The adhesion and resuspension of nanoparticles is important in applications ranging from semiconductor manufacturing to pollution management. The objective of this work is to understand the effect of particle size on re-entrainment of nanometer scale particles. One of the major contributions is to reduce the randomness introduced in past measurements on resuspension by controlling humidity, temperature, material and the distribution of shape and particle sizes. In the process of studying particle size, the effect of surface roughness was also found. Measurements of the detachment fraction of carbon particles as a function of flow rate show three distinct regimes that we attribute to the dominance of drag, energy accumulation by particles, and collision and agglomeration respectively. Experiments with silica nanoparticles on silica microspheres show the detachment fraction to increase non-linearly with particle diameter and to decrease with the substrate diameter. We attribute the former to the dominance of the drag moment over the adhesive moment. We attribute the influence of the substrates to the surface roughness being comparable to the size of the nanoparticles. This work provides new empirical insight into the interaction of nanoparticles with surfaces and fluid flows.

A Surface Forces Apparatus (SFA) was used in this study to investigate the fundamental surface forces in oil sand processing research. Asphaltene coated surfaces were chosen as the research topic due to the critical role of asphaltenes in oil sands processing, from bitumen extraction, froth treatment to tailings treatment. To mimic the real surface state in industry processing, dip-coated asphaltene surfaces were prepared for surface force experiments. In this study, a SFA 2000 was used to determine intermolecular and surface forces of asphaltene in organic solvents (toluene and heptane). The force vs. distance curves, or so-called force profiles obtained provide valuable information on local material properties such as interaction energies, molecular conformation changes of the interacting asphaltene surfaces or films. Atomic force microscopy (AFM) was used to provide complementary information on the surface morphology of the prepared asphaltene surfaces. / Chemical Engineering

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The focus of this dissertation is on refining atomic force micrscopy (AFM) methods and data analysis routines to measure the viscoelastic mechanical properties of soft polymer and biological materials in relevant fluid environments and in vivo using a range of relevant temperatures, applied forces, and loading rates. These methods are directly applied here to a several interesting synthetic and biological materials. First, we probe poly(n-butyl methacrylate) (PnBMA), above, at and below its glass transition temperature in order to verify our experimental procedure. Next, we use AFM to study the viscoelastic properties of coating materials and additives of silicone-based soft contact lenses in a tear-like saline solution. Finally, a major focus in this dissertation is determining the fundamental mechanical properties that contribute to the excellent sensitivity of the strain sensing organs in a wandering spider (Cupiennius salei) by probing under in vivo conditions. These strain-sensing organs are known to have a significant viscoelastic component. Thus, the cuticle of living spiders is directly investigated in near-natural environments (high humidity, temperatures from 15-40 °C). The main achievements of these studies can be summarized through the following findings: We suggest that full time-temperature-modulus relationships are necessary for the understanding of soft materials systems, and present a practical method for obtaining such relationships. These studies will have a direct impact on both scientists in the metrology field by developing practical experimental procedures and data analysis routines to investigate viscoelastic mechanical properties at the nanoscale, and future materials scientists and engineers by showing via spider mechanosensory systems how viscoelasticity can be applied for functional use in sensing technology.

Bacterial adhesion is the first step of biofilm formation that plays various roles in the environment and the human body. Examples of undesirable roles of biofilm formation include metal rust, sewage sludge and bacteria-related diseases. Desirable roles are biofiltration and bioremediation.For a decade, Atomic Force Microscopy (AFM) has been the primary tool used to study the adhesion and elastic properties of individual bacteria. In this work we show it is possible to use a Surface Forces Apparatus (SFA) to measure elastic and adhesive properties of small collections of surface bound bacteria. The measurements are conducted with incomplete, patterned bacterial films and we have developed a protocol to image the contact area with AFM after the experiment. Using the SFA, we measured the force profile between a P. Aeruginosa PAO1 film and a bare mica surface. We repeated the measurement in the same contact position for up to ten days to determine the effect of desiccation on the film material properties, and then moved to the new contact area to measure the film thickness and elastic properties. A large shrinkage of the bacterial film thickness was measured during the first few days due to the bacterial film desiccation and rearrangement. The proportion of shrinkage depends on factors such as the bacterial film coverage, roughness, temperature and relative humidity. Thickness compressibility was estimated from the force curves. As a force approximation, the stress at the center of the contact (σ) and the area of the contact were estimated by applying the Hertz model. Since the film is incomplete the calculated area in contact was reduced by a factor estimated from the optical image of the contact zone. Adhesiveness was measured in receding force profiles. Maximum adhesive force was detected in the first day, due to the high capillary force, decreased by the bacterial film desiccation and increased again due to the conditioning film.

