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S u m m e r 2 0 0 1
New Products —Thermal Analysis
Rheology
TECH Talk
AR 2000 with Mobius Drive™System – A Versatile High
Performance Research RheometerGeorge Dallas and Raoul Smith
The TA Instruments AR 2000 with Mobius
Drive™ system is an advanced
research rheometer that delivers
not only unsurpassed controlled
stress performance, but also
capability comparable with ded-
icated rheometers in controlled
rate measurements.
Scientific Optimization ofThermoset Formulations
Mike Reading, Loughborough University & Liz Colbourn, Oxford Materials UK
Thermosets are one of the most important
categories of polymer systems and yet, in
many cases, there remain significant gaps
in our understanding of how to improve their
properties. Some of the most important
parameters for a cross-linking system are
gel point, cross-link density and pendent
fraction (material that ‘hangs off’ the cross-
linked material but does not contribute to
the elasticity).Full Story Full Story
Featured Technical Articles
Improved DSC Performance UsingTzero™ Technology
G. Dallas, J. Groh, and T. Kelly
Tzero™ is a new Differential
Scanning Calorimetry (DSC)
technology that provides
materials scientists with a fundamentally
more accurate and comprehensive way of
measuring heat flow. The heart of the
technology is the revolutionary Tzero™ cell
that makes more measurements than ever
before, and delivers superior performance
in both heating and cooling modes.
The new technology is implemented in
TA Instruments Q Series™ DSC Modules
(Q1000, Q100, Q10).Full Story
Buy One...Get One
3 REAL RHEOLOGY DEALS
New ProductLiterature
New Staff atTA Instruments
Conferences &Exhibitions
FREE Posters –Rheology
Thermal Analysis
New Products - Thermal Analysis
TA Instruments' latest development, Tzero™ technology, is a
revolutionary approach to DSC that provides a fundamentally
more accurate way of measuring heat flow. It offers significant
improvements in baseline flatness, resolution and sensitivity,
direct measurement of heat capacity, and faster and more
accurate Modulated® DSC experiments than ever before.
Three new and exciting modules (Q1000, Q100, Q10) are now
available that combine the best features of heat flux and power
compensation designs but advance performance to levels
previously unattainable. Customer response to date has been
excellent, and over 150 of these new systems are already
installed in customer laboratories worldwide.
Complementing them are the new Q500 and Q50 high
performance thermogravimetric analyzers. The former is our
top-of-the-line research-grade TGA. Its efficient low mass
furnace, ultra-reliable thermobalance, unique purge gas sys-
tem (with digital mass low control), and advanced automation,
make the Q500 well equipped to handle TGA applications,
from routine to the most demanding.
The Q50 is a cost-effective, easy-to-use, general-purpose thermogravimetric analyzer with many of the basic features of
the Q500. It is ideal for laboratories that need a high quality TGA for standard applications.
See the "Products" section of our website www.tainst.com for more information and to download brochures and
technical papers.New Products–Rheology HOME
New Products - Rheology
New AR 2000Our new AR 2000, with its innovative Mobius Drive™ system, wide
torque range, superior strain resolution, and Smart Swap™ technology,
represents the world's most advanced research rheometer. Mobius
adds capability comparable to dedicated controlled rate rheometers
to its outstanding performance in controlled stress operation. This
seamless mode selection to fit the desired experimental conditions,
offers for the first time, a single rheometer that delivers the
performance, flexibility, and cost effectiveness needed to meet the
most demanding requirements of a busy research laboratory.
Smart Swap technology permits unprecedented ease of interchange between available temperature control systems.
Turn-around times and costs involved are often a fraction of that required by competitive systems, especially when
converting to concentric cylinder systems.
These and other features make the AR 2000 the most complete research rheometer commercially available. For more
information on the AR 2000 with Mobius Drive connect to our website www.tainst.com/products/ar2000.html.
Rheology Advantage SoftwareWe are pleased to introduce the latest version of Rheology Advantage software designed to compliment the high
performance AR Series rheometers. Many of its new and exciting features were created in response to customer input.
The result is intuitive, quality software that more than meets the challenges of today's modern laboratory.
Rheology Navigator SoftwareNavigator is an optional intelligent software package that automates all features of
Rheology Advantage instrument control and data analysis. Navigator can also make
intelligent decisions about experimental steps and data analysis, based on previously
obtained results.
FUTURE NEW PRODUCT
21 CFR Part 11 Compliant SoftwareThermal Advantage and Rheology Advantage Software will be enhanced to become compliant with the latest FDA
regulations contained in 21 CFR Part 11. Thermal Advantage will be compliant by year-end 2001 and Rheology Advantage
by March 2002.New Products–Thermal Analysis HOME
RHEOLOGY NAVIGATOR•RHEOLOGY
NAVIGATOR•RHEOLOGYNAVIGA
TOR
Tech Talk
This section will provide technical notes, helpful hints, and service advice, and specific information on thermal analysis and
rheology instrumentation and use. The goal is to help you get maximum value from your TA Instruments equipment.
