SEM Lab
Several samples will be imaged using the SEM. The lab highlights some applications of SEM to scientific issues in polymer science.
- Calculation of dispersion and correlation in phase separated domains by calculation of the correlation function and the particle size distribution.
- Observation and description of crazing in polymers
- Observation and description of polymer crystal structure
- Observation and description of fibrillation in semi-crystalline polymers.
- Observation and description of mass fractal structure in two common polymer additives, organic pigments and inorganic filler aggregates.
Several web pages will be of use as background for the lab, Iowa State site, UK site,list of other sites
Experimental:
The following samples will be prepared prior to lab, a technician will assist you in obtaining images from these samples.
Samples:
- HIPS Phase Separated Domains
- HIPS, PS, PP Crazes
- PE, PP, PHB Crystals
- Fiber PP from mechanical testing
- Organic Pigment, Fractal Structure
- Titania, Fractal Structure
Analysis
- Crazing: Carefully measure the major features of a craze, fiber gap distance, average fiber diameter, standard deviation of fiber diameter, craze tip angle, length of craze growth zone, length of craze.
- Crazing: Carefully describe the interaction of rubber domains and the craze in HIPS.
- Phase separated domains: Measure the diameter, aspect ratio of a number of rubber domains in HIPS. Also measure the size of a number of inclusions within the rubber domains. Calculate the mean and standard deviation for these two structures. Plot a particle size distribution curve for both of these structures.
- Measure the separation distances for rubbery domains in HIPS and use these values to calculate the particle/particle correlation function for these domains. Determine if these domains are randomly distributed.
- Measure the average fiber diameter and standard deviation for fibrils in the PP fibers.
- Measure the mean primary particle size, mean aspect ratios and standard deviations for the organic pigment and the titania samples. Measure the mean aggregate size and standard deviation. Estimate the mass fractal dimension for both of these samples.
Questions
- Comment on the problems you encountered in quantifying sizes from micrographs.
- From your micrographs give support for common descriptions of crazes. Propose a mechanism for toughening in HIPS compared to PS.
- Are rubber domains in HIPS randomly distributed? Give support from your data.
- Give support from your data for common theories of fibrillation in semicrystalline polymers.
- Describe the differences between the two mass fractal structures observed.
- Do the mass fractal structures reflect reaction or transport limited growth? Give a possible aggregate growth mechanism for both systems and support it with your data.