Single-Molecule Perspective on Mass Transport in Condensed Water Layers over Gradient Self-Assembled Monolayers

Giri, Dipak K.; Ashraf, Kayesh M.; Collinson, Maryanne M.; Higgins, Daniel A.

doi:10.1021/acs.jpcc.5b01958

Cited by 27 publications

(47 citation statements)

References 69 publications

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“…As RH increased, water nanofilms grew in thickness, and rhodamine molecules became significantly more mobile (see Supplemental Movies), as previously observed. 14,15 Specifically, molecular trajectories evolved from confined to exploratory with increasing RH, with ex-ploratory trajectories often exhibiting alternation between slow diffusion and long jumps ( Fig. 1a).…”

Section: Evolution Of Molecular Mobility With Nanofilm Thicknessmentioning

confidence: 99%

Temporally Anticorrelated Subdiffusion in Water Nanofilms on Silica Suggests Near-Surface Viscoelasticity

Sarfati

Schwartz

2020

ACS Nano

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We used single-molecule tracking to probe the local rheology of interfacial water.Fluorescent rhodamine molecules were tracked on silica surfaces as a function of ambient relative humidity, which controlled the thickness of condensed water nanofilms. At low humidity, the molecules exhibited confined diffusion in the vicinity of isolated adsorption sites characterized by a broad distribution of binding stiffness constants; subsequent chemical or physical surface passivation selectively eliminated stiffer binding sites. At increased humidity, molecularly thin water films condensed, permitting near-surface transport of rhodamine molecules. Motion was subdiffusive, with an anomalous exponent increasing with the nanofilm thickness. Molecular trajectories were temporally anticorrelated, ergodic, but also featured transient binding and intermittent diffusion.Statistical modeling demonstrated that this complex motion in water nanofilms had the characteristics of fractional Brownian motion combined with a continuous time random walk. This was consistent with diffusion within viscoelastic nanofilms, suggesting persistent molecular structuring in the vicinity of the silica surface. 1 arXiv:2001.06072v1 [cond-mat.soft] 16 Jan 2020 Keywords silica, water nanofilm, single-molecule tracking, anomalous diffusion, confined diffusion, molecular structuringThe interface between water and silica (or related silicate minerals) is central to a wide range of geological and industrial processes, 1,2 yet many of its properties remain elusive, notably in the nanoscale limit where molecules are highly confined and constrained. The different forms of Si-O groups at the surface are believed to interact strongly with water molecules through hydrogen bonding, leading to molecular ordering that extends several Å from the surface. 3Water structuring, in turn, may impact transport properties at the interface, by influencing the hydrodynamic slip or no-slip boundary conditions, 4 and changing local rheology. The viscosity of water nanofilms remains hotly debated. While studies of water confined between two mica (an aluminosilicate mineral) surfaces separated by 5 nm and less found no substantial increase in viscosity, 5,6 experiments using scanning-probe techniques on silica and other hydrophilic surfaces have reported viscosity enhancement by as much as 10 6 . 4,7 Hydrophilic surfaces exposed to water vapor become spontaneously coated by a thin film of water at the Å-to-nm scale, with the exact thickness depending on substrate chemistry, temperature, and vapor pressure. Water physisorption is therefore ubiquitous in the Earth's subsurface, surface, and atmosphere, including on aerosol particles and ice (glacier and snow), 8 with significant consequences for environmental processes, for example in heterogeneous chemical reactions. 9 Thus, there is significant interest in understanding molecular transport in water nanofilms, despite the uncertainty with respect to the structure of these thin films. 10 Recent studies have elucidated the mechanisms o...

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Section: Evolution Of Molecular Mobility With Nanofilm Thicknessmentioning

confidence: 99%

Temporally Anticorrelated Subdiffusion in Water Nanofilms on Silica Suggests Near-Surface Viscoelasticity

Sarfati

Schwartz

2020

ACS Nano

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“…Fig. [39][40][41] Previous studies primarily employed single molecule tracking as a means to determine the mass transport mechanism and the dominance of desorptionmediated diffusion was revealed by a characteristic change in the single molecule step size distribution. Diffusion within the tubes clearly does not occur by a Fickian mechanism alone.…”

Section: Model For Srb Mass Transport In Bolaamphiphile Nanotubesmentioning

confidence: 99%

Imaging fluorescence correlation spectroscopy studies of dye diffusion in self-assembled organic nanotubes

Nagasaka

Kameta

et al. 2016

Phys. Chem. Chem. Phys.

