A Unified Approach for Patterning via Frontal Photopolymerization

Vitale, Alessandra; Hennessy, Matthew G.; Matar, Omar; Cabral, João T.

doi:10.1002/adma.201502607

Cited by 57 publications

(67 citation statements)

References 36 publications

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“…This is an intrinsic property of the material resulting from the wavefront propagation kinetics of the solidifying network. In previous works [30,31,32], we have demonstrated that many acrylic and thiol-ene systems photopolymerise following a frontal photopolymerisation (FPP) process, characterised by the development and propagation of a travelling solidification wavefront into the monomer bath, driven by light. In the case of a thick resin bath (Figure 4a), the solidification front kinetics can thus be readily resolved by measuring the cured thickness z f following illumination and removal of the residual liquid monomer (i.e., development).…”

Section: Resultsmentioning

confidence: 99%

“…While this simple relation often holds in practice [32,34], the model can be extended to account for thermal effects [32,35], mass diffusion [36] and the changing of optical properties [32,33,36] during photopolymerisation. However, even in these cases, the conversion profile still maintains a φ sigmoidal shape, whose width and slope are strongly influenced by the absorbing properties of the photopolymerising material (Figure 5).…”

Section: Resultsmentioning

confidence: 99%

“…The values of μ selected to model the conversion profiles are typical for acrylic and thiol-ene photocurable systems [32], commercial photoresists [30,34] and formulations containing absorbing dyes [24] or fillers (e.g., SiO 2 , TiO 2 , carbon nanotubes) [31]. …”

Section: Resultsmentioning

confidence: 99%

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Frontal Conversion and Uniformity in 3D Printing by Photopolymerisation

Vitale

Cabral

2016

Materials

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We investigate the impact of the non-uniform spatio-temporal conversion, intrinsic to photopolymerisation, in the context of light-driven 3D printing of polymers. The polymerisation kinetics of a series of model acrylate and thiol-ene systems, both neat and doped with a light-absorbing dye, is investigated experimentally and analysed according to a descriptive coarse-grained model for photopolymerisation. In particular, we focus on the relative kinetics of polymerisation with those of 3D printing, by comparing the evolution of the position of the conversion profile (zf) to the sequential displacement of the object stage (∆z). After quantifying the characteristic sigmoidal monomer-to-polymer conversion of the various systems, with a combination of patterning experiments, FT-IR mapping, and modelling, we compute representative regimes for which zf is smaller, commensurate with, or larger than ∆z. While non-monotonic conversion can be detrimental to 3D printing, for instance in causing differential shrinkage of inhomogeneity in material properties, we identify opportunities for facile fabrication of modulated materials in the z-direction (i.e., along the illuminated axis). Our simple framework and model, based on directly measured parameters, can thus be employed in photopolymerisation-based 3D printing, both in process optimisation and in the precise design of complex, internally stratified materials by coupling the z-stage displacement and frontal polymerisation kinetics.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Frontal Conversion and Uniformity in 3D Printing by Photopolymerisation

Vitale

Cabral

2016

Materials

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“…Frontal photopolymerization (FPP) ( 18 , 19 ) is a process in which a polymer film is continuously cured from one side in a thick layer of liquid resin. In the presence of strong light attenuation, the solidification front initiates at the surface upon illumination and propagates toward the liquid side as the irradiation time increases.…”

Section: Introductionmentioning

confidence: 99%

Origami by frontal photopolymerization

et al. 2017

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“…This approach has been validated with commercial and custom formulated thiol–ene resists, as well as filled systems (with nanoparticles, nanotubes and dyes), and for a wide range of temperatures and light intensities . However, we have recently found that certain acrylate systems are not fully described by the model . Oxygen inhibition is unlikely to play a role in this process since the monomer bath is confined by impermeable (glass) substrates.…”

Section: Introductionmentioning

confidence: 99%

Coarse‐grained models for frontal photopolymerization with evolving conversion profile

Purnama

Hennessy

Vitale

et al. 2017

Polymer International

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We introduce a series of ‘minimal’ models to describe a common light-driven directional solidification process, known as frontal photopolymerization (FPP), focusing on experimental observables: the solidification kinetics, light attenuation and spatiotemporal monomer-to-polymer conversion. Specifically, we focus on FPP propagation that yields conversion profiles that are not invariant with time, and which cannot be simply described by the presence of mass or heat diffusion. The models are assessed against experimental data for the photopolymerization of a model trimethacrylate system. We find that the simplest model, comprising a single equation of motion for the conversion fraction ϕ and a generalized Beer–Lambert law, can only describe the experimental data by assuming an unphysical variation in optical absorption. Introducing a ϕ-dependent reaction constant Keff is found to require a time dependence, regardless of the functional form in ϕ. We conclude by introducing a ‘minimal’ chemical model, which is based on a simple three-step reaction scheme involving the spatiotemporal evolution of the photoinitiator fraction, relative fraction of radicals and monomer conversion fraction, that is able to capture the experimental data with a small number of parameters and under reasonable FPP assumptions. Our framework provides important predictive ability for ubiquitous solidification and patterning processes, including three-dimensional printing, via photopolymerization

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A Unified Approach for Patterning via Frontal Photopolymerization

Cited by 57 publications

References 36 publications

Frontal Conversion and Uniformity in 3D Printing by Photopolymerisation

Frontal Conversion and Uniformity in 3D Printing by Photopolymerisation

Origami by frontal photopolymerization

Coarse‐grained models for frontal photopolymerization with evolving conversion profile

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