Nondestructive testing of defects in adhesive joints

polymers with ceramic fillers have lower melting
points in a close range of 153.4, 153.8 and 154.9
ºC for membranes with BaTiO3, SiO2 and Al2O3,
respectively. The small change in the melting
points of the composite membranes probably
results from the orientation of the polymer
chains along the fiber axis when drawn into the
fibers rather than the interactions of the ceramic
nanoparticles with the polymer. The %
crystallinity values obtained from the DSC data
follows the order BaTiO3 (47.1%) < SiO2 (47.9)
< Al2O3 (49.2) < membrane without filler
(74.5%) [8]. The mechanical properties of the
membranes (based on the estimated values at the
failure of the samples) are given in Table 1.
endo
Heat flow
4
2
0
-2
-4
153.4 °C
153.8 °C
154.9 °C
49.35 J/g
50.15 J/g
51.54 J/g
80 100 120 140 160 180 200 220
Temperature (°C)
Fig. 2. Thermal properties (DSC) of electrospun
P(VdF-HFP) membranes with 6% (a) Al2O3, (b) SiO2
and (c) BaTiO3.
3.3. Porosity, electrolyte uptake and electrolyte
retention
The results of porosity determination by nbutanol
uptake method are presented in Table 1.
The porosity varies in the narrow range of 84-
87% for the membranes, showing a slightly
increasing trend with the filler content in the
order BaTiO3 > SiO2 = Al2O3 > membrane
without filler.
Fig. 3 presents a comparison of the
electrolyte uptake (1M LiPF6 in EC/DMC) of the
membranes and the maximum uptake value of
each membrane is also presented in Table 1. The
fully interconnected pore structure of these
membranes helps fast liquid penetration into the
membrane, and hence the uptake process gets
(c)
(b)
(a)
- 3 -
stabilized within a span of only 10 min. The
relative absorption ratio (R) of the NCPEs and
the PE without filler are presented in Fig. 3. It
was seen that the electrolyte leakage reaches an
equilibrium state within 1 h and all the PEs
exhibit a high retention of the electrolyte with a
cumulative leakage ∼ 11% and ∼ 14% after 1 h,
respectively, in the case of the NCPEs and the
PE without filler.
Electrolyte uptake (%)
450
375
300
225
150
75
0
Relative absorption ratio (R)
1.00
0.95
0.90
0.85
0.80
0.75
0.70
No filler
Al 2 O 3
0 20 40 60 80 100 120
Time (min)
0 10 20 30 40 50 60
SiO 2
BaTiO 3
Wetting time (min)
Fig. 3. Electrolyte uptake (%) of electrospun P(VdF-
HFP) membranes with different ceramic fillers
(liquid electrolyte: 1M LiPF6 in EC/DMC).
3.4. Ionic transport properties
The ionic conductivity of the NCPEs at 25 ºC
varies in the order BaTiO3 > SiO2 > Al2O3 > PE
without filler. The higher ionic conductivity
results from the interactions of O/OH groups on
the filler surface and the large amorphous phase
of the polymer [9]. And also the well knit porous
structure of the membranes is one factor that
facilitates the diffusion of the ions, hence high
ionic conductivity was observed even for the PE
without filler.
The tortuosity values calculated from the
porosity and the ionic conductivity are listed in
Table 1. As is evident from Table 1, the
tortuosity of P(VdF-HFP) membranes with
ceramic fillers decreases as a consequence of the
nature of the filler, and follows the reverse order
as is observed for the porosity of the membranes.
These results are in agreement with those
reported by Abraham et al. [6]. Song et al. also