Studying dynamics of magnetization relaxation in excited magnetic materials is important both for understanding the rates and pathways of magnetization relaxation and for the potential use in spin-based electronics and data storage devices in the future. Previous studies have demonstrated that the size of nanocrystals is an important factor for energy relaxation in quantum dots and metal nanoparticles. Since magnetization relaxation is one of energy relaxation pathways, the size of nanocrystals may be also an important factor for magnetization relaxation in nanoscale magnetic materials. The goal of this study is to have a better understanding of magnetization relaxation in nanoscale magnetic materials. In particular, we focused on the correlation between the nanocrystal size and the rates of spin-lattice relaxation (SLR), a magnetization relaxation pathway, in magnetic nanocrystals. The size-dependent magnetization relaxation rate after optically induced demagnetization in colloidal Fe3O4 nanocrystals was measured by using time-resolved Faraday rotation (FR). Fe3O4 nanocrystals were chosen as the model system to study the correlation between the size of nanocrystals and the rates of SLR due to the wellestablished synthetic procedure of making nanocrystals with various sizes and narrow size dispersion. Faster SLR rates were observed in smaller Fe3O4 nanocrystals. The results suggested the surface of nanocrystals have higher efficiency of SLR than the interior region by using a simple model to analyze the SLR rates of Fe3O4 nanocrystals with various sizes. Higher efficiency of SLR at the surface may be due to the stronger spin-orbit coupling at the surface relative to the interior region. In addition to magnetization dynamics studies, the effect of oxidation on static FR in iron oxide nanocrystals (between Fe3O4 and y-Fe2O3) was studied. The results indicated FR signal is linearly correlated to the strength of optical transition between Fe2 and Fe3 in Fe3O4 for a given size of nanocrystals.

This thesis consists of two parts. The first part deals with the magnetic properties of Fe3O4 nanocrystals and their possible application in water remediation. The second part is on the delamination of layered materials and the preparation of new layered hybrids from the delaminated sheets. In recent years, nanoscale magnetic particles have attracted considerable attention because of their potential applications in industry, medicine and environmental remediation. The most commonly studied magnetic nanoparticles are metals, bimetals and metal oxides. Of these, magnetite, Fe3O4, nanoparticles have been the most intensively investigated as they are, non-toxic, stable and easy to synthesize. Magnetic properties of nanoparticles such as the saturation magnetization, coercivity and blocking temperature are influenced both by size and shape. Below a critical size magnetic particles can become single domain and above a critical temperature (T B , the blocking temperature) thermal fluctuations can induce random flipping of magnetic moments resulting in loss of magnetic order. At temperatures above the blocking temperature the particles are superparamagnetic. Magnetic nanocrystals of similar dimensions but with different shapes show variation in magnetic properties especially in the value of the blocking temperature, because of differences in the surface anisotropy contribution. The properties of magnetic nanoparticles are briefly reviewed in Chapter 1. The objective of the present study was to synthesize Fe3O4 nanocrystals of different morphologies, to understand the difference in magnetic properties associated with shape and to explore the possibility of using Fe3O4 nanocrystals in water remediation. In the present study, oleate capped magnetite (Fe3O4) nanocrystals of spherical and cubic morphologies of comparable dimensions (∼10nm) have been synthesized by thermal decomposition of FeOOH in high-boiling octadecene solvent (Chapter 2). The nanocrystals were characterized by XRD, TEM and XPS spectroscopy. The nanoparticles of different morphologies exhibit very different blocking temperatures. Cubic nanocrystals have a higher blocking temperature (T B = 190 K) as compared to spheres (T B = 142 K). From the shift in the hysteresis loop it is demonstrated that the higher