Thermal Analysis
InformationA new 2001 edition of American Society for Testing and Materials (ASTM) Practice for Calculation of Hazard Potential
Figures-of-Merit for Thermally Unstable Materials (E1231) has been released (see http://www.astm.org). Four (4) new
hazard potential tools are added to this Practice, including explosion potential, shock sensitivity, instantaneous power
density, and NFPA instability rating. These new terms plus the traditional ones of time-to-thermal runaway, critical half
thickness, critical temperature, and adiabatic decomposition temperature rise are all determined using DSC data. The
Thermal Stability Kinetics software, included in the TA Instruments' Specialty Software Library, includes the calculation of
all eight (8) of these figures-of-merit. Contact your TA Instruments Representative for more details.
HintDSC and TGA experiments often benefit from the use of finely divided samples. A large surface
area (provided by small particle size) enhances outgassing from thermoset cure or decomposition
thermal events. Grinding samples in a cryogenic mill provides small sample size without affecting
the thermal history of the sample. One source of a cryogenic mill suitable for this purpose is SPEX
Certiprep, Inc. Contact them at their website (http://www.spexcsp.com) for information on their
Freezer/Mill product. (Source: Larry Upchurch, S & C Electric)
HintWhen performing DSC kinetic analysis, it is assumed that the sample temperature is being
controlled by the temperature programmer and that no self-heating occurs. Self-heating results
when the energy of the reaction increases the sample temperature through its heat capacity
(T = H/Cp). Adjusting the sample size such that the peak heat flow is less than 8 mW normally
ensures that no self heating takes place. (Source: Roger Blaine, TA Instruments)
Rheology
Technical DocumentsAn informative three page article on how to set up and operate an AR Series rheometer (AR 2000, AR 1000, AR 500)
written by Fred Mazzeo of our rheology applications staff. read document
A second document by Mazzeo entitled "How to Analyze an Unknown Sample" is also available for download.
This outlines experiments in flow, steady state flow, creep and oscillation modes that will be useful for inexperienced users
of the AR Series rheometers. read documentHOME
New Product LiteratureA new TA Instruments Rheometer brochure (RH075A) is now available.
Contact TA Instruments to order a copy, or download one from our website.
HOME
New Staff at TA Instruments
Dr. Bruce Cassel, a well-known thermal analysis expert, has joined TA Instruments as a Senior
Marketing Associate. Bruce holds a Ph.D from Clark University, and brings nearly 30 years experience
in thermal analysis applications, instrument development, and product management as part of the
Perkin-Elmer organization. He is the author of more than 75 journal articles, a Fellow of the American
Society for Testing and Materials (ASTM), and a long time member of the North American Thermal
Analysis Society (NATAS). Bruce played an active part in the successful launch of the new Q Series™
DSC Modules with revolutionary Tzero™ technology. We welcome Bruce and look forward to his many
contributions to our business.
Dr. Abel Gaspar-Rosas has recently joined TA Instruments as an International Sales Manager,
with responsibility for Latin America and part of South East Asia. Abel is an experienced rheologist and
was for many years Latin American Sales Manager and Technical Director for Paar-Physica. He is well
known in Latin America, where he has lectured extensively at rheological conferences. Abel received an
MS (Electrical Engineering) from the University of the Americas (Mexico), and his Ph.D in Biomedical
Engineering from the University of Texas. We welcome Abel and look for him to play an important part
in our international business.
HOME
Major Conferences and Exhibitions
North American Thermal Analysis Society 2001 Short Course & ConferenceAdams Mark Hotel, St. Louis, MO, USA
Short Course – September 22-23; Conference – September 24-26
The Conference consists of 11 Symposia, a General Session, a Poster Session, a Tutorial
Session, plus an Instrument Exhibit and the Annual Awards Banquet.
For more technical and registration information on the NATAS Short Course and
Conference call 916-922-7032, or connect to www.natasinfo.org.
TA Instruments fully supports NATAS and encourages our users and prospects
to attend. Our NATAS contribution will be:
•Ten technical papers
•Host a "working lunch" (Tuesday, September 25), where Dr. Roger Blaine
will discuss some recent advances in isothermal crystallization.
•Exhibit the new Q Series™ DSC and TGA thermal modules, plus the
AR 2000 Advanced Rheometer.
•Present a Modulated DSC® training course in the hotel immediately
following the conference (September 26-27).
The MDSC course fee is $195 for NATAS attendees, $295 for
non-NATAS attendees, and $50 for students. This course is always
well attended, so to assure your place, register early at our website
www.tainst.com.
Society of Rheology (SOR)The 73rd Annual Meeting will be held at the Hyatt Regency Hotel (Bethesda, MD, USA) from October 21-25, 2001. The
technical program will consist of 10 Symposia, a General Session, a Poster Session, and a Tutorial Session.
The conference features an instrument exhibit and a banquet. For further information on registration and the technical
programs, connect SOR directly at www.rheology.org.
