A Molecular Dynamics Study of the Damping Properties of AO‐80/ACM Hybrids

Physical Chemistry Communications, Volume 2 Issue 2, October 2015 www.bacpl.org/j/pcc

A Molecular Dynamics Study of the Damping Properties of AO‐80/ACM Hybrids Huifang Su*1, Xiuying Zhao2, Dawei Yang3, Sizhu Wu4 Beijing Engineering Research Center of Advanced Elastomers Beijing University of Chemical Technology, Beijing 100029, P.R. China *1

su206914@163.com; 2zhaoxy@mail.buct.edu.cn; 3yangdw1990@126.com; 4wusz@mail.buct.edu.cn

Abstract Hindered phenol AO‐80/polyacrylate rubber (AO‐80/ACM) damping hybrids were prepared to investigate the influence of the content of hindered phenol AO‐80 on the thermal and damping properties. Meanwhile, molecule dynamics (MD) simulation, a molecular‐level method, was applied to elucidating the microstructure and mechanism of the hybrids. The computed results revealed that three types of hydrogen bond, namely, type A (AO‐80) ‐OH∙∙∙OC‐ (ACM), type B (AO‐80) ‐OH∙∙∙OC‐ (AO‐80), and type C (AO‐80) ‐OH∙∙∙OH‐ (AO‐80), were formed in the AO‐80/ACM hybrids. Moreover, the experiment was highly consistent with the MD simulation results in showing that the introduction of AO‐80 improved the damping properties.

Keywords Polyacrylate Rubber; AO‐80; Hydrogen Bonds; Molecular Dynamics Simulation

Introduction Polyacrylate (ACM) materials have superior damping properties, as well as excellent adhesive performance, mechanical properties and heat‐resistant at room temperature due to its innumerable ester functional groups as the side groups [1]. However the effective damping temperature range of ACM is quite narrow and the loss factor couldn’t satisfy some particular fields. Our previous studies[2] have discovered that AO‐80 can dramatically improve the damping properties of NBR, including the temperature range of Tg and the maximum loss factor.

In this study, the molecular dynamics (MD) simulation method was applied to investigating the microstructure and relevant parameters of AO‐80/ACM hybrids. Scientists have studied the theoretical and experimental aspects of hydrogen bond, leading to rapid development about this theory [3]. Fractional free volume (FFV) was calculated to analyze the interactions between AO‐80 and ACM. We would also make a comparison between the experimental and the simulation results.

Experimental and Simulation Methods The Chemical Structural Formula of AO‐80 /ACM The chemical structural formulae of AO‐80 and ACM are shown in figure 1. As an AO‐80 molecule has several kinds of polar functional groups, including carbonyl, hydroxyl, and ether, which can form strong molecular interactions with ACM chains, the AO‐80/ACM hybrids are expected to have high internal binding capacity.

(a)

(b)

FIG. 1 CHEMICAL STRUCTURE OF AO‐80 (a), ACM (b)

Construction Process of the AO‐80/ACM cells The ACM polymer chains and AO‐80 small molecules were first built in a 3D cubic cell with periodic boundary

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conditions. Figure 2 shows the process of construction of the amorphous cell. Each cell consisted of four ACM chains with 30 repeat units, respectively.

FIG. 2 MODELS FOR MD SIMULATION OF AO‐80/ACM HYBRIDS (GREY ATOM IS H, RED ATOM IS O, GREEN ATOM IS H AND GREEN DASHED LINE REPRESENTS HYDROGEN BOND).

Results and Discussion Hydrogen Bonds in AO‐80/ACM Hybrids Since first discovered in 1953 by Pauling [4], hydrogen bond had ushered in a new era in material chemistry and biochemistry. Molecular simulation results discovered that three kinds of hydrogen bonds were formed in the AO‐ 80/ACM hybrids, termed Type A, Type B and Type C (Fig.3), and only Type A was helpful to the improvement of the damping performance[5].

