We investigated the force induced dissociation of single specific bonds between protein A and immunoglobulin G. In these experiments both proteins were tethered to microbeads. Pi-conewton forces were applied by means of an ultrasoft spring. Upon bond formation the thermal fluctuations of this soft spring were reduced. This resulted in a sizeable contribution to the free enthalpy of bonding. Including this effect we calculated the relation between the lifetime of bonds connecting both microbeads and the lifetime of the bond between free molecules. We found that the lifetime depended on the stiffness of the force probe. Moreover, the lifetime was reduced by almost two orders of magnitude. Both predictions were verified in our experiments.

Model amorphous silica pores have been developed for use in molecular dynamics simulations. Specifically, roughly cylindrical pores have been constructed with hydrophilic, hydroxyl-terminated surfaces. The approach is designed to allow systematic variation of the pore radius and surface functionality. Thus, these pores are suitable for studying the variability in solvent structure, energy transfer and reaction dynamics occurring inside the pore due to surface modification. The method is described and the properties of the generated pores are discussed.

Rheology and dynamic light scattering capture re-entrant behavior of laponite-polymer systems. Neat laponite under basics conditions and concentrations of 2wt% or greater forms a viscoelastic soft glass due to electrostatic repulsions. We show that that addition of low molecular weight poly(ethylene oxide) (PEO) melts the glass due to a depletion force. The depletion force speeds up dynamics in the system resulting in a low viscosity solution. A re-entrant viscoelastic solid is formed with the addition of high molecular weight PEO due to the polymer chains bridging between laponite particles. As expected the transition from a low to high viscosity solution scales with the polymer mean square end-to-end distance and gap between laponite particles.

We report the results of the investigations of the influence of confinement on the glass transition and dynamics of the a-relaxation processes in poly(octylmethacrylate) (POMA) by dielectric spectroscopy. The polymer was synthesized directly in pores of the porous glass matrix with interconnected and randomly oriented pores with an average pore size of 100 nm by free radical polymerization of the monomer. We found that confinement is resulted in the reduction of the glass transition temperature Tg of the polymer. This change in Tg was mainly due to the existence of a developed pore wall-polymer interface and difference in the dynamic behavior of polymer in the surface layers compared to that in the bulk. Complementary light scattering experiments show that in 100 nm matrices containing the polymer an anomalous change in light scattering, which switches the composite from the opaque state to the transparent, in a narrow temperature range around T = 60 °C. These changes could be explained by assuming that at low temperatures (opaque state) the orientational order of the relatively long linear aliphatic side groups is induced by the inner pore surface. The assumption of the formation of the orientationally ordered regions at the pore wall in confined POMA is in agreement with the molecular structures of the polymer and the surface of silica.

We present molecular dynamics simulation of molecules transporting through carbon nanotubes for applications in engineered flow channels, focusing on the dynamics of molecules spontaneously inserted into the nanotube channel in aqueous environment. The molecules studied include a C60 molecule, a finite segment of carbon nanotube with smaller diameter, and single/double- stranded DNA molecules. We show that in the absence of water solvation, the van der Waals interaction between the molecule and the nanotube wall can induce a rapid spontaneous encapsulation of the molecule inside the nanotube channel. The encapsulation process is strongly impeded for nanotube dissolved in water due to the competition between the van der Waals, hydrophobic and hydrogen bonding interactions in the nanotube/water/molecule complex. Water adsorption inside the nanotube channel plays an important role in determining the dynamics of the spontaneous insertion process.

Dynamic light scattering was applied to study the influence of randomness, boundary conditions (planar-axial and homeotropic-radial) and layer thickness (at nanoscale) of 5CB and 8CB confined to cylindrical pores and filled with Aerosil particles on relaxation of director orientational fluctuations. For confined 8CB in the nematic phase two well-defined relaxation processes were observed for both axial and radial orientations of the liquid crystal. The first process is qualitatively associated with bulk-like nematic director fluctuations. The second relaxation process (with slower relaxation time than the first one) is most likely due to the fluctuations in layers nearest the wall surface. The separation between the first and the second (slow) processes is clearer for thinner layers and the amplitude of the slow process is greater for thinner layers. This suggests that the slow process is surface related relaxation. The mode due to relaxation of fluctuations of director orientation in the vicinity of the surface of Aerosil particles was observed in filled liquid crystals as well.

