Study of cationic UV curing and UV laser ablation behavior of coatings sensitized by novel sensitizers

Photocurable Epoxy Acrylate Coatings Preparation by Dual Cationic and Radical Photocrosslinking

In this work, epoxy acrylate resin (EA) based on the industrial-grade bisphenol A-based epoxy resin (Ep6) and acrylic acid (AA) has been synthesized in order to develop hybrid resin comprising both epoxide group and reactive, terminal unsaturation. Obtained epoxy acrylate prepolymer was employed to formulate photocurable coating compositions containing, besides the EA binder, also cationic or radical photoinitiators. Hence, when cationic photoinitiators were applied, polyether-type polymer chains with pending acrylate groups were formed. In the case of free radical polymerization, epoxy acrylates certainly formed a polyacrylate backbone with pending epoxy groups. Owing to the presence of both epoxy and double carbon–carbon pendant groups, the reaction product exhibits photocrosslinking via two distinct mechanisms: (i) cationic ring-opening polymerization and (ii) free radical polymerization. Therefore, photopolymerization behavior of synthetized hybrid resin with various photoinitiators was determined via photo-differential scanning calorimetry (photo-DSC) and real-time infrared spectroscopy (RT-IR) methods, and properties of cured coatings were investigated. The performance of the following type of photoinitiators was tested in the cationic photopolymerization: diaryliodonium cations or triarylsulfonium cations, and the following type of photoinitiators were used to induce free radical photopolymerization: α-hydroxyketones, acylphosphine oxides, and their mixtures. Lastly, the basic physicomechanical properties of cured coatings, such as tack-free time, hardness, adhesion, gloss, and yellowness index, were evaluated. Some structural factors and parameters of cationic and radical photoinitiators and photopolymerization mechanisms affecting the epoxy acrylate hybrid coatings performance are discussed.

Artificial Muscles: Dielectric Elastomers Responsive to Low Voltages

The lack of soft high-dielectric-permittivity elastomers responsive to a low voltage has been a long-standing obstacle for the industrialization of dielectric elastomer actuators (DEA) technology. Here, elastomers that not only possess a high dielectric permittivity of 18 and good elastic and insulating properties but are also processable in very thin films by conventional techniques are reported. Additionally, the elastic modulus can be easily tuned. A soft elastomer with a storage modulus of E = 350 kPa, a tanδ = 0.007 at 0.05 Hz, and a lateral actuation strain of 13% at 13 V µm^-1 is prepared. A stable lateral actuation over 50 000 cycles at 10 Hz is demonstrated. A stiffer elastomer with an E = 790 kPa, a tanδ = 0.0018 at 0.05 Hz, a large out-of-plane actuation at 41 V µm^-1 , and breakdown fields of almost 100 V µm^-1 is also developed. Such breakdown fields are the highest ever reported for a high-permittivity elastomer. Additionally, actuators operable at a voltage as low as 200 V are also demonstrated. Because the materials used are cheap and easily available, and the chemical reactions leading to them allow upscaling, they have the potential to advance the DEA technology.