Q. I've seen a device similar to the SER being
marketed by another instrument manufacturer. What's the difference between
the SER and this other fixture?
A. This answer requires a brief background...
Development of the SER technology first began
in 1997 with the pioneering work of Dr. Martin Sentmanat at the Goodyear Tire &
Rubber Company in Akron, OH. This revolutionary dual wind-up drum rheometer
technology was patented by Goodyear
and later licensed exclusively to Xpansion Instruments, LLC. Since its
introduction back in 2003, the SER has generated a tremendous amount of interest
not only in the global rheological community but in the physical material
characterization community as well. In 2004, another instrument manufacturer
looking to capitalize on the breakthrough success of the SER
launched an imitation technology similar in appearance to the original model SER-HV and began
marketing the device as an extensional viscosity fixture for an ARES rotational
rheometer. Although this imitation technology has the identical drum dimensions,
securing means, and sample geometry of the original model SER-HV, it has serious shortcomings and
is far less capable.
The SER's significant performance advantages are summarized on a dedicated page
(click here to learn more).
Q. How do you
control the strain rate and is it possible to measure it during the
A. For many homogeneous and soft materials,
the applied strain rate is EQUAL to the true
strain rate. This has been verified
for Hencky strain rates up to 20+ s-1 using stop frame videography
(laser micrometers have also been used in the past). Unlike the
stretching means incorporated by other melt extensional rheometers,
SER sample deformation remains in a fixed plane and is
clearly visible AT ALL TIMES, and
with each incremental drum rotation the sample becomes
less and less likely to slip during stretching. For very high
modulus materials (solids and cured
elastomers), the use of a thin double-sided adhesive (such as carpet
tape) or sandpaper strips have been found to be very effective in
preventing slip during a stretching experiment, and thus you can get
the true strain rate to EQUAL the applied strain rate even for high
Q. Is the SER sensitive/reproducible enough to
distinguish between good and bad polymer samples for quality control purposes?
A. As described on our
Principle of Operation page, uniaxial extensional is the "strongest" flow
field one can generate. Because of the high level of reproducibility and the
degree of molecular orientation and chain
stretch that can be achieved with the SER, extensional rheology measurements
with the SER are ideally suited for distinguishing subtle differences in
molecular architecture, examples of which are provided on our
mode of operation page.
Q. How do you compensate for “sag” and
gravity effects in the case of low viscosity samples?
minimum recommended sample viscosity for extensional
characterization with the SER is a zero-shear viscosity of 10,000
Pa-s when operated under a gas environment.
For molten polymers with such a viscosity, the operator has to
work rather quickly (approx. 60-90 seconds after sample loading in
the pre-heated oven) to prevent any large effects due to sag. Unlike other
extensional melt rheometers, the SER has a small distance between
points of contact (1.27 cm) and holds the sample on its side instead
of flat such that the width dimension of the sample actually deters
sagging to a large extent due to the increased moment of inertia
with regard to sample/beam flexure. As witnessed by the excellent
superposition between the low strain portions of the tensile stress
growth curves and the LVE shear stress growth curves presented in
Rheology Results section, sag is typically not an issue for
materials with a zero-shear viscosity above this recommended value
of 10,000 Pa-s.
Because both of the detachable drums are cantilevered and suspended
from the SER3 base chassis, the
SER3 models that are configured for
use on controlled stress/strain rotational rheometers such as the
SER3-P, SER3-G, SER3-T, and SER3-M are capable of fluid immersion
testing. The drums of said SER3 models can be raised from and lowered
into a controlled temperature fluid environment contained within a
jacketed beaker or other such fluid containment vessel.
Applications include biomaterials testing as well as high-temperature
silicon oil bath testing to eliminate any effects associated with
molten sample sag at low viscosities.
Q. Does the air flow in a forced convection oven disturb
the measurements at low rates?
A. Hencky strain rates as low
as 0.00001 s-1 have been run with no problems due to air flow in most forced
convection environmental chambers.
Q. What size of sample is needed?
It depends on the mode of deformation being employed with the SER, but thin, narrow samples
are recommended for uniaxial modes of operation in order to ensure that the deformation mode
remains purely uniaxial. In general, the more elastic in nature the material, the thickness and width
of the sample should tend towards the mid to lower scales of the recommended sample dimension ranges.
The following is the recommended range of sample sizes for
use on the SER:
Minimum Length = 15 mm
Width = 1 - 12.7
Thickness = 0.005 - 1 mm
Mass = 5 - 200
Q. What is the maximum reachable Hencky
strain with the SER?
A. One complete drum rotation
corresponds to a Hencky strain of 5, however, beyond a Hencky strain
of about 4 the sample begins to overwrap the securing clamps and the
previously wound sample. With proper care, the SER can be
operated well beyond a single drum rotation with little to no
problem for molten polymers with large extensability. If the polymer
does survive to such strains, sample overwrapping typically does not
affect the torque signal by an appreciable degree and is usually
observed as a brief perturbation in the torque signal as the sample
overwraps the securing clamps. Usually by this
point either the polymer has reached its plateau viscosity or the sample
has already initiated its failure mode. At high rates
(>1 s-1), most melts will rupture prior to sample
Q. What happened to the XIM Miniature Mixer Attachment
for the SER?
A. Due to a lack of customer interest,
our XIM product line was discontinued along with the retirement of our SER2 model line.
Q. What happened to the friction armature attachment
for the SER?
A. Due to a lack of customer interest and in an effort to reduce retail costs to our customers,
the friction measurement attachments are no longer included with our standard SER Universal Testing