Lithium-ion battery (LIB) technology is currently the most promising candidate for power sources in applications such as portable electronics and electric vehicles. In today's state-of-the-art LIBs, non-aqueous electrolytes are the most widely used family of electrolytes. In the present thesis work, efforts are devoted to improve the conventional LiPF6-based electrolytes with additives, as well as to develop alternative lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI)-based electrolytes for silicon anodes. In addition, electrode/electrolyte interfacial chemistries in such battery systems are extensively investigated. Two additives, LiTDI and fluoroethylene carbonate (FEC), are evaluated individually for conventional LiPF6-based electrolytes combined with various electrode materials. Introduction of each of the two additives leads to improved battery performance, although the underlying mechanisms are rather different. The LiTDI additive is able to scavenge moisture in the electrolyte, and as a result, enhance the chemical stability of LiPF6-based electrolytes even at extreme conditions such as storage under high moisture content and at elevated temperatures. In addition, it is demonstrated that LiTDI significantly influences the electrode/electrolyte interfaces in NMC/Li and NMC/graphite cells. On the other hand, FEC promotes electrode/electrolyte interfacial stability via formation of a stable solid electrolyte interphase (SEI) layer, which consists of FEC-derivatives such as LiF and polycarbonates in particular. Moreover, LiTDI-based electrolytes are developed as an alternative to LiPF6 electrolytes for silicon anodes. Due to severe salt and solvent degradation, silicon anodes with the LiTDI-baseline electrolyte showed rather poor electrochemical performance. However, with the SEI-forming additives of FEC and VC, the cycling performance of such battery system is greatly improved, owing to a stabilized electrode/electrolyte interface. This thesis work highlights that cooperation of appropriate electrolyte additives is an effective yet simple approach to enhance battery performance, and in addition, that the interfacial chemistries are of particular importance to deeply understand battery behavior.

No description available.

Surface immobilization of probe molecules in surface based assays is a key area of research in the continued development of immunoassay microarrays. Interest continues to grow in microarray based immunoassays given their potential as a high throughput technique for immunodiagnostics. Therefore, it is important to thoroughly study and understand the implications of interfacial chemistry and immobilization conditions on the performance of the assay. This thesis presents a body of work that examines the impact of probe density, interfacial chemistry, and enhancement factors for arrays read with surface plasmon resonance (SPR) imaging. An array of structurally similar Salmonella disaccharides was immobilized at varying densities and the interface formed was thoroughly investigated to determine the properties of the interface. The arrays were then used with SPR imaging to evaluate the binding of an antibody specific for one disaccharide of the three stereoisomers on the array. A dilute disaccharide surface was found to provide optimal antibody binding. Higher densities result in steric hindrance of antibody binding by not allowing the disaccharide to insert into the antibody binding pocket. The role of interfacial chemistry in antibody attachment was studied to determine optimum conditions. The study examined physical adsorption, covalent attachment, and affinity capture. It was found that covalent attachment provided the most stable attachment and resulted in the lowest levels of antigen detection. Both the physical adsorption and affinity capture provided larger antigen binding capacity and therefore more sensitive antigen detection. The covalent attachment was chosen to evaluate an enhanced assay with the incorporation of gold nanoparticles. These particles provided detection limits that were an order of magnitude improved over those excluding the nanoparticles. A novel surface chemistry for antibody immobilization in SPR imaging studies was evaluated. This involved the electrochemical driven formation of mono- to multilayers of diazonium benzoic acid films. The studies showed the ability to control the thickness of the films formed and also the ability of the antibody chips to capture antigen from solution.

