ATR IV: Depth Profiling and Analyzing Filled Polymers

It is finally time to resume our ongoing discussion of the Attenuated Total Reflectance (ATR) sample preparation technique. Recall from my earlier posts that the depth of penetration (DP) in an ATR experiment is a measure of how far the infrared beam penetrates into a sample. The equation that allows us to calculate the DP has a number of variables in it, each of which will be the subject of a separate blog post. The subject of this post will be the refractive index of the ATR crystal, nc. This parameter appears in the denominator of the DP equation, so as nc goes up depth of penetration goes down.

There are a number of materials that can be used as ATR crystals that have different refractive indices. For example, diamond has an nc of 2.4 while germanium (Ge) has an nc of 4.0. Depths of penetration from less than 1 micron to up to 10 microns are possible depending upon the crystal used. This means that if these two crystals are used to measure spectra of the same sample, spectra from different depths in the sample are obtained without having to take the sample apart. This ability of ATR is called “depth profiling”. Many ATR accessories allow the ATR crystal to be changed easily, making taking spectra of the same sample with different crystals straightforward. Now to be clear, the spectra are taken from the outside in; spectra of “slices” or layers internal to the sample by themselves are not obtained. For example, to analyze different layers in a polymer laminate non-destructively, spectra at a shallow DP using a germanium crystal and at a greater DP using a diamond crystal are obtained. The Ge spectrum is then subtracted from the diamond spectrum to reveal the spectrum below the surface of the sample. The depth profiling ability of ATR can be used on any sample where you need to know how composition changes with depth.

An excellent example of how the change of DP with nc can be put to good use is the analysis of filled polymers. A filled polymer consists of an organic resin, such as a rubber, and a filler such as carbon black, silica, or limestone. One of the purposes of the filler is to add bulk to the material and reduce cost; fillers are cheaper than resins. When FTIR spectra are obtained of filled polymers it is generally the spectrum of the resin that is desired. The problem is that many types of filler, particularly carbon black, have broad, intense absorbances that can mask the spectrum of the resin. This is illustrated in the bottom spectrum, which is the spectrum of an O-ring filled with carbon black. Note the strong absorbances, sloping baseline and distorted peak shapes caused by the presence of the carbon black. It is very difficult to identify the resin from such a low quality spectrum.


The top spectrum shows the spectrum of the same O-ring obtained using a Ge ATR crystal. Note that although the spectrum is not perfect the absorbances have been reduced, there is less baseline slope, and the peak shapes are no longer distorted. This spectrum is interpretable, and gives reasonable library matches when searched. The Ge ATR crystal, having a higher refractive index than diamond, has a lower DP. In the diamond spectrum the DP is great enough that the carbon black contributes significantly to the spectrum. With Ge the carbon black contribution is reduced and the spectrum of the resin is easier to see. These results indicate that Ge ATR is the method of choice for obtaining FTIR spectra of filled polymers. This is also a neat illustration of how the dependence of DP on nc allows a normally difficult sample to yield a usable spectrum.

Training Delivery Options Part III: Public Training Courses

My definition of a public training course is one that is open to anyone who can pay the admission fee and features good old fashioned in-person training. This type of training is offered by private companies such as Spectros Associates, by professional groups such as the American Chemical Society, and at scientific meetings such as the Pittsburgh Conference. These courses are frequently held in hotel meeting rooms or at conference centers. No doubt many of you have taken this type of training before.

One of the advantages of public training courses is the ability to interact with the instructor fostering the transfer of information from lecturer to attendee. Another advantage of public courses is it allows attendees to receive hands-on training. A nice thing about public courses is that it gets people away from the distractions of their offices and the need to “put out fires”; allowing attendees to focus more fully on learning. A unique advantage of public training courses is the opportunity to interact with people from different companies. It has been my experience after teaching hundreds of these courses that attendees not only learn from me, but from each other as well. Public courses also give people the opportunity to socialize and make new friends.

The disadvantages of public courses revolve around money and convenience. Since these courses are held at a central location attendees typically have to travel to them to attend. This involves travel time and costs and means one’s work and personal lives are put on hold to attend the training. Cost wise public training courses are the most expensive on a per-head basis since there are travel costs in addition to the cost to attend the seminar.

It’s time to pull together the three blog posts on training delivery options. Public training courses make the most sense if there are one or a few people who need training. For groups of 4 or more onsite training is more cost efficient with the advantage the training is in-person and can be customized. Online training works well for groups scattered at different locations, for people who cannot travel for some reason, or at companies looking to slash their travel budgets.

Spectros Associates offers FTIR training courses via all three of these delivery methods. For more info click here: www.spectros1.com .

