Challenges and limits of Mechanical Stability in 3D Direct Laser Writing

Sedghamiz, Elaheh; Liu, Modan; Wenzel, Wolfgang

doi:10.21203/rs.3.rs-151096/v1

Cited by 2 publications

(1 citation statement)

References 79 publications

(98 reference statements)

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“…The strong spatial confinement of the exposed region in two-photon polymerization (TPP) enables resolutions that cannot be achieved using traditional one-step one-photon absorption (1PA) processes 2,4,5 . Despite the tremendous progress in recent years 6 , 3D laser nanoprinting using TPP still faces different limitations [7][8][9][10] in resolution and speed that correlate strongly with the threshold laser power. This, in part, results from the limitations of the available photoinitiators (PIs) and resins: Kiefer et al 11 have recently reported a strong dependence of the printing sensitivity on the TPP initiation and, therefore, on the photochemical properties of the photoinitiator.…”

Section: Introductionmentioning

confidence: 99%

Two- and three-photon processes in photoinitiators for 3D laser printing

Mauri

Wegener

Neidinger

et al. 2022

Preprint

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The performance of a photoinitiator is key to control efficiency and resolution in 3D laser nanoprinting. Upon light absorption, a cascade of competing excited states and photoreactions leads to the radical formation that initiates free radical polymerization. Here we investigate 7-diethylamino-3-thenoylcoumarin (DETC), one of the most efficient photoinitiators for two-photon polymerization (TPP). Depending on the presence of a co-initiator, DETC causes radical generation either with two-photon or with a unique three-photon excitation, but the mechanism for these processes is not well understood. Here we show that the unique three-photon based radical formation of DETC in the absence of a co-initiator results from the excitation of special highly excited triplet states followed by multiple bond scission possibilities generating radicals. In contrast, photoinitiation in the presence of a co-initiator proceeds via intermolecular electron transfer or hydrogen atom transfer after the photosensitization of the photoinitiator to the lowest triplet excited state. Our quantum mechanical calculations explain the different pathways for the multiphoton activation mechanism of DETC and its radical formation, which enables the rational design of efficient photoinitiators to increase the speed and sensitivity of 3D laser nanoprinting.

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Section: Introductionmentioning

confidence: 99%

Two- and three-photon processes in photoinitiators for 3D laser printing

Mauri

Wegener

Neidinger

et al. 2022

Preprint

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Tough, Transparent, 3D‐Printable, and Self‐Healing Poly(ethylene glycol)‐Gel (PEGgel)

et al. 2022

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These gels represent a class of soft materials with unique properties resembling soft biological tissues, such as tendons, ligaments, cartilage, muscles, and skin. [6] Hydrogels, obtained by cross-linking hydrophilic polymer chains in aqueous solutions, [7] possess the intrinsic lowmodulus nature and tissue-like properties, which make them applicable to tissue engineering, [8] optical devices, [9] biomedicine [10] and actuators. [11] In the pursuit of high performance, most research in the field of polymer gels has been focused on the chemical nature and polymer network architectures and their interactions, [12] such as ideal polymer networks, [13] interpenetrating polymer networks, [14] nano/micro composite polymer networks, [10,15] and hierarchically structured polymer networks. [16] The small molecule solvent is the second component of gels and is often considered to be a nonfunctional liquid that impregnates and expands a functional polymer network. Recently, ionic liquids have been used to replace water in hydrogels, [17] resulting in soft materials with long-term stability. [18] Multicomponent solvent systems, in which water is mixed with organic solvents (such as glycerol, [19] ethylene glycol [20] and sorbitol [21] ), were introduced into gel networks to maintain the performance of materials in harsh environments. However, because of the low molecular weight of solvents used and weak interactions with polymer networks, the reported Polymer gels, such as hydrogels, have been widely used in biomedical applications, flexible electronics, and soft machines. Polymer network design and its contribution to the performance of gels has been extensively studied. In this study, the critical influence of the solvent nature on the mechanical properties and performance of soft polymer gels is demonstrated. A polymer gel platform based on poly(ethylene glycol) (PEG) as solvent is reported (PEGgel). Compared to the corresponding hydrogel or ethylene glycol gel, the PEGgel with physically cross-linked poly(hydroxyethyl methacrylate-co-acrylic acid) demonstrates high stretchability and toughness, rapid self-healing, and long-term stability. Depending on the molecular weight and fraction of PEG, the tensile strength of the PEGgels varies from 0.22 to 41.3 MPa, fracture strain from 12% to 4336%, modulus from 0.08 to 352 MPa, and toughness from 2.89 to 56.23 MJ m -3 . Finally, rapid self-healing of the PEGgel is demonstrated and a self-healing pneumatic actuator is fabricated by 3D-printing. The enhanced mechanical properties of the PEGgel system may be extended to other polymer networks (both chemically and physically cross-linked). Such a simple 3D-printable, self-healing, and tough soft material holds promise for broad applications in wearable electronics, soft actuators and robotics.

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Challenges and limits of Mechanical Stability in 3D Direct Laser Writing

Cited by 2 publications

References 79 publications

Two- and three-photon processes in photoinitiators for 3D laser printing

Two- and three-photon processes in photoinitiators for 3D laser printing

Tough, Transparent, 3D‐Printable, and Self‐Healing Poly(ethylene glycol)‐Gel (PEGgel)

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