The technology employed by human beings for the generation, storage and usage of energy is presently undergoing the fastest and most profound change since the industrial revolution. The changes in the generation and usage of energy necessitate the development of new methods of energy storage. In these systems, electrochemical energy storage will play a crucial role and to this end new electrolytes need to be explored to complement these changes. One such class of liquids is ionic liquids, a class of salts that are molten at room temperature. These liquids have a broad applicability to batteries and supercapacitors. This thesis details work where molecular dynamics simulations have been used to explore the nanostructure of ionic liquids and their mixtures with various molecular solvents at simplistic electrodes. The thesis has two broad sections. The first is covered in Chapter 3, and explores the nanostructure of ionic liquid propylene carbonate solutions, developing a framework through which these nanostructures can be understood. The section concludes that the increasing dilution of ionic liquids decreases the surface charge at which the characteristic ionic liquid oscillatory interfacial structure gives way to a different structure featuring monotonic charge decay. The behaviour of ionic liquids at interfaces is found to be correlated to ion size and type, as well as concentration. A wide divergence in the observed behaviour is shown at positive and negative electrodes due to the asymmetry of propylene carbonate. The second section, consisting of two chapters, explores the interfacial nanostructure of solvate ionic liquids using two different boundary conditions to model the electrode. This work is the first simulation of solvate ionic liquids at electrified interfaces. This section will explore the effect of electrode model on the behaviour of these ionic liquids at the electrode. Chapter 4 uses a fixed charge electrode, whereas Chapter 5 uses one with a fixed potential. The section concludes that regardless of electrode model, the idealised portrait of a solvate ionic liquid - one where the liquid behaves exactly as an aprotic ionic liquid - is not applicable. In Chapter 4's exploration of fixed charged electrodes, the formation of 2 glyme to lithium complexes contradicts the idealised portrait of the liquid. A different change is observed in Chapter 5's exploration of fixed potential electrodes, with both lithium glyme and lithium anion clusters forming at the interface. The key difference between the two studies is that lithium does not coordinate to the electrode in the fixed charge simulations, while in the fixed potential case it does. At the end of Chapter 5 the results are compared against experimental data, with the efficacy of the two models discussed. The aim of both studies is to look at the nanostructure of ionic liquids, when the symmetry between co-ion and cation repulsion - and related effects - is broken by the presence of a non ionic constituent in the liquid.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24443号 / 理博第4942号 / 新制||理||1706(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 若宮 淳志, 教授 依光 英樹, 教授 畠山 琢次 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The distinct structure and dynamics of interfacial water are due to a break in the extended hydrogen bonding network present in bulk water. At solid-aqueous interfaces, the presence of surface charge, which induces a static electric field, and the electrolytes, which are present in most naturally relevant systems, can additionally perturb the hydrogen bonding environment due to polarization. The interplay between the surface-charge-induced electric field and the ions in changing the structure of interfacial water has important consequences in the chemistry of processes ranging from protein-water interactions to mineral-water reactivity in oil recovery. Accessing information about the first few layers of water at buried interfaces is challenging. Vibrational sum-frequency generation (vSFG) spectroscopy is a powerful technique to study exclusively the interfacial region and is used here to investigate the role of interfacial solvent structure on surface reactivity. It is known that the rate of quartz dissolution increases on addition of salt at neat water pH. The reason for this enhancement was hypothesized to be a consequence of perturbations in interfacial water structure. The vSFG spectra, which is a measure of ordering in the interfacial water structure, shows an enhanced effect of salt (NaCl) at neat pH 6~8. The trend in the effect of salt on vSFG spectra versus the bulk pH is remarkably consistent with the enhancement of rate of quartz dissolution, providing the first experimental correlation between interfacial water structure and silica dissolution. If salt alters the structure of interfacial water, it must affect the vibrational energy transfer pathways of water, which is extremely fast in bulk water (~130 fs). Thus far, the role of ions on the vibrational dynamics of water at charged surfaces has been limited to the screening effects and reduction in the depth of the region