We present a study of polystyrene-metal interfaces and discuss the relationship between the interfacial structure and anomalies in the measured glass transition temperature (Tg) of thin metal capped polystyrene (PS) films. The PS films used in these studies were coated with an evaporated metal layer of either Aluminum (Al) or gold (Au) and the Tg values were measured with ellipsometry. Uncoated PS films were also measured and these samples showed Tg values that were reduced relative to the bulk value for film thicknesses (h) less than 40 nm. Films coated with Au were shown to have measured Tg values that were the same as the bulk value (Tgbulk=370 K) for all the film thicknesses studied (h ≥ 8nm). The Al coated PS films had measured Tg values that were the same as the uncoated PS films. The observed differences are discussed in terms of the differences in the structure of the metal-polymer interfaces produced during thermal evaporation of the metal layers. A novel sample preparation procedure was developed to enable us to use Atomic Force Microscopy (AFM) to directly measure the structure of the buried polymer-metal interfaces. The measurements performed on these systems support the suggestion that the interfacial structure is different for the two metal-polymer interfaces studied and that these differences may be the cause of the anomalies in the measured Tgs of these samples.

Weak non-covalent interactions between single molecules govern many aspects of microscopic biological structure and function, e.g. cell adhesion, protein folding, molecular motors and mechanical enzymes. The dynamics of a weak biomolecular bond are suitably characterized by the kinetic transport of molecular states over an effective energy landscape defined along one or more optimal reaction pathways. Motivated by earlier developments [1,2], we present a novel method to quantify subtle features of weak chemical transitions by analyzing the 3D Brownian fluctuations of a functionalized microsphere held near a reactive substrate. A weak optical-trapping potential is used to confine motion of the bead to a nanoscale domain, and to apply a controlled bias field to the interaction. Stochastic interruptions in the monitored bead dynamics report formation and release of single molecular bonds. In addition, variations in the motion of a bead linked to the substrate via a biomolecule (a protein or nucleic acid) signal conformational changes in the molecule, such as the folding/unfolding of protein domains or the unzipping of DNA. Thus, energy landscapes of complex biomolecular interactions are mapped by identifying distinct fluctuation regimes in the 3D motion of a test microsphere, and by quantifying the rates of transition between these regimes as mediated by the applied confining potential.

The 3D motion of the bead is tracked using a reflection interference technique combined with high-speed video microscopy. The position of the bead is measured over 100 times per second with a lateral resolution of ∼3–5 nm and a vertical resolution of ∼1–2 nm. Crucial to the interpretation of results, a Brownian Dynamics simulation has been developed to relate the statistics of bead displacements to molecular-scale kinetics of chemical interactions and structural transitions. The experimental approach is designed to enlarge the scope of current techniques (e.g. dynamic force spectroscopy [3]) to encompass near-equilibrium forward/reverse transitions of weak-complex interactions with multiple binding configurations and more than one transition pathway.

The phase separation behaviour and the dynamics of concentration fluctuations of binary liquid mixtures are strongly influenced by confinement effects. We have investigated this confinement effect for the binary system isobutyric acid iBA + D2O imbibed into a mesoporous silica glass (CPG-10). The dynamics of the mixture are studied in the one-phase region as well as in the phase-separated state by means of neutron spin echo spectroscopy (NSE). Moreover, the averaged structures of the liquid are explored by means of small angle neutron scattering (SANS) leading to a length scale 4 < ξ < 9 nm for the fluctuations. The associated effective diffusion coefficient Deff as obtained for NSE is found to decrease with temperature ny nearly one order of magnitude in the temperature range from 75°C to 25°C.

Thermal effects may affect the velocity dependence of friction on the nanoscale in different ways. In a dry environment the stick-slip motion of a nanotip sliding across a crystalline surface is modified by thermal vibrations, which leads to a logarithmic increase of friction with the sliding velocity at very low speeds (v < 10 μm/s). At higher speeds the role of thermal activation is negligible, and friction becomes velocity-independent. An analytical expression, which explains both regimes of friction vs. velocity, is introduced. In a humid environment the situation is complicated by water capillaries formed between tip and surface, which act as obstacles for thermally activated jumps. Depending on the wettability of the surface, different tendencies in the velocity dependence are observed.

