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Conjugated block copolymers provide a pathway to achieve thermally stable nanostructured thin films for organic solar cells. We characterized the structural evolution of poly(3-hexylthiophene)-block-poly(diketopyrrolopyrrole-terthiophene) (P3HT-b-DPPT-T) from solution to nanostructured thin films. Aggregation of the DPPT-T block of P3HT-b-DPPT-T was found in solution by small-angle X-ray scattering with the P3HT block remaining well-solvated. The nanostructure in thin films was determined using a combination of wide and small-angle X-ray scattering techniques as a function of processing conditions. The structure in solution controlled the initial nanostructure in spin-cast thin films, allowing subsequent thermal annealing processes to further improve the ordering. In contrast to the results for thin films, nanostructural ordering was not observed in the bulk samples by small-angle X-ray scattering. These results suggest the importance of controlling solvent induced aggregation in forming nanostructured thin films of conjugated block copolymers.

We report an effective strategy for the synthesis of semi-crystalline block copolyethers with well-defined architecture and stereochemistry. As an exemplary system, triblock copolymers containing either atactic (racemic) or isotactic (R or S) poly(propylene oxide) end blocks with a central poly(ethylene oxide) mid-block were prepared by anionic ring-opening procedures. Stereochemical control was achieved by an initial hydrolytic kinetic resolution of racemic terminal epoxides followed by anionic ring-opening polymerization of the enantiopure monomer feedstock. The resultant triblock copolymers were highly isotactic (meso triads [mm]% ~ 90%) with optical microscopy, differential scanning calorimetry, wide angle x-ray scattering and small angle x-ray scattering being used to probe the impact of the isotacticity on the resultant polymer and hydrogel properties.

We herein report a new facile strategy to ellipsoidal block copolymer nanoparticles that exhibit a pH-triggered anistropic swelling profile. In a first step, elongated particles with an axially stacked lamellae structure are selectively prepared by utilizing functional surfactants to control the phase separation of symmetric polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) in dispersed droplets. In a second step, the dynamic shape change is realized by cross-linking the P2VP domains, thereby connecting glassy PS discs with pH-sensitive hydrogel actuators.

The surface properties and self-adhesion mechanism of self-healing poly(butyl acrylate) (PBA) copolymers containing comonomers with 2-ureido-4[1H]-pyrimidinone quadruple hydrogen bonding groups (UPy) are investigated using a surface forces apparatus (SFA) coupled with a top-view optical microscope. The surface energies of PBA-UPy4.0 and PBA-UPy7.2 (with mole percentages of UPy 4.0% and 7.2%, respectively) are estimated to be 45-56 mJ m-2 under dry condition by contact angle measurements using a three probe liquid method and also by contact and adhesion mechanics tests, as compared to the reported literature value of 31-34 mJ m-2 for PBA, an increase that is attributed to the strong UPy-UPy H-bonding interactions. The adhesion strengths of PBA-UPy polymers depend on the UPy content, contact time, temperature and humidity level. Fractured PBA-UPy films can fully recover their self-adhesion strength to 40, 81, and 100% in 10 s, 3 h, and 50 h, respectively, under almost zero external load. The fracture patterns (i.e., viscous fingers and highly "self-organized" parallel stripe patterns) have implications for fabricating patterned surfaces in materials science and nanotechnology. These results provide new insights into the fundamental understanding of adhesive mechanisms of multiple hydrogen-bonding polymers and development of novel self-healing and stimuli-responsive materials. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A series of bis(phenoxyketimine)titanium dichloride complexes are prepared and analyzed as catalysts for living, isoselective propylene polymerization upon activation with methylaluminoxane (MAO). Mechanical testing has shown that each of these polymers have exhibited good elastomeric properties.

The effects of surface roughness on the deformations and loading and unloading forces of various polymeric surfaces were studied. The results show that depending on the nature of the roughness and also the load time some polymer surfaces may exhibit a roughness-dependent adhesion but a sharp roughness-independent repulsive regime while others a=having the same RMS roughness may exhibit an adhesion that is largely independent of the roughness.

Thermoelastic poly 4,4'-oxydiphenylene oxydiphthalimide (ODPA-ODA) is an effective adhesive layer for binding commercial Upilex and Kapton films. ODPA-ODA has a glass transition temperature of 270 degrees celsius and its modulus and dielectric constant are comparable with those of pyromellitic dianhydride/4-amino phenyl ether films (PMDA-ODA). A thin layer of ODPA-ODA as the interlayer enhances fracture energy roughly one order of magnitude.

A fracture mechanics approach was used to study the problem of adhesion at the interface between two polymers. Results show the presence of four distinct regions of the crack opening displacement profile behind the adhesive zone tip. However, the region of displacement discontinuity across the interface due to loss of adhesion is found to be small compared with typical specimen dimensions. In addition, the amount of inelastic or viscous energy dissipation is strongly coupled to the interface behavior and the measured interface fracture toughness can be much higher than the intrinsic interface fracture toughness.

A study was done on the interface fracture and viscoelastic deformation in finite size specimens. It was shown that the viscoelastic energy dissipation and predicted fracture toughness of the interface between two viscoelastic polymers in the small scale yielding unit are functions of the crack growth rate. It was also shown that maximum viscoelastic energy dissipation is dependent on the micromechanical properties of the interface and specimen dimensions.

