Bifurcations in the non-dissipative dynamics of ultra cold atoms

We present the first experimental observation of several bifurcations in a controllable non-linear Hamiltonian system. Dynamics of cold atoms are used to test predictions of non-linear, non-dissipative Hamiltonian dynamics.

Design and development of a time of flight fast scattering spectrometer : a quantitative surface analysis technique and a new approach towards the experimental investigation of the surface particle interactions

A new surface analysis technique has been developed which has a number of benefits compared to conventional Low Energy Ion Scattering Spectrometry (LEISS). A major potential advantage arising from the absence of charge exchange complications is the possibility of quantification. The instrumentation that has been developed also offers the possibility of unique studies concerning the interaction between low energy ions and atoms and solid surfaces. From these studies it may also be possible, in principle, to generate sensitivity factors to quantify LEISS data. The instrumentation, which is referred to as a Time-of-Flight Fast Atom Scattering Spectrometer has been developed to investigate these conjecture in practice. The development, involved a number of modifications to an existing instrument, and allowed samples to be bombarded with a monoenergetic pulsed beam of either atoms or ions, and provided the capability to analyse the spectra of scattered atoms and ions separately. Further to this a system was designed and constructed to allow incident, exit and azimuthal angles of the particle beam to be varied independently. The key development was that of a pulsed, and mass filtered atom source; which was developed by a cyclic process of design, modelling and experimentation. Although it was possible to demonstrate the unique capabilities of the instrument, problems relating to surface contamination prevented the measurement of the neutralisation probabilities. However, these problems appear to be technical rather than scientific in nature, and could be readily resolved given the appropriate resources. Experimental spectra obtained from a number of samples demonstrate some fundamental differences between the scattered ion and neutral spectra. For practical non-ordered surfaces the ToF spectra are more complex than their LEISS counterparts. This is particularly true for helium scattering where it appears, in the absence of detailed computer simulation, that quantitative analysis is limited to ordered surfaces. Despite this limitation the ToFFASS instrument opens the way for quantitative analysis of the 'true' surface region to a wider range of surface materials.

Interlamellar modification of smectite clays

Clay minerals, both natural and synthetic, have a wide range of applications. Smectite clays are not true insulators, their slight conductivity has been utilized by the paper industry in the development of mildly conducting paper. In particular, the synthetic hectorite clay, laponite, is employed to produce paper which is used in automated drawing offices where electro graphic printing is common. The primary objective of this thesis was to modify smectite clays, particularly laponite, to achieve enhanced conductivity. The primary objective was more readily achieved if the subsidiary objective of understanding the mechanism of conductivity was defined. The cyclic voltammograms of some cobalt complexes were studied in free solution and as clay modified electrodes to investigate the origin of electroactivity in clay modified electrodes. The electroactivity of clay modified electrodes prepared using our method can be attributed to ion pairs sorbed to the surface of the electrode, in excess of the cationic exchange capacity. However, some new observations were made concerning the co-ordination chemistry of the tri-2-pyridylamine complexes used which needed clarification. The a.c. conductivity of pressed discs of laponite RD was studied over the frequency range 12Hz- 100kHz using three electrode systems namely silver-loaded epoxy resin (paste), stainless-steel and aluminium. The a. c. conductivity of laponite consists of two components, reactive (minor) and ionic (major) which can be observed almost independently by utilizing the different electrode systems. When the temperature is increased the conductivity of laponite increases and the activation energy for conductivity can be calculated. Measurement of the conductivity of thin films of laponite RD in two crystal planes shows a degree of anisotropy in the a.c. conductivity. Powder X-ray diffraction and 119Sn Mossbauer spectroscopy studies have shown that attempts to intercalate some phenyltin compounds into laponite RD under ambient conditions result in the formation of tin(IV) oxide pillars. 119Sn Mossbauer data indicate that the order of effectiveness of conversion to pillars is in the order: Ph3SnCl > (Ph3Sn)2O, Ph2SnCl2 The organic product of the pillaring process was identified by 13C m.a.s.n.m.r. spectroscopy as trapped in the pillared lattice. This pillaring reaction is much more rapid when carried out in Teflon containers in a simple domestic microwave oven. These pillared clays are novel materials since the pillaring is achieved via neutral precursors rather than sacrificial reaction of the exchangeable cation. The pillaring reaction depends on electrophilic attack on the aryl tin bond by Brønsted acid sites within the clay. Two methods of interlamellar modification were identified which lead to enhanced conductivity of laponite, namely ion exchange and tin(IV) oxide pillaring. A monoionic potassium exchanged laponite shows a four fold increase in a.c. conductivity compared to sodium exchanged laponite RD. The increased conductivity is due to the appearence of an ionic component. The conductivity is independent of relative humidity and increases with temperature. Tin(IV) oxide pillared laponite RD samples show a significant increase in conductivity. Samples prepared from Ph2SnCl2 show an increase in excess of an order of magnitude. The conductivity of tin(IV) oxide pillared laponite samples is dominated by an ionic component.

