Molecular simulation of crystallization in n -alkane ultrathin films:Effects of film thickness and substrate attraction

Crystallization in n -alkane ultrathin films supported by solid substrates is investigated by molecular dynamics simulation. We consider a relatively short n -alkane, undecane C 11 H 24 , on a flat substrate of varied degree of attraction. By the use of the united atom model for n -alkane, we reveal...

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Bibliographic Details
Published in:The Journal of chemical physics 2007-10, Vol.127 (15), p.154704-154704-10
Main Authors: Yamamoto, Takashi, Nozaki, Koji, Yamaguchi, Aki, Urakami, Naohito
Format: Article
Language:English
Subjects:
Alkanes - chemistry
Chemistry, Physical - methods
Computer Simulation
Crystallization
Models, Statistical
Molecular Structure
Phase Transition
Substrate Specificity
Surface Properties
Temperature
Time Factors
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Summary:Crystallization in n -alkane ultrathin films supported by solid substrates is investigated by molecular dynamics simulation. We consider a relatively short n -alkane, undecane C 11 H 24 , on a flat substrate of varied degree of attraction. By the use of the united atom model for n -alkane, we reveal several characteristics of the thin film crystallization. It is found that the crystalline films consist of thin crystalline lamellae where chains are either parallel or perpendicular to the substrate. The relative amount of both types of lamellae changes systematically with film thickness, substrate attraction, and crystallization temperature; thicker films on substrates of higher attraction comprise dominant parallel lamellae, while thinner films on substrates of weaker attraction prefer the perpendicular lamellae. A clue to the morphogenesis is suggested to be the marked preference of the chain ends to locate on the free surface and on the effectively repulsive substrate. It is also shown that the perpendicular crystals, both on the free surface and on the solid substrate, have melting points higher than that of the bulk.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.2781390