Friday May 4th – Presentations

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Photoreversible Covalent Hydrogels for Soft-Matter Additive Manufacturing

Christopher P. Kabb,† Christopher S. O’Bryan,§ Christopher C. Deng,† Thomas E. Angelini,§, ‡,⊥ and Brent S. Sumerlin*,†

†George & Josephine Butler Polymer Research Laboratory, Center for Macromolecular Science & Engineering, Department of Chemistry, University of Florida, Gainesville, FL 32611, USA.
§Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA.
‡J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611, USA.
⊥Institute for Cell and Regenerative Medicine, University of Florida, Gainesville, FL 32611, USA.

10:15 AM
Additive Manufacturing

Reversible-covalent chemistry provides access to robust materials with the ability to be degraded and reformed upon exposure

to an appropriate stimulus. Photoresponsive units are attractive for this purpose, as the spatial and temporal application of light is easily controlled.

Coumarin derivatives undergo a [2+2] cycloaddition upon exposure to long-wave UV irradiation (365 nm), and this process can be

reversed using short-wave UV light (254 nm). Therefore, polymers crosslinked by coumarin groups are excellent candidates as reversiblecovalent

gels. In this work, copolymerization of coumarin-containing monomers with the hydrophilic comonomer N,N-dimethylacrylamide

yielded water-soluble, linear polymers that could be cured with long-wave UV light into free-standing hydrogels, even in the absence of a photoinitiator.

Importantly, the gels were reverted back to soluble copolymers upon short-wave UV irradiation. This process could be cycled,

allowing for recycling and remolding of the hydrogel into additional shapes. Further, this hydrogel can be imprinted with patterns through a

mask-based, post-gelation photoetching method. Traditional limitations of this technique, such as the requirement for uniform etching in one

direction, have been overcome by combining these materials with a soft-matter additive manufacturing methodology. In a representative

application of this approach, we printed solid structures in which the interior coumarin-crosslinked gel is surrounded by a nondegradable gel.

Upon exposure to short-wave UV irradiation, the coumarin-crosslinked gel was reverted to soluble prepolymers that were washed away to

yield hollow hydrogel objects.

Fabrication of Triboluminescence Sensors via Additive Manufacturing

Tawakalt Mayowa Akintola, Jolie Breaux Frketic, Roy Madhuparna, Phong Tran, Tarik Dickens

Department of Industrial and Manufacturing Engineering, FAMU-FSU College of Engineering, 2525 Pottsdamer St., Tallahassee, Florida 32310 United States
High-Performance Materials Institute, 2005 Levy Ave, Tallahassee, Florida 32310 United States

10:35 AM
Additive Manufacturing

In this presentation, functional 3D printing parts were produced using ZnS:Mn powder/Polystyrene (PS) composites. ZnS:Mn is a triboluminescence (TL) material which produces light emission under mechanical loads such as impact, stress, and fracture.
By combining TL materials with additive manufacturing, we can achieve unique TL structures that once restrained by conventional methods. Additionally, 3D printing of TL materials will allow us to strategically embed functionalized material for self-sensing in applications for damage detection and monitoring. The processing-performance relationship has been investigated by TGA, DSC and SEM to understand the effect of TL crystal sizes and distribution on the performance of TL printed parts.
Flexural testing beams were 3D printed and their fracture/deformation energy emission was estimated via J-integral
analysis of three-point bend test.

Interfacial Dynamics in Additively Manufactured Polymer Matrix Composites

Kyle J. Johnson, Andrew Abbott, Lutz Wiegart, Jeff Baur, Hilmar Koerner

UES Inc., University of Dayton Research Institute, Brookhaven National Laboratory (NSLS II), Air Force Research Laboratory

10:55 AM
Additive Manufacturing

Additive manufacturing (AM) is pervasive across many disciplines at the Air Force Research Laboratory (AFRL). AFRL is investing in these novel manufacturing processes because of their appeal in rapid prototyping, part reduction and the ability to manufacture complex parts using design and topology optimization. Before AM is robust enough for metals, polymers, ceramics and composite manufacturing, morphology/processing/performance relationships have to be established. The presentation will give a brief overview of the different AM areas that AFRL is working on with focus on AM for polymer matrix composites. The road to road interface in additively manufactured composite parts is crucial for part performance. As an example, weakness and anisotropy at this interface have been key areas of study in the pursuit of more robust additively manufactured parts. Here, the dynamics and morphology at road-to-road interfaces were explored in an epoxy/nanoclay  composite ink using X-Ray photon correlation spectroscopy (XPCS). We observe a time scale associated with equilibrium dynamics, and observe substantially faster dynamics perpendicular to the road-to-road interface than parallel. This anisotropy in dynamics is shown to pass through a maximum both into the recently printed and previously printed road. The behavior is discussed relative to the alignment of the composite particles during shear of the ink through the extrusion head. The ultimate goal of this research is to use the in-situ data to calibrate more conventional techniques that can be implemented within an AM machine and use this to advance close-loop feedback control in AM processes in the future.