A molecular dynamics study combining with entropy calculation on the packing state of hydrophobic chains in micelle interior

摘要

Micelle plays an important role both in scientific research and practical applications. However, the problem about the state of micelle interior has not been completely solved. Based on the molecular dynamics (MD) simulation, absolute configurational entropies of hydrophobic chain are calculated to give a correct description of micelle hydrophobic interior. N-dodecyl betaine (NDB) and n-tridecane (C13), which have the same number of methylene group, are investigated in the present study. Results including total entropy, translational entropy, rotational entropy as well as vibrational entropy are calculated and compared between alkyl chains of NDB micelle and liquid C13. Local entropies along NDB alkyl chain and those between micelle and C13 are also considered. Through these comparisons, we explicitly propose that innermost groups of hydrophobic chains, where carbon number is no more than two, are identical to pure alkane whilst the outer core in the micelle shows the liquidlike state at the molecular level. The detailed information of micelle interior is the foundation for understanding micelle applications, such as solubilization, drug delivery and catalysis. (C) 2019 Elsevier B.V. All lights reserved.