Molecular Orbital Analysis of Adhesive Molecules UsingMolecular Simulation

Abstract

接着剤分子を新たに設計する際には, 理論と実験の両面からその接着機構に関して考察することが重要である．本研究では,新規接着剤分子である2-メルカプトピリジル基(2MP基)をもつビニルモノマーについて，被着体表面との吸着状態を解析することを最終目的とした．同モノマーに対し密度汎関数法に基づいた第一原理量子力学計算を実行し,その分子軌道を算出した．2MP基の平衡反応(互変異性化反応)によって得られるチオール型とチオン型の電子状態を比較したところ，HOMOとLUMOの分子軌道の状態から，被着体表面と分子軌道を介して相互作用を起こすときはチオン型の方が優位であることが確認された．

Translated Abstract

In recent years, adhesives have been studied and used in many fields. Both basic and applied researches have been conducted. But, the adhesion mechanism is still not understood in detail. The purpose of this study is to analyze the adsorption state of a vinyl monomer having a 2-mercaptopyridyl (2MP) group. The vinyl monomer is used as a component of adhesive materials. 2MP groups attach to the surface of the adherend, and they undergo tautomerization reactions where thione- or thiol-type chemical structures are taken. Computational analyses were performed according to density general function method and the first principles of quantum mechanics.

We calculated the molecular orbitals of vinyl monomers of including the 2MP group. Our evaluation revealed the electronic states of each chemical structure through the equilibrium reaction．The influence of the electronic states on the adsorption by 2MP groups was then analyzed and compared.

Figures

Figure 1.

 Equilibrium reaction of a vinyl monomer containing a 2MP group.

Figure 2.

 2-Hydroxyethyl methacrylate (HEMA).

Figure 3.

 .Modeling of the thione-type vinyl monomer containing a 2MP group.Atoms of carbon, hydrogen, nitrogen, and oxygen are shown in green, yellow, blue, and red, respectively. A sulfur atom is shown as a larger yellow ball.

Figure 4.

 (a) The optimized structure of the thione-type target molecule,(b) The charge magnitude of each atom (red: negative, blue: positive).

Figure 5.

 .(a) The optimized structure of the thiol-type target molecule,(b) The charge magnitude of each atom (red: negative, blue: positive).

Figure 6.

 .Mulliken charge of each atom of thione-type target molecule.

Figure 7.

 .Mulliken charge of each atom of thiol-type target molecule.

Figure 8.

 .Shape of molecular orbitals of thione- and thiol-type target molecules.

(a) Thione-HOMO (b) Thione-LUMO (c) Thiol-HOMO (d) Thiol-LUMO

Figure 9.

 .The optimized structure of the HEMA. Atoms of carbon, hydrogen, and oxygen are shown in green, yellow, and red, respectively.

Figure 10.

 .Shape of molecular orbitals of HEMA.

(a) HEMA-HOMO (b) HEMA-LUMO

Tables

Table 1.  Molecular orbitals and relative energies of thione-type target molecule

Item	Result
HOMO	No.71
LUMO	No.72
HOMO-LUMO Gap	8.6723 [eV]
HOMO Energy	−7.2736 [eV]
LUMO Energy	1.3987 [eV]

Table 2.  Molecular orbitals and relative energies of thiol-type target molecule

Item	Result
HOMO	No.71
LUMO	No.72
HOMO-LUMO Gap	10.8437 [eV]
HOMO Energy	−8.3131 [eV]
LUMO Energy	2.5307 [eV]

Table 3.  Molecular orbitals and relative energies of HEMA

Item	Result
HOMO	No.35
LUMO	No.36
HOMO-LUMO Gap	11.7689 [eV]
HOMO Energy	−10.4601 [eV]
LUMO Energy	1.3089 [eV]

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