Liquid crystal epoxy resins based on biphenyl group cured with aromatic amines - studied by dielectric spectroscopy

Abstract

In this paper we investigate the dielectric response of cured epoxy resins based on biphenyl group. We chose two monomers, which were earlier synthesised, containing the same mesogen but with long and short symmetric tails. They were cured with standard amines (DDM, DMAP). Firstly we optimised conditions of the curing process by dielectric and optical observation in situ. Small differences in the dynamics of the curing process were observed in different mixtures. For the four selected products we made dielectric measurements in a wide range of frequency and temperature. Although, generally, dielectric response is similar in all the cured materials, differences can be seen in the details. At lower temperatures, quite strong relaxation process is seen in all products, its low activation energy points towards a β-process, which appears in many polymers. The Havriliak-Negami formula was fitted to the data and characteristic parameters of the observed relaxation processes were compared in detail. In some cases the α-process also appears. We conclude how the longer spacer and the type of curing process influence the electrical properties of the resin.

Curing Reaction and Dielectric Properties of Rigid and Elastic Liquid Crystal Epoxy Networks Modified with Nanofillers

“…Although the activation energy of the observed process varies slightly among the studied mixtures, such variations may be due to differences in the energy barrier, reflecting differences in the internal structure of the network. A similar process was also observed in materials with different lengths of the mesogen [24]. An interesting case was found in the LCM/PA mixtures cured with the addition of nanorods, where an additional growth of the imaginary part of the permittivity was observed at high frequencies and low temperatures (Figure 4(b), inset).…”

“…Although the complex permittivity ε * is most commonly used to discuss the results, another representation was proposed for polymers with high ionic conductivity: the electric modulus [22]. It is defined as the inverse of the complex permittivity [22][23][24]:…”

Microstructured Photopolymerization of Liquid Crystalline Elastomers in Oxygen‐Rich Environments

“…Here, we address this environmental constraint by developing epoxide LCM to prepare LCEs within oxygen‐rich environments via the photocationic (acidic) polymerization mechanism . Unlike radical polymerization in acrylate‐based LCEs, photocationic polymerization bypasses issues related to oxygen inhibition that may limit accessible form factors or constrict fabrication protocols.…”

Relationship between crosslinking structure and low dielectric constant of hydrophobic epoxies based on substituted biphenyl mesogenic units

“…Liquid crystalline epoxides (LCEs) are superior to conventional amorphous epoxies in the performance of good water resistance properties, better mechanical properties, better dimensional stability, lower coefficients of thermal expansion, increased fracture toughness and noticeable high temperature properties. [17][18][19][20][21][22][23][24] It was reported that the oriented structure of LCEs could increase packing density of the segments, resulting in increased crosslink network density. 25,26 The molecular motivation of liquid crystalline epoxies under electric eld was hindered by the enhanced intermolecular interactions caused by oriented and increased cross-linked networks, resulting in ultra-low dielectric constant and low dielectric loss compared with current polymeric matrix without introducing pores or uorine.…”