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Applications of Polymer Engineering Self-Healing Polymers Through Encapsulation
Author: Christopher Kriebel
Source: This material is based upon work completed at The University of Akron’s Polymer Engineering Department under the Guidance of Dr. Cavicchi supported by the National Science Foundation under Grant No. EEC-1542358.
Encapsulated polymers have many applications from drug delivery to self-healing materials. Capsules can be designed in a variety of different ways from encapsulating the polymer to using the polymer to form a capsule around the compound. There is a research group out of The University of Akron working on encapsulating an Alkyd polymer inside of a silica shell to be used as an additive in coating agents that will give the coating self-healing properties. In this lesson students will investigate the encapsulation process by using a polymer sodium alginate to form a capsule around fruit juice by crosslinking the polymer when it encounters a calcium lactate solution. The students will then add these capsules to gelatin and test the properties of the capsules and modified gelatin.
What should students know as a result of this lesson?
- Students should be able to explain what a polymer is and how polymers can be used in self-healing applications.
- Students should be able to describe how cross-linking occurs in polymers and identify when the cross-linking is a result of ionic or covalent bonds.
- Students should know how to make a soluation at a specific concentration (Molarity).
What should the students be able to do as a result of this lesson?
- Students should be able to prepare solutions of a speicified concentration (Molarity).
- Students should be able to perform a Bloom Test using a Durometer to test the physical properties of gelatin.
- Students should be able to think critically by analyzing the data they collect and modify their experiment to engineer a superior product.
- Students should be able to report their findings in a scientific manner.
Compounds for Synthesizing
- Sodium Alginate
- Calcium Lactate
- 12 Cup Pan/Gelatin Shot Cups
- 500 ml Food Syringes with Attachments
- Mesh strainer
- 500 ml Measuring Cups
- Plastic Spoons/Knives
Equipment for Synthesizing
- Precise Weighing Scale
- Silicone Mold
- Cooking Spatula
Equipment for Testing
- Modified Scale with a Clamp for Testing Encapsulation
- Pocket Kitchen Scale 0.01g-500g
- Ruler C-Clamp 6"
- Duct Tape
- 8" long 4" x 4" Styrofoam block
This lesson begins with an pre-assessment (Google form) to evaluate what the students know about polymers, what they remember from previously learned content, what they know about future content that will show up in the lesson, and how engineering design works.
Then the teacher will begin the content portion of the lesson using the Google Slides presentation. During the introduction to polymers the teacher will perform the following two demos:
- Polymer Bead Demo: This demo is often used to demonstrate the inertia of objects (which the teacher can briefly mention as a tie to physics), but for this lesson the main focus is to point out that each collared region represents a
molecule that has been added to make up the backbone of the polymer (the entire chain of beads). Once the chain begins to move out of the glass container the students will see the colors repeat until the chain hits the floor. A shorter second chain is then released with only two different colors. Ask the students what is the difference between each polymer? They should say that the first polymer chain was made of more molecules and was longer. Explain to them that the colors (molecules) and length of polymers play a major role in their physical properties and how the polymer will behave.
- Sodium Polyacrylate and Water Demo- Draw the chemical structure of sodium polyacrylate and water on the board and perform the demonstration. Ask the students what is going on? They should begin to saw somehow the water is being absorbed. Continue to lead them through questions until they can use the chemical structure to point out that the water is displacing the sodium ions (this will be important for the laboratory experiment for them to see). Once, they come to this conclusion make sure that they understand that the polymer didn’t dissolve because it was cross-linked to another strand.
The teacher will continue the content section. When the teacher arrives at the material related to Alkyds and their applications make sure to ask the students how they would solve the problem of graffiti and corrosion before going into detail how the group from The University of Akron approached the problem.
Towards the end of the lesson content explain to the students that they will be engineering their own self-healing material.
Give the students time to get in their groups and work on the pre-lab questions. It is important that they can correctly solve problem number 9 as it will be used in the procedure on day 2.
Students will be working in the laboratory to synthesize their engineered material.
Students will perform a rupture test on their synthesized capsules.
Students can test their material and eat the final product.
Optional Extension: students can re-engineer their material. Extends the lesson one more day.
Assessment: Pre-assessment and Formal Assessment
Students will meet with their groups to work on the pre-lab and plans for there engineered material.
Assessment: Formal assessment of pre-lab questions.
Day 2: Synthesis Procedure and Capsule Rupture Test
Students perform the food spherification synthesis following by making a solution of sodium alginate and fruit juice and then dripping it into a solution of calcium lactate and water. The students will then isolate the alginate spheres. The students will then prepare a gelatin with dissolved calcium lactate added. At this point the students will consult their experimental design notes to see what proportions of calcium gelatin and alginate spheres to add to their sample tray. They must also make a control sample of gelatin to compare to their engineered samples. The samples are then placed into the refrigerator and left overnight.
Assessment: Formal assessment of tables for capsule rupture testing. Formal assessment occurs on day two when the samples are removed from the refrigerator for testing.
Students will complete the discussion and conclusion section of the laboratory worksheet. They will answer specific questions related to the chemistry behind the laboratory experience.
Assessment: Summative assessment of discussion and conclussion
Students can elaborate on their design in the discussion section of the laboratory worksheet.
Students will complete the extension activity and present a new product (conceptual) through a five-minute presentation to the class.
Assessment: Formal assessment of the discussion for elaboration and of the extension activity.
