Dispersant effect on coatings of POSS-based poly methylmethacrylate hybrids and their protective performance to sandstones

Three polyhedral oligosilsesquioxanes (POSS) based poly methylmethacrylate (MMA) hybrids designed for coating materials are evaluated to understand the dispersant effect of tetrahydrofuran (THF) or chloroform (CHCl3) on their adhesive strength, mechanical strength and surface wettability of films. The used POSS-based hybrids are obtained as a POSS-ended hybrid of ap-POSS-PMMA-b-P(MA-POSS), a dodecafluoroheptyl methacrylate (DFHM) fluorinated POSS-based hybrid of ap-POSS-PMMA-b-PDFHM and a soft poly dimethylsiloxane (PDMS) modified POSS-based hybrid of PDMS-b-PMMA-b-P(MA-POSS). Their protective performances to sandstone are investigated by pore size distribution, water absorption, water vapor permeability, hardness and salt-resistance of sandstones. Although three hybrids dispersed in THF and CHCl3 can cast into porous and hydrophobic films at ambient, the luminousness of hybrid solutions, the adhesive strength and the elasticity modulus of hybrid films show significant dependence on dispersant. The films casted by CHCl3-dispersed hybrids shows less and smaller pores than that casted by THF-dispersed hybrids ascribed to higher viscosity, more rapid evaporation and lower water immiscible of CHCl3 can THF. CHCl3-dispersed hybrids reveal higher adhesive strength, higher elasticity modulus and higher tensile strength but less transparent and lower elongation than THF-dispersed hybrids because of the larger aggregated micelles in CHCl3 solution and the contribution of lower dielectric constant of CHCl3 (epsilon = 4.81) than THF (epsilon = 7.58). While, CHCl3-dispersed hybrids perform much better protection to sandstone due to higher hardness, higher water vapor permeability, higher resistance to salt damage and less water absorption than THF-dispersed hybrids, owing to that CHCl3 could carry the hybrids to permeate deeply into the sandstone rather than the superficial protection by THF solutions. The best protective performance is found in PDMS-b-PMMA-b-P(MA-POSS) hybrid attributed to the contribution of soft PDMS segment to its mechanical strength, water repellency and salt-resistance.