blocking temperature is a consequence of exchange bias or exchange anisotropy that manifests when a ferromagnetic material is in physical contact with an antiferromagnetic material. In nanoparticles, the presence of an exchange bias field leads to higher blocking temperatures T B because of the magnetic exchange coupling induced at the interface between the ferromagnet and antiferromagnet. It is shown that in these iron oxide nanocrystals the exchange bias field originates from trace amounts of the antiferromagnet wustite, FeO, present along with the ferrimagnetic Fe3O4 phase. It is also shown that the higher FeO content in nanocrystals of cubic morphology is responsible for the larger exchange bias fields that in turn lead to a higher blocking temperature. Magnetic nanoparticles with moderate magnetization can be easily separated from dispersions by applying low intensity magnetic fields. Oleate capped spherical and cubic iron oxide nanocrystals have considerable magnetic moment and hence have the potential as host-carriers for magnetic separation in environmental remediation. These nanocrystals are, however, dispersible only in non-polar solvents like chloroform, toluene, etc. Environmental remediation requires that the nanocrystals be water dispersible. This was achieved by functionalizing the surface of the iron oxide nanocrystals by coordinating carboxymethyl-β-cyclodextrin (CMCD) cavities (Chapter 3). The hydroxyl groups located at the rim of the anchored cyclodextrin cavity renders the surface of the functionalized nanocrystal hydrophilic. The integrity of the anchored CMCD molecules are preserved on capping and their hydrophobic cavities available for host-guest chemistry. The CMCD capped iron oxide particles are water dispersible and separable in modest magnetic fields (<0.5 T). Small molecules like naphthalene and naphthol can be removed from aqueous media by forming inclusion complexes with the anchored cavities of the CMCD-Fe3O4 nanocrystals followed by separation of the nanocrystals by application of a magnetic field. The adsorption properties of the iron oxide surface towards arsenic ions are unaffected by the CMCD capping so it too can be simultaneously removed in the separation process. To extend the application of the iron oxide nanocrystals so that they can both capture and destroy organic contaminants present in water, cyclodextrin functionalized water dispersible core-shell Fe3O4@TiO2 (CMCD-Fe3O4@TiO2) nanocrystals have been synthesized (Chapter 4). The application of these particles for the photocatalytic degradation of endocrine disrupting chemicals (EDC), bisphenol A and dibutyl phthalate, in water is demonstrated. EDC molecules that may be present in water are captured by the CMCD-Fe3O4@TiO2 nanoparticles by inclusion within the anchored cavities. Once included they are photocatalytically destroyed by the TiO2 shell on UV light illumination. The magnetism associated with the crystalline Fe3O4 core allows for the magnetic separation of the particles from the aqueous dispersion once photocatalytic degradation is complete. An attractive feature of these ‘capture and destroy’ nanomaterials is that they may be completely removed from the dispersion and reused with little or no loss of catalytic activity. The second part of the thesis deals with the intercalation of surfactants in inorganic layered solids and their subsequent delamination of the functionalized solid in non-polar solvents. The solids investigated were - the anionic layered double hydroxides (LDH), the 2:1 smectite clay, montmorillonite (MMT), layered metal thiophosphates (CdPS3) and graphite oxide (GO). Layered Double Hydroxides (LDH) are lamellar solids of the general chemical formula [M0(1−x)Mx(OH)2], where M0 is a divalent metal ion and M a trivalent ion. The structure of the Mg-Al layered double hydroxide (Mg-Al LDH) may be derived from that of brucite, Mg(OH)2, by isomorphous substitution of a part of the Mg2+ by trivalent Al3+ ions with electrical neutrality maintained by interlamellar exchangeable ions like nitrate or carbonate. The ion exchange intercalation of the anionic surfactant dodecyl sulfate (DDS) in an Mg-Al LDH and the subsequent delamination of the surfactant intercalated LDH in non-polar solvent is reviewed in Chapter 5. Delamination results in