<p dir="ltr">There is a plethora of applications that require chemical patterning on the molecular scale. While the surface science community has made tremendous progress in achieving this level of control on hard, crystalline interfaces, significant challenges are associated with extending this progress to less “perfect” systems such as soft, amorphous interfaces. Applications ranging from soft robotics and wearable electronics to regenerative medicine often utilize polymeric materials such as polydimethylsiloxane (PDMS) and hydrogels. These materials have advantageous properties, including biocompatibility and mechanical tunability. Biological applications, for example, often require the display of functional groups with precise spatial resolution. Cellular behavior is dictated by biochemical and biophysical cues in the extracellular matrix; therefore, substrate properties, including stiffness and ligand density, must be independently tunable. Soft, polymeric materials are highly heterogenous with pore sizes ranging from 10 nm to 1 µm and hence, particularly difficult to pattern below the length scale of substrate heterogeneity. Furthermore, deconvolving mechanical properties such as elastic modulus from the density of surface-active functional groups is especially challenging, with softer materials typically corresponding is lower ligand densities. Additionally, many traditional surface science characterization and patterning methods are incompatible with soft interfaces (e.g. amorphous surface structure, low mechanical strength, hydrated environment). Recently, we have reported a method capable of achieving high-resolution chemical patterning of PDMS and hydrogels. Long studied within the scanning probe community, amphiphiles with long alkyl chains self-assemble into lying down stripe phases on highly ordered pyrolytic graphite (HOPG), generating 1-nm-wide stripes of functional headgroups between 5-nmwide stripes of exposed alkyl chains. Stripe phases of functional diacetylenes (DA) are photopolymerized, producing a polydiacetylene backbone that tethers together adjacent molecules, generating a PDA film on HOPG (sPDA). We have shown that PDA films on HOPG can be transferred to PDMS as well as polyacrylamide hydrogels. When PDMS is cured in contact with sPDAs, the PDA backbones can act as a site for hydrosilylation, the same reaction responsible for PDMS curing, covalently linking sPDAs to the PDMS mesh. Careful exfoliation reveals nm-scale functional patterns on the surface layer of PDMS. 10 Here, we examine the impact of PDMS structural components on the efficiency of interfacial reactions between sPDAs and the PDMS network. We also illustrate the impact of PDAfunctionalized PDMS on the adhesion and spreading behavior of C2C12 murine myoblasts.</p>

Various aspects of the surface chemistry of a ruthenium (1010) single crystal have been investigated under ultra-high vacuum conditions, employing the techniques of Auger Electron Spectroscopy, Low Energy Electron Diffraction, Multimass Thermal Desorption Spectroscopy, photoemission spectroscopies and work function measurements. The studies were undertaken with a view towards the applicability of ruthenium and iron-ruthenium alloys to the ammonia synthesis, though work relevant to the Fischer-Tropsch synthesis was also performed. The interactions of the gases nitrogen, hydrogen and ammonia with the clean surface were all explored. Molecular nitrogen was found to have an extremely low sticking probability of less than 10<SUP>-9</SUP> at room temperature, but surface nitrogen atoms were deposited via two separate means, using either a mixture of nitrogen ions or nitrogen atoms themselves as the impinging species. Both chemisorbed and bulk implanted states were thereby observed. Hydrogen uptake at 310 K saturated at small doses but an estimate of 256 kJ mol<SUP>-1</SUP> was made for the Ru-H bond strength from thermal desorption traces. Ammonia readily adsorbed at and above room temperature. Partial dissociation occurred at 300 K, the extent of fragmentation increasing as the crystal temperature was raised. Strong electron beam perturbations of the adlayer occurred, accelerating the rate of adsorption and resulting in the appearance of otherwise unobservable LEED patterns. The behaviour of the model promoter potassium was relatively typical of alkali metal/transition metal systems, though the anisotropic substrate potential was found to induce a series of interesting one dimensionally incoherent compressed overlayer structures. A further striking observation was the occurrence of substantial bulk dissolution of potassium following small doses at 430 K. The promoting effects of potassium on CO adsorption were investigated and interpreted interms of a recent modification of the Blyholder model, which combines indirect, through metal and direct, through space interactions. Finally, the deposition of iron on Ru(10bar 10) was studied. At 300 K the iron film grew in a metastable layer by layer mode, which rapidly rearranged on heating to either an alloy phase or a regime of 3D crystallites lying above one or two iron monolayers. Adsorption at elevated temperatures produced essentially the same results as heating layers deposited at room temperature.

