京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20406号 / 工博第4343号 / 新制||工||1673(附属図書館) / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 大北 英生, 教授 辻井 敬亘, 教授 竹中 幹人 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

There is a need to discover advanced materials to address the pressing challenges facing humanity, however there are far too many combinations of material composition and processing conditions to explore using conventional experimentation. One powerful approach for accelerating the rate at which materials are explored is by miniaturizing the scale at which experiments take place. Reducing the size of samples has been tremendously productive in biomedicine and drug discovery through standardized formats such as microwell plates, and while these formats may not be the most appropriate for studying polymeric materials, they do highlight the advantages of studying materials in ultra-miniaturized volumes. However, precise and controlled methods for handling diverse samples at the sub-femtoliter-scale have not been demonstrated. In this thesis, we establish that scanning probes can be used as a technique for realizing and interrogating sub-femtoliter scale polymer samples. To do this, we develop and apply methods for patterning materials with control over their size and composition and then use these methods to study material systems of interest. First, we develop a closed-loop method for patterning liquid samples using scanning probes by utilizing tipless cantilevers capable of holding a discrete liquid drop together with an inertial mass sensing scheme to measure the amount of liquid loaded on the probe. Using these innovations, we perform patterning with better than 1% mass accuracy on the pL-scale. While dispensing fluid with tipless cantilevers is successful for patterning pL-scale features and can be considered a candidate for robust nanoscale manipulation of liquids for high-throughput sample preparation, the minimum amount of liquid that can be transferred using this method is limited by number of factors. Thus, in the second section of this thesis, we explore ultrafast cantilevers that feature spherical tips and find them capable of patterning aL-scale features with in situ feedback. The development of methods of interrogating polymers at the pL-scale led us to explore how the mechanical properties of photocurable polymers depend on processing conditions. Specifically, we investigate the degree to which oxygen inhibits photocrosslinking during vat polymerization and how this effect influences the mechanical properties of the final material. We explore this through a series of macroscopic compression studies and AFM-based indentation studies of the cured polymers. Ultimately, the mechanical properties of these systems are compared to pL-scale features patterned using scanning probe lithography and we find that not only does oxygen prevent full crosslinking when it is present during the post-print curing, but the presence of oxygen during printing itself irreversibly softens the material. In addition to developing new methods for realizing ultra-miniaturized samples for study, the novel scanning probe methods in this work have led to new paradigms for rapidly evaluating complex interactions between material systems. In particular, we present a novel method to quantitatively investigate the interaction between the metal-organic frameworks (MOFs) and polymers by attaching a single MOF particle to a cantilever and studying the interaction force between this MOF and model polymer surfaces. Using this approach, we find direct evidence supporting the intercalation of polymer chains into the pores of MOFs. This work lays the foundation for directly characterizing the facet-specific interactions between MOFs and polymers in a high-throughput manner sufficient to fuel a data-driven accelerated material discovery pipeline. Collectively, the focus of this thesis is the development and utilization of novel scanning probe methods to collect data on extremely small systems and advance our understanding of important classes of materials. We expect this thesis to provide the foundation needed to transform scanning probe systems into instruments for performing reliable nanochemistry by combining controlled and quantitative sample preparation at the nanoscale and high-throughput characterization of materials. To conclude, we present an outlook about the necessary technological advancements and promising directions for materials innovations that stem from this work.

Scanning electrochemical microscopy (SECM) is used to deposit gold nanoparticles on a glassy carbon electrode (GCE). Deposition conditions, including the tip-substrate distance, current density, substrate potential, and addition of Ag ions in the electrolyte are changed to study the effects on gold spot size and particle morphology. Atomic force microscopy (AFM) is used to analyze the gold nanoparticles. The size and shape of the nanoparticle can be controlled by different SECM experimental conditions. OMSOL Multiphysics software is used to simulate the results of SECM deposition. By comparing the simulation results and experimental results, the deposition process can be understood better. Heterogeneous irreversible reaction rate constant of the reaction happened on GCE can be estimated.