that contributes to vSFG. Here, we measure the ultrafast vibrational relaxation of the O-H stretch of water at silica at different bulk pH, using time-resolved (TR-vSFG). The fast vibrational dynamics of water (~200 fs) observed at charged silica surfaces (pH 6 and pH 12), slows down (~600 fs) on addition of NaCl only at pH 6 and not at pH 12. On the other hand at pH 2 (neutral surface), the vibrational relaxation shows an acceleration at high ionic strengths (0.5 M NaCl). The TR-vSFG results suggest that there is a surface-charge dependence on the sensitivity of the interfacial dynamics to ions and that reduction in the probe depth of vSFG alone cannot explain the changes in the vibrational lifetime of interfacial O-H. This is further supported by the cation specific effects observed in the TR-vSFG of the silica/water interface. While the vibrational relaxation of O-H stretch slows on addition of all salts (LiCl, NaCl, RbCl, and CsCl), the degree of slowing down is sensitive to the cation identity. The vibrational lifetime of O-H stretch in the presence of different cations follows the order: Li+ < Na+ < Rb+, consistent with previous Hofmeister effect reported in vSFG spectroscopy as well as AFM measurements at silica/water interface. To provide molecular insight on the effect of surface charge density and ionic strength on the changes in interfacial water structure, Molecular Dynamics (MD) simulations were performed on water at different types of surfaces. It was shown that the properties of water near the interface, e.g., a net orientation and the depth to which this persists, depend on the degree of specific adsorption of the counter ions. Our vSFG results, along with the insights from MD simulations, highlight the importance of considering the role of ions on the solvent structure within the electric double layer region, beyond the screening effects predicted by classical electrochemical models. / Chemistry

The increase in microbial resistance to antibiotics underscores the need for novel antibacterial surfaces, particularly for silicone-based implants, because the hydrophobicity of silicones has been linked to undesirable microbial adhesion and biofilm formation. Unfortunately, current strategies for mitigation, such as pretreatment of surfaces with antiseptics/antibiotics, are not consistently effective. In fact, they can facilitate the prevalence of resistant pathogens by exposing bacteria to sublethal concentrations of biocides. Therefore, scientific interest has shifted to preventing initial adhesion (prior to surface colonization) by using surfactants as surface modifiers. Accordingly, Chapter 2 studied the bioactivity of ACR-008 UP (an acrylic-terminated superwetting silicone surfactant) after it was copolymerized in increasing weight percentages with butyl methacrylate (BMA) and/or methyl methacrylate (MMA). Interestingly, copolymers of 20 wt % ACR showed at least 3x less adhesion by Escherichia coli BL21 (E. coli) than any other formulation. This was not a consequence of wettability, which followed a parabolic function with ACR concentration: high contact angles (CA) with sessile water drops were observed at both low (< 20 wt %) and high (> 80 wt %) concentrations of ACR in materials. The CA at 20 wt % ACR was 66°. The lack of E. coli adhesion was ascribed to surfactant-membrane interactions; hence, the antibacterial potential of compounds related to ACR was further probed. Chapter 3, therefore, examines the structure-activity relationships of nonionic silicone polyether surfactants in solution. Azide/alkyne click chemistry was used to prepare a series of eight compounds with consistent hydrophilic tails (8- 44 poly(ethylene glycol) units), but variable hydrophobic heads (branched silicones with 3-10 siloxane linkages, and in two cases phenyl substitutions). The compounds were tested for toxicity at 0.001 w/v %, 2.5 w/v % and their critical micelle concentrations (CMCs), against different concentrations of E. coli in a 3-step assay. Surfactants with smaller head groups had as much as 4x the bioactivity of larger analogues, with the smallest hydrophobe exhibiting potency equivalent to SDS. Smaller PEG chains were similarly associated with higher potency. This data suggests that lower micelle stability, and the theoretically enhanced permeability of smaller silicone head groups in membranes, is linked to antibacterial activity. The results further demonstrate that the simple manipulation of nonionic silicone polyether structures, leads to significant changes in antibacterial action. To ensure similar results were achievable when such surfactants are immobilized on surfaces, 8 compounds with shorter, ethoxysilylpropyl-terminated PEG chains, and branched or linear hydrophobes, were incorporated into a homemade, room temperature vulcanization (RTV) silicone (Chapter 4). The materials, containing 0- 20 wt% surfactants) were then tested for contact killing and cytophobicity against the same E. coli strain. Elastomers modified with 0.5- 1 wt% of (EtO)3Si-PEG- laurate, and separately (EtO)3Si-PEG-tBS, were on average 2x more hydrophilic relative to controls (103°) and