Effect of Water–Water Hydrogen Bonding on the Hydrophobic Hydration of Large-Scale Particles and Its Temperature Dependence

2012 ◽  
Vol 116 (9) ◽  
pp. 2820-2830 ◽  
Author(s):  
Y. S. Djikaev ◽  
E. Ruckenstein
Keyword(s):  
Hydrogen Bonding ◽  
Temperature Dependence ◽  
Large Scale ◽  
Hydrophobic Hydration ◽  
Effect Of Water ◽  
Water Hydrogen

scholarly journals Origin of hydrophobicity and enhanced water hydrogen bond strength near purely hydrophobic solutes

2016 ◽  
Vol 114 (2) ◽  
pp. 322-327 ◽  
Author(s):  
Joze Grdadolnik ◽  
Franci Merzel ◽  
Franc Avbelj
Keyword(s):  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Hydrophobic Hydration ◽  
Bulk Water ◽  
Water Molecules ◽  
Classical View ◽  
Fundamental Level ◽  
Hydrophobic Solute ◽  
Hydrophobic Solutes ◽  
Water Hydrogen

Hydrophobicity plays an important role in numerous physicochemical processes from the process of dissolution in water to protein folding, but its origin at the fundamental level is still unclear. The classical view of hydrophobic hydration is that, in the presence of a hydrophobic solute, water forms transient microscopic “icebergs” arising from strengthened water hydrogen bonding, but there is no experimental evidence for enhanced hydrogen bonding and/or icebergs in such solutions. Here, we have used the redshifts and line shapes of the isotopically decoupled IR oxygen–deuterium (O-D) stretching mode of HDO water near small purely hydrophobic solutes (methane, ethane, krypton, and xenon) to study hydrophobicity at the most fundamental level. We present unequivocal and model-free experimental proof for the presence of strengthened water hydrogen bonds near four hydrophobic solutes, matching those in ice and clathrates. The water molecules involved in the enhanced hydrogen bonds display extensive structural ordering resembling that in clathrates. The number of ice-like hydrogen bonds is 10–15 per methane molecule. Ab initio molecular dynamics simulations have confirmed that water molecules in the vicinity of methane form stronger, more numerous, and more tetrahedrally oriented hydrogen bonds than those in bulk water and that their mobility is restricted. We show the absence of intercalating water molecules that cause the electrostatic screening (shielding) of hydrogen bonds in bulk water as the critical element for the enhanced hydrogen bonding around a hydrophobic solute. Our results confirm the classical view of hydrophobic hydration.

Superlubricity Relevant in Hard Disk Drive Applications

2016 ◽  
Author(s):  
Shou-Mo Zhang ◽  
Cuong-C. Vu ◽  
Qun-Yang Li ◽  
Norio Tagawa ◽  
Quan-Shui Zheng
Keyword(s):  
Temperature Dependence ◽  
Hard Disk Drive ◽  
Large Scale ◽  
Hard Disk Drives ◽  
Hard Disk ◽  
Disk Drive ◽  
Force Sensor ◽  
Lubricant Layer ◽  
Single Crystalline ◽  
Crystalline Graphite

Reduction of head-media spacing (HMS) keeps crucial during the increase of areal density of hard disk drives (HDD). The design of hard disk drive with a superlubric interface is reported with two schemes for HDI design to realize superlubricity. For the first scheme, the DLC layer is kept on the disk while removing the lubricant layer. The DLC layer on the transducer is replaced by graphene-like layer. The direct contact between head and disk could reduce the HMS to about 2.3 nm. For the second scheme, the DLC layer on disk is further replaced by graphene and the HMS could be reduced to below 1 nm. For the first scheme, the basic proof of concept experiments are conducted using micro-scale graphite island samples. Ultralow COF, with the average of 0.0344 on the interface of single crystalline graphite surface and DLC substrate is demonstrated by AFM. What’s more, the temperature dependence of friction between single crystalline graphite and DLC is measured by micro-force sensor mounted on micro-manipulator. The results show that heating helps to significantly decrease the friction. Desorption of contaminants along the interface is speculated to be the key mechanism for temperature dependence of friction. This work provides the concept of large-scale superlubricity relevant in HDD applications, which could be a promising technology to ultimately reduce HMS for future HDI development.

Sign in / Sign up

Export Citation Format

Share Document