Dentin tubule occlusion by a 38% silver diamine fluoride gel: an in vitro investigation

Objective Silver diamine fluoride (SDF) is effective in treatment of dentin hypersensitivity and caries lesions. However, the non-viscous solution does not easily allow clinicians to control the application area. A 38% SDF experiment gel was compared in vitro to commercial SDF for its ability to penetrate and occlude dentinal tubules. Materials and methods Human root surface dentin specimens were treated with gelled or standard 38% SDF or negative control. Penetration behavior was established by Drop Shape Analysis. Precipitates at the surface and within tubules were analyzed by SEM and EDX after treatment; Results: penetration depths up to 500 µm were observed for both SDF formulations. Both formulations occluded dentinal tubules similarly. Precipitates on the dentin surface and within dentinal tubules were found for both SDF formulations, with a slight tendency for the experimental gel SDF product to be more abundant than the commercially available one. Discussion: behavior of the experimental 38% SDF gel formulation appeared indistinguishable from the commercial 38% SDF product with respect to dentinal tubule penetration and occlusion. Conclusions The experimental 38% SDF gel may be a suitable intervention for the prevention of dentin hypersensitivity.

Effect of Viscosity on Bouncing Dynamics of Elliptical Footprint Drops on Non-Wettable Ridged Surfaces

An initial drop shape can alter the bouncing dynamics and significantly decrease the residence time on superhydrophobic surfaces. Elliptical footprint drops show asymmetric dynamics owing to a pronounced flow driven by the initial drop shape. However, the fundamental understanding of the effect of viscosity on the asymmetric dynamics has yet to be investigated, although viscous liquid drop impact on textured surfaces is of scientific and industrial importance. Here, the current study focuses on the impact of elliptical footprint drops with various liquid properties (density, surface tension, and viscosity), drop sizes, and impact velocities to study the bouncing dynamics and residence time on non-wettable ridged surfaces numerically by using a volume-of-fluid method. The underlying mechanism behind the variation in residence time is interpreted by analyzing the shape evolution, and the results are discussed in terms of the spreading, retraction, and bouncing. This study provides an insight on possible outcomes of viscous drops impinging on non-wettable surfaces and will help to design the desired spraying devices and macro-textured surfaces under different impact conditions, such as icephobic surfaces for freezing rain or viscous liquids.

Thermal, Viscoelastic and Surface Properties of Oxidized Field’s Metal for Additive Microfabrication

Field’s metal, a low-melting-point eutectic alloy composed of 51% In, 32.5 Bi% and 16.5% Sn by weight and with a melting temperature of 333 K, is widely used as liquid metal coolant in advanced nuclear reactors and in electro–magneto–hydrodynamic two-phase flow loops. However, its rheological and wetting properties in liquid state make this metal suitable for the formation of droplets and other structures for application in microfabrication. As with other low-melting-point metal alloys, in the presence of air, Field’s metal has an oxide film on its surface, which provides a degree of malleability and stability. In this paper, the viscoelastic properties of Field’s metal oxide skin were studied in a parallel-plate rheometer, while surface tension and solidification and contact angles were determined using drop shape analysis techniques.

Batusatam physical and chemical properties review: A Billitonite tektite in Southeastern Belitung Island, Indonesia

Batusatam considers as Billitonite, a rare Australian strewnfield tektite. Regrettably, the scientific information of this object slightly, especially about the origin, the process of formation, and its uniqueness in the earth’s geological history. This paper reviewed the physical and chemical properties of unearthing Batusatam in Southeastern Belitung Island, Indonesia. Physical properties are examing based on object shape, surface texture pattern, dimensions, volume, mass, density, and hardness. We also analyzed major and minor elements using portable X-ray fluorescence (XRF) and compared them with another Australian tektite. Rod and tear-drop-shape, the unique shapes of Batusatam, were discovered. It had a higher FexOy, CaO, MnO proportion. Also, Sn (tin) is present significantly compared to other tektites. This significant uniqueness of Billitonite could clarify its origin, formation process, and role as a geoheritage.

