Manual Surface and Interfacial Forces – From Fundamentals to Applications

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University of Detroit John F. Drelich, J. Laskowski, and K. Mittal, eds. Neumann and Jan K. Spelt, eds. Jaycock, G. Farinato and Paul L. Dubin, eds. Brady, ed. Contact Angle, Wettability and Adhesion, Vol. Mobius and R. Miller, eds. Dukhen, G. Kretschmar and R. Experimental Methods in the Physical Sciences, Vol. Rimai, L. DeMejo and K. Demajo, Donald S. Rimai and Louis H. Sharpe, eds. Stokes, D. Weast, William H. Bunshah, ed. Noyes Publications Valeri P. Tolstoy, Irina Chernyshova and Valeri A. Lewis and Howell G. Edwards, eds. Riviere and S.

Myhra, eds. Noyes Publications Profos, Pfeifer Hrsg. Handbuch der industriellen Messtechnik R. Efficiency of the current antiviral drugs is severely restricted by their narrow action spectra, development of drug-resistant viral strains and appearance of toxicity effects. Therefore, there is an urgent need for development of new types of antivirals with superior performance.

Importantly, some fullerene derivatives inhibit simultaneously several viral targets, thus suppressing significantly the formation of drug resistance. Recently we reported a number of efficient and selective methods for chemical synthesis of a broad range of water-soluble fullerene derivatives [Chem. Here we present three new synthetic routes for conversion of readily available C60Cl6 and C70Cl8 precursors to a variety of water-soluble fullerene derivatives bearing 4 to 16 carboxylic groups in their molecular frameworks. Multiple compounds revealed low toxicity in combination with a potent activity against Influenza, HIV, CMV, and HSV, which makes them promising lead compounds for the development of novel antiviral drugs.

Resume : Rapid development in two-dimensional nanomaterials and their biomedical applications have raised fundamental questions about their biointeractions1. However, any control over these interactions rely on the understanding their mode of action. Due to their high polydispersity and poorly defined structures, the mechanism of the biointeractions of two-dimensional nanomaterials is a controversial topic2.

For a comprehensive study of these interactions, and to obtain reproducible results at nanobiointerfaces, the structure of these nanomaterials, in particular their exposed surfaces, should be defined. Recently, we have developed a method for a controlled functionalization of different two-dimensional nanomaterials by which we have synthesized several smart systems with well-defined functionalities, dimensions, and isoelectric points pI 3. We found that cellular uptake pathways and intracellular localization of these 2D nanomaterials strongly depended on their surface charge and functionality4.

By manipulating these factors, we were able to construct new two-dimensional nanomaterials with the ability to overcome multiple drug resistance in cancer cells5. Keywords: Two-dimensional nanomaterials, Graphene, Polyglycerol, Cancer 1. Tu, G. Guday, M. Adeli, R. Advanced Materials, , Reina, J. Criado, E. Bianco, M. Prato, Chem. Faghani, I. Donskyi, M. Fardin Gholami, B. Ziem, A. Lippitz, W. Unger, C. Rabe, R. Haag, M. Adeli, Angew. Chemie Int. Tu, K. Achazi, A. Schulz, R. Thierbach, E. Haag, Adv. Tu, H. Qiao, Y.

Yan, G. Guday, W. Chen, M. Haag, Angew. Resume : Diamond possesses unique surface properties that make it an an excellent candidate electron field emitter. Besides its robustness and quasi chemical inertness, the negative electron affinity when H-terminated plays a key role. Nevertheless, to reach its full potential in exhibiting superior electron field emission, the problem of the low electrical conductivity of bulk diamond, due to its wide band gap, must be overcome.

This can be done in several ways, including renuclation during growth, in-situ doping, and post-deposition ion implantation of several active elements. In addition, the fabrication of 3D structures, be it by adapting the deposition conditions, or by post-growth structuring via etching, enable to further influence the surface properties in a beneficial way, with great impact on the observed electron emission currents.

