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Joao Paulo Cosas Fernandes

Co-localized AFM/Raman characterization of multiphase polymer systems

Published on 16 November 2017
Thesis presented November 16, 2017

The comprehension of the intrinsic characteristics and interactions found in complex polymeric systems is important and challenging for the development of new engineering solutions. In order to elucidate the process-structure-properties interplays, the co-localization of different information becomes essential, to obtain reliable answers. The characterization of both the surface and the bulk of materials is also of prime importance, especially for thin polymeric materials (<100 µm) such as membranes, which can present contrasted properties profiles throughout their thickness. To do so, the material must be properly opened with no structural, chemical and morphological modifications. Therefore, the main objective of this thesis was to develop an experimental methodology of characterization allying the co-localization of morphological, nanomechanical and chemical information using a special setup combining Atomic Force Microscopy and Confocal Raman Microspectroscopy to study cross-sections of cryo-ultramicrotomed samples.We applied the developed strategy to three different polymer systems: 1) blends of Polyamide 6 (PA6) and Acrylonitrile-Butadiene-Styrene (ABS), compatibilized with a Styrene-Acrylonitrile grafted with Maleic Anhydride (SAN-MA); 2) hybrid membranes of sulfonated polyether-etherketone (sPEEK) with active networks prepared by Sol-Gel (SG) chemistry; 3) block copolymers based on PS-PEO-PS used as polymer electrolyte membranes. The first study was focused on the impact of the compatibilizer and the mixing protocols on the morphology of an immiscible PA6/ABS blend. Co-localized AFM/Raman established that the addition of the SAN-MA copolymer, at different steps of the blending, favors the formation of the PA6 γ polymorph with amounts and distribution depending on the blending protocols. The different resulting morphologies were found to impact the blends’ rheological properties. The second study focused on the fabrication of hybrid sPEEK/SG membranes for Fuel Cell based on two different SG precursors. The main goal of this study was to qualify the impact of each step of fabrication on the membranes’ physical, nanomechanical and chemical properties, as well as their stability over time. Quantitative nano-mechanical (AFM) and chemical analysis (Raman) of the SG phase revealed its evolution throughout the fabrication process, confirming the efficiency of the applied thermal treatments. For membranes based on (3-mercaptopropyl)-trimethoxysilane SG precursor, it has been shown that the SG phase presents a hierarchically organized system, composed of elementary particles which aggregate into the round shape domains. The presence of SG phase inside the membrane (AFM/Raman) conserves the hydrophobic/hydrophilic nanophase separation of the host sPEEK, but the increasing SG uptake limits the swelling of the host membrane, which can affect its proton conductivity. Finally, the third study was focused on the morphological analysis of a series of triblock copolymers, used as polymer electrolytes in batteries. Their nanomechanical heterogeneities allowed the measurement of the inter-domain distances between the PS and PEO phases directly from the AFM images which were correlated to Small Angle X-Ray Scattering (SAXS) measurements. It has been shown that the material’s surface nanomechanical properties evolve from the dry state to the equilibrium with the room relative humidity.To summarize, the development of the characterization methodology allying co-localized AFM/Raman with multiple complementary techniques allowed for the study of different complex polymeric systems for a variety of applications. In each of the three studies of this thesis, the co-localization and multi-technique strategy provided precious information that could not be accessed by other means. This could only be possible by the adaptation of cryo-ultramicrotomy for sample preparation, especially for thin polymer membranes and water sensitive samples.

Characterization, Electron Microscopy, Afm, Raman, Membrane, Cryo-Ultramicrotomy

On-line thesis.