Subunit vaccines distearoylphosphatidylcholine-based liposomes entrapping antigen offer a neutral alternative to dimethyldioctadecylammonium-based cationic liposomes as an adjuvant delivery system

The adjuvanticity of liposomes can be directed through formulation to develop a safe yet potent vaccine candidate. With the addition of the cationic lipid dimethyldioctadecylammonium bromide (DDA) to stable neutral distearoylphosphatidylcholine (DSPC):cholesterol (Chol) liposomes, vesicle size reduces while protein entrapment increases. The addition of the immunomodulator, trehalose 6,6-dibehenate (TDB) to either the neutral or cationic liposomes did not affect the physiochemical characteristics of these liposome vesicles. However, the protective immune response, as indicated by the amount of IFN-? production, increases considerably when TDB is present. High levels of IFN-? were observed for cationic liposomes; however, there was a marked reduction in IFN-? release over time. Conversely, for neutral liposomes containing TDB, although the initial amount of IFN-? was slightly lower than the cationic equivalent, the overall protective immune responses of these neutral liposomes were effectively maintained over time, generating good levels of protection. To that end, although the addition of DSPC and Chol reduced the protective immunity of DDA:TDB liposomes, relatively high protection was observed for the neutral counterpart, DSPC:Chol:TDB, which may offer an effective neutral alternative to the DDA:TDB cationic system, especially for the delivery of either zwitterionic (neutral) or cationic molecules or antigens.

Ionic and neutral hydrogels for dermal and ophthalmic applications

This thesis is concerned with the use of ionic and neutral hydrogels in dermal and ocular applications with particular reference to controlled release applications. The work consists of three interconnected themes.The first area of study is the use of skin adhesive bioelectrode hydrogels as ground plate electrodes for ophthalmic iontophoresis applications. The work provides a basis of understanding the relative contributions made by ionic monomers (such as sodium s-(acrylamide)-2-methyl propane sulphonate and acrylic acid-bis-(3-sulfopropyl-ester, potassium salt) and neutral monomers (such as acryloymorpholine, N,N-dimethylacrylamide and N-vinyl pyrrolidone) to adhesion, rheology and impedance of bioelectrode gels. The general advantage of neutral monomers, which have been used to successfully replace ionic monomers, is that they enable more effective control of independent anion and cation species (for example potassium chloride and sodium chloride) unlike ionic monomers where polymerisation produces an immobile polyanion thus limiting cation mobility. Secondly, release from a completely neutral hydrogel under the influence of mechanical shaking was studied for the case of crosslinked polyvinyl alcohol (PVA) containing low concentration of linear soluble PVA in a contact lens application. The soluble PVA was observed to be eluting by reptation from the lens matrix due to the mechanical action of the eyelid. This process was studied in an in vitro model, which in this research was used as a basis for developing a lens made with enhanced release polymer. The third area of work is related to the factors that control drug release (in particular non-steroidal anti-inflammatory drugs) from a hydrogel matrix. This links both electrotherapy applications, such as transcutaneous electrical nerve stimulation, in which the passive diffusion from the gel could be used in conjunction with enhanced transmission across the dermal surface with passive diffusion from a contact lens matrix and the development of therapeutic contact lenses.

FemtoNewton force sensing with optically trapped nanotubes

We extract the distribution of both center-of-mass and angular fluctuations from three-dimensional tracking of optically trapped nanotubes. We measure the optical force and torque constants from autocorrelation and cross-correlation of the tracking signals. This allows us to isolate the angular Brownian motion. We demonstrate that nanotubes enable nanometer spatial and femtonewton force resolution in photonic force microscopy, the smallest to date. This has wide implications in nanotechnology, biotechnology, nanofluidics, and material science.

Study of neutral Fe(III) complexes of pyridoxal-N-substituted thiosemicarbazone with desolvation induced spin-state transformation above room temperature

The preparation and characterization of two new neutral ferric complexes with desolvation-induced discontinuous spin-state transformation above room temperature are reported. The compounds, Fe(Hthpy)(thpy).CH3OH.3H2O (1) and Fe(Hmthpy)(mthpy).2H2O (2), are low-spin (LS) at room temperature and below, whereas their nonsolvated forms are high-spin (HS), exhibiting zero-field splitting. In these complexes, Hthpy, Hmthpy, and thpy, mthpy are the deprotonated forms of pyridoxal thiosemicarbazone and pyridoxal methylthiosemicarbazone, respectively; each is an O,N,S-tridentate ligand. The molecular structures have been determined at 100(1) K using single-crystal X-ray diffraction techniques and resulted in a triclinic system (space group P1) and monoclinic unit cell (space group P21/c) for 1 and 2, respectively. Structures were refined to the final error indices, where RF = 0.0560 for 1 and RF = 0.0522 for 2. The chemical inequivalence of the ligands was clearly established, for the "extra" hydrogen atom on the monodeprotonated ligands (Hthpy, Hmthpy) was found to be bound to the nitrogen of the pyridine ring. The ligands are all of the thiol form; the doubly deprotonated chelates (thpy, mthpy) have C-S bond lengths slightly longer than those of the singly deprotonated forms. There is a three-dimensional network of hydrogen bonds in both compounds. The discontinuous spin-state transformation is accompanied with liberation of solvate molecules. This is evidenced also from DSC analysis. Heat capacity data for the LS and HS phases are tabulated at selected temperatures, the values of the enthalpy and entropy changes connected with the change of spin state were reckoned at DeltaH = 12.5 0.3 kJ mol-1 and DeltaS = 33.3 0.8 J mol-1 K-1, respectively, for 1 and DeltaH = 6.5 0.3 kJ mol-1 and DeltaS = 17.6 0.8 J mol-1 K-1, respectively, for 2

Selective functionalisation of Re6 cluster anionic units:from hexa-hydroxo [Re6Q8(OH)6]4− (Q = S, Se) to neutral trans-[Re6Q8L4L′2] hybrid building blocks

The reaction of [Re6Q8(OH)6]4- (Q = S, Se) with p-tertbutylpyridine (TBP) in water leads to neutral trans-[Re6Q8(TBP)4(OH)2] whose hydroxyl reactivity with carboxylic acid and TBP exchange reaction with functional pyridine have been investigated.