at-home measurement for hydrophobicity in surfaces · fig. 1. real galapagos shark skin (left),...

At-Home Measurement for Hydrophobicity inSurfaces

Evan Bretz Tharun [email protected] [email protected]

Ariana Di Landro Lydia Park Phillip [email protected] [email protected] [email protected]

Dr. Thomas Emge* Dr. Sanjeeva Murthy*[email protected] [email protected]

New Jersey’s Governor’s School of Engineering and TechnologyRutgers, The State University of New Jersey New Brunswick, New Jersey 08901-8554

July 18, 2020

*Corresponding Authors

Abstract—With the current COVID-19 crisis, the need for asafe way to combat microbial spread is more vital than ever inorder to protect the public. This study explores implementationtextured, hydrophobic surfaces in public areas as a lastingsolution to prevent the spread of bacteria and viruses. It wasfound that by altering the surface texture of a material by etchingmicroscopic grooves, its hydrophobicity can be increased dueto numerous air pockets pushing on water droplets in abrasivesurfaces. As many common viruses have hydrophilic tails/armsand propagate easily in water, the implementation of hydrophobicmaterials to frequently touched surfaces is expected to reduce thetransmission of microbes to individuals using the same surface.A series of tests utilizing silicone to fabricate the nano- or micro-patterns of the textured surfaces sandpaper and fine powders onglass were conducted in order to analyze the effectiveness of theirhydrophobic surfaces. Key factors that increase hydrophobicitycan subsequently be used to modify various surfaces peoplecommonly interact with.

I. INTRODUCTION

Bacteria, germs, and viruses can be found almost every-where. The average person comes into contact with 60,000bacteria daily. They survive in air, plants, food, and evenhuman beings. In fact, nearly 90 percent of the human bodyis composed of germ cells. These specific microbes allow thebody to synthesize vitamins and aid digestion, maintaining thebody’s immune and digestive system healthy. However, thereare various strains of bacteria, germs, and viruses that humansare not immune to yet, such as influenza (flu), norovirus andstaphylococcus (staph) [1]. Often the major form of transmis-sion of these infectious microbes is through surfaces. Surfacessuch as door knobs, ATM machines, bathroom doors and sinks,shopping carts, phones, and money are known as high contactsurfaces because many people come into contact with these

surfaces daily. The reason why these surfaces carry so manyof these germs is because approximately 1,500 bacteria liveper square centimeter of skin on the hand and the surfaces’hydrophilic properties allow the bacteria to adhere to the sur-face, later attaching to the epidermis of the skin and enteringthe human body[2]. Currently, over 50,000 men, women, andchildren die daily through various infectious diseases and thecurrent SARS CoV-2 pandemic has reached nearly 573,000deaths worldwide[3,4]. By manufacturing a superhydrophobicsurface with a silicone sheet the adhesion of viruses andbacteria can be limited, diminishing the transmission betweenhigh traffic surfaces and the human skin.

Infectious diseases have a mortality rate of 50,000 men,women, and children daily. The current SARS-CoV-2 pan-demic has reached nearly 573,000 deaths worldwide[4][5].By manufacturing a superhydrophobic surface with a siliconemold, the adhesion of viruses and bacteria can be limited,diminishing the transmission between high traffic surfaces andthe human skin.

II. BACKGROUND

A. Surface Properties

Surface science is the study of the interaction between twophases at an interface due to differences in their physical andchemical composition. These interactions can occur betweensolids and liquids, solids and gases, gases and liquids, orsolids and liquids. However, for the purpose of this study,the focus will be on the surface interactions between liquidsand solid surfaces with air pockets. The differences betweenliquid-solid and liquid-air surface interactions are due key dif-ferences in their properties, such as degree of hydrophobicity

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or hydrophilicity, friction, viscosity, and the topography ofthe surface, which includes curvature, roughness, and contactstiffness.

