Monthly Archives: April 2014

Directions of DSC Heat Flow Signals

Which way do you plot your DSC thermograph of the heat flow signal?  Do you plot “exo up” or “exo down?  Do you care?  Why are there two conventions anyway?  Have you been confused by it when you compared data from various sources or when you read a literature article?  If you were used to DSC instrument of power compensation design (i.e., by PerkinElmer), you are most likely to see your DSC plotting as “exo down”.  If you were used to DSC instrument designed with heat flux principal, however, you are more likely to see your DSC thermographs plotted as “exo up”.

In a power compensation designed DSC, during an exothermic event, more energy or heat is released from the sample, therefore less than expected energy or power is needed to maintain the temperature, which registers it as a negative event, or plotted as “exo down”.  On the other hand, in a heat flux DSC, during an exothermic event, the temperature of the sample rises faster than it is specified by the heat rate program, therefore it is registered as a positive event, or plotted as “exo up”.

Another way to look at it is by defining your thermodynamic system.  One definition of the system includes only the sample, which means in an exothermic event heat or energy is released to outside environment, making it “positive”.  The other way to define the system is the entire DSC cell, which includes sample, reference, and oven.  With this system definition, less energy is needed to maintain the system during an exothermic event.  Therefore making it “negative”.

One advantage of plotting “exo down” is that your DSC thermograph (y-axis labeled “heat flow”) will trend the same way as the heat capacity of your sample.  By this I mean that your heat flow trends upwards as temperature increases, which is the same way heat capacity behaves: heat capacity increases as temperature increases.

Regardless of how you plot your DSC thermograph, it certainly pays to pay attention on which way is up!

AFM and Roughness


AFMs can measure nanoscale roughness from sub micron to less than an angstrom.  However, there are two main factors which need to be considered when using these instruments for this type of measurement:

1) Vertical Resolution – How the system scans in Z
2) Spatial Resolution – How the system scans in XY

Vertical Resolution.  How well the system measures vertically is a function of the noise floor of the system.  If the sample feature size is 1nm, the system needs to have a vertical noise floor less than 1nm in order to measure the feature adequately.  The largest vertical feature that you can measure will be equal to the noise floor or the Z resolution limit.  This noise floor measures all of the mechanical and electrical movement or noise in the system.  It is easiest measured by setting the scan size to 0, using the parameters that you will use to measure the sample.  When the tip is not moving across the surface any measured variation over time is due to noise int he system and will mask any surface features once the tip starts to move.  For measuring the lowest noise floor achievable, many companies use a standard set of parameters so that they compare values.

Spatial Resolution.  Since the movement in XY is almost always larger than that in Z.  The lateral resolution of the an AFM isn’t limited by system noise, but by the radius of curvature (ROC) of the tip.  The sharper the tip, the better the resolution.  Super sharp commercial cantilevers have a ROC about 2-3nm.  Standard AFM probes have a nominal ROC of 6nm.  Any probe used for advanced modes usually has a coating not the to make them sensitive to a particular signal of interest.  These probes can have have ROCs 20nm or more.

In addition to the ROC, it is important to keep the tip sharp without blunting the tip to maintain a) the highest resolution possible and b) to maintain a stable and consistent image.  If the tip wears during the coarse of imaging.  The first image may look dramatically different from the last image on the same sample surface.  In cases where the feature size is much smaller than the tip size, a condition called tip imaging (tip self imaging, reverse imaging) will occur where the features surface features will be representative of the end of the tip rather than the surface itself.

What to do?  Understand the noise floor of your system.  This will determine what are the limits of the machine. Know what the specifications of your probe are and what condition it is in.  This will provide you with confidence that the images you are seeing are representative of the sample surface.

Happy Scanning….

But it was by and large a forgettable episode of “SNL,” or maybe just a normal one in a season where there have been more than the usual number of highlights already (and which started with some historic preelection shows) The ride begins at LeTort Park in Carlisle, and cyclists can select routes of 25, 50, 75 or 100 miles He was promoted to director of player personnel in 1993”The 28yearold singer who is currently Alfred Morris Jersey dating John Mayer felt it was appropriate to give her third studio album a title that would represent Authentic Clinton Portis Jersey the positive change she has gone through and the therapeutic healing she’s experiencedVincent, president of the NFL Players Association, will receive his full salary of $2

