Motivation for such research derives from the investigation of a novel principle of mechanical energy dissipation, called surface dissipation, and its attached machine element, named a colloidal damper. Similar to a hydraulic damper, this absorber has a cylinder-piston structure, but oil is replaced by a colloid consisting of a mesoporous matrix and a lyophobic liquid. Here, the mesoporous matrix is from silica gel modified by linear chains of ClSi(CH₃)₂C_mH_2m+1, Cl₂Si(CH₃)C_mH_2m+1 and Cl₃SiC_mF_2m+1 (m = 1-18); water is the associated liquid. Such absorber, being oil-free and employing a mixture of water and silica gel, might be considered as an environment-friendly application of nanotechnology in the field of mechanical engineering. Energy loss can be explained by the dynamic contact angle hysteresis in advancing and receding motion of the interface. Although such hysteresis is not fully understood, it seems to be induced by surface roughness, surface chemical heterogeneity, and a variety of nonequilibrium phenomena, such as dissolution, swelling, and surface reorientation of the functional groups. In this work, the architecture of the used silica gel as well as the structure of the grafted coating is briefly discussed. Test rig and the measurement technique of the dynamic contact angle hysteresis are described. From experimental data one calculates the dissipated energy versus length of the grafted molecule on the silica gel surface. Influence of the interface movement frequency, pre-pressurization and maximum applied pressure on the dynamic contact angle hysteresis and dissipated energy is found for silica gels with different hydrophobic coatings. One finds the optimum length of the grafted molecules which maximizes the dissipated energy of the colloidal damper. Such results are generally useful for the appropriate design of ultrahydrophobic surfaces.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/3519 must be provided.

1. Theoretical investigation of the surface roughness effect on the contact angle hysteresis which occurs at the water adsorption/desorption in/from a hydrophobized mesoporous silica gel matrix