Unraveling the Formation of Two-Photon Polymerized Materials at the Nanoscale

该项目支持一种新兴的微结构制造方法的基础研究，称为双光子聚合（TPP）。在TPP中，聚焦激光束可以写入任何配置的三维聚合物结构，从而能够以比人类头发厚度小许多倍的长度制造复杂的物体和设备。TPP的发展受到无法改善可重复性、结构完整性、机械性能和进一步缩小写入结构的阻碍。这些限制是化学性质的，但在如此小的长度尺度上破译化学成分仍然是一个重大挑战。在这个项目中，这一障碍是克服了使用一种新的方法，能够生成详细的化学地图的TTP微观结构。使用基于光的分析方法称为尖端增强拉曼散射，近距离观察TTP微结构中不断变化的化学变化，获得纳米精度。通过揭开迄今为止隐藏的纳米级化学和结构变化，TTP程序可以得到很大的改进，使TTP技术的大规模实施成为可能。因此，该项目加速了TPP从学术实验室向大规模工业应用的转变。该项目还为一名专家和两名本科生提供培训，他们有机会获得高端仪器仪表方面的抢手技能。此外，该项目还包括面向社区中学生的推广活动，让学生有机会制作他们选择的微米尺寸的3D物体。双光子聚合（TPP）是一种流行的微结构制造技术，然而，TPP的工业应用受到书面结构之间的一致性差的阻碍，这种增材制造技术的规模实施。转化程度、溶剂渗透、体素重叠和材料不均匀性的变化还没有得到很好的理解，从而导致整体重复性较低。这些问题的根源是对纳米级聚合过程的认识不足。该项目解决了几个长期存在的问题，关于TPP的光物理和光化学，限制了更广泛的实施技术。该项目的重点是关于光引发聚合以及由此产生的纳米级形态和化学的时间序列过程中悬而未决的问题。通过超快光谱实验研究了光引发剂的激发动力学、自由基形成和树脂相互作用，并通过针尖增强拉曼散射研究了纳米尺度下的交联度、材料不均匀性和溶剂渗透。在这项工作中获得的见解，使关键TPP参数的优化，产生新的光引发剂开发的指导方针，控制聚合度的方向，新的激光照明策略，提高分辨率和管理的热解过程在纳米级。因此，该项目的成果加速了TPP从学术实验室向大规模工业应用的转化。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project supports fundamental research on an emerging method for the fabrication of microstructures, called two-photon polymerization (TPP). In TPP, a focused laser beam writes three-dimensional polymer structures of any configuration, enabling the fabrication of intricate objects and devices at a length scale many times smaller than the thickness of a human hair. Developments in TPP have been hampered by the inability to improve the repeatability, structural integrity, mechanical properties and further downsizing of the written structures. These limitations are chemical in nature, but deciphering the chemical composition at such small length scales has remained a significant challenge. In this project, this hurdle is overcome by using a new approach capable of generating detailed chemical maps of TTP microstructures. Using a light-based analytical method called tip-enhanced Raman scattering, a close-up view of evolving chemical changes in TTP microstructures is obtained with nanometer precision. By unraveling the hitherto hidden chemical and structural changes at the nanoscale, TTP procedures can be much improved, making a large-scale implementation of TTP technologies possible. This project thus accelerates the translation of TPP from academic labs towards large-scale industrial applications. The project also provides training to a specialist and two undergraduate students who have the opportunity to acquire sought-after skills in high-end instrumentation. In addition, this project includes an outreach effort to middle school students in the community, in which students have the chance to produce micrometer-sized versions of 3D objects of their choosing.Two-photon polymerization (TPP) is a popular technology for the fabrication of micro-structures, yet the industrial use of TPP has been hindered by poor consistency between written structures limiting a large-scale implementation of this additive manufacturing technique. Variations in the degree of conversion, solvent permeation, voxel overlap, and material inhomogeneities are not well understood, giving rise to a low overall repeatability. The root of these problems is insufficient knowledge of the polymerization process at the nanoscale. This project addresses several longstanding questions regarding the photo- physics and photo-chemistry of TPP that have limited a broader implementation of the technique. The project focuses on outstanding questions about the time-sequenced process of photo- initiation followed by polymerization as well as the resulting nanoscale morphology and chemistry. The excitation dynamics, radical formation and resin interactions of photoinitiators are studied by ultrafast spectroscopy experiments, and the degree of cross-linking, material inhomogeneities and solvent permeation at the nanoscale are studied by tip-enhanced Raman scattering. The insights acquired in this work enable an optimization of key TPP parameters, producing new guidelines for photoinitiator development, directions for controlling the degree of polymerization, new laser illumination strategies of improving resolution and management of the pyrolysis process at the nanoscale. Consequently, the deliverables in this project accelerate the translation of TPP from academic labs towards large-scale industrial applications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.