Mirosława Pawlyta

Bio: Mirosława Pawlyta is an academic researcher from Silesian University of Technology. The author has contributed to research in topics: Materials science & Catalysis. The author has an hindex of 17, co-authored 95 publications receiving 1020 citations. Previous affiliations of Mirosława Pawlyta include University of Silesia in Katowice.

Evolution of glassy carbon under heat treatment: correlation structure–mechanical properties

Abstract: In order to accommodate an increasing demand for glassy carbon products with tailored characteristics, one has to understand the origin of their structure-related properties. In this work, through the use of high-resolution transmission electron microscopy, Raman spectroscopy, and electron energy loss spectroscopy it has been demonstrated that the structure of glassy carbon at different stages of the carbonization process resembles the curvature observed in fragments of nanotubes, fullerenes, or nanoonions. The measured nanoindentation hardness and reduced Young’s modulus change as a function of the pyrolysis temperature from the range of 600–2500 °C and reach maximum values for carbon pyrolyzed at around 1000 °C. Essentially, the highest values of the mechanical parameters for glassy carbon manufactured at that temperature can be related to the greatest amount of non-planar sp 2 -hybridized carbon atoms involved in the formation of curved graphene-like layers. Such complex labyrinth-like structure with sp 2 -type bonding would be rigid and hard to break that explains the glassy carbon high strength and hardness.

Structure of Carbon Materials Explored by Local Transmission Electron Microscopy and Global Powder Diffraction Probes

Abstract: Transmission electron microscopy and neutron or X-ray diffraction are powerful techniques available today for characterization of the structure of various carbon materials at nano and atomic levels. They provide complementary information but each one has advantages and limitations. Powder X-ray or neutron diffraction measurements provide structural information representative for the whole volume of a material under probe but features of singular nano-objects cannot be identified. Transmission electron microscopy, in turn, is able to probe single nanoscale objects. In this review, it is demonstrated how transmission electron microscopy and powder X-ray and neutron diffraction methods complement each other by providing consistent structural models for different types of carbons such as carbon blacks, glass-like carbons, graphene, nanotubes, nanodiamonds, and nanoonions.

Energy Migration Up-conversion of Tb3+ in Yb3+ and Nd3+ Codoped Active-Core/Active-Shell Colloidal Nanoparticles

Abstract: The intentional design of chemical architecture of lanthanide doped luminescent nanoparticles through the proper selection of dopants in core–shell and core–shell–shell structures enables optimization of their optical properties. Such an approach allows one to achieve energy transfer up-conversion (ETU) and energy migration mediated up-conversion (EMU) and green emission from Tb3+ ions with the Yb3+ and Nd3+ sensitizers at 980 and 808 nm photoexcitation, respectively. The [Nd3+ → Yb3+]→ [Yb3+ → Tb3+] EMU phenomenon was significantly enhanced by spatial displacement of the sensitizing Nd3+ ions from the activator Tb3+ ions by intentionally introducing an intermediate Yb3+ sensitizer layer forming a [Nd3+ → Yb3+] → [Yb3+] → [Yb3+ → Tb3+] system. Otherwise Tb3+ emission was considerably quenched by Nd3+ ions even though they were spitted between the core and shell, respectively. Moreover, (Tb3+,Yb3+) → (Tb4+,Yb2+) valence change has been discovered to limit the Tb3+ up-conversion emission. The studies explai...

Catalytic coupling of epoxides and CO2 to cyclic carbonates by carbon nanotube-supported quaternary ammonium salts

Abstract: Quaternary ammonium chlorides bound to multi-walled carbon nanotubes as a catalyst for coupling of CO 2 and epoxides to produce cyclic carbonates were explored. Reaction variables such as the epoxide structure, the length of alkyl substituents in the quaternary ammonium salts and the spacer chain on the catalytic performance were discussed. The yield of the cyclic carbonates varied between 7 and 89% after 6 h at 110 °C under low pressure (2 MPa of CO 2 ). The epoxide:catalyst mass ratio was 20–30, while 1 mmol g −1 of the quaternary salt was grafted on the carbon nanotubes. A synergy between carboxyl moiety and ammonium moiety grafted on carbon nanotubes was found, and a strong impact of the length of the spacer group used for grafting of the quaternary ammonium salt on nanotubes was observed. The best performance was achieved with short (2 carbon atoms) and long (10 atoms) spacer groups, while a middle-sized spacer group (6 atoms) was not suitable. The length of the alkyl chain of the substituents of the ammonium salt (head group) had a low impact where ethyl and methyl groups performed better than butyl. The reactivity of epoxides was as follows: epichlorohydrin > propylene oxide > styrene oxide. Observations were rationalized by a mechanism where Bronsted's sites on the surface of nanotubes play an important role during carboxylation of epoxides. The catalyst can easily be separated by filtration recycled without a significant decrease in the catalytic activity if dried properly between the runs.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

A Benchmark Study on the Thermal Conductivity of Nanofluids

Abstract: This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

Advances in highly doped upconversion nanoparticles

Abstract: Lanthanide-doped upconversion nanoparticles (UCNPs) are capable of converting near-infra-red excitation into visible and ultraviolet emission. Their unique optical properties have advanced a broad range of applications, such as fluorescent microscopy, deep-tissue bioimaging, nanomedicine, optogenetics, security labelling and volumetric display. However, the constraint of concentration quenching on upconversion luminescence has hampered the nanoscience community to develop bright UCNPs with a large number of dopants. This review surveys recent advances in developing highly doped UCNPs, highlights the strategies that bypass the concentration quenching effect, and discusses new optical properties as well as emerging applications enabled by these nanoparticles.