Daniel De KeeDaniel C. De Kee
Director, Tulane Institute for Macromolecular Engineering and Science (TIMES)

Phone: (504) 865-5620
Website: TIMES Website

329 Lindy Boggs Building
Department of Chemical and Biomolecular Engineering
Tulane University
New Orleans, LA 70118-5674

Research Interests

In the area of mass transport, we are studying the non-Fickian diffusion of organic materials and gases through nanocomposite polymeric membranes. In particular, we are interested in the effect of mechanical deformation on the diffusion process. In recent Ph.D. dissertations, students considered the effects of imposed deformations on the barrier properties of polymers used in the protective clothing, geomembrane and packaging industries. This work involved designing the apparatus shown in Figure 1, developing mathematical models relating mass flux to time via mesoscopic as well as continuum mechanics theories, performing tests using representative organic chemicals and mixtures thereof and successfully comparing the data with the model predictions.

 Figure 1Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Figure 1. Apparatus forelongatingpolymeric membranes. 1: Mobile heads, 2: Fixed heads, 3: Screw system, 4: Inlet and outlet ports of the permeation cell, 5: Bottom hemisphere of the permeation cell, 6: Membrane sample location.

Our work on rheometry recently resulted in a major contribution in the area of yield stress measurements in suspensions. This work involved the construction of a slotted plate device, shown in Figure 2, to measure the static yield stress of suspensions. A finite element analysis justified the assumptions upon which the measurements are based. We are now in a position to determine yield stress values as low as 10-4 Pa, a ten thousand fold improvement over the nearest competing technique.

Figure 2. Apparatus for measuring suspension yield stress using a slotted plate. The experimental setup involves an analytical balance, a step motor, a linear motion stage and acustomized data acquisition system.

More recently, we proposed a double concentric cylinder rheometer with slotted rotor to reduce wall slip effects associated with rheological measurements of complex structured (yield stress) fluids. The reduction of wall slip effects is being numerically investigated via computational fluid dynamics (CFD) simulations. The results of this study indicate that the slotted rotor design can measure the fluid properties with enhanced accuracy and less sensitivity to the wall slip velocity than a rheometer with a solid (non-slotted) rotor. We also show that the wall slip effects can be further reduced by either increasing the slot ratio or by adding slots to the rotor. This work illustrates that CFD analysis can be a powerful tool in rheometer design.

Figure 3. Computation domain of the proposed design and the CFD mesh scheme.

Figure 4. Cross sectional view of the shear stress distribution in a rheometer with a solid (non-slotted) rotor and a slotted one. S denotes the slot area ratio and N denotes the number of slots. δ refers to the slip length. τ is the shear stress magnitude defined as the second invariant of the shear stress tensor. Larger slip length indicates stronger wall slip.

Polymer – clay nanocomposites are being studied in the polymer processing laboratory. Such materials are lightweight and exhibit excellent mechanical as well as barrier properties.

Figure 5. TEM picture of exfoliated Cloisite©20A / MB100D nanocomposite (5 wt.% clay), prepared in the polymer processing laboratory, via a twin-screw extruder at 190 oC and 200 rpm. MB100D is maleic anhydride grafted high density polyethylene

Figure 6. TEM picture of intercalated Cloisite©30 B /Poly(dimethylsiloxane) (PDMS) nanocomposite (5 wt.% clay).

300 Lindy Boggs Center, Tulane University, New Orleans, LA 70118, T: 504-865-5772, F: 504-865-6744