Acid Neutralization by Marine Cylinder Lubricants Inside a Heating Capillary: Strong/Weak-Stick Collision Mechanisms

Temperature and Salting out Effects on Nicotine Dissolution Kinetics in Saline Solutions

The dissolution rate of nicotine in aqueous solutions of sodium chloride (NaCl) was investigated at room temperature and 70 °C by quantitatively visualizing the shrinkage rate of microscopic nicotine droplets. Four different salt concentrations were used: 15 wt % (3.0 M), 20 wt % (4.3 M), 25 wt % (5.7 M), and the saturation NaCl concentration of 26 wt % (6.0 M). These results, together with the Epstein-Plesset mathematical model, provided estimates of nicotine's diffusion coefficient in the NaCl solutions. At room temperature, the dissolution rate of nicotine and diffusion coefficients decreased with increasing NaCl concentration, and below 15 wt %, the dissolution kinetics were too fast to measure accurately via optical microscopy. At the higher temperature of 70 °C, nicotine's dissolution rate showed a decrease for 15 and 20% NaCl. However, at near-saturation 25% NaCl, nicotine's dissolution rate did not exhibit significant change for the two temperatures, and for 26%, dissolution was higher at 70 °C than at room temperature.

Molecular Dynamics Studies of Overbased Detergents on a Water Surface

Molecular dynamics (MD) simulations are reported of model overbased detergent nanoparticles on a model water surface which mimic their behavior on a Langmuir trough or large water droplet in engine oil. The simulations predict that the structure of the nanoparticle on a water surface is different to when it is immersed in a bulk hydrophobic solvent. The surfactant tails are partly directed out of the water, while the carbonate core maximizes its extent of contact with the water. Umbrella sampling calculations of the potential of mean force between two particles showed that they are associated with varying degrees with a maximum binding free energy of ca. 10 k_BT for the salicylate stabilized particle, ca. 8 k_BT for a sulfurized alkyl phenate stabilized particle, and ca. 5 k_BT for a sulfonate stabilized particle. The differences in the strength of attraction depend on the proximity of nearest approach and the energy penalty associated with the disruption of the hydration shell of water molecules around the calcium carbonate core when the two particles approach. This is greatest for the sulfonate particle, which partially loses the surfactant ions to the solution, and least for the salicylate, which forms the weakest water "cage". The particles are separated by a water hydration layer, even at the point of closest approach.

A molecular dynamics study of CaCO3 nanoparticles in a hydrophobic solvent with a stearate co-surfactant

Stearates containing overbased detergent nanoparticles (NPs) are used as acid neutralising additives in automotive and marine engine oils. Molecular dynamics (MD) simulations of the self-assembly of calcium carbonate, calcium stearate as a co-surfactant and stabilising surfactants of such NPs in a model explicit molecular hydrophobic solvent have been carried out using a methodology described first by Bodnarchuk et al. [J. Phys. Chem. C, 2014, 118, 21092]. The cores and particles as a whole become more elongated with stearate, and the surfactant molecules are more spaced out in this geometry than in their stearate-free counterparts. The rod dimensions are found to be largely independent of the surfactant type for a given amount of CaCO3. The corresponding particles without stearate were more spherical, the precise shape depending to a greater extent on the chemical architecture of the surfactant molecule. The rod-shaped stearate containing nanoparticles penetrated a model water droplet to a greater depth than the corresponding near-spherical particle, which is possibly facilitated by the dissociation of nanoparticle surfactant molecules onto the surface of the water in this process. These simulations are the first to corroborate the nanoparticle-water penetration mechanism proposed previously by experimental groups investigating the NP acid neutralisation characteristics.

Video microscopic high-temperature measurement of surface tension

In this paper, a micropipette-in-microcapillary method and its experimental setup are described for the study of temperature effects on surface tension. Temperature control within the confined space of a capillary was achieved by coating the outer surface of the housing microcapillary with an electrically conductive, transparent, tin-doped indium oxide (ITO) thin film as a heating jacket. The precision of this technique was discussed according to the comparisons of our results with published reference data for water, n-hexadecane, and n-decane at room temperature. The technique was further used to measure the temperature-dependent surface tension of n-decane between 25°C and 110°C and n-hexadecane from 25°C to 200°C. The results were in excellent agreement with available published values, and also indicated linear decrease rates of surface tension with decreasing temperatures.