Phase Behaviors Of Bromobenzene-chlorobenzene And N-alkane (n-C_nH_2n+2,n=10-16,△n=2) Binary Systems Confined In SBA-15

The influence of as size effect, surface effect and pore geometry on thermalproperties of liquids confined in nanospace has been widely studied. However, theinterpretations of the results are sometimes contradictory. Understanding theproperties of confined systems is of practical importance in lubrication, adhesion,nanotribology and fabrication of nanomaterials.Using Pluronic P123triblock copolymer (EO₂₀PO₇₀EO₂₀，Ma=5800) as amicellar template and tetraethoxysilane （TEOS） as silicon source, SBA-15wassynthesized as ordered mesoporous silica through hydrothermal reaction method.SBA-15with different pore diameter was obtained by varying synthesis temperatureand using triisopropylbenzene （TIPB） as a micelle expander. The pore structures ofSBA-15were characterized using transmission electron microscope （TEM）, andnitrogen adsorption/desorption method. It indicated that SBA-15has ordered porestructure, narrow pore size distribution, of which the pore size can regulated from3.8to17.2nm.Phase behavior of confined liquids has been studied by differential scanningcalorimetry （DSC）. Melting points of confined pure alkanes (n-C_nH_2n+2，n=10、12、14、16) were inversely proportional to the pore diameter of SBA-15. Melting pointsof the C₆H₅Br-C₆H₅Cl system confined in SBA-15（7.8nm） were depressed and thephase diagram was simple compared to the bulk. But C₆H₅Br-C₆H₅Cl mixtures couldnot be frozen confined in MCM-41. Normal alkane mixtures（n=10,12,14,16, Δn=2）confined in SBA-15showed the simple behaviors compared to the bulk. With theincrease of the pore diameter, the phase diagrams changed from a straight line （3.8nm）, a curve line （7.8nm） to a loop line （17.2nm）. The pore size had shown a greatinfluence on phase diagram.