a clear dispersion of neutral nanosheets. The delaminated sheets are neutral as the surfactant chains remain anchored to the inorganic sheet. On solvent evaporation, the sheets re-stack to give back the original surfactant intercalated solid. This strategy for delamination of layered solids by intercalation of an appropriate surfactant followed by dispersing in a non-polar solvent has been extended to montmorillonite (MMT) and cadmium thiophosphates (CdPS3) by ion-exchange intercalation of the cationic surfactant dioctadecyldimethylammonium bromide (DODMA) followed by sonication in non-polar solvents e.g. toluene or chloroform as in the case of the LDH (Chapter 6). The nanosheets of the MMT and CdPS3 are electrically neutral as the surfactant chains remain anchored to the inorganic sheet even after exfoliation. Graphite oxide (GO) too can be delaminated by functionalizing the sheets by covalently linking oleylamine chains to the GO sheets via an amide bond. The oleylamine functionalized GO is easily delaminated in non-polar solvents to give electrically neutral GO nanosheets. It is shown in Chapter 7 that the 1:1 mixtures of dispersions of montmorillonite-DODMA with Mg-Al LDH-DDS nanosheets can self assemble, on solvent evaporation, to give a new layered solid with periodically alternating montmorillonite and LDH layers. In this method attractive forces between the neutral exfoliated nanosheets of cationic and anionic ensures self-assembly of a perfectly periodic alternating layered structure. The method has been extended to synthesize new layered solids in which surfactant tethered cationic and anionic inorganic sheets alternate. The hybrid solids synthesized are CdPS3—MgAl-LDH, CdPS3—CoAl-LDH, GO—MgAl-LDH, GO—CoAl-LDH. The procedure outlined in Chapter 7 allows for a simple, but versatile, method for generating new periodically ordered layered hybrid solids by self-assembly.

Knowledge of energy dissipation and relaxation in electron, spin, and lattice degrees of freedom is of fundamental importance from both a technological and scientific point of view. In this dissertation, the electronic and magnetization dynamics of photoexcited colloidal cobalt substituted iron oxide nanocrystals, CoxFe3-xO4, were investigated through transient absorption and pump-probe Faraday rotation measurements. In this dissertation, linearly polarized femtosecond optical pulses at 780 nm were used to excite the weak absorption originating from the intervalence charge transfer transition (IVCT) between Fe2+ and Fe3+ ions of Fe3O4 nanocrystals. The timescale and corresponding relaxation processes of electronic relaxation dynamics of the excited IVCT state were first discussed. Size effect on electronic relaxation dynamics in Fe3O4 nanocrystals is not distinct on the basis of result from this study. One interesting feature of electronic dynamics data of photoexcited Fe3O4 nanocrystals is the creation of coherent acoustic phonons. Information on lattice temperature was obtained by measuring the period of coherent acoustic phonon as a function of excitation fluence and fit into a simple model based on Lamb’s theory. Since optical control of the magnetization can be either through optical or heating mechanisms, quantitative estimation of degree of demagnetization caused by lattice temperature is made by using Langevin function. The result from such estimation indicates the effect of lattice temperature rise on magnetization is too small to significantly affect the magnetization of Fe3O4 nanocrystals. Magnetization dynamics were studied via pump-probe Faraday rotation measurements. Optical excitation with near-infrared pulse resulted in an ultrafast demagnetization in 100fs. The energy of the excited state then relaxed through spin-lattice relaxation (SLR). Effects of surface spin and chemical tuning on the SLR were investigated by comparing the magnetization recovery timescales of nanocrystal with different particle sizes and cobalt concentration respectively. The experimental result is explained by a simple model where interior and surface spins contributed to the spin-lattice relaxation process differently. The observations suggest that spin-orbit coupling of the surface is stronger and less sensitive to stoichiometric variation than the interior spins of the nanocrystals.