1) Hydrophobicity vs. Hydrophilicity: Hydrophilic surfacesmore easily absorb water, while hydrophobic surfaces tendto repel water. The hydrophobic and hydrophilic propertiesof a surface are most commonly identified by measuring thecontact angle of liquid drops. A contact angle is geometricallydefined as the angle formed by a liquid at the intersectionbetween the liquid and solid+gas interface. Additionally, theangle is the result of capillary pressure and surface tensionbetween the surfaces as described be the Young-Laplaceequation:

γSG = γSL+ γLGcosθ

In this equation, γ SG is the solid-gas surface tension, γSL is the solid-liquid surface tension, γ LG is the liquid-gas surface tension, and θ is the contact angle. The generalscientific census is that if θ is <0.5° the surface is superhy-drophilic, if θ is <90° the surface is hydrophilic, if 90°< θ<150° then the surface is hydrophobic, and if θ is >150° thenthe surface is superhydrophobic[5]. However, for the purposeof this experiment, hydrophobic cutoff is 70° rather than 90°,as the surfaces fabricated in at-home labs are not flat norperfectly horizontal, such that at a contact angle of >70° thewater drop may roll off the surface.

Fig. 1. Real Galapagos shark skin (left), sharklet technology pattern (right)[6]

Many scientists [6] have studied the surface chemistryof hydrophobicity and how to achieve superhydrophobicity,utilizing models from nature. A prime example of this is thelayered texture of shark skin causing it to be antimicrobial,allowing the shark to travel safely through disease-infestedzones. The regular alignment of the scales on the shark’sskin also allows the shark to swim with much less frictionbecause the drag is decreased. A model of the shark’s skinwas fabricated by a biomedical lab to simulate the effect ofthe shark’s skin [6]. Figure 1 shows the grooved platelets of ashark’s skin and its imitation in the laboratory. Additionally,plants, such as the lotus leaf, are known to be hydrophobic.The beaded droplets displayed in Figure 2, demonstrate thehydrophobic properties of a lotus leaf. Its cell wall allowsthe droplets to bead and thereby clean itself when dust isincorporated into the water droplets that roll off the surface.

Our focus will be on the hydrophobic properties of asilicone surface nanoimprinted with the sandpaper’s texture.

Fig. 2. A self-cleaning lotus leaf exhibits superhydrophobicity[7]

Specifically, to determine how varying grade sizes of FEPAP-scale sandpaper affect hydrophobicity.

The data collected displays that as the grade of the sand-paper increases the abrasiveness decreases. For example, thecoarse grade is (40 to 60 grit), medium is (80 to 120), fine is(150 to 180), very fine is (220 to 240), extra fine is (280 to320) and super fine is (360 and above).

Thus, the grade of the sandpaper is inversely proportionalto the grit size [8]. As the grade increases the grit, or particlesize, decreases, creating a smoother, finer surface. These dif-ferences in surface roughness that brings about changes in theproperties can be characterized by the microscopic features:height, width, and spacing. This is displayed in Figure 3:

Fig. 3. The dimensions of pillars on the micro-scale with correspondingdroplets[9]

In the case of a sandpaper, when the particle size decreasesthe width and the space between the pillars also decreasesand vice versa. Therefore, the density of the pillars is higher,increasing the gaps between them enabling air pockets to fillthe space. The smaller spaces decrease the chances of thewater to enter the surface and the air pockets push the waterdroplets causing them to bead on the surface, and increase thehydrophobicity of the surface. In other words, the sandpaper

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with higher grade has greater hydrophobicity. Unfortunately, arelationship between the height and the hydrophobicity couldnot be reached due to limitations in our at-home lab equipmentthat gave wide variations in surface textures using the samesandpaper.

