Advanced Rheometric Expansion System (ARES-LS) (TA Instruments)
The ARES-LS is a controlled strain rotational rheometer as well. It is essentially an older version of the ARES-G2 and is used when the ARES-G2 is busy and vice versa. In addition to all the usual geometries such as stainless steel parallel plates and cone & plate geometries of different diameters and cone angles, we have a special addition to the rheology arsenal, the cone-partitioned plate. The cone-partitioned plate is used to delay edge fracture to extend the range for non-linear viscoelastic rheology measurements.

Discovery Hybrid Rheometer DHR-3 (TA Instruments)
The DHR-3 is a controlled stress rotational rheometer. The Discovery HR-3 (DHR-3) is frequently used for rotational and oscillatory measurements of soft and stiff materials. The minimum oscillation and steady-shear torque of the DHR-3 are lower compared to other TA Instrument’s Discovery Hybrid rheometers, which allows precise characterization for low-viscosity fluids and solutions as well as soft materials. Using the purge gas cover, we introduce nitrogen into the sample area to avoid condensation during the test, especially at low temperatures. The temperature control system that is installed on our DHR-3 is the Peltier Plate which provides a wide temperature range from -40 °C to 200 °C.

Advanced Capillary Rheometer, Rosand RH7/10 (NETZSCH)

The capillary rheometer is based on pressure driven flow of polymers through a channel, where in this case the channel is a barrel. It is extremely important for industrial samples as it leads to flow that occurs most often in melt processing, for example in an extrusion die of the runner feeding in an injection mold.

RH10_SOP Form

Shear-Induced Polarized Light Imaging (SIPLI) Rheometer, Modular Compact Rheometer (MCR) 502e (Anton Paar)

The MCR-502e is a controlled stress rotational rheometer. It is essentially the DHR-3 equipped with a polarizer, analyzer and a camera to record the birefringence during shear in the bottom cavity with a quartz plate as a window to the sample. Using the SIPLI the overall behavior of polymers can be detected via changes in the birefringence properties of a material. For example, birefringence occurs due to the flow-induced orientation of polymer chains in polymer melts which creates optical anisotropy.

Polarized Optical Microscopy (POM), Leica DM750P Microscope and DMC2900 Camera

Polarized light microscopy (POM) is a used to image birefringent materials. The polarized light microscope is used to image our polymer samples that are visible primarily due to their optically anisotropic character. The microscope is equipped with both a polarizer, positioned in the light path somewhere before the specimen, and an analyzer placed in the optical pathway between the objective rear aperture and the observation tubes or camera port. The SIPLI is based on the same setup. But imagine the SIPLI is a horse carriage and the Leica Microscope is a McLaren 750S.

Our POM also has a hot stage as an accessory that allows us to monitor thermal transitions like crystallization & melting under a microscope. We can also use a shearing hot stage, based at Penn State Behrend, for getting a visual of what happens during flow-induced crystallization.

Submissions for Materials Visualization Contests by the Colby Group using POM

“POLARIZED OPTICAL MICROSCOPIC IMAGE OF FLOW-INDUCED CRYSTALLIZED NYLON 6/6 AFTER IMPOSING A SHEAR FLOW AT 10 1/S FOR 60 SEC.“

Jiho Seo, Graduate Student, Materials Science and Engineering

SECOND PLACE (MVC 9)

Scientific Process: When a semi-crystalline polymer melt is subjected to flow or deformation prior to crystallization, the nucleation rate is accelerated and the crystal morphology changes from spherulites to anisotropic
structures. These phenomena are called flow-induced crystallization (FIC). The flow-induced morphological transformation of Nylon 6/6 was observed using polarized optical microscopy. A Nylon 6/6 sample, which was fabricated
using 16 mm parallel plates with a shear rate of 10 1/s for 60 s at 270 C, exhibited a mixture of anisotropic cylinderites and smaller spherulites at the edge of the disc.

“Hi, I’m semi-crystalline PEO…”

Arshiya Bhadu, Graduate Student, Department of Materials Science and Engineering 

MVC 16

Artist’s Perspective: I primarily research polymer rheology with a focus on flow-induced crystallization of commonly used polymers. Rheology as a stand-alone is never proof enough, so I ventured into the world of polarized optical microscopy to couple birefringence with my rheology results. Crystals by nature are highly birefringent and I have loved playing around with PEO to understand the fundamentals of crystallization and am exploring all kinds of crystal orientations. The semi-crystalline domain shown here is part of a bigger landscape of interconnected crystals in a sea of amorphous PEO, much like how the 7 continents of the world are comprised of multiple interconnected country domains in a sea of water. This domain of semi-crystalline PEO coincidentally looked so much like Mickey Mouse, and immediately brought back a wave of forgotten memories of my childhood when I used to watch Disney shows. And the accompanying commercial breaks (when people still watched Cable Channels) where the character’s introduction always ended with, “…and you’re watching Disney Channel.” I hope it brings back fond memories for you as well.

Scientific Process: Semi-crystalline polymers crystallize in the form of small spherical domains, called spherulites. The spherulites impinge on each other as they grow losing some of their spherical nature over time, leading to interesting semi-crystalline domains. Here we can see crystal growth in a blend of a low molecular weight PEO + 3 wt% of an order of magnitude larger molecular weight PEO; both are monodisperse. There are three spherulites in the image, where the two smaller spherulites along the edge nucleated off the big one in the middle at a later relative time and hence are smaller in size. Since this was an isothermal crystallization experiment, the two smaller spherulites heterogeneously nucleated off the outer crystal phase of the middle spherulite. Adding even a small percentage of long chains to a neat lower molecular weight PEO sample leads to a different phase of crystal growth as noted by the rings on the outer perimeter of the spherulites.

“Bacterial Cellulose as a Honeycomb Mountain”

Noël McClellan, Undergraduate Student, Department of Materials Science and Engineering

Artist’s Perspective:When I first started looking at the birefringence in both the rheometer and microscope my expectations were low, and I was continually surprised by what I saw. The ability to see a property that had seemingly disappeared in solution to be brought back is almost an impressive show of nature’s tendencies to revert to its basis on a fundamental level. The picture I chose particularly reminded me of honeycomb.

Scientific Process: The image is of bacterial cellulose in a polarized light optical microscope. The cellulose was initially dissolved in the Ionic Liquid (IL) – BMImCl. The sample shown was first sheared using a cone and plate geometry in a DHR3 rotational rheometer. After shearing the plates were washed with water to remove the BMImCl leaving a cellulose gel that was placed on a slide and imaged in a polarized light microscope to see birefringent regions of cellulose that are not present in the BMImCl – Cellulose solution. Images were taken over the course days to see an increase in birefringence, as the cellulose dried further. Cellulose is inherently birefringent, but processing cellulose without degradation from solvents is difficult, and ILs are non-degrading anhydrous solvents. IL-Cellulose solutions have a complex rheology that can make it difficult to determine dissolution vs degradation, but retaining birefringence is a good indicator that the cellulose structure has not degraded.