TA Instruments will be exhibiting our latest AR Series Rheometers, and look forward to meeting with you at the conference.
HOME
AR 2000 with Mobius Drive™ System – A Versatile High Performance Research Rheometer
George Dallas and Raoul Smith
The TA Instruments AR 2000 with Mobius Drive™ system (Figure 1) is an advanced research
rheometer that delivers not only unsurpassed controlled stress performance, but also
capability comparable with dedicated rheometers in controlled rate measurements.
This flexibility is valuable and cost-effective in a busy research laboratory, since high
performance measurements in either mode are now possible.
Controlled rate and controlled stress represent the historical
approaches to rotational rheometer design. In the former, a
displacement or speed (strain or shear rate) is applied to the
sample and the resultant torque (stress) is measured by a
separate transducer. In the latter, a torque (stress) is applied
to the sample, and the resulting displacement (strain or shear rate) is measured. While
for many experiments, the results should be independent of the rheometer type, certain
material properties are often better, or more easily, characterized by a particular mode.
Controlled stress rheometers are often the choice for measuring viscoelastic properties of dispersions (especially
weakly structured ones), for measuring apparent yield stress, and for analysis of materials whose use involves stress
driven processes (sagging, sedimentation, leveling). Creep and recoverable compliance measurements are also
synonymous with controlled stress rheometers. The smooth torque generation from the "drag cup" motors commonly
used in these rheometers produces quality data at shear rates several orders of magnitude lower than available from
controlled rate models.
In contrast, tests specifically mimicking industrial processes involving high shear rates (e.g. stirring), may be better
performed on a controlled rate rheometer, assuming the resulting torque (stress) is measurable. Rheological analysis of
polymer melts including stress relaxation (step strain) has also traditionally been done in this mode.
Faced with a variety of complex analyses to perform, rheologists have long desired a research rheometer capable of per-
forming high performance measurements in both modes. Over the last decade, attempts have been made to address this
matter, either by the development of "hybrid" motors, or by utilizing modern electronics and computer control to simulate
"fast loop" controlled rate operation in a controlled stress instrument.
TA Instruments’ extensive design experience has culminated in the AR 2000 Advanced Rheometer, whose Mobius Drive
combines the two classical approaches in rheometry into a "seamless" system that provides high performance and mode
flexibility. It allows the rheologist to focus on testing for performance and system response (real world situations), since the
AR 2000 automatically engages the drive as required by the experimental conditions. The Mobius system incorporates an
ultra-low inertia motor and triple air bearing, coupled with a 2,000,000: 1 torque range, and high-speed electronics.
Extensive evaluations have proven its ability to swiftly and accurately respond and track changes in input speed or posi-
tion comparable to that of dedicated high performance controlled rate rheometers. Figure 2 shows the AR 2000’s ability to
perform rapid step changes in shear rate (angular velocity) needed to model thixotropic behavior and to control the shear
rate through a ramp. The data is typical of that expected from a good controlled rate rheometer.
(continued)
Figure 1
The ability to perform stress relaxation experiments has also been
synonymous with controlled rate rheometers. However, the limited
torque range transducers normally used, often result in rapid disappear-
ance of the measured data into the noise. With its large torque range, the
AR 2000 actually improves upon data from controlled rate rheometers. It
not only reaches the set strain in a comparable time, but also extends the
G(t) data well beyond the time where data from the controlled rate device
would become too noisy for accurate measurement. Figure 3 shows
stress relaxation data from a PDMS sample. The overall test results
clearly establish that the AR 2000 has capabilities necessary for quality
measurements in the controlled rate mode. Preliminary data also
indicates that the response of the Mobius Drive™ system to input speed
and position control commands, and the quality of stress relaxation data
generated, appear superior to that from the "hybrid" motor approach.
The implementation of the Mobius Drive™ has not compromised the
excellent controlled stress performance of the AR 2000. For example,
creep (step stress) data can be acquired as fast as a point every
millisecond, and used to reveal interesting short timescale sample
properties. Gels and emulsions can show "ringing" behavior (Figure 4)
that can be modeled to derive viscoelastic parameters from less than
1 second of data.
These results show that the AR 2000 with Mobius Drive™ system has
the performance and mode flexibility necessary to meet the needs of the
professional rheologist. With its powerful, yet easy-to-use Rheology
Advantage software, and unique Smart Swap™ interchangeable
temperature control systems, the AR 2000 is arguably the most complete
research rheometer commercially available.
Scientific Optimization of Thermoset FormulationsMike Reading, Loughborough University & Liz Colbourn, Oxford Materials UK
Thermosets are one of the most important categories of polymer systems and yet, in many cases, there remain significant
gaps in our understanding of how to improve their properties. Some of the most important parameters for a cross-linking
system are gel point, cross-link density and pendent fraction (material that ‘hangs off’ the cross-linked material but does
not contribute to the elasticity). However, in many commercially important systems it is very difficult to determine these
parameters. Without the predictive ability that such knowledge provides, formulation can be a lengthy trial and error
process that may not lead to the optimum solution. As a general rule, approaches based on a more complete
understanding of the underlying science leads to better products.
