Quantification of Surface Amorphous Content Using Dispersive Surface Energy: the Concept of Effective Amorphous Surface Area

Manganese oxides with layer and tunnel structures occur widely in nature and inspire technological applications. Having variable compositions, these structures often are found as small particles (nanophases). This study explores, using experimental thermochemistry, the role of composition, oxidation state, structure, and surface energy in the their thermodynamic stability. The measured surface energies of cryptomelane, sodium birnessite, potassium birnessite and calcium birnessite are all significantly lower than those of binary manganese oxides (Mn3O4, Mn2O3, and MnO2), consistent with added stabilization of the layer and tunnel structures at the nanoscale. Surface energies generally decrease with decreasing average manganese oxidation state. A stabilizing enthalpy contribution arises from increasing counter-cation content. The formation of cryptomelane from birnessite in contact with aqueous solution is favored by the removal of ions from the layered phase. At large surface area, surface-energy differences make cryptomelane formation thermodynamically less favorable than birnessite formation. In contrast, at small to moderate surface areas, bulk thermodynamics and the energetics of the aqueous phase drive cryptomelane formation from birnessite, perhaps aided by oxidation-state differences. Transformation among birnessite phases of increasing surface area favors compositions with lower surface energy. These quantitative thermodynamic findings explain and support qualitative observations of phase-transformation patterns gathered from natural and synthetic manganese oxides.

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Relationships between Surface Properties and Snow Adhesion and Its Shedding Mechanisms

Applied Sciences ◽

10.3390/app10165407 ◽

2020 ◽

Vol 10 (16) ◽

pp. 5407

Author(s):

Jamie Heil ◽

Behrouz Mohammadian ◽

Mehdi Sarayloo ◽

Kevin Bruns ◽

Hossein Sojoudi

Keyword(s):

Surface Energy ◽

Surface Temperature ◽

Water Content ◽

Adhesion Strength ◽

Liquid Water ◽

Liquid Water Content ◽

Snow Accumulation ◽

Dispersive Surface Energy ◽

Wet Snow ◽

Intermediate Surface

Understanding the mechanisms of snow adhesion to surfaces and its subsequent shedding provides means to search for active and passive methods to mitigate the issues caused by snow accumulation on surfaces. Here, a novel setup is presented to measure the adhesion strength of snow to various surfaces without altering its properties (i.e., liquid water content (LWC) and/or density) during the measurements and to study snow shedding mechanisms. In this setup, a sensor is utilized to ensure constant temperature and liquid water content of snow on test substrates, unlike inclined or centrifugal snow adhesion testing. A snow gun consisting of an internal mixing chamber and ball valves for adjusting air and water flow is designed to form snow with controlled LWC inside a walk-in freezing room with controlled temperatures. We report that snow adheres to surfaces strongly when the LWC is around 20%. We also show that on smooth (i.e., RMS roughness of less than 7.17 μm) and very rough (i.e., RMS roughness of greater than 308.33 μm) surfaces, snow experiences minimal contact with the surface, resulting in low adhesion strength of snow. At the intermediate surface roughness (i.e., RMS of 50 μm with a surface temperature of 0 °C, the contact area between the snow and the surface increases, leading to increased adhesion strength of snow to the substrate. It is also found that an increase in the polar surface energy significantly increases the adhesion strength of wet snow while adhesion strength decreases with an increase in dispersive surface energy. Finally, we show that during shedding, snow experiences complete sliding, compression, or a combination of the two behaviors depending on surface temperature and LWC of the snow. The results of this study suggest pathways for designing surfaces that might reduce snow adhesion strength and facilitate its shedding.

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Surface Energy of Au Nanoparticles Depending on Their Size and Shape

Nanomaterials ◽

10.3390/nano10030484 ◽

2020 ◽

Vol 10 (3) ◽

pp. 484 ◽

Cited By ~ 4

Author(s):

David Holec ◽

Phillip Dumitraschkewitz ◽

Dieter Vollath ◽

Franz Dieter Fischer

Keyword(s):

Surface Energy ◽

Surface Area ◽

Complex Structure ◽

Characteristic Size ◽

Bulk Crystals ◽

Size And Shape ◽

Nanoparticle Shape ◽

Universal Power Law ◽

Atomistic Study ◽

Surface Facet

Motivated by often contradictory literature reports on the dependence of the surface energy of gold nanoparticles on the variety of its size and shape, we performed an atomistic study combining molecular mechanics and ab initio calculations. We show that, in the case of Au nanocubes, their surface energy converges to the value for ( 0 0 1 ) facets of bulk crystals. A fast convergence to a single valued surface energy is predicted also for nanospheres. However, the value of the surface energy is larger in this case than that of any low-index surface facet of bulk Au crystal. This fact can be explained by the complex structure of the surface with an extensive number of broken bonds due to edge and corner atoms. A similar trend was obtained also for the case of cuboctahedrons. Since the exact surface area of the nanoparticles is an ill-defined quantity, we have introduced the surface-induced excess energy and discuss this quantity as a function of (i) number of atoms forming the nano-object or (ii) characteristic size of the nano-object. In case (i), a universal power-law behaviour was obtained independent of the nanoparticle shape. Importantly, we show that the size-dependence of the surface energy is hugely reduced, if the surface area correction is considered due to its expansion by the electronic cloud, a phenomenon specifically important for small nanoparticles.