The aim of this thesis work was to investigate theadsorption of surfactants to different nonpolar interfaces.Particularly, the effects of the polar group and the nature ofthe hydrophobic interface were elucidated. The interfacialbehavior of the liquid-vapor interface was investigated bymeans of surface tension measurements. Here the effect of thepolar group and the hydrocarbon chain length was investigatedin a systematic manner. It was found that the shorter of thetwo chains examined, decyl, generated a larger surface pressurecontribution than the longer, dodecyl. Furthermore, the sugarbased surfactants behaved differently as compared to theethylene oxide based ones. The former could be modelled byassuming a hard disc behavior of the head group while thelatter displayed polymeric behavior. The influence of saltconcentration on the surface tension behavior of an ionicsurfactant, sodium dodecyl sulphate, was investigated. Theresult could be rationalized by employing the Gouy- Chapmanmodel to the polar region. Furthermore, mixtures of two sugarbased surfactants were investigated by surface tensionmeasurements and the adsorbed amount of the two components atthe interface atdifferent concentrations and fractions in thebulk were obtained by applying the Gibbs surface tensionequation. It was found that the molecule with the smaller headgroup adsorbed preferentially, and more so as the totalsurfactant concentration was increased. These findings could beexplained by considering the interactions generated by thedifferent head groups. The adsorption of sugar surfactants toan isolated hydrophobic surface was studied by means of wettingmeasurements and the behavior was similar to that at theliquid-vapor interface. Wetting isotherms were measured on twodifferent hydrophobic surfaces where the covalently attachedhydrophobic layers were in a crystalline and fluid state,respectively. The wetting results revealed that the sugarsurfactants anchored in the fluid hydrophobic layer. This had asignificant influence on the force profile. For example, at thecrystalline surface the surfactant monolayers were easilyremoved as the surface came into contact at relatively lowapplied loads. This was not the case when the hydrophobic layerwas in a fluid state. Here a significant fraction of thesurfactants remained between the surfaces. Disjoining pressureisotherms were measured using a sugar based surfactant thatwere thoroughly purified and compared to the as receivedsample. Even the purified sample showed a double-layer forcealthough lower as compared to the as received, one. Asignificant difference in foam stability was also observed. / <p>NR 20140805</p>

<p>The aim of this thesis work was to investigate theadsorption of surfactants to different nonpolar interfaces.Particularly, the effects of the polar group and the nature ofthe hydrophobic interface were elucidated. The interfacialbehavior of the liquid-vapor interface was investigated bymeans of surface tension measurements. Here the effect of thepolar group and the hydrocarbon chain length was investigatedin a systematic manner. It was found that the shorter of thetwo chains examined, decyl, generated a larger surface pressurecontribution than the longer, dodecyl. Furthermore, the sugarbased surfactants behaved differently as compared to theethylene oxide based ones. The former could be modelled byassuming a hard disc behavior of the head group while thelatter displayed polymeric behavior. The influence of saltconcentration on the surface tension behavior of an ionicsurfactant, sodium dodecyl sulphate, was investigated. Theresult could be rationalized by employing the Gouy- Chapmanmodel to the polar region. Furthermore, mixtures of two sugarbased surfactants were investigated by surface tensionmeasurements and the adsorbed amount of the two components atthe interface atdifferent concentrations and fractions in thebulk were obtained by applying the Gibbs surface tensionequation. It was found that the molecule with the smaller headgroup adsorbed preferentially, and more so as the totalsurfactant concentration was increased. These findings could beexplained by considering the interactions generated by thedifferent head groups. The adsorption of sugar surfactants toan isolated hydrophobic surface was studied by means of wettingmeasurements and the behavior was similar to that at theliquid-vapor interface. Wetting isotherms were measured on twodifferent hydrophobic surfaces where the covalently attachedhydrophobic layers were in a crystalline and fluid state,respectively. The wetting results revealed that the sugarsurfactants anchored in the fluid hydrophobic layer. This had asignificant influence on the force profile. For example, at thecrystalline surface the surfactant monolayers were easilyremoved as the surface came into contact at relatively lowapplied loads. This was not the case when the hydrophobic layerwas in a fluid state. Here a significant fraction of thesurfactants remained between the surfaces. Disjoining pressureisotherms were measured using a sugar based surfactant thatwere thoroughly purified and compared to the as receivedsample. Even the purified sample showed a double-layer forcealthough lower as compared to the as received, one. Asignificant difference in foam stability was also observed.</p>

