The molecular configuration of a DOPA/ST monolayer at the air–water interface: a molecular dynamics study

Kong, Chui‐Peng; Peters, E.A.J.F.; Zheng, Qing‐Chuan; With, G. de; Zhang, Hongxing

doi:10.1039/c4cp00555d

Cited by 12 publications

(13 citation statements)

References 62 publications

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“…The simulations were performed using GROMACS-5.1.1, 43 and visual molecular dynamics (VMD) 44 was used for visualization of the droplet at the intermediate stages. Extended simple point charge (SPC/E) 45 water model was used for defining water molecules.…”

Section: Simulation Detailsmentioning

confidence: 99%

Molecular Investigation of Contact Line Movement in Electrowetted Nanodroplets

2020

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Molecular dynamics (MD) simulation of an electrowetted nanodroplet is performed to understand the fundamental origin of the involved parameters resulted from the molecular movement in the vicinity of the three-phase contact line (TPCL). During the spreading of the droplet, contact line friction (CLF) force is found to be the controlling one among all other resistive forces. Being molecular in nature, MD study is required to unveil the CLF, which is manifested by the TPCL friction coefficient ζ. The combined effect of temperature, electric field, and surface wettability, manifested by the solid–liquid Lennard-Jones interaction parameter, is studied to explore the droplet spreading. The entire droplet wetting dynamics is divided into two different regimes, namely, spreading regime and equilibrium regime. The molecular frequency during the TPCL movement in the equilibrium regime is affected by the presence of any external perturbation and results in an alteration of ζ. The predetermined knowledge of the alteration of CLF due to the coupling effect of electric field and temperature will have a potential application towards designing electric field-inspired droplet movement devices.

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Section: Simulation Detailsmentioning

confidence: 99%

Molecular Investigation of Contact Line Movement in Electrowetted Nanodroplets

2020

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“…The simulations reported herein were carried out using GROMACS-4.0.7 20-21-22 whereas Visual Molecular Dynamics (VMD) 23 was used for intermittent visualization of the droplet configuration. The well-known L-J [U LJ (r)] potential was used to model the system, 12 6…”

Section: Simulation Detailsmentioning

confidence: 99%

Thermally enhanced self-propelled droplet motion on gradient surfaces

et al. 2015

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Droplet motion over a surface with wettability gradient has been simulated using molecular dynamics (MD) simulation to highlight the underlying physics. GROMACS and Visual Molecular Dynamics (VMD) were used for simulation and intermittent visualization of the droplet configuration respectively. The simulations mimic experiments in a comprehensive manner wherein micro-sized droplets are propelled by surface wettability gradient against a number of retarding forces. The liquid-wall Lennard-Jones interaction parameter and the substrate temperature were varied to explore their effects on the three-phase contact line friction coefficient. The contact line friction was observed to be a strong function of temperature at atomistic scales, confirming the experimentally observed inverse functionality between the coefficient of contact line friction and increase in temperatures. These MD simulation results were successfully compared with the results from a model for self-propelled droplet motion on gradient surfaces.

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“…Besides that, most molecular modeling approaches to surfactant monolayer formation and resulting surface tension have applied to various lung surfactants and other lipid-based monolayer assemblies because of the biological relevance (e.g., refs − ). Martinez et al have examined via molecular modeling SDS monolayers, Phan et al have examined MIBC/CTAB mixtures, and Kong et al have examined simpler biosurfactants at different surface concentrations and have connected the findings to surface tension. The surface coverage dependency of surfactant aggregate morphologies at the interface has also received some molecular modeling attention for various surfactants (e.g., refs − ).…”

Section: Introductionmentioning

confidence: 99%

Surfactant Interactions and Organization at the Gas–Water Interface (CTAB with Added Salt)

et al. 2018

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We have studied adsorbed layers of cetyltrimethylammonium bromide (CTAB) at air-water interfaces in the presence of added electrolyte. Fast bubble compression/expansion measurements were used to obtain the surface equation of state, i.e., the surface tension vs CTAB surface concentration dependence. We show that while a simple model where the surfactant molecules are assumed to be noninteracting is insufficient to describe the measured response of the surfactant layer, a modified Frumkin equation where the local interactions between the molecular components depend on their surface concentration captures the response. The variation of the effective interactions in the surfactant layer in the model shows that the interactions in the surfactant layer change from effectively repulsive to attractive with increasing surface concentration. Molecular dynamics simulations are performed to probe the origins of the change in the interactions. The simulations indicate that already at low surface concentrations the surfactants aggregate as highly dynamic rafts with surfactant orientation parallel to the interface. Increasing the concentration leads to a change in the assembly morphology at the interface: the surfactant layer thickens and the surfactants sample a range of tilted orientations with respect to the interfacial plane. The change from transient raftlike assemblies to dynamical aggregates at the interface involves a clear increase in the degree of counterion binding: we speculate that the flip of the effective interaction parameter in the model used to interpret the experimental results could result from this. The work here presents basic steps toward a proper understanding of the molecular organization and interactions of surfactants at an air-water interface. This is crucially important in understanding macroscopic properties of surfactant-stabilized systems such as foams, emulsions, and colloidal dispersions.

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The molecular configuration of a DOPA/ST monolayer at the air–water interface: a molecular dynamics study

Cited by 12 publications

References 62 publications

Molecular Investigation of Contact Line Movement in Electrowetted Nanodroplets

Molecular Investigation of Contact Line Movement in Electrowetted Nanodroplets

Thermally enhanced self-propelled droplet motion on gradient surfaces

Surfactant Interactions and Organization at the Gas–Water Interface (CTAB with Added Salt)

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