This Ph.D. thesis mainly focused on the investigation of phase transition behaviors of various polymer solutions; namely, 1) map phase diagrams by using a newly developed method that combines the micro-fluidic solution droplets and small angle laser light scattering; and 2) experimentally and computationally study on the morphological transformation of extruding-formed long cylindrical micelles.

Chapter 1 embraces the theoretical background of the subject, including a brief introduction of polymer solutions, the thermodynamics of polymer/solvent pairs, the significance in mapping diagrams of different polymer solutions, along with the classical Flory-Huggins theory, interpreting polymer/solvent mixtures on the scheme of lattice model. Following is a short review of the improvements on the polymer solution theory in the past decades, including theoretical results of polymer solution phase diagrams and the symmetrized method in processing the measured phase diagram data. Significance and difficulties in mapping a well-defined phase diagram of a polymer in a given solvent is explained by summarizing previous methods.

Chapter 2 is mainly divided into three parts: the first part is a very brief introduction of the basics of laser light scattering, theories of both statistic and dynamic measurements, and the laser light scattering device used in the current research; the second part illustrates the working principle of basics of microfluidic devices and explains its advantages and applications in various areas. We also detail how to combine a self-made micro-fluidic device and a small angle laser light scattering detector as well as the droplet preparations.

Chapter 3 first exhibits the validity of such a combined method; and then elaborate our results in mapping the coexistence curves of three polymer/solvent pairs: poly(vinyl acetate)/benzene, poly(vinyl acetate)/isobutanol, polystyrene/cyclohexane. Preliminary analysis is introduced and results are compared with deductions from Flory-Huggins theory and phase diagrams from other researchers. A detailed analysis in the symmetrizing method was performed and relevant parameters used are listed. The results indicate that symmetrized phase diagram can serve as a master curve for a given polymer and can be extended to different polymers by introducing other new parameters. Slight deviation of the scaling exponents from previous theory was observed and interpreted physically after a universal symmetrization of all the polymer solution system investigated.

Chapter 4 briefly introduced the morphological transformation of long cylindrical micelles formed in extrusion, focusing on the computer simulation and theoretical part. The long micelles broke into short segments without an external force, evidenced from the TEM and LLS tests. The mechanism of this process was investigated by the TEM morphology analysis and analyzed using three kinetic models involved in computer simulation. The results indicate that the kinetic process is dominated by a combination of two models, i.e., the Gaussian distribution and end-scission models and the underlying thermodynamic mechanism has been extensively illustrated.