Vat photopolymerization of poly(styrene-b-isoprene-b-styrene) triblock copolymers
Not Available
Bean, Ren H.↗
Engineering topics
Williams, Christopher B.
Publications and source records attributed to Williams, Christopher B..
Temporally Stable Supramolecular Polymeric Salts Enabling High-Performance 3D All-Aromatic Polyimide Lattices
Vat photopolymerization (VP) Additive Manufacturing (AM), in which UV light is selectively applied to cure photo-active polymers into complex geometries with micron-scale resolution, has a limited selection of aliphatic thermoset materials that exhibit relatively poor thermal performance. Ring-opening dianhydrides with acrylate-containing nucleophiles yielded diacrylate ester-dicarboxylic acids that enabled photo-active polyimide (PI) precursors, termed polysalts, upon neutralization with an aromatic diamine in solution. In situ FTIR spectroscopy coupled with a solution and photo-rheological measurements revealed a previously unknown time-dependent instability of 4,4'-oxydianiline (ODA) polysalts due to an aza-Michael addition. Replacement of the electron-donating ether-containing diamine with an electron withdrawing sulfone-containing monomer, e.g., 4,4'-diaminodiphenyl sulfone (DDS), prohibited the aza-Michael addition of the aromatic amine to the activated acrylate double bond. Novel DDS polysalt photocurable solutions are similarly analyzed and validated long-term stability, which enabled reproducible printing of polyimide organogel intermediates. Subsequent VP AM afforded 3-dimensional (3D) structures of intricate complexity and excellent surface finish, as demonstrated with scanning electron microscopy. In addition, the novel PMDA-HEA/DDS solution enabled the production of the first beam latticed architecture comprised of all-aromatic polyimide. Finally, the versatility of a polysalt platform for multi-material printing is further demonstrated by printing parts with alternating polysalt compositions.
36 MATERIALS SCIENCE↗
Rheology guiding the design and printability of aqueous colloidal composites for additive manufacturing
Vat photopolymerization (VP) and direct ink write (DIW) additive manufacturing (AM) provide complex geometries with precise spatial control employing a vast array of photo-reactive polymeric systems. Although VP is recognized for superior resolution and surface finish, DIW provides versatility for higher viscosity systems. However, each AM platform presents specific rheological requirements that are essential for successful 3D printing. First, viscosity requirements constrain VP polymeric materials to viscosities below 10 Pa s. Thus, this requirement presents a challenging paradox that must be overcome to attain the physical performance of high molecular weight polymers while maintaining suitable viscosities for VP polymeric materials. Second, the necessary rheological complexity that is required for DIW pastes requires additional rheological measurements to ensure desirable thixotropic behavior. Further, this manuscript describes the importance of rheological measurements when designing polymeric latexes for AM. Latexes effectively decouple the dependency of viscosity on molecular weight, thus enabling high molecular weight polymers with low viscosities. Photo-crosslinking of water-soluble monomers and telechelic oligomeric diacrylates in the presence of the latex enables the fabrication of a scaffold, which is restricted to the continuous aqueous phase and effectively surrounds the latex nanoparticles enabling the printing of otherwise inaccessible high molecular weight polymers. Rheological testing, including both steady and oscillatory shear experiments, provides insights into system properties and provides predictability for successful printing. This perspective article aims to provide an understanding of both chemical functionality (photo- and thermal-reactivity) and rheological response and their importance for the successful design and evaluation of VP and DIW processable latex formulations.
36 MATERIALS SCIENCE↗
Predicting mechanical property plateau in laser polymer powder bed fusion additive manufacturing via the critical coalescence ratio
Not Available
36 MATERIALS SCIENCE↗
Ageing of PBF‐Grade Poly(Phenylene Sulfide) Powder and its Effect on Critical Printability Properties
Abstract Poly(phenylene sulfide) (PPS) is a high‐performance polymer suiting the needs of powder bed fusion (PBF) early‐adopter industries. Although there are many benefits to PBF's powder bed‐based, one drawback is thermal ageing of the powder not incorporated into printed parts. Ideally, unfused powder can be reused in future builds; however, it is unlikely that critical printability properties of the thermally aged powder will remain unchanged. Changes in properties lead to either limited reuse through a practice of mixing used and new powder, or elimination of all powder after each build. In this paper, the authors report effects of thermal ageing in simulated printing conditions on properties of PPS critical to PBF processing. PBF‐grade PPS powder is exposed to process‐mimicking conditions. Properties relevant to the three PBF manufacturing process sub‐functions are assessed for the aged powders. Single‐layer prints are made using aged powder to observe polymer‐PBF interactions ad machina. Significant and systematic deviations from the as‐received state of the powder are observed for thermal and coalescence related properties with increasing exposure time and temperature. These changes are interpreted both in terms of physical and chemical changes in PPS and in terms of how these changes may impact the PBF printing process.
Chatham, Camden A.↗