論氏名学位論文の題目文内容要豊内秀一旨提出年平成 26 年 Mesoscopic structural changes and visible light emission during nanosecond infrared laser-induced phase separation of binary liquid mixtures (二液混合系のナノ秒赤外レーザー誘起相分離におけるメゾスコピック構造変化と可視発光現象) 論文目次 Chapter 1 Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Chapter 2 Samples and methods - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2-1 Introduction 2-2 Samples 2-2-1 Water/2-butoxyethanol mixtures (a) Reference samples (b) Water/triethylamine mixtures (c) Other binary liquid mixtures (d) Polystyrene beads 2-2-2 Fluorescent dyes 2-2-3 Sample cell 2-3 Methods 2-3-1 Temperature jump method 2-3-2 Spectroscopic studies (a) Streak camera (b) Transient fluorescence measurements 2-3-3 Fluorescence correlation spectroscopy (a) Experimental setup (b) Data analysis 2-3-4 Imaging techniques (a) Shadowgraph imaging (b) Visualization of emission 2-3-5 Nanosecond structured illumination microscopy (a) concept (b) Experimental setup (c) Data analysis 2-3-6 Light scattering technique References Chapter 3 Influence of solution structure on solute diffusion below the LCST 3-1 Preface 3-2 Diffusion times 3-3 Artifacts for diffusion times 3-4 Changes of hydrodynamic radius 3-5 Interaction between dyes and solution structures 3-6 Stabilization of solution structure by fluorescent dye 3-7 Conclusion References Chapter 4 Mesoscopic structural changes in laser-induced phase separation 4-1 Preface 4-2 Comparison of measurement methods 4-3 Nanosecond structure illumination microscopy 4-3-1 Evaluation of nanosecond structured illumination microscopy 4-3-2 Demonstration of observation for laser-induced phase separation ----------1 - - - - - - - - - 11 - - - - - - - 33 - - - - - - - 43 4-3-3 Selection of fluorescent dye 4-4 Early stage of laser-induced phase separation 4-5 A new view of the early stage of spinodal decomposition 4-6 Conclusion References Chapter 5 Bubble formation and light emission during laser-induced T-jump 5-1 Preface 5-2 Observation of bubbles and light emission 5-2-1 Bubbles 5-2-2 Emission spots 5-2-3 Temperature dependent 5-2-4 Composition dependent 5-2-5 Correlation between bubble formation and light emission 5-3 Effects of dissolved gas and addition of salt 5-3-1 Dissolved gas 5-3-2 Addition of salts 5-4 Time-resolved emission spectrum measurements 5-4-1 Emission spectrum 5-4-2 Time decay analysis 5-5 Mechanism of bubble formation and light emission during laser-induced T jump 5-6 Conclusion References Chapter 6 Conclusion - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Acknowledgements - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Appendixes - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 論 - - - - - - - 63 - - - - - - - - - 81 - - - - - - - - 83 - - - - - - - - - -85 文内容要旨 Chapter 1 Introduction Phase separation in binary liquid mixtures can be induced with a near infrared (IR) pulsed laser temperature-jump (T-jump) method. The T-jump allows the observation of phase separation dynamics with a deep quench (several K) due to the direct vibrational excitation of water molecules, resulting in a homogeneous temperature rise of the mixture within several nanoseconds. The dynamics of laser-induced phase separation (LIPS) involves the relaxation from an unstable non-equilibrium state far from the equilibrated state. The relaxation occurs on different time scales through processes such as heat diffusion, hydrogen bond dissociation, mass diffusion, the formation of a new phase, and phase growth. LIPS is an interesting subject because it can provide unique chemical reaction fields for nanomaterial synthesis. At a certain delay time after LIPS was initiated, a UV laser pulse was irradiated for the synthesis of gold nanoparticles in the chemical reaction field. In this way, the shape and size distribution of the photo-products were changed when the delay time was varied from 1 to 10 s. Previous studies have revealed