Degradation-induced changes in the structural and optical properties of the polyfluorene-based blue emitting films and LEDs are examined using spectroscopic (FTIR, UV−vis, photo- and electroluminescence), analytical (FTIR and ESCA), and scanning probe microscopy techniques. The materials studied are oligomers (DP ∼ 10) of 9,9-di-n-hexylfluorene and its random copolymer with anthracene. In situ FTIR monitoring is used to characterize chemical changes in the active layer of operating LED devices. Two primary mechanisms of degradation are identified. In the first, photooxidation of the polymer matrix leads to the formation of an aromatic ketone, most likely fluorenone at the chain terminating monomer units, which quenches the fluorescence. The second process promotes aggregate formation, which then leads to loss of luminous intensity by exciton transfer and relaxation through excimers.

Composite molecular films of (AB)x type are fabricated by self-assembly of dendritic macromolecules of two adjacent generations using the electrostatic layer-by-layer deposition. Polyamidoamine dendrimers with surface amine groups for generations 4, 6, and 10 (G4, G6, G10) and carboxylic groups for generations G3.5, G5.5, and G9.5 have been used as building units. The molecular films are explored by scanning probe microscopy and X-ray reflectivity. All even generations are observed to form homogeneous, stable monolayers on a silicon surface. The thickness of a single monolayer varies with generation (molecular weight) from 1.8 nm (G4) to 2.8 nm (G6) and 5.6 nm (G10). Average thickness of a molecular layer in multilayer films is much smaller than the diameter of ideal spherical dendritic macromolecules. The model of molecular ordering of dendrimer films assumes compressed dendritic macromolecules of oblate shape with the axial ratio in the range from 1:3 to 1:6. The high interaction strength between "sticky" surface groups along with short range van der Waals forces and long range capillary forces are considered to be responsible for formation of compact monolayer structures. A tendency to higher spreading of high generation dendrimers observed here corresponds to the surface behavior predicted by molecular dynamic simulations.

Nanostructured magnetic materials have a variety of promising applications spreading from nano-scale electronic devices, sensors and high-density data storage media to controlled drug delivery and cancer diagnostics/treatment systems. Magnetic nanoparticles offer the most natural and elegant way for fabrication of such (multi-) functional materials. In this review, we briefly summarize the recent progress in the synthesis of magnetic nanoparticles (which now can be done with precise control over the size and surface chemistry), and nanoscale interactions leading to their self-assembly into 1D, 2D or 3D aggregates. Various approaches to self-organization, directed-, or template-assisted assembly of these nanostructures are discussed with the special emphasis on magnetic-field enabled interactions. We also discuss new physical phenomena associated with magnetic coupling between nanoparticles and their interaction with a substrate and the characterization of the physical properties at the nanoscale using various experimental techniques (including scanning quantum interferometry (SQUID) and magnetic force microscopy). Applications of magnetic nanoparticle assemblies in data storage, spintronics, drug delivery, cancer therapy, and prospective applications such as adaptive materials and multifunctional reconfigurable materials are also highlighted.

We report the results of probing adhesion and friction forces between surfaces with functional terminal groups with chemically modified scanning probe microscopy (SPM) tips. Surfaces with terminal groups of CH3, NH2, and SO3H were obtained by direct chemisorption of silane-based compounds on silicon/silicon nitride surfaces. We studied surface properties of the resulting self-assembled monolayers (SAMs) in air and aqueous solutions with different pHs. Work of adhesion, “residual forces”, and friction coefficients was obtained for four different types of modified tips and surfaces. Absolute values of the work of adhesion between various surfaces, W ad, were in the range 0.5−8 mJ/m2. The work of adhesion for different modified surfaces correlated with changes of solid−liquid surface energy estimated from macroscopic contact-angle measurements. Friction properties varied with pH in a register with adhesive forces showing a broad maximum at intermediate pH values for a silicon nitride/silicon nitride mating pair. Similar broad maxima were observed in the acid range for a NH2-terminated SAM and in the basic range for a SO3H-terminated SAM. This behavior can be understood considering the changes of the surface charge state determined by the zwitterionic nature of silicon nitride surfaces with multiple isoelectric points.

Record high efficiencies for a polymer‐based solar cell are reported here for an inorganic/organic composite photovoltaic device containing a single polymer film rather than a polymer/polymer or polymer/nanoparticle blend. The high efficiencies are reported to be due to device construction (see Figure) and the electronic properties of the phenylamino‐p‐phenylenevinylene‐based polymer used.

The topography of a surface is known to substantially affect the bulk properties of a material. Despite the often nanoscale nature of the surface undulations, the influence they have may be observed by macroscopic measurements. This review explores many of the areas in which the effect of topography is macroscopically relevant, as well as introducing some recent developments in topographic analysis and control.

The surface glass transition temperature, T g, of several amorphous polystyrene (PS) samples each with a narrow molecular weight distribution covering the range of M n from 3 900 to 1 340 000 has been measured by force−distance measurements using a scanning force microscope (SFM). Hysteresis in the loading−unloading cycles of the force−distance curves is observed above T g and is ascribed to viscoelasticity at the polymer surface. The hysteresis behavior for different molecular weight samples above T g is described in terms of the contact mechanics of the tip−surface interaction, by consideration of the relative roles of bulk viscoelasticity and peeling viscoelasticity. Data on the molecular mass dependence of thick films of the surface T g are presented, along with the dependence of T g on film thickness for thin films, and the annealing of films with a Langmuir−Blodgett overlayer. The results are related to existing theories describing the T g depression at lower M n as a result of the increased free volume in the system. The change in T g with molecular weight of PS is steeper for the surface than the bulk Fox−Flory relationship. We show that polymer chain entanglement variation rather than the end group localization on the free surface is responsible for the observed surface T g depression effect.

We explored molecular films of polyionic materials built by electrostatic deposition on a charged surface. Formation of self-assembled monolayers is monitored for poly(styrenesulfonate) (PSS) adsorbed on charged surfaces of amine-terminated self-assembled monolayer (SAM) and poly(allylamine) (PAA) on a PSS monolayer. In both cases, polyions are adsorbed on oppositely-charged surfaces. Observations of PSS monolayers at various stages of electrostatic deposition reveal inhomogeneous self-assembly at the earliest stages of deposition. During the first several minutes of deposition, negatively-charged PSS macromolecules tend to adsorb on selected defect sites of positively-charged SAM (scratches, microparticles, and edges) and form islands composed of PSS coils. At this stage, electrostatic adsorption of PSS chains is predominant and equilibration of the surface structure is not achieved by the slow surface diffusion mechanism. Only longer deposition times (>10 min) result in an equilibration of polymer layers and formation of a homogeneous thin PSS layer composed of highly flattened macromolecular chains. The monolayer thickness is between 1.0 and 1.5 nm, with a microroughness of about 0.2 nm. Self-assembly of a second PAA layer on top of a PSS monolayer follows similar tendencies, resulting in the formation of homogeneous PAA/PSS bilayers with an overall thickness of 1.7−2.5 nm.