Several strategies will be discussed and compared. The emission data will be correlated with structural information obtained by advanced transmission electron microscopy techniques. Electron field emission currents, including longterm stability and application in microplasma devices, underpin the observations. Finally, hybrid structures of diamond with other novel materials such as hexagonal boron nitride, graphene, etc, will be considered in relation to their electron emission properties.

Resume : Several techniques have been developed for the detection of carbon nanotubes CNT dispersed under the surface of a nanoscale polymer matrix, but Electrostatic Force Microscopy EFM is a promising tool for obtaining non-invasive subsurface images. However, little is understood about the electrical and spatial parameters in the imaging process. For this reason, in this work is developed a simulation model that allows defining the experimental parameters in the EFM technique such as: vertical resolution for detection, conductive tip voltage, separation between the surface of the polymer matrix and the tip and other parameters related to the dimensions of the polymer matrix based on Polymethylmethacrylate PMMA.

The analysis of this parameters allows the correlation with the capabilities of the EFM technique for detecting the depth of the CNTs and to identify the best conditions for both the polymer matrix and EFM before conducting laboratory experiments. Resume : The properties of graphite, and of few-layer graphene, can be strongly influenced by the edge structure of the graphene planes, but there is still much that we do not understand about the geometry and stability of these edges.

We use computer simulations based on density functional theory to obtain surface energies, and rationalise and quantify the preference for the formation of multiple concentric loops at the edges. We also discuss possible mechanisms for the observed separation of the folded edges in the presence of an electric field. This effect can be used to engineer new carbon-based nanostructures with high porosity. Resume : The recent interest in 2D materials and their applications in a large variety of fields is somehow limited by their vulnerability caused by interaction with the environment.

This feature can be exploited to obtain electronic population changes doping , but can represent a weakness due to reduced charge mobility. Recent studies have highlighted that the origin of doping is the interaction of graphene with the substrate and the interstitial molecules. In particular, it has been revealed that both the activation energy of the doping process and its time dynamics are affected by different substrates, with a significant influence of their hydrophilic properties.

The impact on O2-driven graphene thermal doping was experimentally estimated by Raman spectra and Atomic Force Microscopy. To further corroborate our results, we performed first principle calculations using Density Functional Theory. Herein, by functionalizing the silica surface with apolar groups, we have evaluated the adsorption efficiency of O2 on graphene and how the electronic properties of SiO2 surface affect the charge distribution of the system. Resume : To control the magnetic-related phenomena of a medium with the help of applied voltage is a rapidly developing research field in modern magnetism.

Voltage V control of magnetism, magneto-resistance, magnetic anisotropy, and magnetization in a ferromagnetic layer exchange-coupled to a nonmagnetic layer has recently been reported. However, to explore the origin of observed phenomena by directly studying the spin polarized density of states DOSs of these heterostructures is rare and necessary. Carbon C has also been considered as a potential material for future electronics application. One broad MCD signal feature A in low energy region was obtained, while the other feature B shows a peak in the high energy region while applied a magnetic field.

Interestingly, the OMCD hysteresis loops reveal different behaviors. These results would open new a perspective for C based spintronics application. The authors would like to thank the Ministry of Science and Technology of the Republic of China, Taiwan, for financially supporting this research under Contract No. MOST M Resume : Graphene and other two dimensional 2D materials have unique phenomena because of their ideal atomically-flat surface and their localized density of states at their edges.

Indeed, their features reflect to electrochemical activities such as hydrogen evolution reaction, oxygen reduction reaction. On the other hand, it was argued that the basal plane on 2D materials did not show particularly high reactions in spite of their large surface area.

Recently, it was confirmed by visualization of the electrochemical active sites on graphene by electrochemical microscopy, resulting that their edge sites behave more active than that at the edges A. Kumatani et al. It is therefore necessary to initiate their activities on the basal plane for high performance electrochemical applications.

Takahasi, A. After the process, hydrogen evolution active sites are initiated by scanning the nanopipette. Further, their active sites were recognized by electrocatalytic reaction imaging. It will lead 2D material surface design for energy harvesting application. Sodium-ion batteries SIBs are reviving and flourishing during last decade, with great potential to be practically applied in large-scale energy storage market.

