Preparation and Friction Force Microscopy Measurements of Immiscible, Opposing Polymer Brushes

The goal of the following experiment is to prepare admissible polymer brush systems and compare them to traditional missable polymer brush systems by measuring the frictional response to relative sliding motion for both systems using friction force microscopy. This is achieved by starting with two sets of silicon surfaces and grafting penai Pam onto one set and PMMA onto the other. These will be the flat polymer brush surfaces used to form one part of the polymer brush systems.

As a second step, begin with a gold colloid. Attach to a silicon atomic force microscopy cantilever and graph PMMA onto it to make a force measurement probe. This will also form the second part of the polymer brush system.

Next, mount the force measurement probe into an atomic force microscope. Mount a ated PMMA brush surface as a sample to measure friction admissible. Brush systems mount a ated penai pan brush surface to measure friction for admissible brush systems.

The results show that the friction for admissible systems is approximately 1%of the friction for the traditional permissible systems as measured by friction force microscopy. One key advantage of our technique over existing methods based on industrial oils is that a low viscosity liquid is kept in the contact even when conditions are harsh at the microscopic scale as it happens when you have surface irregularities bumping into each other. Unlike traditional brush systems, our brushes do not interpenetrate because of a fluid fluid interface as you have it between vinegar and oil in a salad dressing.

Because brushes no longer interpenetrate friction is reduced. Even more importantly, damage to the polymers is prevented and ultimately where may be absent. Visual demonstration of this method is critical as the sample preparation and the atomic force microscopy characterization steps are difficult to learn.

Special skills are required for homogeneous and reproducible functionalization of micrometer sized colloidal beets demonstrating the procedure will be added Kansky, a former postdoc and c de bear, a research associate in my laboratory, Consult the manuscript for preparation of silicon surfaces. The experiment requires deposition of initiator on both gold, colloidal probes and gold substrates. To start work with the probes, obtain a small vial that has been flushed with Argonne Roma flask containing 0.2 millimolar concentration.

Monolayer solution Withdraw 1.5 milliliters, transfer the 1.5 milliliters of monolayer solution to the vial. Keep the vial nearby. Next, get the gold colloidal atomic force microscopy probes have ready a vial of ethanol and a vial of chloroform into which the probes can be dipped.

In addition to the vial of monolayer solution, use tweezers to pick up a probe. Be certain to hold it so as not to cause damage. First, dip the probe in the ethanol for a few seconds, then dip it into the chloroform for a few seconds.

Finally, place it into the vial with the monolayer solution. Pose the vial firmly and wrap it in aluminum foil before putting it aside on the bench overnight. Now get cleaned and rinsed gold coated substrates.

All of the substrates used in this experiment are one centimeter by one centimeter. Bring forward the large flask containing the monolayer solution and transfer the substrates into it so they are immersed. Close the flask and store it in a dark place overnight The next day, first, get the substrates and return them to the bench.

Prepare to wash them using a container of chloroform and et ethanol in a squeeze bottle. Have the polymerization flask ready. Remove each substrate from the monolayer solution and immerse it first in the chloroform.

Next, wash it with ethanol. When done, place the substrate in the polymerization flask. When all of the substrates have been placed in the polymerization flask, seal it with a rubber septum.

After setting the substrate flask aside, continue by retrieving the vial with the colloidal probes and opening it. Follow the same washing procedure by first dipping a probe in chloroform and then ethanol. As each is washed, transfer it to an individual polymerization vial.

This video will only show the steps for polymerization of poly n Isop Proppy acrylamide penai Pam. Details for polymethyl methacrylate. PPMA can be found in the manuscript with the substrates and probes in their polymerization vessels.

Start the polymerization process by purging both vessels, demonstrating this with the substrate vessel. Here's the septum with a needle attached to an argon supply. Next, here's the septum with an additional needle for outlet.

Then start the argon flow. Allow the purge to continue 30 minutes as the vessels purge. Work with atom transfer radical polymerization, A TRP.

Medium nyam. Create the mono solution by dissolving the nyam and the PM dta in the medium. Be sure to degas the solution for two hours before use in a separate flask of 76 milligrams of copper bromide and a magnetic stir bar, attach the flask to a vacuum line and an argon source.