Interfacial Tension Measurements at Reservoir Conditions Using X-Ray Imaging

Interfacial tension (IFT) is one of the key parameters governing multiphase flow in reservoir. One of standard IFT measurement techniques is pendant drop shape analysis, which includes an acquisition of the drop snapshots in visible light. Hence, the method is limited by optical transparency of an external fluid. Here we present a new approach, which is free from this limitation. It uses X-rays as an illumination source and provides a number of advantages and additional opportunities in the study of fluid interface behavior. Proposed method includes a drop generation inside a uniquely designed X-ray transparent cell for high pressure and temperature (HPHT) measurements placed inside an X-ray scanner and imaging of its evolution with time till equilibrium state. Since X-ray images significantly differ from the classical optical ones, a novel algorithm was developed for accurate drop shape detection and further mathematical processing for IFT value calculation. As a result, an IFT value evolution curve for a pair of fluids is obtained. Depending on relative densities of the fluids, different experimental schemes can be implemented: pendant or rising drop. The method was validated on various neat fluids with well-known IFT values and then was successfully applied for different real fluids systems. This work demonstrates the unique laboratory studies carried out on different liquid-fluid systems showing that the developed methodology works well at elevated pressure and temperature conditions. The developed method unlocks the possibility for an appropriate IFT measurements in surfactant-rich oil-water systems as well as in systems near the phase transition such as gas-condensates at a wide range of thermobaric reservoir conditions and increases feasibility of HPHT measurements due to simplification of the measuring system design.

Symmetry-Breaking Drop Bouncing on Superhydrophobic Surfaces with Continuously Changing Curvatures

Controlling the residence time of drops on the solid surface is related to a wide spectrum of engineering applications, such as self-cleaning and anti-icing. The symmetry-breaking dynamics induced by the initial drop shape can promote drop bouncing. Here, we study the bouncing features of spherical and ellipsoidal drops on elliptical surfaces that continuously change curvatures inspired by natural succulent leaves. The bounce characteristics highly depend on the geometric relations between the ellipsoidal drops and curved surfaces. Numerical results show that ellipsoidal shapes of the drops amplify asymmetries of the mass and momentum in synergy with an influence of the surface curvature during the impact, which is verified by experiments. Effects of the surface anisotropy and drops’ ellipticity on the residence time are investigated under various surface morphologies and Weber numbers. The residence time is closely associated with an initial surface curvature at the apex. The underlying principle of modifying the residence time via the drops’ ellipticity and initial surface curvature is elucidated based on momentum asymmetry. The understanding of the bouncing features on curved surfaces will offer practical implications for enhanced heat transfer performances and controlled water repellency, etc.

The Direct Cause of Amplified Wettability: Roughness or Surface Chemistry?

Higher contact angles or amplified wettability observed on surfaces of rough solid materials are typically expressed as a function of a physical dimension (roughness factor). Herein, we present a simple experimental approach that demonstrates that roughness may only magnify the inherent surface chemistry that seems to have direct influence on surface wettability. We investigate gradual change in surface chemistry (hydrophobisation) of rough and smooth glass surfaces, from a very low concentration (10−7 M) of dichlorodimethylsilane, DCDMS through various intermediate hydrophilic/hydrophobic states to when the surfaces are maximally hydrophobised with DCDMS at 0.1 M. The wettability of the modified glasses was studied by water contact angle measurements using drop shape analysis system (DSA). The data obtained indicate a deviation from Wenzel model, with the functionalized rough glass surfaces showing higher reactivity towards DCDMS when compared to the smooth glass surfaces, indicating that the two surfaces are not chemically identical. Our study reveals that just like transforming a solid material to powder, a well-divided glass (rough) surface may not only exhibit a greater surface area than the smooth counterpart as rightly predicted by the Wenzel model, but seems to be bloated with functional groups (–OH or –CH3) that can amplify surface interaction when such functional species dominate the solid surface.

The role of drop shape in impact and splash

The impact and splash of liquid drops on solid substrates are ubiquitous in many important fields. However, previous studies have mainly focused on spherical drops while the non-spherical situations, such as raindrops, charged drops, oscillating drops, and drops affected by electromagnetic field, remain largely unexplored. Using ferrofluid, we realize various drop shapes and illustrate the fundamental role of shape in impact and splash. Experiments show that different drop shapes produce large variations in spreading dynamics, splash onset, and splash amount. However, underlying all these variations we discover universal mechanisms across various drop shapes: the impact dynamics is governed by the superellipse model, the splash onset is triggered by the Kelvin-Helmholtz instability, and the amount of splash is determined by the energy dissipation before liquid taking off. Our study generalizes the drop impact research beyond the spherical geometry, and reveals the potential of using drop shape to control impact and splash.