Multi-Scale 3D Printing Using Vat-free Photopolymerization

3D打印具有振兴美国制造业的潜力。立体光刻是一种广泛使用的3D打印工艺，因为它能够以相对较高的分辨率打印复杂的物体。这个过程的工作原理是扫描聚焦的激光或在液体光聚合物的表面上投射一个光模式来打印一系列的层。然而，该工艺的局限性包括无法打印具有微米特征的大型结构。该奖项支持一种新的立体光刻工艺的基础研究，在这种工艺中，利用表面张力在两个光学透明板之间形成的液体桥取代了缸。研究成果可以开发出低成本、高分辨率的3D打印机，用于在大面积上制造微米分辨率的复杂结构。这种结构的例子是3D流体、传感器、致动器、药物输送装置和组织工程支架。本研究的目的是：(1)了解液桥的大小（高度和体积）和光聚合物的材料性质（表面张力和密度）对在两个光学透明板内形成的液桥轮廓的影响；(2)了解界面处（底板与装配式结构之间、装配式结构内部各层之间、顶板与装配式结构之间）表面能对装配式结构稳定性的影响；(3)建立固化参数（光强、扫描速度和光模式）与聚合物表面积累能量之间的关系。为了实现第一个目标，将使用一个修正的平衡准静态液桥模型，使用Young-Laplace方程来预测不同液桥尺寸和聚合物材料性质值下液桥的分布。部分预测结果将通过实验验证。液体桥将通过将聚合物放入两个板中形成，它们的轮廓将通过光学显微镜测量。液体桥架的高度将由一个机动平台在1到5毫米之间变化，其基座面积为4 × 4厘米的体积将由一个注射泵控制。表面张力和密度将通过使用带有表面能还原剂（如氟化醇和硅聚醚）的不同聚合物来控制。对于第二个目标，将使用含有表面能还原剂的不同聚合物来制造各种结构。三个界面的表面能将通过Zisman绘图技术和传统的剥离试验来测量。制备结构的稳定性将通过光学和扫描电子显微镜观察。为了实现第三个目标，将使用改进的Beer-Lambert固化模型和能量积累方程来预测不同光强、扫描速度和光模式值下聚合物表面的累积能量。部分预测结果将通过实验验证。累积能量将通过安装在特定位置的光束剖面相机来测量，这样它就可以测量聚合物表面所获得的累积能量。水平x级，光源（汞灯）和数字微镜装置将用于控制扫描速度，光强和光模式。

3D printing has the potential to revitalize the manufacturing sector in the US. A widely used 3D printing process is stereolithography because of its ability to print complex objects with relatively high resolutions. This process works by scanning a focused laser or projecting a light pattern on the surface of a vat of liquid photopolymer to print series of layers. However, limitations of this process include its inability to print large structures with micron features. This award supports fundamental research on a new stereolithography process where the vat is replaced by a liquid bridge formed between two optically clear plates using surface tension. Research results can enable the development of low-cost, high-resolution 3D printers for manufacturing complex structures with micron resolutions on a large area. Examples of such structures are 3D fluidics, sensors, actuators, drug delivery devices, and tissue engineering scaffolds. The objectives of this research are: (1) to understand effects of the size (height and volume) of the liquid bridge and material properties (surface tension and density) of the photopolymer on the profile of the liquid bridge formed within two optically clear plates; (2) to understand effects of surface energy at interfaces (between bottom plate and fabricated structure, between layers within the fabricated structure, and between top plate and fabricated structure) on the stability of the fabricated structure; (3) to establish relationships between curing parameters (light intensity, scanning speeds, and light patterns) and accumulated energy over the polymer surface. To achieve the first objective, a modified equilibrium quasi-static liquid bridge model using Young-Laplace equations will be used to predict the profile of the liquid bridge with different values of liquid bridge size and polymer material properties. Some predicted results will be verified by experiments. Liquid bridges will be formed by supplying the polymer into two plates and their profiles will be measured by optical microscopy. The height of the liquid bridge will be varied from 1 to 5 mm by a motorized stage and its volume with a base area of 4 by 4 cm will be controlled by a syringe pump. Surface tension and density will be controlled by using different polymers with surface energy reducing agents (such as fluorinated alcohols and silicone polyether). For the second objective, various structures will be fabricated using different polymers containing surface energy reducing agents. Surface energy at three interfaces will be measured by a Zisman plotting technique and the conventional peel test. Stability of fabricated structures will be observed by optical and scanning electron microscopy. To achieve the third objective, a modified Beer-Lambert cure model and the energy accumulation equation will be used to predict accumulated energy on the polymer surface with different values of light intensity, scanning speed, and light pattern. Some predicted results will be verified by experiments. Accumulated energy will be measured by a beam profiling camera installed at a location so that it can measure the accumulated energy the polymer surface would get. A horizontal xy-stage, light source (mercury lamp), and digital micromirror device will be used to control scanning speed, light intensity, and light pattern.