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Research into anti-icing surfaces often conflates the two separate problems of ice accumulation: water adhesion and ice adhesion. The body feathers of perpetually ice-free penguins are very good natural examples of anti-icing surfaces, which use two different mitigation strategies for the two disparate problems. Herein, we mimic the form of the feather's wire-like structure, which is decorated with superimposed nanogrooves by laser micromachining fine woven wire cloths. Post-processing techniques also allow us to isolate the role of surface chemistry by creating both hydrophilic and hydrophobic versions of the synthetic anti-icing surfaces. Our results show that water-shedding and ice-shedding characteristics are indeed derived from different physical functions of the hierarchical structure. The microstructure of the woven wire cloth leads to facile interfacial cracking and therefore extremely low ice adhesion strengths; the superimposed laser-induced periodic surface structures with hydrophobic surface chemistry lead to water shedding. Our work shows that by first taking a fracture mechanics approach to designing the ice-shedding function, a robust anti-icing surface can be engineered by separately designing the water-shedding functions.

Water's viscosity dependence on pressure was also not affected by O-GNFs, except at 10 ppm, where the shuttle effect may have increased the presence of hydrophobic methane bubbles in the solution. Under high pressure, the relative viscosity of the system remained non-Einsteinian at all temperatures except 2C. This may have been because the density anomaly of water was shifted to a colder temperature as the hydrogen bonding network was weaker. The phase transition from liquid to hydrate was identical to that of pure water, indicating that the presence of different stages of growth was not affected by the presence of O-GNF. However, the times to reach a maximum viscosity were faster in O-GNF systems compared to pure water. This said, the hydrate formation limitations inherent to the measurement system were not overcome by the presence of O-GNFs. The times to application-relevant viscosity values were maximized in the 1 ppm system at 49.75 % (200 mPa.s) and 31.93 % (500 mPa.s) faster than the baseline. Therefore, the presence of O-GNFs allowed for shorter times to desired viscosities and at lower driving forces than the baseline, improving the viability of the hydrate technologies to which they can be added.

The viscosity of methane and carbon dioxide hydrate systems were measured using a high-pressure rheometer up to 30 MPag. Where hydrate formation was not detected, the effect of temperature on the viscosity was one order of magnitude higher than the pressure effect on viscosity in most of the experimental pressure range (-0.048 mPa s/C at 1 MPag and 0.009 mPa s/MPag at 2C). The pressure effect on the viscosity of carbon dioxide systems where no hydrate formation was observed was up to one order of magnitude higher than that of the methane systems, due to carbon dioxide's higher solubility in water. Novel rheological phases diagrams were developed to further characterize the gas hydrate systems. Several systems with high driving forces for hydrate formation (2.07 MPag to 4.1 MPag) did not form gas hydrates. System limitations to the formation of hydrates were categorized as kinetic, mass diffusion, and/or heat of crystallization effects.

The viscosity of methane hydrate slurries with poly(vinylpyrrolidone) (PVP) at 700 and 7000 ppm by weight, molecular weights of 40,000 (PVP40) and 360,000 (PVP360) Da, and shear rates of 400 and 80 1/s, were measured in a high-pressure rheometer with pressures up to 30 MPag and compared to pure water systems. The additives successfully reduced the formation of high-viscosity slurries, but at low concentrations were incapable of delaying hydrate agglomeration at the late growth stage. The average relative time required for PVP40 solutions at 700 ppm to grow to 50 mPa.s was 1.9 times the water reference value, but only 1.2 times to reach 200 mPa.s. Improved inhibition was observed for the higher concentration and higher molecular weight sets, where the relative time to reach 50 mPa.s were 8.2 and 2.6 times the water reference value, respectively. While the additives demonstrated anti-nucleation properties and suppressed crystal growth initially, they accelerated the hydrate clusters agglomeration rate, and potentially weakened the hydrate mechanical properties.

