Thin polymer films of block copolymers and blend/nanoparticle composites

In this thesis, atomic force microscopy (AFM), transmission electron microscopy (TEM) and optical microscopy techniques were used to investigate systematically the self-assembled nanostructure behaviour of two different types of spin-cast polymer thin films: poly(isoprene-b-ethylene oxide), PI-b-PEO diblock copolymers and [poly(9,9-dioctylfluorene-co-benzothiadiazole)]:poly[9,9- dioctyfluorene-co-N-(4-butylphenyl)-diphenylamine], F8BT:TFB conjugated polymer blends. In the particular case of the polymer blend thin films, the morphology of their composites with cadmium selenide (CdSe) quantum dot (QD) nanoparticles was also investigated. For the diblock copolymer thin films, the behaviour of the nanostructures formed and the wetting behaviour on mica, varying the volume fraction of the PEO block (fPEO) and the average film thickness was explored. For the polymer blend films, the effect of the F8BT/TFB blend ratio (per weight), spin-coating parameters and solution concentration on the phase-separated nanodomains was investigated. The influence of the quantum dots on the phase separation when these were embedded in the F8BT:TFB thin films was also examined. It was found that in the case of PI-b-PEO copolymer thin films, robust nanostructures, which remained unchanged after heating/annealing and/or ageing, were obtained immediately after spin coating on hydrophilic mica substrates from aqueous solutions. The competition and coupling of the PEO crystallisation and the phase separation between the PEO and PI blocks determined the ultimate morphology of the thin films. Due to the great biocompatible properties of the PEO block (protein resistance), robust PEO-based nanostructures find important applications in the development of micro/nano patterns for biological and biomedical applications. It was also found that sub-micrometre length-scale phase-separated domains were formed in F8BT:TFB spin cast thin films. The nanophase-separated domains of F8BT-rich and TFB-rich areas were close to one order of magnitude smaller (in the lateral direction) than those reported in the literature. When the quantum dot nanoparticles were added to the blend thin films, it was found that the QDs prefer to lie in the F8BT areas alone. Furthermore, adding quantum dots to the system, purer F8BT and TFB nano-phase separated domains were obtained. Conjugated polymer blend thin films are excellent candidates for alternatives to the inorganic semiconductor materials for use in applications such as light emitting diodes and photovoltaic cells, mainly due to the ease of processing, low-cost fabrication and mechanical flexibility. The rather limited optoelectronic efficiency of the organic thin films can be significantly improved by adding inorganic semiconducting nanoparticles

Thermomechanical Properties of Virgin and Recycled Polypropylene—High-Density Polyethylene Blends

This paper provides evidence and discusses the variability in the thermomechanical behaviour of virgin and recycled polypropylene/high-density polyethylene blends without the addition of other components, which is sparse in the literature. Understanding the performance variability in recycled polymer blends is of critical importance in order to facilitate the re-entering of recycled materials to the consumer market and, thus, contribute towards a circular economy. This is an area that requires further research due to the inhomogeneity of recycled materials. Therefore, the thermal and mechanical properties of virgin and recycled polypropylene/high-density polyethylene blends were investigated systematically. Differential scanning calorimetry concludes that both the recycled and virgin blends are immiscible. Generally, recycled blends have lower overall crystallinity and melting temperatures compared with virgin blends while, remarkably, their crystallisation temperatures are compared favourably. Dynamical mechanical analysis showed little variation in the storage modulus of recycled and virgin blends. However, the alpha and beta relaxation temperatures are lower in recycled blends due to structural deterioration. Deterioration in the thermal and mechanical properties of recycled blends is thought to be caused by the presence of contaminants and structural degradation during reprocessing, resulting in shorter polymeric chains and the formation of imperfect crystallites. The tensile properties of recycled blends are also affected by the recycling process. The Young’s modulus and yield strength of the recycled blends are inferior to those of virgin blends due to the deterioration during the recycling process. However, the elongation at break of the recycled blends is higher compared with the virgin blends, possibly due to the plasticity effect of the low-molecular-weight chain fragments

Phase change and complex phenomena in drops and bubbles of pure and binary fluids

