Aaltodoc Repository :: Browsing by Author "Ras, Robin H.A."

Browsing by Author "Ras, Robin H.A."

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3D Printing of Superhydrophobic Objects with Bulk Nanostructure
(WILEY-V C H VERLAG GMBH, 2021-11-11) Dong, Zheqin; Vuckovac, Maja; Cui, Wenjuan; Zhou, Quan; Ras, Robin H.A.; Levkin, Pavel A.; Department of Applied Physics; Department of Electrical Engineering and Automation; Department of Bioproducts and Biosystems; Soft Matter and Wetting; Robotic Instruments; Karlsruhe Institute of Technology
The rapid development of 3D printing (or additive manufacturing) technologies demands new materials with novel properties and functionalities. Superhydrophobic materials, owing to their ultralow water adhesion, self-cleaning, anti-biofouling, or superoleophilic properties are useful for myriad applications involving liquids. However, the majority of the methods for making superhydrophobic surfaces have been based on surface functionalization and coatings, which are challenging to apply to 3D objects. Additionally, these coatings are vulnerable to abrasion due to low mechanical stability and limited thickness. Here, a new materials concept and methodology for 3D printing of superhydrophobic macroscopic objects with bulk nanostructure and almost unlimited geometrical freedom is presented. The method is based on a specific ink composed of hydrophobic (meth)acrylate monomers and porogen solvents, which undergoes phase separation upon photopolymerization to generate inherently nanoporous and superhydrophobic structures. Using a desktop Digital Light Processing printer, superhydrophobic 3D objects with complex shapes are demonstrated, with ultralow and uniform water adhesion measured with scanning droplet adhesion microscopy. It is shown that the 3D-printed objects, owing to their nanoporous structure throughout the entire volume, preserve their superhydrophobicity upon wear damage. Finally, a superhydrophobic 3D-printed gas-permeable and water-repellent microfluidic device and a hierarchically structured 3D-printed super-oil-absorbent are demonstrated.
Antifouling membranes for oily wastewater treatment: Interplay between wetting and membrane fouling
(2018) Huang, Shilin; Ras, Robin H.A.; Tian, Xuelin; Department of Applied Physics; Department of Bioproducts and Biosystems; Soft Matter and Wetting; Sun Yat-sen University
Oily wastewater is an extensive source of pollution to soil and water, and its harmless treatment is of great importance for the protection of our aquatic ecosystems. Membrane filtration is highly desirable for removing oil from oily water because it has the advantages of energy efficiency, easy processing and low maintenance cost. However, membrane fouling during filtration leads to severe flux decline and impedes long-term operation of membranes in practical wastewater treatment. Membrane fouling includes reversible fouling and irreversible fouling. The fouling mechanisms have been explored based on classical fouling models, and on oil droplet behaviors (such as droplet deposition, accumulation, coalescence and wetting) on the membranes. Membrane fouling is dominated by droplet-membrane interaction, which is influenced by the properties of the membrane (e.g., surface chemistry, structure and charge) and the wastewater (e.g., compositions and concentrations) as well as the operation conditions. Typical membrane antifouling strategies, such as surface hydrophilization, zwitterionic polymer coating, photocatalytic decomposition and electrically enhanced antifouling are reviewed, and their cons and pros for practical applications are discussed.
Bright and Photostable Fluorescent Metal Nanocluster Supraparticles from Invert Emulsions
(WILEY-VCH VERLAG, 2022-10-04) Zhou, Shaochen; Peng, Bo; Duan, Yanyan; Liu, Kai; Ikkala, Olli; Ras, Robin H.A.; Department of Applied Physics; Department of Bioproducts and Biosystems; Soft Matter and Wetting; Molecular Materials; Center of Excellence in Life-Inspired Hybrid Materials, LIBER; IMDEA Materials Institute
Fluorescent supraparticles of gold, silver and copper nanoclusters are synthesized by simply drying of invert emulsions, resulting in a dozen-fold increase in photoluminescence quantum yield (up to ≈80 %) and a significant improvement in photostability. The inhibition of the ligand twisting during the intramolecular charge transfer is found to be responsible for the enhancement, especially for the gold nanocluster supraparticles. This research provides a general, flexible, and easy method for producing highly luminescent and photostable metal nanocluster-based materials that promise practical applications in white-light-emitting diodes.
