We report on structural investigations of a series of regioregular poly(3-hexylthiophene) with well-defined molecular weight (5-19 kg/mol) using DSC, small angle and wide-angle X-ray scattering, and AFM. With increasing temperature, we identify three ordered phases, namely 3D crystalline, 2D crystalline with disordered side chains, and a layered phase of smectic symmetry, followed by complete melting. Although all samples crystallize in extended chain conformation, the lower molecular weight material exhibits a lower crystallinity, most likely caused by noncrystallizable end groups. The crystallinity increases strongly with increasing molecular weight, which could be a possible explanation for the known dependence of charge transport properties on molecular weight.

Crystallization is almost always initiated at an interface to a solid. This observation is classically explained by the assumption of a reduced barrier for crystal nucleation at the interface. However, an interface can also induce crystallization by prefreezing (i.e., the formation of a crystalline layer that is already stable above the bulk melting temperature). We present an atomic force microscopy (AFM)-based in situ observation of a prefreezing process at the interface of a polymeric model system and a crystalline solid. Explicitly, we show an interfacial ordered layer that forms well above the bulk melting temperature with thickness that increases on approaching melt-solid coexistence. Below the melting temperature, the ordered layer initiates crystal growth into the bulk, leading to an oriented, homogeneous semicrystalline structure.semicrystalline polymers | AFM | thin films | epitaxy T he fundamental process of crystallization from the liquid or gaseous state is of importance in many areas of condensed matter physics and materials science. In practice, crystallization is, in most cases, initiated at an interface to a solid. Crystal growth on solid substrates from the gaseous state has been studied in depth, and detailed understanding of different growth modes as well as interfacial thermodynamics has been achieved (1-3). Much less experimental data are available for crystallization occurring at the interface from the solid to the melt. Generally, crystallization can be initiated at the solid-melt interface by two processes: heterogeneous nucleation or formation of a crystalline wetting layer (so-called prefreezing) (4-6). In terms of thermodynamics, these processes are very different. Whereas nucleation takes place under nonequilibrium conditions at finite supercooling below the melting temperature T m of the bulk material, the formation of a wetting layer is an equilibrium phenomenon taking place above T m (4). It is often assumed that heterogeneous nucleation is the more relevant process (7), but in simulations, nucleation as well as prefreezing have been shown to occur (4,8). Prefreezing is expected for strongly attractive surfaces or epitaxial systems for which the lattices of the substrate and the crystallizing materials match well (9-12). In the case of polymers, prefreezing can also manifest itself in the conformational degrees of freedom, leading to an interfacial layer with nematic order, which was recently shown in simulations (13). Because of the difficult accessibility of the buried interface between a melt and a solid, direct observation of crystallization of molecular systems at the interface is lacking, and there is only limited, indirect evidence that, in some cases, prefreezing at the solid interface exists (e.g., for the growth of aluminum crystals on TiB 2 particles) (14, 15). Recently, it has been suggested that prefreezing also plays a role during epitaxial crystallization in some polymeric systems (16). It is well-known, however, that one or sometimes several ordered layers of organ...

Starting from established concepts that describe the dynamics of the cantilever in a scanning force microscope operated in intermittent contact mode as that of a driven harmonic oscillator, we introduce effective interaction parameters based on Fourier coefficients to describe the interaction forces. These interaction parameters are linear in the forces and separate conservative from dissipative contributions. They allow a qualitative description of the interaction process and enable a thorough discussion of the influence of experimental parameters on the measured data. Exemplary force spectroscopy data obtained from hard and soft polymeric model surfaces show that consistent data for the interaction parameters can be obtained which can be related to the material properties of the investigated surfaces. Images obtained in intermittent contact mode from a semicrystalline polymer as an exemplary nanostructured surface with hard-soft contrast illustrate that with the approach a clear identification of harder and softer domains is possible.

The tremendous influence of hydrophilic block length tuning on the aggregation behavior of novel water-soluble triphilic (i.e., hydrophilic, lipophilic, and fluorophilic) R,ω-perfluoroalkyl end-capped symmetric ABA triblock copolymers is demonstrated. The hydrophilic A and lipophilic B blocks are comprised of poly(glycerol monomethacrylate) (PGMA) and poly(propylene oxide) (PPO), respectively. The fluorophilic component consists of two "clicked" perfluoroalkyl segments (C 9 F 19 ) at the ends of the block copolymers. Two of the different block copolymers synthesized, namely F 9 -PGMA 24 -PPO 27 -PGMA 24 -F 9 (PB1) and F 9 -PGMA 42 -PPO 27 -PGMA 42 -F 9 (PB2), differ only in the degree of polymerization of the hydrophilic PGMA blocks. Their critical micelle concentrations in water are determined from surface tension measurements. The aggregation behavior in aqueous medium studied by 19 F NMR spectroscopy reveals that the fluorocarbon component forms part of the micelle corona of PB1, while in PB2 it aggregates to form part of the core. Furthermore, the aggregation behavior studied in aqueous medium by temperaturedependent 1 H NMR spectroscopy and DLS measurements showed that PB1 forms only spherical micelles with hydrodynamic radius, R h , of ∼18 nm in solution at all temperatures while PB2 forms mainly aggregate of micelles with R h of 40 nm at 25 °C. The aggregates disintegrate into compact single "flowerlike" micelles with R h of ∼17 nm at high temperatures. AFM and TEM investigations of the structures formed on solid supports after solvent evaporation also confirm the aggregation behavior of the two block copolymers. The marked difference in the aggregation behavior is a result of the inability of the shorter PGMA blocks of PB1 to loop during micellization and is explained based on random coil statistics.

Langmuir monolayers and Langmuir-Blodgett (LB) film morphologies of block copolymers and hydrophobically modified iron oxide nanoparticles were studied by surface pressure-mean molecular area (pi-mmA) measurements and by tapping mode atomic force microscopy (AFM). The amphiphilic diblock copolymers consisted of a hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic poly(isobutylene) (PIB) block. The pi-mmA isotherm of PEO(97)-b-PIB(37) (the subscripts refer to the respective degrees of polymerization) at the air/water interface had an extended plateau reflecting the extension of PEO chains into the water subphase at a surface pressure of 10 mN.m(-1), which is absent for the more hydrophobic PEO(19)-b-PIB(130). Iron oxide (Fe(2)O(3)) nanoparticles capped with oleic acid ligands as the shell were dispersed in the amphiphilic block copolymers at the air/water interface to prevent macroscopic aggregation of the particles. When the nanoparticles were mixed with PEO(97)-b-PIB(37), using a particle to polymer chain ratio of 1:100, macroscopic aggregation of the nanoparticles was not observed, and the pi-mmA isotherm was dominated by PEO(97)-b-PIB(37). Monolayers of block copolymers were transferred at different surface pressures from the air/water interface to hydrophilic silicon substrates using the Langmuir-Blodgett technique. The AFM images of PEO(97)-b-PIB(37) LB films depicted not only the typical finger-like morphology of the crystallized PEO blocks but also PIB blocks arranged in vertical columns growing perpendicular to the substrate surface. The columns are characteristic for PEO(19)-b-PIB(130) LB films after transfer at high surface pressures and can be assigned to a mesomorphic PIB phase with ordered chains. Finally, it was observed that small clusters of a few Fe(2)O(3) nanoparticles occupy the top of PIB phases after compression and transfer of the block copolymer nanoparticle mixtures to solid supports.