Preparation of Light-responsive Membranes by a Combined Surface Grafting and Postmodification Process

The overall goal of the following experiment is to change the permeability of track edged polymer membranes in UV or white light by modifying the surface with photochromic molecules. This is accomplished by first treating the polymeric membrane with plasma to induce radicals on the surface. The second step is to add a methanol monomer solution to perform the surface initiated polymerization on the membrane.

Next, the grafted polymer is post modified with photochromic substances. Ultimately, permeability measurements of the light responsive membranes are used to show how UV light changes the caffeine permeability through the membrane. The main advantage of the plasma ined polymerization is that covalently bound coatings on membranes can easily and homogeneously be created in a reproducible manner.

Visual demonstration is critical, as in our ADE setup. The membranes are allowed to polymerize immediately after plasma treatment and inert conditions. This method helps answer key questions in the fast coating of surfaces and brings covalently bound functionalization to the surface.

We first had the idea for this method when we talked to specialists in the field of plasma coating. Beforehand, we had unsuccessful attempts with classical coating methods such as spin coating and dip coating. Generally, individuals new to this method will struggle because plasma functionalization is a complex technology due to the many parameters that can be adjusted.

Demonstrating the procedure will be Karin Dreher, a student, a technician, and Karin ler, A scientist of my group First dissolve 100 milliliters of two Hydroxyethyl, methacrylate or Hema in 200 milliliters of water. After transferring the mixture to a separating funnel, wash it three times with 100 milliliters of hexane following removal of the hexane washes. Saturate the aqueous phase with sodium chloride and extract the hema with 50 milliliters of dathyl ether.

Following removal of the aqueous phase. Transfer the organic phase to a 500 milliliter round bottom flask and dry it over magnesium sulfate. Following filtration, remove the solvent in vao.

When finished, distill the hema under reduced pressure. Prepare a 0.62 molar methanol solution of the inhibitor free Hema by adding 2.3 milliliters of Hema to 27.7 milliliters of methanol in a one necked flask. After covering the flask with a septum, eliminate oxygen by bubbling Argonne through the solution for one hour.

Next position two polycarbonate membranes next to each other in the plasma chamber. With the shiny side of each membrane pointing towards the gas phase, connect the plasma chamber to a high vacuum for five minutes. After closing the vacuum valve open the valve connected to argon and oxygen gas to purge the chamber with this mixture for two hours with 15 SCCM argon and 2.5 SCCM oxygen.

Initiate the plasma and reduce the power to 12 watts for the polycarbonate membranes. Then treat the membranes for four minutes with the plasma first switch off the plasma and evacuate the chamber by first closing the valve connected to the gas mixture and then the valve connected to the oil pump. In the next step, connect the monomer solution with the chamber.

Connect the monomer solution with the chamber by opening the corresponding valve and pour the solution into the chamber. After ensuring that the membranes are covered with the monomer solution, open the valve connected to argon gas and store the reaction mixture for 12 hours at room temperature. Following removal of the monomer solution, wash the membranes with 100 milliliters of methanol in an ultrasonic bath for five minutes.

When finished, repeat the washing procedure with 100 milliliters of water. Then dry the membrane in vao over molecular thieves for two hours, dissolve 100 milligrams of Spiro benzoin compound 1 55 milligrams of nn cylo heyl carbo diamine, and 33 milligrams of four dimethyl am pyridine in 12 milliliters of turt butyl methyl ether. Next place a stir bar and a protecting grid into a round bottom flask.

After capping and drying the flask flooded with argon gas. Pour the spiro benzo pyran solution into the flask followed by the coated membrane. Then gently stir the mixture at room temperature for 12 hours.

Following this, remove the membrane from the flask and wash the membrane with 50 milliliters of turt beetle, methyl ether in an ultrasonic bath for five minutes. After repeating the washing procedure with 100 milliliters of both ethanol and water, dry the membrane in vao over molecular thieves for two hours. At this point, place the membrane on rough fabric.

Position a drop of nano pure water on the membrane surface. Then measure the contact angle at five different spots of the membrane for testing the long-term stability of the samples. Measure the contact angles at three different spots of the membranes after 0 1, 2, 3, 7, 14, and 21 days.

Next, fill the receptor chamber of a Franz diffusion cell with 12 milliliters of water. Fix the membrane in the Franz diffusion cell ensuring that it is in contact with the water in the receptor chamber. Fill the donor chamber or chamber on top of the membrane with 3.0 milliliters of a 20 millimolar aqueous caffeine solution.

Irradiate the membrane from the top of the donor chamber with white light. When finished, collect 200 microliter samples from the receptor cell. Repeat the experiment as described previously, but radiate the membrane with a 366 nanometer 80 watt per meter squared UV light during the entire permeability test.

To determine the caffeine concentration in the collected samples, plot a calibration curve with 15 different caffeine concentrations between 0.05 millimolar per liter and 1.5 millimolar per liter using a UV vis spectrometer. Following this, determine the concentration of each of the collected samples using the calibration curve. Then plot the determined concentration versus the time of the collected samples.

Make a linear fit through the points and determine delta C from the slope. As seen here, the edge rates for polyester, polyvinyl, aine, fluoride, and polycarbonate membranes are linear, which can be determined from the slope of the linear correlation of the ET time versus mass loss. The polycarbonate membranes show the lowest edge rate of the three polymer membranes.

The contact angle of a water droplet changes when the porous polycarbonate membranes are coated with poly hema via plasma induced polymerization. The difference in the contact angle between the uncoated membranes and poly hemo grafted membranes with poor diameters of 0.2 micrometers and one micrometer is shown here. It is clearly visible that the contact angle of a poly hema coated polycarbonate membrane does not change over time, which is an indication for a long-term stable coating.

The post modification with Spiro benzo pyran compound one increases the contact angle to 100 degrees. However, Spiro benzo pyran can be converted to the more polar marrow cyanide species by illuminating with the UV light, and this transformation reduces the contact angle of the membrane surface to 90 degrees. The permeability of the membranes is measured using a friend's diffusion cell.

The resistance of the permeability change decreases by 97%when the membrane is illuminated with white light, which demonstrates the presence of a light response of membrane Once mastered, this technique can be done in hours if it is performed properly. Following this procedure, other functionalization can be brought to the surface like temperature or pH responsive coatings. After watching this video, you should have a good understanding of how to produce plasma induced light responsive coatings.

The light responsive membranes are an interesting system to explore photo omic properties like color switching in UI and white light, or the fading rate of the colored state. In order to control the permeability of the membranes during the polymerization step, it's important to work in an inner atmosphere. Don't forget that working with high voltage electrodes can be extremely hazardous, and precautions such as a protective shield between you and the plasma chamber should always be in place while performing this procedure.