Fortunately, the thermoset chemist has powerful tools that he can use to better understand his systems. DSC can provide
detailed information on cure kinetics. The TA Instruments Kinetics software is available to help measure these kinetic
parameters and to use them for predicting extent of reaction as a function of time and temperature (the cure schedule).
This combination of characterisation tool (DSC) and modelling software is very useful because it means the experimenter
does not have to carry out endless experiments to try out all of the possible cure schedules. A few experiments plus the
right software can save a great deal of time.
Similarly, DMA can be an excellent technique for measuring the gel point and subsequent build-up of cross-link density.
Alternatively, rheometers can give the same type of information. So, the combination of DSC with DMA or a rheometer can
enable the formulator to understand how gel point and cross-link density are related to extent of cure but only for a given
system. Once any part of the formulation is changed this relationship is changed meaning that the new formulation must
be recharacterized. The missing part of the jigsaw is a tool that provides the link between the components of the resin
systems (polymers, cross-linking reagents etc.) and the gel point and cross-link density growth.
Today there is an easy-to-use computer program, DryAdd, that enables anyone to relate formulation ingredients
(i.e. changes in polymer and cross-linker composition) to gel point and cross-link density and, therefore, to end-use
performance. In some cases it also even enables the kinetic information from DSC to be incorporated to provide a
complete predictive package. It also provides information on the pedant fraction. DryAdd uses a Monte Carlo simulation,
selecting groups at random and seeing whether they can, and will, react on each individual collision. In this way, it
models the inherent randomness of chemical reactions. DryAdd was pioneered by Mike Reading and Tyson Gill in ICI to
provide a versatile but simple approach to complex systems to predict what happens during the cure process and to help
to interpret the results from thermal analysis and characterization studies. Figure 1 shows a typical Materials input screen,
based on easy to use spreadsheet principles, together with the predicted output showing the gel point and cross-link
density build up. Conversion is determined with respect to all groups - including the hydroxyl and oxy species made by ring
opening - so it can go beyond 100% when compared to the original number of groups in the system.
Here, we report on recent work that combines TA Instruments thermal analysis techniques with DryAdd's network models
to understand the evolution of cross-linking in a structural epoxy. Network models can predict the gel point and the
evolution of cross-link density - and hence mechanical properties - post cure. Kinetic models can predict the extent
of chemical reactions as a function of time and temperature. So, combining the two gives a model that predicts evolution
of cross-link density - a model that is a valuable tool for exploring the effect of formulation and processing changes.
Our study was undertaken for the UK's Defence Evaluation Research Agency, and looked at an epoxy thermoset made up
of MY750 resin with a hardener (phthalic anhydride) and an accelerator (a tertiary amine) with the proportions by volume
100:85:2. The amine will ring-open both the epoxide and the anhydride, producing charged oxy and carboxy groups.
(continued)
These act catalytically to open more rings
in a chain reaction. In addition, hydroxide
groups are present, and these can react
with the anhydride, acid and epoxy. The
reaction scheme is very complex, with
about 25 reactions taking place simultane-
ously. Fortunately, DryAdd has a facility
for setting up most of the reactions auto-
matically. Alternatively, the user can take
advantage of its 'generic groups' capability
to assign similar reactivities to similar
groups. As Figure 2 shows, this simplifies
the reaction scheme considerably. In our
study, we made the simplest assumption
that all reactions have the same relative
rate. In reality, many systems are insensi-
tive to changes in the relative rates and in
this case, as we shall see below, this sim-
ple approach proved adequate. However,
where the chemist suspects differences
are important, they can quickly carry out try-and-see simulations to determine which are the key reaction rates and then
measure their kinetics using ‘model’ trial systems. In this way greater insights into the important factors that determine
product performance can be gained in a systematic and scientific way.
A TA Instruments 2920 DSC was used to evaluate the kinetics using multiple heating rate method provided by the
TA Instruments kinetics software package, TS Kinetics. Figure 3 shows the DSC traces and figure 4 shows the Arrhenius
plots for different extent of reaction. Using this information, extent of reaction can be predicted for a given cure schedule.
(continued)
Figure 1. A DryAdd Materials Input screen for an epoxy thermoset,
with plots of results
Figure 2. Reaction scheme assuming that all reactivities are the same.
L/G refers to loss or gain of molecular weight - here due
to formation of water
We carried out an initial simulation that
gave a prediction for the onset of gelation
and how cross-link density would change
with extent of cure. This was tested by
carrying out a DSC and a DMA experiment
under identical conditions. Using the data
from both of these experiments we can
plot gel point and storage modulus from
the DMA against extent of reaction from
the DSC. As shown in figure 5 the agree-
ment between the experiment and the
DryAdd prediction is close, certainly suffi-
cient to guide the formulator. When the
complexity of this system is considered
and the small number of fitted parameters,
this degree of agreement is remarkable.
