such as poly(2-methyl-2-oxazoline) (PMOX), poly(2-(3-butinyl)2-oxazoline) (PBOX), and poly(methyl-3-oxazol-2-yl)pentanoate with Co(III)-salen (PSCoX). From the χ parameters, we demonstrate that the miscibility of reactants/products with polymers has a strong correlation with the experimental reaction rate of the HKR: phenyl glycidyl ether (Reac-OPh) > epoxyhexane (Reac-C4) > styrene oxide (Reac-Ph) > epichlorohydrin (Reac-Cl). To validate this finding, we also conducted the potential of mean force analysis using steered molecular dynamics simulation for the molecular displacement of Reac-Cl and Reac-OPh through PMOX and PSCoX, revealing that the free energy reduction was greater when Reac-OPh molecule enters the polymer phase compared to Reac-Cl, which agrees with the findings from the χ parameters calculations.
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