2) Surface Topography: The topography of a surface de-termines the majority of a material’s surface properties. Eventhough the characteristics of the surface are a result of whatis occurring in the nanoscale they can be measured at themacroscale. The topography can be measured utilizing aprofilometer or Atomic Force Microscopy (AFM). A stylusprofilometer, as shown in Figure 4, utilizes a probe to measurethe surface’s height variation or roughness.

Fig. 4. Basic Elements of a Styulus Profilometer[10]

Atomic Force Microscopy uses a scanning probe micro-scope with a higher resolution than a profilometer and usesoptical scattering. The information collected by the AtomicForce Microscopy is done with a mechanical probe thatresponds to the surface’s height and chemical structure [12].A schematic of an AFM measurement is shown in Figure 5

Fig. 5. Block Diagram of Atomic Force Microscopy[12]

In summary, the rougher the surface the more hydrophobicit is, and water cannot enter the pits on the surface (e.g., viacapillary action or gravity) and will sit on top of the texturedsurface and tend to bead up. The roughness of the surfacehas often been modified to increase hydrophobicity, includingprocesses involving the use of lithography, chemical adher-ents,polishing, grinding, machining and electrical dischargingmachining. For lithography, a flat surface is drawn with wax,etched with acids, and is repeated multiple times for multiplelayers and colors. Machining is translating and cutting thefabricated surface. The electrical discharging machining is thehigh voltage melting of the particulates on the surface. All ofthese processes are utilized to change the roughness or textureof the surface physically [14].

B. Viral and Bacterial Structure

A virus forms when multiple viral proteins come to form aviral wall around the RNA that defines the genetic structureof the virus. Most viruses are filled with a nonpolar innerfluid, causing them to be micelles, or shells of lipids withhydrophilic heads. These hydrophilic heads tend to stick outfrom the viral structure, and allow for the virus to adhere tosurfaces that are typically polar (like water in a cell) [15].

1) Viral Adhesion to Cells: When a virus penetrates thebody, it attacks the cells in a number of ways. The proteinson the surface of the virus must find receptors on the cellon the cell surface . However, this process requires a veryspecific interactions between the protein ligand and the cellreceptor. One of the ways viruses spread is by being adsorbedonto various surfaces that are often touched by people. Inthis adsorption step, the same proteins that interact withcell surfaces play a role. The ideas is to eliminate viraltransmission by preventing virus proteins, and the virus lipidcoatings being adsorbed onto surfaces. Since the virus particlesare usually associated with water droplets, if we can preventwater being adsorbed onto the surface, then the virus cannotstick to said surface.

2) Polarization of a Virus: Viruses have polar heads on theoutside, allowing them to stick and adhere to water. However,if a surface has no water, or a very little amount, the virus willnot attach to it. It would either stay with the host body, becomeinactive on the surface due to not adhering properly, or simplyfall off the surface. As mentioned before, more hydrophobicsurfaces are left with less water on them, which also result inless viruses.

III. EXPERIMENTAL PROCEDURE

In order to find the most effective anti-viral surface, severaltests were conducted at home using different grits of sand-paper. These materials were useful in producing surfaces fortesting in order to determine the level of hydrophobicity fromthe contact angles of the droplets. Throughout the experiments,the following materials were utilized: a 2.8 fluid oz. tube ofadvanced water- proof silicone ( General Electric Company);sandpaper of grits P80, P100, P120, P150, P180, P220, P320,P400, P1000, P2000, and P3000 on the FEPA scale; syringes

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ranging from 1.0mL, 3mL, 5mL, 10mL, and 20.0mL involume; needles ranging from 14g, 16g, 18g, 20g, 22g, and25g; and a container of water.

A. Silicone Application

Ideally, the experiment should take place in a cleanworkspace with controlled humidity room temperature toprevent accumulation of dust and moistureSheets of sandpaper(of which each individual sheet measured 9 inches by 11inches) were cut into small a square pieces, about 4 by 4 cm,and laid flat on a workable surface. Slightly larger dimensionscan be utilized if the 4cm by 4cm cut-out was deemed to betoo small for use.