However, the construction of a stable electrochemical interface between anode material and electrolyte is still the bottleneck restraining the development of SIBs, especially on most promising carbon anodes. The regulation and modification of the interfacial electrochemistry is critical to increase the energy density, columbic efficiency and long-term stability of carbon anodes for their practical application in SIBs.

Recently, we found that ether-based electrolytes are unique to modifying electrochemical interface of carbon anodes and largely improve the initial coulombic efficiency ICE of high specific surface area carbons HSSACs. Then, we proposed a simple but effective remedy of deactivating and shielding defects on carbon anodes by Al2O3 nanoclusters. As a result, not only the coulombic efficiency but also the stability and rate capability of HSSACs can be further enhanced. More importantly, we investigated that the energy barrier to charge transfer at the electrochemical interface is a reliable parameter to assess the intricate sodiation dynamics in various anode materials of SIBs including carbon materials, which could definitely guide the design of well-matched novel aprotic electrolytes for carbon anodes and accelerate the commercialization of carbon anodes in metal-ions rechargeable batteries.

References: [1] J. Zhang, S. Zhang, W. Lv, Q. Yang et. Resume : Field-effect transistors based on graphene GFET find application in many fields, especially in biosensing, due to their high sensitivity [1]. The density of charge carriers in the GFET channel can be modulated easily by applying an appropriate potential to the gate [2]. Inkjet-printing technique permits the fabrication of these devices outside of the clean room, reducing the time and the costs of the fabrication process.

In this work, an inkjet-printable graphene oxide GO ink is formulated and deposited by inkjet-printing on the channel of photolithographed transistors. Among different ways to reduce the printed GO into reduced graphene oxide rGO , we developed an in-situ electrochemical approach [3]. The morphology of the printed rGO layer and its electrical characteristics when used as conductive channel in the electrolyte-gated transistor configuration, were investigated.

A strongly marked Dirac point is observed on our transfer curves, as well as an ambipolar behavior, as previously described [2]. We show that the reduction degree of GO is an important parameter, as it affects the charge transport behavior allowing the electrochemical control of the charge carriers mobility and of the doping level [4]. Further, we show that the doping level can be additionally tuned by supramolecular assemblies of N-rich organic adsorbates on rGO. Small, 10 [2] Meric, I.

Nature, 3 [3] Mativetsky, J. Carbon, submitted. Resume : Conductive boron-doped diamond BDD is expected as a functional electrode material that can be used in various electrochemical applications because of its unique electrochemical properties such as wide potential window and low background current. The BDDP printed electrodes showed lower background current and larger signal-to-background ratio in the electrochemical detection of some analytes than conventional carbon-printed electrodes as well as BDD thin film electrodes.

Thus, the BDDP-printed electrode is expected to be used as an inexpensive, disposable and sensitive electrochemical platform. CV in 1. In addition, when using boron-doped nanodiamond BDND with large specific surface area, the energy and power density in the aqueous electrolyte was greater than when using activated carbon. Therefore, it was suggested that the conductive diamond particles are useful as an electrode material for aqueous EDLCs exhibiting both high energy and power density. Resume : The low-dimensional modifications of carbon like nanodiamonds, graphene, fullerenes and nanotubes present a particular interest for the developing fields of nano- and optoelectronics.

The studies of one-dimensional chained materials remain undervalued due to the limitations of the synthesis techniques, especially those for free-standing carbyne. Raman measurements are performed to control the changes in bonding and atomic structure of the chained films. Photoemission results reveal a thermodynamic and photoelectric threshold values around 4. Electron emission intensity depends on film thickness, while average work function difference reflects the changes in carbyne-containing film morphology.

In view of the lack of rapid and comprehensive technique for characterization of linear-chained carbon and carbyne-containing nanocomposites the search for new methods is of great importance. Electron emission in atmospheric conditions APS proves to be a capable tool for assessment of carbon coating thickness, while emission in vacuum reveals its morphology. In combination with Raman spectroscopy these techniques could be used for characterization of composite coatings containing carbon chains.

Even at a low absorbent content of only 0. The mechanism for the enhancement of polarization relaxation loss and conductive loss was explicitly investigated. The formation of the thin graphitic layer is depending both on time 2 , temperature and gas environment. The location of the metallic nanoparticles was investigated by XPS while the formation of graphitic domains was investigated by Raman spectroscopy.

The choice of the transition metals has been operated as a function of their high reactivity to carbon-carbon bond reactivity but also to their ability to absorb carbon. We observed an optimum in the fluence as well as the thickness of the DLC layer.

Surface and Interfacial Forces - From Fundamentals to Applications | Günter Auernhammer | Springer

Stock, F. Antoni, F. Le Normand, D. Muller, A. Abdesselam, N. Boubiche and I. Boubiche, J. El Hamouchi, J. Hulik, M. Abdesslam, C. Speisser, F. Djeffal and F. Le Normand, Diamond and Related Materials, 91 Resume : Carbon can form crystalline graphite under a certain high temperature environment. The graphitization degree can be increased by increasing the temperature, changing the temperature rise rate, or extending the retention time of the graphitization reaction section of carbon, and different electric conduction and electromagnetic wave attenuation capacities can be formed.

The continuous laser ablative carbonization experiment of epoxy resin-based quartz fiber reinforced composite materials is carried out under the same incident laser energy. The experimental results show that the dielectric constant increases significantly in the range of 7GHz to 17GHz compared with the initial state. The Fourier transform infrared spectrum FTIR , XRD test results and surface scanning electron microscopy images of the ablative products on the surface of the sample show that the thermal decomposition, pyrolysis and other changes of the epoxy resin occur under laser irradiation, and the graphitized carbon of island chain formed in situ on the surface of the material is the cause of dielectric constant increase.

At the same time, the rough surface state and loose state caused by laser ablation increase the reflection of electromagnetic wave. Resume : High-performance carbon nanotubes CNTs with adjustable electro-conductivity have been widely used as electromagnetic EM waves absorption materials to achieve stealth of weapons and equipment. Curls of CNTs formed a three-dimensional network structure and large amounts of interfaces, resulting in multiple reflections and scattering of EM waves. The defect concentrations can be optimized by tuning reaction times.

The existing defects will produce dipole polarization and affect the band gap of CNTs as well. Using density functional theory as first principle calculations, we calculate and simulate the relationship between band gap and vacancy-defects of CNTs. The exploration results provide a useful reference to EM wave absorption materials with strong absorption, wide bandwidth and thin thickness.

Resume : Degradation efficiency of the catalysts is of primary concern for photoelectrochemical PEC processes. Namely, the catalysts featuring excellent charge separation and transfer, as well as high photoelectrochemical performance are needed. A photolithography method was utilized for the construction of such patterns.

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Resume : Carbon nanotubes and graphene can show excellent light absorbing ability on near-infrared laser irradiation. Using the photothermal properties of the graphene, photo-responsive actuators can be fabricated with the shape memory polymers. To achieve high performance photo-actuators, enhanced interaction between polymer and graphene is needed. In this study, epoxy-functionalized graphene oxide epoxy-GO was synthesized and used to fabricate photo-actuators of epoxy-functionalized GO, epoxy and hyperbranched polyurethane HBPU.

The covalently bonded functionalization of GO with epoxy group was confirmed and the surface morphology of the composites was observed with TEM measuremetns. Photo-responsive shape recovery actuation of composites was evaluated by irradiating the near infrared laser on the composites. The composites showed good photo-actuation stress and enhanced mechanical properties. The results indicate that the epoxy-f-GO is very effective to fabricate the laser-driven remote-controllable photo-actuator. Resume : Pressure-retarded membrane distillation PRMD is an emerging membrane process to recover energy from low-grade heat sources.

The applied hydraulic pressure on the cold-water side in PRMD may strongly affect both energy conversion efficiency and membrane performance. Here, we report the first systematic study on this critical issue. Our results show that the theoretically projected constant water vapor flux decreases significantly with the increase of the applied pressures, which can be attributed to the severe membrane deformation induced by pressures.

The membrane in the active-layer-facing-hot-solution orientation is mechanically unstable with the complete loss of water vapor flux under 2 bar. In contrast, the membrane in the active-layer-facing-cold-solution orientation can still work under 10 bar. Combining theoretical analysis and detailed characterization of membrane physical structures, we show that the properties of membrane active layers i. Deformed membranes have lower permeability and higher temperature polarization in PRMD, resulting in the observed lower water vapor fluxes.

Our results suggest that improving the mechanical stability of membranes would be the first critical step in realizing practical applications of PRMD for low-grade heat recovery. Potential research directions for developing novel PRMD membranes are also proposed. Resume : Nanodiamonds have a variety of, mainly oxygen-containing, functional groups on the surface and that makes it complicated to control surface chemistry.

Many efforts were made so far to uniform, or reset, surface chemistry such as hydrogenation, carboxylation, hydroxylation, graphitization, and so on. As each modification method gives different surface charge and other properties, different condition should be applied to give dispersion of each modified nanodiamonds.

We prepared single-digit nanosized water dispersion of vacuum-annealed, graphitized detonation nanodiamonds using bead-milling. We will report and discuss some adsorption properties of the dispersion as well as dispersion condition. On the other hand, recently, we found out that the significant reduction of gas permeance during a long-term stability test of CMS membrane, attributing to physical packing of imperfect graphene-like layers at the early stage after carbonization. The loss of gas permeance was accelerated at higher operating pressure. Herein, in order to prevent the physical aging in CMS membrane, the pre-crosslinking reaction of polyimide precursor prior to pyrolysis was employed.

Surprisingly, the pre-crosslinking was effectively affected on the mitigation of aging in CMS membrane. Resume : Intense pulsed light IPL using a Xenon flash lamp with a broad wavelength spectrum is a technology used mainly in sintering of metal particle-based electrodes for printed electronics. One of the key points in the IPL sintering process is to maximize the light absorption of printed metal-based electrodes, because photo sintering efficiency is considerably related to the surface plasmon polariton which is resulted from coupling of surface plasmons with light.

In this regard, oxide-free, small sized metal particles are a prerequisite, but the production cost should be increased. Resume : Resume : We have prepared various all-organic magnetic soft materials containing a cyclic nitroxide radical moiety as a spin source [1].

Surface and Interfaces of Nanocarbons

In this talk, we report the preparation of all-organic magnetic nanoemulsions composed of the non-ionic surfactant and the hydrophobic nitroxide radical compound [2]. The nanoemulsions showed high colloidal stability, high reduction resistance to ascorbic acid, low cytotoxicity and an enough contrast enhancement in the proton longitudinal relaxation time T1 -weighted MR images in - -PBS in vitro and in vivo. We expect that the drug-loaded nanoemulsions can be used as a biocompatible magnetic drug carrier for MRI-visible targeted delivery system. Soft Matter , 11, [2] K.

Nagura, N. Komatsu, R. Tamura, et al. Resume : Since thin layer 2D materials have been attracting enormous interest, various processes have been investigated so far to obtain these materials efficiently. In view of their practical applications, the most desirable source is the pristine bulk material with stacked layers such as pristine graphite. On their exfoliation, we have many options in terms of conditions such as wet or dry, with or without additive, and kind of solvent. In this context, we have found versatile exfoliant, 2,3,6,7,10,hexahydroxytriphenylane, which works efficiently for exfoliation of typical 2D materials, graphene, MoS2, and h-BN, in both wet and dry processes using sonication and ball-milling, respectively, in aqueous and organic solvents [1,2].

