Absorption of octadecanethiol and p-nitrobenzenethiol onto gold surfaces from ethanol solutions has been studied by means of contact angle, optical ellipsometry, angle-resolved XPS (ARXPS), and with grazing angle total reflection FTIR. Growth of the monolayers from dilute solutions has been monitored and Langmuir isotherm adsorption curves were fitted to experimental data. A saturated film is formed within approximately 5h after immersion in solutions of concentrations ranging from 0.0005mM to 0.01mM. We found, that the final density of monolayer depends on the concentration of the solution.

Advances in microfabrication and surface chemistry techniques have provided a new paradigm for the creation of in vitro systems for studying problems in biology and medicine in ways that were previously not practical. The ability to create devices with micro- to nano-scale dimensions provides the opportunity to non-invasively interrogate and monitor biological cells and tissue in large arrays and in a high-throughput manner. These systems hold the potential to, in time, revolutionize the way problems in biology and medicine are studied in the form of point-of-care devices, lab-on-chip devices, and biological microelectromechanical systems (BioMEMS). With new in vitro models, it will be possible to reduce the overall cost of medical and biological research by performing high-throughput experiments while maintaining control over a wide variety of experimental variables. A critical aspect of developing these sorts of systems, however, is controlling the device/tissue interface. The surface chemistry of cell-biomaterial and protein-biomaterial interactions is critical for long-term efficacy and function of such devices. The work presented here is focused on the application of surface and analytical chemistry techniques for better understanding the interface of biological elements with silica substrates and the development a novel Bio-MEMS device for studying muscle and neuromuscular biology. A novel surface patterning technique based on the use of a polyethylene glycol (PEG) silane self-assembled monolayer (SAM) as a cytophobic surface and the amine-terminated silane diethyeletriamine (DETA) as a cytophilic surface was developed for patterning a variety of cell types (e.g. skeletal muscle, and neural cells) over long periods of time (over 40 days) with high fidelity to the patterns. This method was then used to pattern embryonic rat skeletal muscle and motor neurons onto microfabricated silicon cantilevers creating a novel biological microelectromechanical system (BioMEMS) for studying muscle and the neuromuscular junction. This device was then used to study the effect of exogenously applied substances such as growth factors and toxins. Furthermore, a whispering-gallery mode (WGM) biosensor was developed for measuring the adsorption of various proteins onto glass microspheres coated with selected silane SAMS commonly used in BioMEMS system. With this biosensor it was possible to measure the kinetics of protein adsorption onto alkylsilane SAMS, in a real-time and label-free manner.

No description available.

No description available.

Over the past two decades one class of oligomers, polyhedral oligomeric silsesquioxanes (POSS), has attracted considerable attention because of their unique hybrid organic/inorganic molecular structures and nanoscopic sizes. While surface and interfacial properties may play a key role in many potential POSS applications, relatively little is actually known about the surface properties of POSS. This dissertation provides studies of the interfacial aspects of both POSS molecules and POSS/polymer blends at the air/water interface (A/W) through surface pressure-area per molecule (π-<i>A</i>) isotherm, Brewster angle microscopy (BAM), and interfacial stress rheometry (ISR) studies. Results for POSS Langmuir thin films at A/W show that trisilanol-POSS derivatives are a new class of amphiphiles, that exhibit multiple phase transitions in going from traditional 2D Langmuir monolayers (1 POSS molecule thick) to various 3D multilayer films upon compression. With small length/diameter ratios and bulky shapes, the monolayer phase behavior and packing states of different POSS are simpler than the traditional rod-like lipids. Meanwhile trisilanol-POSS derivatives have very different collapse behavior and multilayer organization showing strong substituent effects even though they have similar molecular sizes. While trisilanolisobutyl-POSS (TiBuP) monolayers undergo collapse around π ≈ 18 mNm⁻¹ and form various ordered or disordered solid-like 3D aggregates at different compression rates, trisilanolcyclohexyl-POSS (TCyP) monolayers collapse into trilayers via instantaneous nucleation with hemispherical edge growth around π ≈ 3.7 mNm⁻¹. ISR results reveal three different non-Newtonian flow regimes that correlate with phase transitions in the Pi-A isotherms. Further symmetric compression after trilayer formation induces TCyP thin films to self-assemble into highly ordered crystalline-like hydrophobic multilayers (≈8 POSS molecule thick) with unique rod-like morphologies, which are dramatically different from –collapsed– morphologies seen in other systems. By treating POSS derivatives as ideal nanofiller for studying confinement effects on filled polymer systems, amphiphilic poly(dimethylsiloxane) (PDMS) derivatives with different polar functional groups are studied as blends with TiBuP and octaisobutyl-POSS at A/W to resolve one of the key challenges for current nanocomposite applications: How to control nanofiller dispersion in polymer matrices? The results in this dissertation reveal that introducing polar groups into polymeric matrix polymers is a good way to control dispersion. / Ph. D.