This lesson should be taught along with stoichiometry section specifically when students are required to perform molecular calculations. Prior to this the students should be familiar with the types of chemical bonding, how to represent chemical compounds, quantifying matter, and intermolecular/intramolecular forces. Students need to be comfortable working in groups in a laboratory setting. Students should also be proficient in laboratory safety procedures and techniques.
Best Teaching Practices
- Communicating assignment procedures
- Providing students with the materials they need to complete the assignement
- Use of models
- Clearly presenting the goal of the laboratory assesment
- Offering feedback to the students
- Monitoring student work
Alignment with Standards
- HS-PS1-3. Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
- HS-PS2-6. Communicate scientific and technical information about why the molecular-level structure is important in the functioning of design materials.
Common Core Standards:
- RST.9-10.7: Translate quantitative or technical information expressed in words in a text into visual form and translate information expressed visually or mathematically into words.
- RST.6-8.3: Follow precisely a multistep procedure when carrying our experiments, taking measurements, or performing technical tasks.
- HSN-Q.A.3: Choose a level of accuracy appropriate to limitations on measurement when reporting quantities.
- C.PM.4: Representing Compounds
- Formula Writing
- Lewis Structures
- C.PM.5: Quantifying Matter
- C.PM.6: Intermolecular Forces of Attraction
- Types and Strengths
- Implications for Properties of Substances
- C.IM.3: Stoichiometry
- Molecular Calculations
Students should be able to recognize the physical changes occurring when the sodium alginate and calcium lactate are dissolved into their respective solutions. Students should be able to identify that there is an ionic bond between the calcium ion’s and the alginate polymer that is created when they interact and this ionic bonding is occurring because the calcium has a two plus charge will the sodium was only a one plus, therefore allowing one calcium ion to interact with to alginate strands holding them together.
Students need to be aware of the various intermolecular and intramolecular forces that are also playing a role in the gelatin molds.
Students should be able to calculate the molarity of a solution using the molecular mass of the compound, the mass of the compound added and the total volume of the solution. They should also be able to determine how much of a solution should be added to a specific mass to produce a predetermined molarity.
- This laboratory was designed to be an edible activity for the students. All chemicals being used are food grade. Consuming large quantities of sodium and calcium can be dangerous, so students should only try a small sample of their design if they are consuming it. The recommended daily value for sodium and calcium is around 2.0 g and 1.0 g respectively. The students will be using either a Bunsen burner or hot plate to boil their water and need to be aware of the dangers associated with those devices. Students should follow all appropriate safety procedures and best practices when operating these devices. Students should wear safety goggles for this laboratory and gloves to prevent the spread of germs.
Students encounter polymers everyday in their life, but vary rarely are they aware of what the polymer is or why it was made. Students may recognize plastics as polymers, but vary few would be able to point to polymers in coating agents. This lesson is designed to make the students aware of polymers in their everyday lives along with introducing how they can be used to engineer solutions to everyday problems. At the end of the lesson the students will need to create a conceptual application for self-healing polymers that can be used in everyday life.
Many times students make solutions at home, but are unaware of what they are actually doing to the concentration of the solution or how that will affect the final product; they just simply follow the directions on the label. This lesson is designed to make them think about the concentration of solutions and how it is affecting their products. They may have to reformulate their design and change the concentration by making a new solution. This is actually a desired outcome of the lesson as the students will have to think critically and understand how the solutions concentration plays an integral role in the final physical properties of their engineered gelatin.
Multiple Assessments should be used throughout this lesson the majority are formal assessments of student progress, understanding, and engineering design. There are opportunities for summative assessment throughout the lesson as well. The assessment opportunities are as follows:
- Pre-assessment - Formal
- Laboratory Worksheet -
- Introduction (pre-lab) - Formal
- Results Section - Formal
- Discussion - Summative
- Conclusion - Summative
- Lesson Extension Presentation - Formal
- Post-assessment - Summative
- Groups should be 3-4 students with different abilities and backgrounds. Students do not need to be familiar working with each other in fact it is encouraged that they have not been in a group before.
- Day 1:
- The pre-assessment should be given no more than 5 minutes to complete and 5 minutes to review. The content lecture portion of the class including the teacher demos should take 30-40 minutes depending on teacher speed and familiarity with the content.
- Following the content portion of the lesson the students are to get in their groups and work on the pre-lab questions for the remainder of the day they should have 30-40 minutes for this.
- Day 2:
- Teacher should spend the first 5 minutes of the class going over the laboratory safety procedures and then an additional 5 minutes checking the students pre-lab, specifically the experimental design question.
- Students will have an opportunity to work in the laboratory for the remainder of the class period they should have about 70 minutes to work on their lab synthesizing their material and testing their capsules. Remind them when there is 10 minutes left to clean up and put their molds in the refrigerator.
- Day 3:
- Students will come to class and immediately head to the laboratory. At this point the will have the entire class to test their molds and record their data. Should the teacher decide to use the optional extension they can tell the students to redesign and engineer new improved molds to be tested on the fourth day. Students should be performing The Bloom Test during this time.
- Any additional class time should the students finish early should be spent reviewing related course content.
- Day 4:
- Students will come to class and immediately head to the laboratory. At this point the will have the entire class to test their molds and record their data. Students should be performing The Bloom Test during this time. At the end of the class the teacher should inform the students of the extension activity to be completed as homework.
- Any additional class time should the students finish early should be spent reviewing related course content.
- Day 5:
- At the beginning of the class the teacher will give the students 10 minutes to take the post-assessment.
- Next the teacher will provide the students with a maximum of 5 minutes per students for their presentation of the extension activity.
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