Bright and stable gold nanocluster assemblies by silica/zirconia double-shell encapsulation
(Royal Society of Chemistry, 2022-07-14) Zhou, Shaochen; Duan, Yanyan; Liu, Kai; Ras, Robin H.A.; Soft Matter and Wetting; IMDEA Materials Institute; Department of Applied Physics
Ultrasmall gold nanoclusters are fascinating fluorescent materials with many unique properties, yet, to render them highly luminescent and stable remains challenging. In this work, solvent-induced aggregates of gold nanoclusters are encapsulated in silica/zirconia nanostructures, realizing a significantly enhanced photoluminescence efficiency and stability. These silica and zirconia coated gold nanocluster aggregates achieved a photoluminescence quantum yield of ∼55%, with high resistance to photobleaching and water, due to the stabilization by the dual-oxide matrix. Furthermore, we demonstrate their suitability for visualizing latent fingerprints.
Compressibility and porosity modulate the mechanical properties of giant gas vesicles
(NATL ACAD SCIENCES, 2023-01-24) Al-Terke, Hedar H.; Beaune, Grégory; Junaid, Muhammad; Seitsonen, Jani; Paananen, Arja; Timonen, Jaakko V.I.; Joensuu, Jussi; Brochard-Wyart, Françoise; Ras, Robin H.A.; Department of Applied Physics; Center of Excellence in Life-Inspired Hybrid Materials, LIBER; Soft Matter and Wetting; Active Matter; VTT Technical Research Centre of Finland; Institut Curie
Gas vesicles used as contrast agents for noninvasive ultrasound imaging must be formulated to be stable, and their mechanical properties must be assessed. We report here the formation of perfluoro-n-butane microbubbles coated with surface-active proteins that are produced by filamentous fungi (hydrophobin HFBI from Trichoderma reesei). Using pendant drop and pipette aspiration techniques, we show that these giant gas vesicles behave like glassy polymersomes, and we discover novel gas extraction regimes. We develop a model to analyze the micropipette aspiration of these compressible gas vesicles and compare them to incompressible liquid-filled vesicles. We introduce a sealing parameter to characterize the leakage of gas under aspiration through the pores of the protein coating. Utilizing this model, we can determine the elastic dilatation modulus, surface viscosity, and porosity of the membrane. These results demonstrate the engineering potential of protein-coated bubbles for echogenic and therapeutic applications and extend the use of the pipette aspiration technique to compressible and porous systems.
Core-Selective Silver-Doping of Gold Nanoclusters by Surface-Bound Sulphates on Colloidal Templates: From Synthetic Mechanism to Relaxation Dynamics
(WILEY-VCH VERLAG, 2023-01-04) Chandra, Sourov; Sciortino, Alice; Shandilya, Shruti; Fang, Lincan; Chen, Xi; Nonappa; Jiang, Hua; Johansson, Leena Sisko; Cannas, Marco; Ruokolainen, Janne; Ras, Robin H.A.; Messina, Fabrizio; Peng, Bo; Ikkala, Olli; Department of Applied Physics; Department of Bioproducts and Biosystems; Center of Excellence in Life-Inspired Hybrid Materials, LIBER; Molecular Materials; Computational Electronic Structure Theory; NanoMaterials; Bioproduct Chemistry; Soft Matter and Wetting; University of Palermo
Ultra-small luminescent gold nanoclusters (AuNCs) have gained substantial interest owing to their low photobleaching and high biocompatibility. While the substitution of silver for gold at the central core of AuNCs has shown significant augmentation of photoluminescence with enhanced photostability, selective replacement of the central atom by silver is, however, energetically inhibited. Herein, a new strategy for in situ site-selective Ag-doping exclusively at the central core of AuNCs using sulphated colloidal surfaces as the templates is presented. This approach exceedingly improves the photoluminescence quantum efficiency of AuNCs by eliminating nonradiative losses in the multi-step relaxation cascade populating the emissive state. Density functional theory predicts the mechanism of specific doping at the central core, endorsing the preferential bonding between Ag+ ions and sulphates in water. Finally, the generic nature of the templating concept to allow core-specific doping of nanoclusters is unraveled.
