| 1. |
- Cao, Wei, et al.
(författare)
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Self-Assembly of Large Magnetic Nanoparticles in Ultrahigh Molecular Weight Linear Diblock Copolymer Films
- 2020
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Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 12:6, s. 7557-7564
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Tidskriftsartikel (refereegranskat)abstract
- The development of diblock copolymer (DBC) nanocomposite films containing magnetic nanoparticles (NPs) with diameters (D) over 20 nm is a challenging task. To host large iron oxide NPs (Fe3O4, D = 27 +/- 0.6 nm), an ultrahigh molecular weight (UHMW) linear DBC polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) is used as a template in the present work. Due to hydrogen bonding between the carboxylic acid ligands of the NPs and the ester groups in PMMA, the NPs show an affinity to the PMMA block. The localization of the NPs inside the DBC is investigated as a function of the NP concentration. At low NP concentrations, NPs are located preferentially at the interface between PS and PMMA domains to minimize the interfacial tension caused by the strong segregation strength of the UHMW DBC. At high NP concentrations (>= 10 wt %), chain-like NP aggregates (a head-to-tail orientation) are observed in the PMMA domains, resulting in a change of the morphology from sphere to ellipsoid for part of the PMMA domains. Magnetic properties of the hybrid films are probed via superconducting quantum interference device magnetometry. All hybrid films show ferrimagnetism and are promising for potential applications in magnetic data storage.
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| 2. |
- Cao, Wei, et al.
(författare)
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Spray-Deposited Anisotropic Ferromagnetic Hybrid Polymer Films of PS-b-PMMA and Strontium Hexaferrite Magnetic Nanoplatelets
- 2021
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Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 13:1, s. 1592-1602
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Tidskriftsartikel (refereegranskat)abstract
- Spray deposition is a scalable and cost-effective technique for the fabrication of magnetic hybrid films containing diblock copolymers (DBCs) and magnetic nanoparticles. However, it is challenging to obtain spray-deposited anisotropic magnetic hybrid films without using external magnetic fields. In the present work, spray deposition is applied to prepare perpendicular anisotropic magnetic hybrid films by controlling the orientation of strontium hexaferrite nanoplatelets inside ultra-high-molecular-weight DBC polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) films. During spray deposition, the evolution of DBC morphology and the orientation of magnetic nanoplatelets are monitored with in situ grazing-incidence small-angle X-ray scattering (GISAXS). For reference, a pure DBC film without nanoplatelets is deposited with the same conditions. Solvent-controlled magnetic properties of the hybrid film are proven with solvent vapor annealing (SVA) applied to the final deposited magnetic films. Obvious changes in the DBC morphology and nanoplatelet localization are observed during SVA. The superconducting quantum interference device data show that ferromagnetic hybrid polymer films with high coercivity can be achieved via spray deposition. The hybrid films show a perpendicular magnetic anisotropy before SVA, which is strongly weakened after SVA. The spray-deposited hybrid films appear highly promising for potential applications in magnetic data storage and sensors.
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| 3. |
- Xia, Senlin, et al.
(författare)
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Magnetic nanoparticle-containing soft-hard diblock copolymer films with high order
- 2018
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Ingår i: Nanoscale. - : ROYAL SOC CHEMISTRY. - 2040-3364 .- 2040-3372. ; 10:25, s. 11930-11941
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Tidskriftsartikel (refereegranskat)abstract
- For sensor applications, superparamagnetic anisotropy is an indispensable property, which is typically achieved by employing an external field to guide the arrangement of magnetic nanoparticles (NPs). In the present investigation, the diblock copolymer polystyrene-block-poly(N-isopropylacrylamide) (PS-b-PNIPAM) is printed as a template to localize magnetic iron oxide NPs without any external field. Via microphase separation, cylindrical nanostructures of PS in a PNIPAM matrix are obtained, aligned perpendicular to the substrate. Since the magnetite NPs (Fe3O4) are functionalized with hydrophobic organic chains showing affinity to the PS blocks, they can selectively aggregate inside the PS cylinders. Moreover, solvent vapor annealing allows the achievement of nanostructures inside the hybrid system with a very high order, even at a high NP loading. Therefore, NPs can accumulate within PS domains to form perpendicularly aligned aggregates with high periodicity. The magnetic properties of the hybrid films are determined at various temperatures in two orthogonal directions (with PS cylinders vertical and parallel to the applied magnetic field). All hybrid films show superparamagnetism and a remarkable magnetic anisotropy is achieved at certain NP concentrations. This investigation shows a facile route to prepare superparamagnetic films with magnetic anisotropy and offers a novel possibility to future magnetic sensor fabrication.
