Page 362 - Flexible Robotics in Medicine

354 Chapter 15

PEDOT:PSS was doped with 5 vol.% dimethyl sulfoxide (DMSO) and 0.75 wt.% xylitol, to
increase conductivity and plasticity. According to Ref. [7], DMSO can separate the PSS
from the conductive PEDOT. As such phase separation of PEDOT and PSS occur, leading
to an increase in the conductivity of PEDOT:PSS film. Meanwhile, xylitol can be added to
increase the plasticity of PEDOT:PSS by weakening the hydrogen bonds, as well as
increase conductivity by increasing the mobility of charge carriers [8]. Thus PEDOT:PSS
doped with DMSO and xylitol was used for the fabrication of films.

15.3.1 Electrical properties of PEDOT:PSS/xylitol/Fe 3 O 4 films

The Fe 3 O 4 NPs are capped to be hydrophilic. Hence, they can be dispersed homogeneously
in the PEDOT:PSS/xylitol solution. Hence, solutions with various weight ratios of PEDOT:
PSS/xylitol and Fe 3 O 4 NPs were prepared, and they were cast into films. Their film
thickness and the corresponding conductivities are shown in Table 15.1.

The PEDOT:PSS/Fe 3 O 4 films after the conductivity enhancements show a much higher
conductivity than the ones without the treatment. This is evidently reflected in the
experimental results displayed in Table 15.1 and Fig. 15.4. The thickness of the film is
maintained to be consistent, as that is determined by the quantity of the components in the
films. As the concentration of Fe 3 O 4 NPs within the solution increases, there seems to be a
decrease in conductivity [9]. It can be seen from Fig. 15.4 that there is an overall decrease in
conductivity as the ratio of Fe 3 O 4 NPs increases. This occurrence is due to the increasing
concentration of nonconductive Fe 3 O 4 NPs in the conductive PEDOT:PSS/xylitol matrix. As
such the conductivity is reduced. Also, as the ratio of PEDOT:PSS/xylitol and Fe 3 O 4 NPs
increase from 1:3 to 1:5, the NPs become increasingly challenging to disperse uniformly in
the PEDOT:PSS solution, which may result into the aggregation of NPs in the films.

15.3.2 Mechanical properties of PEDOT:PSS/xylitol/Fe 3 O 4 films

The 1:1 sample without DMSO and xylitol is stiffer and more brittle, while the 1:1 sample
with DMSO and xylitol is more ductile and softer supported by results in Table 15.2. This
indicates that the additives allow for better performance of the film as a flexible elastic film

Table 15.1: Thickness and conductivity of PEDOT:PSS/Fe 3 O 4 composite film.
Sample Thickness (µm) Conductivity (S/cm)
1:1 without DMSO and xyl 10.2 137.7
1:1 with DMSO and xyl 11.6 2571
1:2 with DMSO and xyl 10.9 2147
1:3 with DMSO and xyl 10.9 2014
1:4 with DMSO and xyl 11.1 1936
1:5 with DMSO and xyl 11.2 1583