Η Πακλιταξέλη (PTX) αποτελεί ένα ευρέως διαδεδομένο αντινεοπλασματικό φάρμακο και ενδείκνυται σε μεταστατικό καρκίνο του μαστού, καρκίνο ωοθηκών, μη μικροκυτταρικό καρκίνο του πνεύμονα και σε σάρκωμα Kaposi ασθενών με AIDS. Παρ’ όλα αυτά, η σημαντική τοξικότητα που εμφανίζει (μυελοκαταστολή, νευροτοξικότητα, αντιδράσεις υπερευαισθησίας), υπογραμμίζει την αναγκαιότητα για μορφοποίησή της σε Συστήματα Ελεγχόμενης Χορήγησης Φαρμάκων (DDS), με σκοπό τη μείωση των ανεπιθύμητων ενεργειών και την αύξηση της βιοδιαθεσιμότητας του φαρμάκου. Τα πολυμερικά μικκύλια έχουν μελετεθεί εκτενώς τα τελευταία χρόνια ως Συστήματα Ελεγχόμενης Χορήγησης Φαρμάκων. Η ενσωμάτωση υπερπαραμαγνητικών νανοκρυσταλλιτών οξειδίου του σιδήρου (SPIONs) στον πυρήνα των PTX-μικκυλίων, παρέχει τη δυνατότητα μαγνητικής στόχευσης του φαρμάκου στην επιθυμητή περιοχή δράσης, καθώς και τη θεραπεία του καρκίνου μέσω επαγωγής μαγνητικής υπερθερμίας, με την εφαρμογή εναλλασσόμενου μαγνητικού πεδίου. Επιπλεόν, η χρήση των SPIONs ως σκιαγραφικά μέσα (Τ2-contrast enhancement) στη μαγνητική τομογραφία πυρηνικού συντονισμού (MRI), εξασφαλίζει το πλεονέκτημα ταυτόχρονης διάγνωσης και θεραπείας (Theranostics), αποκαλύπτοντας την πολυλειτουργικότητα των συστημάτων αυτών. Οι συγκεκριμένοι νανοφορείς, έχοντας μικρό μέγεθος (100-200nm), θεωρούνται κατάλληλοι για να αποφύγουν την οψωνινοποίηση απο τις λιποπρωτεϊνες του αίματος, την επίθεση απο τα φαγοκύτταρα του Δικτυοενδοθηλιακού συστήματος (RES) καθώς και την ταχεία νεφρική κάθαρση, με αποτέλεσμα την παρατεταμένη κυκλοφορία τους στο αίμα (stealth systems) και την εκλεκτική πρόσληψη τους απο τους συμπαγείς καρκινικούς όγκους, μέσω του φαινομένου της ενισχυμένης διαπερατότητας και κατακράτησης (EPR effect). Οι ιδιότητες αυτές, καθιστούν τα συγκεκριμένα συστήματα πολύτιμα εργαλεία στον τομέα της νανοϊατρικής. Η παρούσα μεταπτυχιακή διατριβή πραγματεύεται τη σύνθεση υδρόφοβων SPIONs μέσω της τεχνικής της θερμικής αποικοδόμησης. Μελετήθηκαν οι συνθετικές παράμετροι (πρόδρομη ένωση, ποσότητα ελαϊκού οξέος, θερμοκρασία και διάρκεια αντίδρασης, ρυθμός αύξησης της θερμοκρασίας κ.α) που επηρεάζουν το μέγεθος, το σχήμα και τη διασπορά του μεγέθους των σχηματιζομένων νανοκρυσταλλιτών (5-13nm, σ: 10-20%), καθώς διαδραματίζουν σημαντικό ρόλο στη μαγνητική συμπεριφορά των υβριδικών νανονοφορέων. Στη συνέχεια, πραγματοποιήθηκε σύνθεση υβριδικών νανοφορέων με εγκλωβισμό των SPIONs σε πολυμερικά μικκύλια. Η παρασκευή των υπερπαραμαγνητικών μικκυλίων επιτελέστηκε με την τεχνικη solvent diffusion and evaporation (nanoprecipitation), με χρήση του αμφίφιλου συμπολυμερούς πολυ(γαλακτικό οξύ)-πολυ(αιθυλενογλυκόλη) (PLA-PEG). Στον υδρόφοβο πυρήνα των μικκυλίων (PLA) δεσμεύονται υδρόφοβες ενώσεις (PTX, SPIONs), ενώ το υδρόφιλο κέλυφος (PEG) προσδίδει κολλοειδή σταθερότητα σε υδατικά μέσα (δομή πυρήνα-κελύφους). Διερευνήθηκαν διάφορες συνθετικές παράμετροι (μοριακό βάρος συμπολυμερούς, ποσότητα SPIONs, ρυθμός προσθήκης οργανικής φάσης κ.