differed in their wettability by ~40°, yet both were anti-adhesive; a ~30-fold reduction in adhesion was seen on modified surfaces relative to the control PDMS. Additionally, the (EtO)3Si-PEG-tBS surface demonstrated biocidal behavior, which further highlighted the importance of surfactant chemistry- not just wettability- in observing a specific antibacterial response (if any). Based on the data collated from each Chapter, silicone surfactants seem to have great potential as bioactive agents and warrant further systematic investigations into their mechanisms of action. In so doing, their chemistry may be optimized against different microbes for a variety of applications. In particular, their potential to create non-toxic, cytophobic silicones is particularly encouraging, given the need for anti-adhesive, biofilm preventing material surfaces. / Thesis / Doctor of Philosophy (PhD)

Les problématiques liées aux surfaces et interfaces prennent de plus en plus d’importance dans de nombreux secteurs, aussi bien académiques qu’industriels. Dans de nombreuses applications, il n’est parfois pas nécessaire de conférer la réactivité désirée à la totalité du volume du matériau : une surface aux propriétés bien contrôlées peut suffire.Lieu de discontinuité des propriétés d’un matériau, la surface possède un comportement qui lui est propre, généralement apporté par une étape de fonctionnalisation. Dans ce contexte, ce travail de thèse vise à élaborer des surfaces polymères aux propriétés thermoréversibles, de comprendre les mécanismes réactionnels mis en jeu aux interfaces et de proposer de nouvelles surfaces aux pouvoirs adhésifs réversibles.Il existe de nombreuses techniques permettant de modifier la surface des matériaux. La littérature est abondante et variée, on y trouve notamment des techniques visant à introduire des groupements fonctionnels à la surface d’un substrat. Parmi elles, la polymérisation plasma est une technique de dépôt chimique en phase vapeur, sans solvant, permettant le dépôt de films minces de polymères aux propriétés physico-chimiques contrôlées sur une grande variété de matériaux. Le plasma, état très excité de la matière, est généré grâce à un champ électromagnétique. C’est cette technique de fonctionnalisation qui a été choisie dans ce travail de thèse dans le but de déposer un film mince de polymère possédant des propriétés thermoréversibles sur divers substrats.Les propriétés de thermoréversibilité sont apportées grâce à la présence de groupements furanes, capables de réagir avec un diénophile par une réaction de Diels-Alder (DA). Cette réaction, dite « click », entre un diène et un diénophile a été décrite pour la première fois en 1928 par Otto Diels et Kurt Alder, et fut à l’origine de l’obtention de leur Prix Nobel en 1950. Dans la littérature, les études sur la réaction de DA sont majoritairement réalisées en solution voire sur des matériaux massifs. Cette chimie a été beaucoup moins étudiée sur/dans des films minces, où la notion de confinement prend toute son importance. C’est dans ce contexte que se posent ces travaux de thèse.Dans un premier temps, une étude expérimentale approfondie sur la réactivité de DA (étude cinétique et thermodynamique) a été réalisée. Des polymères plasma ayant des propriétés physico-chimiques variées ont été synthétisés et un couple diène/diénophile modèle, le furane présent dans le polymère plasma et l’anhydride maléique en solution, a été choisi. La compréhension de la réactivité interfaciale de DA sur des polymères plasma constitue la première grande partie de cette thèse. Diverses méthodes de caractérisation des propriétés du film mince fonctionnel (spectroscopie infrarouge, spectrométrie photo-électronique X, mesures d’angle de contact, mesures par microbalance à cristal de quartz avec dissipation, microscopie à force atomique et ellipsométrie) ont été utilisées pour confirmer dans un premier temps la faisabilité du procédé de fonctionnalisation basé sur la polymérisation plasma puis de quantifier la réactivité interfaciale de DA. Dans une seconde partie, la méthodologie développée a été élargie à la compréhension de la réactivité interfaciale de DA et rétro-DA mettant en jeu un autre couple diène/diénophile, à savoir le furane (toujours greffé sur le polymère plasma) et le maléimide (en solution). Enfin, le greffage du maléimide sur un substrat a permis de s’interroger sur la faisabilité d’une adhésion covalente réversible, à l’échelle moléculaire mais aussi macroscopique, entre deux substrats solides fonctionnalisés, l’un avec des groupements furanes, l’autre avec des groupements maléimides. [...] / Should we adapt to materials or can we modify materials to obtain what we want and what we need? Since the beginning of humanity, natural materials (stone, wood, etc.) have allowed civilizations to develop. Thanks to the increase of knowledge in the field of materials and to the development of more and more sophisticated fabrication processes, civilizations have also allowed the development of materials such as metal alloys, ceramics and, more recently, synthetic polymers. Since the second-half of the 20th century, researchers