Molecular Dynamics Simulation of Ice Crystal Growth Inhibition by Hexadecyl-trimethyl-ammonium Bromide

Abstract

Recent experiments have found hexadecyl-trimethyl-ammonium bromide (CTAB) to have superior ice nucleation inhibition properties [ J. Phys. Chem. B 121, 6580]. The mechanism of how the inhibition takes place remains unclear. Therefore, molecular dynamics was used to simulate ice crystallization of a water/CTAB/ice system. The ice crystallization rate for a pure water system was compared for the basal [0001], first prism [101̅0], and secondary prism plane [112̅0], where the basal plane grew the slowest followed by the first prism plane. When CTAB was added to the ice-liquid water system, crystallization was clearly impeded. Even when ice starts growing away from the CTAB molecule, the hydrophilic head would at some point protrude and get caught in the water/ice interface. Once the head of the CTAB was encapsulated in the advancing interface, the hydrophobic body would wriggle around and disrupt the formation of hydrogen bond networks that are essential for ice growth. When the interface clears the length of the body of the CTAB molecule, ice crystallization resumes at its normal pace. In summary, the inhibition of ice growth is a combination of the hydrophilic head acting as an anchor and the dynamic motion of the hydrophobic tail hindering stable hydrogen bonding for ice growth.

Visualizing Molecular-Scale Adsorption Structures of Anti-freezing Surfactants on Sapphire (0001) Surfaces at Different Concentrations by 3D Scanning Force Microscopy

“…These features of the adsorption structure may account for the excellent anti-freezing ability of C 16 TABs over other surfactants. Such an influence of the molecular fluctuation on the anti-freezing effect was previously suggested by an MD simulation, where a disturbance of the hydrogen bonding network was observed around a fluctuating molecular chain . Our interpretation is consistent with such an expectation.…”

Perturbation of Hydrogen Bonding Network Plays an Important Role in Determining Antifreeze Activity

“…There is no doubt that for any molecule with antifreeze activity, its interaction with ice surface provides all the information needed to understand its activity . For that, it is reasonable to pay attention to the ice near the amino acid.…”

“…There is no doubt that for any molecule with antifreeze activity, its interaction with ice surface provides all the information needed to understand its activity. 28 For that, it is reasonable to pay attention to the ice near the amino acid. As shown in Figure 2c, for both amino acids, once they contact with ice, the bottom is nearly static, which makes it possible to study the ice in their vicinity.…”