Multi-Scale 3D Printing Using Vat-free Photopolymerization

3D打印具有重振美国制造业的潜力。一种广泛使用的3D打印工艺是立体平版印刷，因为它能够以相对较高的分辨率打印复杂的对象。这一过程的工作原理是扫描聚焦的激光或将光图案投射到一大桶液体光聚合物的表面，以打印一系列层。然而，该工艺的局限性包括它不能打印具有微米特征的大结构。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，使用表面张力在两个光学透明平板之间形成的液体桥取代了桶。研究成果可以开发低成本、高分辨率的3D打印机，用于大面积制造微米级的复杂结构。这种结构的例子有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)了解液桥的尺寸(高度和体积)和光聚合物的材料特性(表面张力和密度)对在两个光学透明平板内形成的液桥的轮廓的影响；(2)了解界面(底板和装配式结构之间、装配式结构内的层之间和顶板和装配式结构之间)的表面能对装配式结构稳定性的影响；(3)建立固化参数(光强、扫描速度和光图案)与聚合物表面累积能量之间的关系。为了实现第一个目标，我们将使用基于Young-Laplace方程的修正的平衡准静态液桥模型来预测不同液桥尺寸和聚合物材料性质的液桥的轮廓。部分预测结果将通过实验进行验证。通过将聚合物提供到两个板中，将形成液桥，并将通过光学显微镜测量它们的轮廓。液桥的高度由电动工作台控制在1~5 mm之间，体积由注射泵控制，底面面积为4×4 cm。表面张力和密度将通过使用不同的聚合物和表面能降低剂(如氟化醇和硅聚醚)来控制。对于第二个目标，将使用包含表面能量减少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作图技术和常规剥离试验来测量。制作的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、扫描速度和光图案下聚合物表面的累积能量。部分预测结果将通过实验进行验证。累积的能量将由安装在某个位置的光束轮廓相机来测量，这样它就可以测量聚合物表面将获得的累积能量。将使用水平XY工作台、光源(水银灯)和数字微镜装置来控制扫描速度、光强度和光图案。

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.