After each piece has been safely cut out and removed fromits original sheet, sufficient amount of silicone was squeezedfrom the tube. Once the required amount of silicone wasdeposited, the research participant can then begin to spreadout the silicone with their fingers, sheets of printer paper, orcardboard while the silicone is still wet. Additional doses ofsilicone may be applied in order to make sure there is a thick,uniform level of silicone present on all areas of the sandpaperto imprint each grit as accurately as possible; for best results,the silicone layer should not be less than 1 mm in height. Theprocess continues until the entire square of sandpaper with wetsilicone in an even and consistent manner.

When the application of silicone has been successfullycompleted, the squares with its corresponding layer of siliconeshould be set aside. The silicone layer should remain undis-turbed for a period of time so the silicone can dry properlyand preserve the imprints of the sandpaper precisely. Therecommended wait time is at least 4 hours before continuingwith the experiment in order to ensure a perfectly dry andusable sheet of silicone.

B. Silicone Removal

After waiting for the appropriate amount of time for the sil-icone to have dried, the silicone was removed with fingernailsor a gentle prying implement, such as a knife or tweezers.Starting from the edges allows for the silicone and sandpaperto separate, as the boundary between the two objects canbe breached from the outside with the use of force. If onewaits too long, the silicon is quite difficult to remove fromthe sandpaper.

After the initial separation of the silicone and sandpaperat the edges, the process of dividing up the silicone andsandpaper was continued. Working slowly and carefully isimperative for a successful removal; despite the fact that thesilicone can stretch and withstand force up until a certain point,pulling too quickly can create tears and rips in the siliconematerial, resulting in less surface area for testing. Therefore,taking caution to make sure that silicone is not wasted andredoing the experiment in the case of accidental tears wereimportant in this stage. With no errors, the step should resultin a layer of silicone imprint and a square piece of sandpaperwith nothing on top.

Fig. 6. After a successful silicone removal, there should be a solid layerof silicone (left) that is separated from its corresponding sandpaper square(right).

However, some trials have resulted in impossible siliconeremovals, as certain grits of sandpaper cause too muchadhesion with the material, making it difficult to separatewith the human hand without tears in the layer. In thesecircumstances, process A should be redone, but with anadditional step of applying a thin layer of oil on the surfaceof the sandpaper before removing silicone from the tube. Thelubricating properties of oil make it easier to remove thesilicone without producing incomplete silicone imprints. Asidefrom this additional instruction, all other steps in process Aand B should remain the same.

C. Testing Water Droplets on the Silicone Layers

When the silicone layers have been confirmed to be firm andsolid, the step of adding droplets on the surface to measure thehydrophobic properties can begin. The use of a high qualitycamera would be crucial in this process, as photographs willbe used later to determine contact angles. The camera app ona phone would suffice.

A container full of water should be available in order totest droplets on each surface. A syringe of any volume and aneedle of any gauge may be used in this process, but the typesthat were used has be recorded. After a certain syringe andaccompanying needle have been chosen, sufficient amount ofwater from the container was extracted, wiping off any excessfluid from the needle ensures that liquids on the outside donot interfere with the droplet formation.

The syringe and needle should be held over the surfaceof the textured silicone sheet with its imprinted side on top,in which the contents of the syringe can be expelled in acareful and calculated manner to allow a droplet to form. Oncethe droplet has reached a large enough size where it can becomfortably seen and photographed, it should be dropped orplaced on the silicone sheet. The contact angles were evident

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shown so that its data can be recorded and measured in latersteps. The droplet process should be repeated at least five timesso that there is sufficient data to be collected. Droplets couldbe placed in a linear fashion on silicone sheet, or differentdroplets can be placed on the surface one at a time.

