3.2 Characterization of membrane.
The surface and cross section morphology of membranes were observed
using a field-emission scanning electron microscope (FE-SEM, NOVA
NanoSEM 450, FEI, USA). The surface roughness was measured with an
atomic force microscope (AFM; Dimension ICON, Bruker, USA). The porosity
of the membranes was determined by means of the software called Image
Pro Plus. Solution contact angle (CA) of membrane was evaluated using
the JC2000D machine (POWEREACH®, Shanghai zhongchen,
China). The thermal conductivity of the PTFE and the PES hollow fiber
membrane at different temperatures was measured using a thermal
conductivity meter (TC3200, XIATECH, China). Since the hydrophilicities
of the two membranes were different, the porosity of PTFE and PES hollow
fiber membrane were measured by density measurement and water absorption
measurement, respectively.
The microstructure of the two membranes are shown in Figure 2. PTFE
hollow fiber membrane is a microporous membrane with very small surface
porosity, which can be considered as a symmetric membrane with uniform
cross section structure. PES hollow fiber membrane does not have
apparent pore with nano scale on the surface and the cross section of
the membrane indicates its asymmetric structure with a thin skin layer.
The characteristics of the membrane and homemade membrane module are
listed in Table 1 and Table 2, respectively. Membrane modules with
different packaging density φ were assembled to evaluate their
nucleation inducing performance.