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| 4. |
- Xia, Senlin, et al.
(författare)
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Printed Thin Diblock Copolymer Films with Dense Magnetic Nanostructure
- 2019
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Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 11:24, s. 21935-21945
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Tidskriftsartikel (refereegranskat)abstract
- Thin hybrid films with dense magnetic structures for sensor applications are printed using diblock copolymer (DBC) templating magnetic nanoparticles (MNPs). To achieve a high-density magnetic structure, the printing ink is prepared by mixing polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) with a large PS volume fraction and PS selective MNPs. Solvent vapor annealing is applied to generate a parallel cylindrical film morphology (with respect to the substrate), in which the MNP-residing PS domains are well separated by the PMMA matrix, and thus, the formation of large MNP agglomerates is avoided. Moreover, the morphologies of the printed thin films are determined as a function of the MNP concentration with real and reciprocal space characterization techniques. The PS domains are found to be saturated with MNPs at 1 wt %, at which the structural order of the hybrid films reaches a maximum within the studied range of MNP concentration. As a beneficial aspect, the MNP loading improves the morphological order of the thin DBC films. The dense magnetic structure endows the thin films with a faster superparamagnetic responsive behavior, as compared to thick films where identical MNPs are used, but dispersed inside the minority domains of the DBC.
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| 5. |
- Xia, Senlin, et al.
(författare)
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Spray-Coating Magnetic Thin Hybrid Films of PS-b-PNIPAM and Magnetite Nanoparticles
- 2019
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Ingår i: Advanced Functional Materials. - : WILEY-V C H VERLAG GMBH. - 1616-301X .- 1616-3028. ; 29:15
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Tidskriftsartikel (refereegranskat)abstract
- Spray coating is employed to fabricate magnetic thin films composed of the diblock copolymer polystyrene-block-poly(N-isopropylacrylamide) and Fe3O4 magnetic nanoparticles (MNPs) functionalized with hydrophobic coatings. The kinetics of structure formation of the hybrid films is followed in situ with grazing incidence small angle X-ray scattering during the spray deposition. To gain a better understanding of the influence of MNPs on the overall structure formation, the pure polymer film is also deposited as a reference via an identical spray protocol. At the initial spraying stage, the hybrid film (containing 2 wt% of MNPs) exhibits a faster formation process of a complete film as compared to the reference. The existence of MNPs depresses the dewetting behavior of polymer films on the substrate at macroscale and simultaneously alters the polymer microphase separation structure orientation from parallel to vertical. As spraying proceeds, MNPs aggregate into agglomerates with increasing sizes. After the spray deposition is finished, both samples gradually reach an equilibrium state and magnetic films with stable structures are achieved in the end. Superconducting quantum interference device investigation reveals the superparamagnetic property of the sprayed hybrid film. Consequently, potential application of sprayed films in fields such as magnetic sensors or data storage appears highly promising.
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| 6. |
- Akinsinde, Lewis O., et al.
