Tag: materials science

Highly efficient carbon-dot-based photoinitiating systems for 3D-VAT printing

Known as a rising star among carbon nanomaterials, carbon dots (CDs) have attracted considerable interest in various fields in recent years.*

In the article “Highly efficient carbon dot-based photoinitiating systems for 3D-VAT printing” Dominika Krok, Wiktoria Tomal, Alexander J. Knight, Alexander I. Tartakovskii, Nicholas T. H. Farr, Wiktor Kasprzyk and Joanna Ortyl describe how they synthesized different types of carbon dots (CDs) based on citric acid as a precursor using an efficient procedure to purify these materials from low molecular by-products and fluorophores.*

They introduce three types of CDs: citric acid-based, as well as ammonia- and ethylenediamine-doped CDs, and compare their effectiveness to commercially available graphene-based CDs as an element of two- or three-component photoinitiating systems dedicated for free radical photopolymerization processes.*

This approach led to the development of efficient initiating systems and allowed better understanding of the mechanism according to which CDs performed in these processes. *

As the proof of concept, CDs-based photoinitiating systems were implemented in two types of 3D-VAT printing processes: DLP and DLW printing, to obtain high-resolution, 3D hydrogel materials. *

Dominika Krok et al. believe that the research presented in their article will become the basis for further work on carbon dots in the context of the diverse use of photopolymerization processes and avoid errors affecting the misinterpretation of data. *

The morphology and chemical composition of obtained hydrogel printouts were profoundly characterized via scanning electron microscopy (SEM), atomic force microscopy (AFM), nanoscale Fourier transform infrared spectroscopy (Nano-FTIR), and scattering-type Scanning Near-field Optical Microscopy (s-SNOM). *

The s-SNOM system used to collect the data shown in figure 12 of the article cited below, consisted of an AFM within one arm of an interferometer, and a moveable mirror in the other. *

A conductive platinum-iridium coated NanoWorld ARROW-EFM AFM probe was brought into tapping mode operation upon the sample (tapping frequency 77 kHz, tapping amplitude 71 nm), and illumination from a single-wavelength source outputting at 1490 cm−1 was sent into the interferometer. *

Under focused illumination, the conductive AFM tip acts as an optical antenna and a near field is generated at the AFM tip apex (AFM tip radius around 25 nm). The near field interacts with the sample surface and forms a scattering centre that scatters further incoming photons. *

The scattered photons were collected at the detector and interfered with photons returning from the movable mirror in the reference arm of the interferometer. This reference mirror was oscillated in order to induce side-band frequency mixing in the optical signal power spectrum, and the optical amplitude and phase data were extracted at the third harmonic of the AFM tapping frequency. *

The optical amplitude data were normalised to the maximum recorded value. The optical phase data were left unprocessed, and thus the raw values of the phase data in Fig. 12 (cited below) do not hold physical meaning. Only the contrast between two areas of Fig. 12 should be considered. *

AFM data: AFM topology data were recorded using the same instrument as used for the s-SNOM measurements. Conductive AFM cantilevers (Pt/Ir coated ARROW-EFM AFM probes from NanoWorld) were used, at a tapping frequency of 77 kHz and a tapping amplitude of 71 nm. *

Further surface characterization of the hydrogel samples performed with AFM and s-SNOM techniques revealed that, occasionally, carbon dot particles can be found at or emerging from the surface of the hydrogel.  *

Fig. 12D presents the surface topography of an 8 μm by 6.8 μm region of hydrogel as measured through AFM, which is in keeping with the surface characterization data presented in Fig. 12A–C. It is not obvious from the topography data in Fig. 12D alone which features of the sample surface relate to carbon material. *

However, the carbon dot particles can be identified through the mechanical properties of their surface: Fig. 15E in the cited article presents the AFM phase data from the scan shown in Fig. 12D, with AFM phase being sensitive to various mechanical surface properties of the sample material such as hardness and adhesion. *

A strong phase contrast is observed between the soft hydrogel and the harder carbon dot material, allowing for the identification of a carbon dot particle that is only partially covered by the hydrogel. *

Additionally, Fig. 12F presents s-SNOM optical phase data taken during the scan shown in Fig. 12D, using illumination at 1490 cm−1. s-SNOM measurements are sensitive to optical properties such as refractive index and absorption, and the differences in these properties between the hydrogel and carbon dot materials creates strong contrast in s-SNOM phase data, allowing for further verification of the location of the carbon dot particle. *