With this confirmation of the applicability of
the DryAdd approach, the formulator can
proceed to alter formulation variables,
such as relative quantities of polymers and
other components, to investigate how
these changes affect gel point and how
cross-link density changes with extend of
reaction. The TAI Instruments software
can be used to predict how extent of cure
changes with time and temperature.
DryAdd can predict the gel point and
cross-link density as a function of cure.
Together they can provide the complete
predictive tool.
(continued)
Figure 3. DSC results at different heating rates
Figure 4. Arrhenius plots from TS Kinetics Software
Figure 5. Comparison of DryAdd
predictions (blue line) of cross-link density
against conversion and measurement
from DSC and DMA (pink dots) at heating
rate 3 degrees/minute
DryAdd also provides a wealth of other
information such as pendant fraction,
Mw distributions, monomer sequencing,
reaction product concentrations - a com-
plete understanding of the polymer
architecture can be built up. You can
find out more about DryAdd on
http://www.oxmat.co.uk where exam-
ples of other applications are given. Figure 5.
Improved DSC Performance Using Tzero™ TechnologyG. Dallas, J. Groh, and T. Kelly
Tzero™ is a new Differential Scanning Calorimetry (DSC) technology that provides materials
scientists with a fundamentally more accurate and comprehensive way of measuring heat flow.
The heart of the technology is the revolutionary Tzero™ cell that makes more measurements
than ever before, and delivers superior performance in both heating and cooling modes. The new
technology is implemented in TA Instruments Q Series™ DSC Modules (Q1000, Q100, Q10).
DSC is a materials characterization technique, whose measurements include heat capacity, glass transitions (Tg), melting,
crystallization, phase changes, curing processes, and onset of oxidation. The traditional approaches in DSC cell design
are heat flux and power compensation. The former, pioneered by TA Instruments, is used by most suppliers, and offers
superiority in baseline stability and sensitivity, while the latter design is recognized for resolution and fast heating / cooling
capability. Tzero technology incorporates the best attributes of both designs, and elevates performance to unprecedented
levels.
In the traditional heat flux design, a pan containing the sample and an equivalent empty one for reference, are set on
identical platforms on a thermoelectric disk surrounded by a controlled temperature furnace. As the furnace temperature
is programmed, heat is transferred to the sample and reference through the disk. Differential heat flows to and from the
sample and reference are measured by identical chromel area thermocouples welded beneath each
platform. A thermal equivalent of Ohm’s Law provides a simple quantitative, single-term equation relating heat flow to
differential temperature.
Q = ∆T / R
Where: Q = sample heat flow
∆T = temperature difference between the sample and reference
R = resistance of the thermoelectric disk
While this expression has universal acceptance, it is also recognized as an inexact,
representation of the actual sample heat flow, for it assumes equivalence of known resistance
and capacitance imbalances in the sample and reference sides of the cell (1,2). These
imbalances, which are inherent in all DSC cell manufacturing processes, are uncompensated
for in traditional DSC measuring circuitry, and produce thermal curves that are not optimized for
baseline flatness, sensitivity, peak shape and resolution.
Tzero™ technology accounts for these imbalances and produces a more accurate representation of the actual heat flow
to and from the sample. The benefits of Tzero over current DSC technology are:
• Essentially flat baselines with minimum start-up / endset "hooks". Typically an order of magnitude or more better than
competitive designs, especially in subambient operation.
• Superior sensitivity due to flatter baselines and better signal:noise ratio
• The best available resolution (even compared with power compensation devices)
• Direct measurement of heat capacity.
• Faster MDSC® experiments (similar to standard DSC), plus improved data accuracy.
(continued)
Figure 1 illustrates the Tzero™ cell design. The sensor is a machined constantan body
with separate raised sample and reference platforms, which provide signal isolation,
and also aid in reproducible pan placement. Sample and reference temperatures are
measured by area thermocouples on the underside of each platform. The temperature
of the base is measured using a third thermocouple (To thermocouple), which
also functions as the temperature control mechanism for the furnace. Its presence
effectively separates the heat flow contributions from the sample and reference sides
of the cell.
Figure 2 provides the thermal network model of the new
design, from which a new four-term heat flow expression
has been derived (1).
q = -∆T/RR + ∆T0 (RR-RS/RRRS) + (CR-Cs) dTS/dτ - CR (d∆T/dτ)
The first term is the equivalent of the conventional single term DSC heat flow
expression. The next two terms account for thermal resistance and capacitance imbalances
between the sample and reference sides of the cell, which are the primary source of
instrument baseline deviations. Term four accounts for heating rate differences between the sample and reference, and
is maximized during enthalpic events such as melting. The resulting heat flow signal provides a more accurate
representation of the actual heat flowing to and from the sample. This level of implementation is termed Basic Tzero, and
is available in the Q1000 and Q100 Calorimeters.
A higher level of implementation - Advanced Tzero - is available in the Q1000. It accounts for sensor and pan imbalance
effects, and provides an even more accurate representation of the actual heat flows to and from the sample.
