Q1. Evaluation of the surface tension of magnetic surfactants on a complex surface

Primarily, surfactants reduce the surface tension of liquids. Magnetic surfactants do this by an external magnetic field on a molecular field to induce alignment. The magnetic ion surfactants have high concentrations of metal centers which far effective than the conventional counter metal complex anions (www.emerginginvestigators.org). A microbalance is placed between two surfaces when measuring surface tension. In the Du Nouy method, a small ring is positioned on the surface, and the measurement of the force that will pull off the ring took (www.physics.bu.edu). The dimensions of the drops from a needle end measure the surface tension using the formula:

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gh=rgD2H,r is the density difference, g is gravitational acceleration, D is themaxequatorial drop diameter, H is the shape factor.

As per Pendant drop method, a drop is formed within the magnetic field is created. It is for the magneto-responsive properties that magnetic surfactants are investigated. To obtain good results, extreme caution and attention to fine details are needed. Magnetic fields are introduced to these surfactants through a permanent magnetic field or charging of particles in an electric current. When a permanent magnet is introduced, surface tension changes due to change in surface energy. As the surfactant poles get attracted to the permanent magnet, the extra force of magnetism acts in the direction of the gravitational pull of the suspended surfactants (Koehler, 2016).

Q2. Cleaning of surfactants

Surfactants are molecules added to water to reduce its viscosity. It allows it to become penetrable in tubes and surfaces for cleaning purposes. The surfactant molecules act by their hydrophilic and hydrophilic parts which interact with dirt. These are the methods used for cleaning purposes. Capillary Rise Method

The aim for the method is minimizing the surface tension by adjusting its key parameters. Usually, a liquid will move up a thin tube by capillary action. The adhesion forces between the tube material and the liquid are more than the forces due to cohesion within the liquid molecules. To reduce the surface tension in the tubes, we first must determine the amount of force exerted by the tube using the formula. gh=rga2.hcosth. Where;

g = the gravitational constant, h = height of rising liquid. The radius of the tube will be reduced in the design process to decreased the tube's area. Consequently, the surface tension will reduce (www.teachengineering.org).

Stalagmometer - Drop Weight Method

The first step is determining the surface tension of a liquid, preferably water and use the value in determining the best cleaning detergent by comparison method. Usually, the stalagmometer is employed in measuring the surface tension. Drops are let out, their number determined and their individual weight established. The weight of each drop is calculated by the following formula: w=2prgh.

w is the weight of the drop, gh is the surface tension and r the radius. However, as the volume drops, the new drop's weight is expressed by w'=2prghf. Where; f is the ratio of w'/w. It is a function of the radius of the stalagmometer tip, v, the volume of the drop and constant a.

f=f(v,a,v) given by the equation: f=fra=frv1/3 Another liquid's surface tension will be estimated by the formula:

gh1gh2=m1m22/3d1d21/3with an accuracy of up to 0.1%. A liquid with a smaller value of surface tension is settled on (www.physics.bu.edu).

Wilhelmy Plate Method

It uses a tensiometer or a microbalance to measure interfacial tension at the interfaces of air and liquid or between two liquids. The formula for determining the force of surface tension that needs to be broken or reduce is F=Wtotal = Wplate+2lghcosth. When the plate is wet completely, the new surface tension becomes: gh=Wtotal- Wplate2l. Wplate is the plate's weight, F, detaching force of the plate from the liquid surface, l it width. In order to reduce this surface tension, the thickness of the place must be considerably big enough.

Maximum Bubble Pressure Method

Gas bubbles are forced through a liquid to be used as a surfactant. The radius of the bubble reduces as the pressure increases inside the bubble. Maximum pressure difference will be given by the equation: Pmax=P1-P2=2ghr.cap. The maximum value is obtained when the bubble radius equals that of the capillary (Danov et al., 2015).

Methods of Analysing Shape of the hanging liquid drop or gas bubble

Here, a hanging drop is measured by the maximum size of its diameter, ds at a drop diameter of de. The S value of the property is calculated by S= ds/ de. The surface tension is obtained using this formula: gh=dgde2H. For sessile bubbles, we use the formula: gh=dgh22Dynamic Method

It is an old analysis method of dealing with liquid jets in the elliptic orifice. It is rarely used currently. t=kdr3gh1/2 or gh=k2dp2rvm. T- is the oscillation period, r - radius jet, v - flow rate of the jet and m the wavelength (Li, Thomas, & Penfold, 2014).

The above formulas are empirically developed to approximate the true values under the calculation. Slight deviations from the precise values are possible, but the accuracy levels of up to 0.1% are satisfactory enough to work with.

Q3. Flow Rate and Viscosity with Surface Tension

Surface tension is the behavior of liquids in which they act like stretched membranes to reduce the surface area available. It is caused by cohesive forces of the liquid's molecules which don't get equal attraction forces at the surface. Within the liquid, the intermolecular forces cancel out with each other unlike on the surface where the forces act with the lower side of the liquid only. Viscosity is the stickiness of a liquid or its reluctance to flow. For example, the syrup is more viscous than water. The flow rate is the volume of a liquid that flows at a given point per unit time. Thin fluids which have low viscosity have a high flow rate as compared to those with high viscosity. To relate viscosity to surface tension, the flow rate in tubes is determined as the surface tension is measured. It is often postulated when doing experiments that a high viscosity should increase the surface tension of a liquid because molecules are bonded more strongly. Contrary to this notion, solutions with a high viscosity than water exhibit a surface tension of less or equal to the surface tension of water. The justification for this occurrence is that friction caused by interaction between polar atoms and large molecules influences viscosity (Wehking, Gabany, Chew, & Kumar, 2014, p.445).

Capillary Method to Determine Surface Tension:

The height the liquid rises in a capillary tube is measured and surface tension calculated using the formula:

gh=rga2.hcosthFor pure water and working with a clean glass, costh is assumed to be 1, therefore the surface tension becomes: ghrga2h . Surface tension SI unit is J/m2 or N/m.

References

Danov, K. D., Stanimirova, R. D., Kralchevsky, P. A., Marinova, K. G., Alexandrov, N. A., Stoyanov, S. D., ... & Pelan, E. G. (2015). Capillary meniscus dynamometry- Methodfor determining the surface tension of drops and bubbles with isotropic andanisotropic surface stress distributions. Journal of colloid and interface science, 440, 168-178.

Koehler, E. (2016). Eliminating Magnetic Forces from the Surface Tension Measurement of Magnetic Surfactants (Doctoral dissertation, University of Mississippi).

Li, P. X., Thomas, R. K., & Penfold, J. (2014). Limitations in the use of surface tension and the Gibbs equation to determine surface excesses of cationic surfactants. Langmuir, 30(23), 6739-6747.

Wehking, J. D., Gabany, M., Chew, L., & Kumar, R. (2014). The effects of viscosity, interfacial tension, and flow geometry on droplet formation in a microfluidic T-junction. Microfluidics and Nanofluidics, 16(3), 441-453.

http://physics.bu.edu/~duffy/py105/Viscosity.htmlhttp://www.niser.ac.in/sps/sites/default/files/basic_page/Surface%20tension%20by%20capillary%20rise%20method_%202018.pdfhttp://zzm.umcs.lublin.pl/Wyklad/FGF-Ang/2A.F.G.F.%20Surface%20tension.pdf

https://www.emerginginvestigators.org/system/articles/pdfs/000/000/089/original/Wei-2014-viscosity.pdf

https://www.teachengineering.org/lessons/view/duk_surfacetensionunit_less2