Understanding mechanisms at the molecular level is essential for interpreting and predicting the outcome of processes in all fields of chemistry. Insight into gas-surface reaction dynamics can be gained through molecular beam scattering experiments combined with classical trajectory simulations. In particular, energy exchange and thermal accommodation in the initial collision, the first step in most chemical reactions, can be probed with these experimental and computational tools. There are many questions regarding the dynamic details that occur during the interaction time between gas molecules and organic surfaces. For example, how does interfacial structure and density affect energy transfer? What roles do intramonolayer forces and chemical identity play in the dynamics? We have approached these questions by scattering high-energy, rare gas atoms from functionalized self-assembled monolayers. We used classical trajectory simulations to investigate the atomic-level details of the scattering dynamics. We find that approximately six to ten carbon atoms are involved in impulsive collision events, which is dependent on the packing density of the alkyl chains. Moreover, the higher the packing density of the alkyl chains, the less energy is transferred to the surface on average and the less often the incident atoms come into thermal equilibrium with the surface. In addition to the purely hydrocarbon monolayers, organic surfaces with lateral hydrogen-bonding networks create more rigid collision partners than surfaces with smaller inter-chain forces, such as van der Waals forces. Finally, we find some interesting properties for organic surfaces that possess fluorinated groups. For argon scattering, energy transfer decreases with an increasing amount of surface fluorination, whereas krypton and xenon scattering transfer most energy to monolayers terminated in CF₃ groups, followed by purely hydrocarbon surfaces, and then perfluorinated surfaces. / Ph. D.

The structure/function relationship between bacteria and biocidal molecules in the vapor or solution phase is well-understood. However, the fundamental structure/function relationship between covalently-bound biocidal surface molecules and bacteria is not. While a number of antibacterial surfaces have been reported, detailed analysis of the molecular scale surface structure has not been performed. The lack of structural knowledge makes it difficult to determine how alterations to the surface affect the viability of the bacteria. Most of the antibacterial surfaces reported to date are composed of polymer systems. Controlling the properties of large surface-bound molecules like polymers is difficult. Self-assembled monolayers, or SAMs, of alkanethiols on gold have been used extensively in the past 20 years as model surfaces for investigation of a large breadth of surface phenomena. SAMs allow for control of the molecular scale surface structure and are amenable to a great number of characterization techniques. The primary objective of the work in this study is to establish the use of SAMs as a tool to investigate the fundamental relationship between surface structure and bacteria viability. The surfaces were characterized before interaction with bacteria by reflection-absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS). Determination of the viability of Escherichia coli on the surfaces was performed via the antibacterial assay. In the assay, a culture of E. coli was sprayed onto the surfaces using a chromatography sprayer. After addition of growth agar and overnight incubation, the number of colony forming units on the surface were counted. Statistical analyses were performed to compare the number of colony forming units on different surfaces. Surfaces were characterized after the assay by RAIRS. The RAIR spectra indicated that no significant change to the well-ordered alkane chain configuration was evident. The structural stability shown by the SAMs will allow for their use in future studies to determine fundamental relationship between surface structure and bacteria viability. / Master of Science

Interactions of gas-phase molecules with surfaces are important in many ordinary events, such as ozone depletion, corrosion of metals, and heterogeneous catalysis. These processes are controlled by the bonding, diffusion, and reactivity of the impinging gas species. Our research employs molecular beam techniques and well-characterized surfaces to study these processes. The goal of this study is to better understand how the physical and chemical nature of the surface interface influences energy transfer dynamics in gas-surface collisions. An atomic beam is used to probe the energy transfer dynamics in collisions of Argon with model surfaces of functionalized self-assembled monolayers (SAMs) (1-dodecanethiol and 11-mercapto-1-undecanol) on gold. The beam is directed towards the surface at an incident angle of 30 degrees and the scattered Ar atoms are detected at the specular angle of 30 degrees. Time-of-flight scans measure the velocity distributions of atoms leaving the surface, which correlate with the energy transfer dynamics of the impinging gas atoms. Gas-surface energy transfer experiments are accomplished by directing an 80 kJ/mol Ar atomic beam at a clean Au(111) surface and surfaces composed of hydroxyl-terminated or methyl-terminated SAMs on Au(111). The fractional energy transferred to the bare gold surface is 69 %, while it is grater than 77 % for the monolayer-covered surfaces. The extent of thermalization on the surface during the collision is significantly greater for the methyl-terminated surface than for the hydroxyl-terminated surface. Since the two monolayers are similar in structure, packing density, and mass, the differences in scattering dynamics are likely due to a combination of factors that may include differences in the available energy modes between the two terminal groups and the hydrogen-bonding nature of the hydroxyl-terminated SAM. / Master of Science

