Transport of Nanoscale Latex Spheres in a Temperature Gradient

Abstract

We use a micrometer-scale optical beam deflection technique to measure the thermodiffusion coefficient D(T) at room temperature (approximately 24 degrees C) of dilute aqueous suspensions of charged polystyrene spheres with different surface functionalities. In solutions with large concentrations of monovalent salts, < or approximately = 100 mM, the thermodiffusion coefficients for 26 nm spheres with carboxyl functionality can be varied within the range -0.9 x 10(-7) cm2 s(-1) K(-1) < D(T) < 1.5 x 10(-7) cm2 s(-1) K(-1) by changing the ionic species in solution; in this case, D(T) is the product of the electrophoretic mobility mu(E) and the Seebeck coefficient of the electrolyte, S(e) = (Q(C)* - Q(A)*)/2eT, D(T) = -S(e) mu(E), where and are the single ion heats of transport of the cationic and anionic species, respectively. In low ionic strength solutions of LiCl, < or approximately = 5 mM, and particle concentrations < or approximately = 2 wt %, D(T) is negative, independent of particle concentration and independent of the Debye length; D(T) = -0.73 +/- 0.05 x 10(-7) cm2 s(-1) K(-1).

Transport in Charged Colloids Driven by Thermoelectricity

“…• C. In all cases, an inverse Soret effect occurs at low T , changes sign at some intermediate value T * , and seems to saturate above 50 • C. On the other hand, a large negative thermophoretic mobility has been reported for charged latex spheres in a buffered solution at weak acidity and low salinity [10]; adding LiCl or NaCl results in a change of sign and a transport velocity that depends significantly on the cation. These features strongly suggest a single mechanism related to the electric properties of the colloid; the relevance of the thermoelectric effect for colloidal suspensions has been pointed out recently [10].…”

Protein-binding assays in biological liquids using microscale thermophoresis

“…Although the theory of thermophoresis is still under debate, all theoretical descriptions agree that the molecular size and various surface parameters, such as charge and hydrophobicity, have an influence on Soret coefficient S T . Recent theoretical approaches also include the influence of the Seebeck effect: ions in the buffer move along a thermal gradient and give rise to an electric field, which in turn moves the molecules by electrophoresis [31][32][33] . As the buffer systems throughout this work used NaCl to set the ionic strength, the resulting Seebeck contribution was suggested to be small 33 .…”

Steering and guiding light with light in a nanosuspension

“…On the other hand, in [12] the authors use a NIR laser at 808 nm, for which water absorption is almost two orders of magnitude larger than for the green light used in our experiment, and thus thermal gradients are expected to be much stronger in that case. Finally, the conditions to obtain negative thermophoresis, as it is required for a self-focusing nonlinearity, imply a high degree of control on the solvent properties and particlesolvent interface [12][13][14], which we do not have in our experiment.…”