Hands-on Activity Designing Polymers to Clean Water

Learning Objectives

After this activity, students should be able to:

• Predict how changing a component of their design might improve or impair its properties.
• Explain the thinking behind their engineered solutions.
• Test the design for functionality.
• Collaborate in groups to create the best design from a collection of individual designs or features.
• Examine the successes and shortcomings of a design and further iterate upon it. 

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

Each group needs:

• Styrofoam block, approximately 17 cm x 30 cm (6.6 inch x 11.8)
• 20 pipe cleaners 
• 40-50 small pom-pom balls, 1.3 cm (0.5 in)
• 10 large pom-pom balls, 5 cm (2.0 inch)
• 10 rubber bands
• yarn, 2 m (6.5 ft or more)
• aluminum foil, 50 cm x 27 cm (19 in. x 11 in.)
• masking tape, 1 roll
• container or tray to hold and organize group materials
• scissors
• cups (for holding a volume of pom-poms that will be “spilled” on to their designs) 0.5 L (18 oz.)
• Designing Polymers to Clean Water Worksheet (one per student)

Worksheets and Attachments

Introduction/Motivation

(Introduce the Designing Polymers to Clean Water PowerPoint Presentation to the class.)

Let’s start our activity out with a simple question: what does dirty water look like? Think about a pond, a lake, a river, or even an aquarium. What might form on the surface of a pond or lake, or what might collect at the edges of a river? How do we know a filter may not be working in an aquarium? Let’s examine Figure 1 as an example below and then answer the following questions.

• What do you think about this water? (Possible answers: It’s dirty; it’s cloudy; it looks unhealthy.)
• Why do you consider this water as “dirty”? (Possible answers: It doesn’t look clear; it looks like it has a buildup of something on the inside; it looks like it has been sitting, or stagnant, for a while.)
• How can we make this water “clean”? (Possible answers: we could replace it; we could check the filter and replace it.)

Filters are used to purify water from a variety of sources, including freshwater lakes, rivers, and underground wells. Engineers can even build highly complex filters called to remove the salt from ocean water! However, for common household use, filters are commonly used to purify water sources including tap water and collected rainwater. Filters are also important for use in water filtration applications in developing countries where clean water may be scarcer. However, filters come with their own set of problems.

Using a filter means putting it through several stages. A brand-new filter out of the box is highly effective and maintains its properties even after extensive use. However, if a filter is designed effectively, it will eventually become covered with foulants. A foulant is an unwanted substance that adheres to a particular surface.  (See an example of a used filter on Slide 12 of the Designing Polymers to Clean Water PowerPoint Presentation.)  

Foulants can be inorganic or organic in nature. Rust, lime build-up, or corrosion are all examples of inorganic fouling. Organic fouling could consist of algae, plant matter, or even bacteria. Foulants can cause the purification process to be inefficient, lower water quality, and waste energy of the filtration system.

Today you are playing the role of engineers! Your goal: to create a solution that could extend the life and quality of water filtration systems using only available materials. Your invention could be especially important in countries where clean drinking water is hard to find! You will design a model for adding an antifouling surface to a water filtration system.

Procedure

Background

Fouling is when an undesired layer of substances adhere to the surface of a water treatment membrane. In this case, foulants adhere to a water filtration membrane over time of normal use. Fouling is troublesome because it can degrade water quality and make the water filtration process inefficient. All water filtration membranes, the semi-permeable surface where the filtration occurs, are prone to fouling. Finding a way to extend the life of an existing membrane to prevent or resist fouling is important. One such engineering application is in the form of polymer brushes, which are dense layers of polymers attached to a surface. These brush-like polymers have the potential to function as water filtration coating that is also fouling resistant. The polymers have hydrophilic (water-attracting) interactions that serve to form a hydration layer that repels foulants. This hydration layer provides a “self-cleaning” effect on the filter.

Engineering technologies such as polymer brushes can have a wide reaching effect, Because obtaining fresh, clean water can be very difficult in many places around the world, this activity can be used as a model to help the students begin to think of the process of modifying a surface to obtain a more desired outcome, which is a basic goal of the antifouling polymers research and design.

Before the Activity

• Before beginning the activity with the students, collect an appropriate amount of materials and place them in stations around the room, either in a container or on a tray where they will have easy access to the materials in one place.
• Review the activity vocabulary and the Designing Polymers to Clean Water PowerPoint Presentation. Also, talk students through the engineering design process and pay particular attention to the iterative nature of the process (see Figure 2 below):

With the Students

1. Display the Introduction along with the Designing Polymers to Clean Water PowerPoint Presentation. This will introduce the concept of fouling and the design challenge.
2. Using the Engineering Design Process as a reference (see Figure 2), instruct students on how they will use the process to develop a model, or prototype, to solve the problem of fouling by creating an antifouling water filtration membrane coating, using the materials available at their table.