Design of Fluoro-Free Surfaces Super-Repellent to Low-Surface-Tension Liquids
(Wiley-VCH Verlag, 2023-07-20) Wong, William S.Y.; Kiseleva, Mariia S.; Zhou, Shaochen; Junaid, Muhammad; Pitkänen, Leena; Ras, Robin H.A.; Department of Applied Physics; Department of Bioproducts and Biosystems; Soft Matter and Wetting; Biopolymer Chemistry and Engineering; Center of Excellence in Life-Inspired Hybrid Materials, LIBER
Super-liquid-repellent surfaces feature high liquid contact angles and low sliding angles find key applications in anti-fouling and self-cleaning. While repellency for water is easily achieved with hydrocarbon functionalities, repellency for many low-surface-tension liquids (down to 30 mN m−1) still requires perfluoroalkyls (a persistent environmental pollutant and bioaccumulation hazard). Here, the scalable room-temperature synthesis of stochastic nanoparticle surfaces with fluoro-free moieties is investigated. Silicone (dimethyl and monomethyl) and hydrocarbon surface chemistries are benchmarked against perfluoroalkyls, assessed using model low-surface-tension liquids (ethanol–water mixtures). It is discovered that both hydrocarbon- and dimethyl-silicone-based functionalization can achieve super-liquid-repellency down to 40–41 mN m−1 and 32–33 mN m−1, respectively (vs 27–32 mN m−1 for perfluoroalkyls). The dimethyl silicone variant demonstrates superior fluoro-free liquid repellency likely due to its denser dimethyl molecular configuration. It is shown that perfluoroalkyls are not necessary for many real-world scenarios requiring super-liquid-repellency. Effective super-repellency of different surface chemistries against different liquids can be adequately predicted using empirically verified phase diagrams. These findings encourage a liquid-centric design, i.e., tailoring surfaces for target liquid properties. Herein, key guidelines are provided for achieving functional yet sustainably designed super-liquid-repellency.
Designed inorganic porous nanovector with controlled release and MRI features for safe administration of doxorubicin
(2019-01-10) Näkki, Simo; Wang, Julie T.W.; Wu, Jianwei; Fan, Li; Rantanen, Jimi; Nissinen, Tuomo; Kettunen, Mikko I.; Backholm, Matilda; Ras, Robin H.A.; Al-Jamal, Khuloud T.; Lehto, Vesa Pekka; Xu, Wujun; Department of Applied Physics; Department of Bioproducts and Biosystems; Soft Matter and Wetting; University of Eastern Finland; King's College London; Fourth Military Medical University
The inability of traditional chemotherapeutics to reach cancer tissue reduces the treatment efficacy and leads to adverse effects. A multifunctional nanovector was developed consisting of porous silicon, superparamagnetic iron oxide, calcium carbonate, doxorubicin and polyethylene glycol. The particles integrate magnetic properties with the capacity to retain drug molecules inside the pore matrix at neutral pH to facilitate drug delivery to tumor tissues. The MRI applicability and pH controlled drug release were examined in vitro together with in-depth material characterization. The in vivo biodistribution and compound safety were verified using A549 lung cancer bearing mice before proceeding to therapeutic experiments using CT26 cancer implanted mice. Loading doxorubicin into the porous nanoparticle negated the adverse side effects encountered after intravenous administration highlighting the particles’ excellent biocompatibility. Furthermore, the multifunctional nanovector induced 77% tumor reduction after intratumoral injection. The anti-tumor effect was comparable with that of free doxorubicin but with significantly alleviated unwanted effects. These results demonstrate that the developed porous silicon-based nanoparticles represent promising multifunctional drug delivery vectors for cancer monitoring and therapy.
