Synchrotron X-ray Scattering and Reflectivity Studies on Topological Polymers and Polymeric Nanoparticles

Abstract

By synchrotron grazing incidence X-ray scattering and quantitative data analysis, crystalline characteristics of poly(ε-caprolactone) (PCL) in thin films were investigated. Particularly, topology effect (linear and cyclic) and molecular weight dependence were discussed in detail. Also, three types of polymer nanoparticle structures in solution were quantitatively studied and compared by small angle X-ray scattering, including highly branched single polymer nanoparticles (stars and dendrimers), self-assembled polymer micelle nanoparticles and synthetic anionic polystyrene nanoparticles. In Chapter II, higher equilibrium melting temperature of cyclic PCL compared with two types of linear PCLs was obtained by both linear and nonlinear Hoffman-Weeks analysis of isothermal crystallization experimental data. Grazing Incidence Small Angle and Wide Angle X-ray Scattering (GISAXS and GIWAXS) were employed to explore the morphology and crystalline characteristics in nanoscale thin films. Upon quantitative analysis of GISAXS data, detailed information of lamellar morphology in each PCL thin film was revealed. Cyclic PCLs were proved to have smaller long periods but greater crystal size than linear precursors. Molecular weight dependence of morphology features was also discussed for both linear and cyclic PCLs. GIWAXS data analysis provided the lattice parameters of orthorhombic lattice formed in each PCL thin film, and no significant difference was recognized for crystal lattice formed by linear and cyclic PCLs. Relative crystallinity was calculated through peak separation of crystalline and amorphous peaks appeared in circularly averaged WAXS data. By X-ray reflectivity analysis, cyclic PCLs were found to have a higher averaged electron density as well as higher electron density of each sublayers in the formed nanostructures. In Chapter III, single polymer nanoparticles of stars and dendrimers in solution were examined by synchrotron solution X-ray scattering, including three groups of homo star polymers PMMA, PMA and PnBA with same molecular weight but different number of arms, two groups of diblock star polymers s-(PMEA-b-PnBA)24 and s-(PnBA-b-PMEA)24, 4-generration dendrimer (PMMA-G4) and 5-generation dendrimer (PMMA-G5). Through quantitative data analysis, 3, 4, 6, 8, 12arm- star polymers were found to be ellipsoids rather than sphere with the degree of distortion strongly dependent on the topology (i.e., the number and length of the arm). 24arm- diblock star polymers quite approximate globular shape in solution. Two dendrimers greatly shifted away from a perfect sphere and appeared to be oblate ellipsoids in solution. The overall size, segmental dimension and radial density distribution features were quantitatively determined as well. Also, star polymers in thin film state were subjected to X-ray reflectivity analysis and electron density was obtained which reflected topology possesses both positive and negative effect on the dense packing of star polymers to form thin films. In Chapter IV, a series of block copolymers of various topologies (symmetric and asymmetric linear diblock and triblock, and star-shaped) were synthesized, and inverse micelles were successfully formed in hexane or hexane/THF cosolvents investigated by synchrotron solution X-ray scattering. Discriminated by topology, core-shell micelles, 4-, 8-, 10-layer “onion-like” micelles were discovered. Surprisingly, linear triblock copolymer D10M20D10 was able to form several nanostructures varied with changing volume ratio of hexane/THF cosolvent. Structures of all micelles were explained through quantitative analysis of X-ray scattering data. Effects of polymer topology on micelle size, structural characteristics, aggregation number, micelle stability as well as critical micellization concentration were discussed. In Chapter V, a group of anionic polymer nanoparticles with radius ranging from 19nm to 460nm were synthesized via soup free emulsion polymerization. DLS was conducted to determine hydrodynamic radii and polydispersities of these anionic particles. More comprehensive structure analysis was done by solution X-ray scattering, which provided quantitative data describing particle shape, size and radial density characteristics. X-ray scattering data were well fitted by a sphere model with local density fluctuation, which revealed that anionic particles were almost spherical in shape with locally fluctuated density inside the particles. Size distributions for each particle were also determined by model fitting and compared with DLS results. These particles were found to be close to monodisperse in size. In Chapter VI, Bacillus licheniformis α-amylase (BLA) in a biomimetic buffer and extrinsic solutions (various pH values, temperatures, and metal ions) has been investigated for the first time in the view of three-dimensional (3D) structure by synchrotron X-ray and dynamic light scattering analyses. BLA in buffer is determined to have a structure resembling its crystallographic structure; but the 3D structure is slightly larger than the crystal structure. Such a structure is maintained with little variations in extrinsic solutions of pH 4.09.7, temperature 455 C, and metal ions such as Ba2+, Mg2+, and Li+. These results collectively inform that BLA tends to favorably form a stable monomeric structure, which could provide structural clues to its enzymatic activities in moderate levels. Interestingly, BLA is found to reveal highly expanded structures at 6575 C and in Co2+ solution, which could correlate to the significantly pronounced enzymatic activities. However, BLA shows somewhat shrunken structures at pH 3.0 and in Hg2+ solution, supporting for the suppressed activities under these conditions.