Influence of the initial chemical conditions on the rational design of silica particles

The influence of the water content in the initial composition on the size of silica particles produced using the Stöber process is well known. We have shown that there are three morphological regimes defined by compositional boundaries. At low water levels (below stoichiometric ratio of water:tetraethoxysilane), very high surface area and aggregated structures are formed; at high water content (>40 wt%) similar structures are also seen. Between these two boundary conditions, discrete particles are formed whose size are dictated by the water content. Within the compositional regime that enables the classical Stöber silica, the structural evolution shows a more rapid attainment of final particle size than the rate of formation of silica supporting the monomer addition hypothesis. The clearer understanding of the role of the initial composition on the output of this synthesis method will be of considerable use for the establishment of reliable reproducible silica production for future industrial adoption

Development of Highly Repellent Silica Particles for Protection of Hemp Shiv Used as Insulation Materials

New bio-materials have recently gained interest for use in insulation panels in walls, but wider adoption by the building industry is hindered by their intrinsic properties. The fact that such materials are mainly composed of cellulose makes them combustible, and their hydrophilic surface presents a high water uptake, which would lead to faster biodegradation. A hydrophobic treatment with silica particles was successfully synthesised via Stöber process, characterised, and deposited on hemp shiv. The surface of hemp shiv coated several times with 45 and 120 nm particles were uniformly covered, as well as extensively water repellent. Those samples could withstand in humidity chamber without loss of their hydrophobic property and no sign of mould growth after 72 h of exposure

Improvement of Water Resistance of Hemp Woody Substrates through Deposition of Functionalized Silica Hydrophobic Coating, While Retaining Excellent Moisture Buffering Properties

This paper reports on the development of a novel treatment for hemp shiv that improves resistance to liquid water and protects hemp shiv from biodegradation without impacting the natural ability of the shiv to buffer moisture vapor. The hydrophobic surface was produced by depositing silica nanoparticles, which were prepared by the functionalization of silica nanoparticles with hexamethyldisilazane (HMDS). The surface chemical composition was determined showing replacement of surface silanols on the silica nanoparticles with trimethyl groups. The specific surface area of silica nanoparticles decreased after the trimethylsilyl treatment. The surface modifications reduced the level of hysteresis between absorption and desorption isotherms and also the total amount of moisture absorbed by the silica nanoparticles. The surface of the hemp shiv was initially hydrophilic but became hydrophobic once the material was treated, demonstrating contact angle with water of 120°. The results show the coating layer of functionalized silica on the hemp shiv reduced water absorption from 400% (untreated shiv) to 250%. However, the moisture buffer value results showed that the coating films do not limit the access of moisture to adjacent pores in the hemp shiv, and the functionalized silica coating layer retains the moisture buffering ability of hemp shiv