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Micro/Nanotribology and Micro/Nanomechanics of MEMS Devices
Published in Bharat Bhushan, Handbook of Micro/Nano Tribology, 2020
For lubrication of microdevices, a more effective approach involves the deposition of organized, dense molecular layers of long-chain molecules on the surface contact (Bhushan et al., 1995b). Such monolayers and thin films are commonly produced by Langmuir—Blodgett (LB) deposition and by chemical grafting of molecules into self-assembled monolayers (SAMs). Based on measurements, SAMs of octodecyl (C18) compounds based on aminosilanes on oxidized silicon exhibited a lower coefficient of friction (0.018) and greater durability (Figure 16.25) than LB films of zinc arachidate adsorbed on a gold surface coated with octadecylthiol (ODT) (coefficient of friction 0.03) (Bhushan et al., 1995b). LB films are bonded to the substrate by weak van der Waals attraction, whereas SAMs are chemically bound via covalent bonds. Because of the choice of the chain length and terminal linking groups that SAMs offer, they hold great promise for boundary lubrication of microdevices.
Measurement Techniques for Refractive Index and Second-Order Optical Nonlinearities
Published in Hari Singh Nalwa, Seizo Miyata, Nonlinear Optics of Organic Molecules and Polymers, 2020
Toshiyuki Watanabe, Hari Singh Nalwa, Seizo Miyata
The fatty acids such as hexadecanoic acid [CH3-(CH2)14-COOH], stearic acid [CH3-(CH2)i6- COOH], arachidic acid [CH3-(CH2)I8-COOH], ?-tricosenoic acid [CH2=CH(CH2)20-COOH], docosanoic (behenic) acid [CH3-(CH2)20-COOH] which contain long alkyl chains and a highly polar COOH end group, are the most suitable amphiphiles for developing LB films. The long alkyl chain is a hydrophobic part whereas the COOH group is a hydrophilic part and such a structural amphiphilicity is a prerequisite for a LB molecule. The amphiphilic molecules cannot dissolve in water because of the hydrophobic aliphatic chain, and they can not leave the water surface because of the hydrophilic COOH part. The deposition process by the LB technique is not straightforward and requires some preparation before experiments were conducted. The fabrication of the monolayer is affected by concentration of solvent, temperature, surface pressure, barrier speed, subphase, and its pH. Generally, the subphase is water, but mercury, glycerol, and other liquid subphases can be used. The monolayer deposited on a subphase is transferred to a clean, solid substrate such as glass slides, quartz plate, metal-coated slides, or mica. Organic solvents such as chloroform, acetone, hexane, benzene, toluene, and xylene are used for spreading the monolayer in accordance with the solubility"' of the amphiphiles. A typical LB film deposition procedure involves three steps:
Minimizing Evaporation Loss from Irrigation Storages
Published in Guangnan Chen, Advances in Agricultural Machinery and Technologies, 2018
Pam Pittaway, Nigel Hancock, Michael Scobie, Ian Craig
Monolayers are films one molecule thick, formed at the air-water interface by amphiphilic compounds (Barnes, 2008). Some monolayers are capable of spontaneously spreading to form a surface film that reduces evaporative loss. The long-chain, linear (unbranched), fully saturated fatty alcohols cetyl and stearyl alcohol (hexadecanol and octadecanol) pack together to produce a condensed phase that maintains the high surface pressure required to retard evaporative loss. These compounds have been studied most commonly, as they are biodegradable, and are considered sufficiently benign for application in the food and cosmetics industries. Under laboratory conditions, monolayers of cetyl alcohol and stearyl alcohol reduce evaporation by up to 50%. However, results from field trials are extremely variable, ranging from 0% to 40% (McJannet et al., 2008). Poor monolayer performance has most commonly been attributed to wind speed (Barnes, 2008), with turbulence breaking up and beaching the film. Some air movement is certainly helpful, and perhaps necessary, to ensure full monolayer coverage of the water surface, but winds greater than 2–4 m.s−1 progressively destroy the film (Frenkiel, 1965). Automatic dispensing overcame this problem, with monolayer applied only during periods of low wind speed, conducive to film formation (Figure 12.7).
C–H…N hydrogen bonding in an overlayer of s-triazine physisorbed on a graphite surface
Published in Molecular Physics, 2020
Jonathan A. Davidson, Stephen J. Jenkins, Fabrice Gorrec, Stuart M. Clarke
Due to the negligible amount of material at the surface compared to the bulk, monolayers are comparatively difficult to study. Historically, scanning probe techniques (STM, AFM) have been the preferred method, particularly in ambient conditions. However, complementary techniques that are non-invasive are sought to better understand possible perturbations that can be introduced by the scanning probe [1–3]. Powder X-ray diffraction (XRD) using a high surface area substrate has previously been successfully used to study several halogen bonding systems [4,5]. As well as the potential ligands [6,7]. However, the requirement for synchrotron radiation has limited the ability to fully explore the capabilities of the technique. In this work, we successfully employed a commercially available X-ray diffractometer to collect high-quality data and characterise the formation of solid monolayers of 1,3,5-triazine (Figure 1) on a graphitic surface at ambient pressure to sub-angstrom precision.
Hydrophilic and hydrophobic materials and their applications
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2018
Darem Ahmad, Inge van den Boogaert, Jeremey Miller, Roy Presswell, Hussam Jouhara
Monolayers can be formed from organic molecules which adsorb onto the solid surface. The organic molecules can be sourced from a solution or a vapor phase. This ultimately changes the wetting characteristics of the surface (Ulman n.d.). Many research studies have been conducted on densely pack molecular structures that are used on metals. Alkanethiols have been generally used on gold (Bain et al. 1989; Bain and Whitesides 1989), silver (Laibinis, Bain, and Whitesides 1991; Laibinis and Whitesides 1992; Laibinis et al. 1991), copper (Laibinis, Bain, and Whitesides 1991; Laibinis and Whitesides 1992; Laibinis et al. 1991), platinum (Lang et al. 1998; Shimazu et al. 1994), and palladium (Love et al. 2003). Chlorosilanes have been used on silicon oxide (Fadeev and McCarthy 1999; Goodwin, Harbron, and Reynolds 1990; Sagiv 1980; Sugimura et al. 2002), aluminum (Kallury et al. 1992; Kurth and Bein 1992), and titanium (Fadeev, Helmy, and Marcinko 2002). Phosphoric acids can also be used on titanium (Adden et al. 2006; Pawsey, Yach, and Reven 2002), and aluminum (Pellerite et al. 2003; Sun and Leggett 2007).
Nanomaterial and fatigue cracking of hot mix asphalt
Published in Road Materials and Pavement Design, 2018
Ali Reza Azarhoosh, Fereidoon Moghadas Nejad, Ali Khodaii
Monolayer capacity is the number of molecules required to cover the aggregate surface in a single layer. It can be determined from the slope S and intercept I of the best-fit straight line between and , where p, p0, and n are partial vapour pressure, maximum saturation vapour pressure, and mass of vapour adsorbed per unit mass of aggregate, respectively. The straight line is fit only for partial vapour pressure, or , ranging from 0 to 0.35, as the BET equation is valid only for this range.