Rapid Covalent Modification of Silicon Oxide Surfaces through Microwave-Assisted Reactions with Alcohols

Abstract

We demonstrate the method of a rapid covalent modification of silicon oxide surfaces with alcohol-containing compounds with assistance by microwave reactions. Alcohol-containing compounds are prevalent reagents in the laboratory, which are also relatively easy to handle because of their stability against exposure to atmospheric moisture. The condensation of these alcohols with the surfaces of silicon oxides is often hindered by slow reaction kinetics. Microwave radiation effectively accelerates this condensation reaction by heating the substrates and/or solvents. A variety of substrates were modified in this demonstration, such as silicon oxide films of various thicknesses, glass substrates such as microscope slides (soda lime), and quartz. The monolayers prepared through this strategy demonstrated the successful formation of covalent surface modifications of silicon oxides with water contact angles of up to 110° and typical hysteresis values of 2° or less. An evaluation of the hydrolytic stability of these monolayers demonstrated their excellent stability under acidic conditions. The techniques introduced in this article were successfully applied to tune the surface chemistry of silicon oxides to achieve hydrophobic, oleophobic, and/or charged surfaces.

Organic Monolayers by B(C6F5)3-Catalyzed Siloxanation of Oxidized Silicon Surfaces

“…21−23 Despite the simplicity of these approaches, uniform monolayers are difficult to obtain using solution-phase deposition methods, and undesirable polysiloxane networks are often formed. 24,25 In addition, these surface modification approaches often require long reaction times, commonly taking 2–24 h. 26 Silicon nanowires (SiNWs) can function as a specific example.…”

Covalent Surface Modification of Silicon Oxides with Alcohols in Polar Aprotic Solvents

“…The silicon substrates were further cleaned by immersion into a piranha solution followed by rinsing with water prior to the formation of the monolayers as described in previous literature. 37 CAUTION: Piranha solution is a strong oxidizing agent and reacts violently with organic compounds. This solution should be handled with extreme care.…”

“…These peaks agree with the previously reported peak positions for these respective species based on the high resolution C1s XPS of fluorinated monolayers. 37,39,[46][47][48] Monolayers derived from either glycolic acid or 5hydroxypentanal contained three distinct peaks in their high resolution C1s XPS analyses. For the substrate reacted with glycolic acid, the peaks attributed to C−C, C−O, and C=O were located at binding energies of 285.3 eV, 287.1 eV, and 289.4 eV, respectively.…”

“…Alcohols are an attractive alternative for their widespread availability, low toxicity, and minimal susceptibility to side reactions with moisture. [35][36][37][38] Both hydrogen-terminated silicon and hydroxyl-terminated silicon oxide surfaces have been functionalized with alcohol reagents using reactions initiated by convective heating, 35 UV radiation, 36 or microwave heating. 37,39 These reports relied on reactions carried out at relatively high temperatures in mostly neat solutions.…”

“…[35][36][37][38] Both hydrogen-terminated silicon and hydroxyl-terminated silicon oxide surfaces have been functionalized with alcohol reagents using reactions initiated by convective heating, 35 UV radiation, 36 or microwave heating. 37,39 These reports relied on reactions carried out at relatively high temperatures in mostly neat solutions. While these approaches provide a simple reaction strategy for the formation of monolayers, it can limit the choice alcohols available for the reaction due to possible thermal degradation or other side reactions at high temperatures.…”