We study, by means of Grand Canonical Monte Carlo simulations, the effect of disorder in pore morphology and topology on adsorption of simple fluids at 77 K. We consider the case of microporous carbons and mesoporous silicas. For both systems, we found that morphological and topological disorder affects the adsorption isotherm. Consequently, we show that complex porous networks cannot be modeled as a collection of unconnected pores of simple geometry. In the case of microporous carbons, the isosteric heat of adsorption for disordered systems differs significantly from that obtained for an assembly of unconnected slit pores. In contrast, the isosteric heat of adsorption for the disordered mesoporous silica sample compares reasonably well with that observed for a silica material having regular cylindrical pores.

Conception and industrial production of viable high specific energy/power batteries is a central issue for the development of non-polluting vehicles. In terms of stored energy and safety, solid-state devices using polymer electrolytes are highly desirable. One of the most studied systems is PEO (polyethylene oxide) complexed by Li salts. Polymer segmental motions and ionic conductivity are closely related. Bulk PEO is actually a biphasic system where an amorphous and a crystalline state (Tg ≈ 213 K, Tm ≈ 335 K) coexist. To improve ionic conduction in those systems requires a significant increase of the amorphous phase fraction where lithium conduction is known to mainly take place. Confinement strongly affects properties of condensed matter and in particular the collective phenomena inducing crystallization. Confinement of the polymer matrix is therefore a possible alternative route to the impractical use of high temperature.

Results of a quasi-elastic incoherent neutron scattering study of the influence of confinement on polyethylene oxide (PEO) and (PEO)8Li+[(CF3SO2)2N]− (or (POE)8LiTFSI) dynamics are presented. The nano-confining media is Vycor, a silica based hydrophilic porous glass (characteristic size of the 3D pore network ≈ 50 Å). As expected, the presence of Li salt slows down the bulk polymer dynamics. The confinement also affects dramatically the apparent mean-square displacement of the polymer. Local relaxational PEO dynamics is described KWW model. We also present an alternate model and show how the detailed polymer dynamics (correlation times and local geometry of the motions) can be described without the use of such stretched exponentials so as to access a rheology-related meaningful physical quantity: the monomeric friction coefficient.

Molecular dynamics computer simulations are used to study the structure and dynamics of 1nm wide films of poly(ethylene oxide)(PEO) confined between mica type layered silicates of different cation exchange capacities(CEC). The simulation setup mimics the experimental systems formed by intercalation of PEO in silicate clays with differing numbers of inherent charges. Counterbalancing lithium cations are present in the interlayer gallery to offset the negative charge on the silicate platelets created by the isomorphic substitution of trivalent aluminum by divalent magnesium ions. It is seen that the presence of the lithium has a significance influence on the behavior of the system, with PEO segmental motion strongly dependent on the number of Li+ present in the slit pore. In particular, the coexistence of fast and slow modes for C-H bond dynamics is heavily affected due to the strong interaction between the Li+ ions and partially charged PEO oxygen. In conjunction with local density inhomogeneities, the coordination between lithium and oxygen is responsible for the anomalous segmental dynamics of nanoconfined PEO.

We studied the kinetics of a diffusion-limited trapping reaction A + T → T in an effective one-dimensional geometry by experiments, supported by simulation calculations. The experiments are based on the photobleaching reaction of fluorescein dyes. The main parameter of interest is the θ-distance, which is related to the expansion of the depletion zone and can be measured directly from experiment. We found that θ-distance scales with t1/2 asymptotically, as predicted by previous theory. In addition, we found that the θ-distance increases faster than t1/2 inside the trap at early times, which has not been explored previously. Furthermore, there is a third, intermediate regime, with a slow increase of slope. Our experimental results are consistent with our simulation results.

