Title

Magnetic and dielectric properties of sulfonated (S) poly[(styrene)-(ethylene-co-butylene)]-styrene (SEBS) block copolymer/magnetic metal oxide nanocomposites synthesized via an in-situ precipitation method

Date of Award

2009

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

First Advisor

Kenneth Mauritz

Advisor Department

Polymers and High Performance Materials

Abstract

Block copolymer/magnetic metal oxide nanocomposites were synthesized by growing metal oxide nanoparticles (cobalt ferrite, CoFe2 O 4 and iron oxide, α-Fe2 O3 ) in sulfonated (s) poly (styrene) (PS) block domains of sulfonated poly [(styrene)-(ethylene-co-butylene)-(styrene)] (SEBS) BCP preformed films via an in-situ precipitation method by dissolving the salts of respective metal chloride (s) in a suitable solvent that selectively swells the sPS regions. Inorganic uptake was determined using thermogravimetric analysis (TGA), and it was observed that none of the samples incorporated more than 5 wt % of the inorganic component. Dynamical mechanical analysis was used to observe the changes in the glass transition temperatures (T g ) in both blocks of the BCP by plotting tan δ vs. temperature responses in tensile mode on all samples. The results showed that the T g of the sPS block domains increased with sulfonation level and further increased with the incorporation of both nanoparticles in the same blocks, indicating that growth of nanoparticles takes place only in sPS blocks. The crystalline structure of the nanoparticles was observed using wide angle X-ray diffractometry (WAXD), and it was determined that cobalt iron oxide nanoparticles in 20 mole % sulfonated SEBS exhibited an inverse spinel structure confirming the structure to be CoFe 2 O4 . And with iron oxide nanoparticles in 10 mole % sulfonated SEBS exhibiting a hematite (α-Fe2 O 3 ) phase. Transmission electron microscopy (TEM) was used to investigate the particle size and distribution of nanoparticles in sBCP matrices at all sulfonation levels. Select area electron diffraction in TEM was used to determine crystalline structures of individual nanoparticles to compare with the structure observed from WAXD. The changes in thickness of interfaces between the individual PS and EB block domains with increase in sulfonation of PS blocks were investigated semi-quantitatively using tapping mode atomic force microscopy. The interfacial thickness decreased with the increase in sulfonation level up to 16 mole % and then increased from there onwards until 20 mole % sulfonation. Magnetometric measurements were conducted on samples incorporated with inorganic metal oxide nanoparticles using an alternating gradient magnetometer at room temperature; and the samples showed superparamagnetism. Magnetic properties at temperatures near absolute zero and above were measured using a superconducting quantum interference device magnetometer and samples exhibited some magnetic hysteresis; hence they are ferrimagnetic. Zero field cooled and field cooled measurements were conducted on samples to determine the transition temperature at which the inorganic metal oxide transitions from being ferri- to superparamagnetic. Dielectric spectroscopy measurements were conducted on iron oxide nanoparticles in sSEBS matrices to observe the presence of nanoparticles in the PS blocks; the effect of nanoparticles on relaxation times and glass transition temperatures was investigated.