(1) Introduction: New technologies that leverage gas hydrates phenomena include carbon capture and sequestrations. These processes are often semi-continuous and require regulation of the system's flow properties for proper operation. Accurate computational models for the viscosity of carbon dioxide hydrate systems at pre-nucleation conditions can be important for process design and control of such technologies. (2) Methods: This work validates the viscosity predictions of molecular dynamics simulations using previously measured experimental data. The TIP4P/Ice force field was used to model water, while the EPM2, TraPPE, and Zhang force fields were used for carbon dioxide. The Green-Kubo and Einstein formulations of viscosity and diffusivity were used in this work. (3) Results: All force fields overpredicted viscosity when compared to experimental data, but EPM2 resulted in lower discrepancies. Additionally, EPM2 was determined to model molecular behavior expected from the macroscopic trends in viscosity with respect to temperature and pressure. (4) Conclusions: The EPM2 force field more accurately predicted the viscosity of carbon dioxide hydrates systems at pre-nucleation conditions relative to TraPPE and Zhang.

In this study, using direct digital and infrared imaging techniques, the freezing of up to three simultaneous THF hydrate droplets was investigated for the first time. Nucleation was initiated at the aqueous solution-air interface. Two pseudo-heterogeneous mechanisms created additional nucleation interfaces: one from cavitation effects entraining microbubbles and another from subvisible ice particles, also called hydrate nucleating particles (HNPs), impacting the droplet surface. For systems containing droplets in both the second and third positions, nucleation was statistically simultaneous between all droplets. This effect may have been caused by the high liquid-solid interfacial pressures that developed at nucleation, causing some cracking in the initial hydrate shell around the droplet and releasing additional HNPs (now of hydrate) into the air. During crystallization, the THF hydrate droplets developed a completely white opacity, termed optical clarity loss or OCL. It was suggested that high hydrate growth rates within the droplet resulted in the capture of tiny air bubbles within the solid phase. In turn, light refraction through many smaller bubbles resulted in the OCL. These bubbles created structural inhomogeneities, which may explain how the volumetric expansion of the droplets upon complete solidification was 23.6% compared with 7.4% in pure, stationary THF hydrate systems. Finally, the thermal gradient that developed between the top and bottom of the droplet during melting resulted in a surface tension gradient along the air-liquid interface. In turn, convective cells developed within the droplet, causing it to spin rapidly about the horizontal axis.

The adhesion of ice to external surfaces is an important challenge in many industries. This has sparked much research into fabricating surfaces with low ice adhesion strengths. Our novel approach to designing ice-shedding surfaces leverages the dynamics of water solidification to induce beneficial stress concentrations throughout the iced interface. We have chosen a bare woven metal wire cloth substrate to demonstrate these principles. The pore geometries of the wire cloths lead to stress concentrations upon freezing and expansion of the water/ice, while their microstructural topography allows for facile crack opening. We have discovered that by leveraging knowledge of the underlying physical processes involved in ice formation and delamination, we can engineer a robust metal surface to have an extremely low ice adhesion strength (12.5 kPa) without using chemical coatings.

This review presents theory and simulation of liquid crystal phase ordering in biological fibrous materials, solutions, and composites in the presence of elastic fields, second phase inclusions, and transport phenomena, including complex shear-extensional flow and mass transfer. Liquid crystal self-assembly through phase ordering on elastic deformable membranes is first applied to characterize the mechanisms that control the structures in plant cell walls, highlighting how curvophobic and curvophilic effects introduce new structuring fields beyond hard-core repulsion. Then chiral nematic self-assembly is simulated in a mesophase containing fibrillar colloidal inclusions (liquid crystal-fibre composites) to demonstrate how the inclusion positional order generates defects and disclinations as shown in the plant cell wall. Coupling phase ordering to tuned transport phenomena is shown how and why it leads to self-organization such as paranematic states of dilute acidic aqueous collagen solutions. Further directed dehydration of well-organized paranematic collagen leads to defect free cholesteric films only when directed dehydration is synchronized with chirality formation. In addition, the ubiquitous surface nanowrinkling of cholesterics is captured with surface anchoring. In these four representative systems, the new mechanisms that enhance the well-known exclude volume interactions are identified quantified and validated with experimental data. Future directions to create new advanced multifunctional materials based on principles of self-assembly and self-organization are identified by leveraging the new couplings between material structure, geometry, and transport phenomena.

