Chemically Controlled Bending of Compositionally Anisotropic Microcylinders
Chemically Controlled Bending of Compositionally Anisotropic Microcylinders
复制标题
DOI：
10.1002/anie.201105387
复制
发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Lahann, Joerg
中科院分区：
文献类型：
--
作者：
Saha, Sampa;Copic, Davor;Lahann, Joerg
可以响应外部刺激（如温度、光、pH值或离子强度的变化）而进行机械致动的软材料[1-7]，由于其作为薄膜致动器[8-10]、智能缝线[11，12]和软机器人的潜在用途而受到越来越多的关注。[13这些材料通常需要特殊聚合物，例如形状记忆聚合物[15]或使用宏观分层膜。[16在层状膜中，两种聚合物或聚合物和金属的各向异性分布是必要的。这会造成机械性能的不匹配，从而导致定义的弯曲。原则上，这个概念并不局限于宏观多层膜，而是可以用胶体材料来实现，只要能够实现所需的各向异性，并且胶体物体的不同部分将对外部刺激做出不同的响应。近年来，使用一系列不同的合成方法，包括微流体和平版印刷技术，[18]在低表面能模板中的颗粒复制，[19]三元共聚物中聚丁二烯链段的选择性交联，[20]微球的平版印刷图案化，[21]电化学[22]和光化学[23]还原，[24]纳米颗粒和纳米颗粒的组成各向异性已经被设计出来。多孔膜[24，25]和纳米管的模板化，[26]表面活性剂辅助生长，[27]接枝聚合，[28-30]和基于受控表面成核的工艺。[31]或者，电流体动力学共喷射是一种通过将流体转移通过一组可以处理不同材料的毛细管来制备具有多个隔室的颗粒和纤维的方法。[32]在过去，电流体动力学共喷射已经产生具有多个隔室的颗粒，所述多个隔室含有不同的聚合物共混物、染料、低分子量添加剂、反应性分子和甚至无机纳米颗粒。[33如果将反应性添加剂（例如官能化聚合物）添加到其中一个隔室中，则选择性表面改性是可能的，并且可以导致蛋白质或肽的空间受控固定。[35-37]由于不同的隔室可以装载不同的材料，因此可以从独特的协同效应中产生全新的功能集，[36]而不仅仅是增加单个隔室的属性。在这里，我们报告了一种新型的成分各向异性的微柱，在同一微柱内的定义的隔间进行差异膨胀由于表面层的选址性生长。不对称膨胀产生表面应力，导致微柱体的显著且可控的弯曲，这取决于颗粒几何形状和表面层的结构。使用有限元模拟，我们验证所观察到的弯曲趋势，并推导出一个家庭的性能曲线，预测一个大范围的可调性的致动冲程的基础上的气缸的几何形状和膨胀量。
Soft materials that can undergo mechanical actuation in response to external stimuli,[1–7] such as changes in temperature, light, pHvalue, or ionic strength, have attracted increasing attention because of their potential use as thinfilm actuators,[8–10] smart sutures,[11, 12] and soft robots.[13, 14] These materials typically require specialty polymers, such as shape-memory polymers [15] or use macroscopically layered films.[16, 17] In layered films, the anisotropic distribution of two polymers, or a polymer and a metal, is essential. This creates a mismatch in mechanical properties that gives rise to a defined bending. In principle, this concept is not limited to macroscopic multilayer films, but can be achieved with colloidal materials, as long as the required anisotropy can be realized and different parts of the colloidal object will respond differently to the external stimulus. In recent years, compositionally anisotropic micro-and nanoparticles have been devised using a range of different synthesis methods including microfluidic and lithographic techniques,[18] particle replication in low surface energy templates,[19] selective crosslinking of polybutadiene segments in terpolymers,[20] lithographic patterning of microspheres,[21] electrochemical [22] and photochemical [23] reduction, templating of porous membranes [24, 25] and nanotubes,[26] surfactant aided growth,[27] graft polymerization,[28–30] and processes based on controlled surface nucleation.[31] Alternatively, electrohydrodynamic co-jetting is a method to prepare particles and fibers with multiple compartments by transferring fluids through a set of capillaries that can process dissimilar materials.[32] In the past, electrohydrodynamic co-jetting has resulted in particles with multiple compartments that contain different polymer blends, dyes, low-molecular weight additives, reactive molecules and even inorganic nanoparticles.[33, 34] If a reactive additive, such as a functionalized polymer, is added to one of the compartments, selective surface modification is possible and can result in spatially controlled immobilization of proteins or peptides.[35–37]Because different compartments can be loaded with dissimilar materials, entirely new sets of functions can arise from unique synergistic effects,[36] not just from the addition of the properties of the individual compartments. Herein, we report a new type of compositionally anisotropic microcylinders, where defined compartments within the same microcylinder undergo differential expansion due to the site-selective growth of a surface layer. The asymmetric expansion creates surface stresses resulting in significant and controllable bending of the microcylinders, which depends on the particle geometry and the architecture of the surface layers. Using finite element simulations, we verify the observed bending trends and derive a family of performance curves that predict a wide-range tunability of the actuation stroke based on the cylinder geometry and the amount of swelling.