Construction of a unique dough extension rheometer
Eric Lindskog¹, Tam Sridhar², Alan Oppenheimer¹, and Sumana Chakrabarti^1
1General Mills Technology, Minneapolis, MN 55414; ²Department of Chemical Engineering, Monash University, Clayton, Victoria, Australia

Extensibility may be the most important property for assessing dough quality. However, to obtain true measures for extensibility, dough should be stretched at constant stretch rates, which means the extensional velocity has to increase exponentially with time. We have built such a rheometer for dough testing. Controlling motion for a high speed, linear motor generally requires expensive automation controllers. For our lab scale instrument with flow visualization capabilities, National Instruments hardware and Labview software were used to create an inexpensive solution with complex motion capabilities. A simple PC was used to integrate all functions including motion control and data acquisition. The presentation will cover the hardware and software used, the programming process, the functionality of the machine and the results of comparison of test data with an external laboratory.

Micromechanics of self-assembling peptides studied through multiple particle tracking
Thierry Savin and Patrick S. Doyle
Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

We use multiple particle tracking to investigate the micromechanics of a self-assembling polypeptide. The probe microspheres are dispersed in the mixture to monitor the formation of the biological hydrogel in real-time. We report individual studies of the probes at different gelation times that show the evolution of spatial heterogeneity in the gel. Time averaging is performed on these individual tracks to analyze local structural and micromechanical properties. We observe two distinct classes of probe motion. We compare the local diffusive probe data to bulk rheological measurements and AFM studies of fiber formation.

Shear rheology of fluoropolymers in the melt and solution states
Nafaa Mekhilef¹ and Cattaleeya Pattamaprom^2
1Research and Development Center, Atofina Chemicals, Inc., King of Prussia, PA 19406; ²Chemical Engineering, Thammasat University, Bangkok, Thailand

This work presents an investigation of the rheological behavior of poly(vinylidene fluoride) in the molten and solution states. Shear data generated in small amplitude oscillatory and transient modes showed a peculiar behavior reflected in the zero-shear viscosity molecular weight correlation. The scaling factor of h₀~M_w was found to be 6, much higher than the experimental value of 3.4 found for most linear polymers. Further analysis using the time-temperature superposition principle showed a correlation between the activation energy and molecular weight. Inherent viscosity measurement performed on dilute solutions showed a Mark-Houwink constant of 0.7 indicating a linear-type structure in PVDF. In the concentrated solution regime, the zero-shear viscosity molecular weight correlation resulted in a slope of 3.4 in agreement with literature data for linear polymer melts. However, it was also found that by aging the solutions for long periods of time resulted in an increase of the slope indicating the formation of strong chain interactions especially between the fluorine and hydrogen atoms. These interactions are responsible for the peculiar behavior in the melt as well as the dielectric properties of PVDF yet no effect is observed on the plateau modulus.