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The rate and mechanism of diffusion by anionic sulforhodamine B (SRB) dye molecules within organic nanotubes self-assembled from bolaamphiphile surfactants were investigated by imaging fluorescence correlation spectroscopy (imaging-FCS). The inner and outer surfaces of the nanotubes are terminated with amine and glucose groups, respectively; the former allow for pH-dependent manipulation of nanotube surface charge while the latter enhance their biocompatibility. Wide-field fluorescence video microscopy was used to locate and image dye-doped nanotubes dispersed on a glass surface. Imaging-FCS was then used to spatially resolve the SRB transport dynamics. Mobilization of the dye molecules was achieved by immersion of the nanotubes in buffer solution. Experiments were performed in pH 6.4, 7.4 and 8.4 buffers, at ionic strengths ranging from 1.73 mM to 520 mM. The results show that coulombic interactions between cationic ammonium ions on the inner nanotube surface and the anionic SRB molecules play a critical role in governing mass transport of the dye. The apparent dye diffusion coefficient, D, was found to generally increase with increasing ionic strength and with increasing pH. The D values obtained were found to be invariant along the nanotube length. Mass transport of the SRB molecules within the nanotubes is concluded to occur by a desorption-mediated Fickian diffusion mechanism in which dye motion is slowed by its coulombic interactions with the inner surfaces of the nanotubes. The results of these studies afford information essential to the use of organic nanotubes in controlled drug release applications.

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“…[24,[39][40][41][42][43]. The results presented here provide a comprehensive picture of how and why adsorbate-surface interactions influence interfacial motion.…”

Section: Prl 119 268001 (2017) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 78%

3D Imaging of Hopping Molecules

Barkai

Garini

2017

Physics

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Theoretical predictions have suggested that molecular motion at interfaces-which influences processes including heterogeneous catalysis, (bio)chemical sensing, lubrication and adhesion, and nanomaterial self-assembly-may be dominated by hypothetical "hops" through the adjacent liquid phase, where a diffusing molecule readsorbs after a given hop according to a probabilistic "sticking coefficient." Here, we use three-dimensional (3D) single-molecule tracking to explicitly visualize this process for human serum albumin at solid-liquid interfaces that exert varying electrostatic interactions on the biomacromolecule. Following desorption from the interface, a molecule experiences multiple unproductive surface encounters before readsorption. An average of approximately seven surface collisions is required for the repulsive surfaces, decreasing to approximately two and a half for surfaces that are more attractive. The hops themselves are also influenced by long-range interactions, with increased electrostatic repulsion causing hops of longer duration and distance. These findings explicitly demonstrate that interfacial diffusion is dominated by biased 3D Brownian motion involving bulk-surface coupling and that it can be controlled by influencing short-and long-range adsorbate-surface interactions. DOI: 10.1103/PhysRevLett.119.268001 Molecular transport in fluid phases is understood in terms of the Brownian motion of individual molecules and particles, and can, therefore, be predicted and controlled by parameters including the hydrodynamic radius and fluid viscosity. In contrast, the analogous behavior at the interfaces remains poorly understood despite its fundamental interest and technological relevance; i.e., the dynamics of macromolecules at solid-liquid interfaces underlie many applications including chemical sensing, catalysis, lubrication, and adhesion [1][2][3][4][5][6]. While interfacial diffusion is nominally two dimensional (2D) and conventionally described in terms of 2D Brownian motion, longstanding theoretical models [7][8][9][10][11][12][13][14][15][16] have predicted that interfacial mass transport could actually be dominated by "flights" through an adjacent liquid phase, which would dramatically alter the nature of interfacial molecular motion; an understanding of this process is necessary in order to rationally control mass transport at surfaces. Recent experimental results indirectly support these predictions by measuring the 2D projection of trajectories for atoms, molecules, polymers, and nanoparticles, in thin films, at solid-liquid interface, and on lipid bilayers, which can be represented as an intermittent process with periods of apparent immobility alternating with long flights comprising a heavy-tailed distribution [17][18][19][20][21][22][23][24][25][26]. However, the evidence for the presence of three-dimensional (3D) hops remains indirect, and critical aspects of the proposed "hopping" process remain a mystery. For example, theoretical models represent a flight as a series of hops (i.e., ...

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Single-Molecule Perspective on Mass Transport in Condensed Water Layers over Gradient Self-Assembled Monolayers

Cited by 27 publications

References 69 publications

Temporally Anticorrelated Subdiffusion in Water Nanofilms on Silica Suggests Near-Surface Viscoelasticity

Temporally Anticorrelated Subdiffusion in Water Nanofilms on Silica Suggests Near-Surface Viscoelasticity

Imaging fluorescence correlation spectroscopy studies of dye diffusion in self-assembled organic nanotubes

3D Imaging of Hopping Molecules

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