Droplet Friction on Superhydrophobic Surfaces Scales With Liquid-Solid Contact Fraction
(Wiley-VCH Verlag, 2024-09-17) Lepikko, Sakari; Turkki, Valtteri; Koskinen, Tomi; Raju, Ramesh; Jokinen, Ville; Kiseleva, Mariia S.; Rantataro, Samuel; Timonen, Jaakko V.I.; Backholm, Matilda; Tittonen, Ilkka; Ras, Robin H.A.; Department of Applied Physics; Department of Electronics and Nanoengineering; Department of Chemistry and Materials Science; Department of Electrical Engineering and Automation; Soft Matter and Wetting; Ilkka Tittonen Group; Microsystems Technology; Active Matter; Living, Fluid, & Soft Matter; Center of Excellence in Life-Inspired Hybrid Materials, LIBER
It is generally assumed that contact angle hysteresis of superhydrophobic surfaces scales with liquid–solid contact fraction, however, its experimental verification has been problematic due to the limited accuracy of contact angle and sliding angle goniometry. Advances in cantilever-based friction probes enable accurate droplet friction measurements down to the nanonewton regime, thus suiting much better for characterizing the wetting of superhydrophobic surfaces than contact angle hysteresis measurements. This work quantifies the relationship between droplet friction and liquid–solid contact fraction, through theory and experimental validation. Well-defined micropillar and microcone structures are used as model surfaces to provide a wide range of different liquid–solid contact fractions. Micropillars are known to be able to hold the water on top of them, and a theoretical analysis together with confocal laser scanning microscopy shows that despite the spiky nature of the microcones droplets do not sink into the conical structure either, rendering a diminishingly small liquid–solid contact fraction. Droplet friction characterization with a micropipette force sensor technique reveals a strong dependence of the droplet friction on the contact fraction, and the dependency is described with a simple physical equation, despite the nearly three-orders-of-magnitude difference in liquid–solid contact fraction between the sparsest cone surface and the densest pillar surface.
Dual emitting Ag35nanocluster protected by 2-pyrene imine thiol
(ROYAL SOC CHEMISTRY, 2020-10-25) Jana, Arijit; Chakraborty, Papri; Dar, Wakeel Ahmed; Chandra, Sourov; Khatun, Esma; Kannan, M. P.; Ras, Robin H.A.; Pradeep, Thalappil; Department of Applied Physics; Department of Bioproducts and Biosystems; Molecular Materials; Soft Matter and Wetting; Indian Institute of Technology Madras
In this communication, we present the synthesis of 2-pyrene imine thiol (2-PIT)-protected Ag35 nanoclusters using a ligand exchange-induced structural transformation reaction. The formation of the nanocluster and its composition were confirmed through several spectroscopic and electron microscopic studies. The UV-vis absorption spectrum showed a set of characteristic features of the nanocluster. This nanocluster showed blue emission under UV light due to pyrene to metal corecharge-transfer, and NIR emission due to charge-transfer within the metal core. This is the first report on dual emitting pyrene protected atomically precise silver nanoclusters.
Efficient separation of immiscible oil/water mixtures using a perforated lotus leaf
(ROYAL SOC CHEMISTRY, 2019-01-01) Zhang, Chunhui; Zhang, Yuheng; Xiao, Xiao; Liu, Guoliang; Xu, Zhe; Wang, Bing; Yu, Cunming; Ras, Robin H.A.; Jiang, Lei; Department of Applied Physics; Biohybrid Materials; Soft Matter and Wetting; CAS - Technical Institute of Physics and Chemistry; Beihang University
The ecosystem and human society are nowadays greatly threatened by oily wastewater or spilled oils. To address these severe issues, considerably advanced methods, such as those using polymer membranes and polymer-coated meshes with special wettability, have been developed to achieve efficient oil/water separation. However, a single superhydrophobic- or superhydrophilic-based membrane or mesh can only allow either oil or water to pass through, which restricts their applications. Besides, these artificial materials and their fabricating processes may also involve hazardous substances and enormous energy consumption. Therefore, powerful and green oil/water separation approaches are still urgently needed. Herein, we report that the natural lotus leaf with Janus wettability can be a potential candidate for efficient oil/water separation after simple punching by a needle. The proposed approach has the advantages of easily obtained and low-cost natural origin materials and a simple fabrication process and shows potential applicability for building a greener world.