(författare)
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Surface characterization and resistance changes of silver-nanowire networks upon atmospheric plasma treatment
- 2021
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 550
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Tidskriftsartikel (refereegranskat)abstract
- Highly conductive silver-nanowire (Ag-NW) networks are used in composite materials as conductive channels. Their resistance tuning can be accomplished by changing the Ag-NW concentration, and, therefore, changing the network structure. In this study, an alternative pathway to resistance engineering of conductive Ag-NW networks by local atmospheric plasma treatment is employed. The corresponding changes in nanowire network morphology and crystallinity as a function of plasma etching time are investigated by time-resolved grazingincidence X-ray scattering, field-effect scanning electron microscopy, and X-ray photoelectron spectroscopy. Three characteristic etching phases are identified. The first two phases enable the controlled engineering of the electrical properties with different rates of resistance change, which results from changes in nanowire shape, network morphology, and different oxidation rates. Phase III is characterized by pronounced fragmentation and destruction of the Ag-NW networks. These results show the feasibility of atmospheric plasma treatments to tune the local electrical properties of conductive Ag-NW networks. Furthermore, we present a physical Monte Carlo model explaining the electrical network properties as a function of plasma etching time based on the network connectivity and a constant plasma etching rate of 570 ng s-1 cm-2.
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| 7. |
- Bera, Anup Kumar, et al.
(författare)
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Morphology induced large magnetic anisotropy in obliquely grown nanostructured thin film on nanopatterned substrate
- 2022
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 581
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Tidskriftsartikel (refereegranskat)abstract
- The artificial tailoring of magnetic anisotropy by manipulating surface and interface morphology is attracting widespread interest for its application in spintronic and magnetic memory devices. Here oblique angle deposition on a nanopatterned rippled substrate is presented as a novel route of inducing large in-plane uniaxial magnetic anisotropy (UMA) in magnetic thin films. For this purpose, Cobalt films and rippled SiO2 substrates have been taken as a model system for the present study. Here, nanopatterned substrates are prepared by low energy ion beam erosion (IBE), above which films are deposited obliquely along and normal to the ripple directions. A clear anisotropy in the growth behavior has been observed due to the inhomogeneous in-plane organization of adatoms in the form of columns. The increased shadowing effect in the films deposited obliquely normal to the direction of the ripple patterns causes preferential coalescence of the columns along the substrate ripples, resulting in stronger in-plane UMA in the film. This peculiarity in magnetic behavior is addressed by considering the morphological anisotropy governed by enhanced shadowing effect, the shape anisotropy and the dipolar interactions among the magnetostatically coupled ripple structure.
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| 8. |
- Betker, Marie, et al.
(författare)
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Sprayed Hybrid Cellulose Nanofibril-Silver Nanowire Transparent Electrodes for Organic Electronic Applications
- 2023
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 6:14, s. 13677-13688
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Tidskriftsartikel (refereegranskat)abstract
- In times of climate change and resource scarcity, researchers are aiming to find sustainable alternatives to synthetic polymers for the fabrication of biodegradable, eco-friendly, and, at the same time, high-performance materials. Nanocomposites have the ability to combine several favorable properties of different materials in a single device. Here, we evaluate the suitability of two kinds of inks containing silver nanowires for the fast, facile, and industrial-relevant fabrication of two different types of cellulose-based silver nanowire electrodes via layer-by-layer spray deposition only. The Type I electrode has a layered structure, which is composed of a network of silver nanowires sprayed on top of a cellulose nanofibrils layer, while the Type II electrode consists of a homogeneous mixture of silver nanowires and cellulose nanofibrils. A correlation between the surface structure, conductivity, and transparency of both types of electrodes is established. We use the Haacke figure of merit for transparent electrode materials to demonstrate the favorable influence of cellulose nanofibrils in the spray ink by identifying Type II as the electrode with the lowest sheet resistance (minimum 5 ± 0.04 Ω/sq), while at the same time having a lower surface roughness and shorter fabrication time than Type I. Finally, we prove the mechanical stability of the Type II electrode by bending tests and its long-time stability under ambient conditions. The results demonstrate that the mixed spray ink of silver nanowires and cellulose nanofibrils is perfectly suitable for the fast fabrication of highly conductive organic nanoelectronics on an industrial scale.
