NAME: Hour: LAB (Part 1): HYDROGELS In this lab, we are going to investigate how chemicals are used in everyday disposable diapers. In this activity, you will isolate the super absorbent polymer in a disposable diaper and we will study how this polymer interacts with water. Objective: The purpose is to understand what is in disposable diapers that keep babies dry. Question: How are polymers used to keep a baby dry? What substances do diapers contain that makes them successful in their purpose? KEY VOCABULARY hydrophilic: hydrophobic: lipophilic: MATERIALS Eye protection Gloves Thin (“ultra”) disposable diaper Scissors Ziploc baggie Beaker 100 ml water table salt PROCEDURE 1) Cut down the center of the inside surface and remove the fluffy filling and place it in a ziplock baggie. Some diapers have a cotton layer that can be split down the middle. Try to peel apart the cotton layer in the middle, because that is where a lot of the poly absorb crystals are. 2) Pull the filling apart into smaller pieces and tie a knot to close the plastic grocery bag. 3) Shake the bag to dislodge the absorbent crystals within. 4) Open the plastic grocery bag and tilt the bag to collect the dislodged crystals in the corner of the bag. 5) Cut a small hole in that corner and empty the crystals into a beaker. 6) Add 100mL of water to the crystals. 7) After a couple of minutes, add 2 tablespoons of salt. 8) Record the results on the chart. BEFORE WATER IS ADDED AFTER WATER IS ADDED AFTER SALT IS ADDED VOLUME (ml) DIAGRAM DESCRIPTION LAB (Part 2): AEROGELS MATERIALS Eye protection Gloves 3cm x 3cm piece of Aerogel insulation Beaker 100 ml water 10 ml oil PROCEDURE 1) Measure 100 ml water into the beaker. 2) Measure 10 ml oil and pour on top of the water. 3) Push the 3 cm x 3 cm square of aerogel insulation into the beaker with the oil and the water. 4) Record results on the chart. BEFORE AEROGEL IS ADDED AFTER AEROGEL IS ADDED DIAGRAM DESCRIPTION ANNOTATE THE FOLLOWING READING. CIRCLE KEY WORDS and UNDERLINE KEY EXPLANATIONS. Draw arrows to connect important concepts. The secret, water-absorbing chemical in a diaper is a superabsorbent polymer called sodium polyacrylate. A polymer is simply a long chain of repeating molecules. If the prefix “poly” means many, then a polymer is a long chain of molecules made up of many smaller units, called monomers, which are joined together. Some polymers are made up of millions of monomers. Superabsorbent polymers expand tremendously when they come in contact with water because water is drawn into and held by the molecules of the polymer. They act like giant sponges. Some can soak up as much as 800 times their weight in water. Just imagine how much water a giant diaper could hold! HOW DO HYDROGEL POLYMERS WORK? A polymer is a very long chain that’s made up of identical, repeating molecules – they’re the “links” in the chain. Think of these links as tiny sponges waiting to connect with water molecules. In the absence of water, the polymer chain is very tightly twisted and piled up on itself so the water connection points are tightly buried inside the nugget. When water is available, the molecular links on the outside of the nugget grab it and hold on through simple cross-link bonding. The more water is available, the more the polymer has to unwind to get it. Each link gets larger as it hooks up to more and more water. The chain begins to swell on the outside surface and that allows more water to get farther into the polymer to available link points. Water is cross-linked farther in and the polymer expands to make room for it. If enough water is available, this bonding and swelling continues until there are no more available places to collect water. Absorption stops but water that’s linked to the polymer has expanded it to about 300 times it’s original weight and it’s not tightly twisted at all. The crystal is now about 98% water and 2% polymer. That’s a lot of water! Polymers are very common and you see and use them everyday: silk, wool, nylon, cotton, cellulose, proteins, rubber, PVC, epoxy materials, silicone, hair conditioner, paint, polystyrene, adhesives, gelatin, Silly Putty®, polyester, Kevlar®, CDs, eyeglasses, Teflon®, and the list goes on and on! QUESTIONS 1. What happened when you added water to the hydrogel? What do you think was happening at the particle level to make this occur? Use information from the reading to explain. 2. Describe what happened when you added salt to the hydrogel/water combination. At the particle level, describe what you think was happening. 3. What happened when you pushed the aerogel insulation into the beaker with oil and water? Use what you know from the reading about hydrogels to form a hypothesis about why this happened. 4. Which material – hydrogel or aerogel – was hydrophilic? Which was hydrophobic? Provide evidence from the LAB to support your decision.