After the droplets have settled on the surface, a camera ofsome kind was used to produce images for measurements. Thelens were held parallel to the surface, so in the resulting image,the top of the surface should not be seen as much as possible.Thus, the bottom of the droplet should appear completelystraight in relation to the viewer. Moreover, there was enoughlighting in the setting so the droplet is clearly visible. Whenthe preview image seems to satisfy these requirements, thepicture should be taken and saved in a safe location where itdoes not get erased. Multiple retakes may be possible until acompetent image is produced.

Fig. 7. An ideal image of a droplet; the lens is held parallel to the lens anddoes not expose the surface excessively.

D. Data Measurement

With the compilation of all the images of the droplets, thecontact angles were analyzed, as they indicate the level ofhydrophobicity of the textured silicone surfaces. The imagesshould be displayed on a digital medium, such as a phone,tablet, or computer screen. Then, a straight line should bedrawn at the bottom of each droplet as a base ray of the angle,and another straight line, or arm, should be made tangent tothe base of the droplet at both the left and right locations.

After both lines have been drawn to create an angle, aprotractor should be held up to the screen to measure theangle inward respective to the droplet, and the angle weremeasured through the droplet.. The origin should coincide withthe vertex of the angle, and the protractor was held completelyin line with the base ray (which should be the bottom ofthe droplet). The other arm should point to a correspondingangle on the protractor, of which value could be recorded. Thestandard unit of each angle should be in degrees.

In order to make sure that there is an abundant amountof data to analyze and inaccuracies are eliminated, each

Fig. 8. In order to measure the left and right contact angles, the bottom lineand the arms of each angle show the hydrophobicity of the surface.

sandpaper grit should have at least three different sets of trialsfrom different individuals. Thus, the data will be less likelyto be skewed by the actions of one person. Moreover, due tohuman error, some of the outlier data points may be excluded.If any of the average contact angles of the silicone sheetseem to be too small or too large, they were considered forremoval in order to determine if they are statistical outliers incomparison with the rest of the measurements using standarddeviation. If they are found to be outliers, they should beremoved from the final data calculations to ensure an accuratedepiction of data.

IV. RESULTS

The results of the experiment consistently display a positivecorrelation between the fineness of the imprinted sand paperand contact angle, and thus hydrophobicity.

A. Substrate 1: Post-it Notes (The Control)

Before the hydrophobicity of textured silicone sheet of thesandpapers was measured, silicone molds of Post-It NotesTMwere created as control data for the experiment, as Post-ItNotesTM provide a relatively smooth surface in comparisonto abrasive sandpaper. Data Table 1 shows that the averagecontact angle for the water droplets was 79.7°.

TABLE IWATER DROPLETS ON POST-IT NOTE SILICONE MOLD

Average Contact Angle(°) Standard Deviation(°)79.7° 5.47°

B. Substrate 2: Silicone Sandpaper Molds

Figure 9shows that the average contact angle increases asthe particle size decreases. An overall positive correlation canbe seen between the sandpaper grade (particle size) and theaverage contact angle of the water droplets. In general, highersandpaper grades tend to have smaller particle sizes and lower

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sandpaper grades tend to have larger particle sizes. Thus sand-papers with high grades tend to be much more hydrophobic.Upon inspection of the 201.0 µm silicone surface, which isfrom the lowest sandpaper grade and possesses largest particlesize, and the 35.0 µm silicone surface, which is from a highersandpaper grade, the average contact angles were 58.5° and93.1°, respectively. There was a 159 percent increase in theaverage contact angle between the 201.0µ m silicone moldand the 35.0µm silicone mold. When observing the 35.0µm.silicone mold in comparison to the 10.3µm silicone mold, thecontact angles were 93.1° and 100.1°, respectively. There wasa 108 percent increase in the average contact angle betweenthe 10.3µm silicone mold and the 35.0µm silicone mold.Upon comparison of the 7.0µm silicone mold and the 10.3µmsilicone mold, the average contact angles were 107.5° and100.1°, respectively. There was a 107 percent increase in theaverage contact angle between the 7.0µm silicone mold andthe 10.3µm silicone mold. Thus, it is determined from theincreases of hydrophobicity that lower the size of microscopicfeatures on the surface, water will be more likely to berepelled.

