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RISS 인기검색어
- 검색키워드
- 저자 : Frank Scheffold (검색결과 3 건)
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Yoon, Jiwon,Scheffold, Frank,Ahn, Kyung Hyun Elsevier 2019 Colloids and surfaces. A, Physicochemical and engi Vol.576 No.-
<P><B>Abstract</B></P> <P>We report on the colloidal dynamics and rheology of liquid droplet emulsions and solid particle suspensions over a wide range of volume fractions. Diffusing wave spectroscopy and rheometry were utilized to study the micro/macroscale properties of 1-eicosene wax particles dispersed in water. By changing the temperature, the wax droplets change their properties from soft to hard or vice versa, which, depending on the density, may affect the system properties in a different way. Our measurements in the high volume fraction regime focus on the elasticity index and the plateau storage modulus, G p ′ . The results show a more pronounced increase of the modulus for the wax particle suspensions around the random close packing volume fraction compared to the emulsion.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Chi Zhang,Mathias Reufer,Danila Gaudino,Frank Scheffold 한국유변학회 2017 Korea-Australia rheology journal Vol.29 No.4
Diffusing wave spectroscopy (DWS) can be employed as an optical rheology tool with numerous applications for studying the structure, dynamics and linear viscoelastic properties of complex fluids, foams, glasses and gels. To carry out DWS measurements, one first needs to quantify the static optical properties of the sample under investigation, i.e. the transport mean free path l* and the absorption length la. In the absence of absorption this can be done by comparing the diffuse optical transmission to a calibration sample whose l* is known. Performing this comparison however is cumbersome, time consuming, and prone to mistakes by the operator. Moreover, already weak absorption can lead to significant errors. In this paper, we demonstrate the implementation of an automatized approach, based on which the DWS measurement procedure can be simplified significantly. By comparison with a comprehensive set of calibration measurements we cover the entire parameter space relating measured count rates (CRt , CRb) to (l*, la). Based on this approach we can determine l* and la of an unknown sample accurately thus making the additional measurement of a calibration sample obsolete. We illustrate the use of this approach by monitoring the coarsening of a commercially available shaving foam with DWS.
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Brownian dynamics of colloidal microspheres with tunable elastic properties from soft to hard
Yoon, Jiwon,Cardinaux, Fré,dé,ric,Lapointe, Clayton,Zhang, Chi,Mason, Thomas G.,Ahn, Kyung Hyun,Scheffold, Frank Elsevier 2018 Colloids and surfaces. A, Physicochemical and engi Vol.546 No.-
<P><B>Abstract</B></P> <P>We study the Brownian thermal motion of a colloidal model system made by emulsifying hot liquid <I>α</I>-eicosene wax into an aqueous surfactant solution of sodium dodecyl sulfate (SDS). When this waxy oil-in-water emulsion is cooled below <I>α</I>-eicosene's melting point of <I>T</I> <SUB> <I>c</I> </SUB> ≃ 25 °C, the microscale emulsion droplets solidify, effectively yielding a dispersed particulate system. So, the interiors of these wax droplets can be tuned from a viscous liquid to an elastic solid through very modest changes in absolute temperature. Using the multiple light scattering technique of diffusing wave spectroscopy (DWS), which is very sensitive to small-scale motion and shape fluctuations of dispersed colloidal objects, we show that the thermal fluctuations of the interfaces of these liquid droplets at higher temperature, seen in the DWS intensity–intensity correlation function at early times, effectively disappear when these droplets solidify at lower temperature. Thus, we show that the early-time behavior of this DWS correlation function can be used to probe mechanical properties of viscoelastic soft materials dispersed as droplets.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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