A combination of atomic force microscopy (AFM) and reflection interference contrast microscopy (RICM) was used to measure simultaneously the interaction force and the spatiotemporal evolution of the ...thin water film between a bubble in water and mica surfaces with varying degrees of hydrophobicity. Stable films, supported by the repulsive van der Waals–Casimir–Lifshitz force were always observed between air bubble and hydrophilic mica surfaces (water contact angle, θw < 5°) whereas bubble attachment occurred on hydrophobized mica surfaces. A theoretical model, based on the Reynolds lubrication theory and the augmented Young–Laplace equation including the effects of disjoining pressure, provided excellent agreement with experiment results, indicating the essential physics involved in the interaction between air bubble and solid surfaces can be elucidated. A hydrophobic interaction free energy per unit area of the form: W H (h) = −γ(1 – cos θw)exp(−h/D H ) can be used to quantify the attraction between bubble and hydrophobized solid substrate at separation, h, with γ being the surface tension of water. For surfaces with water contact angle in the range 45° < θw < 90°, the decay length D H varied between 0.8 and 1.0 nm. This study quantified the hydrophobic interaction in asymmetric system between air bubble and hydrophobic surfaces, and provided a feasible method for synchronous measurements of the interaction forces with sub-nN resolution and the drainage dynamics of thin films down to nm thickness.
In 1756, Leidenfrost observed that water drops skittered on a sufficiently hot skillet, owing to levitation by an evaporative vapour film. Such films are stable only when the hot surface is above a ...critical temperature, and are a central phenomenon in boiling. In this so-called Leidenfrost regime, the low thermal conductivity of the vapour layer inhibits heat transfer between the hot surface and the liquid. When the temperature of the cooling surface drops below the critical temperature, the vapour film collapses and the system enters a nucleate-boiling regime, which can result in vapour explosions that are particularly detrimental in certain contexts, such as in nuclear power plants. The presence of these vapour films can also reduce liquid-solid drag. Here we show how vapour film collapse can be completely suppressed at textured superhydrophobic surfaces. At a smooth hydrophobic surface, the vapour film still collapses on cooling, albeit at a reduced critical temperature, and the system switches explosively to nucleate boiling. In contrast, at textured, superhydrophobic surfaces, the vapour layer gradually relaxes until the surface is completely cooled, without exhibiting a nucleate-boiling phase. This result demonstrates that topological texture on superhydrophobic materials is critical in stabilizing the vapour layer and thus in controlling--by heat transfer--the liquid-gas phase transition at hot surfaces. This concept can potentially be applied to control other phase transitions, such as ice or frost formation, and to the design of low-drag surfaces at which the vapour phase is stabilized in the grooves of textures without heating.
Though topological aspects of energy bands are known to play a key role in quantum transport in solid-state systems, the implications of Floquet band topology for transport in momentum space (i.e., ...acceleration) have not been explored so far. Using a ratchet accelerator model inspired by existing cold-atom experiments, here we characterize a class of extended Floquet bands of one-dimensional driven quantum systems by Chern numbers, reveal topological phase transitions therein, and theoretically predict the quantization of adiabatic transport in momentum space. Numerical results confirm our theory and indicate the feasibility of experimental studies.
Summary Background Prospective assessment of pharmacogenetic strategies has been limited by an inability to undertake bedside genetic testing. The CYP2C19*2 allele is a common genetic variant ...associated with increased rates of major adverse events in individuals given clopidogrel after percutaneous coronary intervention (PCI). We used a novel point-of-care genetic test to identify carriers of the CYP2C19*2 allele and aimed to assess a pharmacogenetic approach to dual antiplatelet treatment after PCI. Methods Between Aug 26, 2010, and July 7, 2011, 200 patients were enrolled into our prospective, randomised, proof-of-concept study. Patients undergoing PCI for acute coronary syndrome or stable angina were randomly assigned to rapid point-of-care genotyping or to standard treatment. Individuals in the rapid genotyping group were screened for the CYP2C19*2 allele. Carriers were given 10 mg prasugrel daily, and non-carriers and patients in the standard treatment group were given 75 mg clopidogrel daily. The primary endpoint was the proportion of CYP2C19*2 carriers with high on-treatment platelet reactivity (P2Y12 reactivity unit PRU value of more than 234) after 1 week of dual antiplatelet treatment, which is a marker associated with increased adverse cardiovascular events. Interventional cardiologists and data analysts were masked to genetic status and treatment. Patients were not masked to treatment allocation. All analyses were by intention to treat. This study is registered with ClinicalTrials.gov , NCT01184300. Findings After randomisation, 187 patients completed follow-up (91 rapid genotyping group, 96 standard treatment). 23 individuals in each group carried at least one CYP2C19*2 allele. None of the 23 carriers in the rapid genotyping group had a PRU value of more than 234 at day 7, compared with seven (30%) given standard treatment (p=0·0092). The point-of-care genetic test had a sensitivity of 100% (95% CI 92·3–100) and a specificity of 99·3% (96·3–100). Interpretation Point-of-care genetic testing after PCI can be done effectively at the bedside and treatment of identified CYP2C19*2 carriers with prasugrel can reduce high on-treatment platelet reactivity. Funding Spartan Biosciences.
Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are life-threatening disorders. Our study objective was to describe the incidence, costs of care, length of stay, comorbidities, ...and mortality of SJS and TEN in US adults. The Nationwide Inpatient Sample 2009–2012, containing a 20% sample of all US hospitalizations, was analyzed. We used a validated approach involving International Classification of Disease, 9th edition, Clinical Modification codes to identify SJS, SJS/TEN, and TEN (n = 2,591, n = 502, and n = 564, respectively). The mean estimated incidences of SJS, SJS/TEN, and TEN were 9.2, 1.6, and 1.9 per million adults per year, respectively. SJS/TEN was associated with nonwhite race, particularly Asians (odds ratio = 3.27, 95% confidence interval = 3.02–3.54) and blacks (odds ratio = 2.01, 95% confidence interval = 1.92–2.10). Significantly prolonged length of stay and higher costs of care (SJS: 9.8 ± 0.3 days, $21,437 ± $807; SJS/TEN: 16.5 ± 1.0 days, $58,954 ± $5,238; TEN: 16.2 ± 1.0 days, $53,695 ± $4,037) were observed compared with all other admissions (4.7 ± 0.02 days, $11,281 ± $98). Mean adjusted mortality was 4.8% for SJS, 19.4% for SJS/TEN, and 14.8% for TEN. SJS, SJS/TEN, and TEN pose a substantial health care burden. Predictors of mortality included increasing age, increasing number of chronic conditions, infection (septicemia, pneumonia, tuberculosis), hematological malignancy (non-Hodgkin’s lymphoma, leukemia), and renal failure (P ≤ 0.03 for all). Further studies are needed to confirm mortality findings to improve prognostication of SJS/TEN.
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Pendant drop tensiometry offers a simple and elegant solution to determining surface and interfacial tension – a central parameter in many colloidal systems including emulsions, foams ...and wetting phenomena. The technique involves the acquisition of a silhouette of an axisymmetric fluid droplet, and iterative fitting of the Young–Laplace equation that balances gravitational deformation of the drop with the restorative interfacial tension. Since the advent of high-quality digital cameras and desktop computers, this process has been automated with high speed and precision. However, despite its beguiling simplicity, there are complications and limitations that accompany pendant drop tensiometry connected with both Bond number (the balance between interfacial tension and gravitational forces) and drop volume. Here, we discuss the process involved with going from a captured experimental image to a fitted interfacial tension value, highlighting pertinent features and limitations along the way. We introduce a new parameter, the Worthington number, Wo, to characterise the measurement precision. A fully functional, open-source acquisition and fitting software is provided to enable the reader to test and develop the technique further.
The hydrophobic force: measurements and methods Tabor, Rico F; Grieser, Franz; Dagastine, Raymond R ...
Physical chemistry chemical physics : PCCP,
09/2014, Letnik:
16, Številka:
34
Journal Article
Recenzirano
The hydrophobic force describes the attraction between water-hating molecules (and surfaces) that draws them together, causing aggregation, phase separation, protein folding and many other inherent ...physical phenomena. Attempts have been made to isolate the range and magnitude of this interaction between extended surfaces for more than four decades, with wildly varying results. In this perspective, we critically analyse the application of common force-measuring techniques to the hydrophobic force conundrum. In doing so, we highlight possible interferences to these measurements and provide physical rationalisation where possible. By analysing the most recent measurements, new approaches to establishing the form of this force become apparent, and we suggest potential future directions to further refine our understanding of this vital, physical force.
Interfacial nanobubbles (INBs) on a solid surface in contact with water have drawn widespread research interest. Although several theoretical models have been proposed to explain their apparent long ...lifetimes, the underlying mechanism still remains in dispute. In this work, the morphological evolution of INBs was examined in air-equilibrated and partially degassed water with the use of atomic force microscopy (AFM). Our results show that (1) INBs shrank in the partially degassed water while they grew slightly in the air-equilibrated water, (2) the three-phase boundary of the INBs was pinned during the morphological evolution of the INBs. Our analyses show that (1) the lifetime of INBs was sensitive to the saturation level of dissolved gases in the surrounding water, especially when the concentration of dissolved gases was close to saturation, and (2) the pinning of the three-phase boundary could significantly slow down the kinetics of both the growth and the shrinkage of the INBs. We developed a one-dimensional version of the Epstein–Plesset model of gas diffusion to account for the effect of pinning.
Understanding the normal-metal state transport in twisted bilayer graphene near magic angle is of fundamental importance as it provides insights into the mechanisms responsible for the observed ...strongly correlated insulating and superconducting phases. Here we provide a rigorous theory for phonon-dominated transport in twisted bilayer graphene describing its unusual signatures in the resistivity (including the variation with electron density, temperature, and twist angle) showing good quantitative agreement with recent experiments. We contrast this with the alternative Planckian dissipation mechanism that we show is incompatible with available experimental data. An accurate treatment of the electron-phonon scattering requires us to go well beyond the usual treatment, including both intraband and interband processes, considering the finite-temperature dynamical screening of the electron-phonon matrix element, and going beyond the linear Dirac dispersion. In addition to explaining the observations in currently available experimental data, we make concrete predictions that can be tested in ongoing experiments.
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► Atomic force microscopy measures forces between drops and bubbles. ► Modelling frameworks for quasi-equilibrium and dynamic forces are presented. ► Highlights of recent experimental ...advances in forces from soft matter AFM. ► Van der Waals, electrical double-layer, structural and hydrodynamic forces.
The use of atomic force microscopy to measure and understand the interactions between deformable colloids – particularly bubbles and drops – has grown to prominence over the last decade. Insight into surface and structural forces, hydrodynamic drainage and coalescence events has been obtained, aiding in the understanding of emulsions, foams and other soft matter systems. This article provides information on experimental techniques and considerations unique to performing such measurements. The theoretical modelling frameworks which have proven crucial to quantitative analysis are presented briefly, along with a summary of the most significant results from drop and bubble AFM measurements. The advantages and limitations of such measurements are noted in the context of other experimental force measurement techniques.
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