(688d) The Effect of Thermal Treatment on Eelectrospun Ceramic Nanofibers

O. Elishav, V. Beilin, G. E. Shter, and G. S. Grader.

Ceramic nanofibers
with desired architecture and properties are highly promising for improving and
developing new applications. Electrospinning is a simple approach to produce
polymer, ceramic and composite fibers of various diameters and morphologies. Usually,
the electrospinning stage is followed by thermal treatment stage to remove the
polymer and obtain the final structure and phase. This step often includes shrinkage,
potential deleterious deformation and phase and morphologies changes. Understanding
the processes that occur during thermal treatment on the electrospun fibers is
highly important. Therefore, the effect of thermal treatment on
electrospun nanofibers was investigated in different electrospun
systems: PVP, PbZrTi, Al₂O₃ and Fe-Al-O.

Integration
of nanofibrous mat into small-scale device requires a certain degree of
flatness. This in turn can become a challenge when the part undergoes severe
shrinkage and deformation during thermal treatment. Therefore, the linear
shrinkage of fibrous mats was investigated in three systems: pure
PVP, PZT/PVP and Al2O3/PVP. During electrospinning, the fibers undergo
tremendous stretching aligning the polymer chains along the fiber axis.
However, above
the polymer glass transition temperature the polymer relaxes during the
thermal stage leading to substantial shrinkage. The goal in the
investigation was to understand the interplay between the precursor solution
composition, the fibers morphology and the mats thermal shrinkage enables
process optimization that minimizes the mat deformation during thermal
treatment (Figure 1).

Figure
1. Linear shrinkage percentage and viscosity vs. PVP concentration.

Following
the above linear shrinkage investigation, we expand the investigation to the Fe-Al-O
system, designated for heterogeneous catalysis. By controlling the thermal treatment,
we succeed to synthesize ceramic nanofibers with a unique mesoporous structure,
consisting of elongated lamellar-like pores (Figure 2).

Figure
2. HRSEM images of white Fe–Al–O fibers

A
general mechanism for the formation of this morphology is suggested. The final
structure depends greatly on the heating rate and chemical composition of the metal
oxide precursors and polymer matrix. The presented nanofibers can be beneficial
for cases that require an accessible open porous structure and high surface
area. In summary, we show that careful design of the initial composition and thermal
treatment leads to unique macro- and nano-structure in electrospun fibers.