Fig. 9. The graph shows the various contact angles for the water dropletsas it is deposited onto surfaces with different particle sizes. *There were noobserved contact angles between 0.0° and 55.0°*

C. Substrate 3: Printer Toner

Furthermore, the toner from a printer was tested, whichfurther corroborated the fact that smaller particle sizes producea much more hydrophobic surface. The toner size is estimatedto be 2-7 µm [16], which is smaller than any of the particlesizes of the sandpaper surfaces. According to Data Table 1,the printer toner surface was hydrophobic due to the fact thatwater had an average of a 130.7° contact angle.

D. Classification of Substrates 1-3

Due to the fact that 201.0 µm silicone mold had the lowestaverage contact angle, it was the least hydrophobic surfaceout of all of the sandpapers tested. Since it has a contactangle that was less than 70°, it is considered hydrophilic.To this end, the 141.0µm and the 125.0 µm silicone moldswith average contact angles of 66.6° and 64.6° would alsobe considered hydrophilic. All of the other silicone molds

Fig. 10. The figure shows a water droplet on a glass slide coated with printertoner.

have contact angles that exceed 70°, thus making them hy-drophobic. Similarly, the Post-It Note and the printer tonersurface are also hydrophobic.Notably, the printer toner wasthe most hydrophobic surface out of all of the ones tested.With an average contact angle of 130.7°, it is the closestsurface to be considered superhydrophobic, and water beadsup considerably when dropped on this surface.

E. The Limitations of Sandpaper

By inspecting Fgiure 9, as the particle sizes exceeding 68µm approach 0 µm, the data starts to mirror the curve of asquare root function which gradually changes at a significantlyslower rate than that of the particle size. However, the particlesize approaches the limit of 0 µm it seemingly does not reach acontact angle around 150° or greater. This is due to the fact thatthe manufacturers of sandpaper intend to make their productsfor smoothing surfaces, and do not create sandpaper for thepurpose of it being hydrophobic. The height of the particlesin the sandpaper cannot be lower to meet the conditions forthe surface to be close to attaining superhydrophobicity. Also,the sandpaper itself is extremely varied and the spacing canbe inconsistent which creates less air pockets, thus decreasingthe hydrophobicity of the sandpaper.

V. CONCLUSIONS

The characteristics of surface features such as the height,width, and spacing of particles or voids, are key factorsthat contribute to their hydrophobicity. As the particle sizedecreased, the horizontal width of each particle decreased andthe amount of space between the particles on the horizontalsurface decreased. The higher density of particles have moregaps which allows more air pockets to occupy a given areacompared to surfaces with lower density of particles. These airpockets serve to push up the water droplets, thus increasinghydrophobicity. Also, since the spacing decreases, it alsomakes it harder for water molecules to enter these gaps, e.g.,via capillary action, which also increases hydrophobicity of thematerial’s surface. However, in terms of height of the particles,

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a precise trend cannot be found due to the varying heights ofthe sandpaper’s particles.

A. Tilt Angle and Gravity

Despite the fact the water droplets on the sandpaper texturedsilicone sheets did not have average contact angles closeto 150°, the sandpaper silicone molding may still preventthe spread of bacteria and viruses, since the contact angleswere large for some surfaces. During the experiments, if thetextured silicone molding was hydrophobic enough (18.3 µmor lower) then the water droplets were susceptible to theinfluence of gravity if the silicone molding experienced eventhe slightest angular displacement. The angle which causesthe water droplets to slide off the silicone molding is knownas the tilt angle. Typically, the less hydrophobic a surfaceis, then tilt angle will increase to cause the water dropletsslide off, as water particles adhere more strongly to thesurface. For example, a 201.0 µm silicone sandpaper moldwill require a large angular displacement to have the waterdroplets slide off, if the force of gravity is strong enough toovercome the hydrophilic nature of the substrate. Conversely,a much more hydrophobic surface such as a 18.3 µm siliconesandpaper molding will require a significantly smaller angulardisplacement due to the fact that the hydrophobic nature of thesubstrate gives the water droplets less support, thus allowinggravity to slide the droplet off of the substrate. Therefore, ifwater particles were placed on curved or tilted surfaces insteadof flat ones, then they can roll off instead of staying on thesurface.

