Dataset Information

Investigation of Thermal-Induced Changes in Molecular Order on Photopolymerization and Performance Properties of a Nematic Liquid-Crystal Diacrylate.

ABSTRACT: Polymerization shrinkage and associated stresses are the main reasons for dental restorative failure. We developed a series of liquid crystal diacrylates and dimethacrylates which have markedly low polymerization shrinkage. In order to fully understand the effects of temperature-induced changes of molecular order on the photopolymerization process and performance properties of the generated polymers, the photopolymerization of a difunctional acrylate, 2-t-butyl-1,4-phenylene bis (4-(6-(acryloyloxy)hexyloxy)benzoate), which exists in the nematic liquid crystalline phase at room temperature, was investigated as a function of photopolymerization temperature over the nematic to isotropic range. Morphological studies suggested that a mesogenic phase was immediately formed in the polymer even if polymerization in thin films occurred above the nematic-to-isotropic (N→I) transition temperature of the monomer (T_n-i = 45.8 °C). Dynamic mechanical analysis of 2 × 2 mm cross-section bar samples polymerized at 60 °C showed reduced elastic moduli, increased glass transition temperature and formation of a more crosslinked network, in comparison to polymers formed at lower polymerization temperatures. Fractography analysis showed that polymers generated from the nematic liquid crystalline phase underwent a different fracture pattern in comparison to those generated from the isotropic phase. Volumetric shrinkage (2.2%) found in polymer polymerized from the nematic liquid crystalline phase at room temperature was substantially less than the 6.0% observed in polymer polymerized from an initial isotropic phase at 60 °C, indicating that an organized monomer can greatly contribute to reducing cure shrinkage.

SUBMITTER: Wang Q

PROVIDER: S-EPMC9267439 | biostudies-literature |

REPOSITORIES: biostudies-literature

ACCESS DATA

Similar Datasets

Project description:The structure and molecular order in the thermotropic ionic liquid crystal (ILC), [choline][geranate(H)octanoate], an analogue of Choline And GEranate (CAGE), which has potential for use as a broad-spectrum antimicrobial and transdermal and oral delivery agent, were investigated by magic-angle spinning (MAS) nuclear magnetic resonance (NMR), polarizing optical microscopy, small-angle X-ray scattering (SAXS), and mass spectrometry. Mass spectrometry and the 1H NMR chemical shift reveal that CAGE-oct is a dynamic system, with metathesis (the exchange of interacting ions) and hydrogen exchange occurring between hydrogen-bonded/ionic complexes such as [(choline)(geranate)(H)(octanoate)], [(choline)(octanoate)2(H)], and [(choline)(geranate)2(H)]. These clusters, which are shown by mass spectrometry to be significantly more stable than expected for typical electrostatic ion clusters, involve hydrogen bonding between the carboxylic acid, carboxylate, and hydroxyl groups, with rapid hydrogen bond breaking and re-formation observed to average the 1H chemical shifts. The formation of a partial bilayer liquid crystal (LC) phase was identified by SAXS and polarizing optical microscopy at temperatures below ∼293 K. The occurrence of this transition close to room temperature could be utilized as a potential temperature-induced "switch" of the anisotropic properties for particular applications. The presence of an isotropic component of approximately 23% was observed to coexist with the LC phase, as detected by polarizing optical microscopy and quantified by both 1H-13C dipolar-chemical shift correlation (DIPSHIFT) and 1H double-quantum (DQ) MAS NMR experiments. At temperatures above the LC-to-isotropic transition, intermediate-range order (clustering of polar and nonpolar domains), a feature of many ILs, persists. Site-specific order parameters for the LC phase of CAGE-oct were obtained from the MAS NMR measurement of the partially averaged 13C-1H dipolar couplings (DCH) by cross-polarization (CP) build-up curves and DIPSHIFT experiments, and 1H-1H dipolar couplings (DHH) by double-quantum (DQ) build-up curves. The corresponding order parameters, SCH and SHH, are in the range 0-0.2 and are lower compared to those for smectic (i.e., layered) phases of conventional nonionic liquid crystals, resembling those of lamellar phases formed by lyotropic surfactant-solvent systems.

Dataset Information

Investigation of Thermal-Induced Changes in Molecular Order on Photopolymerization and Performance Properties of a Nematic Liquid-Crystal Diacrylate.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets