Ultrahigh-vacuum techniques in the measurement of contact angles. II. Water on gold

Schräder, Malcolm E.

doi:10.1021/j100705a013

Cited by 61 publications

(37 citation statements)

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“…This result is in line with other studies that have shown graphite surfaces to be mildly hydrophilic with a contact angle of about 50ᵒ, 35,36,37 Although higher aqueous contact angle values have been reported in the literature, 38,39,40 variations are expected depending on the sample quality, measurement environment (including surface contamination which increases the contact angle) and droplet size. 35,36,41 Given the short timescale (<5 s) on which the droplet was deposited after cleavage of surface, 9 the value we report can be taken as the intrinsic CA of 1 mM NaClO4 at AM HOPG, and is in line with theoretical predictions.…”

Section: Voltage Effect On Electrowettingsupporting

confidence: 91%

Low-Voltage Voltammetric Electrowetting of Graphite Surfaces by Ion Intercalation/Deintercalation

2016

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We demonstrate low-voltage electrowetting at the surface of freshly cleaved highly oriented pyrolytic graphite (HOPG). Using cyclic voltammetry (CV), electrowetting of a droplet of sodium perchlorate solution is observed at moderately positive potentials on high-quality (low step edge coverage) HOPG, leading to significant changes in contact angle and relative contact diameter that is comparable to the widely studied electrowetting on dielectric (EWOD) system, but over a much lower voltage range. The electrowetting behavior is found to be reasonably fast, reversible and repeatable for at least 20 cyclic scans (maximum tested). In contrast to classical electrowetting, e.g. EWOD, the electrowetting of the droplet on HOPG occurs with the intercalation/de-intercalation of anions between the graphene layers of graphite, driven by the applied potential, observed in the CV response, and detected by X-ray photoelectron spectroscopy. The electrowetting behavior is strongly influenced by those factors that affect the extent of the intercalation/de-intercalation of ions on graphite, such as scan rate, potential polarity, quality of the HOPG substrate (step edge and step height), and type of anion in the solution. In addition to perchlorate, sulfate salts also promote electrowetting, but some other salts do not. Our findings suggest a new mechanism for electrowetting based on ion intercalation and the results are of importance to fundamental 2 electrochemistry, as well as diversifying the means by which electrowetting can be controlled and applied.3

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Section: Voltage Effect On Electrowettingsupporting

confidence: 91%

Low-Voltage Voltammetric Electrowetting of Graphite Surfaces by Ion Intercalation/Deintercalation

2016

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“…Experimentally, the results reported for the wetting of water on gold are quite scattered, with, in general, a large contact angle hysteresis. Results obtained under UHV conditions (18,19) report a low contact angle (Ͻ30°or close to a wetting situation). On the other hand, the force fields that exist in the literature, and have been based on density functional theory DFT calculations (12,20), yield higher contact angles.…”

Section: Gold Nanoparticles In Watermentioning

confidence: 90%

Heat transfer from nanoparticles: A corresponding state analysis

Mérabia

Shenogin

Joly

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

199

168

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In this contribution, we study situations in which nanoparticles in a fluid are strongly heated, generating high heat fluxes. This situation is relevant to experiments in which a fluid is locally heated by using selective absorption of radiation by solid particles. We first study this situation for different types of molecular interactions, using models for gold particles suspended in octane and in water. As already reported in experiments, very high heat fluxes and temperature elevations (leading eventually to particle destruction) can be observed in such situations. We show that a very simple modeling based on Lennard-Jones (LJ) interactions captures the essential features of such experiments and that the results for various liquids can be mapped onto the LJ case, provided a physically justified (corresponding state) choice of parameters is made. Physically, the possibility of sustaining very high heat fluxes is related to the strong curvature of the interface that inhibits the formation of an insulating vapor film.interfaces ͉ liquids ͉ Kapitsa resistance S ubmicron-scale heat transfer is attracting a growing interest, motivated by both fundamental and technological points of view. In fluids, considerable attention has been devoted to the so-called nanofluids (1, 2), in which nanoparticles in dilute suspension appear to modify both bulk heat transfer and critical heat fluxes. Although the former effect can presumably be understood in terms of particle aggregation (3, 4), the latter is still poorly understood.More generally, heat transfer from nanoparticles or nanostructures to a fluid environment is a subject of active research, stimulated by the development of experimental techniques such as time-resolved optical absorption or reflectivity or photothermal correlation spectroscopy (5). Applications include, e.g., the enhancement of cooling from structured surfaces, local heating of fluids by selective absorption from nanoparticles, with possible biomedical hyperthermia uses (6, 7). Recent experiments demonstrated the possibility of reaching very high local temperatures by using laser heating of nanoparticles (8-10), even reaching the melting point of gold particles suspended in water. From a conceptual point of view, such experiments raise many interesting questions compared with usual, macroscopic heattransfer experiments. How are the phase diagram and heattransfer equations modified at small scales? How relevant is the presence of interfacial resistances, and how do they change with temperature?The case of nanofluids (11) is a good illustration of the role that can be played by molecular simulation in the interpretation of such complex situations. Although many interpretations have been proposed to explain the reported experimental results, it is only simulation of simple models that has been able to disprove some of these interpretations and to demonstrate the validity of the alternative, aggregation scenario. Interestingly, the use of complex models with accurate interaction force fields is not, in genera...

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“…On the other hand, by keeping the samples in the evaporation chamber, we also noticed a drop of the surface energy from 46.25 to 30.01 mJ/m 2 while increasing the storage time from 5 to 24 h. It is believed that the fresh BST surface with high energy would adsorb organic materials or other low surface energy contaminants in the ambient air or evaporation chamber and result in a decrease of the surface energy. [ 17 ] From the X-ray photoelectron spectroscopy (XPS) results shown in the Figure S1 in the Supporting Information, a signifi cant rise of the peak around 286 eV (C1s) in the sample stored in the chamber for 5 h. It suggests the decreases of the BST surface energy is related to the adentitious carbon from the environment. The reduction of the BST surface energy after stored in the chamber can be recovered by performing 10 min UV-Ozone treatment again ( Figure S3 in the Supporting Information).…”

mentioning

confidence: 99%

Low Cost Universal High‐k Dielectric for Solution Processing and Thermal Evaporation Organic Transistors

Wang

Ren

Fan

et al. 2014

Adv Materials Inter

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SAM is needed to reduce the leakage current through the gate and dielectric. Some of the SAMs would require relatively long preparation time [12][13][14] and usually the functional head groups of SAMs is dielectric specifi c. It is challenging to develop a universal SAMs suitable for different dielectric insulators. More importantly, the SAM also modifi es the surface energy of the dielectric and affects the crystallinity of the organic semiconductors. It is necessary to employ a suitable SAM to achieve high crystallility and carrier mobility in the OFETs. [ 14 ] To date, it is still a great challenge in the research fi eld to develop a universal high-k material which does not require SAM, and can be processed at moderate temperature, ambient air environment, and adjustable surface energy for both thermal evaporation and solution processing of organic semiconductors.To address these challenges, we recently reported a high-k (ε r = 11) barium strontium titanate (BST) thin fi lm treated by UV-Ozone and deposited by multi-layer spin coating deposition. [ 15 ] The high-k fi lms are spin coated in ambient air and heated to a temperature of around 85 °C during the UV-Ozone process. The UV emits at 184.9 nm and 253.7 nm under ambient air conditions converting oxygen into reactive O species, which then diffuse into the amorphous BST thin fi lm and reacts with the oxygen vacancies to form lattice oxygen. The reactive oxygen also removes the organic impurities in the fi lm, which results in a high quality amorphous BST thin fi lm with better stoichiometry. [ 16 ] The compatibility with ambient air environment, low processing temperature, and no SAM requirement suggest the BST dielectric has extremely high potentials to be applied in developing low cost OFETs on plastic fl exible substrates and have advantages over other polymers and inorganic materials. In the current study, we investigate the surface energy modifi cation effect by varying the storage environment and time of the BST thin fi lm in order to achieve a universal high-k material for OFET fabrications without using SAM. Based on the contact angle measurements, we calculated the surface energy and the wetting envelope of the BST high-k dielectric stored under different fi ve different conditions. The fresh BST with hydrophilic surface is suitable for spin coating or drop casting of organic semiconductor deposition where surface wetting is needed for the alignment of organic molecules. On the other hand, the BST thin fi lms stored under different conditions show different surface energy, which will directly affect the crystallinity of the organic semiconductors. On the current BST high-k dielectric without SAM and further optimization, dinaphtho[2,3-b:2′,3′-f ] thieno[3,2-b] thiophene (DNTT) and 6,13-Bis (triisopropylsilylethynyl) pentacene (TIPS-pentacene) organic transistors with average mobility of 1.51 cm 2 V −1 s −1 and 0.11 cm 2 V −1 s −1 are formed by thermal evaporation and droplet-pinned crystallization (DPC) method (one of the solution processing methods...

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Ultrahigh-vacuum techniques in the measurement of contact angles. II. Water on gold

Cited by 61 publications

References 0 publications

Low-Voltage Voltammetric Electrowetting of Graphite Surfaces by Ion Intercalation/Deintercalation

Low-Voltage Voltammetric Electrowetting of Graphite Surfaces by Ion Intercalation/Deintercalation

Heat transfer from nanoparticles: A corresponding state analysis

Low Cost Universal High‐k Dielectric for Solution Processing and Thermal Evaporation Organic Transistors

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