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Ishraaq R, Akash TS, Bera A, Das S. Hydrophilic and Apolar Hydration in Densely Grafted Cationic Brushes and Counterions with Large Mobilities. J Phys Chem B 2024; 128:381-392. [PMID: 38148252 DOI: 10.1021/acs.jpcb.3c07520] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2023]
Abstract
We employ an all-atom molecular dynamics (MD) simulation framework to unravel water microstructure and ion properties for cationic [poly(2-(methacryloyloxy)ethyl) trimethylammonium chloride] (PMETAC) brushes with chloride ions as counterions. First, we identify locally separate water domains (or first hydration shells) each around {N(CH3)3}+ and the C═O functional groups of the PMETAC chain and one around the Cl- ion. These first hydration shells around the respective moieties overlap, and the extent of the overlap depends on the nature of the species triggering it. Second, despite the overlap, the water molecules in these domains demonstrate disparate properties dictated by the properties of the atoms and groups around which they are located. For example, the presence of the methyl groups makes the {N(CH3)3}+ group trigger apolar hydration as evidenced by the corresponding orientation of the dipole of the water molecules around the {N(CH3)3}+ moiety. These water molecules around the {N(CH3)3}+ group also have enhanced tetrahedrality compared to the water molecules constituting the hydration layer around the C═O group and the Cl- counterion. Our simulations also identify that there is an intervening water layer between the Cl- ion and {N(CH3)3}+ group: this layer prevents the Cl- ion from coming very close to the {N(CH3)3}+ group. As a consequence, there is a significantly large mobility of the Cl- ions inside the PMETAC brush layer. Furthermore, the C═O group of the polyelectrolyte (PE) chain, due to the partial negative charge on the oxygen atom and the specific structure of the PMETAC brush system, demonstrates strongly hydrophilic behavior and enforces a specific dipole response of water molecules analogous to that experienced by water around anionic species of high charge density. In summary, our findings confirm that PMETAC brushes undergo hydrophilic hydration at one site and apolar hydration at another site and ensure large mobility of the supported Cl- counterions.
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Affiliation(s)
- Raashiq Ishraaq
- Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, United States
| | - Tanmay Sarkar Akash
- Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, United States
| | - Arka Bera
- Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, United States
| | - Siddhartha Das
- Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, United States
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Telles IM, Arfan M, Dos Santos AP. Effects of electrostatic coupling and surface polarization on polyelectrolyte brush structure. J Chem Phys 2023; 158:144902. [PMID: 37061472 DOI: 10.1063/5.0147056] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/17/2023] Open
Abstract
In this work, we perform molecular dynamics simulations to study a spherical polyelectrolyte brush. We explore the effects of surface polarization and electrostatic coupling on brush size and distribution of counterions. The method of image charges is considered to take into account surface polarization, considering a metallic, an unpolarizable, and a dielectric nano-core. It is observed that, for all cases, a moderate shrinking-swelling effect appears with an increase in the electrostatic coupling parameter. This effect occurs under high Manning ratios. The curves relating the average size of polyelectrolyte brush as a function of coupling show a minimum. The results show that the grafting density of polyelectrolytes on the nano-core surface plays an important role in the polarization effect. We consider a modified Poisson-Boltzmann theory to describe the counterion profiles around the brush in the case of unpolarizable nano-cores and weak electrostatic coupling.
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Affiliation(s)
- Igor M Telles
- Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP 91501-970 Porto Alegre, RS, Brazil
| | - Muhammad Arfan
- Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP 91501-970 Porto Alegre, RS, Brazil
| | - Alexandre P Dos Santos
- Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP 91501-970 Porto Alegre, RS, Brazil
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Hanssen KØ, Malthe-Sørenssen A. Perineuronal nets restrict transport near the neuron surface: A coarse-grained molecular dynamics study. Front Comput Neurosci 2022; 16:967735. [DOI: 10.3389/fncom.2022.967735] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2022] [Accepted: 11/02/2022] [Indexed: 11/18/2022] Open
Abstract
Perineuronal nets (PNNs) are mesh-like extracellular matrix structures that wrap around certain neurons in the central nervous system. They are hypothesized to stabilize memories in the brain and act as a barrier between cell and extracellular space. As a means to study the impact of PNNs on diffusion, the nets were approximated by negatively charged polymer brushes and simulated by coarse-grained molecular dynamics. Diffusion constants of single neutral and single charged particles were obtained in directions parallel and perpendicular to the brush substrate. The results for the neutral particle were compared to different theories of diffusion in a heuristic manner. Diffusion was found to be considerably reduced for brush spacings smaller than 10 nm, with a pronounced anisotropy for dense brushes. The exact dynamics of the chains was found to have a negligible impact on particle diffusion. The resistance of the brush proved small compared to typical values of the membrane resistance of a neuron, indicating that PNNs likely contribute little to the total resistance of an enwrapped neuron.
