Multi-Scale 3D Printing Using Vat-free Photopolymerization

3D打印有可能振兴美国的制造业。一种广泛使用的3D打印工艺是立体光刻，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一个聚焦的激光或投射一个光图案在一桶液体光聚合物的表面上打印一系列的层。然而，该工艺的局限性包括其不能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，其中缸被利用表面张力在两个光学透明板之间形成的液体桥所取代。研究结果可以开发低成本，高分辨率的3D打印机，用于在大面积上制造具有微米分辨率的复杂结构。这样的结构的示例是3D流体、传感器、致动器、药物递送装置和组织工程支架。本研究的目的是：（1）了解大小效应（高度和体积）的液体桥和材料性能（表面张力和密度）在两个光学透明板内形成的液体桥的轮廓上的光聚合物;（2）了解界面表面能的影响（在底板和装配式结构之间，在装配式结构内的层之间，以及在顶板和装配式结构之间）对装配式结构的稳定性的影响;（3）建立固化参数（光强度、扫描速度和光图案）与聚合物表面上的累积能量之间的关系。为了实现第一个目标，一个修改后的平衡准静态液桥模型，使用杨拉普拉斯方程将被用来预测液桥的轮廓与不同值的液桥尺寸和聚合物材料的性能。一些预测结果将通过实验得到验证。将通过将聚合物供应到两个板中来形成液体桥，并且通过光学显微镜来测量它们的轮廓。液体桥的高度将通过电动载物台在1至5 mm之间变化，并且其具有4 × 4 cm基底面积的体积将通过注射泵控制。表面张力和密度将通过使用具有表面能降低剂的不同聚合物（例如氟化醇和硅酮聚醚）来控制。对于第二个目标，将使用含有表面能降低剂的不同聚合物制造各种结构。通过Zisman绘图技术和常规剥离试验测量三个界面处的表面能。将通过光学和扫描电子显微镜观察制造的结构的稳定性。为了实现第三个目标，将使用修改的Beer-Lambert固化模型和能量累积方程来预测聚合物表面上的累积能量，其中具有不同的光强度、扫描速度和光图案值。一些预测结果将通过实验得到验证。累积能量将由安装在某个位置的光束轮廓照相机测量，以便它可以测量聚合物表面将获得的累积能量。将使用水平xy载物台、光源（汞灯）和数字化扫描设备来控制扫描速度、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.