GOALI: Additive Manufacturing of High Performance Elastomers via Vat Photopolymerization of Aqueous Polymer Dispersions

添加制造工艺，通常被称为3D打印，已经显示出作为一种制造具有复杂几何形状的部件的方法的前景，这些部件可以根据个人客户和应用而量身定做。VAT光聚合是一种添加剂制造方法，可提供卓越的特征分辨率、精度和表面光洁度。然而，尽管与其他工艺相比具有这些优势，但VAT光聚合在制造最终用途产品方面的工业应用有限，主要是因为其可加工材料的多样性和质量有限。适用材料的范围狭窄可以归因于工艺强加的限制。例如，在打印下一层之前，树脂必须具有低粘度(易于流动)，以帮助部件重新涂覆。这样可以防止使用高分子量的聚合物，从而限制印刷材料的强度和弹性。为了克服这一限制，GOALI学术联络机会(GOALI)计划研究项目计划使用由悬浮在低粘度介质(如水和溶剂)中的高相对分子质量聚合物‘颗粒’组成的树脂。成功了解此类树脂的最佳组成和印刷适宜性将使先进的制造能力能够实现橡胶和乳胶部件的印刷。这可以通过促进轮胎、垫圈和衬套的印刷，为美国的主要汽车和航空航天行业带来好处。由于这是一个产学合作项目，参与的研究生将了解行业的挑战和驱动因素，从而加强他们对未来劳动力的准备。将为本科生和代表性不足的少数族裔提供更多的教育机会，以进一步扩大对先进制造和材料科学主题的参与。该GALI项目奖的研究目标是(I)了解形成稳定的水性聚合物分散体的要求，(Ii)了解分散体的特性如何影响坯体强度和光固化动力学，(Iii)模拟分散体的LayerWise光固化行为，以及(Iv)绘制可加工材料的设计空间。这项研究将检验基于初步实验的三个假设：(I)力学性能的改善是由于分散的聚合物颗粒在干燥时在支架上形成了高分子量、缠绕的网络，(Ii)在低应变下观察到的强度急剧增加是由于印刷过程中在连续的水相中产生的刚性支架，(Iii)现有的将散射现象与曝光和固化深度相关联的还原聚合模型必须加以调整，以解决分散体动态变化的折射率。这项研究将导致(I)基本了解VAT聚合分散体的结构-性能-过程关系，(Ii)考虑折射率动态变化的聚合物分散体的光固化行为模型，以及(Iii)一系列具有可调机械性能的新型VAT聚合弹性体。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Additive manufacturing processes, often referred to as 3D Printing, have shown promise as a means for fabricating parts featuring complex geometries that can be tailored to an individual customer and application. Vat Photopolymerization is one method of additive manufacturing that offers superior feature resolution, accuracy, and surface finish. However, despite these advantages relative to other processes, Vat Photopolymerization has seen limited industrial adoption for fabricating end-use products primarily due to the limited diversity and quality of its processable materials. The narrow range of suitable materials can be attributed to process-imposed constraints. For example, the resins must have a low viscosity (flow easily) to aid part recoating prior to printing the next layer. This prevents the use of polymers with high molecular weight, which limits the printed material's strength and elasticity. To overcome this limitation, this Grant Opportunity for Academic Liaison with Industry (GOALI) Program research project plans to use resins that consist of high-molecular weight polymer 'particles' suspended in a low viscosity medium, e.g. water and solvent. Successfully understanding the optimal composition and printability of such resins will enable advanced manufacturing capabilities to realize the printing of rubber and latex parts. This can be beneficial to key US based automotive and aerospace industries by facilitating the printing of tires, gaskets, and bushings. As this is an industry-university collaborative project, the graduate students involved will gain an understanding of industrial challenges and drivers, thus increasing their preparedness for the future workforce. Additional educational opportunities will be provided for undergraduate students and underrepresented minorities to further broaden engagement in advanced manufacturing and material science topics. The research objectives of this GOALI program award are to (i) understand requirements for forming stable aqueous polymer dispersions, (ii) understand how characteristics of dispersions influence green body strength and photocuring kinetics, (iii) model the layerwise photocuring behavior of dispersions, and (iv) map the processable material design space. The research will test three hypotheses based on preliminary experiments: (i) improvement in mechanical properties is due to the coalescence of the dispersed polymer particles and formation of a high molecular weight, entangled network throughout the scaffold upon drying, (ii) the observed sharp increase in strength seen at low strains is attributable to the rigid scaffold created in the continuous, aqueous phase during printing, and (iii) existing Vat Polymerization models for relating scattering phenomena with exposure and cure depth must be adapted to account for the dispersions' dynamically changing refractive index. This research will result in (i) fundamental understanding of structure-property-process relationships of Vat Polymerization dispersions, (ii) a model of the photocuring behavior of polymeric dispersions that accounts for dynamically changing refractive index, and (iii) a series of novel Vat Polymerization elastomers with tunable mechanical properties.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.