Thermal diffusion forced Rayleigh scattering results on thermal diffusion of poly(ethylene oxide) (PEO) in ethanol/water mixtures are presented. In water-rich solvent mixtures, PEO is found to migrate towards regions of lower temperature. This is typical for polymer solutions and corresponds to a positive Soret coefficient of PEO. In solvent mixtures with low water content, however, the polymer is found to migrate towards higher temperatures, corresponding to a negative Soret coefficient of PEO in ethanol-rich solutions. To our knowledge, this is the first observed sign change of the Soret coefficient of a polymer in solution. We also present a simple lattice model for the polymer solvent system and calculate Soret coefficients with statistical mechanics methods. The calculated values agree qualitatively with the experimental results. DOI: 10.1103/PhysRevLett.91.245501 PACS numbers: 61.25.Hq, 61.43.Bn, 66.10.Cb A temperature gradient applied to a fluid mixture generally induces net mass flows which lead to the formation of concentration gradients. This effect is known as thermal diffusion or the Ludwig-Soret effect [1,2]. In the stationary state where the mass flows vanish, the magnitude of the effect is described by the Soret coefficients S T;i :where c i is the mass fraction of component i, c i0 is its equilibrium value, and where T is the temperature. S T;i is positive if component i moves to the low temperature region. Since the mass fractions add up to unity, P i c i 1, a K-component mixture has K ÿ 1 independent Soret coefficients.Typically, the Soret coefficient of the heavier component of a binary liquid mixture is positive. This is not always the case, however, and the Soret coefficients in some low molecular weight liquid mixtures are known to change sign [2]. A sign change of the Soret coefficient was also observed in very recent thermophoresis experiments on protein solutions [3]. While there is no theory which reliably predicts the sign of the Soret effect in liquid mixtures, approaches based on the ''heat of transfer'' concept [2] suggest that molecular interactions play an important role. In recent experiments, Debuschewitz and Köhler [4] identified two distinct contributions to the Soret coefficients of isotope substituted liquid mixtures of benzene and cyclohexane. The first contribution, due to differences in the molecules' masses and moments of inertia, was found to be independent of composition of the mixture. The second, reflecting chemical differences of the molecules, was found to vary with composition and change sign, inducing a sign change of the total Soret coefficients.With only two known exceptions, polymers in solution conform to the rule that the heavier component migrates to the colder regions of the fluid. Giglio and Vendramini [5] found a negative Soret coefficient for poly(vinyl alcohol) in water. Very recently, we reported our first thermal diffusion results for poly(ethylene oxide) (PEO) in ethanol-rich ethanol/water mixtures which indicated that the polymer migrates to th...
Summary: A study is presented on ink‐jet printing polymers, aiming at library generation for combinatorial material science applications, using (optimized) micropipettes. Solvents were successfully ink‐jet printed, up to 160 mPa s viscosity. Printability of polymer solutions decreases strongly with $\overline M _{\rm w}$ and polymer concentration, due to elastic stresses originating from elongational flow in the pipette nozzle. The feasibility of ink‐jet printing to generate arrays of polymer dots and films was demonstrated.An array of square films is shown that was created by printing a solution containing polydisperse polystyrene in acetophenone and 0.1% disperse red 1 to improve the contrast.magnified imageAn array of square films is shown that was created by printing a solution containing polydisperse polystyrene in acetophenone and 0.1% disperse red 1 to improve the contrast.
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