The work described in this thesis is concerned with the study of ph-ysisorbed phases by x-ray diffraction using a conventional sealed x-ray tube source. Diffraction data has been collected for a number of adsorption systems using graphite, a montmorillonite clay (Gel White) and zeolite rho as the substrate. It is well known that phases of unique two-dimensional character can be formed on the surface of graphite, and the structure of adsorbed benzene and hexaflurobenzene on graphite have been studied in this thesis. Contrary to current theoretical predictions the >/7x T/7R19" commensurate structure of submonolayer benzene has been confirmed. Submonolayer hexaflurobenzene appears to form a striped domain structure based upon the commensurate x3 lattice in which the molecules are incommensurate with the surface. ' In contrast to the homogeneous surface of graphite, the surface of a clay is microporous and heterogenous, and this gives rise to broad diffraction lines from an adsorbed phase. Despite this, the surface area of Gel White has been deduced from the evolution of the diffraction pattern of a krypton adlayer as a function of krypton loading. The formation of bulk krypton is readily identified and the small size of the three-dimensional crystallites suggests that they are formed within the micropores of the clay. The structure of adlayers of krypton and xenon within the interlayer spacing of Al-pillared Gel White has been studied in order to determine the mean inter-pillar separation. At all the coverages studied, xenon forms a close packed single layer structure whilst krypton appears to form a more complex bilayer phase. A tentative suggestion as to the mean pillar separation from this work is 30X. The adsorption site of krypton, xenon and CH3CI within zeolite rho has been determined using the method of x-ray Rietveld whole profile refinement. The principal site of adsorbed krypton and xenon is at the centre of the octagonal prism. The chlorine atom of CH3CI sits in the centre of the face of the octagonal prism and the methyl group is slightly displaced from the centre of the prism. 37-5354 Hydrodynamics of liquid encapsulation czochralski crystal growth Hicks, T.W. Bristol Ph.D. 1989 Dig. Certain aspects of crystal growth from a melt are investigated. We begin by describing the methods of producing single crystals. Particular emphasis is placed on the need for a better understanding of the hydrodynamics of the encapsulant region of the Liquid Encapsulation Czochralski (LEG) technique. We also introduce the basic physical processes which govern crystal growth. In Chapter 2 we develop a mathematical model of the encapsulant region of the LEC crystal growth system. The equations and boundary conditions that govern the encapsulant flow are formed using a vorticity-stream-function approach, after which the problem is recast in a dimensionless form. In Chapter 3 the equations of motion are represented in a finite difference form and a numerical method for solving the time-marching problem presented by the parabolic equations is developed. The elliptic stream-function equation is solved at each time level using the successive over-relaxation technique. Solutions of the model equations for the growth of GaAs crystals through B3O3 encapsulant are presented in Chapter 4. In all cases considered the flow field tends towards a steady state. For shallow encapsulants, the heat transfer in the encapsulant is conduction dominated, but for deeper encapsulants, advective heat transfer can be significant. In the last chapter we investigate the effect of Soret diffusion on the morphological stability of a freezing interface using linear stability theory. A Soret flux directed towards the interface has a destabilising effect. Over-stable modes of instability exist for very low crystal growth rates, but we are unable to find conditions under which the overstable mode is the most unstable.

Three alkyldihydrochlorosilanes were synthesized; ethyldihydrochlorosilane, octyldihydrochlorosilane and octadecyldihydrosilane. Ethyldihydrochlorosilane was produced by the reaction of ethylsilane with mercuric chloride and the other two chlorosilanes were produced by the reaction of the alkyl Grignard reagent with dichlorosilane. Each alkyldihydrochlorosilane was reacted with porous silica in an attempt to discover the extent of reaction or the highest surface concentration of bonded groups attainable. The reaction between these alkydihydrochlorosilanes and porous silica was compared to the reaction between silica and the analogous alkyldimethylchlorosilane. The rate of reaction of both type of chlorosilane was found to be essentially the same. The maximum surface concentration of bonded surface groups attainable by alkyldihydrochlorosilanes was found to be approximately 1.3 #moles/m² greater than that attainable by alkyldimethylchlorosilanes. This increased surface coverage seemed to depend very little on the chain length of the alkyl group and was attributed to the decrease in steric hindrance of the bonding silicon atom of the silane. Surface bound silyl hydrides could be oxidized selectively and sequentially to form silane silanols. Surface silanes also appeared to reduce chloroplatinic acid, but were not observed to add efficiently to olefins. The chromatographic properties of silica modified with alkyldihydrochlorosilanes were compared to those of equivalent silicas modified with alkyldimethylchlorosilanes and alkyltrichlorosilanes before and after the surface silanes were oxidized. Both normal and reversed-phase liquid chromatographic studies were conducted. In general, it was found that alkyldihydrochlorosilanes yielded the most polar modified silicas. This greater surface polarity was attributed to an increase in the activity of water in the near surface region of the bonded phase.

