Gomathy Sandhya Subramanian

Individually Addressable Patterned Multilayer Microchambers for Site-Specific Release-On-Demand

Patterned arrays of light-responsive microchambers are suggested as candidates for site-specific release of chemicals in small and precisely defined quantities on demand. A composite film is made of poly(allylammonium)-poly(styrene sulfonate) multilayers and gold nanoparticles incorporated between subsequent stacks of polyelectrolytes. The film shaped as microchambers is loaded with colloid particles or oil-soluble molecules. The microchambers are sealed onto a glass slide precoated with an adhesive poly(diallyldimethylammonium)-poly(styrene sulfonate) multilayer film. A focused laser beam is used for remote addressing the individual microchambers and site-specific release of the loaded cargo.

In vitro evaluation of Ficoll‐enriched and genipin‐stabilised collagen scaffolds

Polysaccharides are frequently incorporated into scaffolds for tissue engineering applications to improve mechanical and biological properties. We evaluated the influence of a Ficoll® scaffold on collagen films, a scaffold that is extensively used for soft and hard tissue repair. To avoid cytotoxicity issues associated with chemical reagents, the influence of genipin, a naturally occurring crosslinking agent, was assessed. Ultra‐structural level collagen films formed with and without Ficoll showed a fine fibrillar structure whereas genipin crosslinked films showed a coarse fibrillar and partially nodular structure. In contrast, glutaraldehyde crosslinked films lost their fibrillar pattern. Crosslinking significantly increased denaturation temperature (p < 0.001), stress (p < 0.0001) and force (p < 0.0001) at break. Collagen/Ficoll and collagen/Ficoll/genipin films showed the highest WI38 fibroblast attachment than any other scaffold (p < 0.003) and significantly greater WI38 fibroblast metabolic activity than other scaffolds (p < 0.001). By day 6. collagen/Ficoll/genipin films also induced higher and more aligned fibronectin matrix deposition than other scaffolds. Overall, this study indicates the suitability of collagen/Ficoll/genipin for tissue engineering applications. Copyright

Fabrication and mechanical properties of microchambers made of polyelectrolyte multilayers

A highly ordered array of hollow chambers ranging from 2 to 25 μm in size are fabricated using the layer-by-layer assembly of poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate) on sacrificial templates with imprinted patterns of wells. Polyelectrolyte multilayer (PEM) chambers collapse if made of shells that are thinner than a critical value. This critical thickness of the shells is measured experimentally and is found to depend on the chambers geometry. Eulers model of critical stress is used to describe the collapse of the chambers. Adhesive contact of the chamber’s roof with the support is suggested as a major mechanism responsible for the collapse. Deformation of individual PEM chambers made of thicker shells is studied using a sharp indenter and varying the loading speed. At loading speeds of less than 0.33 mN s−1, the elastic theory describes the experimental data well for small deformations, yielding a Youngs modulus of 4 ± 1 GPa for the PEM shell, while further deformation causes severe plastic buckling of the chamber. If the loading speed exceeds 0.33 mN s−1, the sharp indenter starts to pierce the chambers roof and the size of the resulted hole can be precisely controlled by changing the penetration depth of the indenter. Filling the PEM chambers with oil micro-droplets by solvent-exchange method is also demonstrated.

Nanoscale phase domain structure and associated device performance of organic solar cells based on a diketopyrrolopyrrole polymer

We investigate the blend morphology and performance of bulk heterojunction organic photovoltaic devices comprising the donor polymer, pDPP-TNT (poly{3,6-dithiophene-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1, 4-dione-alt-naphthalene}) and the fullerene acceptor, [70]PCBM ([6,6]-phenyl C71-butyric acid methyl ester). The blend morphology is heavily dependent upon the solvent system used in the fabrication of thin films. Thin films spin-coated from chloroform possess a cobblestone-like morphology, consisting of thick, round-shaped [70]PCBM-rich mounds separated by thin polymer-rich valleys. The size of the [70]PCBM domains is found to depend on the overall film thickness. Thin films spin-coated from a chloroform:dichlorobenzene mixed solvent system are smooth and consist of a network of pDPP-TNT nanofibers embedded in a [70]PCBM-rich matrix. Rinsing the films in hexane selectively removes [70]PCBM and allows for analysis of domain size and purity. It also provides a means for investigating exciton dissociation efficiency through relative photoluminescence yield measurements. Devices fabricated from chloroform solutions show much poorer performance than the devices fabricated from the mixed solvent system; this disparity in performance is seen to be more pronounced with increasing film thickness. The primary cause for the improved performance of devices fabricated from mixed solvents is attributed to the greater donor-acceptor interfacial area and resulting greater capacity for charge carrier generation.

New solid-state Eu(III)-containing metallo-supramolecular polymers: morphology control and optical wave-guiding properties

Herein, we report the solution phase self-assembly between Eu(III) and a rigid ditopic tridentate terpyridine ligand which results in the formation of supramolecular metallo-networks in the solid state. Depending on the ligand to metal ratio used for the initial self-assembly process, the morphology of these materials can be altered from one-dimensional micron-sized fibres to a three-dimensional coordination network. The terpyridine-based ditopic ligand can act as an efficient sensitizer for Eu(III) emission whereby the emission lifetimes and ligand triplet state energies of the metallo-polymers strongly depend on the ligand to metal ratio. The obtained micron-sized fibres can act as an efficient optical wave-guide for Eu(III) emission.

Studies into the Yb-doping effects on photoelectrochemical properties of WO3 photocatalysts

Yb-doped WO3 photocatalysts were prepared by co-sputtering Yb and WO3 on FTO glass and then sintering at elevated temperatures in air. At sintering temperatures between 450 and 550 °C, the photocurrent densities of Yb-doped WO3 photocatalysts were higher and more stable than those of pristine WO3 photocatalysts. The Yb-doping effects on the photoelectrochemical properties were investigated using Raman, transient absorption and electrochemical impedance spectroscopies. Compared to pristine WO3 photocatalysts, Yb-doped photocatalysts sintered at up to 550 °C consist of sub-stoichiometric WO3−x due to the substitution of W6+ cations with Yb3+ dopants, displaying shorter electron–hole recombination times and higher levels of donor densities.

Synthesis and characterization of large-grain solid-phase crystallized polycrystalline silicon thin films

n-type polycrystalline silicon (poly-Si) films with very large grains, exceeding 30 μm in width, and with high Hall mobility of about 71.5 cm2/V s are successfully prepared by the solid-phase crystallization technique on glass through the control of the PH3 (2% in H2)/SiH4 gas flow ratio. The effect of this gas flow ratio on the electronic and structural quality of the n-type poly-Si thin film is systematically investigated using Hall effect measurements, Raman microscopy, and electron backscatter diffraction (EBSD), respectively. The poly-Si grains are found to be randomly oriented, whereby the average area weighted grain size is found to increase from 4.3 to 18 μm with increase of the PH3 (2% in H2)/SiH4 gas flow ratio. The stress in the poly-Si thin films is found to increase above 900 MPa when the PH3 (2% in H2)/SiH4 gas flow ratio is increased from 0.025 to 0.45. Finally, high-resolution transmission electron microscopy, high angle annular dark field-scanning tunneling microscopy, and EBSD are used t...