LabVIEW Program to Study the Viscoelastic Response of Polymers Using an Optical Mouse as the Sensor

Author(s):
Pedro Antonio Galera Gómez - Universidad Complutense de Madrid

Industry:
University/Education

Products:
LabVIEW

The Challenge:
To write a program in order to automate the measurements of viscoelasticity in polymers studies using a home made experimental setup. The aim of this work is to improve the accuracy in the measurements, to save time and money in the labs, to make the experimentation easier, and to encourage students to develop programs and instrumentation.

The Solution:
An optical mouse includes both an optical sensor and an interface with the computer. A program in LabVIEW was used to track the deformation of a polyethylene film using an optical mouse as sensor of movement. Position data as a function of time are automatically acquired. The results are displayed in a graph and may be saved for further studies

In the Journals concerned with education in experimental sciences appear more and more papers that deal with the development of experiments. A primary goal of the advanced instrumental method courses is to provide students with the skills to construct an instrument. These skills include the design and fabrication of electronics and computer programming in a data acquisition language. This practice is useful to introduce students in many fields of modern chemistry and physics using low cost instrumentation that may be reused in several experiments. Therefore, funds in the teachings labs can be saved if student and professors develop some instrumentation. National Instruments’ LabVIEW is a data acquisition program that provides many built-in functions that facilitates fast program development.  On the other hand LabVIEW is an intuitive graphical programming environment specifically useful for data acquisition and analysis that allows students to draw a visual representation of a software process rather than written a procedural code following syntax. 

 

Viscoelastic materials simultaneously exhibit a combination of elastic and viscous behaviour. While all the substances are viscoelastic to some degree, this behaviour is especially prominent in polymers.  A simple test of viscoelasticity can be carried out attaching a weight to a plastic film and watching its enlargement with time. This article provides a LabVIEW program and low cost hardware to study viscoelasticity. With resolution currently reaching of 0.032 mm, an optical mouse is a good motion sensor in the experiment described in this work.

 

Material and Methods:

 

The samples used in this experiment  were a pieces o polyethylene film 20 mm width 100 mm long and 0.1mm thick  The set up  used to accomplish the experiments  is shown in (figure 1). It   includes two pieces of angle-iron fixed to  a table by two   C clamps  . One of these  angle-iron pieces contain a holder for an  additional optical mouse connected to the USB port of the PC. The other angle-iron  contain upper part of a  fixture holder  that consist of   two rectangular pieces of aluminium that can be loosened and tightened  using two screws.  Between these two aluminium  pieces it was  slipped one end of  the polyethylene film and  then the screws were  tightened .

 

The lower potion of the fixture, also  consist   of  two pieces of aluminium  as  the above described . This lower fixture  portion  was  positioned on   one end of  an  iron plate (2mm thick) 40 mm width   200 mm long ).  The lower part of the fixture was used   to fix the other end of polyethylene film. On  the above  iron plate  end  it was weld a small  iron  hook to hang a weight. This  iron  plate also contain  a  ruler on one side and a  thin piece of    wood is glued on the reverse side . This piece of wood  is faced to the   optical  mouse. Therefore when a weigh is hanged on  the hook, the wood surface  slip down as the piece of  polyethylene film  is stretched  whereas the mouse  remain stationary  .

For data acquisition it was used a program written in LabVIEW version 7.1 full development  system that run in a PC using Windows XP operating system. Figure 2 shows the from panel of the vi to acquire  elongation data as a function of time. The program is  used to convert the acquired numeric  y axis  data  in distances from  any reference position that is selected with the regular mouse of  the computer. The program can be used for  movement of cursor in both directions   i.e., increasing and decreasing pixels. The mouse position differences  may be transformed in real word units by calibration.

The delay between measurements can be also controlled  in the program because the speed of  deformation  changes with  the  polymer nature and other factors.

 

Results:

 

In Figure 2 , the graph on the  front panel   shows the results of elongation versus time for a sample of polyethylene film of low density. In this  experiment it  was applied t a load of 906 g.  for  a period of time, after which the load was removed in order to observe  the  creep recovery. This behaviour is typical of this polymer,   It worth to note that this setup may be used to investigate some factors that  have an affect on  the viscoelastic behaviour as may be  crystallinity, molecular weight , temperature,  the presence of additives etc. . 

 

Acknowledgements:        

The author acknowledge  financial support  from the  Vice-Chancellor office of Innovation and European  Higher Education Space,   Grants 644

 

For more information on this Case Study, contact:
Pedro  Antonio Galera Gómez

Universidad Complutense de Madrid, Facultad de Farmacia

Departamento de Química Física II 

 28040 Madrid.

 

Author Information:
For more information on this Case Study, contact:
Pedro Antonio Galera Gómez
Universidad Complutense de Madrid

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