As the flask sits on a stir plate, start evacuating it by opening the vacuum line. When evacuation is complete, about 30 minutes, close the valve to the pump and open the valve to the Argonne supply. Repeat the evacuation and backfill cycle three times before proceeding.

Once the mono solution has been Degas, transfer it to the flask with the copper bromide and begin to stir the mixture. After about 15 minutes, a clear green polymerization solution is observed. Use an argon flushed two milliliter syringe and needle to withdraw one milliliter of the polymerization solution.

Transfer the collected solution into a vial with a colloid probe by injection through the septum. Continue to use the syringe to withdraw some of the remaining polymerization solution. Inject the collected solution into the flask containing the substrates.

Add enough to submerge each sample completely. Allow polymerization to proceed for two hours at room temperature. When two hours have passed, open the polymerization vials.

Next, start with a probe and remove it for washing. Wash a sample by first dipping in ethanol and then dip in water. Repeat this several times after washing a probe, immerse it in 0.1 molar EDTA for a few seconds.

Lace the probe alone in a vial containing purified water for storage. Proceed with washing each substrate. Do this in the same manner as the probes going through several cycles of pouring water.

Then ethanol over it. Note that the changing color of the substrate indicates the presence of the brush. After washing a substrate, transfer it to a well plate.

Place each substrate in an individual well and cover it with 0.1 molar EDTA solution. Leave the washed substrates for at least 12 hours to remove all copper. The next day.

Wash each substrate in water and ethanol. Again, place the substrates in a well plate store the well plate in a nitrogen box for this video. The next step is to perform an atomic force microscopy measurement.

Here, A-P-M-M-A covered silicon substrate has been mounted into the microscope and the probe has been mounted into a liquid cell. Complete the preparation of the A FM scan head and continue by completing preliminary atomic force microscopy steps, including aligning the laser, calibrating the spring constant, and finding the quality factor upon completion of the preliminary steps. Have ready a syringe filled with aceto phon that will be applied to the brush sample.

Remove the a FM head to access the sample. Then unmount the sample from the microscope. Gently apply the aceto phon to sulfate the brush.

Note that the color of the sample changes as the solvent evaporates, allowing for the drying process to be followed. Remount the sample in the atomic force microscope and replace the A FM head. Next, return to the controls to set the deflection set point and place the cantilever in contact with the surface.

This causes the aceto phon to move into the brush to create a capillary bridge. These traces were obtained using the height and friction image channels. The scan sizes 40 microns and slow scan axes are disabled.

Record the height and the friction image channels when the images are captured and the cantilever withdrawn. Begin preparing to switch the PMMA substrate to a penai PAM. Brush covered sample.

First, retrieve the pinot PAM substrate. Then apply a drop of water on it to ate the brush. Next, make the switch.

Lift the head of the A FM and quickly replace the PMMA surface with the penai PAM surface. Move quickly to avoid the evaporation of acetophenone from the PMMA brush on the colloidal probe. After mounting the sample, place the A FM head back in its position.

Return to the A FM controls to reengage the tip and surface and record images as before. Here are filtered and smoothed force traces for the sliding surfaces. These traces are for the MISSABLE PMMA systems and show both forward and backward motion.

These traces are for the immiscible P nine PAM systems and also show forward and backward motion in the plots. The force is normalized by the steady state sliding force for the symmetric missable system. The normal load is 30 nano newtons, and the speed of traversal is 80 microns per second.

Note, the steady state force for the permissible system is 90 times that of the admissible system. Many machines and devices have moving parts, producing friction, and wearing off with time limiting the lifetime. We see applications for many of them, all the way from axles and pistons to medical syringes providing ultra low dosages and perhaps even artificial joints.

Of course, chemical engineers or ologists will have to design optimal solutions for each specific application. After watching this video, you should have a good understanding of how to prepare polymer brush systems. Functionalize force microscopy probes and perform friction force microscopy experiments While attempting the friction force microscopy experiments.

It's important to remember not to apply too much liquid because you want the capillary to form between the two brushes and not between the brush and the cantilever, because that would distort the laser signal. Don't forget that working with chemicals can be extremely hazardous and precautions such as working in a valve ventilated fume hood wearing gloves and goggles should always be taken while performing this procedure.