Several industries have steadily gained interest in gas hydrate technologies for their potential use in natural gas transport and storage applications. Additives which optimize the efficiencies of ...

Thermal properties of gas hydrates and their underlying fundamental characterization are limited and incomplete but crucial in ongoing basic science research and technological applications. The con...

Egg cartons, known as doubly sinusoidal surfaces, display a rich variety of saddles-cylinder-spherical patches organized with different spatial symmetries and connectivities. Egg carton surfaces, rich in functionalities, are observed in synthetic and biological materials, as well as across atomic and macroscopic scales. In this work we use the liquid crystal shape equation in the absence of elastic effects and normal stress jumps to predict and classify a family of uniaxial, equibiaxial, and biaxial egg cartons, according to the periodicities of the surface director field in nematic (N) and cholesteric (N*) liquid crystals under the presence of anisotropic surface tension (anchoring). Egg carton surface shape periodic solutions to the nonlinear and linearized liquid crystal shape equations predict that the mean curvature is a linear function of the orthogonal (along the surface normal) splay and bend contributions. Mixtures of egg carton surfaces (uniaxial, equibiaxial, and biaxial) emerge according to the symmetries of the nonsingular director field, and the spatial distributions of the director escape into the third dimension; pure uniaxial egg cartons emerge when the director escape has linelike geometries and mixtures of egg cartons arise under source or sink orientation lattices. Orientation symmetry and permutation analysis are incorporated into a full curvature (Casorati, shape parameter, mean curvature, and Gaussian curvature) characterization. Under a fixed anchoring parameter, conditions for maximal nanoscale curvedness and microscale maximal shape gradient diversity are identified. The present results contribute to various pathways to surface pattern formation using intrinsic anisotropic interfacial tension.

Understanding the crystallization of atmospheric water can require levitation techniques to avoid the influence of container walls. Recently, an acoustic levitation device called the TinyLev was designed, which can levitate multiple droplets at room temperature. Proximal crystallization may affect droplet phase change and morphological characteristics.In this study, acoustically levitated pure water droplets were frozen individually and in pairs or triplets using a TinyLev device. Nucleation, bulk crystal growth, and melting were observed using digital and infrared cameras concurrently.Initially, the acoustic field forced the droplets into an oblate spheroid shape, though the counteracting force of the cooling stream caused them to circularize. Droplet geometry was thus the net result of streaming forces and surface tension at the acoustic boundary layer/air-liquid interface. Nucleation was determined to be neither homogeneous nor heterogeneous but secondary, and thus dependent on the cooling rate and not on the degree of supercooling. It was likely initiated by aerosolized ice particles from the air or from droplets that had already nucleated and broken up. The latter secondary ice production process resulted in multi-drop systems with statistically identical nucleation times. Notably, this meant that the presence of interfacial rupture at an adjacent droplet could influence the crystallization behaviour of another. After the formation of an initial ice shell around the individual droplets, dendritic protrusions grew from the droplet surface, likely seeded by the same ice particles that caused nucleation, but at a quasi-liquid layer. When freezing was complete, it was determined that the frozen core had undergone a volumetric expansion of 30.75%, compared to 9% for pure, sessile water expansion. This significantly greater expansion may have resulted from entrained air bubbles at the inner solid-liquid interface and oscillations at the moving phase boundary caused by changes in local acoustic forces. Soon after melting began, acoustic streaming, the buoyancy of the remaining ice, and convective currents caused by both an inner thermal gradient and thermocapillary effects along the air-liquid interface, all contributed to the droplet spinning about the horizontal axis.