Evaporation, wetting and multiphase flows of drops and bubbles are everyday life phenomena with potential impact in many industrial, biological, medical or engineering applications. The understanding and controlling of the physical and chemical mechanisms governing these phenomena have become of paramount importance. This thesis encompasses three topics: evaporation of sessile droplets of polymer solutions, the role of thermocapillarity on self-rewetting fluid dynamics and migration of bubbles in liquid flows. Firstly, the evaporative behaviour of sessile droplets of aqueous polymer solutions and the effect of different molecular weights on the drying process has been studied. Drop shape analysis allowed monitoring the evolution of all stages during drying and indicating the transitions between stages. The mechanisms taking place during the crucial stages of pinning and depinning were illustrated, revealing the effects of adhesion and contact line friction forces on the final morphology of the dried polymeric deposits. Additionally, the effect of varying substrates from hydrophilic to hydrophobic was examined demonstrating the importance of interfacial interaction phenomena. The initial spreading dynamics of binary alcohol mixtures (and pure liquids) deposited on different substrates in partially wetting situations, under non-isothermal conditions was systematically investigated. Moreover, the temporal and spatial thermal dynamics within pure droplets and alcohol mixtures using IR thermography revealed the existence of characteristic thermal patterns due to thermal and/or solutal instabilities. The contribution of the Marangoni effect as an important heat transport mechanism within the evaporating droplets was investigated. The motion of buoyancy-driven bubbles in a vertical microchannel and the significant role of thermocapillarity was reported in this series of experiments. The behaviour of the bubbles in self-rewetting fluid flows departed considerably from that of pure liquids flows. Furthermore, heat transfer coefficient calculations in the single and two phase flows demonstrated that the presence of Marangoni (surface tension) stresses resulted in the enhancement of the heat transfer distribution in the self-rewetting fluid flows compared with the pure ones

Study of a novel methodology and tool for the support of the systematic production of educational material for modern e-learning systems.

128 σ.Η εν λόγω διπλωματική εργασία επικεντρώνεται στη μελέτη μιας νέας μεθοδολογίας και τον προσδιορισμό ενός σχετικού, εύχρηστου υπολογιστικού εργαλείου για την υποστήριξη της συστηματικής παραγωγής εκπαιδευτικού υλικού και, γενικότερα, την υποστήριξη της διαδικασίας μεταφοράς γνώσης. Η μεθοδολογία αυτή στηρίζεται στον τρόπο που οργανώνει στο μυαλό του τη γνώση οποιοσδήποτε πεπειραμένος και αποτελεσματικός εκπαιδευτικός, δηλαδή τον προσδιορισμό ενδιάμεσων στόχων ή βημάτων, τα οποία αυτός προσδιορίζει με τρόπο κατάλληλο, ώστε να καταστήσει ευκολότερη τη λήψη της πληροφορίας από το ακροατήριό του. Στη μεθοδολογία αυτή βασίζεται και το προτεινόμενο υπολογιστικό εργαλείο, το οποίο με χρήση κατάλληλων γραφικών στοιχείων, εύκολα κατανοήσιμων από το ανθρώπινο μυαλό και εκμεταλλεύσιμων από αυτό, επιτρέπει την αποτελεσματική οπτικοποίηση της παράστασης των ενδιάμεσων στόχων ή βημάτων και της σχετικής πληροφορίας που πρέπει να δοθεί προς το ακροατήριο. Ιδιαίτερο βάρος δόθηκε στον προσδιορισμό ενός πρώτου συνόλου κατάλληλων προδιαγραφών του υπολογιστικού εργαλείου. Το εργαλείο αυτό βασίζεται στην αξιοποίηση διαγραμμάτων (ένα για κάθε προς εξέταση ζήτημα), τα οποία παρέχουν την πληροφορία των σημειώσεων του εκάστοτε ζητήματος. Αυτά τα διαγράμματα χρησιμοποιούν «αναδρομικά μπλοκ» (recursive modules) περιγραφής πληροφορίας και ειδικές δομές χρονισμού, για την εκτέλεση σειριακών κλάδων διαδικασιών (παροχής πληροφορίας), αλλά και για την υπό συνθήκη εκτέλεση παράλληλων διαδικασιών. Η επιλογή εκτέλεσης μίας εκ των παράλληλων διαδικασιών γίνεται με βάση την προτεραιότητα των αντίστοιχων πληροφοριών, ή/και την βαρύτητα αυτών, ή/και τη χρονική διάρκεια που απαιτείται για την παροχή της αντίστοιχης γνώσης, ή/και το προφίλ γνώσεων του στοχευόμενου ακροατηρίου. Διερευνήθηκαν, λοιπόν, οι πληροφοριακές δομές καθώς και το περιεχόμενο αυτών, που απαιτούνται για την υλοποίηση ενός τέτοιου υπολογιστικού εργαλείου. Η μελετηθείσα μεθοδολογία και το σχετικό υπολογιστικό εργαλείο που θα βασίζεται στις προσδιορισθείσες σε αυτή την εργασία προδιαγραφές, ευελπιστούμε ότι μπορεί να βρει ευρεία εφαρμογή σε συστήματα ηλεκτρονικής εκπαίδευσης, έτσι ώστε να διευκολύνει τους καθηγητές στην οργάνωση της διαδικασίας μετάδοσης της γνώσης καθώς και στην παροχή ποιοτικών και φιλικών προς το χρήστη μαθημάτων e-learning.This diploma thesis focused on the study of a new methodology and the development of a relevant, easy to use computational tool for the support of the systematic production of educational material and, generally, the support of the process of knowledge transfer. This methodology is based on the way that any experienced and effective educator organizes knowledge in his mind, in order to convey this knowledge to its audience: Basically, he determines a necessary number of intermediate “knowledge targets” or “knowledge steps”, the succession of which makes it easier for the audience to gradually accept the corresponding knowledge. For each new knowledge target, he designs the necessary educational material in such a way, so that the audience can easily reach the corresponding knowledge level. This methodology has also been used as the base of a novel computational tool, which would make use of graphical elements easily understandable and exploitable by the human mind, in order to enable the efficient visualization of both the intermediate knowledge targets, and the relevant information that should be provided to the audience. Particular emphasis was given to identifying a first set of appropriate standards of this computational tool. The knowledge and the gradual release of the necessary information to the audience will be presented in the form of suitably designed diagrams, will make use of recursive information modules and specific timing structures for effectively representing the flow of information to the audience. Furthermore they will support the conditional execution of alternative or additional processes, depending on the priority and the significance of the information, the time required for the target audience to accept this knowledge and the knowledge profile of the target audience. The informational structures required for the creation of this tool, and their content has been investigated. The proposed methodology and the relevant computational tool, which will be based on the specifications identified in this paper, can hopefully find wide application in e-learning systems, by facilitating the teacher to organize the transfer of knowledge and ultimately provide high quality and user friendly e-learning courses to his audience.Μιχαήλ Καλλούδη

