The Molecular Boat: A Hands-On Experiment To Demonstrate the Forces Applied to Self-Assembled Monolayers at Interfaces

Abstract

Demonstrating how surface chemistry and self-assembled monolayers (SAMs) control the macroscopic properties of materials is challenging as it often necessitates the use of specialized instrumentation. In this hands-on experiment, students directly measure a macroscopic property, the floatation of glass coverslips on water as a function of modifying the terminal surface groups of the glass. The glass surface is chemically modified by the self-assembly of monomolecular layers formed by two organosilanes, 3aminopropyltriethoxysilane and 1-octadecyltrimethoxysilane, which change the water contact angles. These SAMs alter the ability of the modified glass to support a mass, thus demonstrating that the bulk material property can be directly controlled by molecular surface chemistry.

Superhydrophobic Substrates from Off-the-Shelf Laboratory Filter Paper: Simplified Preparation, Patterning, and Assay Application

“…Organosilanes have been commercially used to achieve hydrophobicity on various materials; in the field of surface chemistry, silanization has also been extensively studied. − It has been widely accepted that long-chain alkylsilanes (e.g., OTS) can form ordered monolayers on the surface, , whereas short alkylsilane (e.g., MTS) produces rough surfaces with three-dimensional (3D) nanostructures (because of the polymerization and condensation of the silanols) which end up with superhydrophobicity on the surface. − Our initial tests to treat filter paper with MTS did not produce satisfactory results (not superhydrophobic, as discussed below), we have then explored the binary silanization approach, which was to treat the surface with a binary solution of long and short alkylsilanes (vide infra).…”

“…Both OTS and MTS have been widely used for the modification of hydroxyl (-OH) terminated solid surfaces (silicon oxide, metal, glass, as examples), 20,[41][42][43][44][45][46][47][48][49] but with a less extent for paper. 22 It is also known that their reactivity towards hydroxylated surfaces are different, i.e., OTS tends to form ordered monolayers on SiO 2 or glass as of the strong inter-chain van der Waal forces, while MTS would form three-dimensional, aggregated nano/nanostructures, as discussed above.…”

Preparation of Transparent Superhydrophobic Glass Slides: Demonstration of Surface Chemistry Characteristics

“…Schematic representation of a normal hydrophilic glass surface after treatment with (A) octadecyltrichlorosilane that results in the formation of a highly ordered self-assembled monolayer , (hydrophobic) and (B) methyltrichlorosilane that results in the formation of a 3D polymethylsiloxane network (superhydrophobic). The inset shows a SEM image of the superhydrophobic surface.…”

“…11 The difference between the two reactions stems from the different reactivities of the two alkyltrichlorosilanes (different alkyl chain lengths). Octadecyltrichlorosilane forms a well-ordered methyl-(Me-) terminated monolayer at the surface (Figure 3A) 28 that changes the polarity of the glass (giving water contact angles of 112 ± 2°), whereas methyltrichlorosilane forms a 3-dimensional polymethylsiloxane network that has the ability to trap air pockets when water droplets are deposited on the slide (Figure 3B). 29 The air pockets, according to the Cassie−Baxter equation, increase the contact angle of the water droplet and thereby make the surface superhydrophobic (>150°).…”

Bouncing Droplets: A Hands-On Activity To Demonstrate the Properties and Applications of Superhydrophobic Surface Coatings

“…Although the literature offers a few laboratory activities on surface wetting modification, − most deal with simple hydrophilic and hydrophobic surfaces. Very few reports offer laboratory activities presenting the preparation of superhydrophobic surfaces. − However, these experiences require long waiting times (from several hours to 2 days), and the preparation and characterization steps often require uncommon equipment for teaching laboratories, like UV–ozone cleaners or spin coaters, and expensive instrumentation, such as contact angle measurement instruments and electron microscopes.…”