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Retraction of large liquid strips

Journal of Fluid Mechanics ◽

10.1017/jfm.2015.432 ◽

2015 ◽

Vol 778 ◽

Cited By ~ 3

Author(s):

Cunjing Lv ◽

Christophe Clanet ◽

David Quéré

Keyword(s):

Surface Tension ◽

Surface Energy ◽

Surface Area ◽

Driving Force ◽

Large Scale ◽

Horizontal Surface

We study the behaviour of elongated puddles deposited on non-wetting substrates. Such liquid strips retract and adopt circular shapes after a few oscillations. Their thickness and horizontal surface area remain constant during this reorganization, so that the energy of the system is only lowered by minimizing the length of the contour (and the corresponding surface energy); despite the large scale of the experiments (several centimetres), motion is driven by surface tension. We focus on the retraction stage, and show that its velocity results from a balance between the capillary driving force and inertia, due to the frictionless motion on non-wetting substrates. As a consequence, the retraction velocity has a special Taylor–Culick structure, where the puddle width replaces the usual thickness.

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Effect of milling temperatures on surface area, surface energy and cohesion of pharmaceutical powders

International Journal of Pharmaceutics ◽

10.1016/j.ijpharm.2015.08.061 ◽

2015 ◽

Vol 495 (1) ◽

pp. 234-240 ◽

Cited By ~ 27

Author(s):

Umang V. Shah ◽

Zihua Wang ◽

Dolapo Olusanmi ◽

Ajit S. Narang ◽

Munir A. Hussain ◽

...

Keyword(s):

Surface Energy ◽

Surface Area ◽

Pharmaceutical Powders

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Shattering of a liquid drop due to impact

Proceedings of the Royal Society of London. Series A: Mathematical and Physical Sciences ◽

10.1098/rspa.1991.0157 ◽

1991 ◽

Vol 435 (1895) ◽

pp. 483-503 ◽

Cited By ~ 35

Keyword(s):

Surface Energy ◽

Statistical Model ◽

Surface Area ◽

Liquid Drop ◽

Drop Impact ◽

Drop Breakup ◽

Viscous Effects ◽

Consistent Manner

Based on energy and entropy principles, a statistical model describing the shattered state of a single spherical liquid drop after being subjected to a relatively sudden but uniform (over the whole surface area of the drop) impact is developed. The problem is addressed from a fundamental standpoint, with the intention of providing a predictive framework for the various modes of breakup and the size and number of droplets produced. Upon neglecting viscous effects, several results in terms of the energy of impact, non-dimensionalized with respect to the surface energy of the drop before impact, are derived. The model is quite simple and straightforward, yet it appears to predict in a fairly consistent manner certain experimental observations that have been made repeatedly in relation to drop breakup in stirred dispersions, by collision, and exposure to shocks.

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Reverse Coarsening and the Control of Particle Size Distribution through Surfactant

Applied Sciences ◽

10.3390/app10155359 ◽

2020 ◽

Vol 10 (15) ◽

pp. 5359

Author(s):

Victor M. Burlakov ◽

Alain Goriely

Keyword(s):

Particle Size ◽

Surface Energy ◽

Particle Size Distribution ◽

Size Distribution ◽

Surface Area ◽

Particle Nucleation ◽

Size Evolution ◽

Energy Renormalization ◽

In Situ Replacement

The minimization of surface area, as a result of the minimization of (positive) surface energy, is a well-known driving force behind the spontaneous broadening of (nano) particle size distribution. We show that surfactant molecules binding to particle surfaces effectively decrease the surface energy and may change its sign. In this case, contrary to the expected broadening behavior, a minimum of free energy is achieved at the maximum surface area for all particles, i.e., when the particles are identical. Numerical simulations based on the classical Lifshitz–Slyozov–Wagner theory with surfactant-induced surface energy renormalization confirm the collapse of the particle size distribution. As the particle size evolution is much slower than particle nucleation and growth, the manipulation of surface energy with in-situ replacement of surfactant molecules provides a method for controlling particle size distribution with great potential for creating mono-disperse nanoparticles, a key goal of nanotechnology.

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Quantitative Study on Solubility Parameters and Related Thermodynamic Parameters of PVA with Different Alcoholysis Degrees

Polymers ◽

10.3390/polym13213778 ◽

2021 ◽

Vol 13 (21) ◽

pp. 3778

Author(s):

Siqi Chen ◽

Hao Yang ◽

Kui Huang ◽

Xiaolong Ge ◽

Hanpeng Yao ◽

...

Keyword(s):

Molecular Dynamics ◽

Molecular Dynamics Simulation ◽

Surface Energy ◽

Chain Length ◽

Dynamics Simulation ◽

Solubility Parameters ◽

Specific Surface Energy ◽

Surface Parameters ◽

Surface And Interface ◽

Dispersive Surface Energy

In recent years, inverse gas chromatography (IGC) and molecular dynamics simulation methods have been used to characterize the solubility parameters and surface parameters of polymers, which can provide quantitative reference for the further study of the surface and interface compatibility of polymer components in the future. In this paper, the solubility parameters and surface parameters of two kinds of common alcoholysis, PVA88 and PVA99, are studied by using the IGC method. The accuracy of the solubility parameters obtained by the IGC experiment is verified by molecular dynamics simulation. On the basis of this, the influence of repeated units of polyvinyl alcohol (PVA) on solubility parameters is studied, so as to determine the appropriate chain length of the PVA for simulation verification calculation. The results show that the solubility parameters are not much different when the PVA chain length is 30 and above; the numerical trends of the solubility parameters of PVA88 and PVA99 at room temperature are the same as the results of molecular dynamics simulation; the dispersive surface energy γsd and the specific surface energy γssp are scattered with the temperature distribution and have a small dependence on temperature. On the whole, the surface energy of PVA99 with a higher alcoholysis degree is higher than that of PVA88 with a lower alcoholysis degree. The surface specific adsorption free energy (∆Gsp) indicates that both PVA88 and PVA99 are amphoteric meta-acid materials, and the acidity of PVA99 is stronger.

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