Why do objects self-assemble into larger structures? July 2012

Students can visit activity stations to explore some factors that influence self-assembly. Shapes: Two and three dimensional objects are provided at a number of stations that can be used to assemble structures and patterns. Forces Some stations have magnets glued into bottle caps that can be used to explore the role of attractive and repulsive forces. Some stations explore the role that gravitational force plays in the self-assembly of a structure or pattern. A web site can be used to explore the role of electrical attractive and repulsive forces (and shape) in self-assembly. Agitation At some stations, students will need to provide the agitation that results in assembly. They can push objects into a structure or pattern or they can tap on a container to cause objects to self-assemble.

Frame 4 thru 19 of this PowerPoint can be used to print questions and/or tasks for each station. Station 1 has 4 activity options. Stations 2A and 2B activity options can have duplicate set-ups. Station 3 has 3 activity options. Station 4 has 3 activity options. Station 5 has 3 activity options and can have duplicate set-ups. The charge animation web site document can be made available for students. Note: The number of stations can be reduced to accommodate class size or class time.

Experiment with Self-Assembly Processes: Use the following web site to explore the role of electric charge and shape on the self-assembly process. Go to a Concord Consortium web site at: http://www.concord.org/ Go to “Activities for School and Home” menu and select Molecular Workbench software. Click on “Run this Experiment in MW (Molecular Workbench). Download Molecular Workbench software. Read the Introduction on the Table of Contents page. Choose “Fibers” in the Menu. Experiment with Self-Assembly Processes: Read directions for “Challenge: Designing a self-assembling fiber. Record your observations of the affect of the location and amount of charge on a fiber on the self-assembly process. Use the “Previous” and “Next” buttons in the upper left corner at the top of the page to explore and record your observations of other factors that influence the self-assembly process. Close the Molecular Workbench web site.

Station 1A Two Dimensional Tiling Which shape of tiles can pack tightly and completely fill the area of a rectangular or square area? Why won’t some shapes completely fill a defined area? What property of a tile would affect how much of a circular area is filled with tiles? What property of the tiles could cause them to self-assemble if they were agitated?

Station 1B Two Dimensional Tiling What arrangement of heart shaped tiles fills the greatest portion of a rectangular area? How would you calculate the maximum possible percentage of an area of a rectangle that can be filled with circular tiles? What property of the tiles could cause them to self-assemble if they were agitated?

Station 1C Two Dimensional Tiling Pentagon and star shaped tiles are available at this station. Which shape can form a periodic pattern when the tiles fill the maximum area? What property of the tiles could cause them to self-assemble if they were agitated?

Station 1D Two Dimensional Tiling Asymmetric Corks and Trapezoidal Tiles are available at this station. What are different types of structures can form using asymmetric tiles if you try alternative arrangements? What property of the tiles could cause them to self-assemble if they were agitated?

Station 2A Components in Containers Straws and two different containers are available at this station. How does the shape or dimensions of a container affect the lattice pattern? What are the defects in the lattice patterns? How might the dimensions of the container affect the lattice?

Station 2B Components in Containers Straws and a container are available at this station. How does a force or agitation influence the assembly of a lattice pattern of straws in a container? How might the dimensions of the container affect the lattice?

Station 3A Floating Shapes Symmetric and asymmetric floating objects are available at this station. Gently tap on the table or the rim of the pan to create agitation as floating objects of a specific shape are added (one at a time) to a pan of water. How does shape influence the geometry of the pattern that forms?

Station 3B Floating Shapes Symmetric and asymmetric floating objects are available at this station. Gently tap on the table or the rim of the pan to create agitation as floating objects of a specific shape are added (one at a time) to a pan of water. How does shape influence the geometry of the pattern that forms? Are the arrangements periodic or random?

Station 3C Floating Shapes Symmetric and asymmetric floating objects are available at this station. Gently tap on the table or the rim of the pan to create agitation as floating objects of a specific shape are added (one at a time) to a pan of water. How stable are the structures that form? For a given shape, is there a most stable structure?

Station 4A floating magnets Magnets glued into bottle caps are available at this station. Select bottle caps with magnets where the magnetic poles were oriented in the same direction when glued into the bottle caps. Add identically oriented magnets one by one to a pan of water. If necessary, gently tap on the table or the rim of the pan to create agitation Describe the patterns that form.

Station 4B floating magnets Magnets glued into bottle caps are available at this station. Create a sample where half of the caps have magnetic poles oriented one way and half of the sample have magnetic poles oriented in the opposite direction. Add alternately oriented magnets one by one to a pan of water. If necessary, gently tap on the table or the rim of the pan to create agitation Describe the patterns that form.

Tap on the table to provide agitation. Station 4C Magnets Repeat the procedures for the activity at Station 4A or 4B by placing the caps on a dry table top. Tap on the table to provide agitation. What forces inhibit the self-assembly process in this activity?

Station 5A Floating Cereal Bowls of skim milk and cereal are provided at this station. Put one piece of oat cereal onto the surface of skim milk. Why does a piece of oat cereal form a small indentation in the surface of the skim milk? Note: Polarized sunglasses can be used to view the surface of the liquid. Experiment with self-assembly by placing multiple pieces of cereal on the surface of skim milk. One option is to determine how the distance between pieces of cereal affects the self-assembly process.

Station 5B Floating Cereal Bowls of heavy cream and cereal are provided at this station. Put one piece of oat cereal onto the surface of skim milk. Note: Polarized sunglasses can be used to view the surface of the liquid Why does a piece of oat cereal for a small indentation in the surface of the heavy cream? Experiment with self-assembly by placing multiple pieces of cereal on the surface of heavy cream. One option is to determine how the distance between pieces of cereal affects the self-assembly process.

Station 5C Floating Cereal Bowls of skim milk, heavy cream and cereal are provided at this station. Put one piece of cereal onto the surface of skim milk in one bowl and one piece of cereal onto the surface of heavy cream. Design and conduct an experiment to compare the self-assembly of cereal on the surface of two different liquids. What can you conclude from your experiment?

An example of factors that affect self-assembly often discussed in MS and HS Life Science. The mechanism by which enzymes catalyze chemical reactions begins with the binding of the substrate to the active site on the enzyme. Charge and shape both play a role in this process.

On Monday, you observed assembly influenced by electrical forces. The hydrophilic ends of oleic acid molecules were attracted to the surface of water in a tray.

On Tuesday, we observed a factor that influenced self-assembly during an electrodeposition activity. Using a 6 Volt battery caused large, irregular clusters of zinc to rapidly form. Many clusters would not adhere to the copper electrode.

Other factors that affect self-assembly include Fluidic forces Convection currents Thermal agitation Stochastic (random) agitation Reversibility

In what ways do these activities illustrate any of the “Big Ideas in Self-Assembly” ? Structural components are mobile. The goal is a low energy equilibrium state. Ordered structures result from a less ordered system. Assembly is a result of attractive or repulsive forces between the components. An environment is selected to induce designed interaction. Components retain physical identity through and after. The process is reversible or adjustable. Whitesides & Boncheva (2002)