As for graphene, stable dispersions with relatively high concentration up to 0. In addition, the exfoliant can be easily removed from the precipitated composite by heat treatment without disturbing the graphene structure. Bulk MoS2 and h-BN were also exfoliated in both wet and dry processes. Liu, N. Resume : In this paper, we report simple, scalable and high-yield production of MoS2 and WS2 nanosheets through solid phase exfoliation using ball milling in the presence of sodium cholate SC [1].

The exfoliated MoS2 and WS2 nanosheets are stored as? While solid phase exfoliation using ball milling has been applied to the production of graphene nanosheets, this methodology has not been demonstrated in the exfoliation of TMDs such as MoS2 and WS2. Although we have reported scalable method using hexahydroxytriphenylene as an exfoliant through ball milling, bath sonication for half an hour has been required to obtain stable dispersion [2]. As compared with wet-grinding and liquid phase ball milling, the dry process reported here is considered to be more preferable to keep the solid as it is for longer time, because the presence of liquid may facilitate aggregation as mentioned above.

In addition, simple dispersion with controlled concentration can be prepared from the dry ball milled solid, while the liquid used for exfoliation under wet conditions may make solvent system complicate, and concentration less precise and less controllable. First, the effect of surfactant amount in the ball milling process was studied; the amount of MoS2 was fixed at 0. The powder obtained after ball milling was dispersed in deionized water mL and the resulting dark-greenish suspension was centrifuged at rpm g for 60 min.

The yield of MoS2 saturated around 0. Resume : Nanodiamonds NDs have excellent mechanical and optical properties, large surface areas and tunable surface structures. They were found to be relatively less toxic among nanoparticles, making them well suited to biomedical applications [1]. In order to enhance the intrinsic properties and append new properties, hybridization of NDs with other nanoparticles seems promising technique.

However, most of the related work towards such fundamental hybridization is limited to top-down lithography which is typically a very complicated and time-consuming process, and is difficult to be scaled up. Here, we develop a facile bottom-up synthetic approach to prepare ND-superparamagnetic iron oxide nanoparticle SPION nanohybrid using solvothermal method and investigate its magnetic resonance imaging MRI contrast ability and heat generation property in alternating magnetic field. Then, appropriate amount of ND-PG 5. We believe that our button-up synthetic strategy can be applied to hybridize various kind of nanoperticles on the ND surface.

Photonics 5, Komatsu, et al. Resume : Diamond color centers are chemically stable fluorescent defect. Silicon vacancy SiV center is one of those color centers, which indicates the sharp photo luminescence PL spectrum at near-infrared region nm. This feature will make it possible to externally excite and detect fluorescence of defect-containing diamond delivered inside living tissues.

SiV center can be fabricated by silicon ion implantation into high-purity IIa type diamond. Also, there have been reports that SiV center was introduced in diamond thin film by chemical vapor deposition CVD on Si substrate. Concentration of SiV center by those methods, however, was not enough for bio-imaging application. We explored and found the method to introduce SiV center in high concentrations.

Second, high energy beam such as helium ion was irradiated just to introduce vacancies at appropriate concentration. Then annealing was performed to form SiV center. Diamond nanoparticles containing SiV center should be obtained by disintegration of the polycrystalline diamond thin film using conventional procedure such as bead-milling. Resume : For several decades, industrial processes consume a huge amount of raw water for various objects that consequently results in the generation of large amounts of wastewater. There effluents are mainly treated by conventional technologies such are aerobic, anaerobic treatment and chemical coagulation.

But, there processes are not suitable for eliminating all hazardous chemical compounds form wastewater and generate a large amount of toxic sludge. Therefore, other processes have been studied and applied together with these techniques to enhance purification results. These techniques include photocatalysis, absorption, advanced oxidation processes, and ozonation, but also have their own drawbacks. In recent years, electrochemical techniques have received attention as wastewater treatment process that show higher purification results and low toxic sludge. There are many kinds of electrode materials for electrochemical process, among them, boron doped diamond BDD attracts attention due to good chemical and electrochemical stability, long lifetime and wide potential window that necessary properties for anode electrode.

But, Si substrate is hard to apply electrode application due to the brittleness and low life time.

Contact angle hysteresis: a review of fundamentals and applications

And other substrates are also not suitable for wastewater treatment electrode due to high cost. To solve these problems, Ti has been candidate as substrate in consideration of cost and properties. But there are critical issues about adhesion that must be overcome to apply Ti as substrate. TiN has higher electrical and thermal conductivity, melting point, and similar crystalline structure with diamond. There are no significant differences in surface grain size despite of various interlayer.

In wastewater treatment results, the BDD electrode with TiN 50nm showed the highest electrolysis speed at livestock wastewater treatment experiments. It is thought to be that TiN with thickness of 50 nm successfully suppressed formation of TiC that harmful to adhesion. Resume : Carbon spiroids [1] are the relatively new and one of the least studied carbon allotropes.

They are good candidates for the nanocpacitors[2], hydrogen storage [3] and in catalysis due to the unique open structure. Electron beam-induced structural transformations of carbon nanostructures were an interesting topic for the few last decades [3,4]. We've chosen carbon spiroids C [3] and C [4] as the model objects and applied the the framework of ab-initio approach implied in the Gaussian program package[5]. Ozawa, H. Goto, M. Kusunoki, E. Osawa, J. Zeiger, N. Jackel, V. Mochalin 1.

Presser, J. A, , 4, — Yastrebov, M. Chekulaev, A. Siklitskaya, J. Ajayan, Naturevolume , pages — 4. Lin Lai and Amanda S. Barnard, J. Yastrebov, R. Smith, A. Siklitskaya, Mont. Frisch, G.

Trucks, H. Schlegel, G. Robb et. Among the most investigated materials, metal oxides like zinc oxide ZnO and carbon-based materials have been playing an important role in the field due to their versatility and unique properties, namely their biochemical stability, biocompatibility and functionalisation simplicity. As such, the synergetic combination of these materials should result in advanced functional properties, which can be tailored to the desired application.

Hence, a fundamental understanding of the contact forces between single nanoparticles is necessary to achieve high-efficiently processes and high-quality products. In general, contact forces are the summation of van der Waals, capillary, electrostatic, and double layer forces. Furthermore, it is questionable if state-of-the-art continuum theories sufficiently describe molecular interactions which become increasingly important at the nanoscale.

Besides air humidity, the capillary force depends strongly on the macroscopic water contact angle of the material. The molecules take discrete positions in the gap, leading to discrete energetically favorable gap distances. We analyze all experimentally determined contact forces in this work with regard to these three force models.

Measuring contact forces between nanosized objects is challenging. Typically, the atomic force microscope AFM is used. Friedlander studied the mechanical behavior of nanoparticle agglomerates under strain with an AFM. We showed that penetrating highly porous nanoparticle agglomerates with an AFM-tip is a reliable technique to measure contact forces directly between two individual nanoparticles.

Parts of the agglomerate adhere to the AFM-tip. During retraction this parts unfold and finally detach at a particle—particle contact. Analyzing this particle—particle breakage, our study suggested that contact forces between nanoparticles can be described by combination of capillary and solvation forces revealing the necessity to consider noncontinuum effects.

So far, no accurate characterization of the contact forces between two individual nanoparticles is available in the literature. This paper elucidates the major interparticle forces between metal oxide nanoparticles in the gas-phase based on force spectroscopy. We show that these forces can be explained by a combination of capillary and solvation forces. To highlight the importance of surface properties and to show the general validity of our force concept, we analyze systematically two different metal oxides.

We then propose a mathematical description which calculates the contact forces in agreement with our experimental results. Both materials were purchased in two surface variations, hydrophilic and hydrophobic. The hydrophobic surfaces were achieved by hydrophobization of the hydrophilic nanoparticles.

Further, the infrared spectra of the nanopowders were obtained by Diffuse Reflectance Infrared Fourier Transform spectroscopy DRIFT measurements using a IF spectrometer Bruker equipped with a praying mantis accessory and a temperature reaction chamber Harrick. Also, TGA analysis was performed on all four powders.