Gas hydrate technologies have steadily gained interest in several industries for their potential use in natural gas transport and carbon dioxide sequestration applications. To further develop these emerging technologies, significant focus has been placed on additives, and particularly nanoparticles, which optimize their efficiencies. The addition of materials such as graphene nanoflakes (GNFs) has previously been proven to enhance the production of methane hydrates and other hydrate systems. In this study, the growth rates of methane hydrates were measured in the presence of both hydrophobic (as-produced) and hydrophilic (plasma-functionalized) GNFs at 2 °C and 4646 kPa. The effect of GNF loading in the aqueous phase for both types was also determined. Small-scale agglomeration limited the growth rate enhancement effect of hydrophobic GNFs at low concentrations of around 0.5 ppm while significantly increasing the formation kinetics by about 101% at concentrations of 5 ppm. At even higher concentrations (10 ppm), the performance decreased due to large-scale agglomeration. Enhancement rose rapidly at low concentrations (0.1–1 ppm) of hydrophilic GNFs, peaking at about 288% before dropping to around 215% at 5 ppm due to mean free path limitations then rising again as surface area increased.

Structure-H (sH) hydrate is one of the canonical gas hydrates with significant potential applications and scarce characterised material properties despite the wide knowledge available on other gas ...

Tetrahydrofuran (THF) hydrates are often used as analogues for natural gas hydrates in experimental research because they can form at atmospheric pressure, despite the fundamental differences betwe...

The water-methane interface plays an important role in mass transfer between the phases. In this work, we employ molecular dynamics to investigate and characterize the mechanics, thermodynamics, and composition of water-methane interfaces applying a unique methodology known as the NPNAT ensemble. We systematically increase the pressure (1–50 MPa) and temperature (25–105 °C) to calculate the interfacial tension from its mechanical definition. We predict the surface tension via pressure and temperature relations in agreement with the classical scaling laws such as the Eotvos rule. It is found that the surface adsorbs methane molecules as per high interfacial excess and local density of methane. The methane practically remains insoluble in water due to favorable interactions with a dense hydrogen bonded region near the surface. The obtained macroscopic interfacial tension properties and sensitivity to pressure and temperature and the corresponding molecular mechanisms contribute to the evolving understanding and practical applications of this important interface.

Gas and liquid mole fraction were experimentally obtained for the CH 4 + CO 2 + H 2 O system at four different time intervals during hydrate growth. In order to validate the procedure, equilibrium mole fractions were also obtained and satisfactorily compared to literature values. Using a 70.0% CH 4 – 30.0% CO 2 loading composition in combination with a 1.6 MPa driving force at 274 K, results showed that both the liquid and gas mole fraction of methane and carbon dioxide were independent of time during the early stages of growth. For comparison purposes, samples were also obtained during the induction period. After the nucleation event, methane liquid mole fractions dropped below induction values while no change was observed for carbon dioxide. It is therefore postulated that methane consumption is favored during the early stages of growth. The rates of crystal growth were acquired and in parallel with all other parameters obtained experimentally, were proven critical to understand multicomponent gas hydrate kinetics.

This study showed a significant variability in gas consumption rate values during gas hydrate growth at a same experimental condition for a specific experimental setup. This is important since many studies report a singular gas consumption rate or no associated statistics. Carbon dioxide hydrate gas consumption rates had of coefficient of variation of 2.7% for 204 kPa, 9.7% for 317 kPa and 9.6% for 435 kPa driving forces. The gas consumption rates decreased with increasing induction time following a first-order response. A high induction time resulted in a higher bulk liquid temperature increase meaning a greater amount of initial carbon dioxide hydrates formed. Methane hydrates did not exhibit the same behaviour of gas consumption rate with induction time. Variations in methane gas consumption rates were 4.8% for 698 kPa and 2.4% for 1564 kPa driving forces. A regression of metastable dissolution during these kinetic experiments demonstrated that the liquid mole fraction limit increased with increasing driving force. The dissolution time constant decreased with increasing mixing rate. Finally, the maximum experimental liquid mole fraction supersaturation achieved during all experiments was 75 times smaller than the thermodynamically predicted spinodal limit.