FIG. 3 THREE TYPES OF HYDROGEN BONDS IN AMORPHOUS CELL OF AO‐80/ACM

Free Volume in AO‐80/ACM Hybrids To validate the efficiency of chain packing and the amount of free space in AO‐80/ACM hybrids, the fractional free volume (FFV) theory was performed to confirm the influences of the hydrogen bonds on these matrixes[6], as is shown in Fig. 4, with the introduction of AO‐80, fraction free volume in the hybrids decreases rapidly and then gets a slow decline as the ratio of AO‐80 exceed 18.

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Physical Chemistry Communications, Volume 2 Issue 2, October 2015 www.bacpl.org/j/pcc

0/100 FFV=0.4712

37/100 FFV=0.4016

18/100 FFV=0.4141

61/100 FFV=0.3847

80/100 FFV=0.3705

99/100 FFV=0.3584

FIG. 4 FREE VOLUME OF DIFFERENT RATIOS HYBRIDS. THE BLUE COLOR CORRESPONDS TO THE FREE VOLUME, AND THE RED COLOR CORRESPONDS TO THE OCCUPIED VOLUME OF THE SYSTEM.

Thermal Properties of AO‐80/ACM Hybrids The determination of Tg is a good approach to identify the influence of AO‐80 on the thermal properties of AO‐ 80/ACM hybrids because the hydrogen bond network would increase the thermal stability of the manufactured materials. Figure 5 shows the DSC curves of the AO‐80/ACM hybrids with different AO‐80 contents. The Tg increases linearly with the AO‐80 content, an indication that AO‐80 increases the thermal stability of the hybrids.

AO-80/ACM(99/100)

8.55℃

Endothermic

AO-80/ACM(80/100) 6.00℃ AO-80/ACM(61/100) -1.80℃

AO-80/ACM(37/100)

-6.34℃

AO-80/ACM(18/100)

-7.77℃ AO-80/ACM(0/100) -15.22℃

-50

-40

-30

-20

-10

0

10

20

30

40

50

Temperature / ℃ FIG. 5 DSC THERMOS GRAMS OF ACM AND AO‐80/ACM HYBRIDS

Dynamic Mechanical Thermal Analysis of AO‐80/ACM Hybrids DMA was carried out to study the damping properties and phase structure of the AO‐80/ACM hybrids. This study can provide an accurate analysis of the miscibility of AO‐80 with ACM. Polymer materials obtained the maximal damping performance between the glassy and rubbery states (around Tg) because the macromolecular chain segments in this region tended to vibrate in phase with an external vibration. Therefore, a higher tan δ corresponds to a better damping performance of the material. DMA results (Fig. 6) revealed that the hindered phenol AO‐80 can remarkably enhance the loss factor of the hybrids.

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www.bacpl.org/j/pcc Physical Chemistry Communications, Volume 2 Issue 2, October 2015

AO-80/ACM(0/100) AO-80/ACM(18/100) AO-80/ACM(37/100) AO-80/ACM(61/100) AO-80/ACM(80/100) AO-80/ACM(99/100)

4

Tanδ

3

2

1

0

-20

0

20

40

60

80

Temperature/℃ FIG. 6 TEMPERATURE DEPENDENCE OF LOSS FACTORS FOR AO‐80/ACM HYBRIDS WITH VARIOUS MASS RATIOS

Conclusions MD simulation and experimental method was applied to investigating the microscopic structure and damping mechanism of AO‐80/ACM hybrids. FFV, DSC and DMA were calculated to analyze the types and influences of hydrogen bonds in AO‐80/ACM hybrids. We discovered that the hindered phenol AO‐80 can help to increase the damping performance of the ACM matrixes evidently. The simulation and experimental results could provide a fundamental understanding of the damping mechanism of AO‐80/ACM hybrids at a molecular level.

ACKNOWLEDGEMENT

The financial supports of the National Natural Science Foundation of China under Grant No. 51473012 are gratefully acknowledged.

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[2]

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[3]

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[4]

L. C. Pauling. ʺThe Nature of Chemical Bond, 3rd edn.,(translated into Japanese) Kyoritsu Shuppan.ʺ Tokyo, Japan (1963): 257.

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