Environment-Controlled Tethering by Aggregation and Growth of Phosphonic Acid Monolayers on Silicon Oxide

Abstract

Phosphonic acid monolayers are being considered as versatile surface modification agents due to their unique ability to attach to surfaces in different configurations, including mono-, bi-, or even tridentate arrangements. Tethering by aggregation and growth (T-BAG) of octadecylphosphonic acid (ODPA) on silicon oxide surfaces has proven to be a robust method to establish a strong chemical bond. However, it requires a long processing time (> 48 h) that is a substantial drawback for industrial applications. We demonstrate here that the humidity level during processing is the most important parameter controlling the reaction. Using in situ Fourier Transform Infrared Spectroscopy (FTIR), we first show that the initially physisorbed layer obtained upon immersion in ODPA is composed of well-ordered bilayers and only reacts with the SiO(2) surface at 140 °C. Importantly, we show that the presence of water at the interface (determined by the humidity level) greatly influences the reaction time and completion. In humid environments (relative humidity, RH > 40%), there is no reaction, while in dry environments (RH < 16%), the reaction is essentially instantaneous at 140 °C. Ab initio calculations and modeling confirm that the degree of chemical reaction with the surface OH groups depends on the chemical potential (i.e., concentration) of interfacial water molecules. These findings provide a workable modification of the traditional T-BAG method consistent with many industrial applications.

Unraveling the Coupled Processes of (De)hydration and Structural Changes in Na+-Saturated Montmorillonite

“…The dispersion was heated at 105 °C until complete evaporation ( ≈ 12 h) of the liquid and the clay mineral particles covered both sides of the wafer surface. 31,41 In the course of the preparation of the homoionic BV-M0.2Na traces of glycerol were inherited from the dialysis tube. Unfortunately, glycerol is very IR active and bands superimpose with bands of interlayer water.…”

Application of Organophosphonic Acids by One-Step Supercritical CO2 on 1D and 2D Semiconductors: Toward Enhanced Electrical and Sensing Performances

“…14,17,47 In the aliphatic region, ( Figure 2B-a) the broad spectral positions of the strong asymmetric and symmetric stretch modes of the (−CH 2 −) at 2915 and 2850 cm −1 respectively and asymmetric stretch mode of the (−CH 3 ) at 2960 cm −1 , indicate that the physisorption step takes advantage of the arrangement of amphiphilic molecules at the liquid/gas interface. 14 The FTIR spectrum in Figure 2A-b shows the resulting IR spectrum at the end of the conventional process after heating the physically adsorbed ODPA at 140°C for 48h and followed by cleaning. The presence of the (PO) mode at 1250 cm −1 rules out the formation of the primarily tridentate bonding and the absence of the (P−O−H) mode at 956 cm −1 rules out the monodentate configuration.…”

Rational design of a material for rapid colorimetric Fe2+ detection

“…The phosphonate functional group not only makes L water soluble, but allows for the formation of robust self-assembled monolayers on a variety of surfaces. Thus, phosphonates have been utilized for the surface modification of a wide range of oxide substrates [47] such as titania [48,49], alumina [50], iron oxides [51], hafnium oxide [52], indium-tin oxide (ITO) [53], and silica [54]. Phosphonate-anchored SAMs are easily prepared in air, and form well-ordered strongly bound films on oxide surfaces with molecular densities close to those found in single crystals [55].…”