Unique diffusion behavior observed in supercritical ethanol

Abstract

We have systematically investigated the diffusion behavior of silica nanoparticles within supercritical ethanol, in terms of solvent properties by varying temperature ͑T͒ and pressure ͑P͒, to elucidate how the inhomogeneous solvent structures and density fluctuations in the solvent affect the diffusion behavior of solute particles. Results show that at a constant pressure, the diffusion coefficient ͑D͒ of the particles increases with increasing temperature, reaches the maximum ͑D max ͒ within the gaslike supercritical fluid ͑slightly below the ridge͒, and finally decreases abruptly at very low fluid density when temperature is increased further. Results reveal that D is appreciably larger than the theoretical prediction ͑Einstein-Stokes relationship͒ in the vicinity of the critical density ͑ c ͒ of the solvent. We interestingly observed that D becomes maximum ͑D max ͒ at a particular thermodynamic condition ͑T i , P i ͒, which is expressed by the empirical formula T ri = P ri 0.16 ͑for T ri Ͼ 1, P ri Ͼ 1͒. Here, T ri = T i / T c and P ri = P i / P c ; T c and P c are the temperature and the pressure at critical point, respectively. Results further reveal that D max increases significantly with decreasing solvent density within the gaslike supercritical fluid where the changes in viscosities are negligible. These findings are unique, novel, and intriguing. We suggest that the enhancement of the diffusion coefficient in the vicinity of the critical density and the abrupt decrease in the diffusion coefficient in very low density gaslike fluid are associated with the change in the solvent-solvent and solute-solvent direct correlation function ͑related to the effective interaction potential͒ upon density change when the fluid crosses the ridge of density fluctuations and within the gaslike fluid.

Effects of Temperature on Hand Sanitizer Efficiency

“…Hand sanitizers are known to be one of the effective ways to kill microbes and clean hands. Components that make up sanitizers, such as ethyl alcohol, are known to be affected by environmental factors (1); ethyl alcohol's reactance is dependent on changes in temperature and pressure (2). Although the effectiveness of liquid soap and hand sanitizer against specific viruses, such as Norwalk, and hand sanitizer as an alternative to handwashing have been studied thoroughly previously, little is known regarding the environmental temperature effects on hand sanitizers (3)(4)(5)(6).…”