Tesi di Dottorato

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Author: search.filters.author.Cipparrone, GabriellaSubject: search.filters.subject.Polimeri

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    Study of physical, mechanical and transport properties of polymeric membranes for gas separation
    (Università della Calabria, 2022-01-31) Longo, Mariagiulia; Cipparrone, Gabriella; Giorno, Lidietta; Carolus Jansen, Johannes
    The work in this thesis is organised in different main topics. The first part is devoted to present Atomic Force Microscopy (AFM), carried out in force spectroscopy mode, as a powerful alternative to the more commonly used tensile tests for the analysis of the mechanical properties of polymers, and MMMs in particular. AFM force spectroscopy measurements are carried out with nanometric and micrometric tips on dense membranes of neat Pebax®1657 and on mixed matrix membranes of Pebax®1657 with different concentrations of an ionic liquid. This offers good perspectives for the analysis of samples where traditional tensile tests cannot be used, for instance composite membranes or particularly small samples. The second part of the research is focused on the relationship, between the transport properties and Young’s modulus for films of polymers of intrinsic microporosity (PIM) and on the effect of physical aging, investigated using pure gas permeability and atomic force microscopy (AFM) measurements in force spectroscopy mode. In the third part, the transport properties of polymer blend membranes are evaluated. In the last part, using a computational approach, it is possible to predict missing values for permeability starting with a collection of existing permeability values for other polymers. The data are estimated by means of machine learning models that correlate the behaviour of different gases. Thus, this thesis is structured as follows: Chapter 1 and Chapter 2 provide a general introduction on membrane technology and characterization methods used in this thesis, as well as the theoretical background and the description of all experimental techniques used; Chapter 3 describes the mechanical study on MMMs of blends of Pebax® and the ionic liquid ([BMIM][BF4]); Chapter 4 describes mechanical and gas transport studies on PIMs; Chapter 5 presents the gas transport analysis on Matrimid®5218/AO-PIM blend membranes; Chapter 6 discusses the results of the machine learning model. Chapter 7 presents the overall conclusions of the work and gives a brief future outlook of possible and desired developments in the field.
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    Polarization holographic recording in polymeric and liquid crystalline materials
    (2006) Provenzano, Clementina; Cipparrone, Gabriella; Longeri, Marcello
    Optical studies related to polarization holographic recording in photosensitive materials, as azo compounds, liquid crystals and polymeric mixtures, and dye doped polymers, were carried out. The interest in this type of holographic recording is due to the improved signal to noise ratio and the possibilities for image and signal processing, optical switch, beam steering, optical polarizers and selective erasure. We focused our investigation on the mechanisms that can possibly induce diffraction gratings in these different types of photosensitive materials, on the peculiarities of the achieved diffractive devices and on their possible applications. In particular we investigated the effects of polarization holography on azo-dye Langmuir-Blodgett films, on polymer dispersed liquid crystal (PDLC), and on liquid crystal films confined by dye-doped polymers aligning layers. In the first system, conventionally used for polarization holographic recording, we investigated the influence of the particular Langmuir-Blodgett deposition technique on the features of the recorded structures in order to obtain pure polarization gratings. The absence of surface reliefs gratings (SRG), the stability of the recorded devices and the high induced birefringence of the selected material, open up the possibility of interesting applications. In particular, we report the design and the implementation of a photopolarimeter for simultaneous measurements of Stokes parameters of light, in which the basic element is the actual polarization grating. PDLC is a non conventional system for polarization holographic recording, because no azocompounds are present in the polymeric and liquid crystalline mixtures. Polarization holographic storage produces diffraction gratings that originate mainly from the liquid crystal alignment inside the droplets of the solid polymeric matrix, created during the polymerization and phase separation processes. Polarization properties and electro-optical switching behaviour of the gratings are studied. We also report the unexpected observation of SRG in a system without azo compound, where photoisomerization and chromophore reorientation processes do not occur. In the last systems, we exploit a new method for spatially varying liquid-crystal alignment using patterned surfaces obtained by means of a polarization holographic exposure on a dye-doped polyimide. This idea is based on the fact that holographic gratings on some photosensitive material provide a periodic alignment of the nematic liquid crystals. In fact, putting in contact a Polarization holographic recording in polymeric and liquid crystalline materials ii thin film of liquid crystal with the aligning layers, we obtain a replica-grating in the bulk with the same properties of the gratings recorded on photosensitive layers. We describe the high flexibility of these replica-gratings, related to the control of the diffraction efficiency by means of an external electric field, and the very singular properties of the polarization states of the beams diffracted from this device. We also obtain two dimensional (2D) gratings consisting of a 2D array of differently twisted structures of nematic liquid crystal, achieved by a crossed assembling of polarization holograms recorded at the surfaces of the aligning substrates. These devices diffract the incident beam in several diffracted beams with various polarization states at the same time. The energy distribution can be controlled by means of the polarization state of the incident beam. Additionally, the distribution of the intensity on the diffracted beams can be completely controlled by means of a low external applied voltage. These features make the optical devices very interesting for beam steering, beam shaping and other modifications of light intensity or phase.