Three different segmented copolymer systems: (a) amorphous (b) semi-crystalline and (c) liquid crystalline polymers were selected for surface composition study using x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The amorphous polymer was poly(ethersulfone) which has different numbers of low-surface-energy CF₂ units in the backbone. The semi-crystalline polymer was monodisperse bromine-terminated poly(bisphenol-A etheroctane) (BA-C8)_n with n = 3 and 5. (BA-C8)₃ formed both chain-extended and chain-folded lamellar structures. The wide-angle x-ray scattering spectra indicated that their crystal lattices were similar. The last one was a linear copolymer of fluorocarbons and hydrocarbons [(CF₂)_n-(CH₂)_m] with well-defined lengths of CF...[ Read more ]

Three different segmented copolymer systems: (a) amorphous (b) semi-crystalline and (c) liquid crystalline polymers were selected for surface composition study using x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The amorphous polymer was poly(ethersulfone) which has different numbers of low-surface-energy CF₂ units in the backbone. The semi-crystalline polymer was monodisperse bromine-terminated poly(bisphenol-A etheroctane) (BA-C8)_n with n = 3 and 5. (BA-C8)₃ formed both chain-extended and chain-folded lamellar structures. The wide-angle x-ray scattering spectra indicated that their crystal lattices were similar. The last one was a linear copolymer of fluorocarbons and hydrocarbons [(CF₂)_n-(CH₂)_m] with well-defined lengths of CF₂ and CH₂ units. Thermal analysis exhibited multiple first order transitions revealing its liquid crystalline property.

Results from the surface studies showed that the surface energy difference between the components and the segment length of the low-surface-energy segment are the two key parameters controlling the surface segregation in the amorphous polymers. In the semi-crystalline polymers, the crystallizable components are transported into the crystalline core of the lamellae while the non-crystallized components including the end groups, the fold turns and cilia are expelled to the fold surfaces. The segregation on the fold surfaces is related to the lamellar thickness governed by the crystallization temperature and the molecular weight of the polymers. Surface segregation of semi-crystalline polymers is a balance between the interfacial energies of the lamellae and the free energy change due to the melt to crystal transition. Similarly in the liquid crystalline polymers, the ordering of rod-like mesogens (fluorocarbons) near the surface induces placement of the anchoring segments (hydrocarbons) at the air-polymer interfaces notwithstanding their surface energy difference. The extent of surface segregation is related to the alignment of the mesogens with respect to the surface normal which also depends on the ratio of the length of the fluorocarbon and hydrocarbon segments.