Defective alkanethiol monolayers were studied as a model system to understand the stress changes observed in microcantilever-based DNA hybridization experiments. An exponential relationship between defect density and surface stress was found by performing simultaneous electrochemical/stress-sensing experiments. Microcantilevers with a range of defective alkylthiol self assembled monolayers were prepared and stress change/electrochemical data were collected in perchlorate, chloride, and bromide-containing electrolytes. Defects were probed using a ferrocene-thiol labeling technique which provides quantitative measurement of defect area. Using defects and solutions containing charge transferring adsorbates is suggested as a method for enhancing the surface stress signals in cantilever sensor systems. The best response from this study was obtained in bromide, as its exponential function had the sharpest increase with defect density.

Thesis (Ph. D.)--Lehigh University, 1998. / Includes vita. Includes bibliographical references.

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One-, two- and three-phase mixing systems have been extensively studied. The experiments were performed in a range of standard (baffled) vessel geometries of diameter varying between 0.22 - 1.83 m. Rushton disc turbines and mixed flow impellers (both pumping directions) were fully investigated. Water and glucose solution (~ - 120 mPas) were employed. For single phase systems, the work has shown that the power number of disc turbines depends on disc thickness and scale of vessel. For the mixed flow agitators the power number is dependent upon the blade thickness and (D/T) ratio. Correlations enabling the ungassed power number to be calculated as a function of these parameters are given. For gassed systems, the power drawn by each type of impeller is explained by local impeller hyarodynamics (cavity structure) and the bulk flow pattern. The fiooding-Ioading transition (NF) and the complet~ dispersion condition (NeD) have also been studied. A large mixed flow impeller (6MFU45 ; D - T/2) with a large ring sparger is the most energy efficient at NF and NCD speeds as compared with the other geometries studied and correlations enabling the prediction of NF and NCD for all geometries studied are presented. Hold-up correlations are also given for each impeller firstly as a function of specific energy dissipation rate and superficial gas velocity and secondly as' a function of agitator speed and volumetric gassing rate. For each impeller, each method is equally good statistically for scale-up but the latter is more explicit. All impellers give approximately the same hold-up under equal specific power inputs and superficial gas velocity but there are small but statistically significant differences. These differences are discussed. For solid-liquid systems, correlations in the literature for the calculation of the minimum speed to just suspend solids, NJS ' are tested for each system geometry with glass Ballotini particles. The correlation proposed by Chapman et al. is shown to fit the present experimental data best. The specific power input per unit mass (ET)JS - constant, is proposed as a scale-up criterion for solids suspension. Large 6MFD45 (D - T/2) is the most energy efficient for suspension but 6MFU45 (D - T/2) is only slightly worse. In the three-phase mixing systems, the 6MFD 45 , D - T/2, is most energy efficient for solid suspension (ET)JSg' at low gassing rates (up to 1 vvm) but exhibits large flow pattern and torque fluctuations. Above _ 1 vvm, 6MFU45 (D = T/2) becomes the most energy efficient for solid suspension. In addition the minimum impeller speed for solid suspension NJSg for this impeller is almost independent of gassing rate and gives very stable flow patterns and torque. output throughout the whole gassing range. Again (eT)JSg - const is the recommended scale-up criterion for solids suspension under gassed conditions. Large (D - T/2) impellers are found to be more energy efficient and correlations for predicting N 45 45 . JSg for 6DT. 6MFD and 6MFU are obta~ned. Increase in liquid viscosity has a rather small effect on gas dispersion. Up to 120 mPas: (N) Q:I (N ) and (N ) Q:I F viscous F water CD viscous (NCD) water uO.06 On the other hand, viscosity has a significant effect on NJS and 3 to 5 times more energy is required for solid suspension at 120 ,mPas.

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The phase behaviour, rheological effects and interfacial properties of binary and ternary liquid mixtures have been studied near critical points. In particular, measurements have been made of the viscosity-at the bulk macroscopic level by capillary viscometry and at the microscopic level by fluorescence depolarisatiorr-and of critical-point wetting and adsorptiorr-at the solid-liquid interface using evanescent-wave-generated fluorescence spectroscopy and at the liquid-vapour interface using specular neutron reflection. The systems investigated have been mostly alkane + perfluoroalkane mixtures or 2-butoxyethanol + H20 or D20 mixtures, although in some cases hexamethyldisiloxane, propanenitrile and perfluorooctyloctane have also been the components of mixtures. The main outcomes of this study are: • Macroscopic viscosity: The divergence to infinity in the shear viscosity of hexane + perfluorohexane at the critical endpoint for approach along the path of constant critical composition both from the single phase and along both limbs of the coexistence curve is described well using the Renormalisation Group Theory critical exponent y = 0.04. The correlation length amplitude obtained by fitting the sheargradient dependence of the viscosity is ~o = (S.S±l.S) A. • Microscopic viscosity: The product of the rotational correlation time and the temperature 'tR"T, often taken as a measure of the microscopic viscosity, exhibits an anomaly as the critical point is approached as a function of temperature. This anomaly mirrors that in the macroscopic viscosity for some fluorescent dye probes, but for others the anomaly is in the opposite sense indicating that other effects such as solvent structure must playa part in the near-critical behaviour of'tR·T. • Critical-point wetting at the solid-liquid interface: The wetting transition temperature has been identified for heptane + perfluorohexane at the quartz-liquid interface from fluorescence lifetime measurements of a probe. The wetting layer is of the same composition as the bulk heptane-rich phase and the transition is tentatively identified as first-order. • Adsorption and wetting at the liquid-vapour interface: The surface structure of several mixtures has been determined by neutron reflection. The results are in general agreement with the expectations of critical-point wetting and adsorption. The surface is complex and in some mixtures an oscillatory scattering length density profile through the interface is required to model the reflectivity data. • Ternary mixtures: The phase behaviour of three mixtures exhibiting tunnel phase behaviour has been studied experimentally and various characteristics of the shape of the twmel identified. A theoretical study on one of the mixtures predicts the drop in temperature for the locus of maximum phase separation temperatures which is observed experimentally.

