(695f) Effects of Fabrication Conditions on the Microstructures and Performances of Smart Gating Membranes with in Situ assembled Nanogels As Gates

ABSTRACT

Smart gating membranes
with in situ assembled poly(N-isopropylacrylamide) (PNIPAM) nanogels as gates are successfully prepared via vapor induced phase
separation (VIPS) with different exposure time periods, temperatures and
relative humidities of the water vapor.  Effects of the fabrication conditions on
the microstructures as well as the thermo-responsive and mechanical performances
of the membranes are investigated.  Both
the membrane microstructure and the movement of blended PNIPAM nanogels in the
membrane forming solution can be controlled by adjusting the fabrication conditions.  With increasing the exposure time, the membrane
microstructure undergoes a transition from typical liquid-induced phase separation (LIPS) structure (unsymmetrical
finger-like porous structure) to typical VIPS structure (symmetric
cellular-like porous structure).  The
critical time periods for the microstructure transition of membranes prepared with
vapor temperature and relative
humidity of 25 ºC/90%, 25 ºC/70%
and15 ºC/70%
are about 1.5
min, 2 min and 10 min respectively. 
The performances
of membranes are heavily dependent on the microstructures.  The membranes with unsymmetrical
finger-like porous structures show large thermo-responsive factor (R_39/20, the ratio of water flux at 39 ºC to that at 20
ºC), with
the maximum R_39/20 value
being 43.2.  All the membranes with symmetric cellular-like
porous
structures exhibit strong mechanical property and large water flux at 39
ºC, which is higher
than the volume phase transition temperature (VPTT) of PNIPAM nanogels.  The results provide valuable
guidance for rational design and fabrication of smart gating membranes with desirable performances.