Session: 17-15-01: Society-Wide Micro/Nano Poster Forum

Paper Number: 99404

99404 - Freezing Point Depression of Water in Calcium Chloride Solution Using Molecular Dynamic Simulations 

The presence of water plays a vital role in the formation of solutions as well as the variability upon different behaviors that solutions can display. The amount of water within a system as well as its state it exhibits can make great contributions upon several of these behaviors. One behavior that can be portrayed when comparing freshwater and saltwater is the phase change temperature. Implications have shown that solutes and additives that are salt based can lower the phase change temperature to a certain degree. The molarity of the salt-based solute has impact upon the decrease in phase change temperature. It has been demonstrated that an increase in molarity correlates to a larger decrease in phase change temperature. However, freshwater is used within our system while a replacement for a sodium-based additive has been proven to make greater improvements to the phase change temperature. An aqueous solution formed using Calcium and Chloride ions along with the TIP4P (four site transferable intermolecular potential) water model was tested to determine the freezing point from a selection of different molarities below the eutectic point. These tests were run using molecular dynamic simulations using the direct coexistence method, where the solution is in contact with the ice within the simulation box. The following simulation box was subjected to a procedure in which its contents were held to short periods of time when several variables were either altered or constant. During the equilibration procedure, there was an instance of energy minimization as well as several instances of NPT and NVT time periods. NPT time periods occur when the number of molecules, pressure, and temperature remain constant while the volume varies within the system. The pressure and amount molecules held for NPT was always 1 bar and 8,000 molecules respectively for each portion added to the simulation box whether it being an ice slab or the solute while the temperature varied depending upon the part of the procedure that was performed. NVT time periods occur when the number of molecules, volume, and temperature remain constant while the pressure varies within the system. The same can be said for NVT which is the number of molecules and volume remained the same for each portion of the simulation box, but the constant temperature was varied based upon the testing procedure. The simulation box used 8,000 molecules of the aqueous calcium chloride solution were sandwiched between two 16,000 molecule slabs of ice. The freezing point temperatures were found by comparing the potential energy of the solution to the amount of time the solution was subjected under a certain temperature. The arrangement of the ice and solution within the model allowed for periodic boundary conditions to be used effectively due to the sandwiching of the simulation box. The resulting data portrays an accurate correlation to existing Calcium Chloride phase diagrams within a scale factor resulting in the difference in melting temperature from the TIP4P water model.

Presenting Author: Ganesh Balasubramanian Lehigh University

Presenting Author Biography: Associate Professor of the Mechanical Engineering and Mechanics Department at Lehigh University

Authors:

Derek Scott Lehigh University
Lida Yan Lehigh University
Ganesh Balasubramanian Lehigh University