Dominika Krok et al. note that often large areas of the hydrogel surface had to be scanned before any carbon dot particles partially above the surface were identified, and that no carbon dot particles were found either entirely or mostly above the surface of the hydrogel. *

It is therefore assumed that the CDs embedded within the 3D-VAT prints do not congregate on the surface of the material but instead are distributed throughout the matrix. *

Fig. 12 from “Highly efficient carbon dot-based photoinitiating systems for 3D-VAT printing” by Dominika Krok et al. (2023):(A) Low magnification secondary electron (SE) image of a 3D-VAT printout taken using an Everhart–Thornley Detector (ETD). (B) High resolution SE image of a 3D-VAT printout taken using a Through Lens Detector (TLD). (C) Backscattered election (BSE) image taken using a concentric backscatter (CBS) detector. (D): AFM height topography of a carbon dot at the surface of a hydrogel sample. (E) AFM mechanical phase data taken simultaneously with the data in (D). AFM phase data is sensitive to a number of surface properties (hardness, adhesion, etc.) and is often difficult to interpret. In this case, we simply note that the AFM phase contrast observed in (E) allows for easy distinction between areas of the hydrogel (high AFM phase) and the carbon dot surface (low AFM phase). (F): s-SNOM phase data taken simultaneously with the data in (D), with incident illumination at 1490 cm−1. The s-SNOM data was demodulated at the 3rd harmonic of the AFM tapping frequency to reduce the influence of background effects. The hydrogel and the carbon dot particle have different optical responses under the incident illumination, and so s-SNOM phase contrast is observed between the different regions of the AFM scan. Corresponding s-SNOM amplitude data is shown in Fig. S22 of the ESI.† The s-SNOM system used to collect the data shown in this figure consisted of an AFM within one arm of an interferometer, and a moveable mirror in the other. * A conductive platinum-iridium coated NanoWorld ARROW-EFM AFM probe was brought into tapping mode operation upon the sample (tapping frequency 77 kHz, tapping amplitude 71 nm), and illumination from a single-wavelength source outputting at 1490 cm−1 was sent into the interferometer. *
Fig. 12 from “Highly efficient carbon dot-based photoinitiating systems for 3D-VAT printing” by Dominika Krok et al. (2023):
(A) Low magnification secondary electron (SE) image of a 3D-VAT printout taken using an Everhart–Thornley Detector (ETD). (B) High resolution SE image of a 3D-VAT printout taken using a Through Lens Detector (TLD). (C) Backscattered election (BSE) image taken using a concentric backscatter (CBS) detector. (D): AFM height topography of a carbon dot at the surface of a hydrogel sample. (E) AFM mechanical phase data taken simultaneously with the data in (D). AFM phase data is sensitive to a number of surface properties (hardness, adhesion, etc.) and is often difficult to interpret. In this case, we simply note that the AFM phase contrast observed in (E) allows for easy distinction between areas of the hydrogel (high AFM phase) and the carbon dot surface (low AFM phase). (F): s-SNOM phase data taken simultaneously with the data in (D), with incident illumination at 1490 cm−1. The s-SNOM data was demodulated at the 3rd harmonic of the AFM tapping frequency to reduce the influence of background effects. The hydrogel and the carbon dot particle have different optical responses under the incident illumination, and so s-SNOM phase contrast is observed between the different regions of the AFM scan. Corresponding s-SNOM amplitude data is shown in Fig. S22 of the ESI.†

*Dominika Krok, Wiktoria Tomal, Alexander J. Knight, Alexander I. Tartakovskii, Nicholas T. H. Farr, Wiktor Kasprzyk and Joanna Ortyl
Highly efficient carbon dot-based photoinitiating systems for 3D-VAT printing
Polymer Chemistry, 2023, 14, 4429-4444
DOI:  https://doi.org/10.1039/D3PY00726J

The article “Highly efficient carbon dot-based photoinitiating systems for 3D-VAT printing” by Dominika Krok, Wiktoria Tomal, Alexander J. Knight, Alexander I. Tartakovskii, Nicholas T. H. Farr, Wiktor Kasprzyk and Joanna Ortyl is licensed under a Creative Commons Attribution 3.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third-party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/3.0/.