Interphase phenomenon gains more and more interest throughout the research community. An interphase is formed between a filler particle and a polymeric matrix, and it may constitute almost the entire volume of a nanocomposite. If the interphase have favorable mechanical properties it will thus result in a nanocomposite with such properties. Therefore, understanding the principles of its formation and properties are crucial in order to design advanced nanocomposites. This thesis focuses on PDMS-carboxylic acid modified latex nanoparticles (PDMS-CML) surface composites investigated by means of Atomic Force Microscopy (AFM). A new sample preparation method was designed and utilized together with the Gel Trapping Technique (GTT). Quantitative Imaging Mode and Contact Mode were utilized in the AFM studies. Topography and nanomechanical properties were investigated and compared for pure PDMS and PDMS containing the nanoparticles. Further, Contact Mode was used to investigate nanoscale wear of the samples in order to elucidate the interactions strength between the nanoparticles and the matrix. / Egenskaper hos interfaser är ett område som röner allt större intresse hos forskarna inom materialområdet. En interfas bildas mellan en fillerpartikel och en polymermatris, och den kan utgöra den största volymen i en nanokomposit. Ifall interfasen har fördelaktiga mekaniska egenskaper så resulterar det alltså i att nanokompositen också får det. Det är därför viktigt att först principerna för hur interfasen bildas och får sina egenskaper om man vill framställa avancerade nanokompositer. I det här avhandlingsarbetet lades fokus på PDMS och karboxylsyrefunktionaliserade latex nanopartiklar som bildade en nanokomposit yta, vilken studerades med atomkraftsmikroskopi (AFM). En ny framställningsmetod togs fram och utnyttjades tillsammans med den så kallade ”Gel Trapping” tekniken (GTT). Quantitative Imaging och kontakt mode utnyttjades vid AFM studierna. Topografin och de nanomekaniska egenskaperna studerades för ren PDMS och PDMS blandat med nanopartiklarna. Nötning på nanometernivå studerades också, och dä med AFM i kontakt mode.

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Polydopamine (PDA) surfaces have attracted much attention, both for their innate capability as a versatile biomaterial and their standalone antibacterial and adhesive properties. However, the mechanics of PDA deposition as well as the attributes of PDA-coated surfaces remain relatively underexplored despite their adaptability and ease of deposition. Two polydopamine surfaces from literature, smooth and rough PDA (sPDA and rPDA), were compared to a novel surface, inverted PDA (iPDA), to further explore their mechanochemical and bioactive properties. The iPDA surface displayed, by design, a smoother topography when compared to sPDA, with smaller aggregate structures covering 2.7% of the overall surface. However, the chemical signature obtained via Raman spectroscopy of these aggregates shared remarkable similarities at the 1370 cm-1 peak with the rougher rPDA surface, leading to the conclusion that gas exchange at the solution surface may play a critical role in determining PDA subunit composition despite dissimilar deposition methods. Atomic force microscopy (AFM) analysis concluded that the iPDA surface was ~17% more adhesive than other PDA types, while also displaying relatively large hysteresis and a small Young’s modulus. Human osteoblastic MG-63 cells cultured on all three surfaces revealed that a smoother surface topography correlated to more pronounced anisotropic spread independent of cell size, while a serum-independent component was also noted. This work provides a clearer insight into the nature of polydopamine surfaces by the creation of a viable new deposition method, providing an analysis of its mechanochemical and bioactive properties as well as a deeper understanding of the PDA coating process.

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Botulinum Neurotoxin (BoNT) is one of the most potent toxins known to human kind. The Atomic Force Microscope (AFM) was employed to investigate the conditions under which BoNT type A heavy chain would bind and/or insert into mica supported dipalmitoylphosphatidylcholine (DPPC) lipid bilayers. As an alternate technique, DPPC/GT1b or total ganglioside extract (80:20) monolayers of a Langmuir Blodgett (LB) Trough were adapted to be artificial membrane models for toxin insertion studies. We conclude that LB monolayer studies are a promising candidate for BoNT/A membrane insertion investigation. Botulinum neurotoxin serotype A insertions into the LB monolayers in the presence of BoNT/A low affinity ganglioside receptor alone, independent of pH. This thermodynamic evidence indicates that BoNT/A may begin its heavy chain insertion into the cholinergic nerve ending before endocytosis and acidification.