Surface Tension Uncertainties Research Articles

Unexpected finite size effects in interfacial systems: Why bigger is not always better-Increase in uncertainty of surface tension with bulk phase width.

We present an unexpected finite size effect affecting interfacial molecular simulations that is proportional to the width-to-surface-area ratio of the bulk phase Ll/A. This finite size effect has a significant impact on the variance of surface tension values calculated using the virial summation method. A theoretical derivation of the origin of the effect is proposed, giving a new insight into the importance of optimising system dimensions in interfacial simulations. We demonstrate the consequences of this finite size effect via a new way to estimate the surface energetic and entropic properties of simulated air-liquid interfaces. Our method is based on macroscopic thermodynamic theory and involves comparing the internal energies of systems with varying dimensions. We present the testing of these methods using simulations of the TIP4P/2005 water forcefield and a Lennard-Jones fluid model of argon. Finally, we provide suggestions of additional situations, in which this finite size effect is expected to be significant, as well as possible ways to avoid its impact.

Surface tension of ethyl fluoride (HFC161) from (233 to 373) K

The surface tension of ethyl fluoride (R161) was measured over the temperature range from (233 to 373)K with a differential capillary rise method, together with the surface tension of isobutane (R600a) measured in the temperature range from (275 to 343)K for verifying the experimental system. The temperature and surface tension uncertainties were estimated to be within ±20mK and ±0.2mNm−1 respectively. The surface tension values of R161 were correlated as a function of temperature with an average absolute deviation of 0.043mNm−1.

Effect of Surface Tension from MD Simulations on Size-Dependent Deliquescence of NaCl Nanoparticles

The deliquescence of sodium chloride is size dependent for particles smaller than 100 nm, with some discrepancies between measured and predicted deliquescence relative humidity as a function of size. Two sources of uncertainty in current models are the solid–liquid/solid–vapor surface tensions and the curvature dependence of surface tension. Molecular Dynamics simulations are used to calculate surface tensions and their corresponding upper bounds, which compare well with measured values of liquid–vapor (LV) interfaces and significantly reduce uncertainty compared to experimental estimates of solid–liquid (SL) and solid–vapor (SV) interfaces. Surface tensions calculated for nanoparticles in the 2–10 nm size range are related to the corresponding flat interface values using the first-order Tolman length ( δ ). At 1 atm and 300 K, the Tolman length determined from the test-area method is of the order of 0.1 nm with a precision between 5% and 10%. The δ LV (water–air) is 0.15 nm, δ LV (soln–air) is 0.10 nm, δ SL (NaCl–soln:) is 0.13 nm, and δ SV (NaCl–air) is 0.14 nm, with positive values corresponding to a decrease in surface tension for smaller particles. The size-dependent deliquescence relative humidity is calculated using a thermodynamic model of water uptake with these new surface tension estimates and with Tolman length corrections. The reduced uncertainties in surface tension significantly improve agreement with measured deliquescence relative humidity of sodium chloride nanoparticles with 5–150 nm diameters. The size-dependent corrections to surface tension produce a minor improvement in the comparison of predicted and measured deliquescence relative humidity of particles smaller than 3 nm.

Theoretical investigation of size and shape effects on the melting temperature of ZnOnanostructures

We report a theoretical investigation concerning the melting temperature,Tm, of ZnO and Zn nanoparticles (NPs), nanowires (NWs) and nanotubes (NTs). The shapesconsidered here for the zinc oxide low dimensional structures include sphericalNPs, NWs with circular, rectangular (nanobelts) and hexagonal sections andNTs with circular and hexagonal sections. A comparison between ZnO and Znnanostructures demonstrates a higher stability of ZnO for most size and shape rangesconsidered. Moreover, the size effect on the melting temperature for ZnO is found to bequite strong: for a spherical ZnO NP with a radius of 5 nm, the size effect onTm correspondsto a decrease of ∼36% relative to the bulk melting temperature, whereas the reductionfor the case of a metallic Zn NP with the same dimension is∼13%. Basedon Tm estimations as a function of size and shape, we predict that certain ZnO nanostructures, such as small(<10 nm) NTs, may not be viable for nanoelectronics or nanophotonic devices, sinceTm is too close to, or in some cases even below, room temperature. Theinfluence of the surface tension uncertainties on the calculated meltingtemperatures is also discussed. Finally, based on the determination ofTm at the nanoscale, the maximal intrinsic residual stress in ahexagonal ZnO NW and in a cylindrical Zn NW is estimated to be∼45 MPaand ∼1.9 GPa, respectively.