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| 9. |
- Chen, Qing, et al.
(författare)
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Layer-by-Layer Spray-Coating of Cellulose Nanofibrils and Silver Nanoparticles for Hydrophilic Interfaces
- 2021
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 4:1, s. 503-513
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Tidskriftsartikel (refereegranskat)abstract
- Silver nanoparticles (AgNPs) and AgNP-based composite materials have attracted growing interest due to their structure-dependent optical, electrical, catalytic, and stimuli-responsive properties. For practical applications, polymeric materials are often combined with AgNPs to provide flexibility and offer a scaffold for homogenous distribution of the AgNPs. However, the control over the assembly process of AgNPs on polymeric substrates remains a big challenge. Herein, we report the fabrication of AgNP/cellulose nanofibril (CNF) thin films via layer-by-layer (LBL) spray-coating. The morphology and self-assembly of AgNPs with increasing number of spray cycles are characterized by atomic force microscopy (AFM), grazing-incidence small-angle X-ray scattering (GISAXS), and grazing-incidence wide-angle X-ray scattering (GIWAXS). We deduce that an individual AgNP (radius = 15 +/- 3 nm) is composed of multiple nanocrystallites (diameter = 2.4 +/- 0.9 nm). Our results suggest that AgNPs are assembled into large agglomerates on SiO2 substrates during spray-coating, which is disadvantageous for AgNP functionalization. However, the incorporation of CNF substrates contributes to a more uniform distribution of AgNP agglomerates and individual AgNPs by its network structure and by absorbing the partially dissolved AgNP agglomerates. Furthermore, we demonstrate that the spray-coating of the AgNP/CNF mixture results in similar topography and agglomeration patterns of AgNPs compared to depositing AgNPs onto a precoated CNF thin film. Contact-angle measurements and UV/vis spectroscopy suggest that the deposition of AgNPs onto or within CNFs could increase the hydrophilicity of AgNP-containing surfaces and the localized surface plasmon resonance (LSPR) intensity of AgNP compared to AgNPs sprayed on SiO(2 )substrates, suggesting their potential applications in antifouling coatings or label-free biosensors. Thereby, our approach provides a platform for a facile and scalable production of AgNP/CNF films with a low agglomeration rate by two different methods as follows: (1) multistep layer-by-layer (LBL) spray-coating and (2) direct spray-coating of the AgNP/CNF mixture. We also demonstrate the ability of CNFs as a flexible framework for directing the uniform assembly of AgNPs with tailorable wettability and plasmonic properties.
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| 10. |
- Chen, Wei, et al.
(författare)
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Colloidal PbS quantum dot stacking kinetics during deposition via printing
- 2020
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Ingår i: Nanoscale Horizons. - : Royal Society of Chemistry (RSC). - 2055-6764 .- 2055-6756. ; 5:5, s. 880-885
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal PbS quantum dots (QDs) are attractive for solution-processed thin-film optoelectronic applications. In particular, directly achieving QD thin-films by printing is a very promising method for low-cost and large-scale fabrication. The kinetics of QD particles during the deposition process play an important role in the QD film quality and their respective optoelectronic performance. In this work, the particle self-organization behavior of small-sized QDs with an average diameter of 2.88 +/- 0.36 nm is investigated for the first time in situ during printing by grazing-incidence small-angle X-ray scattering (GISAXS). The time-dependent changes in peak intensities suggest that the structure formation and phase transition of QD films happen within 30 seconds. The stacking of QDs is initialized by a templating effect, and a face-centered cubic (FCC) film forms in which a superlattice distortion is also found. A body-centered cubic nested FCC stacking is the final QD assembly layout. The small size of the inorganic QDs and the ligand collapse during the solvent evaporation can well explain this stacking behavior. These results provide important fundamental understanding of structure formation of small-sized QD based films prepared via large-scale deposition with printing with a slot die coater.
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