The Q10 DSC module offers the performance advantages of the Tzero cell, but employs only the traditional single term
heat flow expression.
The new technology dramatically improves DSC baseline performance as
seen in Figure 3. Traditional DSC baselines often deviate 100µW or more
during a scan, and some may not be reproducible over the day, thus limiting
the utility of baseline subtraction routines after a sample has been analyzed.
The Tzero design yields baselines that are stable and can deviate less than
10µW with minimal initial / final upsets.
(continued)
Figure 3
Figure 2
Figure 1
Baseline flatness is also the most important factor when considering DSC
"sensitivity". A flat baseline is crucial to detection of subtle transitions, such as
weak Tg’s in highly crystalline, reinforced, or cross-linked polymers, and in
lyophilized materials. The Tzero™ cell is able to detect the Tg of polypropy-
lene, a measurement normally very difficult with traditional designs (Figure 4).
Resolution is also vastly improved. Figure 5 illustrates a comparison of Tzero
and conventional DSC signals on the melt of high-purity indium, a common
DSC calibrant. Similar results have been observed from comparisons of data
from samples that exhibit polymorphism. Higher peaks, sharper onsets, and
faster returns to baseline confirm the superiority of the Tzero approach over
traditional heat flux and power compensation designs.
Another benefit, especially for engineers, is a direct, continuous measurement
of sample heat capacity, which normally requires three separate experiments
in a traditional design. Accuracy and productivity are also improved in this
measurement of a fundamental material property that is crucial in structure
determination and in material processing.
Tzero technology also makes Modulated DSC® (MDSC®) experiments more
productive, since reduced dependence on the period of measurement permits
the use of faster heating rates, akin to that used in standard DSC.
Quantitative accuracy is also improved.
A major feature of the new Q Series™ DSC Modules involves performance on
cooling. The Tzero cell is unique in that it is designed both for heating and
cooling performance. A symmetrical array of nickel cooling rods attach the
furnace and sensor housing to a nickel cooling flange, which is directly coupled
to either the new mechanical or liquid nitrogen cooling systems. Figure 6
shows the optimized design, which produces faster cooling rates, lower
subambient temperatures, rapid temperature equilibration, and zero frosting
problems. A new 50-position intelligent auto sampler further optimizes
performance in unattended temperature cycling experiments.
References:
1. R. L. Danley and P.A Caulfield, NATAS Proceedings, 2001
(and references therein).
2. G. Dallas, J. Groh, T. Kelly and R. Danley, American Laboratory, August, 2001
Figure 4
155 156
Temperature (˚C)
157 159158 160 161
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-15
-10
-20
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Hea
t Flo
w (
mW
)
0Q1000
Q100
Q10
Figure 5
Figure 6
1/4
ADVANCED RHEOMETER
AR 2000, AR 1000 & AR 500Prepared byFred A. Mazzeo
Guide to Setting Up the Rheometer
Outline 1. Turn on the computer controller.2. Always make sure that the air supply is turned on to the rheometer.3. Remove the black bearing lock by holding it in place while turning the
draw rod knob at the top in a counter-clockwise direction. Once thebearing lock is removed, make sure that the spindle rotates freely.NOTE : When using the AR2000, please ensure that the drive-shaft slidelock is pulled-out.
4. Turn on the power to the instrument and, if present, the ETC controller.NOTE : If step 4 is performed before step 3, an alarm will sound and theinstrument controller display will read ‘optical init. fail’. At this pointjust follow step 3 and the alarm will stop.
5. Please ensure that the water supply is turned on.6. When instrument has finished the system check, turn on the instrument
control software.
7. Go to the Instrument Status Page to make certain thatcommunication has been established between the computer and theinstrument.
8. Instrument Inertia: Determine the instrument inertia by selectingOptions>Instrument>Inertia and run the ‘calibrate’ wizard.
9. B e a r i n g F r i c t i o n C o r r e c t i o n : S e l e c tOptions>Instrument>Miscellaneous and make sure that the bearingfriction correction box has a value and the bearing friction correction isactivated.
a . If there is no value, perform the bearing fiction correctionprocedure via the wizard, (Rheology Advantage 3.0), or using theHelp>Index under the phrase ‘friction: calibration>determiningbearing friction correction’. When using a version of softwareless than version 3.0, uncheck the bearing friction correction boxlocated within Options>Instrument>Miscellaneous before runningthe calibration procedure.
10. Geometry: Attach test geometry by holding it in place while turning thedraw rod knob at the top in a counter-clockwise direction. Choose theappropriate geometry, if the file already exists (Geometry>Open…), orcreate a new geometry by selecting Geometry>New, and follow theguide.
11. Geometry Inertia: Calibrate the geometry inertia by following thewiza rd tha t i s found in the Geometry Page
>Settings>Inertia: Calibrate.