Protein PEGylation (covalent attachment of poly(ethylene glycol) or PEG to proteins) is an excellent example of a drug delivery system that improves pharmacokinetics and pharmacodynamic properties of therapeutics. However, although PEGylation is clinically proven and attracts both scientific and commercial interest, the technique is associated with many process constraints, in particular related to controlling the number of conjugated PEG chains. A novel, solid-phase PEGylation methodology was attempted to overcome the drawbacks of the commonly used solution-phase methods for preparing PEGylated products. The solid-phase PEGylation methodology involved conjugating protein onto a tethered PEG derivative attached onto a solid matrix, followed by hydrolytic cleavage of the PEG chain from the solid matrix under mild conditions to yield PEGylated protein in free solution. PEGs with molecular weights (MWs) 2000 and 4000 Da were used and a heterobifunctional PEG derivative, α-(β-alanine)-ω-carboxy PEG, with a cleavable β-alanine ester terminal was prepared for surface grafting and protein conjugation. The amine terminal of this PEG derivative was used for grafting PEG onto carboxy functionalized hydrophilic Sephadex and hydrophobic polystyrene derivatives. The free carboxyl terminal was used for protein conjugation via amine coupling. A kinetic study of PEG-surface grafting was performed to understand the influence of a number of parameters on the PEG surface concentration and its conformation, including temperature, reaction time, nature of the matrix, solvent and base, and MW of PEG. PEG grafted matrices were characterized using various surface characterization tools including Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Higher PEG grafting was observed with polystyrene matrices (up to 0.3 mmol/g) than either of the Sephadex derivatives (less than 0.15 mmol/g) using both molecular weights. Detailed surface characterization using XPS studies showed a layer thickness of 11.87 nm was achieved with polystyrene matrices using 4000 Da PEG derivatives after a grafting period of 72 hours at 40°C, indicating the presence of brush conformations for the grafted PEGs. In contrast, mushroom conformations were observed for PEG molecules grafted on both carboxymethyl and carboxypentyl Sephadex derivatives after the same reaction period, with a layer thickness of 2.62 nm and 4.14 nm respectively. Optimized PEG grafting and hydrolysis conditions were developed for solid-phase protein PEGylation using Cytochrome c as a model protein. The presence of PEGylated species were detected by size exclusion chromatography (SEC) from Sephadex derivatives but were absent when using polystyrene matrices. Both Sephadex derivatives gave mainly multi-PEGylated species with poor yields, in place of the expected mono-PEGylated products. A solution-phase PEGylation using the same PEG derivatives was performed successfully and various PEGylated species were identified and characterized using SEC and gel electrophoresis, based on their viscosity radius. An examination of the surface characteristics of the PEG-grafted was carried out by XPS, showing that protein conjugation was greatly influenced by surface force interactions, which depended on the PEG grafting densities and the nature of the solid matrices. Finally, fluorescent images obtained using confocal microscope with fluorescein isothiocyanate labelled Cytochrome c provided supporting evidence regarding the factors that constrained the solid-phase PEGylation process.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23217号 / 工博第4861号 / 新制||工||1759(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 作花 哲夫, 教授 安部 武志, 教授 佐藤 啓文 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Slippery liquid-infused porous surfaces (SLIPS) – a new class of bio-inspired liquid-repellent surfaces – comprise arbitrarily porous architectures filled with oils that exhibit high interfacial tensions to probe liquids and present ultralow contact angle hysteresis (<〖10〗^°). However, before practical technologies based on SLIPS can be designed at large-scale, a number of fundamental questions remain to be answered. For instance, depending on the sign of the spreading coefficient of the Vapor(V)-lubricant oil(O)-liquid(L) system, defined as S_(OL(V))=γ_LV-γ_LO-γ_OV>0, the lubricating layer forms a layer at the liquid-vapor interface (here, γ_LV is a liquid-vapor interfacial tension, γ_LO – liquid-oil, and γ_OV – oil-vapor). This “cloaking” of liquid drops can deplete SLIPS’ lubricant over time and contaminate the probed liquid. So far, cloaking has been investigated by contact angle goniometry and confocal microscopy, which cannot resolve films of molecular thickness and factors that govern the equilibrium thickness of those films are not entirely clear. Here, we report on the development and application of a reflective-mode SFA platform to characterize the cloaking of water droplets placed on SLIPS. A multilayer matrix method is utilized to analyze the interferometry data. Using this complementary experimental and analytical approach, we determined the thickness of the cloaking layer for the FDTS(solid)-VF-40(lubricant)-water(probe liquid)-air system to be z3= 7±1 nm. Towards deeper insights into the intermolecular and surface forces responsible for cloaking, we demonstrate that repulsive van der Waals interactions are responsible for stabilizing the cloaking film at the water-air interface. Our experimental platform and the analytical framework should facilitate investigations of other SLIPS and probe liquid systems down to the molecular-scale resolution. These findings might aid the rational design of SLIPS, e.g., for drag reduction, anti-biofouling, and anti-corrosion. In addition to investigating SLIPS, We addressed the following questions with the help of atomic force microscopy (AFM): (i) how do zwitterionic osmolytes modulate electrostatic and hydrophobic interactions in nanoscale confinement, and (ii) is it possible to have two negatively charged surfaces attract each other? Our findings are presented as appendices in this thesis.