Studies on Phase Separation of Poly(ethylene glycol)/Poly(ethylene glycol-ran-propylene glycol) Mixtures by Time-Resolved Small-Angle Light Scattering

• Main Authors: Di-Yao Hsu, 許迪堯
• Other Authors: Po-Da Hong
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/80688218540134114659

博士 === 國立臺灣科技大學 === 材料科學與工程系 === 104 === 　　During the past decades, many remarkable results have been achieved in the phase separation of polymer mixtures, especially for the spinodal decomposition, while the small-angle light scattering (SALS) plays an important role. In view of the improvement of scattering technique and subsequent data analysis, we have enough ability to study the complex phase separation behavior of PEG/PEG-ran-PPG polymer mixtures by using time-resolved small-angle light scattering apparatus. 　　In this study, since involving different area researches of phase separation, we will focus on the following topics: 　　(1) Thermodynamics and phase diagram of PEG/RAN mixture: in the temperature-traced turbidity experiments, the boundary of the phase separation can be approximation by the cloud point. However, in order to avoid the artificial distortion, we prefer to use the slice of τ-ϕ profile to analyze the “coexistence points”. Then, we use the Flory-Huggins lattice theory and melting point depression to calculate the coexistence, spinodal, and melting curves, respectively. On the other hand, time-traced peak position q_m is measured by using SALS, while the corresponding growth exponent α can define the kinetic transition to get percolation line. Here, we consider the reason why the percolation line is asymmetric with the diameter, and try to obtain an accurate phase diagram. 　　(2) Ultra-fast hydrodynamic coarsening in near-critical quench: we have mentioned that the growth exponent for the percolation region is higher than the hydrodynamic coarsening (α>1), which depending on the temperature, composition, and sample thickness; moreover, we also found the existence of double structures. Inasmuch as the wetting effect in our system, we consider the double structures are represented the structures of bulk and surface phases, respectively. However, the preliminary result shows that the prediction seems not to be correct, and these two structures are 3D growth. 　　(3) Validity of dynamic scaling hypothesis in off-critical quench: since the percolation spinodal decomposition (PSD) region is narrower than the spinodal region, it will inevitably heighten the importance of the droplet spinodal decomposition (DSD) region. In this chapter, we consider the validity of “dynamic scaling hypothesis”, that is, the structural evolution can be scaled by a single length parameter, in the process of DSD structural evolution; however, we believe that it does not hold here. There are several reasons, such as more than one length parameters, the formation of double structures, and the extinction effect of the scattered lights by large droplets (the so-called anomalous diffraction problem). Finally, we try to propose an alternative method to reduce the structure factor of DSD structure, and also superimpose the ultra-wide q-range scattering profiles. We hope to develop an exact scattering modeling for a quantitative analysis of the DSD structure in the future.