Flexible Polyurethane Foams Modified with Novel Coconut Monoglycerides-Based Polyester Polyols

The products of the polyurethane (PU) industry such as foams, coatings and adhesives are numerous and can be found in many areas of everyday life. *

Polyols are an essential component in the production of polyurethane. Nowadays they mostly come from petroleum products. *

In view of potential risk factors such as the running out of fossil fuels, supply chain issues, environmental concerns and economic risks it is important to develop alternatives as substitutes and supplements to the existing petroleum derived polyols. *

Vegetable oils can be used to manufacture biobased polyols and various oils such as linseed oil, rapeseed oil, canola oil, grapeseed oil, corn oil, rice bran oil, palm oil, olive oil, castor oil and soybean oil have already been used to make polyols for different purposes.*

Most of the polyols derived from vegetable oils that are already commercially available are made from soybean and castor oil and are mainly used for rigid PU foam applications. *

So far biobased materials for flexible polyurethane foams (FPUFs) have not been studied as much as their rigid counterpart. This is because, due to their chemical composition, there are limits to how much biobased materials can be used in the flexible foam without having an undesired effect on the foam’s mechanical properties. *

Coconut oil is not often used to manufacture flexible foam because the coconut oil’s high level of saturation makes it less compatible with many common methods of creating polyols, as the widely used polyol-forming processes mostly rely on the unsaturation of vegetable oil for functionalization.

To make coconut monoglycerides (CMG) or other plant-based oils usable for polyol-forming processes they need to fulfil the same structural requirements as the fossil-based products. *

In the article “Flexible Polyurethane Foams Modified with Novel Coconut Monoglycerides-Based Polyester Polyols “ Christine Joy M. Omisol, Blessy Joy M. Aguinid, Gerson Y. Abilay, Dan Michael Asequia, Tomas Ralph Tomon, Karyl Xyrra Sabulbero, Daisy Jane Erjeno, Carlo Kurt Osorio, Shashwa Usop, Roberto Malaluan, Gerard Dumancas, Eleazer P. Resurreccion, Alona Lubguban, Glenn Apostol, Henry Siy, Arnold C. Alguno, and Arnold Lubguban describe how they investigated the potential of coconut monoglycerides (CMG) as a polyol raw material specifically for flexible polyurethane foam (FPUF) applications.*

The authors synthesized high-molecular-weight polyester polyols from coconut monoglycerides (CMG), a coproduct of fatty acid production from coconut oil, via polycondensation at different mass ratios of CMG with 1:5 glycerol:phthalic anhydride.*

The resulting CMG-based polyols were shown to work well in making flexible foam. *

Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) were used for the foam characterization. *

The modification of the foam formulation increased the monodentate and bidentate urea groups, shown using Fourier transform infrared (FTIR) spectroscopy, that promoted microphase separation in the foam matrix, confirmed using atomic force microscopy (AFM) and differential scanning calorimetry (DSC). *

Atomic force microscopy (AFM) was used to evaluate the hard–soft domains phase separation of the foam. *

The atomic force microscope was operated at a scan rate of 1.0 Hz in non-contact mode using NanoWorld Pointprobe® NCHR Silicon AFM probes for standard tapping mode applications. (typical resonance frequency 320 kHz, typical force constant 42 N/m). *

It could be shown that density of the CMGPOL-modified polyurethane foams (CPFs) decreased, while a significant improvement in their tensile and compressive properties was observed. *

The investigations by Christine Joy M. Omisol et al. resulted in a new sustainable polyol raw material that can be used to modify petroleum-based foam and produce flexible foams with varying properties that can be tailored to meet specific requirements. *

Figure 11 from Christine Joy M. Omisol et al (2024) “Flexible Polyurethane Foams Modified with Novel Coconut Monoglycerides-Based Polyester Polyols”:Atomic force microscopy (AFM) phase images of CMGPOL-modified polyurethane foams (CPF) and control foam measured with a size scan of 3 μm × 3 μm showing soft and hard regions represented by red and yellow colors, respectively. The foam samples in Figure 11 that exhibited a relatively high degree of microphase separation compared with other samples are CPF-8 and CPF-20. These foams appear to have relatively lighter areas of urea-rich regions separated more prominently from the darker, polyol-rich regions. In contrast, the control foam and CPF-16 show more dispersed hard and soft domains. CPF-24 and CPF-12 are at the middle of the scale, displaying light regions but with more dispersion than CPF-8 and CPF-20. These observations from the phase images of the foam samples are in agreement with the monodentate and bidentate urea contents of the samples, wherein the foams that exhibit greater H-bonding also manifest a higher degree of microphase separation. The same results were obtained by Baghban et al. NanoWorld Pointprobe® NCHR standard tapping mode/non-contact mode silicon AFM probes were used for the foam characterizations with atomic force microscopy.
Figure 11 from Christine Joy M. Omisol et al (2024) “Flexible Polyurethane Foams Modified with Novel Coconut Monoglycerides-Based Polyester Polyols”:
Atomic force microscopy (AFM) phase images of CMGPOL-modified polyurethane foams (CPF) and control foam measured with a size scan of 3 μm × 3 μm showing soft and hard regions represented by red and yellow colors, respectively.