12. Mapping: Perform a mapping on the geometry by using the icon or use Instrument>Mapping. Select either the number of iterations ormapping type within the icon dialog window (Rheology Advantage 3.0)
2/4
or under Options>Settings>Mapping and Options>Instrument>Miscellaneous: Mapping Type, respectively.
a . Mapping only needs to be performed when using a flowprocedure and when the lower two decades of torque isnecessary for data acquisition.
b. The number of iterations should be set greater than one whentesting a very low viscosity material. When performing a Creepprocedure the number of iterations should be set to 4, if theRecovery step is set to zero. Otherwise, setting the number ofiterations greater than three has diminishing returns in themapping performance.
c. The mapping type can be set to fast, standard or precision. It isrecommend that ‘standard’ should be selected for most materials,but for more critical measurements, ‘precision’ mapping is moresuited.
13. Temperature System Selection: Select the temperature system andattach the appropriate bottom assembly.
a . For AR1000/500/QCR instruments, the temperature read andcontrol must be set to the appropriate temperature system. Thisis accomplished by choosing Options>Instrument>Temperature:Temperature Read and Temperature Control setting both to‘Peltier’, if using the Peltier Plate, or ‘Temperature System’ if anyother system is being used.
b. This selection is not necessary for the AR2000.
14. Zero Gap: Zero the gap by choosing the zero gap icon , or byselecting Instrument>Gap>Zero Gap and follow the directions onscreen.
a. If equipped with normal force, there are two options that onecan used to zero the gap, deceleration or normal force.Generally, the normal force method is recommended. Thischoice is made in the Options>Instrument>Gap>Gap Zero Mode:Normal Force. Set the value equal to 1 N.
NOTE : The upper geometry should be at the testing temperaturebefore zeroing the gap. This will account for the change in dimensionsdue to the coefficient of thermal expansion of the testinggeometry/system.
15. Gap Compensation: If you have the normal force option, you canobtain the gap compensation value by using the gap compensationwizard located in the Geometry Page >Settings (Rheology Advantage 3.0)or by performing an oscillation temperature ramp (torque of 0.1 µNm @a frequency of 1 Hz conducted at a ramp rate of 2°C/min) under globalnormal force control (1N +/- 0.1, 1000 µm up/down, compression, setinitial value) with a conditioning step temperature equal to the startingvalue of the temperature range of the experiment with an equilibrationtime equal to 5 minutes. Plot the data and then fit a straight line to thegraph of Gap vs. Temperature. The slope must be then entered in theOptions>Instrument>Temperature: Temperature Calibration regionwithin the cell located to the right of the appropriate temperaturesystem. The gap compensation check box should be activated, whichis located within the Options>Instrument>Temperature dialog window.If the normal force option is unavailable, then predetermined values
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must be entered.NOTE : The gap compensation value must be set to zero before this stepis performed.NOTE : If controlling normal force throughout an experiment, the gapcompensation value is recommended to be activated.NOTE : Gap Compensation needs only to be used when testing over atemperature range.NOTE : Zero the normal force before running the gap compensationtest.
16. Procedure: Set up procedure by selecting the appropriate file, ifpreviously created, by choosing Procedure>Open or create a newprocedure by selecting Procedure>New. The procedure can be adapted
in the Procedure Page 17. Notes: Enter sample information within the Notes Page
or by selecting Notes>New.
18. Sample Loading: Load sample, lower geometry to appropriate gap andtrim if applicable (for additional help, go to Help>Video Clips: Loadingand Trimming a Sample).
a. The gap can be set by three different methods. i. Manually enter the desired gap by selecting the enter gap
icon or by selecting Instrument>Gap>Enter Gap… ii. Automatically have the instrument go to the gap value
entered in the Geometry Page >Dimensions by using the
go to gap icon or select Instrument>Gap>Go ToGeometry Gap.
iii. Manually raise or lower the gap by using the icons. NOTE : These icons are only available when in theInstrument Status Page .