Erratum: Efficient separation of immiscible oil/water mixtures using a perforated lotus leaf (Green Chemistry (2019) 21 (6579-6584) DOI: 10.1039/C9GC03254A)
(ROYAL SOC CHEMISTRY, 2020-01-21) Zhang, Chunhui; Zhang, Yuheng; Xiao, Xiao; Liu, Guoliang; Xu, Zhe; Wang, Bing; Yu, Cunming; Ras, Robin H.A.; Jiang, Lei; Department of Applied Physics; Department of Bioproducts and Biosystems; Soft Matter and Wetting; CAS - Technical Institute of Physics and Chemistry; Beihang University
The authors regret that Fig. 2 and 3 are incorrect. The correct figures are as follows: (Figure Presented) The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers. Green Chemistry, 1463-9262, Volume 22, Issue 2
Fabrication of a Waterborne Durable Superhydrophobic Material Functioning in Air and under Oil
(2018-06) Baidya, Avijit; Das, Sarit Kumar; Ras, Robin H.A.; Pradeep, Thalappil; Department of Applied Physics; Department of Bioproducts and Biosystems; Soft Matter and Wetting; Indian Institute of Technology Madras
A fundamental challenge in artificially structured/ chemically modified superhydrophobic surfaces is their poor chemical, mechanical, and structural robustness toward different mechanical abrasions. This limits their application potential in different fields of science and technology. Herein, a waterborne superhydrophobic material composed of clay particles is developed through a one-pot chemical modification in ambient conditions, forming durable micro-nano dual-structured coatings over a range of substrates, without adhesive. This chemical modification inverts the inherent hydrophilic nature of clay particles and provides an excellent superhydrophobic surface having a water contact angle >170° (±2°) and contact angle hysteresis <5° (±2°). The coating shows excellent durability against various induced damages and works efficiently both in air and within oils. The observed property is due to the controlled surface energy obtained by the incorporated chemical functionalities and enhanced surface roughness facilitated by the hydrophobic effect during slow evaporation of water from the coating material. Being a stable water dispersion, it enables large area coatings, thereby minimizing safety and environmental concerns. Use of this material to develop rugged waterproof-paper for paper-based technologies is also demonstrated. As clay is commercially available and economical, it is believed, this scalable organic-solvent-free superhydrophobic material will have a positive impact on various industries.
Ferrofluid Microdroplet Splitting for Population-Based Microfluidics and Interfacial Tensiometry
(Wiley, 2020-07) Latikka, Mika; Backholm, Matilda; Baidya, Avijit; Ballesio, Alberto; Serve, Amandine; Beaune, Grégory; Timonen, Jaakko V.I.; Pradeep, Thalappil; Ras, Robin H.A.; Department of Applied Physics; Department of Chemistry; Department of Bioproducts and Biosystems; Soft Matter and Wetting; Active Matter; Indian Institute of Technology Madras
Ferrofluids exhibit a unique combination of liquid properties and strong magnetic response, which leads to a rich variety of interesting functional properties. Here, the magnetic-field-induced splitting of ferrofluid droplets immersed in an immiscible liquid is presented, and related fascinating dynamics and applications are discussed. A magnetic field created by a permanent magnet induces instability on a mother droplet, which divides into two daughter droplets in less than 0.1 s. During the splitting process, the droplet undergoes a Plateau–Rayleigh-like instability, which is investigated using high-speed imaging. The dynamics of the resulting satellite droplet formation is shown to depend on the roughness of the supporting surface. Further increasing the field results in additional splitting events and self-assembly of microdroplet populations, which can be magnetically actuated. The effects of magnetization and interfacial tension are systematically investigated by varying magnetic nanoparticles and surfactant concentrations, and a variety of outcomes from labyrinthine patterns to discrete droplets are observed. As the splitting process depends on interfacial tension, the droplet splitting can be used as a measure for interfacial tension as low as 0.1 mN m−1. Finally, a population-based digital microfluidics concept based on the self-assembled microdroplets is presented.
Ferrofluidic Manipulator: Automatic manipulation of nonmagnetic microparticles at the air-ferrofluid interface
(IEEE, 2021-08) Cenev, Zoran; Harischandra, P. A. Diluka; Nurmi, Seppo; Latikka, Mika; Hyninen, Ville; Ras, Robin H.A.; Timonen, Jaakko V.I.; Zhou, Quan; Department of Mechanical Engineering; Department of Applied Physics; Department of Electrical Engineering and Automation; Active Matter; Robotic Instruments; Soft Matter and Wetting; Molecular Materials; NanoMaterials; Aalto University
Manipulation of small-scale matter is a fundamental topic in micro and nanorobotics. Numerous magnetic robotic systems have been developed for the manipulation of microparticles in an ambient environment, liquid, as well as on the air-liquid interface. These systems move intrinsically magnetic or magnetically tagged objects by inducing a magnetic torque or force. However, most of the materials found in nature are nonmagnetic. Here, we report a ferrofluidic manipulator for automatic 2-D manipulation of nonmagnetic objects floating on top of a ferrofluid. The manipulation system employs 8-cm-scale solenoids, which can move nonmagnetic particles by deforming the air-ferrofluid interface. Using linear programming, we can control the motion of the nonmagnetic particles with a predefined trajectory of a line, square, and circle with a precision of 25.1 ± 19.5, 34.4 ± 28.4, and 33.4 ± 26.6 μm, respectively. The ferrofluidic manipulator is versatile with the materials and the shapes of the objects under manipulation. We have successfully manipulated particles made of polyethylene, polystyrene, a silicon chip, and poppy and sesame seeds. This article shows a promising venue for the manipulation of living and nonliving matter at the air-liquid interface.