Though great blue herons hunt alone, they typically nest in coloniesThe infants Bashaud Breeland Jersey are in intensive care with hopes that with the right medication and treatment their condition John Riggins Jersey will improve rapidlyThe clerk said the man was the same person who robbed the shop two weeks earlier The Steelers Ben Roethlisberger (2004) and the Bucs Shaun King (1999) are the only other rookie quarterbacks to win a playoff gameKings defenseman Willie Mitchell, playing for the first time since he fractured his left wrist on Nov

“Mugabe DenouncesZimbabwe’s rabidly antigay President Robert Mugabe has slammed Great Britain and the European Union for imposing an asset freeze and travel ban on him and his inner circle 20 as Detroit Tigers fall to Boston Red Sox, 21Blog recap: Detroit Authentic Ryan Clark Jersey Tigers give up 8 homers, most in franchise history, fall Authentic Jarvis Jenkins Jersey to Boston Red Sox, 2042 Michigan State trustees displeased with professor’s classroom rant against RepublicansMichigan State investigates professor who tells students Republicans ‘raped this country’ $26 (AP photo)TUSCALOOSA Alabama’s string in which its defense has held opposing players to fewer than 100 rushing yards now stands at 41 gamesSenatore was found guilty at a SANZAR disciplinary hearing of biting South Africa lock Eben Etzebeth on the forearm in a test last weekend

He said he promised to address their concerns Wright, Washington State 9 Ryan Bartholomew, West Texas A 28 Marshall Williams, West Virginia Logan Paulsen Redskins Jersey 15 Thomas Keiser, West Virginia 16 Taiwan Jones, West Virginia 20 Ollie Ogbu, West Virginia 20 Rashad Carmichael, West Virginia 7 Joe Lefeged, Wisconsin 15 Justin Burke, Wisconsin 3 Cameron Jordan, Wisconsin 3 Luke Stocker, Wisconsin 4 Derek Sherrod, Wisconsin 8 Clint Boling, Wisconsin 26 Graig Cooper, WRBoston College 2Williams, Southern Mississippi 24 Derrell JohnsonKoulianos, SS, Stanford 15 DeMarcus Love, Stanford 16 Adrian Moten, Stanford 16 Greg Salas, Stanford 16 Martin Parker, Stanford 16 Willie Smith, Stanford 4 Anthony Sherman, Syracuse 10 Colin Baxter, Syracuse 13 Scott Lutrus, Syracuse 8 Jordan Toddman, TCU 18 Dane Sanzenbacher, TCU 5 Jason Kelce, TCU 6 Benjamin Ijalana, TCU 9 Colin Kaepernick, TE, Temple 10 Ahmad Black, Temple 6 Marvin Austin, Tennessee Authentic Russ Grimm Jersey 15 Ryan Whalen, Tennessee 4 Jordan Cameron, Texas 14 Pierre Allen, Texas 22 Chris L Comments that include any offensive material are prohibitedThere’s a need, and the least we can do is giveIt is a measure of Brown’s popularity with his former teammates that many of them were on hand for the ceremony, including Deion Branch, who was released by the team on Aug

Get it herePolice are asking for the public’s help in locating Leandra DeSean Jackson Jersey In high school Lane’s art teacher recognized his talents and encouraged him to enroll in art schoolBaron Clinton Portis Jersey Davis makes his debut tonightBill Haber / Associated PressBaron Davis and coach Byron Scott are reunited and feels so goodList of national signing day signees for football1

Thermoset Cure Characterization Using Dynamic Mechanical Analyzer (DMA)

One person’s question on the LinkedIn discussion forum “Dynamic Mechanical Analysis (DMA / DMTA)” prompted me to write this blog entry. Do you know that DMA is an effective tool to study cure of a thermoset material? Typically, cure characterization of a thermoset is studied by DSC for kinetics information and by rheometer for viscosity information.  However, in some
instances – such as instrumentation constraint or material constraint – you can study cure with DMA. The most effective way to study cure in DMA is by supporting your thermoset material with a mesh material, such as a plain weave glass fabric. You then run it in the cantilever mode or film mode with a constant heat rate. (My personal preference is to run it in single cantilever mode.) And you should get a DMA thermograph similar to the one illustrated below.

DMA cure

DMA cure

A good reference is the book “Thermal analysis of polymers” edited by J. Menszel & B. Prime. Look into chapter 5, section 5.7.3.2 “DMA Techniques for Developing Cure Parameters”. Figure 5.44 shows a technique with wire mesh using a tensile fixture.