molecular-level and macroscopic dynamics of LIPS. Time-resolved (TR) Raman spectra showed that molecular level changes terminated within 1 s after the T-jump. TR shadowgraph imaging showed that the domain size L(t) increased during phase separation following a power law. However, the shadowgraph-imaging showed the phase domain development only after the phase size became larger than several hundreds of nanometers due to the diffraction limit of an optical microscope, and there remained a big temporal and spatial gap between early molecular level events and later macroscopic changes. In this study, to overcome the diffraction limit, we attempted to extend the temporal resolutions of light scattering technique and structured illumination microscopy (SIM) to the nanosecond time scale. By using these methods, the dynamics of mesoscopic phase growth during LIPS in a water/2-butoxyethanol (2BE) mixture was successfully observed, for the first time. According to the observation and the previous Raman studies, we propose that the formation of new phases proceeds by increasing density fluctuation of mesoscopic solution structure like micellar aggregates. Additionally, bubble formation and sonoluminescence-like light emission spots were found at the early stage of LIPS. To our knowledge, this is the first observation of the light emission by LIPS. Some imaging and spectroscopic techniques were employed for the investigation of the mechanism of these phenomena and we found that the light emission may be one of the causes of the bubble formation. Chapter 2 Samples and methods Details of samples are described. In this study, water/2BE mixture was mainly used as sample solution. For investigation on dynamics of LIPS, and accompanying bubble formation and light emission, some imaging and spectroscopic techniques were used. Details of these methods are also described. Chapter 3 Influence of solution structure on solute diffusion below the LCST By FCS analysis, non-classical diffusion of the hydrophobic dye, BPDI, in water/2BE mixtures was observed, i.e. the translational diffusion of the dye was unusually slow when the water/2BE mixture was close to its critical composition but still well below its LCST. Although the apparent hydrodynamic radius of the amphiphilic dye ATTO532 remained largely unchanged with 2BE concentration, the apparent radius of BPDI almost doubled close to critical composition. In contrast, radii remained almost unaffected in water/MeOH mixtures. These observations were explained by virtue of the different affinities of the fluorescent dyes for less or more polar solvents and thus by the different interactions with local solution structures that are transiently formed in water/2BE mixtures but not in water/MeOH. Moreover, our data suggest that the presence of the hydrophobic dye BDPI stabilizes otherwise unstable 2BE micellar aggregates by at -4 least ~10 s. In this perspective, the observed increase in the hydrodynamic radius of BPDI can be explained by a change in the size of micellar aggregates that form around BDPI, which change to bulk solvent shell structures at higher 2BE concentrations. From our experiments, it was concluded that translational diffusion of the solvated-dye depends on both the properties of the solutes and the solvent. Thus, it was found that different solutes can experience different environments even within the same solvent mixtures and even far below LCST. Chapter 4 Mesoscopic structural changes in laser-induced phase separation The nanosecond SIM successfully demonstrated the observation of super-high spatial frequency. The method showed considerable potential for the detection of a periodic structure with nanosecond temporal resolution. In addition, it was found that different solutes could experience different environments even within the same solvent mixtures. Changes of solvent environment for hydrophobic dye