Separation of Particles in Nonaqueous Suspensions by Thermal Field-Flow Fractionation

Shiundu, Paul M.; Liu, Guangyue; Giddings, J. Calvin

doi:10.1021/ac00111a032

Cited by 47 publications

(50 citation statements)

References 18 publications

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“…1, molecules characteristically deplete from regions with an increased temperature, but they can also show the inverted effect and accumulate (2,3). Moreover, the size scaling of thermodiffusion recorded by thermal field flow fractionation showed fractional power laws with a variety of exponents that are hard to interpret (4,5). The latter effect might be resolved by revealing nonlinear thermophoretic drift for the strong thermal gradients used in thermal field flow fractionation (our unpublished observations).…”

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confidence: 88%

Why molecules move along a temperature gradient

Duhr

Braun

2006

Proc. Natl. Acad. Sci. U.S.A.

902

987

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Molecules drift along temperature gradients, an effect called thermophoresis, the Soret effect, or thermodiffusion. In liquids, its theoretical foundation is the subject of a long-standing debate. By using an all-optical microfluidic fluorescence method, we present experimental results for DNA and polystyrene beads over a large range of particle sizes, salt concentrations, and temperatures. The data support a unifying theory based on solvation entropy. Stated in simple terms, the Soret coefficient is given by the negative solvation entropy, divided by kT. The theory predicts the thermodiffusion of polystyrene beads and DNA without any free parameters. We assume a local thermodynamic equilibrium of the solvent molecules around the molecule. This assumption is fulfilled for moderate temperature gradients below a fluctuation criterion. For both DNA and polystyrene beads, thermophoretic motion changes sign at lower temperatures. This thermophilicity toward lower temperatures is attributed to an increasing positive entropy of hydration, whereas the generally dominating thermophobicity is explained by the negative entropy of ionic shielding. The understanding of thermodiffusion sets the stage for detailed probing of solvation properties of colloids and biomolecules. For example, we successfully determine the effective charge of DNA and beads over a size range that is not accessible with electrophoresis.DNA ͉ fluorescence ͉ microfluidic ͉ Soret ͉ thermodiffusion T hermodiffusion has been known for a long time (1), but its theoretical explanation for molecules in liquids is still under debate. The search for a theoretical understanding is motivated by the fact that thermodiffusion in water might lead to powerful all-optical screening methods for biomolecules and colloids. Equally well, thermodiffusion handles and moves molecules alloptically and therefore can complement well established methods: for example, electrophoresis or optical tweezers. For the latter, forces of optical tweezers scale with particle volume and limit this method to particles of only Ͼ500 nm. Electrophoresis does not suffer from force limitations but is difficult to miniaturize because of electrochemical reactions at the electrodes.On the other hand, thermodiffusion allows the microscale manipulation of small particles and molecules. For example, 1,000-bp DNA can be patterned arbitrarily in bulk water (Fig. 1). The temperature pattern ''DNA,'' heated by 2 K, was written into a water film with an infrared laser scanning microscope. The concentration of 1,000-bp DNA was imaged by using a fluorescent DNA tag. In an overall cooled chamber at 3°C, DNA accumulates toward the heated letters ''DNA'' (negative Soret effect), whereas at room temperature DNA is thermophobic (positive Soret effect) as seen by the dark letters.In the past, the apparent complexity of thermodiffusion prevented a full theoretical description. As seen for DNA in Fig. 1, molecules characteristically deplete from regions with an increased temperature, but they can also show the inver...

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mentioning

confidence: 88%

Why molecules move along a temperature gradient

Duhr

Braun

2006

Proc. Natl. Acad. Sci. U.S.A.

902

987

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“…Many questions still remain, one of which is the dependence of thermophoresis on particle size. Practically, the characteristic of size dependent thermophoresis has a potential application for the separation of particles of different sizes [9][10][11], the manipulation of DNAs [12][13][14], and the enhancement of heat transfer of nanofluids [15][16][17][18][19][20][21][22]. In the literature, although numerous theoretical and experimental studies have been reported on the size dependence of thermophoresis for dilute polystyrene (PS) beads dispersed in aqueous solutions, the results of these investigations are inconsistent and inconclusive.…”

Section: Introductionmentioning

confidence: 99%

Thermophoresis of charged colloidal particles in aqueous media – Effect of particle size

Zhou

Yang

Lam

et al. 2016

International Journal of Heat and Mass Transfer

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“…Typically, the particle velocity v is assumed to be a linear function of the temperature gradient rT: v ¼ ÀD T rT, with the thermophoretic mobility D T ¼ S T D, where the Soret coefficient is S T and the diffusion coefficient is D. Several competing models have been proposed to describe the microscopic cause [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Recent experiments aim to distinguish between the models [18][19][20][21].…”

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confidence: 99%

“…The driving mechanism also differs from hydrodynamic attraction in sedimentation [28,29] or during electrophoretic deposition [30][31][32], where the mutual attraction is predominantly driven by an electro-osmotic fluid flow at the barrier surface [32] rather than on the particle surface. The reported particle attraction in a thermal gradient is likely to disturb thermal field flow fractionation for large particles [18]. Temperature gradients on a surface can be structured by patterning the thermal conductivity of the substrate, allowing for considerable technical applications such as the formation of photonic crystals [33] or biomolecule detection.…”

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confidence: 99%

Observation of Slip Flow in Thermophoresis

2008

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Two differing theories aim to describe fluidic thermophoresis, the movement of particles along a temperature gradient. While thermodynamic approaches rely on local equilibrium, hydrodynamic descriptions assume a quasi-slip-flow boundary condition at the particle's surface. Evidence for slip flow is presented for the case of thermal gradients exceeding (aS_(T)(-1) with particle radius a and Soret coefficient S_(T). Thermophoretic slip flow at spheres near a surface attracts or repels tracer particles perpendicular to the thermal gradient. Moreover, particles mutually attract and form colloidal crystals. Fluid dynamic slip explains the latter quantitatively.

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Separation of Particles in Nonaqueous Suspensions by Thermal Field-Flow Fractionation

Cited by 47 publications

References 18 publications

Why molecules move along a temperature gradient

Why molecules move along a temperature gradient

Thermophoresis of charged colloidal particles in aqueous media – Effect of particle size

Observation of Slip Flow in Thermophoresis

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