Cycle II Materials Science

John Dewey High School

Mr. Klimetz

Polyvinyl Alcohol "Slime" Synthesis and Analysis

Laboratory Data Processing Instructions, Equations, and Questions

Part I: Basic Sample Properties

Mass of Sample:________ g 

Volume of Sample:    ________ cmexp3

Density of Sample     ________ g/cmexp3

Part II: Stress/Strain Test Observations

Tensile Stress

Suspended Sample (Low Stress/Low Strain Rate)

Gently Pulled Sample (Moderate Stress/Moderate Strain Rate)

Compressive Stress

Drop Sample from 0.70 m Height (High Stress/High Strain Rate [Low Impact])

Throw Sample Against Wall or Floor (Very High Stress/Very High Strain Rate [High Impact])

Part III: Creep Test Observations and Data Processing

A. Measure the horizontal surface area of the sample in one minute intervals at room temperature immediately after removal from its container. This is to be accomplished by inverting the sample-filled container onto a sheet of glossy graph paper and immediately tracing the outline of the sample onto the graph paper with pencil or with a pen filled with water insoluble ink. This is to be repeated in one minute intervals for a total of ten minutes. [If the sample is noticeably warm to the touch extend the observation and data gathering period to twenty minutes.] Determine the area of each of the traced outlines by counting the total number of graph paper grid squares that are confined within each drawn loop. Record your data.

B. Plot an Area versus Time Graph of your data gathered in part A. Area should appear along the y-axis of your graph and time should appear along the x-axis of your graph.

C. Calculate the Average Creep Rate of your sample by the following equation:

Average Creep Rate = (Area of Sample at End - Area of Sample at Start)/Time

D. Calculate the Average Sample Thickness* at Each One Minute Time Interval by the following equation:

Average Thickness (cm) = Volume of Sample (cmexp3)/Area of Sample (cmexp2)

(*Note that in order for this equation to yield meaningful values, the areas of the sample at each one minute interval must be expressed in units of square centimeters before being substituted into the equation.)

E. Based on your data, express the observed relationship between area, thickness, and time.

F. Suppose we were to extend the period of observation to one year. Briefly explain the type of surface area and thickness data we might obtain. Briefly explain the appearance of our Surface Area versus Time graph over this time period, assuming that temperature and pressure remained constant, and the properties of the material remained constant.

Questions

1.   Briefly describe the affect of sodium tetraborate on polyvinyl alcohol molecules both chemically and behaviorally.

2.   Briefly describe the meaning of "cross-linking" of polymers and its effect on the behavior of such materials.

3.   List at least three potential practical uses for our polyvinyl alcohol "slime."

4.   Briefly explain the methods you employed to determine the mass, volume, and density of your sample as well as any practical difficulties you encountered.

5.   Briefly summarize the relationship between stress type and the rate of its application to the behavior of your samples. Polyvinyl alcohol "slime" is referred to as a "smart" material in view of its stress/strain behavior. Briefly explain what this means and how your observations of its behavior support this claim.

6.   What modifications or changes in our experimental setting could have been initiated to both increase and decrease the rate of creep of our sample? Briefly explain.

7.   Briefly express your enjoyment of and satisfaction with this exercise. Suggest any possible modifications or improvements to make this exercise more meaningful.