and engineers have found interest in responsive materials and particularly responsive polymers, able to adapt to their surrounding environment such as the mostly studied poly(N-isopropylacrylamine). The number of studies to design new smart materials keeps increasing because they play an important role in the development of advanced technologies. Today, we can find smart materials in all areas of activity.According to the targeted application, different stimuli are considered and can be classified amongchemical or physical stimuli.Recently, chemical stimuli have been studied for various applications, such as the elaboration of pH-stimuli responsive materials to control drug delivery and separation processes. The presence of specific molecules, for instance containing polar groups or able to form hydrogen bonds, can also modify the properties of materials and may be used to induce self-healing processes. Biomolecules may also provide chemical signals for the selective conjugation of proteins or sugars. Besides, physical stimuli have also gained interest because they can be remotely applied. Indeed, electro- or magneto-active polymers respond to an applied electric or magnetic field by changing their size or shape for instance. They are used to elaborate sensors, robotic muscles, to store data and in nanomagnetic materials for various biomedical applications. Photo-sensitive polymers can change their physicochemical properties in response to light irradiation at a given wavelength and intensity. The photoresponsive polymers are broadly used in nano- or bio-technology, such as for bio-patterning and photo-triggered drug delivery. Another highly-studied physical stimulus consists in the variation of the environmental temperature. This method is used for drug delivery, in liquid chromatography to vary the power of separation without changing the column and/or the solvent composition or to elaborate self-healing materials (composites) thanks to weak (H-bonds) or covalent interactions forinstance.In the former examples, the whole composition of the system is usually specifically formulated to react to environmental conditions, although many phenomena locally occur at the surface of the material. This strategy is thus economically non-viable because only few percents of the material volume are exploited for their smart properties. Consequently, industrial renewal can be stimulated by the fabrication of stimuli-responsive coatings that could cover any material, preserving the characteristics of the bulk material and limiting the cost of these additional smart properties. [...]

Methods of slab-geometry molecular dynamics computer simulation were tested, compared, and applied to the prediction of activity coefficients, interfacial electrochemistry characterization, and ion transport through a model biological channel-membrane structure. The charged-sheets, 2-D Ewald, corrected 3-D Ewald, and corrected particle-particle-particle-mesh (P3M) methods were compared for efficiency and applicability to slab-geometry electrolyte systems with discrete water molecules. The P3M method was preferred for long-range force calculation in the problems of interest and was used throughout. The osmotic molecular dynamics method (OMD) was applied to the prediction of liquid mixture activity coefficients for six binary systems: methanol/n-hexane, n-hexane/n-pentane, methanol/water, chloroform/acetone, n-hexane/chloroform, methanol/ chloroform. OMD requires the establishment of chemical potential equilibrium across a semi-permeable membrane that divides the simulation cell between a pure solvent chamber and a chamber containing a mixture of solvent and solute molecules in order to predict the permeable component activity coefficient at the mixture side composition according to a thermodynamic identity. Chemical potential equilibrium is expedited by periodic adjustment of the mixture side chamber volume in response to the observed solvent flux. The method was validated and shown to be able to predict activity coefficients within the limitations of the simple models used. The electrochemical double layer characteristics for a simple electrolyte with discrete water molecules near a charged electrode were examined as a function of ion concentration, electrode charge, and ion size. The fluid structure and charge buildup near the electrode, the voltage drop across the double layer, and the double layer capacitance were studied and were found to be in reasonable agreement with experimental findings. Applied voltage non-equilibrium molecular dynamics was used to calculate the current-voltage relationship for a model biological pore. Ten 10-nanosecond trajectories were computed in each of 10 different conditions of concentration and applied voltage. The channel-membrane structure was bathed in electrolyte including discrete water molecules so that solvation, entry, and exit effects could be studied. Fluid structure, ion dynamics, channel selectivity, and potential gradients were examined. This work represents the first such channel study that does not neglect the vital contributions of discrete water molecules.