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Li M, Zhuang B, Yu J. Effects of Ion Valency on Polyelectrolyte Brushes: A Unified Theory. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c01464] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Minglun Li
- School of Materials Science and Engineering, Nanyang Technological University, 639798 Singapore
| | - Bilin Zhuang
- Division of Science, Yale-NUS College, 138527 Singapore
| | - Jing Yu
- School of Materials Science and Engineering, Nanyang Technological University, 639798 Singapore
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Ehtiati K, Moghaddam SZ, Klok HA, Daugaard AE, Thormann E. Specific Counterion Effects on the Swelling Behavior of Strong Polyelectrolyte Brushes. Macromolecules 2022. [DOI: 10.1021/acs.macromol.2c00411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Koosha Ehtiati
- Department of Chemistry, Technical University of Denmark, 2800 Kgs Lyngby, Denmark
| | - Saeed Z. Moghaddam
- Department of Chemistry, Technical University of Denmark, 2800 Kgs Lyngby, Denmark
| | - Harm-Anton Klok
- Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratoire des Polyméres, Institut des Matériaux and Institut des Sciences et Ingénierie Chimiques, Bâtiment MXD, Station 12, CH-1015 Lausanne, Switzerland
| | - Anders E. Daugaard
- Danish Polymer Center, Department of Chemical and Biochemical Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| | - Esben Thormann
- Department of Chemistry, Technical University of Denmark, 2800 Kgs Lyngby, Denmark
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Luo Y, Pang AP, Lu X. Liquid-Solid Interfaces under Dynamic Shear Flow: Recent Insights into the Interfacial Slip. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:4473-4482. [PMID: 35377658 DOI: 10.1021/acs.langmuir.2c00037] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The development of micro/nanofluidic techniques has recently revived interest in dynamic shear flow at liquid-solid interfaces. When the nature of the liquid-solid boundaries was revisited, the slip of the fluids relative to the solid wall was predicted theoretically and confirmed experimentally. This indicates that the molecular-level structures of the liquid-solid interfaces will be influenced by the liquid flow over certain temporal and spatial criteria. However, the fluid flow at the boundary layer still cannot be precisely predicted and effectively controlled, somehow limiting its practical applications. Here, we summarize the recent advances for the microscopic structures at the liquid-solid interfaces upon shear flow. Special attention was given to a second-order nonlinear optical technique, sum frequency generation vibrational spectroscopy, which is a powerful tool for exploring the molecular-level structures and structural dynamics at the liquid-solid interfaces and offering new insights into the molecular mechanisms of the fluid slip at the interfaces. Moreover, we discuss the possible approaches for controlling the interfacial slip at the molecular level and highlight the current challenges and opportunities. Although the theoretical framework of the slip at the liquid-solid interfaces is still incomplete, we hope that this Perspective will complement and enhance our understanding of various interfacial properties and phenomena with respect to practical non-equilibrium dynamic processes happening at the interfaces.
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Affiliation(s)
- Yongsheng Luo
- The State Key Laboratory of Bioelectronics, School of Biological Science & Medical Engineering, Southeast University, Nanjing 210096, Jiangsu, P. R. China
| | - Ai-Ping Pang
- The State Key Laboratory of Bioelectronics, School of Biological Science & Medical Engineering, Southeast University, Nanjing 210096, Jiangsu, P. R. China
| | - Xiaolin Lu
- The State Key Laboratory of Bioelectronics, School of Biological Science & Medical Engineering, Southeast University, Nanjing 210096, Jiangsu, P. R. China
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Luo Y, Pang AP, Zhu P, Wang D, Lu X. Demonstrating the Interfacial Polymer Thermal Transition from Coil-to-Globule to Coil-to-Stretch under Shear Flow Using SFG and MD Simulation. J Phys Chem Lett 2022; 13:1617-1627. [PMID: 35142518 DOI: 10.1021/acs.jpclett.1c03866] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Revealing interfacial shear-induced structural responsiveness has long been an important topic in that most fluids in nature and human life are in motion and cause interesting boundary phenomena. It is amazing how the polymer chain conformation or local structural features at a boundary change under the effective shear condition. In this study, microfluidic-assisted sum frequency generation (SFG) vibrational spectroscopy and all-atom molecular dynamics (MD) simulation are combined to reveal that the shear flow can effectively block the so-called thermal coil-to-globule transition of the poly(N-isopropylacrylamide) (PNIPAM) brushes on the solid substrate, and the normal coil-to-globule transition transfers to a coil-to-stretch one under shear flow with increasing ambient temperature. Such findings are attributed to the balance between the shear flow and the molecular interaction with respect to the polymer chains and adjacent water molecules, thus demonstrating the significant effect of the shear flow on the structural and dynamic behaviors of the polymer chains at the boundaries from the molecular level.
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Affiliation(s)
- Yongsheng Luo
- State Key Laboratory of Bioelectronics, School of Biological Science & Medical Engineering, Southeast University, Nanjing 210096, Jiangsu Province, P. R. China
| | - Ai-Ping Pang
- State Key Laboratory of Bioelectronics, School of Biological Science & Medical Engineering, Southeast University, Nanjing 210096, Jiangsu Province, P. R. China
| | - Peizhi Zhu
- College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225009, Jiangsu Province, P. R. China
| | - Dayang Wang
- State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, Jilin Province, P. R. China
| | - Xiaolin Lu
- State Key Laboratory of Bioelectronics, School of Biological Science & Medical Engineering, Southeast University, Nanjing 210096, Jiangsu Province, P. R. China
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