Brittle-ductile transition of double network hydrogels: Mechanical balance of two networks as the key factor

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• 作者：Saika Ahmed ; Tasuku Nakajima ; Takayuki Kurokawa ; Md. Anamul Haque ; Jian Ping Gong
• 关键词：Double network hydrogels ; Brittle-ductile transition ; Fracture
• 刊名：Polymer
• 出版年：12 February, 2014
• 年：2014
• 卷：55
• 期：3
• 页码：914-923
• 全文大小：1771 K

文摘

Tough double network (DN) hydrogels are a kind of interpenetrating network (IPN) gels with a contrasting structure; they consist of a rigid and brittle 1st network with dilute, densely cross-linked short chains and a soft and ductile 2nd network with concentrated, loosely cross-linked long chains. In this work, we focus on how the brittle gel changes into a tough one by increasing the amount of ductile component. By comparing the molecular structures of the individual first network and second network gels, we found that the true key mechanical factor that governs the brittle-ductile transition is the fracture stress ratio of the two networks, 蟽_f,2/蟽_f,1. This ratio is related to the density ratio of elastically effective polymer strands of the two networks, 谓_e,2/谓_e,1, where the inter-network topological entanglement makes dominant contribution to 谓_e,2. When 谓_e,2/谓_e,1聽<聽k聽=聽3.8鈭?.5, the second network fractures right after the fracture of the first network, and the gels are brittle. When 谓_e,2/谓_e,1聽>聽k, only the first network fractures. As a result, the brittle first network serves as sacrificial bonds, imparting toughness of DN gels. The study also confirms that the load transfer between the two networks is via inter-network topological entanglement. This result provides essential information to design tough materials based on the double network concept.