The growing technological application of metallic lithium has produced a greater need to understand its fundamental surface chemical properties. The use of lithium as an anode in high-energy density battery systems represents one application where this knowledge is required to optimize system performance. The surface chemistry of lithium will be discussed in terms of oxidants which represent the reductive half-cell components of these batteries, contaminants present during cell fabrication, and solvents used as the electrolytic medium. These systems have been studied in the low pressure limit ( < 1 millitorr) at atomically clean lithium surfaces using X-ray Photoelectron Spectroscopy (XPS). The lithium/sulfur dioxide system has been singled out for detailed study in order to explore the relationship between gas-phase and solution-phase processes. Electrochemical characterization of the lithium anode has been conducted as a function of controlled surface composition within this system. The ability of lithium to induce corrosion at structural components of these batteries (i.e., glass insulators) has also been investigated. A description of the chemical activity of lithium and its consequence has been developed from these results.

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We quantified the chemical species present at polycrystalline cesium tin bromide perovskite, CsSnBr3 and cesium titanium bromide antifluorite, Cs2TiBr6. For CsSnBr3, experiments utilized the orthogonal reactivity of the Cs+ cation, the Sn2+ cation, and the Br– halide anion. Ambient- pressure exposure to BF3 solutions probed the reactivity of interfacial bromines. Reactions with p-trifluoromethylanilinium chloride probed the exchange reactivity of the Cs+ cation. A complex-forming ligand, 4,4’-bis(trifluoromethyl)-2,2’-bipyridine, probed for interfacial Sn2+- site cations. For Cs2TiBr6, both BF3 and (C6F5)3B probed the reactivity of interfacial bromines. Fluorine features in x-ray photoelectron spectroscopy (XPS) quantified reaction outcomes for each solution-phase species. XPS indicated adsorption of BF3 on CsSnBr3 and (C6F5)3B on Cs2TiBr6 indicating surface-available halide anions on both surfaces. For CsSnBr3, temperature- programmed desorption (TPD) quantified a ~215 kJ mol–1 desorption energy of BF3 on the surface. Adsorption of the fluorinated anilinium cation included no concomitant adsorption of chlorine as revealed by the absence of Cl 2p features within the limits of XPS detection. The bipyridine ligand demonstrated adsorption to CsSnBr3. We discuss the present results in the context of interfacial stability, passivation, and reactivity for solar-energy conversion devices.

We quantified the chemical species present at polycrystalline cesium tin bromide perovskite, CsSnBr3 and cesium titanium bromide antifluorite, Cs2TiBr6. For CsSnBr3, experiments utilized the orthogonal reactivity of the Cs+ cation, the Sn2+ cation, and the Br– halide anion. Ambient- pressure exposure to BF3 solutions probed the reactivity of interfacial bromines. Reactions with p-trifluoromethylanilinium chloride probed the exchange reactivity of the Cs+ cation. A complex-forming ligand, 4,4’-bis(trifluoromethyl)-2,2’-bipyridine, probed for interfacial Sn2+- site cations. For Cs2TiBr6, both BF3 and (C6F5)3B probed the reactivity of interfacial bromines. Fluorine features in x-ray photoelectron spectroscopy (XPS) quantified reaction outcomes for each solution-phase species. XPS indicated adsorption of BF3 on CsSnBr3 and (C6F5)3B on Cs2TiBr6 indicating surface-available halide anions on both surfaces. For CsSnBr3, temperature- programmed desorption (TPD) quantified a ~215 kJ mol–1 desorption energy of BF3 on the surface. Adsorption of the fluorinated anilinium cation included no concomitant adsorption of chlorine as revealed by the absence of Cl 2p features within the limits of XPS detection. The bipyridine ligand demonstrated adsorption to CsSnBr3. We discuss the present results in the context of interfacial stability, passivation, and reactivity for solar-energy conversion devices.