Reverse micelles (RMs) are aggregates in which nanoscale droplets of a polar liquid, usually water, are surrounded by a surfactant layer in a nonpolar continuous phase. They are widely used as media for reactions in which the extent of confinement or the presence of a surfactant interface play a central role. We have used molecular dynamics (MD) computer simulation and quasielastic neutron scattering (QENS) and to investigate the mobility of water molecules in reverse micelles. The contribution of water to the QENS signal is enhanced by deuterating the surfactant and the nonpolar phase. Our studies of water mobility have focused on the effects of water pool size, determined by the water/surfactant mole ratios w0, as well as on the properties of the water-surfactant interface. Specifically, we have examined the effects of varying w0 and of substituting other alkali ions for the usual Na+ counterion of the anionic surfactant AOT (bis (2-ethylhexyl) sulfosuccinate)). We find good agreement between the QENS signal and its prediction from MD simulation. This allows us to obtain additional insight into water mobility by analyzing the MD self-intermediate scattering function (ISF) of water hydrogens in terms of contributions from molecular rotation and translation and from molecules in different interfacial layers. MD data indicate that the translational ISF decays nonexponentially due to lower water mobility close to the interface and to confinement-induced restrictions on the range of translational displacements. Rotational relaxation also exhibits nonexponential decay. However, rotational mobility of O-H bond vectors in the interfacial region remains fairly high due to the lower density of water-water hydrogen bonds in the vicinity of the interface.

The influence of film thickness and polymer molecular weight on the diffusion coefficient of water in poly(methyl methacrylate) thin films supported on gold coated surfaces has been studied using vapor sorption experiments via quartz crystal microbalance (QCM) methods. Diffusion coefficients for films ranging in thickness from approximately 1 μm to 50 nm were determined. It is observed that the diffusion coefficient of water in PMMA on weakly interacting substrates is a strong function of film thickness, and that the diffusion coefficient decreases drastically as film thickness is reduced below a critical thickness value. Furthermore, it is found that polymer molecular weight also appears to play an important role in determining the diffusion behavior of such polymer thin film systems.

Pulsed field gradient (PFG) NMR technique has been applied to study molecular transport in two different types of nanostructured materials, viz. in fluid catalytic cracking (FCC) catalysts and in lipid membranes. Diffusion studies have been performed for a broad range of molecular displacements covering displacements that are as small as a fraction of a micron. The effective diffusivities recorded on various length scales are used to evaluate the relevance of various transport modes in the particles of FCC catalysts for the rate of molecular exchange between catalyst particles and the surrounding atmosphere. This rate is shown to be primarily related to the diffusion in the meso- and macropores of the particles under the condition of fast molecular exchange between these pores and the zeolite crystals located in the particles. Studies of lipid membranes are focused on developing fundamental understanding of the influence of various types of domains on lateral mobility of lipids. A meaningful study of this influence requires an ability of monitoring lipid diffusion for different displacements that are smaller and larger than the domain size. First PFG NMR data along this direction are presented.

Optical tweezers, atomic force microscopes, patch clamping, or fluorescence techniques make it possible to study both the equilibrium conformations and dynamics of single DNA molecules as well as their interaction with binding proteins. In this paper we address the dynamics of local DNA denaturation (bubble breathing), deriving its dynamic response to external physical parameters and the DNA sequence in terms of the bubble relaxation time spectrum and the autocorrelation function of bubble breathing. The interaction with binding proteins that selectively bind to the DNA single strand exposed in a denaturation bubble are shown to involve an interesting competition of time scales, varying between kinetic blocking of protein binding up to full binding protein-induced denaturation of the DNA. We will also address the potential to use DNA physics for the design of nanosensors. Finally, we report recent findings on the search process of proteins for a specific target on the DNA.

