Introduction: Phase Inversion Process for Membrane Formation

To use these instructions your are expected to have a knowledge of basic lab safety and equipment. These instructions will explain how to make a membrane using the phase inversion technique, meaning to create a solution and remove the solvent quickly by changing the phase of the solution leaving a porous, solid membrane behind. These instructions are intended for lab researchers that want to try a new technique. In this example I will be making a polysulfone membrane.

Step 1: Materials

  • Vial with lid large enough to hold solution
  • Materials to create solution
  • Stir bar
  • Stir plate
  • Doctor blade
  • Glass plate to use Doctor Blade on
  • Large tub of water

Step 2: Prepare Your Materials

WARNING: make sure you know the possible hazards of the chemicals you are using and wear appropriate personal protection equipment.

  1. Decide what ratio of materials to use.
  2. Calculate how much of each material you will use using the molar mass and density for each substance.
  3. Measure out the correct amounts for each material.

Step 3: Create the Solution

If you are using a volatile solvent make sure to cover it while you measure out the other materials or measure it last and add it directly to the container holding the solution.

  1. Add the measured materials to the vial with lid.
  2. Add a stir bar to the solution and cap the vial.
  3. Place the vial on the stir plate and stir until fully dissolved. Make sure the stir bar can move fully but is not splashing the solution.

Step 4: Create the Membrane

Make sure the doctor blade is ready before uncapping the vial. This Step must be performed quickly to prevent skinning. Performing this step under a fume hood will prevent dangerous gaseous substances from being inhaled and help the membrane dry faster.

  1. Set the doctor blade to the desired membrane thickness.
  2. Uncap the vial and quickly pour the solution onto the glass plate. The solution can vary dramatically in viscosity depending on what material proportions are used.
  3. SLOWLY drag the doctor blade over the solution making sure no pooling occurs at the edge of the blade. Do not drag the blade back over the membrane because it could lead to a nonuniform membrane.
  4. Dunk the area of the glass plate with the membrane on it in the water. The membrane should distinctly change phase. For my PSF membrane it immediately changes white.
  5. Repeat steps 2-4 until the rest of the solution is used up.

Step 5: Removing the Membrane

Remember every solution is different so this Instructable does not guarantee that the membrane will remove cleanly.

  1. Try to remove the membrane with a GLOVED hand. If it easily slides off place it on a paper towel.
  2. If the membrane does not slide off easily use a sharp object like a razor blade to separate the membrane from the glass plate.

Note: it may be necessary to leave the membrane in water to prevent the pores from closing.