Porous materials, concentrated colloidal suspensions are example of confining systems developing large specific surface and presenting a rich variety of shapes. Such an interfacial confinement strongly influences the molecular dynamics of embedded fluids and the diffusive motion of entrapped Brownian particles. An individual trajectory near the interface can be described as an alternate succession of adsorption steps and random flights in the bulk. Statistical properties of these random flights in various interfacial confining systems are determinant to understand the full transport process. Related to first passage processes, these properties play a central role in numerous problems such as the mean first exit time in a bounded domain, heterogeneous catalytic reactivity and nuclear magnetic relaxation in complex and biological fluids. In the present work, we first consider the various possibilities to connect two points of a smooth interface by a random flight in the bulk. Second, we analyze at the theoretical and experimental points of view a way to probe Brownian flights statistics. Implications concerning diffusive transport in disordered porous materials are discussed.

Template-synthesized silica nanotubes offer a unique and interesting opportunity for studying fluids in confined spaces. Their versatility stems from our ability to independently vary the inside diameter and surface chemistry. In this work we investigated capillarity for binary mixtures of water and methanol in hydrophobic nanotubes with internal diameters of both 30 and 170 nm. An improved sol-gel template synthesis process was used to prepare silica nanotubes with smooth and uniform walls within the pores of alumina template membranes. The pore diameter and thickness of the template membrane determined the outer diameter and length of the nanotube, respectively. The number of deposition cycles controlled the wall thickness. An octadecylsilane coating was selectively applied to the nanotube interior while leaving the nanotube exterior unmodified. The interiors of hydrophobic nanotubes prepared in this way were then labeled with trace amounts of adsorbed dyes. The diffusion of the dye molecules inside individual immersed nanotubes was investigated using fluorescence recovery after photobleaching (FRAP) experiments. Dye diffusion was used to determine the wettability of the nanotube interior as a function of solvent composition. Several important observations are reported here. First, a clear transition is observed in which all nanotubes change from non-wetting to wetting when the methanol mole fraction approaches 0.5. This transition appears at the same solvent composition for both nanotube sizes. Interestingly, the Young-Laplace equation fails to accurately predict the wetting transition. The difference between the observed and predicted wetting transition may be due to reliance on macroscopic values of contact angles or surface tensions in our predictions or may be related to the presence of liquid phase instability, dry-layers or non-spherical menisci within the hydrophobic pore.

The effect of nanostructure on the thermal oxidation of atomized iron has been investigated. Above 500°C atomized iron is oxidized in the presence of air. However, when iron is compacted with multiwalled carbon nanotubes (MWCNT) this oxidation is shifted by more than 100°C. Iron is protected by the nanostructure environment A large number of compositions of atomic ratios of iron and MWCNT have been examined in this study to understand the effect in detail. The effect of nanostructure in the thermal oxidation of iron is interpreted as due to iron atom experiencing extensive overlap and confinement effect. causing spin transfer. Based on theoretical calculations reported in the literature this confinement effect of iron is suggested to produce a transformation from 3d64s2 to an effective configuration of 3d84s0 producing spintronics effect.

It is well established that properly structured surface exhibits a lower friction drag, when exposed to a turbulent boundary layer, than a smooth surface under the same flow conditions. The observed drag decrease is usually attributed to an increased thickness of the viscous sublayer. In this work we examine the friction drag reducing mechanism. Two parallel approaches towards achieving this goal are presented. Photolithography was used to manufacture rectangular riblets in the 10∝m range on a standard 4” silicon wafer. A special compact plane channel system was designed and used for measurements of the frictional drag on structured surfaces in the turbulent flow covering a wide Reynolds number range. Navier-Stokes equation, for the examined drag reducing geometry, was solved in the laminar regime with appropriate boundary conditions. The resulting velocity field was used to extract the protrusion heights difference for streamwise and spanwise flows over the structured surface. The latter was then related to the experimentally measured drag reduction slope. We show that in case of a rectangular riblet, with a size of the order of one wall unit, the observed drag reduction can be accounted for within the above model.