【作者】 张永清；

【导师】 孙桃林；

【作者基本信息】 华南理工大学 ， 材料科学与工程， 2021， 硕士

【摘要】 热刺激响应性水凝胶材料是一类对外界施加的热场能够做出相应结构或性能改变的智能材料。传统的热刺激响应性水凝胶,由于网络结构的不均匀性以及缺乏在高应力水平下能够耗散能量的结构,为此大多应用在药物释放、组织工程、智能变色窗户等对力学性能要求比较低的领域。近些年来,随着热刺激响应性水凝胶在驱动器、形状记忆元件、防护器件等工程领域的应用需求,不仅要求材料本身具有高的模量和韧性,而且要求凝胶在热刺激前后有显著的力学性能变化。通过热刺激敏感基团以及水凝胶结构设计,制备具有热致变硬功能的水凝胶材料是软物质材料领域的研究热点。在新型热致变硬水凝胶材料的制备仍存在以下亟需解决的问题:(i)制备高模量、高韧性热致变硬水凝胶材料的工艺简单。水凝胶本身力学性能的提高有利于拓展新型热致变硬水凝胶材料在工程领域的应用。通过在高分子侧链上接枝具有热刺激敏感的大分子等方法可以制备具有高韧性的热致变硬水凝胶材料,但是其制备工艺复杂不适合大批量生产,且凝胶的模量比较低。(ii)在盐溶液环境中的结构和性能稳定性。利用疏水缔合和离子交联协同作用可以实现水凝胶的热致变硬效应,然而这种靠离子交联特性的水凝胶在具有盐溶液环境中使得水凝胶的性能大幅度的降低,从而会丧失水凝胶的热致变硬效果。本论文围绕上述问题展开研究工作,提出利用疏水缔合和氢键协同作用来实现水凝胶的热致变硬效应,主要内容包括以下两个部分:(i)利用带有温敏性和能形成氢键结构官能团的氨基酸衍生物单体与丙烯酰胺单体来设计一种在盐溶液环境中具有高模量、高韧性的热致变硬功能的水凝胶材料。该水凝胶具有优异的力学性能,如断裂应变可以达到～2050%,断裂应力达到～2.5MPa,拉伸功可达到22.3 MJ/m~3,可以与现有报道的最强水凝胶(DN水凝胶)、天然橡胶和软骨的力学性能相媲美。(ii)该水凝胶材料在具有超高杨氏模量(～22MPa)的情况下,经过热处理后其拉伸强度、断裂功和模量仍可分别提高至初始的4倍、2倍和13倍左右。该性能有望在对模量要求比较高的,且加热前后力学性能变化比较大的工程器件领域上发挥作用。(iii)分子结构对照和表征手段表明,水凝胶的热致变硬机制来源于在加热的过程中,疏水相互作用力稳定了高分子链之间的氢键从而诱导高分子网络聚集产生相分离结构,实现水凝胶材料的力学性能增强。更多还原

【Abstract】 Thermoresponsive hydrogel is a kind of intelligent material that can change their structural and physical properties with variations in ambient temperature.The traditionally thermoresponsive hydrogels show the weak mechanical behavior due to their structure inhomogenity or lack of the energy dissipation mechanism under the deformation,and thus they are applied in the field of drug delivery,tissue engineering,and switchable window and so on.Recently,with the great demand in the engineering area,such as actuator,shape memory materials and protective device,they require not only their high mechanical strength but also the high mechanical difference before and after stimulation.Therefore,a strategy to design thermally stiffened hydrogels by using different polymer structures,and thermoresponsive groups attracts much attention and exhibits the research highlights recently.To expend the application of hydrogels,following challenges need to be addressed:(i)A simple way to fabricate thermally stiffened hydrogels with high strength and stiffness.Tough and strong the thermally stiffened hydrogels with high toughness and strength have a great potential in the engineering area.The reported thermally stiffened hydrogels are prepared based on the polymer brush method,where the thermoresponsive group are attached to the main polymer chains.While,such synthesis method is very complicated and not suitable for the large-scale-production.Furtherly,the obtained thermally stiffened hydrogels often show the low elastic modulus.(ii)The unstable structure and mechanical behavior in saline solutions.The other reported thermally stiffened hydrogels are developed based on the cooperative effects of hydrophobic interaction and ionic interaction,and these hydrogels become mechanically weak and lost the thermally stiffened features when they are immersed in saline solutions.To solve the issues mentioned above,we did the following investigations:(i)A novel thermally stiffened hydrogel was designed by the randomly copolymerization of the thermoresponseive monomer from the amino acid derivatives and acrylamide.These hydrogels not only show the high toughness(～22.3 MJ/m~3),strength(～2.5MPa),and extremely high stretchability(～2050%),but also mechanically stable in saline solutions.The high toughness of the hydrogels is comparable with the tough double-network hydrogels,nature rubbers and cartilages.(ii)The hydrogels exhibit the super high mechanical transition behavior in strength,toughness and stiffness by up to 4-,2-,and 13-folds,respectively,when the thermal treatment was applied or not,even the hydrogels show the high stiffness(～22MPa).This work provides a pathway for developing thermally stiffened materials and may be applied in the engineering field which requires the hydrogels with high stiffness and high mechanical difference before and after thermal treatment.(iii)The results show that the thermally stiffened effect is from the cooperative effects of hydrophobic interaction and hydrogen bonding interaction,which induced the structural phase separation during the thermal treatment,and thus enhance their mechanical behavior.更多还原