*Christine Joy M. Omisol, Blessy Joy M. Aguinid, Gerson Y. Abilay, Dan Michael Asequia, Tomas Ralph Tomon, Karyl Xyrra Sabulbero, Daisy Jane Erjeno, Carlo Kurt Osorio, Shashwa Usop, Roberto Malaluan, Gerard Dumancas, Eleazer P. Resurreccion, Alona Lubguban, Glenn Apostol, Henry Siy, Arnold C. Alguno, and Arnold Lubguban
Flexible Polyurethane Foams Modified with Novel Coconut Monoglycerides-Based Polyester Polyols
ACS Omega 2024, 9, 4, 4497–4512
DOI: https://doi.org/10.1021/acsomega.3c07312

The article “Flexible Polyurethane Foams Modified with Novel Coconut Monoglycerides-Based Polyester Polyols” by Christine Joy M. Omisol, Blessy Joy M. Aguinid, Gerson Y. Abilay, Dan Michael Asequia, Tomas Ralph Tomon, Karyl Xyrra Sabulbero, Daisy Jane Erjeno, Carlo Kurt Osorio, Shashwa Usop, Roberto Malaluan, Gerard Dumancas, Eleazer P. Resurreccion, Alona Lubguban, Glenn Apostol, Henry Siy, Arnold C. Alguno and Arnold Lubguban is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third-party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.

Bi2Se3 interlayer treatments affecting the Y3Fe5O12 (YIG) platinum spin Seebeck effect

Spin Seebeck effects (SSE) arise from spin current (magnon) generation from within ferri-, ferro-, or anti-ferromagnetic materials driven by an applied temperature gradient. *

Longitudinal spin Seebeck effect (LSSE) investigations, where the spin current and temperature gradient evolve along a common z axis, while the magnetic field is applied in the y axis and the voltage contacts are spaced along the x axis, have become the most popular spin Seebeck device architecture. *

In article “Bi2Se3 interlayer treatments affecting the Y3Fe5O12 (YIG) platinum spin Seebeck effect”, Yaoyang Hu, Michael P. Weir, H. Jessica Pereira, Oliver J. Amin, Jem Pitcairn, Matthew J. Cliffe, Andrew W. Rushforth, Gunta Kunakova, Kiryl Niherysh, Vladimir Korolkov, James Kertfoot, Oleg Makarovsky and Simon Woodward present a method to enhance the longitudinal spin Seebeck effect at platinum/yttrium iron garnet (Pt/YIG) interfaces. *

The introduction of a partial interlayer of bismuth selenide (Bi2Se3, 2.5% surface coverage) interfaces significantly increases (by ∼380%–690%) the spin Seebeck coefficient over equivalent Pt/YIG control devices. *

Optimal devices are prepared by transferring Bi2Se3 nanoribbons, prepared under anaerobic conditions, onto the YIG (111) chips followed by rapid over-coating with Pt. The deposited Pt/Bi2Se3 nanoribbon/YIG assembly is characterized by scanning electron microscope. The expected elemental compositions of Bi2Se3 and YIG are confirmed by energy dispersive x-ray analysis. *

A spin Seebeck coefficient of 0.34–0.62 μV/K for Pt/Bi2Se3/YIG is attained for the authors’ devices, compared to just 0.09 μV/K for Pt/YIG controls at a 12 K thermal gradient and a magnetic field swept from −50 to +50 mT. *

Superconducting quantum interference device magnetometer studies indicate that the magnetic moment of Pt/Bi2Se3/YIG treated chips is increased by ∼4% vs control Pt/YIG chips (i.e., a significant increase vs the ±0.06% chip mass reproducibility). *