A spinodal demixing technique was employed for the preparation of linear poly(ethylene oxide) (PEO) confined to nanoscopic strands which in turn are embedded in a quasi-solid and impenetrable methacrylate matrix. Both the molecular weight of the PEO and the mean diameter of the strands are variable to a certain degree. Chain dynamics of the PEO in the molten state was examined with the aid of field-gradient NMR diffusometry (time scale: 10−2 s … 100 s) and field-cycling NMR relaxometry (time scale: 10−9 s … 10−4 s). The dominating mechanism for translational displacements probed in the nanoscopic strands by either technique is shown to be reptation. A corresponding evaluation formalism for NMR diffusometry is presented. It permits the estimation of the mean PEO strand diameter. Depending on the chemical composition of the matrix, the diameters range from 9 to 58 nm. The strands were visualized by electron microscopy. On the time scale of spin-lattice relaxation time measurements, the frequency dependence signature of reptation, that is T1 ∝ ν3/4, showed up in all samples. A “tube” diameter of only 0.6 nm was concluded to be effective on this time scale even when the strand diameter was larger than the radius of gyration of the PEO random coils. This “corset effect” is traced back to the lack of the local fluctuation capacity of the free volume in nanoscopic confinements. The confinement dimension is estimated at which the cross-over from “confined” to “bulk” chain dynamics is expected.

The influence of film thickness and polymer molecular weight on the diffusion coefficient of a series of small molecule penetrants (including water, benzene, and trifluoroacetic acid) in thin films of two different model photoresist polymers (poly(p-hydroxystyrene) and bis-triflouromethyl carbinol substituted poly(norbornene)) 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 small molecules in a thin polymer film is a strong function of film thickness, and that the diffusion coefficient decreases drastically as film thickness is reduced below a critical thickness value. This critical thickness value is found to be a function of both the type of polymer used and the polymer molecular weight.

Broadband dielectric spectroscopy was used to study the influence of boundary conditions and layer thickness of liquid crystal (LC) confined to cylindrical pores on low frequency and high frequency relaxation processes. Low frequency measurements provided information on the relaxation of surface polarization that arose at LC – pore wall interface. The dynamics of molecular reorientations were investigated in high frequency experiments. In samples with axial orientation of molecules, the dielectric mode due to reorientation of molecules around their short axis was investigated. The homeotropic alignment of molecules facilitated the investigation of the librational mode. The behavior of this mode was different from the behavior observed in investigations of relaxation due to reorientation of molecules around their short axis. Broadening of the dielectric spectra was observed in confined LC. The broadening increases with decreasing liquid crystal layer thickness.

The thermal expansion and viscosity of water and salt solutions in porous silica glasses have been systematically investigated, and the effect of salts on the properties of water in confined geometry has been addressed. A dilatometric method has been devised and utilized to measure the thermal expansion of confined liquids. A beam-bending method that was developed to study the permeability of porous bodies has been used to measure the relative viscosity of salt solutions to water inside the silica pores. This work has demonstrated that water when confined in nanopores shows anomalous behavior and its thermal expansion is higher than bulk water. This work has also suggested that the presence of ions in water could enhance the anomaly of water in confined space and the extent of the ion effect is dependent on the ion charge.

The effect of a nanometer confinement on the molecular dynamics of poly(methyl phenyl siloxane) (PMPS) was studied by dielectric spectroscopy (DS), temperature modulated DSC (TMDSC) and neutron scattering (NS). 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. 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. At the same pore size Δcp vanishes. These results give strong evidence that the glass transition has to be characterized by an inherent length scale of the relevant molecular motions. Quasielastic neutron scattering experiments reveal a strong change even in the microscopic dynamic.

Terahertz (THz) time-domain spectroscopy (TDS) has been used to study far infrared absorption spectra of chloroform confined within nanoporous glasses of various pore sizes. Intermolecular interactions and dynamics in the confined system are discussed.

We have studied the deterministic dynamics of underdamped single and multiparticle ratchets associated with current reversal, as a function of both the amplitude and the frequency of an external driving force. We show that control of current reversals in deterministic inertia ratchets is possible as a consequence of a locking process associated with different mean velocity attractors. Control processes employing small perturbations on the frequency and the amplitude of the external force may be designed in view of the intermixed fractal nature of the domains of attraction of the mean velocity attractors. The range where each control parameter is capable of reversing the current is determined. Quenched noise has significant effect on the basins of attraction. In particular, with increasing disorder the direction of a packet of particles can be reversed, leading to disappearance or weakening of the negative velocity attractor. The influence of the mass of the particles is also considered in order to design control techniques capable of separating particles of different masses.