B. Sources of Error

Given the unique circumstances of the COVID-19 pan-demic, the high tech laboratory equipment was not accessi-ble. The contact angles were not measured with the utmostprecision since a 60X microscope was not available. To thisend, cell phone photographs and a protractor were used tomeasure the angles, which has a degree of error associatedwith inaccurate responses of the human eye and human hand.Additionally, the photos that were taken of the water dropletswere not all taken at the exact same angle, nor at exactlyperpendicular positions. These varying angles produced anartificial tilt on the water droplets which can alter the truecontact angle of the water droplet. This could produce largerthan usual or smaller than usual contact angles. An unevensilicone layer could have contributed to errors as well. Thecomplete removal of the silicone layer was hard to achievesince tiny remnants of the silicone mold would often stick tothe sandpaper. Also, 10 trials were found to be outliers andthey were excluded from the data in order to eliminate humanerror as much as possible. Lastly, elements like human skincells and dust could have filled up spaces between the grits ofsandpaper and on the mold as well.

C. The Trajectory of Silicon Molding

The rudimentary methods of conducting the experiment athome with some success highlights the fact that a silicone

mold can be made into a protective layer to prevent thespread of bacteria, viruses, and other germs via contact onobjects that people frequently touch in public. Objects such ashandrails, elevator buttons, doorknobs, and more can greatlybenefit from a silicone molded coating or wrapping. Evenafter the pandemic, a much more health conscious public maychoose to continue the use of the hydrophobic silicone moldingof sandpaper or other extremely textures surfaces. With suchsurfaces, the spread of the COVID-19 virus may slow downconsiderably and help to protect the public until the release ofthe vaccine. People can manufacture silicone surfaces at homein the manner of this experiment to sanitize any surface, sothat the consequences of this research can promote a safe andviable method for preventing the spread of microbial diseasein their everyday lives.

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ACKNOWLEDGMENTS

The authors gratefully acknowledge their project mentors,Dr. Sanjeeva Murthy and Dr. Thomas Emge of Rutgers Uni-versity Department of Chemistry and Chemical Biology. Withtheir efforts, the experimentation process was designed in thecomfort of home, and their guidance was useful in formattingthe paper and data. Dr. Murthy provided valuable backgroundinformation on the principles of hydrophobicity. Dr. Emgetaught the chemical and biological explanations behind sur-faces to demonstrate cell processes and lipid structures. Hisassignments prompted discussion and inspection into the fieldof microscopy. Furthermore, the authors would like to expresstheir gratitude to their project liaison, Elizabeth Strother,an undergraduate biomedical engineering student attendingRutgers University; her dedication to the project facilitatedthe development of this research paper with her consistentattendance in meetings and receptiveness to questions andconversation. Additionally, the authors would like to acknowl-edge: Dean Jean Patrick Antoine for leading the Governor’sSchool of Engineering and Technology; Head Counselor RajasKarajgikar in managing the program; and Research Coordi-nator Benjamin Lee for regulating the research aspect. Theywould also like to mention former Dean Ilene Rosen for herpast work in maintaining the New Jersey Governor’s Schoolof Engineering and Technology before her retirement.

