【作者】 宋玲玲；

【导师】 秦海利； 朱春华；

【作者基本信息】 合肥工业大学 ， 化学工程（专业学位）， 2024， 硕士

【摘要】 4D打印在3D打印基础上引入第四维度时间,允许3D打印创建的静态物体在暴露于特定的外部刺激（例如光、电、磁等）时随着时间的推移有意识地改变其形状、特性或功能。其中直接墨水书写（DIW）技术因具有操作简单、低成本等优点,成为目前4D打印领域的研究热门。水凝胶作为DIW挤出技术的重要墨水之一,受墨水挤出扩散的限制,无法打印形貌稳定的纤维。传统方法通过在喷嘴处光固化或在支撑浴中打印,虽然在一定程度上抑制了细丝的扩散问题,但光固化法不仅需要打印前驱体具有高化学活性,而且易堵塞针头,支撑浴打印出现支撑材料难移除的问题。因此,本文从分子自身性质和组装结构出发,开发了一种由小分子自组装的新型水凝胶墨水,借助该墨水独特的温度响应自身粘度变化来抑制DIW墨水挤出扩散,为DIW打印油墨的制备提供了一种新策略。基于小分子组装的液晶双分子膜结构,打印图案在不同外界刺激作用下显现出优异的颜色变化,在传感、信息加密等领域具有重要研究前景。（1）通过有机合成制备双亲性小分子十六烷基马来酸甘油酯（HGM）,在Krafft点（37 ^oC）以上,借助表面活性剂十二烷基硫酸钠（SDS）在水溶液中自组装成具有周期性双分子层液晶相结构,通过控制溶液中HGM的浓度可实现颜色在可见光范围内进行调控,其中水层间距在139-263 nm范围可控可调。利用HGM分子组装体系在低于Krafft点下发生相转变得到稳定的凝胶相（L_α相）,实现溶液体系温度响应的粘度自调节。体系的小分子氢键网络结构赋予材料理想的流变性能,如剪切变稀、剪切屈服、粘弹性模量恢复行为。基于上述行为,发展低温DIW打印技术,即利用温度自调节粘度行为,构建低温打印平台打印来抑制纤维扩散,通过调节各打印参数实现精细的复杂结构打印。（2）HGM液晶体系主要由HGM组装的双分子膜与水层构成。鉴于HGM分子独特的温度响应下带来的层间距变化,可实现基于HGM液晶双分子膜体系的3D打印结构在外界刺激下（如温度、光、磁）发生独特的颜色变化,即4D打印智能响应材料。如利用HGM墨水特有的周期性光子晶体结构以及相转变带来的周期结构变化来实现4D变色打印,可实现打印图案在室温25 ^oC与40 ^oC间的可逆响应变化。为实现多响应变色4D打印,向双分子膜间的水层引入外加刺激响应性材料是一个可行策略。为保证外加材料下液晶双分子膜体系的稳定性,我们选择了弱电荷作用的光热材料多壁碳纳米管（MWCNTs）和磁热材料Fe₃O₄@PDA。通过系统探讨多功能纳米结构在不同浓度下的产热行为与变色时间的影响关系,实现了4D打印智能响应材料在交变磁场和近红外光下优异的变色行为。更多还原

【Abstract】 4D printing introduces the fourth dimension of time into the basis of 3D printing,allowing static objects created by 3D printing to consciously change their shape,properties,or functions over time when exposed to specific external stimuli such as light,electricity,or magnetism.Among various technologies,direct ink writing（DIW）has become a research hotspot in the field of 4D printing due to its simplicity and low cost.Hydrogels,as an important ink type in DIW extrusion techniques,are limited by the diffusion of the extruded ink,preventing the stable formation of fibers.Traditional methods attempt to mitigate the filament diffusion problem by photocuring at the nozzle or printing in a support bath.However,photocuring not only requires the precursor to have high chemical reactivity but also tends to clog the needle,while support bath printing encounters difficulties in removing the support material.Therefore,this paper develops a novel hydrogel ink from small molecule self-assembly,leveraging the unique temperature-responsive viscosity change of the ink to inhibit DIW ink extrusion diffusion,providing a new strategy for DIW ink preparation.Based on the liquid crystal bilayer membrane structure assembled from small molecules,the printed patterns exhibit excellent color changes under different external stimuli,showing significant research prospects in sensing and information encryption.（1）Amphiphilic small molecule hexadecyl maleate glycerol ester（HGM）was synthesized through organic synthesis.Above the Krafft point（37°C）,HGM self-assembles in aqueous solution into a periodic bilayer liquid crystal phase structure with the aid of surfactant sodium dodecyl sulfate（SDS）.By controlling the concentration of HGM in the solution,the color can be regulated within the visible light range,with the water layer spacing adjustable between 139-263 nm.The HGM molecular assembly system undergoes a phase transition below the Krafft point,resulting in a stable gel phase（L_αphase）,achieving temperature-responsive viscosity self-regulation of the solution system.The small molecule hydrogen bond network structure of the system endows the material with ideal rheological properties,such as shear thinning,shear yielding,and viscoelastic modulus recovery behavior.Based on these behaviors,low-temperature DIW printing technology was developed,utilizing the temperature self-regulating viscosity behavior to construct a low-temperature printing platform that inhibits fiber diffusion,achieving precise and complex structure printing by adjusting various printing parameters.（2）The HGM liquid crystal system is mainly composed of bilayer membranes assembled by HGM and water layers.Given the unique interlayer spacing changes brought about by the temperature response of HGM molecules,the 3D printed structures based on the HGM liquid crystal bilayer membrane system can exhibit unique color changes under external stimuli（such as temperature,light,magnetism）,that is,4D printing of smart responsive materials.For instance,4D color-changing printing can be achieved using the unique periodic photonic crystal structure of HGM ink and the periodic structure changes brought about by phase transitions,enabling reversible response changes in printed patterns between room temperature（25°C）and 40°C.To achieve multi-responsive color-changing 4D printing,introducing externally stimuli-responsive materials into the water layers between bilayer membranes is a feasible strategy.To ensure the stability of the liquid crystal bilayer membrane system under the addition of external materials,we selected photothermal material multi-walled carbon nanotubes（MWCNTs）and magnetothermal material Fe₃O₄@PDA with weak charge interactions.Through systematic exploration of the relationship between the heat generation behavior of multifunctional nanostructures at different concentrations and the color change time,we achieved excellent color-changing behavior of 4D printed smart responsive materials under alternating magnetic fields and near-infrared light.更多还原