The Influence of Vitrification on the Formation of Densely Crosslinked Networks Using Photopolymerization

Kloosterboer, J. G.; Lijten, G. F. C. M.

doi:10.1007/978-94-009-1343-1_23

Cited by 9 publications

(8 citation statements)

References 14 publications

(2 reference statements)

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“…These first addition products, taking the chain-addition polymerization principle into account, are also free radicals, intrinsically reactive, but again hindered by diffusion limitations as long as the sample is in its vitrified state below the glass transition temperature. Electronic paramagnetic resonance (EPR) studies revealed that, in the vitrified state, the free radicals are known to remain stable for days [ 34 , 35 ]. The heating of the sample promotes molecular mobility; monomers can reach the reactive sites by diffusion, and thus, polymerization can take place selectively in the high-intensity regions of the interference pattern.…”

Section: Resultsmentioning

confidence: 99%

Nano-Second Laser Interference Photoembossed Microstructures for Enhanced Cell Alignment

et al. 2021

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Photoembossing is a powerful photolithographic technique to prepare surface relief structures relying on polymerization-induced diffusion in a solventless development step. Conveniently, surface patterns are formed by two or more interfering laser beams without the need for a lithographic mask. The use of nanosecond pulsed light-based interference lithography strengthens the pattern resolution through the absence of vibrational line pattern distortions. Typically, a conventional photoembossing protocol consists of an exposure step at room temperature that is followed by a thermal development step at high temperature. In this work, we explore the possibility to perform the pulsed holographic exposure directly at the development temperature. The surface relief structures generated using this modified photoembossing protocol are compared with those generated using the conventional one. Importantly, the enhancement of surface relief height has been observed by exposing the samples directly at the development temperature, reaching approximately double relief heights when compared to samples obtained using the conventional protocol. Advantageously, the light dose needed to reach the optimum height and the amount of photoinitiator can be substantially reduced in this modified protocol, demonstrating it to be a more efficient process for surface relief generation in photopolymers. Kidney epithelial cell alignment studies on substrates with relief-height optimized structures generated using the two described protocols demonstrate improved cell alignment in samples generated with exposure directly at the development temperature, highlighting the relevance of the height enhancement reached by this method. Although cell alignment is well-known to be enhanced by increasing the relief height of the polymeric grating, our work demonstrates nano-second laser interference photoembossing as a powerful tool to easily prepare polymeric gratings with tunable topography in the range of interest for fundamental cell alignment studies.

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Section: Resultsmentioning

confidence: 99%

Nano-Second Laser Interference Photoembossed Microstructures for Enhanced Cell Alignment

et al. 2021

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“…Such a delay of shrinkage with respect to conversion was observed experimentally. 2,20 This causes part of the reaction to take place in a volume that is larger than it would be in the fully relaxed state, so there is a temporal excess of the free volume. This, in turn, enhances the local mobility and thereby the rate of polymerization.…”

Section: Degree Of Polymerizationmentioning

confidence: 98%

Influence of the reaction mechanism on the shape accuracy of optical components obtained by photoreplication

Verstegen

Faasen

Stapert

et al. 2003

J of Applied Polymer Sci

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Light-induced crosslinking polymerization of both bis-methacrylates and bis-epoxides yields highly transparent glassy products, suitable for optical applications. Rheological changes of vitrifying liquids during photopolymerization strongly influence the shape accuracy of the final product. Comparison of a free-radical-initiated methacrylate polymerization and a cationically initiated ring-opening polymerization of an epoxide showed that different reaction mechanisms led to very different chemorheological responses and, hence, to pronounced differences in the shape accuracy of the products obtained with either of these materials. An ethoxylated bisphenol-A dimethacrylate (HEBDM) gels below 1-2% conversion and vitrifies at 15%. At higher conversion, large stresses develop through polymerization shrinkage. Relaxation occurs upon release of a product from its mold, leading to large shape deviations. Ring-opening polymerization of the diglycidyl ether of bisphenol-A (DGEBA) has an intrinsically lower polymerization shrinkage. Moreover, gelation of DGEBA polymer networks occurs at 25-30% conversion, leading to much lower stresses since most of the volume change occurs in the liquid state in which replenishment of a monomer can still occur. Upon release from a mold, there is hardly any driving force for relaxation, so a much better copy of the mold is obtained.

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“…Kloosterboer and Lijten [12] studied the influence of vitrification on the formation of densely crosslinked networks using photopolymerization of diacrylates near ambient temperature. It resulted in the formation of densely crosslinked glassy polymers.…”

Section: Free Radical Photopolymerizationmentioning

confidence: 99%

Photopolymerization: A Review

Kaur

Srivastava

2002

Journal of Macromolecular Science, Part C: Polymer Reviews

126

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The Influence of Vitrification on the Formation of Densely Crosslinked Networks Using Photopolymerization

Abstract: ABSTRACT

Cited by 9 publications

References 14 publications

Nano-Second Laser Interference Photoembossed Microstructures for Enhanced Cell Alignment

Nano-Second Laser Interference Photoembossed Microstructures for Enhanced Cell Alignment

Influence of the reaction mechanism on the shape accuracy of optical components obtained by photoreplication

Photopolymerization: A Review

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