Drop-casting hydrogels at a liquid interface: the case of hydrophobic dipeptides

Hydrophobic dipeptide molecules have been induced to self-assemble into thin interfacial films at the air–water interface via drop-casting. The mechanism involves fiberlike strands, which exist in the high-pH spreading solvent, becoming intertwined at the surface of a low-pH subphase. Atomic force microscopy (AFM) reveals that the strands are ∼40 nm wide and ∼20 nm high and are woven together to form layers that can be up to ∼800 nm thick. The use of Thioflavin T (ThT) fluorescence suggests that the dipeptides are ordered in a β-sheet configuration irrespective of whether they form an interfacial film, while Fourier transform infrared spectroscopy (FTIR) shows the protonation effect for those which do form an interfacial film. The entanglement between protonated strands results in the formation of an elastic sheet. The interfacial films buckled under compression in a Langmuir trough and have the ability to convey long-term stability to large air bubbles

Thin Films of Poly(isoprene‑<i>b</i>‑ethylene Oxide) Diblock Copolymers on Mica: An Atomic Force Microscopy Study

The structural behavior of three amphiphilic semicrystalline poly­(isoprene-<i>b</i>-ethylene oxide) block copolymers (PI-<i>b</i>-PEO) with different PEO volume fraction (<i>f</i>_PEO = 0.32, 0.49, and 0.66), spin-coated on freshly cleaved mica surfaces from aqueous solutions, was investigated by atomic force microscopy. We focus on the dependence of the resulting thin film nanostructures on the molecular characteristics (<i>f</i>_PEO and molecular weight) and the adsorbed amount. The nanostructures obtained immediately after spin-coating were robust and remained unchanged after annealing and/or aging. The PEO affinity for the highly hydrophilic mica and the tendency of the hydrophobic and low surface energy PI to dewet and be at the free interface caused the soft PI-<i>b</i>-PEO micelles to collapse leading to the formation of 2D dendritic networks over mica. We show that, for all three polymers, the dendritic monolayer thickness can be predicted by a model consisting of a PEO crystallized layer (directly on top of mica) of the same thickness in all cases and a PI brush layer on top. In thicker areas, polymer material self-assembled into conelike multilamellar bilayers on top of the monolayer and oriented parallel to the substrate for both symmetric and asymmetric diblock copolymers with the lowest <i>f</i>_PEO. We compare the lateral morphology of the films and discuss the thickness heterogeneity, which results from the coupling and competition of crystallization kinetics, phase separation, and wetting/dewetting phenomena highlighting the role of the two blocks to inhibit or enhance certain morphologies. We show that the deviation of the <i>f</i>_PEO = 0.32 thin film from its bulk phase structure (cylinders in hexagonal lattice) continues for several lamellar bilayers away from the substrate. For the asymmetric PI-<i>b</i>-PEO polymer with the higher PEO volume fraction (<i>f</i>_PEO = 0.66) and higher APT, laterally extensive stacks of flat-on lamellar crystallites formed on the surface demonstrating the crucial role of the PEO crystallization