Flattened and Wrinkled Encapsulated Droplets : Shape Morphing Induced by Gravity and Evaporation
(American Physical Society, 2023-05-26) Riccobelli, Davide; Al-Terke, Hedar H.; Laaksonen, Päivi; Metrangolo, Pierangelo; Paananen, Arja; Ras, Robin H.A.; Ciarletta, Pasquale; Vella, Dominic; Department of Applied Physics; Soft Matter and Wetting; Center of Excellence in Life-Inspired Hybrid Materials, LIBER; Polytechnic University of Milan; VTT Technical Research Centre of Finland; University of Oxford; Häme University of Applied Sciences
We report surprising morphological changes of suspension droplets (containing class II hydrophobin protein HFBI from Trichoderma reesei in water) as they evaporate with a contact line pinned on a rigid solid substrate. Both pendant and sessile droplets display the formation of an encapsulating elastic film as the bulk concentration of solute reaches a critical value during evaporation, but the morphology of the droplet varies significantly: for sessile droplets, the elastic film ultimately crumples in a nearly flattened area close to the apex while in pendant droplets, circumferential wrinkling occurs close to the contact line. These different morphologies are understood through a gravito-elastocapillary model that predicts the droplet morphology and the onset of shape changes, as well as showing that the influence of the direction of gravity remains crucial even for very small droplets (where the effect of gravity can normally be neglected). The results pave the way to control droplet shape in several engineering and biomedical applications.
Force-Based Wetting Characterization of Stochastic Superhydrophobic Coatings at Nanonewton Sensitivity
(WILEY-V C H VERLAG GMBH, 2021-10-21) Hokkanen, Matti J.; Backholm, Matilda; Vuckovac, Maja; Zhou, Quan; Ras, Robin H.A.; Department of Applied Physics; Department of Electrical Engineering and Automation; Department of Bioproducts and Biosystems; Soft Matter and Wetting; Robotic Instruments
Superhydrophobic coatings have extraordinary properties like self-cleaning and staying dry, and have recently appeared on industrial and consumer markets. The stochastic nature of the coating components and coating processes (e.g., spraying, painting) affects the uniformity of the water repellency across the coated substrate. The wetting properties of those coatings are typically quantified on macroscale using contact angle goniometry (CAG). Here, highly sensitive force-based methods, scanning droplet adhesion microscopy (SDAM), and micropipette force sensor (MFS), are used, to quantify the microscale heterogeneity in the wetting properties of stochastic superhydrophobic coatings with irregular surface topography that cannot be investigated by CAG. By mapping the wetting adhesion forces with SDAM and friction forces with MFS, it is demonstrated that even the best coatings on the market are prone to heterogeneities that induce stick–slip motion of droplets. Thus, owing to their high spatial and force resolution, the advantages of these techniques over CAG are demonstrated.
Free-Decay and Resonant Methods for Investigating the Fundamental Limit of Superhydrophobicity
(2013) Timonen, Jaakko V.I.; Latikka, Mika; Ikkala, Olli; Ras, Robin H.A.; Department of Applied Physics; Molecular Materials
The recently demonstrated extremely water-repellent surfaces with contact angles close to 180° with nearly zero hysteresis approach the fundamental limit of non-wetting. The measurement of the small but non-zero energy dissipation of a droplet moving on such a surface is not feasible with the contemporary methods, although it would be needed for optimized technological applications related to dirt repellency, microfluidics and functional surfaces. Here we show that magnetically controlled freely decaying and resonant oscillations of water droplets doped with superparamagnetic nanoparticles allow quantification of the energy dissipation as a function of normal force. Two dissipative forces are identified at a precision of ~ 10 nN, one related to contact angle hysteresis near the three-phase contact line and the other to viscous dissipation near the droplet–solid interface. The method is adaptable to common optical goniometers and facilitates systematic and quantitative investigations of dynamical superhydrophobicity, defects and inhomogeneities on extremely superhydrophobic surfaces.
