TY - THES

T1 - Influence of anion and cation structure on ionic liquid based epoxy systems as reversible adhesives

AU - Trausner, Carina

N1 - embargoed until 04-09-2028

PY - 2023

Y1 - 2023

N2 - The aim of this master's thesis was to synthesize dynamic epoxy-based networks based on ionic liquids (IL) with selected anion and cation structures and to establish structure-property relationships for their applicability as reversible adhesives. Via external electrical stimulation, the adhesive joints should be debonded on demand and rebonded through the macroscopic reflow induced by thermo-activated dynamic bond-exchange reactions. The imidazolium cation was used as the basis for the synthesis of the epoxy monomers and an anhydride hardener was used to cure the epoxy resins. In this work, five epoxy based IL consisting of a combination of three different anions and three different cations were synthesized and characterized. The synthesized IL epoxy resins were characterized via nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy to confirm their chemical composition. In addition, the influence of the anion and cation structure on the thermal, mechanical and thermal healing properties was analyzed. Due to the exchange of the ions, thermosets with a thermal stability of 286-324 °C and glass transition temperatures of 1 °C to 59 °C were acquired. Furthermore, the different ion combinations allowed to tailor the mechanical properties and materials with 0.98-942 MPa tensile modulus, an elongation at break of 7-76% and tensile strength of 0.24-24 MPa were achieved. In order to investigate the healing efficiency of the adhesives, lap shear tests were performed. In a further step, the tested specimens were rejoined under pressure and increased temperature and tested again in the lap shear test. Healing efficiencies between 38% and 88% were obtained depending on the network structure. A DC voltage of 0.2 kV was used to separate the adhesive joints. However, no separation occurred, even after 30 min. The addition of a non-covalently attached IL facilitated the debonding of the adhesive joints successfully after 1.5 min. Consequently, mobile salt is required to enable electrical debonding as the covalent bonds of the ions hinder their movement. Summing up, a successful application as a reversible adhesive with an optimized composition could be proven and debonding was achieved under the influence of electrical stimulation.

AB - The aim of this master's thesis was to synthesize dynamic epoxy-based networks based on ionic liquids (IL) with selected anion and cation structures and to establish structure-property relationships for their applicability as reversible adhesives. Via external electrical stimulation, the adhesive joints should be debonded on demand and rebonded through the macroscopic reflow induced by thermo-activated dynamic bond-exchange reactions. The imidazolium cation was used as the basis for the synthesis of the epoxy monomers and an anhydride hardener was used to cure the epoxy resins. In this work, five epoxy based IL consisting of a combination of three different anions and three different cations were synthesized and characterized. The synthesized IL epoxy resins were characterized via nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy to confirm their chemical composition. In addition, the influence of the anion and cation structure on the thermal, mechanical and thermal healing properties was analyzed. Due to the exchange of the ions, thermosets with a thermal stability of 286-324 °C and glass transition temperatures of 1 °C to 59 °C were acquired. Furthermore, the different ion combinations allowed to tailor the mechanical properties and materials with 0.98-942 MPa tensile modulus, an elongation at break of 7-76% and tensile strength of 0.24-24 MPa were achieved. In order to investigate the healing efficiency of the adhesives, lap shear tests were performed. In a further step, the tested specimens were rejoined under pressure and increased temperature and tested again in the lap shear test. Healing efficiencies between 38% and 88% were obtained depending on the network structure. A DC voltage of 0.2 kV was used to separate the adhesive joints. However, no separation occurred, even after 30 min. The addition of a non-covalently attached IL facilitated the debonding of the adhesive joints successfully after 1.5 min. Consequently, mobile salt is required to enable electrical debonding as the covalent bonds of the ions hinder their movement. Summing up, a successful application as a reversible adhesive with an optimized composition could be proven and debonding was achieved under the influence of electrical stimulation.

KW - Ionische Flüssigkeiten

KW - Elektrische Ablösung

KW - Reversible Klebstoffe

KW - Dynamische Polymernetzwerke

KW - Ionic liquids

KW - Electrical debonding

KW - Reversible Adhesives

KW - Dynamic polymer networks

M3 - Master's Thesis

ER -