19. Run Test: Run test by selecting the run experiment icon .
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Instrument Inertia (see 8) Monthly
Bearing Friction Correction(see 9)
Monthly
Geometry Inertia (see 11) Once during the geometry setupVerification of value is
recommended daily, but notrequired
Mapping (see 12 a, b, c) Once daily (if same geometry)Every time the geometry is
changed
Zero Gap (see 14) Every time geometry isremoved/replaced
Gap Compensation (see 15) Once if using samegeometry/heating system
Run Standard Oil Monthly
Table 1.Calibration
Guide
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ADVANCED RHEOMETERAR 2000, AR 1000 & AR 500
Prepared byFred A. Mazzeo
Testing an Unknown Material
1. Determine Pseudo-Linear Viscoelastic Region (LVR) [Refer to Figures on Page 2]Use an Oscillatory Stress Sweep ( OSS )
Conditioning step- Set temperature of test- Equilibration time = ~ 5 minutes
- NOTE: (This is an approximate time in order for anystructure to build and/or sample and upper geometry tocome to thermal equilibration before data acquisitionbegins, this should be adjusted if sample being tested needsmore or less time)
Stress Sweep step- Broad shear stress range
- NOTE: (Since this is an unknown sample, a good rule ofthumb is to test over the allowable shear stress/torque rangeof the instrument. In subsequent testing, this shear stressrange/torque range can be reduced appropriately to collectonly reliable data)
- Frequency = 1 Hz- 10 pts per decade (log mode)
2. Determine Pseudo-Viscosity profile [Refer to Figures on Page 3]Use a Stepped Flow test ( SF )
Conditioning step- Set temperature- Equilibration time = Same time in Step 1
Stepped Flow step- Broad shear stress/torque range- 10 pts per decade (log mode)- Constant time = 15 seconds
* Data then can be viewed as viscosity vs. torque/stress and converted toviscosity vs. shear rate
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100000.1000 1.000 10.00 100.0 1000osc. stress (Pa)
1.000E5
1000
10000
G' (Pa)
1.000E5
1000
10000
G'' (
Pa)
Stress sweep step
100.001.0000E-3 0.010000 0.10000 1.0000 10.000% strain
1.000E5
1000
10000G
' (Pa)
1.000E5
1000
10000
G'' (
Pa)
Stress sweep step
LVR
Suggestedvalues to
choose forsubsequent
testing
LVR
Suggestedvalues to
choose forsubsequent
testing
Convert x-axis of osc. stress/torque to % strain
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100.00.01000 0.1000 1.000 10.00shear stress (Pa)
1000
0.01000
0.1000
1.000
10.00
100.0
viscosity (Pa.s)
Continuous flow step
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100001.000E-4 1.000E-3 0.01000 0.1000 1.000 10.00 100.0 1000shear rate (1/s)
1000
0.01000
0.1000
1.000
10.00
100.0
viscosity (Pa.s)
Continuous flow step
3. Determine the necessary amount of time to form a stable structure [See Figure Below]Use an Oscillatory Time Sweep ( OTS )
Conditioning step- Set temperature- Pre-shear = value of shear rate beyond the 1st Newtonian plateau
from SF in Step 2- Equilibration time = 0
Time Sweep step- Choose time duration of experiment ~ 15 minutes- Frequency = 1 Hz- Control Variable: Choose a value of oscillation shear stress/torque
within the LVR from Step 1- Sampling time= 5 seconds
Convert x-axis of shear stress/torque to shear rate
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10000 100.0 200.0 300.0 400.0 500.0 600.0 700.0 800.0 900.0time (s)
1.000E5
1000
10000
G' (Pa)
Time sweep step
4. Determine True LVR (*Perform test if value of time to form a stable structure in Step 3is greater than equilibration time in Step 1)
Use an Oscillatory Stress Sweep ( OSS )Conditioning step
- Set temperature- Pre-shear = value of shear rate beyond the 1st Newtonian plateau
from SF in Step 2- Equilibration time = the amount of time necessary to obtain a
stable structure from OTS in Step 3, by determining when theelastic modulus G’ becomes relatively constant or stable
Stress Sweep step- Adjusted shear stress/torque range from Step 1 to collect only
reliable data- Frequency = 1 Hz- 10 pts per decade (log mode)
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The following additional procedures can be used in conjunction with the above preliminarytesting:
A. Oscillatory Frequency Sweep (OFS)Conditioning step
- Set temperature- Pre-shear = value of shear rate beyond the 1st Newtonian plateau
from SF in Step 2- Equilibration time = the amount of time necessary to obtain a
stable structure from OTS in Step 3, by determining when theelastic modulus G’ is relatively constant
Frequency sweep step- Frequency range = 100Hz - 0.1Hz- 5 pts per decade (log mode)- Controlled variable
- Shear stress = value within the LVR from OSS in Step 4- % Strain = value within LVR found from the OSS in Step 4 by
plotting G’ vs. % strainB. Steady State Flow (SSF)
Conditioning step- Set temperature- Pre-shear = value of shear rate beyond the 1st Newtonian plateau
from SF in Step 2- Equilibration time = the amount of time necessary to obtain a
stable structure from OTS in Step 3, by determining when theelastic modulus G’ is relatively constant
Steady State Flow step- Adjusted Shear stress range from Step 2 to collect only reliable
data- 10 pts per decade- Percent tolerance= 10%- Consecutive within tolerance = 3- Maximum point time = 1:30
* Data then can be viewed as viscosity vs. torque/stress and converted to viscosityvs. shear rate
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C. Creep / Recovery test (C/R)Conditioning step
- Set temperature- Pre-shear = value of shear rate beyond the 1st Newtonian plateau
from SF in Step 2- Equilibration time = the amount of time necessary to obtain a
stable structure from OTS in Step 3, by determining when theelastic modulus G’ is relatively constant
Retardation- Select a shear stress from within the 1st Newtonian plateau of SSF- Duration should be set to ~15 minutes or enough time for slope to
be constant (Equilibrium settings can be used to detect steady stateconditions)
Recovery- Shear stress = 0- Duration should be set to ~10 minutes or enough time for slope to
be constant (Equilibrium settings can be used to detect steady stateconditions)