理论与实验揭示聚α-甲基苯乙烯 mandrel 材料的快慢相混合降解过程

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本研究论文聚焦于一种理想的管芯材料——聚α-甲基苯乙烯（Poly-α-methylstyrene, PAMS）的联合快速和慢速降解过程。《高功率激光科学与工程》(HighPowerLaserScienceandEngineering)于2021年发表了这一研究，卷9，第1期，共7页，DOI:10.1017/hpl.2020.48。作者通过对理论计算和实验方法的结合，揭示了PAMS材料降解的两种主要机制：聚合物链的分解（depolymerization）和氢转移引发的链断裂（hydrogen-transfer-induced chain scission）。理论计算表明，聚合物链分解的能量壁垒较低，范围在0.68-0.82电子伏(eV)，相比之下，氢转移导致的链断裂能量壁垒较高，大多在1.39-4.23 eV之间。这意味着分解过程对于PAMS而言是相对容易发生的，其速率相对较快。而氢转移反应由于能量障碍大，速度明显较慢，这可能导致在550 K温度下，两种降解过程速率差异达到5-31个数量级。实验结果进一步证实了这一点，热重分析（Thermogravimetric Analysis, TGA）数据支持了理论预测。通过TGA，研究者观察到了这两种不同降解途径对材料质量损失的影响，以及它们随时间的变化规律。这种理解对于优化PAMS在高能激光应用中的性能、延长其使用寿命至关重要，尤其是在极端条件下，如激光加工或熔融过程中的耐久性。该研究揭示了聚α-甲基苯乙烯材料在受到激光或其他热源影响时，其内部结构如何通过两种截然不同的化学过程进行降解，并强调了理解和控制这些过程速率在材料设计和实际应用中的关键作用。这对于材料科学家和工程师来说，提供了深入理解材料性能衰退机制的宝贵信息，有助于开发出更耐久、性能更稳定的激光加工材料。

High Power Laser Science and Engineering, (2021), Vol. 9, e1, 7 pages.

doi:

10.1017/hpl.2020.48

RESEARCH ARTICLE

Mandrel degradation model of combined fast and slow

processes

Yu Zhu

, Zheng Liu

, Famin Yu

, Qiang Chen

, Wei Feng

, Zhanwen Zhang

, and Zhigang Wang

Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China

Laser Fusion Research Center, China Academy of Engineering Physics, Mianyang 621900, China

(Received 11 September 2020; revised 28 October 2020; accepted 24 November 2020)

Abstract

In this paper, we report the study of degradation for a kind of ideal mandrel material called poly-α-methylstyrene based

on theoretical and experimental methods. First-principles calculations reveal two types of process: depolymerization

and hydrogen-transfer-induced chain scission. The energy barrier for the former (0.68–0.82 eV) is smaller than that for

most of the latter (1.39–4.23 eV). More importantly, reaction rates suggest that the former is fast whereas the latter is

mostly slow, which can result in a difference of 5–31 orders of magnitude at 550 K. Furthermore, a thermogravimetric

experiment shows that the activation energy of 2.53 eV for degradation is between those of fast and slow processes,

corresponding to the theoretical average value of multiple reaction paths. Thus, a mandrel degradation model combining

fast and slow processes is established at the atomic level. Our work provides a direction for research into the key

technology of target fabrication in inertial conﬁnement fusion.

Keywords: atomic level; degradation; ﬁrst principles; mandrel material; thermogravimetric experiment

1. Introduction

As an important method for fabricating inertial conﬁne-

ment fusion (ICF) targets, the degradable mandrel technique

is the basis of preparing glow discharge polymer (GDP)

microspheres

[

1–4]

. It can be divided into three steps

[2,3]

: ﬁrst,

hollow polymer microspheres are prepared as mandrels;

then, plasma vapour deposition technology is used to prepare

a coating with higher thermal stability on the surface; and,

ﬁnally, the coated mandrels are degraded leaving hollow

microspheres. In these steps, the preparation of hollow

microspheres is directly related to the degradation properties

of polymers. The technique requires that coatings are ther-

mostable at the degradation temperature of polymers, and

degradation products do not affect the formation and surface

ﬁnish of microspheres. To meet these requirements, poly-

α-methylstyrene (PAMS) has become an ideal choice for

mandrel materials (MMs), because of its excellent thermal

degradation properties and good balling performance

[

5,6]

Correspondence to: Z. Wang, No. 2699, Qianjin Road, Changchun

130012, China; Z. Zhang, No. 64, Mianshan Road, Mianyang 621900,

China. Email: wangzg@jlu.edu.cn (Z. Wang); bjzzw1973@163.com

(Z. Zhang)

However, it still presents two key problems in preparing

target pellets, namely how to reduce the thermal degradation

temperature and avoid degradation residues

[

2,7]

. These lead

to the urgent need for a clear understanding of the reaction

mechanism of MM-PAMS degradation.

In the past, there have been numerous reports on the

thermal degradation of MM-PAMS

[

8–17]

. Researchers have

generally believed that degradation was caused by, ﬁrst,

generating free radicals through random chain scission and,

then, depolymerizing to generate monomers

[

9,10]

. However, it

should be noted that these two processes are not recognized

at the atomic level, resulting in an order of magnitude dif-

ference in reaction rate between them that remains unclear.

More importantly, a precise description of these processes

based on the properties of geometric and electronic struc-

tures is necessary for controlling the degradation process and

avoiding degradation residues. It is undeniable that experi-

ments can obtain some reliable results, but calculations and

simulations of quantum mechanics have also become an

indispensable tool in understanding the reaction process and

mechanism of microscopic matter, and have shown sufﬁcient

accuracy in degradation or general chemical reactions to

attract widespread attention

[

16,18–21]

the terms of the Creative Commons Attribution licence (

http://creativecomm ons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and

reproduction in any medium, provided the original work is properly cited.

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