Increased surface magnetization is also detected in magnetic force microscope studies of Pt/Bi2Se3/YIG, suggesting that the enhancement of spin injection is associated with the presence of Bi2Se3 nanoribbons. *

To understand the surface magnetization effects in sample BSYIG1-a further, magnetic force microscope (MFM) measurements were undertaken using a commercial atomic force microscope and magnetic NanoWorld Pointprobe® MFMR AFM probes. *

MFM differs from traditional atomic force microscopy in that the AFM probe, in addition to providing a surface height profile, is also able to detect the magnetic field gradient above the sample. *

MFM surface profiling of BSYIG1-a revealed that a typical ribbon is comprised of multilayers of Bi2Se3, providing thicker sections ca. 250 nm thick [e.g., the profile along vector 1 in Figs. 3(a) and 3(b) cited below] and additional thinner sections ca. 100 nm thick [e.g., the profile along vector 2 in Figs. 3(a) and 3(b)]. Re-running ribbon profiles 1 and 2 with the magnetic probe at a height of 100 nm above the topological surface provided data on the magnetic field gradient variation along the same line profiles. The MFM amplitude [Figs. 3(c) and 3(d) cited below] increases over the Bi2Se3 flake, and furthermore, the magnetic enhancement correlates with the thickness of the Bi2Se3, being larger for the thicker part of the sample. *

This amplitude enhancement suggests that the observed effect is magnetic rather than due to long-range electrostatics, supporting the inference that the surface magnetization is improved by the presence of Bi2Se3 flakes at the interlayer of a Pt/YIG device. However, it was not possible to extract quantitative information about surface magnetization from this study, but Yaoyang Hu et al. are hopeful that future experimental and theoretical work can provide further explanation. *

Figure 3 from Yaoyang Hu et al. “Bi2Se3 interlayer treatments affecting the Y3Fe5O12 (YIG) platinum spin Seebeck effect”:Scanning probe microscopy images of BSYIG1-a: (a) Atomic force microscopy image of a representative Bi2Se3 nanoribbon on a YIG/GGG substrate. (b) Bi2Se3 ribbon profile scans along vectors 1 (pink) and 2 (blue) showing the two differential height responses. (c) Magnetic force microscopy image of the same Bi2Se3 nanoribbon. The measurement was performed at 100 nm above the topological heights determined in the AFM study. (d) MFM profile scans along vectors 1 (pink) and 2 (blue) showing the magnetic response. Magnetic force microscope (MFM) measurements were undertaken using a commercial atomic force microscope and magnetic NanoWorld MFMR AFM probes. *
Figure 3 from Yaoyang Hu et al. “Bi2Se3 interlayer treatments affecting the Y3Fe5O12 (YIG) platinum spin Seebeck effect”:
Scanning probe microscopy images of BSYIG1-a: (a) Atomic force microscopy image of a representative Bi2Se3 nanoribbon on a YIG/GGG substrate. (b) Bi2Se3 ribbon profile scans along vectors 1 (pink) and 2 (blue) showing the two differential height responses. (c) Magnetic force microscopy image of the same Bi2Se3 nanoribbon. The measurement was performed at 100 nm above the topological heights determined in the AFM study. (d) MFM profile scans along vectors 1 (pink) and 2 (blue) showing the magnetic response.

*Yaoyang Hu, Michael P. Weir, H. Jessica Pereira, Oliver J. Amin, Jem Pitcairn, Matthew J. Cliffe, Andrew W. Rushforth, Gunta Kunakova, Kiryl Niherysh, Vladimir Korolkov, James Kertfoot, Oleg Makarovsky and Simon Woodward
Bi2Se3 interlayer treatments affecting the Y3Fe5O12 (YIG) platinum spin Seebeck effect
Applied Physics Letters 123, 223902 (2023)
DOI: https://doi.org/10.1063/5.0157778

The article “Bi2Se3 interlayer treatments affecting the Y3Fe5O12 (YIG) platinum spin Seebeck effect” by Yaoyang Hu, Michael P. Weir, H. Jessica Pereira, Oliver J. Amin, Jem Pitcairn, Matthew J. Cliffe, Andrew W. Rushforth, Gunta Kunakova, Kiryl Niherysh, Vladimir Korolkov, James Kertfoot, Oleg Makarovsky and Simon Woodward is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third-party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.