α) και προσδιορίστηκαν οι βέλτιστες συνθήκες για την παρασκευή υπερπαραμαγνητικών μικκυλίων μεγέθους <200nm, με αξιοσημείωτη κολλοειδή σταθερότητα (μέχρι και έξι μήνες), σε συνθήκες παρόμοιες με αυτές του ανθρώπινου πλάσματος (pH: 7.4, ιοντική ισχύς: 0.15Μ). Στο επόμενο στάδιο της παρούσας εργασίας, μελετήθηκαν οι παράγοντες που επηρεάζουν τη φόρτωση-ενκαψυλίωση της PTX και των SPIONs στα πολυμερικά μικκύλια (ποσότητα PTX, ποσότητα και μέγεθος SPIONs, μοριακό βάρος PLA-PEG, ρυθμός προσθήκης οργανικής φάσης κ.α), σε φυσιολογικές συνθήκες (pH:7.4, ιοντική ισχύς: 0.15Μ). Αναπτύχθηκε πρωτόκολλο μέσω του οποίου έγινε κατορθωτός ο διαχωρισμός των μαγνητικών νανοφορέων απο τους μη μαγνητικούς, καθώς και ο υπολογισμός της φόρτωσης-ενκαψυλίωσης PTX και SPIONs ξεχωριστά, τόσο στους μαγνητικούς και μη μαγνητικούς νανοφορείς, όσο και στο μέιγμα αυτών. Οι συγκεκριμένοι νανοφορείς χαρακτηρίζονται απο εξαιρετικά υψηλή απόδοση ενκαψυλίωσης φαρμάκου (93 %wt.) και φόρτωση φαρμάκου που ανέρχεται στο 4.8 %wt. Oι αμιγώς μαγνητικοί νανοφορείς επιδεικνύουν υψηλή απόδοση ενκαψυλίωσης νανοκρυσταλλιτών (70 %wt.), ενώ η φόρτωση σε φάρμακο και SPIONs ανέρχεται σε 5.2 και 20 %wt. αντίστοιχα. Σε αμφότερες τις περιπτώσεις οι νανοφορείς, μεγέθους (υδροδυναμική διάμετρος) 170nm, χαρακτηρίζονται απο ικανοποιητική μαγνητική συμπεριφορά. Εξετάστηκε η επίδραση του μεγέθους των νανοκρυσταλλιτών στη μαγνητική συμπεριφορά των νανοφορέων. Οι αμιγώς μαγνητικοί νανοφορείς με μεγαλύτερο μέγεθος SPIONs παρουσιάζουν καλύτερη μαγνητική συμπεριφορά. Τέλος, πραγματοποιήθηκαν μελέτες αποδέσμευσης του φαρμάκου σε PBS (0.14Μ, pH:7.4) στους 37oC και διερευνήθηκε η επίδραση της εφαρμογής εναλλασσόμενου μαγνητικού πεδίου στην αποδέσμευση της PTX απο τους μαγνητικούς νανοφορείς (Triggered Drug Release). Σε κάθε περίπτωση, παρατηρήθηκε ελεγχόμενη αποδέσμευση του φαρμάκου για 24 ώρες, σε συνθήκες που προσομοιάζουν με αυτές του πλάσματος. Ο φυσικοχημικός χαρακτηρισμός των νανοφορέων πραγματοποιήθηκε με HPLC, DLS, TGA, TEM και μαγνητοφόρηση. / Paclitaxel (PTX) is one of the most successful anticancer drugs against a broad range of solid tumors, such as metastatic breast cancer, ovarian cancer, non-small-cell lung cancer and AIDS-related Kaposi sarcoma. However, the serious systematic side effects of PTX (myelosuppression, neurotoxicity, hypersensitivity) underline the need for formulation of PTX in Drug Delivery Systems (DDS), in order to reduce the side effects and increase the bioavailability of the drug. Among DDS, polymeric micelles have drawn much attention due to their great flexibility in tuning drug solubility, micelle size, targeted drug delivery and stability. Incorporation of Superparamagnetic Iron Oxide Nanocrystals (SPIONs) inside the core of drug-loaded polymeric micelles, imparts to the final Drug Delivery System the prospect of physical (magnetic) targeting, intrinsic therapeutic function (hyperthermia-based cancer therapy under alternating external magnetic field), T2-based contrast enhancement in magnetic resonance imaging (MRI) and remotely triggered drug release. These core-shell polymeric micelles having small size (100-200nm), are considered appropriate for avoiding both opsonization, macrophages attack by ReticuloEndothelial System (RES) and rapid renal clearance, thus allowing micelles to be taken up preferably by solid tumors through Enhanced Permeability and Retention (EPR) effect. Therefore, such nanoassemblies