Adsorption of xyloglucan (XG) onto thin desulfated nanocrystalline cellulose (DNC) films was studied by surface plasmon resonance spectroscopy (SPR), quartz crystal microbalance with dissipation monitoring (QCM-D), and atomic force microscopy (AFM) measurements. These studies were compared to adsorption studies of XG onto thin sulfated nanocrystalline cellulose (SNC) films and regenerated cellulose (RC) films performed by others. Collectively, these studies show the accessible surface area is the key factor for the differences in surface concentrations observed for XG adsorbed onto the three cellulose surfaces. XG penetrated into the porous nanocrystalline cellulose films. In contrast, XG was confined to the surfaces of the smooth, non-porous RC films. Surprisingly surface charge and cellulose morphology played a limited role on XG adsorption. The effect of the non-ionic surfactant Tween 80 on the adsorption of cellulase onto alkane thiol self-assembled monolayers (SAMs) on gold was also studied. Methyl (-CH3), hydroxyl (-OH) and carboxyl (-COOH) terminated SAMs were prepared. Adsorption of cellulase onto untreated and Tween 80-treated SAMs were monitored by SPR, QCM-D and AFM. The results indicated cellulase adsorption onto SAM-CH3 and SAM-COOH were driven by strong hydrophobic and electrostatic interactions, however, hydrogen bonding between cellulase and SAM-OH was weak. Tween 80 effectively hindered the adsorption of cellulase onto hydrophobic SAM-CH3 substrates. In contrast, it had almost no effect on the adsorption of cellulase onto SAM-OH and SAM-COOH substrates because of its reversible adsorption on these substrates. / Master of Science

The thesis describes the study of structure and dynamics of polymers in confined geometry. We study the finite size effect on the dynamics of non glassy and glassy polymers. Systematic measurement have been performed to address the issue of the possibility of entanglement and hence reptation dynamics of the polymer segments in confinement. The confinement effect on the glassy dynamics has been studied for Langmuir monolayers as well as for polymer nanoparticle hybrid systems. Slow and heterogeneous dynamics are the underlined observed behavior for dynamics in hybrid systems. The available theories explains the slowing down of the dynamics as the system is cooled from the liquid state in terms of increasing cooperative motion of the molecules. The size of the cooperative region is predicted to grow with reducing temperature. Experiments, theories and simulation in confined dimensions have been motivated to detect this length scale of the cooperatively rearranging region. The surface and interface effects on glass transition were studied using measurements based on modulated differential scanning calorimetry and small angle X ray scattering techniques. The dynamical heterogeneity in glassy polymers were studied using advanced X ray photon correlation spectroscopy techniques. Our studies presented in this thesis are also an small step to contribute to the existing experimental results on studying the surface, interface and finite size effects on the morphology and dynamics of confined systems. These effects were studied for, firstly ultra thin Langmuir monolayers and secondly polymer nanoparticle hybrid systems. In Chapter 1, we provide the theoretical background along with brief review of the literature for understanding the results presented in this thesis. The details of the experimental set up and their operating principle along with the details of the experimental conditions are provided in Chapter 2. In Chapter 3 we presents our experimental results on surface morphology and surface dynamics in ultra thin Langmuir monolayer of polymers. Chapter 4 and Chapter 5 discusses the result based on polymer nanoparticle hybrid systems. We provide the summary of our result and the future prospective of the work in Chapter 6. In appendix we have shown the complete derivation of the equation used in Chapter 3 for understanding the surface morphology of Langmuir monoalyers on water surface. Chapter 1 provides in detail the introduction to several aspects related with the dynamics of both glassy and non glassy polymers in confinement. It starts with brief introduction to structure and dynamics of polymers in bulk. In the next section we discuss the macroscopic viscoelastic behavior of materials followed by a very brief discussion on the common techniques used for such measurement. Further it discusses the theory and several available models present in literature to understand the dynamics of glass transition. This section is followed by discussion on surface and interface effects on structure and dynamics of such systems in confinement. Towards the end of this chapter we discuss the universal behavior of slow dynamic observed in soft glassy materials. Chapter 2 contains the details of the experimental techniques which has been used for the study. Brief introduction to basic principles of the measurements followed by details of the material and methods have been provided. The surface morphology and dynamics of Langmuir monolayer of polymers confined at air water interface, under compressive mechanical strain has been discussed in Chapter 3. The results presented for surface morphology are based on the studies using the combination of in situ grazing angle incidence small angle X ray scattering and ex situ atomic force microscopy measurements on monolayers transfered on silicon substrate. The issue of the presence of reptation motion in confinement has been addressed by performing systematic measurements as a function of surface concentration and molecular weight at fixed temperature. The glassy dynamical behavior has been studied on different glassy polymer layer as a function of surface concentration and temperature. In Chapter 4 we show the glass transition behavior of polymer nanoparticle (PMMA gold) hybrid system based on thermal measurements. This chapter discusses the role of the existence of a length scale in deciding the dynamics of the glass transition temperature of polymers. The confinement effect was tuned by the variation of the inter particle spacing between the nanoparticles in the polymer matrix. It also discusses the model to understand the observed behavior of the glass transition temperature in terms of the tunability of the polymer particle interface and the effect of the interface morphology on the dynamics of glass transition temperature. Chapter 5 is about the study of dynamics of polymer nanocomposites near glass transition as a function of temperature, wave vector and volume fraction of gold nanoparticles using X ray photon correlation spectroscopy. Based on our experimental results , we provide a phase diagram for dynamics in 2D space of temperature, wave vector and volume fraction for our PMMA gold nanoparticle hybrid samples. Chapter 6 contains the summary and the future perspective of the work presented.