FAILURE MECHANISMS OF POLYMER INTERFACES REINFORCED WITH BLOCK COPOLYMERS
FAILURE MECHANISMS OF POLYMER INTERFACES REINFORCED WITH BLOCK COPOLYMERS
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DOI：
10.1021/ma00038a010
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发表时间：
1992-06-08
期刊：
影响因子：
5.5
通讯作者：
BROWN, HR
中科院分区：
文献类型：
--
作者：
CRETON, C;KRAMER, EJ;BROWN, HR
用双悬臂梁法测定了聚苯乙烯-b-2-乙烯基吡啶（PVP）增强聚苯乙烯（PS）/PVP界面的断裂韧性（用临界能量释放速率G（c）表征）。定量地研究了PVP嵌段聚合度（N（PVP））和界面处嵌段共聚物链的面密度（SIGMA）对测得的G（c）和断裂机制的影响。PS聚合度（N（PS））保持>280，而N（PVP）在45和870之间变化。当N（PVP）低于200时，随着SIGMA的增加，界面的G（c）只有很小的增加，并且由于PVP短链的拔出而失效。在这种情况下，G（c）与SIGMA呈线性增长，与N（PVP）2大致成比例，与最近提出的链拔出失效模型合理一致。1如果N（PVP）增加到远高于200（大致对应于PVP的缠结之间的平均分子量），则可以区分两种单独的断裂机制。在较低的SIGMA值，G（c）增加缓慢与SIGMA和界面失败的两个嵌段之间的连接附近的共聚物链的断裂。在较高的SIGMA值，界面断裂首先形成一个稳定的银纹的传播裂纹尖端的前面，引起更高的值的测量断裂韧性。在这一制度，G（c）缩放与SIGMA（eff）2，面积密度的链至少有一个“有效”的纠缠，在非常好的协议与布朗2最近提出的模型失败的银纹原纤维断裂。
The fracture toughness (characterized by the critical energy release rate G(c)) of interfaces between polystyrene (PS) and poly(2-vinylpyridine) (PVP) reinforced with poly(styrene-b-2-vinylpyridine) was measured with a double cantilever beam test geometry. The effect of the PVP block degree of polymerization (N(PVP)) and the areal density of block copolymer chains at the interface (SIGMA) on the measured G(c) and on the fracture mechanisms was investigated quantitatively. The PS degree of polymerization (N(PS)) was kept >280, while N(PVP) was varied between 45 and 870. For N(PVP) below 200 the interfaces showed only a small increase in G(c) with increasing SIGMA and failed by pull-out of the short PVP chain. In this regime G(c) increases linearly with SIGMA and scales roughly with N(PVP)2, in reasonable agreement with a recently proposed model of failure by chain pull-out. 1 If N(PVP) was increased well above 200, corresponding roughly to the average molecular weight between entanglements for the PVP, two separate fracture mechanisms could be distinguished. At low values of SIGMA, G(c) increased only slowly with SIGMA and the interfaces failed by scission of the copolymer chains near the joint between the two blocks. At higher values of SIGMA, the interfaces fractured by first forming a stable craze ahead of the propagating crack tip, giving rise to much higher values of the measured fracture toughness. In this regime, G(c) scaled with SIGMA(eff)2, an areal density of chains with at least one "effective" entanglement, in very good agreement with a model recently proposed by Brown 2 for failure by craze fibril breakdown.