Training Course Delivery Options II: Online Training

Online training is a relatively new development in the training world. You may here it called a webinar, internet training, remote training etc. In general, attendees log into a website where the instructor shows PowerPoint slides and talks in real time. All you need is high speed internet access and a phone line to participate. The presenter and trainees speak to teach other using either a traditional telephone line or the internet. Depending on the platform the instructor can annotate and illustrate the slides, engage in chat sessions with students, and show other websites or applications to attendees. A web camera can be used to allow attendees to see each other, and allow the presenter to engage in “show and tell”. Students can chat with the instructor, each other, ask questions by “raising their hand” and so on. Online training courses are typically held in sessions of a few hours or less. It is not practical to do all day sessions like traditional training because it is uncomfortable for people to sit for many hours in front of their computers.

There are number of advantages of online training over traditional training methods, which is why it is an increasingly popular training delivery option. Online training is cheaper than in-person training because it eliminates travel costs. There is no need to transport the trainer to the class or the class to the trainer. Another advantage of online training is that it saves on travel time. The hours that would normally be spent travelling to a seminar can now be spent productively at work. Online training is also convenient, allowing people to participate in a training course from the comfort of their own office. Also, If you have employees scattered at multiple locations it is much easier and cheaper to gather them together in a virtual meeting room for a course rather than gathering them in an actual meeting room. Lastly, by spreading shorter sessions over multiple days, attendees have more opportunity to review what they have learned and do homework, much like a college lecture course.

However, online training has its drawbacks. My great frustration as an instructor of online training courses is the lack of human interaction. No matter how hard I try it seems people are less likely to ask questions and participate in discussions online than they are in person. With in-person training I can tell by an audience’s facial expressions and posture whether I am effectively lecturing or not. This type of feedback is not available with online training making it more difficult for me to customize the course to people’s needs. The lack of human interaction also prevents attendees from talking to me outside of class about specific questions and problems they have, which means a learning opportunity is missed. Another thing attendees miss with online training is interaction with classmates. My experience is that attendees at my training courses learn from me and from each other. So, with online training opportunities to learn from the instructor and classmates are limited compared to in-person training. It is possible then that attendees will learn less in an online setting than they would in person.

Ultimately, because of the cost advantages of online training I believe it will become increasingly popular compared to in-person training.

Training Course Delivery Options I: Onsite Training

As you have probably figured out by now, I teach FTIR training courses for a living. There are a number of ways training courses can be delivered including public courses, onsite training, and online over the internet. This post will be the first in a series discussing training course delivery options, and their relative advantages and disadvantages.

Onsite training refers to training held at a company site. It is “we will come to you” training. Typically, the company provides the training room, facilities, and gathers people from around the company in that room. Sometimes these people all work at the same physical location, other times I have seen a company fly people in from several locations to attend a class at a given site. Then, all the trainer has to do is show up with a PowerPoint presentation, training materials, and impart wisdom to the assembled group.

I feel the most important advantage of onsite training is it gives the instructor the chance to customize the course for you. A good trainer will tailor the content and length of an onsite course to match your experience level, instrumentation, applications, and budget. If the trainer you have hired does not offer course customization or refuses to do it, hire yourself another trainer. It is the customization aspect of onsite training that many companies cite as the main reason they hold such courses in the first place because it gives them the most relevant information per dollar than any other training course delivery option. Another of the beauties of onsite training is convenience; you and your co-workers don’t have to travel anywhere, except perhaps down the hall to your department’s meeting room.

The other advantages of onsite training come from having the instructor “captive” at your facility. This means hands-on training, live demonstrations, and one-on-one consultations are possible. Many people learn better by seeing and doing rather than sitting and listening, which is why hands-on training is such a good idea. Speaking for myself, since I am being paid to be at a company and provide advice, I am happy to answer questions at onsite courses outside of class, particularly over a beer or dinner (hint hint).

The way I and some other trainers charge for onsite training is as a flat rate per day plus a small charge per head for training materials. Travel costs are normally paid for by the client as well. The beauty of this pricing scheme is that it minimizes the cost per head of training. The price for teaching 5 people is almost the same as it is for 15 people. Thus, onsite training is ideal when there is a group of people at a given company that need training. In my experience if there are 5 or more people in a company that need training it is cheaper for the trainer to come them rather than vice versa.

Now, to be fair there are some disadvantages to onsite training. First, I find if attendees have access to their office, phones, and e-mail during the course the frequently get distracted, or worse yet are pulled out of the course to “fight fires”. This is wasteful of company money. It costs thousands of dollars to bring a trainer in for a course, and companies should maximize the transfer of information from the trainer to their employees by making sure each attendee is present for the entire course. To pull people away on other business is short sighted. What leaves me shaking my head is that too frequently the manager who approved the money for the training is the one pulling people out of class to deal with perceived emergencies. To combat this problem, some companies hold “onsite” training at an off-site facility such as a hotel. Without the distractions of work people will learn more, spend more time in class and will be more comfortable. The final disadvantage of onsite training is that it is not cost effective for small groups. If you have only two or three people that need training, training delivery options other than onsite courses should be explored.

In summary then, onsite training is a cost effective way of obtaining customized training for a group of people at a given company. For more on Spectros Associates’ onsite training courses click here: http://www.spectros1.com/course_custom.html .