By employing novel hybrid silica/functional polymer aerogels, control of the course of chemical reactions between reactants confined inside of the aerogels with reactants whose access to the confinement domain is controlled by diffusion has been explored. Thus, monolithic silica/biopolymer hybrid aerogels have been synthesized with coordinated metal ions that can react with amino acids, such as L-cysteine, that are provided externally in a surrounding solution. Metal ions, such as Au(III), that can react in solution with the amino acid to produce one set of products under a given set of stoichiometric or concentration conditions, and a different set of products under a second set of conditions, were selected for incorporation into the aerogel. It was discovered that the course of the reaction can be changed by spatial confinement of the reaction domain in the aerogel. For example, in the case of Au(III) and L-cysteine, the Au(III) ions are confined in nanoscale domains, and when they are reacted with the amino acid, the nature of the reaction products is controlled by diffusion of the L-cysteine into the domains. Exploration of these and related phenomena will be presented.

We report a method for fabricating, anisotropically designed, multiphasic nano-particles with uniform magnetic half-shells. Cobalt layers were deposited onto commercially made non-magnetic polystyrene nanospheres and microspheres, using ultrahigh vacuum vapor deposition, which produced particles with a half-shell of uniform size, shape and magnetic content. Iron was also deposited onto commercially made silica nanospheres and microspheres and was characterized using transmission electron microscopy and scanning electron microscopy. The coercivity of the magnetic material layers, on the substrate-supported spheres, was enhanced compared to the bulk values of such films without spheres. The particles, once removed from the substrate, were amenable to being rotated in solution, which could allow for more accurate physical and chemical measurements in a variety of fluidic environments. Applications for imaging local mechanical, magnetic and electrical environments are also delineated.

We measured the electrowetting behavior of aqueous salt solutions. By varying the conductivity and the frequency of the applied AC voltage we determined the range of the validity perfect conductor assumption of the standard electrowetting theory for the case of AC voltage. We show that the contact angle reduction is dramatically reduced at high frequency and low salt concentration due to Ohmic losses with the liquid. A simple RC-equivalent circuit model explains the observations. It is demonstrated that finite conductivity effects are more pronounced for sessile droplets than for droplets confined between to parallel plates.

The dynamics of surface fluctuations in thin supported polystyrene films have been investigated using x-ray photon correlation spectroscopy (XPCS) in reflection geometry. The results from the films thicker than four times of the radius of gyration (Rg) of polystyrene show the behavior of the capillary waves expected in viscous liquid. However, thinner films show a deviation indicating the need to account for viscoelasticity. Theoretical considerations with viscoelastic liquid model has been performed by introducing frequency dependent viscosity and compared with Fredrickson’s brush model (Macromolecules, 25, 2882 (1992)). The theory has been extended to the surface and interfacial modes in a bilayer film system. The results will be discussed in terms of surface tension, viscosity, and shear modulus.

First-principles calculations are performed for the radial-breathing mode of all 105 single-walled carbon nanotubes within the rolling-geometry diameter range of 0.4 to 1.4 nm. The diameter dependence of the frequencies is analyzed in some detail, and compared with measurable parameters of bulk graphite. The frequencies are compared with those available from other first-principles work, and experimental studies.

The effect of a nanometer confinement on the molecular dynamics of poly(methyl phenyl siloxane) (PMPS) was studied by dielectric spectroscopy (DS) and temperature modulated DSC (TMDSC). As confining hosts random nanoporous glasses with nominal pore sizes of 2.5 nm – 20 nm have been used. Epically it is focused on the influence of a surface treatment on the dynamical behavior. DS and TMDSC experiments show that for PMPS in 7.5 nm pores the molecular dynamics is faster than in the bulk which originates from an inherent length scale of the underlying molecular motions. There is no influence of the surface treatment on the glassy dynamics for this pore size.

At a pore size of 5 nm the temperature dependence of the relaxation times changes from a Vogel / Fulcher / Tammann like behavior to an Arrhenius one where the apparent activation energy depends on pore size. For silanized pores a higher value (102 kJ / mol) is found than for natives pores (73 kJ / mol). For a pore size of 2.5 nm the activation energy is independent of the surface treatment. The value of ca. 40 kJ / mol points to a real localized process.

The increment of the specific heat capacity at the glass transition depends strongly on pore size and vanishes at a finite length scale which can be regarded as minimal length scale for glass transition to appear. The actual value depends on surface treatment. From this difference the thickness of an immobilized boundary layer of about 1 nm is estimated for uncoated pores.

