Brian C. Berry

Dynamic Thermal Field-Induced Gradient Soft-Shear for Highly Oriented Block Copolymer Thin Films

As demand for smaller, more powerful, and energy-efficient devices continues, conventional patterning technologies are pushing up against fundamental limits. Block copolymers (BCPs) are considered prime candidates for a potential solution via directed self-assembly of nanostructures. We introduce here a facile directed self-assembly method to rapidly fabricate unidirectionally aligned BCP nanopatterns at large scale, on rigid or flexible template-free substrates via a thermally induced dynamic gradient soft-shear field. A localized differential thermal expansion at the interface between a BCP film and a confining polydimethylsiloxane (PDMS) layer due to a dynamic thermal field imposes the gradient soft-shear field. PDMS undergoes directional expansion (along the annealing direction) in the heating zone and contracts back in the cooling zone, thus setting up a single cycle of oscillatory shear (maximum lateral shear stress ∼12 × 10(4) Pa) in the system. We successfully apply this process to create unidirectional alignment of BCP thin films over a wide range of thicknesses (nm to μm) and processing speeds (μm/s to mm/s) using both a flat and patterned PDMS layer. Grazing incidence small-angle X-ray scattering measurements show absolutely no sign of isotropic population and reveal ≥99% aligned orientational order with an angular spread Δθ(fwhm) ≤ 5° (full width at half-maximum). This method may pave the way to practical industrial use of hierarchically patterned BCP nanostructures.

Evolution of Block-Copolymer Order Through a Moving Thermal Zone

We investigate block-copolymer (BCP) thin film ordering kinetics during annealing across a moving in-plane temperature gradient. We operate in the so-called cold zone annealing (CZA) regime, where ordering temperatures are above the glass-transition, but well below the order-disorder transition. By measuring the order through the in-plane gradient, using atomic force microscopy and grazing-incidence small-angle X-ray scattering (GISAXS), we confirm that CZA greatly enhances ordering kinetics, as compared to uniform oven annealing. The maximal ordering occurs over a narrow range of the heating-up phase, and not during the subsequent cooling phase. The large grain sizes obtained using CZA are due to enhanced kinetics, and not the preferential formation of certain grain orientations. Kinetic enhancement is apparent even below the bulk glass-transition temperature. We suggest that the in-plane temperature gradient drives enhanced kinetics.

Disordered nanoparticle interfaces for directed self-assembly

Self-assembly is a promising route for controlling the nanoscale structure and material properties of coatings, yet it remains difficult to control the microstructure of these systems. In particular, self-assembling materials typically have complex and delicate energy landscapes, which are sensitive to defects, making it difficult to control morphology or orientation. We present a simple and robust strategy for modulating the film-substrate interaction, which can bias the self-assembly energy landscape and thus enforce a desired microstructure. The technique uses nanoparticles with tunable surface energy to generate a rough interface with controlled properties. The intentionally disordered interface is tolerant to variation in substrate preparation. We apply this technique to block-copolymer lamellae, and demonstrate a remarkable thickness-dependence of the induced orientation, consistent with theoretical predictions. The simultaneous control of substrate energy and topography enables expression of the vertical lamellae state without rigorous control of the preparation conditions. We measure an 8-fold increase in surface energy tolerance compared to flat substrates.

Catalytic Conversion of Graphene into Carbon Nanotubes via Gold Nanoclusters at Low Temperatures

Here, we present the catalytic conversion of graphene layers into carbon nanotubes (CNTs), in the presence of Au nanoparticles (AuNPs) without the need for an additional carbon source. We have demonstrated that this catalytic process takes place at temperatures as low as 500 °C. No other oxide supports decorated with AuNPs were found to grow CNTs at this temperature. These findings highlight the high activity of graphene when used as a support for catalytic reactions.

Observation of surface corrugation-induced alignment of lamellar microdomains in PS-b-PMMA thin films

We report lateral alignment of lamellar microdomains in thin films of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) on corrugated surfaces where surface energy is controlled as non-selective to PS and PMMA by anchoring polymer brushes of a random copolymer of PS and PMMA. The orientational order determined by Hermans orientation function indicates that the lamellae align perpendicular to the direction of surface corrugation within a window of surface corrugation length scales used in this study. The effect of relative scales of periodicity and film thickness of PS-b-PMMA to those of surface corrugation on the alignment of lamellae is discussed in this paper.

Comparative Aging Study of Organic Solar Cells Utilizing Polyaniline and PEDOT:PSS as Hole Transport Layers.

UNLABELLED The aging effect on P3HT:PCBM organic solar cells was investigated with camphorsulfonic doped polyaniline (PANI:CSA) or poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT PSS) used as the hole transport layer (HTL). The cells were encapsulated and exposed to a continuous normal atmosphere on a dark shelf and then characterized intermittently for more than two years. The photovoltaic results revealed that the cells with PEDOT PSS HTL showed better initial results than the cells with PANI:CSA HTL. Over time, PEDOT PSS-based cells exhibited faster degradation than PANI:CSA-based cells, where the average efficiency of six cells dropped to zero in less than one and a half years. On the other hand, PANI:CSA-based cells exhibited a much more stable performance with an average efficiency drop of only 15% of their initial values after one and a half years and 63% after two years. A single-diode model was utilized to fit the experimental data with the theoretical curve to extract the diode parameters, such as the ideality factor, to explain the effect of aging on the diodes performance.

Competition between crystallization and dewetting fronts in thin polymer films

We investigate the competition between dewetting and crystallization fronts in thin polymer films where the velocities of these fronts are modulated by varying the temperature from a low temperature regime, where crystallization dominates, to a high temperature regime, where dewetting is more rapid and dominates the film structure. Specifically, thin films of poly(caprolactone) (PCL) on n-octyldimethylchlorosilane (ODS)-treated substrates are investigated as a model system exhibiting this general phenomenon. Structure formation at low temperatures is dominated by polycrystalline spherulitic structures that nucleate at random positions within the plane of the film, but at intermediate temperatures, where the crystallization and dewetting are strongly coupled, dewetting occurs preferentially at the grain boundaries between the spherulites. We term this phenomenon crystallization-induced dewetting (CID) and provide evidence that it arises from the high stresses at the spherulite grain boundaries that accompany local volume changes of the polymer material upon crystallization. CID is prevalent in a temperature range in which the angles between the grains are larger than a critical angle and this effect allows for considerable control over the resulting film morphology.

Ammonia Gas Sensing Behavior of Tanninsulfonic Acid Doped Polyaniline-TiO2 Composite

A highly active tannin doped polyaniline-TiO2 composite ammonia gas sensor was developed and the mechanism behind the gas sensing activity was reported for the first time. A tanninsulfonic acid doped polyaniline (TANIPANI)-titanium dioxide nanocomposite was synthesized by an in situ polymerization of aniline in the presence of tanninsulfonic acid and titanium dioxide nanoparticles. X-ray diffraction and thermogravimetric analysis were utilized to determine the incorporation of TiO2 in TANIPANI matrix. UV-Visible and infrared spectroscopy studies provided information about the electronic interactions among tannin, polyaniline, and TiO2. Scanning electron microscopy (SEM) along with energy dispersive X-ray spectroscopy (EDS) and atomic force microscopy (AFM) surface analysis techniques were used to investigate the metal oxide dispersions inside polyaniline matrix. Gas sensors were prepared by spin coating solutions of TANIPANI-TiO2 and TANIPANI composites onto glass slides. Sensors were tested at three different concentrations (20 ppm, 40 ppm, and 60 ppm) of ammonia gas at ambient temperature conditions by measuring the changes in surface resistivity of the films with respect to time. Ammonia gas sensing plots are presented showing the response values, response times and recovery times. The TANIPANI-TiO2 composite exhibited better response and shorter recovery times when compared to TANIPANI control and other polyaniline composites that have been reported in the literature. For the first time a proposed mechanism of gas sensing basing on the polaron band localization and its effects on the gas sensing behavior of polyaniline are reported.

Sesquiterpene lactones from Gynoxys verrucosa and their anti-MRSA activity

ETHNOPHARMACOLOGICAL RELEVANCE Because of its virulence and antibiotic resistance, Staphylococcus aureus is a more formidable pathogen now than at any time since the pre-antibiotic era. In an effort to identify and develop novel antimicrobial agents with activity against this pathogen, we have examined Gynoxys verrucosa Wedd (Asteraceae), an herb used in traditional medicine in southern Ecuador for the treatment and healing of wounds. MATERIALS AND METHODS The sesquiterpene lactones leucodine (1) and dehydroleucodine (2) were extracted and purified from the aerial parts of Gynoxys verrucosa, and their structure was elucidated by spectroscopic methods and single-crystal X-ray analysis. The in vitro anti-microbial activity of Gynoxys verrucosa extracts and its purified constituents was determined against six clinical isolates including Staphylococcus aureus and Staphylococcus epidermidis strains with different drug-resistance profiles, using the microtiter broth method. RESULTS Compound 1 has very low activity, while compound 2 has moderate activity with MIC(50)s between 49 and 195 μg/mL. The extract of Gynoxys verrucosa has weak activity with MIC(50)s between 908 and 3290 μg/mL. CONCLUSIONS We are reporting the full assignment of the (1)H NMR and (13)C NMR of both compounds, and the crystal structure of compound 2, for the first time. Moreover, the fact that compound 2 has antimicrobial activity and compound 1 does not, demonstrates that the exocyclic conjugated methylene in the lactone ring is essential for the antimicrobial activity of these sesquiterpene lactones. However, the weak activity observed for the plant extracts, does not explain the use of Gynoxys verrucosa in traditional medicine for the treatment of wounds and skin infections.

Preparation of Combinatorial Arrays of Polymer Thin Films for Transmission Electron Microscopy Analysis

We present a new method for harvesting multiple thin film specimens from polymer combinatorial libraries for transmission electron microscopy (TEM) analysis. Such methods are of interest to researchers who wish to integrate TEM measurements into a combinatorial or high-throughput experimental workflow. Our technique employs poly(acrylic acid) plugs, sequestered in an elastomer gasket, to extract a series of film patches from gradient combinatorial libraries. A strategy for simultaneous deposition of the array of film specimens onto TEM grids also is described. We demonstrate our technique using nanostructured polymer thin film libraries as test cases in which the nanoscale details can be successfully imaged. Microscopy of test case specimens demonstrates that these samples are of sufficient quality for morphology screening via TEM, and in some cases are sufficient for more detailed morphological studies.