Rheology of synthetic and natural materials, constitutive equations, transport phenomena and applied mathematics.
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 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.
Polymer – clay nanocomposites are being studied in the polymer processing laboratory. Such materials are lightweight and exhibit excellent mechanical as well as barrier properties.
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
TEM picture of intercalated Cloisite©30 B /Poly(dimethylsiloxane) (PDMS) nanocomposite (5 wt.% clay).
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