Using the recently proposed method of Berthier et al. [11] we determine the number N$_{c}$orr of dynamically correlated molecules as a function of temperature and pore size. results clearly show that silanation removes the liquid-surface interaction, leading to an enhancement of the molecular dynamics in the pores, resulting in a stronger downshift of T$_{g}$ as compared to the uncoated pores. These findings allow to separate the surface effect from confinement induced acceleration, and a simultaneous quantitative statement about negative pressure within one and the same measurement technique and confinement geometry. A comparison with previous dielectric spectroscopy data [25–27] of salol in mesoporous matrices yields excellent agreement. Vycor by Corning Inc., NY is produced via phase separation within a Na$_{2}$O-B$_{2}$O$_{3}$-SiO$_{2}$ melt, and subsequent acid leaching [28], which leaves a 98% pure SiO$_{2}$ skeleton containing interconnected pores of random length, direction and density. A very narrow pore size distribution and an average ratio of pore length l over pore diameter d of l/d ≈ 4.35 is reported [29]. Gelsil samples result from a sol-gel process [30] and consist of randomly formed pure fused SiO$_{2}$ monodisperse spheres [31], touching and penetrating each other, resulting in a mesoporous structure with a rather broad distribution of pore diameters, as N$_{2}$-sorption results showed. Samples are cut and sanded to gain the required orthogonal shapes, and cleaned in a 30% H$_{2}$O$_{2}$ solution at 363 K for 24h. Drying is done under high vacuum ($_{10}$ − 6 mbar) at 393 K for another 24h. In order to deactivate inner surfaces, OH − groups are replaced by OSi(CH$_{3}$)$_{3}$ trimethylsi- lyl groups via exposing cleaned samples to gaseous hexamethyldisilazane (HDMS, from Sigma Aldrich, purity 99.9%) in a closed vessel at 330 K for 24h. Afterwards samples are again evacuated for 24h at 300 K. In order to check pore geometry and pore radius after silanation, mesoporous samples have been tested via N$_{2}$-sorption and BET/BJH analysis of the individual desorption isotherms [32] experiments before and after HDMS treatment. 4 A. Sample preparation II. EXPERIMENTAL