terminated earlier than hydrophilic dye during LIPS. For earlier delay time, light scattering was employed to investigate dynamics of LIPS. The light scattering showed that L(t) remained constant at approximately 300 nm until 10 s after T-jump and the intensity of scattering light increased exponentially with time from 2 to 10 s. This is the first report to show mesoscopic structural changes in this time region. In the early stage of spinodal decomposition, linearized Cahn–Hilliard theory predicts that the domain size remains constant while the scattering intensity increases exponentially with time. Therefore, it is clearly indicated that the early stage of LIPS in the water/2BE mixture lasted for 10 s. Based on the observation and the previous Raman studies, it is indicated that the formation of new phases proceeds by increasing density fluctuation of the mesoscopic structure, that is, 2BE micellar aggregate. Chapter 5 Bubble formation and light emission during laser-induced T-jump In this chapter, experimental results of bubble formation and light emission during laser-induced T-jump are shown. The phenomena were not specific in phase separation and could be observed even in water and some complete dissolution mixture. The phenomena were observed more frequently when phase separation took place, a mixing ratio of organic solvent was high, and salts were added in solutions. Since the emission was observed from outside of the near IR pulse spot, it was indicated that the light emission was not induced directly with irradiation of the near IR pule, and something moved for 100 m within 100 ns. Moreover, the numbers of bubbles and emission spots showed positive correlation with each other. It was therefore speculated that the phenomena were related with each other. The light emission occurred within several hundreds nanoseconds after T-jump, and micrometer size bubbles collapsed after delay time of 50 s. Therefore, it was found the light emission was different from well-known sonoluminescence. Emission spectra were broad and liked Blackbody radiation. The similar shape of emission spectrum was observed even in pure water, suggesting that the emission species was not originated in organic solvent, and due to blackbody radiation from high temperature (~ 5000 k). From these findings, one possible mechanism of bubble formation and light emission was proposed. In the mechanism, a pressure wave is generated with laser-induced T-jump and makes nano-bubbles desorbed from a solid-liquid interface. When the desorbed unstable bubbles collapse, light emission occurs. Some of the desorbed nano-bubbles are stabilized by lowering surface tension with organic solvent molecules, and act as a nucleus. The nano-bubbles grow to micrometer size, so that are observed. Chapter 6 Conclusion In this chapter, results of this study and new viewpoints for laser-induced phase separation are summarized. 論文審査の結果の要旨豊内秀一提出の論文は, 下部臨界点を有する水・ブトキシエタノール混合溶液の相分離に関し，主としてメゾスコピックな観点から研究を行ったものである。これまで観測できなかった時空間領域において，新規で興味深い知見が幾つか得られており，得られた結果について深い考察もなされている。本研究の成果は，溶液の物理化学の立場から意義深いものであり高く評価できる。まず臨界点以下の低温混合領域において，溶液の混合比が蛍光色素の拡散速度に及ぼす効果を蛍光相関分光法により詳細に調べた。この結果，両親媒性色素の場合には巨視的な粘性増加と共に一様な拡散速度の低下が認められたのに対し，疎水性色素の場合には粘性の効果に加えて臨界濃度付近で拡散速度が異常に低下する現象を見出した。従来，低温混合領域においてはミセル様の凝集体が存在することが示唆されていたが，溶質分子の拡散速度が溶媒への親和性に影響されること，このような現象が臨界点から十分に離れた低温領域でも観測できることを実験的に示した意義は大きい。この二液混合溶液にナノ秒赤外パルス光を照射し温度を急激に上昇させると，相分離が誘起されその動的過程を追跡できる。本研究では，全く新たに開発した時間分解構造化照明法と顕微光散乱法を用い，これまで観測が不可能であったサブマイクロメートルの溶液内構造を初めて観測することに成功した。得られた結果に基づき，ミセル様凝集体がさらに凝集して微小相を形成するという階層的な相分離ダイナミクスの提案を行っている。これらの研究成果は極めて優れたものとして高く評価できる。さらに，溶液の相分離に伴う発光現象を初めて見出し，気泡発生との関連についても詳細に調べた。この結果，ナノ秒温度ジャンプの直後から可視領域に幅広く構造の不明瞭な発光が観測されること，数百ナノ秒から発生する気泡の数とも相関があることを明らかにした。このような発光現象は，水などの均一液体では観測できないことから，溶液内に存在する凝集体などが機械的に破断することが原因であり，この結果として気泡発生の原因になるのではないかと考察している。この研究成果も高い独創性を有している。以上のように卓越した複数の研究成果は，本人が自立して研究活動を行うに必要な高度の研究能力と学識を有することを示している。したがって，豊内秀一提出の論文は博士（理学）の学位論文として合格と認める。