title: Enhanced translational diffusion of rubrene in sucrose benzoate.
abstract: The translational diffusion of rubrene in the fragile molecular glass former, sucrose benzoate (SB) (fragility index m approximately 94), has been studied from T(g)+6 K to T(g)+71 K(T(g)=337 K) by using the technique of holographic fluorescence recovery after photobleaching. In the temperature range of the measurements, the translational relaxation functions were observed to decay exponentially, indicating that Fick's law of diffusion governs the translational motion of rubrene in sucrose benzoate. The value of the translational diffusion coefficient D(T) obtained from the 1e time of the translational relaxation function varied from 5.3 x 10(-15) cm2 s(-1) at 343 K to 5.0x10(-9) cm2 s(-1) at 408 K. The temperature dependence of D(T) for diffusion of rubrene in SB is compared with that of the viscosity and the dielectric relaxation time tau(D) of SB. The temperature dependence of D(T) is weaker than that of Teta for T<1.2T(g) but tracks the reciprocal of the dielectric relaxation time 1tau(D) for 1.05T(g)<T<1.21T(g). The translational diffusion coefficient at T(g) is enhanced by a factor of approximately 2.5x10(2) over the value predicted by the Stokes-Einstein equation. The decoupling of probe diffusion from the viscosity is characterized by a scaling law, D(T) approximately eta(-xi), with xi=0.729.
authors.affiliation: Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409-1061, USA.
authors.forename: Justin
authors.initials: J
authors.lastname: Rajesh Rajian
authors.forename: Wei
authors.initials: W
authors.lastname: Huang
authors.forename: Ranko
authors.initials: R
authors.lastname: Richert
authors.forename: Edward L
authors.initials: EL
authors.lastname: Quitevis
mesh_terms: D001565:Benzoates / Q000737:chemistry*; D002627:Chemistry, Physical / Q000379:methods*; D004058:Diffusion; D036681:Fluorescence Recovery After Photobleaching; D008956:Models, Chemical; D015233:Models, Statistical; D008962:Models, Theoretical; D009279:Naphthacenes / Q000737:chemistry*; D013395:Sucrose / Q000031:analogs & derivatives* / Q000737:chemistry; D013696:Temperature
chemical_list: D001565:Benzoates; D009279:Naphthacenes; C067056:sucrose octabenzoic acid; C045049:rubrene; D013395:Sucrose