Actions for On the electric and magnetic field assembly of particulate polymer composites

Email RIS file
Bookmark
Report an Issue

On the electric and magnetic field assembly of particulate polymer composites

Author
Al Masud, Md Abdulla
Published
[University Park, Pennsylvania] : Pennsylvania State University, 2019.
Physical Description
1 electronic document
Additional Creators
Ounaies, Zoubeida
Access Online

Availability

I Want It
I Want It

Finding items...

Graduate Program
Restrictions on Access
Open Access.
Summary
The spatial distribution, orientation, and connectivity of particles are critical components to how the particles contribute to the bulk properties of particulate-filled polymer composites. Control of particles spatial distribution and orientation using an external field can lead to a significant increase in the materials elastic, dielectric, magnetic and conductive properties. This external field-guided organization of particles in the polymer can be achieved while the polymer is in a liquid state. External fields such as electric and magnetic have been individually used to orient and position micro and nanoparticles in polymer solutions and their resulting material properties were investigated, but the combined effect of using more than one external field on the material properties has not been studied in details. There is evidence in the literature that applying different configurations of electric and magnetic fields on geometrically and magnetically anisotropic particulates can produce varying microarchitectures with a range of material properties. The goal of this research is to investigate the effect of combined electric and magnetic fields on the microstructure-property relationship in particulate-filled polymer composites. To achieve this goal, first geometrically and magnetically anisotropic barium hexaferrite (BHF) platelets are synthesized via the hydrothermal synthesis route. Second, since BHF particles exhibit magnetic and geometric anisotropy which make them sensitive to both electric and magnetic fields, we systematically probe the effect of combined electric and magnetic fields on the microstructure formation of BHF in polydimethylsiloxane (PDMS). Third, magnetic and dielectric properties resulting from different microstructures are characterized and microstructure-property relationship is analyzed.Our study reveals that hydrothermal duration has a significant effect on the crystal size of the BHF. With the increase of hydrothermal duration from 10 min to 24 hours, BHF size was found to increase from 10 nm to 200 nm. When surfactant was used during the hydrothermal reaction, small size (20 nm) and round shaped superparamagnetic BHF were formed whereas, without surfactant, relatively large crystal size BHF (100-300 nm) with triangular/hexagonal morphology was formed. The synthesized particles were post-annealed at 800C (without external field) at different durations in order to improve the magnetic properties. A 4-hour annealing increased the crystallinity and crystal size of the nano BHF. The magnetic properties, i.e. magnetic coercivity and saturation magnetization, were also found to improve by 70% and 25% respectively after annealing. Compared to commercially available micro BHFs, the annealed synthesized nano BHFs were found to have 50% lower remnant magnetization, saturation magnetization, and coercivity. The reduced magnetic properties are attributed to the incomplete coordination of surface atoms due to the smaller particle size and the low crystalline order through the thickness direction due to the thin platelet crystals.Next, we investigated the effect of electric field amplitude, frequency, and duration on the microstructures using optical microscope (OM) images. We found that, when the electric field magnitude was below 2kV/mm, no change in microstructure resulted. With the increase of electric field magnitude, the degree of alignment was increased and continuous macro-chain formation resulted at 4kV/mm. A lower frequency (10 Hz) led to continuous macro-chains formation whereas at higher frequency (10 kHz) there was shorter and less number of chains. With the increase of electric field duration, the number of macro-chains reduced and chain thickness increased. After 10 minutes of electric field alignment, no change in microstructure was observed. After determining the suitable electrical alignment conditions (electric field magnitude, frequency, and duration), those parameters are used to study the multifield processing involving both electric and magnetic fields alignment.We found that a variety of microstructures can be produced using multifield processing depending on the type of applied external field and the curing conditions. For example, application of an electric field created macro-chains where the orientation of the BHF stacks inside the macro-chains was random. On the other hand, application of a magnetic field rotated the BHF stacks within the macro-chain in the direction dictated by the magnetic field. When electric and magnetic fields were applied in the same direction simultaneously, enhanced rotation of BHF stacks inside the macro-chains was observed. When electric and magnetic fields were applied simultaneously but perpendicular to each other, no macro-chains formation was observed. Applying an electric field, then applying a magnetic field (after partial curing) results in macro-chain formation inside which the BHF stacks were arranged in the direction parallel to the magnetic field. Our study also revealed that multiple levels of hierarchy were present in the microstructure i.e. particle, stack, micro-chain and macro-chain. In order to quantitatively assess the alignment at each hierarchical level, a spanning tree algorithm was used next. Spanning tree analysis of the microstructures confirms that multiple levels of hierarchies are present in the microstructure. The BHF orientation for electrically aligned composites is found to be random at the particle, stack and micro-chain level, but aligned at the macro-chain level. Composites processed with just magnetic field were found to have increased alignment compared to just electric field processed composites at the particle, stack and micro-chain level; but showed similar level of alignment at the macro-chain level. Simultaneously electric and magnetic field processed composites are found to have increased alignment at particle, stack and micro-chain level compared to just magnetically processed composites. Multifield processed composites with partial curing was found to have less BHF orientation at all hierarchical level than multifield processed composites without partial curing. For all cases, less orientation of BHF at the stack, micro-chain and macro-chain level was observed compared to particle level due to the side-branching of the trees. We found that while orientation from the spanning tree analysis offers insights into the microstructural hierarchy as a direct result of processing conditions, there are other metrics (i.e. polar moments of inertia, average distances between neighbors etc.) that need to be studied as well to further understand different aspects of the microstructure besides spatial and particle alignments.We observed that using a multifield processing technique not only made possible a variety of microstructures, but also a range of dielectric and magnetic properties. For example, for a 1 vol% BHF-PDMS composites, the dielectric permittivity is found to vary from 2.84 to 5.12 and the squareness ratio is found to vary from 0.55 to 0.92 from different microstructures resulted from this technique. In addition, the resulting structural hierarchy impacted the properties in different ways. While macro-scale orientation of BHFs did not affect the magnetic properties, micro-scale orientation of BHFs inside the macro-chains significantly affected the magnetic properties. For example, higher orientation at the particle, stack and micro-chain level lead to a 70% increase in squareness ratio (remnant magnetization over saturation magnetization). On the other hand, dielectric properties are found to be significantly affected by the macro-scale arrangement of BHFs, and less so by the micro-scale orientation inside the macro-chains. The ability to produce a variety of microstructures with a range of properties from a single material set using multifield processing technique will be particularly beneficial for resin pool based additive manufacturing and 3-D printing
Other Subject(s)
Genre(s)
Dissertation Note
Ph.D. Pennsylvania State University 2019.
Reproduction Note
Microfilm (positive). 1 reel ; 35 mm. (University Microfilms 28123335)
Technical Details
The full text of the dissertation is available as an Adobe Acrobat .pdf file ; Adobe Acrobat Reader required to view the file.
View MARC record | catkey: 27984130