Dipartimento di Fisica - Tesi di Dottorato

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Questa collezione raccoglie le Tesi di Dottorato afferenti al Dipartimento di Fisica dell'Università della Calabria.

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Subject: 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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    Strategies to control linear anisotropy and chirality in polymeric materials:from the basic issues to the micro-devices developments
    (2016-10-05) Lepera, Eugenia; Bartolino, Roberto; Versace, Carlo C.; Cipparrone, Gabriele
    The development of devices with increasing levels of functionality represents an important technological issue. To this aim, innovative materials with tunable functionalities play a crucial role. The challenge is to obtain multifunctional materials through simple procedures with high performance and low cost, and eventually external control parameters. Moreover the understanding of multifunctionality of materials is hence an exciting scientific opportunity. For these purpose, the main objectives of the present work have been to explore two main strategies. In the first one, azobenzene based materials and their light induced functionalities has been exploited to develop microdevices for polarimetric applications. Already know effects of linear and circular photoinduced optical anisotropies in azobenzene based polymers was investigated coupling the materials properties with holographic techniques, both to characterize the photoinduced properties of the materials and to develop diffractive devices useful for the above cited applications. The second topic is addressed towards the development of a materials science approach to build up polymeric matrices with controllable supramolecular chiral structures and subnanometric cavities. Both explored features are connected to intriguing topics as chirality and small size cavities. Their chirooptical properties and supramolecular structures suggest high potentiality for development of chiral sensors or filtration devices. Key words: micro-devices, azo-polymers, polarization holography, syndiotactic polystyrene, supramolecular chirality.
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    Characterization of thin transparent polymeric films obtained by plasma polymerization technique and their application to liquid crystal cells
    (2008-10-17) Nicastro, Gaetano; Scaramuzza, Nicola; Versace, Carlo
    The aim of this work Although liquid crystal displays (LCD) are quite ubiquitous in the modern world, there is still a great run for better and cheaper LCD. The main physical phenomenon that makes LCD as valuable consists in the particular way polarized light propagates through anisotropic media in general and liquid crystals in particular. Different from solid anisotropic media, the actual anisotropy of liquid crystals is imposed by surface interactions. The concepts of aligning layer and anchoring have been coined. Normally, a thin lightly dielectric polyimide film separates the liquid crystal from conducting transparent electrodes. An applied electric field between these electrodes can reorient the liquid crystal inside (the bulk) and change the transmittance of the cell. An electric field can rather easily do so such that the response time to the applied film, τon, is normally less than 1 ms. Switching off the field, liquid crystal relaxes to the initial state, the only “driving force” now, in the absence of the electric field, remains the anchoring of the liquid crystal to the surface. If this anchoring is not very strong the relaxation time, τoff, can be as large as seconds, a unsuitable value for practical purposes. Much stronger anchoring overwhelms this shortcut by the expense of using thin film transistors, difficult to insert and quite costly. Not long ago, a “fast switching response” has been observed using conducting polymers. [1] as aligning films. Conducting electro active polymers such as polypyrrole (PPyr), Polyaniline (PAn), polythiophene (PTh), or poly-o-anisidine (PoA) are complex dynamic structures that captivate the imagination of those involved in intelligent materials research [2]. Although promising response times, τoff 1. The chemical nature of the substance used, for instance polyaniline, or polypyrrole; , of 1-2 ms, even 0.5 ms, have been observed, the rate of defected samples is unacceptable high. Therefore, there is a strong incentive to carry on investigation in the field. There are many parameters that should be considered; among them we quote: 2. The way of inducing the polymerization process, either chemically, electrelectro-chemically, by DC or Rf plasma reactor; 3. the nature and number of doping or included ions; 4. Their mobility 5. Possible red-ox reactions at ITO/polymer and/or polymer/liquid crystal interfaces; 6. Thickness of the aligning films 7. Roughness or porosity of the film In this thesis we will present all the results obtained with these films about “the fast switching response”, a characterization study made with various instruments like SEM, AFM ecc. on these films and other measurements like current curves on the LC cells made with these films, all realized for better understand the properties of these films deposited via DC plasma polymerization
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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.