130 V. Bazargan and B. Stoeber
Figure 6.10. Experimental setup for the demonstration of passive ﬂow control using
thermally responsive Pluronic solutions at constant ﬂow rate in microchannels. For color
reference, see page 268.
syringe pump with ﬂexible polymer tubing, and a gauge pressure sensor was
attached between the syringe pump and the microchannel as shown in Fig. 6.10.
The ﬂuid drained from the channel through a piece of tubing to atmosphere.
The gauge pressure recorded therefore corresponded to the pressure along the
microchannel, neglecting the pressure drop along the wide ﬂexible tubing on either
end of the microchannel. The microchannel was submerged in a temperature-
controlled water bath to achieve well-deﬁned temperature conditions.
A 13 wt% Pluronic F127 solution was pumped through the microchannel at
aﬂowrateQ =0.5μL/min using a syringe pump. The device temperature was
maintained at 27
C with the temperature-controlled water bath, which is well
below the gel formation temperature of 31
C of the Pluronic solution. After
initiating the ﬂow, the pressure along the channel reached a constant value as
shown in Fig. 6.11. The pressure then increased, ﬁrst slowly, and then more rapidly
at a nearly constant rate. After holding ice against the device, the pressure rapidly
Figure 6.11. Pressure recorded along a 10 mm long microchannel with rectangular cross
section (150 μm × 100 μm) for a 13 wt% Pluronic F127 solution at 27
channel at a ﬂow rate 0.5 μL/min. At around 34 minutes, ice was held against the device to
lower its temperature.
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