a) b - École Polytechnique de Montréal

substantially reduced pore sizes, and annealing of the multi-component is used to increase the
phase sizes of porous material. It has been observed that for a constant void volume, a range of
pore diameters from 0.9 to 72 μm can be obtained(Sarazin & Favis, 2003).
2.1.3.1.1 Coarsening of Binary and Ternary Polymeric Systems
In some works, large porous media are needed for facilitating penetration of the solution through
the empty interconnected network of a porous substrate. In order to perform controlled
annealing, the sample must be in contact with hot press surfaces for a certain time. In this case, a
temperature gradient, which is defined as the change in temperature over the change in distance
from hot surfaces, is present throughout the samples. At each point in the sample (x,y,z) in time
t, the temperature is T(z,t). By increasing temperature, the magnitude of gradient rises and T
equals T(z,t) until it reaches the set temperature. At this point the gradient is no longer a function
of time and just changes in height. It is concluded that for thick samples(larger than 0.5cm
thickness), the annealing method is not a suitable technique to fabricate porous substrates with
uniform pore sizes.
In a detailed work about annealing of immiscible co-continuous blends, Zhenhua et al.(Zhenhua
Yuan, 2005) proposed that the driving force for the coarsening process during static annealing is
a capillary pressure effect. Siggia(Siggia, 1979) explained that although capillary pressure is
proportional to the interfacial tension, it is inversely proportional to the rod thickness. It was
described that in a blend, thin part structures with small cross-sections generate capillary forces
larger than thick parts with large cross-sections. It demonstrates a force gradient from thin parts
to thick parts and a continuous merging of thin parts toward the thick ones resulted from the
difference in capillary pressure throughout the co-continuous structure (Figure 2-14).
Hence, there are a lot of thin rods or branches attached to thick rods which continuously feed
them. Important factors in coarsening were reported as temperature and time of the annealing,
interfacial tension, and zero shear viscosity of components. Increasing the time and temperature
of annealing results in increasing the droplet motions and coalescence of droplets, which leads to
average domain size growth and also size distribution growth(Willemse, Ramaker, van Dam, &
38