Reducing the Interfacial Tension of Magnetic Surfactants in Magnetic Fields - SMBHC Thesis Repository

Paul Scovazzo for their help and guidance in the laboratory, for teaching me concepts related to this research, and for assisting with my dissertation. Thank you, Emily Kohler, for training me in the lab, teaching me how to use the analysis software, explaining the calculation process, and always being available to answer questions even after you graduate. Thank you, Brady Weyrauch, for assisting with the design of the two permanent magnet devices, ordering the permanent magnets, ensuring the permanent magnet devices were built, helping me move labs, assisting with ordering a new microscopic camera , and always available to answer questions and help in the laboratory.

Anne Pringle, for ordering all the necessary laboratory equipment and for encouraging me, especially after setbacks. Finally, I thank Sally McDonnell Barksdale Honors College for the wonderful experiences I have gained in the past four years as a member and for the opportunity to write this thesis as a learning and growing experience. Surface tension decreased as surfactant concentrations increased with a slight decrease and increase in surface tension.

Surfactants

All hydrophobic groups are sequestered from water; ordered shell of H2O molecules is minimized, and entropy is further increased. There are four types of head groups that surfactants can have anionic, cationic, zwitterionic and nonionic. Magnetic surfactants can be created by replacing the head group of a non-magnetic surfactant with a metal.

In this research, the non-magnetic surfactant hexadecyltrimethylammonium bromide (C-TAB), with the chemical formula C19H42BrN, was used as the control surfactant. The magnetic surfactants were synthesized from C-TAB with the following head groups: cobalt, dysprosium and iron.

Figure 1-1. Micelle formation resulting from an increase in entropy.

Theory behind Surface Tension of Magnetic Surfactants in Magnetic Fields

Measuring Surface Tension

Also, since a needle can produce the point and the tip of the needle can be covered using a glass, capillary tube, there is no interaction and interference of the magnetic field with the needle. Although this method can be easily incorporated into a magnetic field, it requires extreme cleanliness of the needle and a careful and consistent procedure to produce reproducible results. The two dimensions are the equatorial diameter, D, and the diameter, d, at a distance, D, from the bottom of the drop [3].

An example of these dimensions measured for a drop from the laboratory can be seen in Figure 1-5. The shape-dependent parameter can be calculated using the following empirical formula shown in Equation 1.3. Using Equation 1.1 and all known variables, the interfacial tension for each droplet can be calculated.

Figure 1-4. The dimensions of a droplet used to find the surface tension using the pendant drop method [3]

Previous Research

The surface tension of the magnetic surfactants decreased when the surfactants were exposed to the permanent magnet compared to when they were not [4]. Since the permanent magnetic field has an attraction to the magnetic surfactant monomers, the attraction could have created an overall increase in the net force pulling the droplet down toward the magnet in the direction of gravity. Since it was unclear whether the decreased surface tension was the result of the attraction of the magnetic field to the magnetic surfactant monomers or an induced alignment, two other magnets, the solenoid magnet and the two permanent magnet devices, were used to investigate the hypothesis.

In Figure 1-7 (A) and (B), the magnetic field lines are parallel to the embedded droplet. Since the magnetic field lines are parallel to the embedded droplet, the magnetic field does not pull the droplet down in the direction of gravity. If the surface tension increases, indicating the absence of induced monomer alignment, the magnetic field only attracts the monomers and pulls the droplet in the direction of the field.

Figure 1-7. Magnetic field lines of solenoid and permanent magnets.

Equipment

A fan is placed in front of the coil to keep the temperature inside the coil as close as possible to ambient temperatures. A Gauss meter measured the magnetic field strength within the coil at the height at which the needle was placed in the coil and between the two permanent magnets for each apparatus.

Materials for Magnetic Field induced by Solenoid Magnet

Materials for Magnetic Field Induced by two Permanent Magnets

Procedure for diluting Surfactant Solutions

Once the mass of surfactant was determined, the fraction of the maximum concentration of each solution required for dilution was calculated. Equation 2.3 was used to determine the volume (mL) of maximum concentration for each diluted solution. For each of the diluted solutions, the calculated volume of the maximum concentration was added to a 50 ml volumetric flask with a 100 ml graduated cylinder and a Finn pipette.

The volumetric flask was gently stirred to evenly mix the concentrated surfactant with the diluted water.

Experimental Setup for Solenoid Magnet

Procedure for Solenoid Magnet

The magnetic surfactant was drawn into the syringe a third time to be placed in the coil. Before the needle was placed in the coil, the syringe was rotated 180 degrees and tapped lightly to bring air bubbles to the bottom of the syringe. Air bubbles were driven out of the syringe to reduce the frequency of air bubbles in the droplets.