Recent studies have revealed that, in contrast to non-associating liquids such as oils or organic solvents, salt-free water retains a viscosity close to its bulk value even when confined to films thinner than some 3 nm, indeed down to only one or two monolayers thick [1,2]. For the case of high concentration aqueous salt solution compressed down to subnanometer films between charged surfaces, the trapped hydrated ions serve to act as molecular ball-bearings, sustaining a large load while remaining very fluid under shear [3]. This behaviour is attributed to the tenacity of the hydration sheaths together with their rapid relaxation time. Finally, a very recent study [4] has shown that when charged polymer brushes in aqueous media are compressed and slid past each other, they provide a lubrication that is considerably superior to that afforded by neutral brushes: This is attributed on the one hand to the resistance to mutual interpenetration of the chains due to entropic barriers in the good-solvent conditions, and, on the other hand, to the hydration-sheaths on the charged polymer segments which can act – as noted above – as molecular ball-bearings.

We investigate the translocation of a single stranded DNA (ssDNA) through a pore, which fluctuates between two conformations, by using coupled master equations (ME). The probability density function (PDF) of the first passage times (FPT) of the translocation process is calculated, displaying a triple, double or mono-peaked behavior, depending on the system parameters. An analytical expression for the mean first passage time (MFPT) of the translocation process is derived, and provides an extensive characterization of the translocation process.

Dynamic light scattering (DLS) has been used to study the influence of boundary conditions (planar-axial and homeotropic-radial) and layer thickness of liquid crystal (8CB) confined to cylindrical pores on phase transitions and 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 relaxation is qualitatively associated with bulk-like nematic director fluctuations. The second relaxation (with relaxation time slower than the first one) is most likely due to the fluctuations in the layers nearest the wall surface. In samples with radial boundary conditions, we observed the onset of smectic-A phase order formation on the pore wall even though the rest of the liquid crystal could be in the nematic phase. The influence of pore wall-liquid crystal interactions on the properties of the confined 8CB was stronger for radial boundary conditions of confined liquid crystal, than in the case of axial orientation‥ The separation between the first and the second (slow) process was clearer for thinner layers and the amplitude of the slow process was greater for thinner layers. This suggests that the slow process was related to surface relaxation of director fluctuations.

Although the volume relaxation of bulk homopolymer glasses is thoroughly understood, many questions remain about the volume relaxation of polymers cast from solvent. Furthermore, in polymer thin films, the possible effects of confinement, surfaces and interfaces on relaxation are largely unexplored. Measurements of the film thickness of spin-cast poly(methyl methacrylate) thin films over extended periods of time, using spectroscopic ellipsometry, reveal that the characteristic time for relaxation increases with film thickness. This result is consistent with the idea of enhanced molecular mobility in thin films, and it might reflect the conformation and a reduced extent of entanglements of the polymers when spin-cast from dilute solution.

We have applied sum frequency generation (SFG) vibrational spectroscopy, a submonolayer surface sensitive analytical technique, to study interfacial structures of poly (ethylene glycol) (PEG), poly (propylene glycol) (PPG), their solutions, their copolymers, and copolymer solutions while contacting different media including air, fused silica, and various polymers.

For the first time, conformations of polyether materials at various interfaces have been shown at the molecular level in situ. Depending on the hydrophobicity of the solid contacting media, the liquid polymers PEG and PPG show different conformations at different interfaces, which can be correlated to molecular interactions at these interfaces. The favorable interaction between hydrophobic media and the hydrophobic segments, methylene or methyl groups, of polyethers causes an ordered conformation with these groups standing up at the interface. The unfavorable interaction between hydrophilic media and hydrophobic segments of the polyethers induces interfacial methylene or methyl groups to have a random structure or to lie down at the interfaces, indicated by the weakening or even absence of SFG signals. For comparison, interfaces between aqueous PEG or PPG solutions and air, polystyrene (PS), poly(methyl methacrylate) (PMMA), and fused silica have also been investigated. In addition, we have studied conformations of pluronics at various interfaces, showing that different blocks have different interface activities. The interfaces are always dominated by the PPG segments. The studies on molecular level interfacial structures of PEG, PPG and pluronics will help us to understand and control the interfacial behavior of liquids at interfaces.