The effects of oxygen-functionalized multi-walled carbon nanotubes (MWCNTs) on tetrabutylammonium bromide (TBAB)-water-carbon dioxide semi-clathrate system was investigated. A system comprised of 9.5 ppmw MWCNTs and 40 wt % TBAB was chosen and the average gas consumption rate was calculated for different conditions. At 14 °C, the average gas consumption rate during growth decreased to a plateau with increasing induction time at 3.0 °C subcooling for systems with and without MWCNTs. The addition of MWCNTs increased the gas consumption rate during growth for induction times less than one hour but did not affect it at longer induction times. The maximum gas consumption enhancement from the added MWCNTs was 15%. Dissolution runs at equilibrium conditions indicated that the presence of MWCNTs improved the dissolution rate of carbon dioxide gas into the liquid by lowering the time constant τ by 5%. This suggests that the gas-liquid interfacial resistance of carbon dioxide gas mass transfer is not the limiting factor for hydrate growth in this TBAB semi-clathrate system with and without nanoparticles. At a lower subcooling of 1.5 °C, there was no significant difference in the gas consumption rates with the addition of MWCNTs, due to prolonged induction times.

Biological plywoods are multifunctional fibrous composites materials, ubiquitous in nature. The chiral fibrous organization is found in chitin (insects), cellulosics (plants), and collagen I (cornea and bone of mammals) and is a solid analog of that of cholesteric liquid crystals. The surface and interfaces of plywoods are distinguished by hierarchical topographies and nanowrinkling. In this paper, we present a theory to model the emergence of these surfaces and interfaces using liquid crystal-based shape equations that directly connect material properties with geometric wrinkling. The model applies to liquid crystal precursors of the plywood solid analoges. We focus on wrinkling geometry, wrinkling mechanics, and the mechanogeometry relationships that underlie multifunctionality ubiquitous in biological surfaces. Scaling wrinkling laws that connect mechanical pressures and stresses to folding and bending are formulated and quantified. A synthesis of the connections between mechanics and geometry is achieved using the topology of stress curves and curvature of the wrinkles. Taken together the results show that anchoring is a versatile surface morphing mechanism with a rich surface bending stress field, two ingredients behind many potential multifunctionalities.

Hypothesis Solutions of water and methane gas at favorable thermodynamic conditions lead to the formation of crystalline methane hydrates. In natural and industrial environments, the nucleation process might occur in the solution’s bulk or at the solid-liquid and liquid-gas interfaces, which evolve into distinct morphologies. A complete molecular level understanding and material characterization of preferred nucleation sites and morphologies is required to inhibit or promote crystallization, as required. Methodology Computational simulations are utilized in this work in combination with analytical theory to calculate the supersaturation and interfacial tension as the driving force and suppressor, respectively, in the hydrate crystal formation process. We employ accurate molecular dynamics (MD) techniques to obtain critical thermodynamic and mechanical properties, and subsequently, analyze the formation using the classical nucleation theory (CNT). Findings We report the interfacial tension at all possible interfaces in water-methane gas solutions. We apply both our direct numerical simulation method and Antonow’s rule to find the tension at the methane hydrate and gas interface, and importantly conclude that Antonow’s rule overestimates the values. We calculate the work of formation and nucleation rate of the methane hydrate with and without additives. The nucleation probabilistically forms in the ranked order of film-shaped, cap-shaped, lens-shaped, and homogeneous. We postulate that the premelting of hydrate crystals at the hydrate-gas interface creates an intermediate quasi-liquid layer, which works in favor of the lens-shaped formation compared to homogeneous cases. However, the subtle difference in surface energy indicates high concentration of water and gas molecules at the interface is the main reason behind lens-shaped clustering. We lastly show that ice properties cannot be used to approximate the hydrate formation work.

