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Creating the greatest bubble

  1. Sep 23, 2008 #1
    My name is Ben and I am a senior in highschool, enrolled in a college prep physics class. As the first lab of the year, my class was assigned the task of creating a bubble making solution and testing it's effectiveness. For my solution I chose a mixture of Dawn soap, corn syrup, glycerine, and water. Respectively 45ml, 40ml, 20ml, 450ml. The lab was a success as I measured dome bubbles, height and width, and full bubbles, width.

    Now that I have completed the lab I am posed to write my report on the experiment. My hypothesis was that my mixture would create the largest bubbles in the class (5 other groups participated). Part of my report though is to talk about how one goes about creating the greatest bubble. I believe the rest of the groups will probably be talking about different solutions they found online and the key ingredients, this does not really answer the question though. I need to understand what it is that makes a bubble... well what makes it a bubble.

    In my experiment I used a straw dipped into the solution to make the dome bubbles and a wire hangar bent into a wand with a circular tip to create my full bubbles. In order to understand how to create a better bubble I think I need to explore the physics of what made those bubbles successful.

    I understand that its the surface tension of the solution binding all the molecules together around the air that makes the bubble form. I also understand the law that states a bubble takes up the surface area for it's volume and that their is equal tension on all parts of the bubble keeping it round.

    What would it take though to make my bubble hold together better, so presumably i could make it larger before it pops?

    I have read that when you add soap it lowers the surface tension and that is what allows the bubble to form and hold... So would trying to increase the tension be a bad idea? But if it's not an increased tension that holds the bubble together longer then does that mean it's a decreased tension? Does that even make logical sense? Finally, is there merely balance point between high tension and low tension that is ideal?

    I realize this is somewhat chemistry, but the answer Im looking for must be physics since I'm the a physics class. At least i hope so =D
  2. jcsd
  3. Sep 24, 2008 #2

    Andy Resnick

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    Bubble stability (or equivalently, foam stability) is a tricky problem to solve- there are a lot of physical processes involved and the central process- film rupture- is ill-posed mathematically, although there has been some success in modeling drop pinch-off.

    Conceptually, you seem to have a good grasp on the problem- the different soap solutions are manipulating the surface tension, and specifically lowering it (surfactants). So what you need to understand now is *by what mechanism* lowering the interfacial energy (surface tension) leads to increased bubble stability.

    Think about what interfacial energy means: how much energy it takes to create an interface. If a lot of energy is required (high surface tension), what *equilibrium* behavior is expected (and vice-versa for a low surface tension)?

    If the concept that a bubble is a thin film is confusing the issue, then instead think about liquid-liquid emulsions (water/oil salad dressings, lava lamps..). How can you keep salad dressing from separating?

    Another confounding issue is that you are dynamically "stretching" the bubble by blowing air into the interior, and that the fluid that makes up the bubble is free to flow. The viscosity of the fluid controls how fast it flows (in the case of a bubble, drains), and that leads to how long a bubble remains stable.

    Does that help?
  4. Sep 25, 2008 #3
    That does indeed. Although I'm still a little confused, it is certainly good food for thought and should prove very useful in my gathering understanding of the problem.

    tyty =D
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