Interfaces between donor and acceptor semiconducting polymers are critical to the performance of polymer light-emitting diodes and organic solar cells. Similarly, interfaces between a conjugated polymer and a dielectric play a critical role in organic thin-film transistors. Often, these interfaces are difficult to characterize with conventional methods. Resonant soft x-ray reflectivity (R-SoXR) is a unique and relatively simple method to investigate such interfaces. R-SoXR capabilities are exemplified by presenting or discussing results from systems spanning all three device categories. We also demonstrate that the interfacial widths between active layers can be controlled by annealing at elevated temperature, pre-annealing of the bottom layer, or casting from different solvent mixtures. The extension of R-SoXR to the fluorine K absorption edge near 698 eV is also demonstrated. [ABSTRACT FROM AUTHOR]

Partial (Auger) yield near edge x-ray absorption fine structure (NEXAFS) is a structural analytical technique that has been primarily used to measure the spatial orientation and chemical bonding of small molecules on solid (i.e., inorganic or semiconductor) surfaces. In this article we demonstrate that the building block (BB) scheme proposed by Outka and co-workers [Phys. Rev. Lett. 59, 1321 (1987)] for analyzing NEXAFS spectra can be applied to model the molecular orientation of larger molecules, provided one accounts properly for kinetic energy losses of the Auger electrons traversing through the sample and hence the attenuation in measured Auger yield. We test the applicability of the proposed "modified" BB (MBB) model by measuring the orientation of a self-assembled monolayer (SAM) of -O[sub 1.5]Si-(CH[sub 2])[sub 2]-(CF[sub 2])[sub 8]F, SF-SAM (SiO[sub x]), deposited on top of SiO[sub x]-covered silicon wafer as a function of the entrance grid bias (EGB) of the channeltron photoelectron detector. Our measurements of the EGB-dependent electron escape depth reveal that a crude depth profiling within the top ≈5 nm of the sample is possible by increasing the negative EGB on the channeltron detector, at the highest bias thus selecting only the Auger electrons, which have suffered negligible energy loss. In addition, we discuss how the order parameter method introduced recently by Stöhr and Samant [J. Electron Spectrosc. Relat. Phenom. 98-99, 189 (1989)] can be used to determine the molecular orientation of large organic molecules on surfaces. We also show that by accounting for energy losses of the NEXAFS Auger electrons (attenuation of measured Auger yield), the corrected order parameter (COP) approach gives good estimates of the orientation of molecules. We present a comparison between the MBB and COP models using experimental data collected from NEXAFS experiments from semifluorinated (SF) mesogens, -(CH[sub 2])[sub x](CF[sub 2])[sub y]F, which... [ABSTRACT FROM AUTHOR]

A norbornene monomer containing MeldrumEs acid is effectively copolymerized with polyethylene by using a nickel [alpha]-iminocarbaxamidato complex, which has provided high-melting, semicrystalline polymers with a tunable incorporation of the functional comonomer. The studies have shown the ability to tune cross-linked polyethylene properties by comonomer incorporation and have also analyzed the valuable structure/property relationships in these materials.

Novel binuclear complexes are prepared by linking two nickel centers through a bis(benzyl) fragment. Monotonic and step-cyclic stress-strain tests have shown that the materials have displayed large strains at break and excellent elastic recoveries at large strains and that materials with desirable properties are not achieved by using a mononuclear initiator has shown the advantage of growing the polymer via a telechelic mechanism.

The interfaces of conjugated polyelectrolyte (CPE)/poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) bilayers cast from differential solvents are shown to be very smooth and sharp by using resonant soft X-ray reflectivity (RSoXR). The results have shown that the nonpolar MEH-PPV layer is not much disturbed by casting the CPE layer from a polar solvent and a baseline is used for understanding the role of interfacial structure.

A system is designed consisting of a symmetric poly(styrene-b-2 vinyl pyridine) (PS-PVP) diblock copolymer matrix containing nanoparticles whose surfaces can be modified to be energetically similar to one of the blocks or amphiphilic with respect to the two blocks. By incorporating the particles into the block copolymer matrix, precise control of the location of the particles within the matrix is demonstrated by varying the composition of ligands on the particle surfaces.

A method is demonstrated to self-assemble metal nanoparticle into two-dimensional lattices. The periodic hole pattern of photoresist (PR) fabricated on GaAs substrate by holographic lithography is highlighted.

Presents information on a study which considered the swelling of a polymer glass by sorption of a small molecule penetrant in a regime characterized by so-called case-II diffusion. Methodology of the study; Results and discussion.

Presents information on a study which considered front formation and steady-state front motion in a one-dimensional polymer system undergoing case-II diffusion. Analysis of the problem with a steady-state moving front; Results of the study; Conclusions.

Presents a study which investigated the problem of adhesion at the interface between two polymers using a fracture mechanics approach. Effect of viscoelastic deformation of the bulk polymers; Micromechanical behavior of the interface on the fracture toughness of the interface; Formulation of the governing equations for a small scale yielding problem.

Presents a study that demonstrated the existence of a maximum viscoelastic energy dissipation at a characteristic interface crack velocity which depends on micromechanical properties of the interface, the viscoelastic properties of the bulk polymers and the specimen dimensions. Limitations of the small scale yielding analysis; Formulation of governing differential equations for interface crack growth; Description of the constant adhesive stress model.