**4. Concluding remarks**

distribution shown in **Figure 9**. The plot of the characteristic length scale *ξ* of the morphology versus the net time of curing clearly shows that *ξ* decreases with increasing curing (irradiation) time. This result is opposite to the conventional phase separation in the absence of shrink‐ age, that is, *ξ* increases as phase separation proceeds. Obviously, as curing time increases, the characteristic length scale gradually decreases and finally reaches a stationary value, indicating the termination of the phase separation process. From the results obtained by Mach‐Zehnder interferometry, the elastic strain defined as (Δ*d*/*d*) was calculated and its dependence on cur‐ ing time was examined. It was found that the elastic strain (Δ*d*/*d*) increases with increasing the irradiation intensity and significantly deviates from these decay curves when phase separation starts. The initial slope of the plot (Δ*d*/*d*) vs. irradiation time, that is (*τ<sup>i</sup>* = (d (Δ*d*/*d* ) )/*dt*) can be used as a measure of the characteristic time of shrinkage process induced by the curing

**Figure 9.** Laser scattering profile obtained for a PS/PVME (20/80) blend photo‐cross‐link by irradiation with 365 nm UV light. The data were recorded in situ under irradiation. The number in the figure indicates the curing time [21].

relation between the shrinkage obtained from Mach‐Zehnder interferometry and the evolution of morphology detected by light scattering, demonstrating again the effectiveness of the Mach‐

experiments [20]. The results also reveal the significant roles of Mach‐Zehnder interferometry

A clear correlation was observed between the apparent rate of the phase separation *<sup>k</sup> <sup>ξ</sup>*

from light scattering experiment and the apparent rate of shrinkage *<sup>k</sup> <sup>i</sup>*

in the kinetic studies on polymer phase separation.

can be defined as *ki* = (1/τ*<sup>i</sup>* ). **Figure 10** depicts the clear cor‐

obtained

obtained from MZI

reaction. The rate of shrinkage *k*<sup>i</sup>

Zehnder interferometry.

36 Optical Interferometry

For the applications in polymer research, Mach‐Zehnder interferometer (MZI) would be a simple instrument to in situ monitor the local deformation in the nanometer scales. The current MZI instrument can be improved in two aspects: accessibility to tempera‐ ture dependence measurements and improvement of signal‐to‐noise ratio to increase the data precision. The former requires some careful temperature controls of the experimen‐ tal environments around the sample and the MZI chamber. On the other hand, the later could be solved by introducing lock‐in detection of interference signals. These experiments are underway to prepare for the second generation of Mach‐Zehnder interferometry for research on photocuring of polymers.