encode high potential in nanomedicine, due to their dual nature (Therapeutic+Diagnostic = Theranostics). In particular, we have studied the synthesis of organophilic SPIONs through thermal decomposition. The synthetic parameters (precursor, precursor:oleic acid ratio, reaction temperature and duration, heat rate, etc.) affecting the size, shape and size distribution of the nanocrystals have also been examined thoroughly, since they play a key-role concerning the magnetic behavior of the final hybrid. Nanosized SPIONs with narrow size distribution were synthesized (5-13nm, σ: 10-20%). The preparation of poly(lactic acid)-block-poly(ethyleneglycol) (PLA-PEG) micelles encapsulating hydrophobic SPIONs, by varying the molecular weight of the polymers, the amount of SPIONs and the addition rate during micelle assembly, has also been investigated. The core-shell superparamagnetic micelles were prepared through solvent diffusion and evaporation technique (nanoprecipitation). PTX and SPIONs are being incorporated into the micelle’s hydrophobic core (PLA) through hydrophobic interactions, whereas the hydrophilic shell (PEG) stabilizes the micelles in aqueous dispersions, optimizing their colloidal stability and providing prolonged circulating time. The optimum parameters were determined, conferring to the micelles (Hydrodynamic Diameter < 200nm) high colloidal stability (up to six months) at biorelevant conditions (pH:7.4, ionic strenght: 0.15M). The next phase of the present master thesis focused on studying the factors (amount of PTX and SPIONs, molecular weight of PLA-PEG, addition rate, etc.) affecting the Loading of PTX and SPIONs into the polymeric micelles and how they can be fine-tuned towards high drug loading, while retaining their size at a scale where long circulation would not be precluded. Through protocol establishment, we have managed to separate the magnetic and non magnetic micelles, and to determine individually the loading of PTX and SPIONs for magnetic, non magnetic micelles, as well as for the mixture of them. The micelles’ mixture exhibits very high Drug Encapsulation Efficiency (93 %wt.) and 4.8 %wt. Drug Loading (D.L). Magnetic nanocarriers display high Magnetic Encapsulation Efficiency (70 %wt.), with D.L and Magnetic Loading of 5.2 and 20 %wt. respectively, In both cases, micelles demonstrate adequate magnetic behavior and small sizes (hydrodynamic diameter: 170nm), under conditions which simulate with human plasma (pH:7.4, ionic strenght: 0.15M). The effect of SPIONs’ size on the magnetic behavior of hybrid colloids, was also examined. Magnetic nanocarriers encapsulating SPIONs of greater size exhibit better magnetic behavior. Finally, we have conducted Drug release studies in PBS (0.14M, pH:7.4) at 37oC. The effect of SPIONs presence on the release profile of PTX, including triggered drug-release by application of AC magnetic field, has also been investigated. PTX-magnetic micelles exhibit Controlled Drug release for 24 hours. Several techniques have been used for the characterization of such nanoassemblies, like: HPLC, DLS, TGA, TEM, XRD, Magnetophoresis and Triggered Drug release by application of AC magnetic field.