4D打印形状记忆高分子的打印方法、驱动原理、变形模式和应用

Printing Method,Driving Mechanism,Deformation Mode and Application of 4D Printing Shape Memory Polymers

形状记忆高分子(Shape memory polymer,SMP)是指能够感知外界环境变化的刺激并响应这种变化,对其状态参数进行调整,从而回复到预先设定状态的一类高分子材料。相对于形状记忆合金和形状记忆陶瓷,SMP具有可回复形变量大、响应温度便于调节、刺激响应方式丰富、材料属性多样化、形状记忆效应种类多等优点,在医疗器械、柔性电子、纺织品、信息载体、航空航天以及软体机器人等领域展示了巨大的应用潜力。但SMP的原始形状或回复后的永久形状都较为单一,而且成型过程高度依赖模具并受脱模工艺的巨大限制,其形状难以制作得非常复杂,难以进一步满足新兴高科技领域对智能结构复杂性的需求。针对上述难题,国内外学者在该领域已进行了一些创新性的研究,当前的研究热点主要集中在以下两个方面:(1)在热固性高分子材料中引入动态共价键,通过交联网络结构重排实现固态塑性,进而对形状记忆材料的几何结构进行复杂化,这类形状记忆高分子材料也称为热适性形状记忆高分子;(2)利用3D打印(Three-dimensional printing)技术打印智能材料,实现材料几何结构的复杂化,并产生了一类新的打印技术,称为4D打印(Four-dimensional printing)。其中,SMP材料是当前4D打印使用最多的智能材料。近年来,研究者以SMP材料为研究对象,结合最新的4D打印技术,采用熔融沉积成型、立体光刻成型、墨水直写和聚合物喷射技术制备了3D形状复杂的具有各种刺激响应方式和形状记忆效应的形状记忆材料。基于驱动原理不同,热、光、电、磁和水刺激响应形状记忆4D打印结构已经被成功设计和制备,丰富了具有复杂几何形状记忆材料的刺激响应类型;在变形模式上,实现了具有双形形状记忆效应、双向形状记忆效应、多重形状记忆效应和顺序梯度响应的4D打印形状记忆材料的设计、制备和应用。本文综述了4D打印SMP的打印方法、驱动原理、变形模式和应用,最后概述了4D打印SMP材料存在的问题及展望了其未来的发展方向。

Shape memory polymer(SMP)refers to a class of stimuli-responsive polymer materials that can sense the change of the external environment and respond to this change,and adjust its state parameters to return to the preprogrammed state.Compared with shape memory alloys and shape memory ceramics,SMPs have been demonstrated great potential application in the fields of medical devices,flexible electronics,textiles,information carriers,aerospace and soft robotics etc.,due to large recoverable strain,tunable response temperature,diverse stimulus methods,multiple material attribute,and versatile shape memory effects.However,the original shape of the SMPs or the permanent shape after the recovery is relatively simple,and the molding process is highly dependent on the mold and is greatly limited by the demolding process.Thus,its shape is difficult to be complicated,which is difficult to further meet the demand for the complexity of intelligent structures in emerging high-tech fields.Aiming at above problems,domestic and foreign researchers have carried out some innovative research in this field.The current research hotspots mainly focus on the following two aspects:(1)The dynamic covalent bonds are embedded into thermosetting polymers and then solid-state plasticity is fulfilled by the rearrangement of the cross-linked network,leading to geometrically complex permanent shapes.This type of the shape memory polymer is also called thermadapt SMP;(2)The complexity of material geometry can be achieved by 3D printing(Three-dimensional printing)technology to print intelligent materials,and the new type of printing technology is termed as Four-dimensional(4D)printing.At present,the most widely used smart materials is the SMP for 4D printing.In recent years,combined with the latest 4D printing technology,the geometrically complex shape memory materials with diverse stimulus responses and shape memory effects are prepared by researchers using the SMP as research objects and using fused deposition modeling,stereolithography,direct ink writing and PolyJet as the 3D printing methods.Based on different driving mechanisms,thermal-responsive,photo-responsive,electrical-responsive,magnetic-responsive,and water-responsive 4D printing SMPs have been successfully designed and prepared,enriching the types of stimulus response with complex geometric shape memory materials;in terms of the deformation mode,the design,preparation and application of 4D printed shape memory materials with double-shape shape memory effect,two-way shape memory effect,multiple shape memory effect and sequentially gradient 4D printing SMPs are realized.This paper mainly reviews the printing method,driving mechanism,deformation mode and application of 4D printing SMP.Finally,the problems of 4D printing SMP are summarized in current research and the development direction is prospected in the future.