S. Kopyl

Temperature-driven phase transformation in self-assembled diphenylalanine peptide nanotubes

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. S Online supplementary data available from stacks.iop.org/JPhysD/43/462001/mmedia (Some figures in this article are in colour only in the electronic version)

Evidence of ferroelectricity and phase transition in pressed diphenylalanine peptide nanotubes

Self-assembled peptide nanotubes (PNT) are unique nanoscale objects having a great potential for a multitude of applications. Strong piezoactivity and polar properties in aromatic dipeptides were recently observed in stand-alone nanotubes using piezoresponse force microscopy and 2nd harmonic generation. In this work, we report macroscopic dielectric and polarization vs. field measurements on pressed PNTs before and after annealing at 150 °C. The results corroborate nanoscale study and present a clear evidence of ferroelectric-like behaviour and phase transition in this technologically important material. The dielectric constant of PNT pellets obeys apparent Curie-Weiss (CW) law with the CW constant C ≈ 230 °C and transition temperature at T ≈ 142 °C.

Piezoelectric resonators based on self-assembled diphenylalanine microtubes

Piezoelectric actuation has been widely used in microelectromechanical devices including resonance-based biosensors, mass detectors, resonators, etc. These were mainly produced by micromachining of Si and deposited inorganic piezoelectrics based on metal oxides or perovskite-type materials which have to be further functionalized in order to be used in biological applications. In this work, we demonstrate piezoelectrically driven micromechanical resonators based on individual self-assembled diphenylalanine microtubes with strong intrinsic piezoelectric effect. Tubes of different diameters and lengths were grown from the solution and assembled on a rigid support. The conducting tip of the commercial atomic force microscope was then used to both excite vibrations and study resonance behavior. Efficient piezoelectric actuation at the fundamental resonance frequency ≈2.7 MHz was achieved with a quality factor of 114 for a microtube of 277 μm long. A possibility of using piezoelectric dipeptides for biosensor a...

Polarization switching and patterning in self-assembled peptide tubular structures

Self-assembled peptide nanotubes are unique nanoscale objects that have great potential for a multitude of applications, including biosensors, nanotemplates, tissue engineering, biosurfactants, etc. The discovery of strong piezoactivity and polar properties in aromatic dipeptides [A. Kholkin, N. Amdursky, I. Bdikin, E. Gazit, and G. Rosenman, ACS Nano 4, 610 (2010)] opened up a new perspective for their use as biocompatible nanoactuators, nanomotors, and molecular machines. Another, as yet unexplored functional property is the ability to switch polarization and create artificial polarization patterns useful in various electronic and optical applications. In this work, we demonstrate that diphenylalanine peptide nanotubes are indeed electrically switchable if annealed at a temperature of about 150 °C. The new orthorhombic antipolar structure that appears after annealing allows for the existence of a radial polarization component, which is directly probed by piezoresponse force microscopy (PFM) measurements...

Filling carbon nanotubes with magnetic particles

Magnetic carbon nanotube composites were obtained by filling carbon nanotubes with paramagnetic iron oxide particles. Measurements indicate that these functionalized nanotubes are superparamagnetic at room temperature. Details about the production and characterization of these materials are described along with the experimental procedures employed. These magnetic carbon nanotubes have the potential to be used in a wide range of applications, in particular, the production of nanofluids, which can be controlled by appropriate magnetic fields.

BioFerroelectricity: Diphenylalanine Peptide Nanotubes Computational Modeling and Ferroelectric Properties at the Nanoscale

Ferroelectricity and piezoelectricity are two of the common ferroelectric material properties, which have widespread observations in many biological systems, and these are referred to as biopiezoelectricity and bioferroelectricity. This paper presents a short overview of the main issues of piezoelectricity and ferroelectricity, their manifestation in organic, biological, and molecular systems. As a showcase of novel biopiezomaterials, the investigation of diphenylalanine (FF) peptide nanotubes (PNTs) is described by computational molecular modeling, as well by experimental AFM/PFM measurements. FF PNTs present a unique class of self-assembled functional biomaterials, owing to their wide range of useful properties, including nanostructural piezoelectric and ferroelectric properties.

Piezoelectricity and ferroelectricity in biomaterials: Molecular modeling and piezoresponse force microscopy measurements

Piezoelectricity is one of the important functional properties inherent to many biomaterials. It stems from the non-centrosymmetric crystal structure of most biopolymers including proteins, polysaccharides, and lipids. Understanding the relationship between the generated electric field and applied mechanical stress has become the main motivation to studying piezoelectricity in biological systems and artificial biomaterials at the nanoscale. In this work, we present a review of the piezoelectric and ferroelectric properties of several molecular systems and nanomaterials revealed by Piezoresponse Force Microscopy (PFM) and compare the results with molecular modeling and computer simulations. Experimentally observed by PFM and calculated dielectric, piezoelectric, and ferroelectric properties of these materials are analyzed in the context of their possible role in functionality of biological systems.

Bioferroelectricity in Nanostructured Glycine and Thymine: Molecular Modeling and Ferroelectric Properties at the Nanoscale

Nanostructured aminoacid glycine and nucleobase thymine are very important for various biomedical applications. Experimentally, these structures demonstrate piezoelectric and polar properties. But the value of polarization and its switching behavior are not clear yet. In this work, computational modeling of glycine polymorphic phases (α and β) and thymine nanostructures was performed using a combined method with LDA first principle calculations of atomic optimized crystal structures in AIMPRO code on Linux cluster combined with molecular semi-empirical PM3 calculations by HyperChem 8.0. The developed molecular model and calculated parameters are compared with recent measurements using piezoresponse force microscopy (PFM) at the nanoscale.

Computational study of hydroxyapatite properties and surface interactions

The results of computational modeling for Hydroxyapatite (HAP) nanostructures and surface interactions properties are presented in this work. HAP were studied from first principles approaches using Local Density Approximation (LDA) method in combination with various quantum-chemical (QM), including Density Functional Theory (DFT) methods, and molecular mechanical (MM, BIO CHARM) methods from HypemChem 7.5/8.0 package. Obtained data then were used for studies of interactions of HAP clusters with various species (citrates, carbon nanotubes, living cells - osteoblasts, etc.).

Graphene/graphene oxide and polyvinylidene fluoride polymer ferroelectric composites for multifunctional applications

ABSTRACT We perform computational molecular modeling of graphene/graphene oxide (G/GO) and polyvinylidene fluoride (PVDF) ferroelectric polymer composite nanostructures, using semi-empirical quantum approximation PM3 in HyperChem. Piezoelectric properties of these nanostructures are analyzed in comparison with experimental data obtained for poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE)-GO thin films. Modeling shows qualitative agreement of properties and lowering of piezoelectric coefficient d33eff values under influence of G/GO layers. Modeling of GO-methane-hydrates nanostructures based on hexagonal ice model shows that after relaxation the system keeps a stable deformed state. This can serve for gas-hydrates storage and separation. Modeled composites could be used as multifunctional molecular units.