Processing-property relationships in epoxy resin/titanium dioxide nanocomposites
- ORNL
In situ precipitated titanium dioxide nanoparticles improve the physical properties of polymer composites. Since the pioneering work at Toyota Research Center on exfoliated montmorillonite nanoparticles in a nylon matrix, extensive studies have been performed on polymer nanocomposites in an effort to better integrate organic and inorganic phases. Inorganic fillers, such as silicon and titanium oxides, are widely used because of their remarkable enhancement of the mechanical, electrical, barrier, and flame-retardancy properties of organic polymers. The dispersion and size of the fillers determine the performance of nanocomposites and, despite numerous methods and processing conditions reported in the literature, a universally simple method to scale up the distribution of nanofillers remains a challenge. A significant part of our research involves formulation of novel nanodielectrics that can withstand high electric fields and exhibit superior mechanical performance. Focusing on nanocomposites operating at cryogenic temperatures, our group developed an in situ method for nucleating titanium dioxide (TiO{sub 2}) nanoparticles in polyvinyl alcohol. We also applied this method to a variety of polymer matrices. Here, we present our recent work on a cryogenic resin filled with TiO{sub 2} nanoparticles. Using a particle-precursor solution from which TiO{sub 2} precipitates, we nucleated nanoparticles within the cryogenic epoxy resin Araldite 5808 (Huntsman Advanced Materials Inc., USA). We fabricated nanocomposite films at low weight percentages ({approx}2.5%) to avoid formation of large aggregates and interfaces. The morphology and dispersion of the in situ synthesized nanoparticles are shown by low- and high-magnification transmission-electron-microscopy (TEM) images. The TiO{sub 2} particles ({le}5nm in diameter) are uniformly nucleated and form evenly distributed nanometer-sized clusters in the polymer matrix. This morphology differs significantly from nanocomposites obtained from conventional, ex situ synthesis that requires high shear mixing of the organic and inorganic phases. Using the ex situ technique, we synthesized TiO{sub 2} particles (also {le}5nm in diameter) in a polyethylene glycol solution - see Figure 1(c) - and subsequently mixed them with the resin. The mixing process, even at low concentrations (1% by weight), resulted in the formation of aggregates of several hundred nanometers in size. We performed optical, thermomechanical, and electrical measurements of systems with similar weight fractions of TiO{sub 2} to evaluate the impact of particle size and dispersion on the macroscopic properties of the nanocomposite. In agreement with the TEM images, UV-visible transmittance spectra show the same optical properties for the unfilled resin and in situ nanocomposite owing to the small particle-cluster size. Because of the formation of clusters of comparable size to the wavelength of light in the visible range, the ex situ specimen showed decreased transmittance, producing an opaque composite. Moreover, we found that creating large and weak interfaces between the phases degrades the macroscopic thermomechanical and electrical properties of the specimen. The in situ nanocomposite exhibited superior mechanical performance compared to both the unfilled resin and ex situ nanocomposite over the entire temperature range. Notably, at the lowest measured temperature (-145 C), the increase in the storage modulus (G') relative to that of the unfilled resin is approximately 30%. Furthermore, the in situ technique did not degrade the thermodynamic properties of the polymer network. The glass-transition temperature (T{sub g}) remains unchanged. In contrast, the ex situ nanocomposite displayed a 55% relative decrease in Tg because of the formation of weak and large interfaces. This morphology is also associated with significant degradation of dielectric properties under high electric fields. The dielectric-breakdown strength (EBD) of the ex situ nanocomposite is significantly lower than that of the unfilled resin. On the other hand, the small size and uniform distribution of TiO{sub 2} particles in the in situ system yielded a 40% improvement in EBD at 0.1% failure probability. In conclusion, we synthesized TiO{sub 2} nanoparticles in an epoxy-resin matrix. We found that the small size of the particles ({le}5nm in diameter) and their uniform spatial distribution in the polymer matrix improves the macroscopic properties of the composite. The noteworthy increase in the dielectric-breakdown strength, combined with an improvement in the mechanical properties, can be used to develop advanced electrical insulation materials. Additionally, the in situ method does not require high shear mixing and can potentially be applied to fabricate robust, optically transparent nanocomposites on large scales.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- OE USDOE - Office of Electric Transmission and Distribution
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 1033518
- Journal Information:
- SPE Plastics Research Online, Journal Name: SPE Plastics Research Online
- Country of Publication:
- United States
- Language:
- English
Similar Records
Properties of a nanodielectric cryogenic resin
Breakdown properties of epoxy nanodielectric
Related Subjects
DIELECTRIC PROPERTIES
DISTRIBUTION
ELECTRIC FIELDS
ELECTRICAL INSULATION
ELECTRICAL PROPERTIES
MECHANICAL PROPERTIES
MORPHOLOGY
OPTICAL PROPERTIES
ORGANIC POLYMERS
PARTICLE SIZE
PERFORMANCE
PHYSICAL PROPERTIES
POLYETHYLENE GLYCOLS
PROCESSING
PVA
RESINS
SPATIAL DISTRIBUTION
THERMODYNAMIC PROPERTIES
TITANIUM
TITANIUM OXIDES
TRANSMISSION ELECTRON MICROSCOPY