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Seyedhosseini E.,University of Aveiro | Ivanov M.,University of Aveiro | Bystrov V.,University of Aveiro | Bystrov V.,Institute of Mathematical Problems of Biology | And 8 more authors.
Crystal Growth and Design | Year: 2014

Glycine is the simplest amino acid and one of the basic and important elements in biology, as it serves as a building block for proteins. The interest in this material has recently arisen from its useful functional properties, such as its high value of nonlinear optical susceptibility and ferroelectricity. Three polymorphic forms with different physical properties are possible in glycine, the most useful β-polymorph being much less stable than the other two. In this work, we could grow stable microcrystals of β-glycine using a (111)Pt/SiO2/Si substrate as a template. The effects of the solution concentration and Pt-assisted nucleation on the crystal growth and phase evolution were evaluated using X-ray diffraction analysis and Raman spectroscopy. A second harmonic generation (SHG) method confirmed that the 2-fold symmetry is preserved in as-grown crystals, thus reflecting the expected P21 symmetry of the β-phase. Spontaneous polarization direction is found to be parallel to the monoclinic [010] axis and directed along the crystal length. These data are confirmed by computational molecular modeling. Optical measurements revealed also relatively high values of the nonlinear optical susceptibility (50% greater than in the z-cut quartz). The potential use of stable β-glycine crystals in nonlinear optical applications is discussed. © 2014 American Chemical Society.

Bdikin I.,University of Aveiro | Heredia A.,National Autonomous University of Mexico | Neumayer S.M.,University College Dublin | Bystrov V.S.,University of Aveiro | And 5 more authors.
Journal of Applied Physics | Year: 2015

Thymine (2-oxy-4-oxy-5 methyl pyrimidine) is one of the four nucleobases of deoxyribonucleic acid (DNA). In the DNA molecule, thymine binds to adenine via two hydrogen bonds, thus stabilizing the nucleic acid structure and is involved in pairing and replication. Here, we show that synthetic thymine microcrystals grown from the solution exhibit local piezoelectricity and apparent ferroelectricity, as evidenced by nanoscale electromechanical measurements via Piezoresponse Force Microscopy. Our experimental results demonstrate significant electromechanical activity and polarization switchability of thymine, thus opening a pathway for piezoelectric and ferroelectric-based applications of thymine and, perhaps, of other DNA nucleobase materials. The results are supported by molecular modeling of polarization switching under an external electric field. © 2015 AIP Publishing LLC.

Hudzinskyy D.,TU Eindhoven | Hudzinskyy D.,Dutch Polymer Institute | Lyulin A.V.,TU Eindhoven | Baljon A.R.C.,San Diego State University | And 2 more authors.
Macromolecules | Year: 2011

We have performed molecular dynamics simulations to explore the influence of confinement on the glass-transition temperature Tg for supported atactic-polystyrene (aPS) thin films of different thickness (1-10 nm) and different strengths of attraction to the substrate (0.1-3.0 kcal/mol). The aPS films have been equilibrated in a melt at 540 K and further cooled down with a constant cooling velocity of 0.01 K/ps below Tg to room temperature, 300 K. On the basis of the density measurements, we have defined three different (substrate, middle, and surface) layers for each film. We found that the monomers close to the surface and in the substrate layer are partially oriented, which leads to more effective monomer packing. For the whole film the average density-based Tg value remains almost constant for films down to 2 nm thickness, where the middle layer vanishes. For the middle layer itself T g does not depend on the total film thickness, while an increase up to 70 K is measured for the substrate layer depending on the strength of attraction to the actual substrate. The surface layer remains liquidlike in the whole temperature range (300-540 K). We claim that the redistribution of mass in the three film layers may explain the change with film thickness of the average Tg, if the latter is determined from linear fits of the average glass and melt densities. © 2011 American Chemical Society.

Baljon A.R.C.,San Diego State University | Williams S.,San Diego State University | Balabaev N.K.,Institute of Mathematical Problems of Biology | Paans F.,TU Eindhoven | And 3 more authors.
Journal of Polymer Science, Part B: Polymer Physics | Year: 2010

In this article, we investigate the glass transition in polystyrene melts and free-standing ultra-thin films by means of large-scale computer simulations. The transition temperatures are obtained from static (density) and dynamic (diffusion and orientational relaxation) measurements. As it turns out, the glass transition temperature of a 3 nm thin film is ∼60 °K lower than that of the bulk. Local orientational mobility of the phenyl bonds is studied with the help of Legendre polynomials of the second-order P2(t). The α and β relaxation times are obtained from the spectral density of P2(t). Our simulations reveal that interfaces affect α and β relaxation processes differently. The β relaxation rate is faster in the center of the film than near a free surface; for the α relaxation rate, an opposite trend is observed. © 2010 Wiley Periodicals, Inc.

Heredia A.,University of Aveiro | Bdikin I.,University of Aveiro | Kopyl S.,University of Aveiro | Mishina E.,Moscow State Institute of Radioengineering | And 7 more authors.
Journal of Physics D: Applied Physics | Year: 2010

Diphenylalanine (FF) peptide nanotubes (PNTs) represent a unique class of self-assembled functional biomaterials owing to a wide range of useful properties including nanostructural variability, mechanical rigidity and chemical stability. In addition, strong piezoelectric activity has recently been observed paving the way to their use as nanoscale sensors and actuators. In this work, we fabricated both horizontal and vertical FF PNTs and examined their optical second harmonic generation and local piezoresponse as a function of temperature. The measurements show a gradual decrease in polarization with increasing temperature accompanied by an irreversible phase transition into another crystalline phase at about 140-150 °C. The results are corroborated by the molecular dynamic simulations predicting an order-disorder phase transition into a centrosymmetric (possibly, orthorhombic) phase with antiparallel polarization orientation in neighbouring FF rings. Partial piezoresponse hysteresis indicates incomplete polarization switching due to the high coercive field in FF PNTs. © 2010 IOP Publishing Ltd.

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