Once the air bubbles were removed, the needle tip was wiped with Kimwipes® soaked in methanol; this ensured that the outer needle tip was clean and prevented surfactant solutions from adhering to the side of the needle. The needle tip was then placed in the magnetic coil and the syringe was held in place by clamps attached to the stand placed above the coil. The droplets were captured for 0 A, 5 A, 10 A, 15 A, and 19.5 A currents flowing through the coil, the Tesla values of which can be found in Table 3-1, and three droplets were captured for each magnetic surfactant concentration and power.

A current of 19.5 A was used instead of 20 A to prevent the fuse from blowing and for safety measures in the laboratory. Images were not captured if the droplets were shaking violently, contained air bubbles, or adhered to the tip of the needle, so a new droplet was constructed to address these droplet imperfections.

Experimental Setup for Two Permanent Magnets

A block of wood was taped to the edge of the ring stand, and a microscopic camera was taped to the table so it would stand in front of the permanent magnets. The arrangement for this setup is shown in Figure 2-2, and the apparatus used to hold the two permanent magnets in place is shown in Figure 2-3.

Procedure for two Permanent Magnets

Air bubbles were ejected from the syringe to reduce the number of air bubbles in the droplets while the needle was in the coil. Once air bubbles were removed, the needle tip was placed between the permanent magnets, and the syringe was held in place using clamps attached to the stand above the permanent magnets.

Surface Tension for Magnetic Surfactants in a Solenoid Magnet

Based on the hypothesis, the surface tension values in Table 3-2 and Table 3-3 should decrease from top to bottom as the concentration increases, and the surface tension values should decrease from left to right as the magnetic field strength increases. Although these general trends were seen, the trends were not explicitly seen for all values in Table 3-2 and Table 3-3. The numerical values for surface tension were plotted against concentration and are presented in Figure 3-1 and Figure 3-2.

Surface tension values for C-TADy exposed to the solenoid magnet as the concentration increases at different magnetic field strengths. Surface tension values for C-TACo exposed to the solenoid magnet as the concentration increases at different magnetic field strengths. To easily see the trends between surface tension and magnetic field strength, Figure 3-3 is shown below for the surface tension of C-TACo in the absence of a magnetic field and with a magnetic field strength.

Graphs for each magnetic field strength of C-TADy and C-TACo can be found in the appendices. Surface tension for varying concentration values of C-TACo at 0.0 Amp and 10.0 Amp passing through the magnetic magnet. As the surfactant concentration increases, surface tension values should decrease because more surfactant monomers are available to adsorb onto the interface of the system.

If the hypothesis for this research were true, the surface tension should also decrease as the strength of the magnetic field or the amount of amperes sent through the coil increases. According to the trends shown in the graphs, the overall surface tension decreased as the surfactant concentration decreased, but the graphs show a slight drop and rise in surface tension as the concentration increases. While some surface tension values decreased as the magnetic field strength increased, the opposite trend was also seen as shown in Figure 3-3.

Table 3-3. Surface tension values for C-TACo.

Surface Tension for Magnetic Surfactants in between Two Permanent Magnets

Surface voltage trend for C-TADy at different concentrations for 0.0 A and 5.0 A flowing through an electromagnetic magnet. Surface voltage trend for C-TADy at different concentrations for 0.0 A and 19.5 A flowing through an electromagnetic magnet. Surface voltage trend for C-TACo at different concentrations for 0.0 A and 5.0 A flowing through an electromagnetic magnet.

Surface tension trend for C-TADy at different concentrations for magnetless and N42-1in x 1in permanent magnets. Surface tension trend for C-TADy at various concentrations for magnetless and N42-2in x 2in permanent magnets. Surface tension trend for C-TADy at different concentrations for magnetless and N52-1in x 1in permanent magnets.

Surface tension trend for C-TADy at varying concentrations for no magnet and N52- 2in x 2in permanent magnets. Surface tension trend for C-TACo at varying concentrations for no magnet and N42-1in x 1in permanent magnets. Surface tension trend for C-TACo at varying concentrations for permanent magnets without magnet and N42-2in x 2in.

Surface tension trend of C-TACo at varying concentrations for no magnet and N52-1in x 1in permanent magnets. Surface tension trend of C-TACo at varying concentrations for no magnet and N52- 2in x 2in permanent magnets. Surface tension trend of C-TAB at varying concentrations for no magnet and N42-1in x 1in permanent magnets.

Surface tension trend of C-TAB at varying concentrations for no magnet and N42-1.5 in. x 1.5 in. permanent magnets. Surface tension trend of C-TAB at varying concentrations for no magnet and N52-1in x 1in permanent magnets. Surface tension trend of C-TAB at varying concentrations for No Magnet and N52- 2in x 2in permanent magnets.