Periodic micro and nano-structured surfaces in nature are responsible for functionalities including structural colour, superhydrophobicity, where wrinkling plays a significant role. The Bouligand architecture of fibrous composites such as insect exoskeleton and plant cell walls has been shown to generate uniaxial single and multiscale nanowrinkling through the chiral capillarity effect due to anisotropic surface tension and the helical fibre arrangement. The helical arrangement in Bouligand structures is a solid analogue of a cholesteric liquid crystal, which is an intermediate stage in the self-assembly formation process of fibrous composites. We extend uniaxial wrinkling predictions to biaxial wrinkling and show, using the liquid crystal shape equation, how and why egg carton surfaces with orthogonal patterning arise, since a planar helix tangential to a surface is unstable to oblique wrinkling modes. Taken together this work contributes to novel surface pattern formation and engineering principles to study surfaces of biological materials.

Gas hydrates are at the center of current materials research due to their critical importance to the environment and energy supply, and further progress requires knowledge of their mechanical properties. In this work we use molecular dynamics to study the molecular mobility in carbon dioxide hydrates. Specifically, the influences of induced vacancy defects and changes in composition on diffusion coefficients were studied. Introducing few water vacancy defects and a 3% change in cage occupancy changed the diffusion coefficient by almost two orders of magnitude and a factor of four, respectively. The diffusion coefficient of the water molecules was also influenced but to a much lesser extent.

The melting of frozen water droplets is a fundamental and ubiquitous process and the study of the transport processes occurring within the system during phase change is essential to understanding the forces that govern it. Multiwall carbon nanotubes (MWCNTs) can be added to liquid systems prior to crystallization in order to modify the properties of the phase change process and of the liquid or solid systems themselves. In this study, the melting behavior of frozen sessile droplets composed of water and 50 ppm of either functionalized or non-functionalized aqueous MWCNTs is investigated. Droplets are thawed from their base on a hydrophobic substrate set to temperatures between 1 and 30 °C. Tracking of MWCNT clusters during melting shows convective fluid motion occurring within the liquid melt at temperatures above 5 °C. This circulation is contingent on the presence of the ice phase above. The internal fluid dynamics are attributed predominantly to thermocapillary effects as a result of temperature-induced surface tension gradients along the air/liquid interface in the melt. Further, the melting times of MWCNT-containing systems were longer than pure water samples. These results highlight new and important mechanisms driving the melting processes within water droplet systems.

This paper presents visual observations aiming to clarify the underlying physics of surfactant effects on clathrate hydrate crystal growth at the interface between methane gas and water with surfactant. Sodium dodecyl sulfate (SDS), which is commonly used in industrial processes, was used in this study. Various SDS mass fractions from 0 to wSDS = 100 ppm with a step of size 10 ppm were examined, where wSDS represents the mass fraction of SDS aqueous solution. The crystal growth behavior and the crystal morphology of the methane hydrate at the interface varied depending on surfactant concentration and ΔTsub. In systems with wSDS ≤ 20 ppm, the nucleation occurred on the droplet surface (gas/liquid interface), then grew laterally, and finally covered the whole droplet surface. On the contrary, at wSDS ≥ 30 ppm, the droplet shape was not maintained and enhanced hydrate crystal growth was observed compared to those systems with wSDS ≤ 20 ppm. Individual hydrate crystals at wSDS = 20 ppm were observed to be sma...