Optical Kerr effect spectroscopy has been used to study the orientational dynamics of benzene and benzene-d6 confined in nanoporous sol-gel glasses. Orientational diffusion was found to be inhibited considerably in confinement due to the strong wetting of benzene on silica. The orientational dynamics of benzene-d6 were found to be affected less than those of benzene, which is in agreement with the somewhat larger contact angle of benzene-d6 on silica. Comparison of our results to Raman data for confined benzene-d6 suggests that this liquid is considerably more organized at the pore surfaces than in the bulk.

Molecular dynamics (MD) simulations of atomistic processes of nucleation and crystal growth of silicon (Si) on SiO2 substrate have been performed using the Tersoff potential based on a combination of Langevin and Newton equations. A new set of potential parameters was used to calculate the interatomic forces of Si and oxygen (O) atoms. It was found that the (111) plane of the Si nuclei formed at the surface was predominantly parallel to the surface of MD cell. The values surface energy for (100), (110), and (111) planes of Si at 77 K were calculated to be 2.27, 1.52, and 1.20 J/m2, respectively. This result suggests that, the nucleation leads to a preferred (111) orientation in the poly-Si thin film at the surface, driven by the lower surface energy.

With increased molecular complexity of organic thin film electronics, novel characterization methods are required to provide nanoscale material property information. Particularly important in polymer thin film electronics are methods characterizing the mobility properties of materials that are in amorphous unsteady states. If the unsteady nature of materials is paired with dimensional and interfacial constraints in anisotropic systems, such as thin films, it produces material systems of great challenges with enormous engineering potentials. Two examples are addressed in this paper, involving desired and undesired supramolecular alignments in polymer thin films, the spectral stability in organic blue-light emitting diodes and the electro-optical (EO) activity in organic non-linear optical (NLO) materials, in conjunction with novel scanning probe microscopy (SFM) based characterization tools. The nanoscopic methods discussed here, i.e., shear modulation force microscopy (SM-FM), and nanoscale isothermal friction analysis (NIFA), offer a quantitative approach for investigating the mobility/stability of organic semiconductor polymer films. Thereby, local properties such as energy barriers for sub-molecular motions (relaxations) and critical transition temperatures can be directly inferred from organic films that are used in actual electronic devices.

The formation of nanobubbles at solid-liquid interfaces has been studied using the atomic force microscopy (AFM) imaging technique. Nanobubble formation strongly depends on both the hydrophobicity of the solid surface and the polarity of the liquid subphase. While nanobubbles do not form on flat hydrophilic (silicon oxide wafer) surfaces immersed in water, they appear spontaneously at the interface of water against smooth, hydrophobic (silanized wafer) surfaces. From the experimental observations we draw the conclusion that the features observed in the AFM images are deformable, air-filled bubbles. In addition to the hydrophobicity of the solid surface, differences in solubility of air between two miscible fluids can also lead to formation of nanobubbles. We observe that nanobubbles appear at the interface of water against hydrophilic silicon oxide surfaces after in-situ mixing of ethanol and water in the fluid-cell.

The shapes of the nanobubbles are well approximated by spherical caps, with width much larger than the height of the caps. We quantify the morphological distribution of nanobubbles by evaluating several important bubble parameters including surface coverage and radii of curvature. In conjunction, with an analytical model available in the literature, we use this information to estimate that the present nanobubble morphology may give rise to slip lengths ∼1–2 µm in pressure driven flows for water flowing over the hydrophobic surface. The consistency of the calculated slip length with the experimental values reported in the literature, suggests that the apparent fluid slip observed experimentally at hydrophobic surfaces may arise from the presence of nanobubbles.

Pre-thinned foils composed of amorphous silicon and polycrystalline cobalt were irradiated using femtosecond pulse-length lasers at fluences sufficient for ablation (material removal). The resultant ablated hole and surrounding vicinity was studied using transmission electron microscopy to determine modifications to the structure. Evidence of cobalt silicide formation was observed within a 3 micron radius of the laser hole edge by use of selected area electron diffraction (SAED). In addition, elongated grains of crystalline silicon was observed within 500 nm of the laser hole edge, indicating melting of the amorphous silicon and heat dissipation slow enough to allow recyrstallization. This initial work demonstrates the use of pre-designed nanostructured multilayer systems as a method for nanoscale profiling of heat dissipation following pulsed laser irradiation.

