CO₂ Diffusion In Various Carbonated Beverages:A Molecular Dynamics Simulation

Carbonated beverages are widely enjoyed in spare time and have many interesting physics,chemistry and biology science,yet there remain many physical,chemical and biological processes clouded at the molecular level,such as the sink of Guinness bubbles,beer tapping,etc.The diffusion of dissolved gas in solution is considered as the important processes for these phenomenons.But it is difficult for us to estimate the diffusion coefficient of dissolved gas in solution by experimental tools,because the diffusion of dissolved gas is very slow in solution and it is difficult to trace quantities of gas.The experimental data have large uncertains,so we need more reliable tools to estimate the diffusion coefficient of dissolved gas,such as molecular dynamics simulation.Unlike those studies,we pay more attention to the diffusion of CO₂ in various carbonated beverages,including sparkling wines,cola drinks,and carbonated mineral water,to investigate the effect of different solutes,including ethanol,sugar and mineral salt,rather than the effect of temperature in champagne.We used the TIP5 P water model and employed molecular dynamics simulations to calculate the diffusion coefficient of CO₂ in various carbonated beverages.First and foremost,we calculated the Van Hoff correlation function to ensure that it is enough to estimate the diffusion coefficient of CO₂ in each system by the generalized Fick law.Then we analyze the hydrogen bond network of solution,these are amost no CO₂-solute hydrogen bond in each system,but the water-water hydrogen bond network has different levels of changes.So we think the solutes have indirect effect on CO₂ diffusion.We carbonated the water tetrahedral order parameters and reorientation correlation function and found that the addition of solute other than CO₂ to aqueous solutions leads to the changes of structure and dynamics of solutions,resulting in direct effect on viscosity of solution and indirect effect on CO₂ diffusion and the size and stability of bubble.These three different solutes have obvious specificity.Ethanol is an amphiphilic molecule;the part of hydroxyl group can form hydrogen bond with water and the part of hydrophobic group affect the water molecules by hydrophobic interactions.Sucrose has many hydroxyl groups,so it will increase the number and probability of hydrogen bond formation significantly.Bicarbonate ion can directly form stronger hydrogen bond with water molecules,because it has a negative charge.The simulated diffusion coefficients of CO₂ are in good agreement with existing experimental results and we investigate the effect of different solutes on CO₂ diffusion.Moreover,this study is not only to have directing sense on the brewing technology of carbonated beverages,but also to have reference value for the study of interactions between dissolved gas and solution,such as the formation and conservation of gas hydrate,volcanic eruption,etc.