黏结剂PLA, PCL及其共聚物与CL-20/TNT共晶黏结性能的分子动力学模拟

doi:10.7503/cjcu20180331

摘要/Abstract

摘要：

运用分子动力学(MD)模拟方法, 对绿色黏结剂聚乳酸(PLA)、聚己内酯(PCL)和聚乳酸-己内酯共聚物(P(LA-co-CL))在六硝基六氮杂异伍兹烷/三硝基甲苯(CL-20/TNT)炸药共晶4个晶面(001), (100), (010)H和(010)T上的黏结性能进行了计算研究. 对高聚物PLA, PCL和P(LA-co-CL)的密度、体积和玻璃化转变温度进行模拟以验证力场的适用性, 结果显示, 计算值与实验值吻合较好. 分子动力学模拟计算结果表明, 组成界面的晶面和高分子极性较高时, 润湿性能明显较好; 对相关函数计算发现, 晶面和黏结剂之间H-O原子对在0.5 nm范围内数量明显增多. 对于极性最小的PCL, 在所有晶面上的润湿性能都明显降低.

关键词: 六硝基六氮杂异伍兹烷/三硝基甲苯(CL-20/TNT)共晶, 绿色黏结剂, 黏结性能, 分子动力学模拟, 聚乳酸, 聚己内酯

Abstract:

Molecular dynamics simulations were performed to study the adhesion properties of green adhesives onto four different co-crystal surfaces of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexazisowurtziane/2,4,6-trinitrotoluene(CL-20/TNT). The green adhesives studied in this article include polyactic acid(PLA), polycaprolactone(PCL) and their copolymer[P(LA-co-CL)]. Simulations of the bulk polymers were employed over a wide range of temperatures including the volumetric glass transition temperature, so as to validate the force field used. The computed glass transition temperatures and densities compare well with experiment and calculation based on group additive method. Simulations of the interfaces show that the wettability are obviously greater for the crystal surfaces and adhesive molecules both having much polarity. The pair correlation function computations illustrate that in this case, there are apparently a number of H-O atom pairs in 0.5 nm ranges among these interfaces. The wettability for PCL with lowest polarity among the three adhesive molecules on all crystal surfaces studied here are all significantly smaller.

Key words: 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexazisowurtziane/2,4,6-trinitrotoluene(CL-20/TNT) co-crystal, Green adhesive, Adhesion property, Molecular dynamics(MD) simulation, Polyactic acid, Polycaprolactone

中图分类号:

TrendMD:

刘蓓, 高培, 李慎慎, 肖运钦, 肖继军. 黏结剂PLA, PCL及其共聚物与CL-20/TNT共晶黏结性能的分子动力学模拟. 高等学校化学学报, 2018, 39(11): 2556.

LIU Bei, GAO Pei, LI Shenshen, XIAO Yunqin, XIAO Jijun. Molecular Dynamics Investigation of Adhesion Between CL-20/TNT Co-crystal Surfaces and Adhesives of PLA, PCL, P(LA-co-CL)^†. Chem. J. Chinese Universities, 2018, 39(11): 2556.

图/表 11

Fig.1 Primitive cell of CL-20/TNT co-crystal(A) and primary cell of CL-20/TNT co-crystal(B)CL-20 in line mode and TNT in ball-stick mode.

Fig.2 Four side views of different surface models of CL-20/TNT co-crystalCL-20 in line mode and TNT in ball-stick mode. (A)(001); (B)(100); (C)(010)H; (D)(010)T.

Fig.3 Initial (001) CL20/TNT co-crystal/PLA interface used in the MD simulation(co-crystal in CPK and PLA in ball-stick)

Fig.4 Specific volume vs. temperature for PLA(A), PCL(B) and P(LA-co-CL)(C) at 105 Pa as determined from MD simulations

Table 1 Densities and glass transition temperatures of the polymers

Polymer	Density/(g·cm^-3)(298 K)			T_g/℃
Polymer	Experiment	This work	Synthia^[27]	Experiment	This work
PLA	1.24^[28]	1.17±0.01	1.25	55—60^[30]	59
PCL	1.15^[29]	1.11±0.01	1.10	-60^[31]	-57
P(LA-co-CL)		1.12±0.01	1.16	-15^[31]	-15

Table 2 Surface tension(γ), interfacial tension(γ12), work of adhesion(W12) and spreading coefficient(S) for the polymers(γ2) interfaced to the CL-20/TNT co-crystal(γ1)(10-3 J/m2)

Crystal surface	Polymer	γ₁	γ₂	γ₁₂	W₁₂	S
(001)	PLA	131	28±4	-477±1	636	580
	PCL	131	49±2	-56±4	236	138
	P(LA-co-CL)	131	42±1	-486±3	659	575
(100)	PLA	144	28±4	-28±3	200	144
	PCL	144	49±2	-8±5	201	103
	P(LA-co-CL)	144	42±1	12±4	174	90
(010)T	PLA	140	28±4	-65±4	233	177
	PCL	140	49±2	-40±2	229	131
	P(LA-co-CL)	140	42±1	-53±4	235	151
(010)H	PLA	140	28±4	-252±3	420	364
	PCL	140	49±2	-49±3	238	140
	P(LA-co-CL)	140	42±1	-354±2	536	452

Fig.5 Comparison of the work of adhesion(W12)(A) and the spreading coefficient(S)(B) for PLA, PCL and P(LA-co-CL) interfaced to the different CL-20/TNT co-crystal surfaces

Fig.6 Carbon density profiles for PLA at (001)(A), (010)H(B), (010)T(C) and (100)(D) surfaces of CL-20/TNT co-crystal

Fig.7 Snapshots of the time evolution of a single PLA polymer chain at (001)(A), (010)H(B), (010)T(C) and (100)(D) surfaces of CL-20/TNT co-crystal interface at 0.2 intervalsFrom left to right: the chronological order is 0, 0.2, 0.4 ns.

Fig.8 PCFs for atom pairs of H and O atoms in PLA with O[H(P)—O, a] and H[O(P)—H, b] atoms in CL-20/TNT co-crystal at(001) surface at 380 K, respectively(A) g(r) converged to 1; (B) close-up g(r) of the region of interest.

Table 3 Integral areas of PCF curves for different atom pairs in the interfaces between polymers and co-crystal surfaces

Crystal surface	Polymer	Distance/nm	H(P)—O	O(P)—H
(001)	PLA	0.20—0.31	1.87	3.04
	PCL		1.37	2.45
	P(LA-co-CL)		1.89	3.31
	PLA	0.31—0.50	5.57	5.84
	PCL		5.03	4.97
	P(LA-co-CL)		5.68	5.92
(010)H	PLA	0.20—0.31	2.14	0.75
	PCL		1.57	0.59
	P(LA-co-CL)		2.33	0.78
	PLA	0.31—0.50	6.18	4.59
	PCL		5.73	4.27
	P(LA-co-CL)		6.45	5.03
(010)T	PLA	0.20—0.31	1.73	0.68
	PCL		1.69	0.57
	P(LA-co-CL)		1.78	0.72
	PLA	0.31—0.50	4.45	3.46
	PCL		4.33	3.27
	P(LA-co-CL)		4.48	3.57
(100)	PLA	0.20—0.31	1.02	0.33
	PCL		1.03	0.29
	P(LA-co-CL)		1.07	0.32
	PLA	0.31—0.50	2.82	3.22
	PCL		2.78	3.19
	P(LA-co-CL)		2.87	3.04

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