We have performed a photoemission study of various alkanethiolate- (AT-) passivated Au nanoparticles with diameter of 4 nm on the highly oriented pyrolytic graphite (HOPG) substrates. It is found that the photoemission spectra in the vicinity of Fermi level of all the present AT-passivated Au nanoparticles on the HOPG substrates do not exhibit the usual metallic Fermi edge, with the steep slope being away from the Fermi level. Moreover, it is found that these spectral features depend on the surface-passivant molecules. We attribute the unusual spectral features in the vicinity of Fermi level to the dynamic charging effect in photoemission final-state, indicative of the interaction between the nanoparticle and substrate through the surface-passivants on a femtosecond time scale.

Particles diffusing in a confined space should encounter one another with a probability that depends on the size and dimension of the space. The present work uses pairs of random walkers on a lattice to investigate the encounter probability in one, two, and three spatial dimensions. There is an initial rapid decay of the survival-time distribution that is followed by an exponential decay in time. The characteristic time for this latter decay is strongly dependent on the model space size and scales as a power law in the size. The exponent of the power law depends on the number of spatial dimensions. For a fixed L, the exponential tail of the survival-time distribution has a similar slope when the initial separation of the two walkers is varied. The spacing between the exponential decay curves scales with the initial separation in 1-D, but not in 2-D or 3-D. In addition, the mapping of two random walkers to an equivalent single walker is explored.

We present measurements on the spontaneous imbibition of water, a linear hydrocarbon (n-C16H34) and a liquid crystal (8OCB) into the pore space of monolithic, nanoporous Vycor glass (mean pore radius 5nm). Measurements of the mass uptake as a function of time, m(t), are in good agreement with the Lucas-Washburn - prediction typical of imbibition of liquids into porous hosts. The relative capillary rise velocities scale as expected from the bulk fluid parameters.

The melting transition in hexane and decane monolayers are studied through use of a canonical ensemble molecular dynamics (MD) simulation method, where the monolayer is physisorbed onto a single, infinite graphite slab, with another confining graphite slab some varying vertical distance from the monolayer. Using a simple united-atom model to depict the alkanes, simulations suggest that the monolayer melting transition is largely dependent upon the average density of the physisorbed monolayer in addition to the spacing between the two graphite slabs. In particular, hexane is studied at two distinct coverages: (i) a fully commensurate (FC) monolayer, and (ii) a uniaxially incommensurate (UI) monolayer with an average density 0.9 times that of the FC monolayer. In the case of no confinement, both the FC hexane and decane monolayers exhibit a power law relation between the melting temperature of the monolayer and the graphite slab separation. In contrast, the UI hexane monolayer deviates from this behavior, suggesting that the power law behavior is an effect of the in-plane space, and how the monolayer melting transition depends upon this in-plane space. Finally, the role of the top (confining) layer corrugation in the power-law relationship, and the importance of this study toward future applications are briefly discussed.

A theoretical analysis based on self-consistent dynamical simulations is presented of electromigration- and stress-induced surface morphological response of voids confined in metallic thin films. The analysis predicts the onset of stable time-periodic states for the void surface morphological response, which is associated with current-driven wave propagation on the void surface. This time-periodic response is demonstrated under certain electromigration conditions and detailed response diagrams are presented which map the corresponding parameter space to regions of steady, time-periodic, and unstable surface morphological response. The evolution of the electrical resistance of these thin films also is computed, providing an interpretation for experimentally observed time-periodic response of the electrical resistance of metallic interconnect lines on the basis of current-driven void morphological evolution. In addition, we demonstrate significant effects on the electromigration-induced morphologically stable void migration of mechanical stress application in a metallic thin film. Specifically, we find that under certain electromechanical conditions, elastic stress can cause substantial retardation of void motion, as measured by the constant speed of electromigration-induced translation of morphologically stable voids. More importantly, this effect suggests the possibility for complete inhibition of void motion under stress.