Surface Tension of Difluoromethane (R-32) + 1,1,1,2,3,3,3-Heptafluoropropane (R-227ea) from (253 to 333) K

The surface tension of difluoromethane (R-32) (1) + 1,1,1,2,3,3,3-heptafluoropropane (R-227ea) (2) binary mixtures was measured at five nominal mass fractions of w1‘ = 0.3083, 0.3639, 0.4064, 0.5519, and 0.7345 over the temperature range from (253 to 333) K using the differential capillary rise method (DCRM) under vapor−liquid equilibrium conditions. The temperature and surface tension uncertainties were estimated to be within ±10 mK and ±0.15 mN·m-1, respectively. A new correlation based on the mass fraction was developed to represent the surface tension in the R-32 + R-227ea system.

Surface Tension of 1,1,1-Trifluoroethane (HFC-143a), 1,1,1,2,3,3,3-Heptafluoropropane (HFC-227ea), and Their Binary Mixture HFC-143a/227ea

The surface tension of 1,1,1-trifluoroethane (HFC-143a), 1,1,1,2,3,3,3-hepta-fluoropropane (HFC-227ea), and their binary mixture HFC-143a/227ea at 3 nominal mass fractions of 27.91%/72.09%, 49.44%/50.56%, and 74.11%/25.89% were measured in the temperature range from 253 to 333K using the differential capillary rise method (DCRM) under vapor-liquid equilibrium conditions. The temperature and surface tension uncertainties were estimated to be within ±10 mK and ±0.15 mN⋅m−1, respectively. The present data were used to develop a van der Waals-type surface tension correlation for pure HFC-143a and HFC-227ea. Correlations for pure HFC-143a and HFC-227ea were used to develop a surface tension correlation for the experimental data of the HFC-143a/227ea mixtures as a function of the mass fraction.

Surface tension measurements of 1,1,1,3,3-pentafluoropropane (HFC-245fa) and 1,1,1,3,3,3-hexafluoropropane (HFC-236fa) from 254 to 333 K

The surface tension of 1,1,1,3,3-pentafluoropropane (HFC-245fa) and 1,1,1,3,3,3-hexafluoropropane (HFC-236fa) were measured over the temperature range of 254–333 K, using the differential capillary rise method (DCRM) under vapor–liquid equilibrium conditions. The temperature and surface tension uncertainties were estimated to be within ±10 mK and ±0.15 mN m −1, respectively. The present data were used to develop van der Waals-type surface tension correlations for HFC-245fa and HFC-236fa, respectively.

Surface Tension Measurements of Propane (R-290) and Isobutane (R-600a) from (253 to 333) K

The surface tensions of propane (R-290) and isobutane (R-600a) were measured over the temperature range (253 to 333) K using a differential capillary rise method (DCRM) under vapor−liquid equilibrium conditions. The temperature and surface tension uncertainties were estimated to be within ±10 mK and ±0.15 mN·m-1, respectively. The present data were used to develop van der Waals-type surface tension correlations for propane (R-290) and isobutane (R-600a). Present results were compared with the available literature data.

Surface tension of the binary refrigerant mixture HFC-32 + HFC-125

The surface tension of the binary mixture HFC-32+HFC-125 was measured at three nominal mass fractions of 24.95%/75.05%, 44.83%/55.17% and 66.75%/33.25% over the temperature range from 253 to 333 K using the differential capillary rise method under vapor–liquid equilibrium conditions. The temperature and surface tension uncertainties were estimated to be within ±10 mK and ±0.15 mN m −1, respectively. Correlations for pure HFC-32 and HFC-125 were used to develop a van der Waals-type correlation for the experimental data of the HFC-32+HFC-125 mixtures as a function of the mass fraction.

Effects of Sample Size on Surface-Tension Measurements of Nickel in Reduced-Gravity Parabolic Flights

Surface tensions of molten metals have been reported in the literature by application of many “standard” techniques: sessile-drop, maximum bubble pressure, pendant-drop, and capillary-rise methods. Great experimental care must be exercised to ensure the absence of contamination, and containerless techniques based upon the classical theory of oscillations of a liquid drop are being developed for high-precision measurements on reactive alloys. Droplet positioning and heating can be efficiently accomplished by electromagnetic levitation, although additional modes of oscillation can be excited and the fundamental oscillation mode can be shifted to higher frequencies due to asymmetries in droplet shape when experiments are performed in earth-based laboratories. These additional factors associated with 1 g experiments significantly complicate data analysis. An electromagnetic levitator has been developed at Auburn University to test containerless processing methods for characterizing the surface tension of high temperature, reactive melts. Recent oscillating drop experiments with nickel samples utilizing electromagnetic levitation in the low-g environment of NASA's KC-135 research aircraft have shown droplet oscillations in the primary mode and at the fundamental frequency. A series of experiments was performed with droplets covering a range of sizes (i.e., mass), and the largest samples exhibited the largest deviations from Rayleigh's simple theory. The smallest samples exhibited oscillatory behavior consistent with Rayleigh's simple theory. An uncertainty analysis showed that the oscillating-drop technique should provide uncertainties in surface tension of ±0.1 to 2.0percnt; depending upon the uncertainty in the mass of the sample.