Clathrate hydrate promotion research has often focused on hydrate growth rate differentiation, however little work has been done to understand the kinetics of dissolution. The dissolution of gas into the bulk liquid phase is of great importance to hydrate growth, as it is the first step in hydrate formation. Furthermore, understanding the influence of additives on hydrate systems may provide significant insight into the mechanisms of their function. The effect of the hydrate promoter sodium dodecyl sulphate (SDS) on methane dissolution was thus investigated at the three-phase (H-Lw-V) equilibrium condition of 275.1 K and 3145 kPa. Experiments with concentrations of SDS ranging from 0.01 mM to 4 mM were conducted. The purpose of this study was to investigate the effects on the methane equilibrium saturation values as well as the kinetics of dissolution. The effects on saturation were found to be negligible. The rate of dissolution was measured using a first-order response model and the time constant tau (τ). It was found that the values of τ for SDS increased with an increasing loading of 0.01 mM–0.75 mM and then plateaued for concentrations ranging between 0.75 and 4 mM producing a sigmoidal trend.

Polymer based kinetic hydrate inhibitors are increasingly used in the oil and gas industry to prevent hydrate formation. It is well known that the effectiveness of inhibitors decreases as the driving force for hydrate formation increases. The current study assesses whether the inhibitory effect of polyvinylpyrrolidone (PVP) can be completely masked by high driving forces for hydrate growth. Methane hydrate kinetic experiments were performed with solutions of pure water and 0.007 wt% PVP in water at 277 K and pressures ranging from 23.83 MPa to 31.33 MPa. Results showed that as the driving force for hydrate formation increases, the effect of PVP as a hydrate growth inhibitor diminishes and may be entirely masked for a significant amount of time. With the current system, hydrate growth appeared uninhibited at subcoolings greater than 17.4 K (26.33 MPa). The time of uninhibited growth was found to increase linearly with subcooling to a maximum of 537 s at a 19 K subcooling (31.33 MPa). Under such high driving forces, inhibitory effects have been shown to take time to manifest themselves, indicating that under these conditions additives have no effect on hydrate nucleation but solely on hydrate growth following nucleation.

The effects of ice formation and accretion on external surfaces range from being mildly annoying to potentially life-threatening. Ice-shedding materials, which lower the adhesion strength of ice to its surface, have recently received renewed research attention as a means to circumvent the problem of icing. In this work, we investigate how surface wettability and surface topography influence the ice adhesion strength on three different surfaces: (i) superhydrophobic laser-inscribed square pillars on copper, (ii) stainless steel 316 Dutch-weave meshes, and (iii) multiwalled carbon nanotube-covered steel meshes. The finest stainless steel mesh displayed the best performance with a 93% decrease in ice adhesion relative to polished stainless steel, while the superhydrophobic square pillars exhibited an increase in ice adhesion by up to 67% relative to polished copper. Comparisons of dynamic contact angles revealed little correlation between surface wettability and ice adhesion. On the other hand, by considering the ice formation process and the fracture mechanics at the ice-substrate interface, we found that two competing mechanisms governing ice adhesion strength arise on nonplanar surfaces: (i) mechanical interlocking of the ice within the surface features that enhances adhesion, and (ii) formation of microcracks that act as interfacial stress concentrators, which reduce adhesion. Our analysis provides insight toward new approaches for the design of ice-releasing materials through the use of surface topographies that promote interfacial crack propagation.

Structure-H gas hydrate is recognized by its hexagonal symmetry and anisotropy. The available structure-mechanical properties relations of this hydrate from an atomistic scale are scarce. This work presents the main mechanical properties of sH hydrate addressing its structural anisotropy based on ab initio atomic simulations. The empty metastable and filled sH hydrates of neohexane and different help gases are simulated to establish their mechanical and anisotropic characteristics. Guest molecules increase the stiffness and rigidity of sH hydrate, and they define its anisotropy. The anisotropy of sH hydrate was reflected in its high moduli values along the c-axis as compared to the a-axis. Analyzing sH hydrate response to applied triaxial stress reveals its maximum tensile strength. The hydrogen and the covalent O-H bonds were found to behave in an opposite manner under applied stress. This work contributes to the fundamental understanding and potential technological applications of this less known gas hydrate.