Friction and Wetting Transitions of Magnetic Droplets on Micropillared Superhydrophobic Surfaces
(2017-10-11) Al-Azawi, Anas; Latikka, Mika; Jokinen, Ville; Franssila, Sami; Ras, Robin H.A.; Department of Applied Physics; Department of Chemistry and Materials Science; Department of Bioproducts and Biosystems; Soft Matter and Wetting; Microfabrication
Reliable characterization of wetting properties is essential for the development and optimization of superhydrophobic surfaces. Here, the dynamics of superhydrophobicity is studied including droplet friction and wetting transitions by using droplet oscillations on micropillared surfaces. Analyzing droplet oscillations by high-speed camera makes it possible to obtain energy dissipation parameters such as contact angle hysteresis force and viscous damping coefficients, which indicate pinning and viscous losses, respectively. It is shown that the dissipative forces increase with increasing solid fraction and magnetic force. For 10 µm diameter pillars, the solid fraction range within which droplet oscillations are possible is between 0.97% and 2.18%. Beyond the upper limit, the oscillations become heavily damped due to high friction force. Below the lower limit, the droplet is no longer supported by the pillar tops and undergoes a Cassie–Wenzel transition. This transition is found to occur at lower pressure for a moving droplet than for a static droplet. The findings can help to optimize micropillared surfaces for low-friction droplet transport.
Gold Au(I)6 Clusters with Ligand-Derived Atomic Steric Locking: Multifunctional Optoelectrical Properties and Quantum Coherence
(WILEY-VCH VERLAG, 2023-04-18) Chandra, Sourov; Sciortino, Alice; Das, Susobhan; Ahmed, Faisal; Jana, Arijit; Roy, Jayoti; Li, Diao; Liljeström, Ville; Jiang, Hua; Johansson, Leena Sisko; Chen, Xi; Nonappa; Cannas, Marco; Pradeep, Thalappil; Peng, Bo; Ras, Robin H.A.; Sun, Zhipei; Ikkala, Olli; Messina, Fabrizio; Department of Applied Physics; Department of Electronics and Nanoengineering; OtaNano; Department of Bioproducts and Biosystems; Center of Excellence in Life-Inspired Hybrid Materials, LIBER; Molecular Materials; Centre of Excellence in Quantum Technology, QTF; Zhipei Sun Group; Harri Lipsanen Group; NanoMaterials; Bioproduct Chemistry; Computational Electronic Structure Theory; Soft Matter and Wetting; University of Palermo; Indian Institute of Technology Madras; Tampere University
An atomically precise ultrasmall Au(I)6 nanocluster where the six gold atoms are complexed by three sterically interlocking stabilizing ligands is reported, allowing a unique combination of efficient third harmonic generation (THG), intense photoluminescence quantum yield (35%), ultrafast quantum coherence, and electron accepting properties. The reaction of 6-(dibutylamino)-1,3,5-triazine-2,4-dithiol (TRZ) with HAuCl4 leads to complexation by thiolation. However, intriguingly, another reduction step is needed to form the centrosymmetric Au(I)6TRZ3 clusters with the multifunctional properties. Here, ascorbic acid is employed as a mild reducing agent, in contrast to the classic reducing agents, like NaBH4 and NaBH3CN, which often produce mixtures of clusters or gold nanoparticles. Such Au(I)6 nanocluster films produce very strong THG response, never observed for nanoclusters. The clusters also produce brilliant single and multiphoton luminescence with exceptional stability. Density functional theory calculations and femtosecond transient absorption studies suggest ultrafast ligand-to-metal charge transfer, quantum coherence with long decoherence time 200–300 fs, and fast propagation of excitation from the core to the surrounding solvent. Finally, novel electron-accepting ground state properties allow p-doping of 2D field-effect transistor devices. Summarizing, the potential of ultrasmall sterically interlocked Au(I) clusters, i.e., complexes allowed by the new sequential reduction protocol, towards multifunctional devices, fast photoswitches, and quantum colloidal devices is shown.

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