Nanopowders were cautiously heaped up onto a double-sided tape on a microscope slide. Then the microscope slide was knocked off to remove loosely bounded agglomerates. The spring constant of the cantilever were 0. The applied force was between 2. The measured contact force between two single nanoparticles was determined by a statistical analyses of the last peak in the corresponding force curves, as described in detail in ref Since surface properties strongly influence the strength of acting contact forces we investigate two different metal oxides of general interest, TiO 2 and Al 2 O 3.

The Brunauer—Emmett—Teller BET diameter is given from the supplier and based on nitrogen adsorption—desorption measurements. E TEM-based primary particle size distributions reveal no significant size differences based on the hydrophobization process. Compared to the BET values see Table 1 , the obtained values are about 3—4 nm smaller. However, this discrepancy is based on the single measurement techniques as already reported in The TEM analysis reveals no change in primary particle size due to surface treatment.

For all considered contact force models the structure of the surface is very important. The amount of OH-surface groups determines the physisorption of water molecules. TGA analysis shows an OH surface density of 6. The amount of physisorbed water is decreased for the hydrophobic counterparts. A distinction between the OH groups and the organics was not possible. However, it is obvious that even in pure N 2 atmosphere, all four powders carry a noticeable amount of water which only disappears by increasing the temperature.

To analyze the contact forces between two individual nanoparticles, AFM force spectroscopy was performed on all four powders ambient conditions by penetrating highly porous agglomerates with the AFM tip and extract single chains of nanoparticles, as described in the methods. During approach the AFM-tip pierces into the agglomerate while nanoparticles are pushed away and rearrange as shown by the peaks in the approach curve.

Surfaces and interfaces

While the first peaks contain information on multiple nanoparticles in contact, we recently showed that the last peak can be related to the breakage of the bond between two individual nanoparticles for clarification, see also Figure S4 in the Supporting Information. Force curves of hydrophilic titania A and hydrophobic alumina B nanoparticle agglomerates. The agglomerates first unfold and finally break at two individual nanoparticles in contact.

The last peak F c refers therefore to the contact force between two individual nanoparticles. A statistical analysis of the last peak F c can give fundamental inside into the acting contact forces between two individual nanoparticles. A Force distributions of the contact force between hydrophilic and hydrophobic titania nanoparticles obtained from the last peak of the measured force curves.

B Force distribution of the contact force between hydrophilic and hydrophobic alumina nanoparticles.

Contact Forces between Single Metal Oxide Nanoparticles in Gas-Phase Applications and Processes

The hydrophobic nanoparticles show much lower contact forces than their hydrophilic counterparts. This trend is less prominent for alumina based on the larger amount of OH-surface groups and physisorbed water. In the case of TiO 2 , the distributions show a log-normal behavior which is in good agreement with previous measurements. For Al 2 O 3 the maximum of the hydrophobic nanoparticles is at 1. The TiO 2 force distributions show a significant difference while the distributions overlap to a certain extent in the case of Al 2 O 3. The surface characterization revealed that all particles carry a certain amount of physisorbed water.

This amount of water corresponds to a layer of 1—2 nm high; so about 1 order of magnitude smaller than the particle diameter 2—40 nm. This network is much weaker for hydrophobic particles leading to decreased contact forces. The interaction via this water molecule network further explains the generally strong measured forces for Al 2 O 3. Recent studies show that the structuring of water molecules and oscillating forces have to be considered for a correct description of water menisci on the scale of a few nanometer. When the applied force exceeds the spring constant of the cantilever the tip jumps away from the sample.

Using a stiffer tip would avoid this problem but decrease the sensitivity of the measurement. Capillary, as well as solvation forces, strongly depend on the physisorbed water. This leads to a stronger capillary as well as a more structured ensemble of water molecules in the gap between the particles, while for hydrophobic particles both effects are less pronounced.

However, describing the molecular interactions by the solvation force model directly excludes the macroscopic van der Waals model, which is typically used to describe the contact forces between particles.