基于分子动力学的橡胶聚合物计算机辅助设计方法

doi:10.11949/j.issn.0438-1157.20181068

摘要/Abstract

摘要：

聚合物分子设计的关键步骤是得到能够满足多种性质要求的重复单元结构。作为化学产品工程中的新型发展手段，计算机辅助分子设计(CAMD)技术可以通过基团贡献法生成满足约束条件的聚合物重复单元结构，分子动力学(MD)技术则可以在微观层面上进行计算机实验模拟系统性质。建立了聚合物的CAMD-MD通用设计方法，并进行轮胎橡胶聚合物的分子设计，首先基于基团贡献法进行重复单元的设计；其次，利用层次分析法确定多性质权重排名，并基于分子动力学方法探究候选结构的性质；最后将方法应用于实际橡胶结构中，模拟得到聚能密度、密度、玻璃化转换温度和热导率性质，验证了方法的可行性。

关键词: 产品设计, 计算机模拟, 分子模拟, 聚合物

Abstract:

A key step in the design of polymer molecules is to obtain repeating unit structures that meet a variety of properties. As a new developing method in chemical engineering, computer-aided molecular design (CAMD) technique can generate the repeat unit structures which satisfy the constraints using group contribution method, molecular dynamics (MD) technique can be used to simulate computer experiments to acquire systems properties at the micro level. This paper establishes a general CAMD-MD method to design polymers. First, repeat unit structures are identified based on group contribution method. Second, the weight of properties is determined respectively by using the analytic hierarchy process and properties of candidate structures are simulated based on molecular dynamics method. The CAMD-MD method is finally applied to the actual rubber structure, and the properties such as cohesive energy density, density, glass transition temperature and thermal conductivity are simulated to verify the feasibility of the method.

Key words: product design, computer simulation, molecular simulation, polymers

中图分类号:

TQ 317.5

梁馨元, 张磊, 刘琳琳, 都健. 基于分子动力学的橡胶聚合物计算机辅助设计方法[J]. 化工学报, 2019, 70(2): 525-532.

Xinyuan LIANG, Lei ZHANG, Linlin LIU, Jian DU. Study on rubber polymer using computer-aided molecular design method based on molecular dynamics[J]. CIESC Journal, 2019, 70(2): 525-532.

图/表 10

图1 分子动力学模拟基本原理

Fig.1 Basic principle of molecular dynamics simulation

表1 重复单元结果

Table 1 Results of repeat unit structures

Property constraints

Lower limit

Upper limit

CED/MPa

T_g/K

thermal conductivity/(W·m^-1·K^-1)

density/(kg·m^-3)

—

0.11

0.7

330

235

—

1.4

Repeat unit structures

CED /MPa

T_g/K

Thermal conductivity/(W·m^-1·K^-1)

Density/(kg·m^-3)

-[-CH₂-]_n-

-[-(CH₂)₆-CH $?$ CF-]_n-

-[-(CH₂)₅-CH $?$ CF-]_n-

-[-(CH₂)₄-CH $?$ CF-]_n-

-[-(CH₂)₆-CH $?$ CH-]_n-

-[-(CH₂)₅-CH $?$ CH-]_n-

-[-(CH₂)₆-CH $?$ C(CH₃)-]_n-

…

-[-(CH₂)-CH $?$ CH-(CH₂)-]_n-

…

264.82

309.32

316.79

327.27

285.57

288.73

281.54

…

308.81

…

168.34

173.77

174.44

175.29

182.79

184.90

188.78

…

197.79

…

0.1250

0.1645

0.1717

0.1820

0.1234

0.1231

0.1281

…

0.1210

…

0.8328

1.093

1.137

1.198

0.8640

0.8688

0.8734

…

0.8990

…

表1 重复单元结果

Table 1 Results of repeat unit structures

Property constraints

Lower limit

Upper limit

CED/MPa

T_g/K

thermal conductivity/(W·m^-1·K^-1)

density/(kg·m^-3)

—

0.11

0.7

330

235

—

1.4

Repeat unit structures

CED /MPa

T_g/K

Thermal conductivity/(W·m^-1·K^-1)

Density/(kg·m^-3)

-[-CH₂-]_n-

-[-(CH₂)₆-CH $?$ CF-]_n-

-[-(CH₂)₅-CH $?$ CF-]_n-

-[-(CH₂)₄-CH $?$ CF-]_n-

-[-(CH₂)₆-CH $?$ CH-]_n-

-[-(CH₂)₅-CH $?$ CH-]_n-

-[-(CH₂)₆-CH $?$ C(CH₃)-]_n-

…

-[-(CH₂)-CH $?$ CH-(CH₂)-]_n-

…

264.82

309.32

316.79

327.27

285.57

288.73

281.54

…

308.81

…

168.34

173.77

174.44

175.29

182.79

184.90

188.78

…

197.79

…

0.1250

0.1645

0.1717

0.1820

0.1234

0.1231

0.1281

…

0.1210

…

0.8328

1.093

1.137

1.198

0.8640

0.8688

0.8734

…

0.8990

…

图2 无定形顺丁橡胶分子

Fig.2 Amorphous butadiene rubber molecule

图3 LAMMPS初始体系

Fig.3 Initial system in LAMMPS

表2 弛豫过程

Table 2 Relaxation process

Stage

Ensemble

Pressure/

MPa

Temperature/

Time step/fs

Number of steps

Run time/ps

NVT

NPT

—

0.1

300

300—600

600

600—100

100—300

300

300000

200000

600000

250000

300000

500000

300

200

600

250

500

图4 弛豫过程密度-温度关系

Fig.4 Density-temperature diagram of relaxation process

图5 模拟顺丁橡胶系统的密度-温度关系

Fig.5 Density-temperature relationship of simulated butadiene rubber system

图6 体系分块

Fig.6 System block diagram

图7 计算热导率

Fig.7 Calculation of thermal conductivity

符号说明

A	——系统在垂直于传导方向的横截面积
a_i(t)	——原子i在t时刻的加速度
C_i, D_j, E_k	——分别为第一、二、三级基团贡献值
F_i(t)	——原子i在t时刻所受的力
J	——热通量, W·m^-2
N_i, M_j, O_k	——分别为第一、二、三级基团分别出现的次数
n_i	——第i种基团在重复单元中出现次数
n_j	——第j种基团在重复单元中出现次数
P(n_i)	——聚合物性质预测值
P_l	——性质约束下限
P_u	——性质约束上限
dT/dx	——温度梯度, K·m^-1
v_i(t)	——原子i在t时刻的速度矢量
v_j	——j基团的化合价
κ	——热导率, W·m^-1·K^-1

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