• Distribute copies of the Designing Polymers to Clean Water Worksheet. Have students complete Questions 1 and 2.

3. Distribute one Styrofoam block per group (this serves as the model of the surface for their water filtration system membrane). Explain that their goal is to make a system that modifies the surface of their water filtration “membrane.” The system should be a design that allows water molecules (small pom-poms) to interact with the membrane (the Styrofoam block), but keep the foulants (the large pom-poms) from interacting with the membrane.

• Tell group to use the following materials: pipe cleaners (which represent the hydrophilic polymer), yarn, aluminum foil, tape (all different types of side chain possibilities), and scissors.

4. Give students several minutes to think about the materials they have, and what they will be able to do with those materials as well as their limitations. 
5. Tell students to brainstorm individually and to make a blueprint of the materials they will use to create a model of an antifouling coating of a water filtration membrane. After they finish brainstorming, have them share their ideas with their groups. Instruct students to select the best parts of each person’s design to create the prototype for their group, which is step four of the engineering design process.

• Provide approximately five minutes for students to follow these directions using their Designing Polymers to Clean Water Worksheet.

6. Have students predict the outcome of what they expect from their blueprint and to outline a system for determining the success of their design. After completing that step, instruct students to build their prototype (step five of the engineering design process) and test it (step six of the engineering design process) to see how well it works. Give students time to test and retest their designs.
7. Let students discuss predictions in their groups for five minutes. Then, have them gather materials and build their models for 15 minutes. Finally, have students test their models and redesign their antifouling systems for another five minutes. Students should complete their Designing Polymers to Clean Water Worksheet during this time.
8. After students finish testing and redesigning, have each group share their results (see the Design Presentation in the Activity Embedded Assessment below). Conduct the Post-Activity Assessment.

Vocabulary/Definitions

antifouling: Properties that to remove foulants (or adhesion of unwanted substances to a surface).

foulant: Unwanted substances that can adhere to a surface.

hydrophilic polymer: A repeating chemical chain that attracts or is attracted to water.

membrane: The semi-permeable surface where filtration occurs.

polymer: A bonded, repeating series of molecules or structures in a chain.

Assessment

Pre-Activity Assessment

Engage Questions: Students will think, pair and share, answering the following questions.

• What effect do you believe foulants could have on the water filtration membrane (without the polymer brush)? (Example answer: They could cause the filter to clog or not work properly.)
• How could the water be affected? (Example answer: Undesired particles could remain in the water, causing people who drink the water to get sick.)

Activity Embedded Assessment

Worksheet: Students complete the Designing Polymers to Clean Water Worksheet which walks them through the steps of the engineering design in the context of designing an antifouling polymer brush model. It includes opportunities to state the problem, brainstorm solutions, plan a design, test how well it works quantitatively, and improve upon their design and share their results with the rest of the class.

Design Presentation: Students will give a two-minute oral presentation on their design to the class, answering the following questions: 

• What would it look like if your membrane was fouled?
• Why did you design it the way you did?
• How well did it work?

Post-Activity Assessment

Revaluation: Ask students the following questions:

• Based on the design that you made, what types of changes could you make to make it work even better?
• What are some potential limitations of the model in comparison to real life?

Investigating Questions

How can we engineer a model for an anti-fouling coating of a water filtration membrane? (Example answers: use the engineering design process to create the model, attach different materials to the pipe cleaners to create hydrophilic polymer chains, etc.)

Troubleshooting Tips

• Make sure that students understand that the water molecules (small pom-poms) should be able to make it through to the membrane, while the foulants need to be kept away from the membrane (Styrofoam board), or ideally even repelled from it.
• Students can cut, rip, or tear any of the materials except for the pom-poms and the membrane (Styrofoam board)
• Make sure the parts of the brainstorming design are labeled so that the students can clearly follow their plans.

Activity Extensions

Students can draw their new and improved design based on their testing and what changes they think they would make their prototype design better. They may also calculate the water flow efficiency and the percentage of foulant blockage (see Designing Polymers to Clean Water Worksheet).

Students may be given the option to bring in their own items to further enhance their designs.

Activity Scaling

• For lower grades, students design a smaller area to cover (size down the Stryofoam block).
• For higher grades, students can consider how they would change the design if the shape of the Styrofoam is different, like the membrane surface is spread over a multidimensional shape.
• Students could use foulants of different sizes and shapes that they have to prevent from getting through to the membrane.

Copyright

Contributors

Supporting Program

Acknowledgements

This curriculum was based upon work supported by the National Science Foundation under Rice University Engineering Research Center for Nanotechnology Enabled Water Treatment Systems (NEWT) RET grant no.1449500. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

Special thanks to Dr. Verduzco, Christina Crawford, Dr. Carolyn Nichol and Hao Mei.