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液滴撞在固體上是個常見現象並且有廣泛的應用，譬如噴墨打印，塗層，工業冷卻以及飛機上的積冰。當液滴撞在乾燥的表面上會出现很多的結果：它可能完全反彈，或平緩的展開，或猛烈地飛濺出許多微小的液滴。影響撞擊過程包括撞擊速度，液體和固體的性質以及周圍的空氣。最近的研究發現降低周圍氣體壓強可以抑制液體飛濺。這表明空氣對於飛濺機制起了關鍵作用。因此，了解在液固撞擊過程中空氣的重要性會給這一基本現象帶來新的發展，並可能改善如控制飛濺和表面塗層等一些實踐過程。 / 採用高速攝影和顯微成像技術，我們做了液滴撞擊光滑且乾燥固體表面的實驗，研究了被困在裡面的氣體。我們觀察了在液體接觸襯底之前一層氣膜被壓縮並形成的過程，發現其壓強比大氣壓值要高得多。壓縮程度取決於撞擊速度，我們通過減速的液體與壓縮空氣的平衡關係給出了解釋。在液體與襯底接觸後，空氣膜的邊緣在豎直方向上擴展，壓強在幾十微秒內迅速降低。這個厚的邊沿在表面張力，慣性力和粘性阻力的複雜相互作用下最終收縮成氣泡。 / 當液滴以很高的速度撞擊平滑固體表面上，液體發生飛濺。人們對這個常見的現象缺乏基本的了解。採用高速攝影技術，我們觀察到是被困在展開液體前沿下的超薄氣膜觸發了飛濺現象。因為這層薄膜比空氣分子的平均自由程更薄，具有與聲速相當的非常高速來轉移動量，並產生一個比常規計算強十倍的應力。如此"強風"在小尺度上開起了開爾文-亥姆霍茲不穩定性並且有效地產生飛濺。我們的模型定量地與實驗驗證相符，並給出了一個對於液滴在光滑表面上飛濺的基本解釋。 / The impacts of liquid drops onto solid substrates are ubiquitous and appear in a variety of applications, such as ink-jet printing, spray coating, industrial cooling processes and ice accumulation on aircraft. When a liquid drop hits a dry substrate, there are many possible outcomes: it can rebound completely, spread smoothly, or splash dramatically ejecting many tiny daughter droplets. Clearly, the hitting dynamics may be influenced by different factors, including the velocity of impact, liquid and surface properties, as well as the surrounding air. Recent study reveals that by lowering the ambient gas pressure, liquid splash could be eliminated. It indicates that the role of air is a significant key to the mechanism of splash creation. Therefore, understanding the behavior of air during liquid-solid impacts will bring new advances to this fundamental phenomenon, and may benefit practical processes such as splash control and surface coating. / Using high-speed photography coupled with optical interference, we experimentally study the air entrapment during a liquid drop impacting a smooth and dry solid substrate. We observe the formation of a compressed air film before the liquid touches the substrate, with internal pressure considerably higher than the atmospheric value. The degree of compression highly depends on the impact velocity, as explained by balancing the liquid deceleration with the large pressure of the compressed air. After contact, the air film expands vertically at the edge, reducing its pressure within a few tens of microseconds and producing a thick rim on the perimeter. This thick-rimmed air film subsequently contracts into an air bubble, governed by the complex interaction between surface tension, inertia and viscous drag. Such a process is universally observed for impacts above a few centimeters high. / When a fast-moving drop impacts onto a smooth substrate, splashing will be produced at the edge of the expanding liquid sheet. This ubiquitous phenomenon lacks a fundamental understanding. With high speed photography, we illustrate that an ultra-thin air film trapped at the expanding liquid front triggers splashing. Because this film is thinner than the mean free path of air molecules, the interior air flow transfers momentum with an unusually high velocity comparable to the speed of sound, and generates a stress ten times stronger than the conventional calculation. Such a "strong wind" initiates Kelvin-Helmholtz instabilities at small length scales and effectively produces splashing. Our model agrees quantitatively with experimental verifications, and brings a fundamental understanding to the ubiquitous phenomenon of drop splashing on smooth substrates. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Liu, Yuan = 液體固體碰撞過程中空氣重要性的研究 / 劉嫄. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 78-80). / Abstracts also in Chinese. / Liu, Yuan = Ye ti gu ti peng zhuang guo cheng zhong kong qi zhong yao xing de yan jiu / Liu Yuan.

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