Finally, the authors would like to express their utmostgratitude to the sponsors for their financial support. Withoutthem, the New Jersey Governor’s School of Engineering andTechnology would not be as impactful as it was. Thus, they ap-preciate the aid from: Rutgers University and Rutgers Schoolof Engineering for providing a summer camp experience;Lockheed Martin, New Jersey Space Grant Consortium, andall other corporate sponsors for their dedication to education;and the New Jersey Governor’s School of Engineering andTechnology alumni for their encouragement of STEM learningto the posterity in their continued contributions to the program.

REFERENCES

[1] Dr.Courtney, 2020. Most People Encounter Roughly 60,000Germs A Day. Here’s What To Know. - Courtney MedicalGroup. [online] Courtney Medical Group. Available at:<https://courtneymedicalgroupaz.com/2019/03/04/4902/> [Accessed15 July 2020].

[2] Vasickova, P., Pavlik, I., Verani, M. and Carducci, A., 2010. IssuesConcerning Survival of Viruses on Surfaces. Food and EnvironmentalVirology, 2(1), pp.24-34.

[3] World Health Organization. 2020. WorldHealth Report. [online] Available at:<https://www.who.int/whr/1996/media_centre/press_release/en/>

[4] Pharmaceutical Technology. 2020. International Update: GlobalCovid-19 Infections Pass 13.8 Million – Record Daily Rise InUS – Trump Pushes To Re-Open Schools. [online] Available at:<https://www.pharmaceutical-technology.com/news/coronavirus-a-timeline-of-how-the-deadly-outbreak-evolved/> [Accessed 17 July2020].

[5] Law, K., 2014. Definitions for Hydrophilicity, Hydrophobicity, andSuperhydrophobicity: Getting the Basics Right. The Journal of PhysicalChemistry Letters, 5(4), pp.686-688.

[6] 3DAG. 2019. Biomimetics Explained | 3D AG Blog. [online] Availableat: <https://3dag.ch/biomimetics-explained/> [Accessed 17 July 2020].

[7] Society for Biomaterials.2020. Sharklet- A Critically Technology ina Pandemic. [online] Available at:<https://biomaterials.org/publications-webinars/sharklet-critical-technology-pandemic>[Accessed 18 July]

[8] Futureprospects. 2010. The Lotus Effect. [online] Available at:<https://futureprospects.wordpress.com/2010/05/17/the-lotus-effect/>[Accessed 16 July 2020].

[9] Grainger. 2017. Sandpaper Grit Chart & Guide - Grainger Knowhow.[online] Available at: <https://www.grainger.com/know-how/equipment-information/kh-sandpaper-grit-chart> [Accessed 02 July 2020].

[10] Hernández, J., Monclús, M., Navarro-Baena, I., Viela, F., Molina-Aldareguia, J. and Rodríguez, I., 2017. Multifunctional Nano-engineeredPolymer Surfaces with Enhanced Mechanical Resistance and Superhy-drophobicity. Scientific Reports, 7(1).

[11] 2020. Quick Guide To Surface Roughness Measurement. Mitutoyo, p.1.

[12] 2020. Styulus Profilometer.[online] Australia Surface Metrology Lab.Available at: <https://australiasurfacemetrologylab.org/new-page> [Ac-cessed 18 July 2020].

[13] Mokobi,F. and Aryal, S., 2020. Atomic Force Microscope(AFM) | Microbe Notes. [online] Microbe Notes. Available at:<https://microbenotes.com/atomic-force-microscope-afm/> [Accessed18 July 2020]. [Accessed 18 July 2020].

[14] Monteiro, N., Martins, A., Reis, R. and Neves, N., 2014. LiposomesIn Tissue Engineering And Regenerative Medicine. National Center forBiotechnology Information.

[15] Marquardt, C., n.d. Toner. [online] Nanopartikel. Available at:<https://www.nanopartikel.info/en/nanoinfo/cross-cutting/1757-toner-crosscutting> [Accessed 17 July 2020].

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APPENDIX

TABLE IIWATER DROPLETS ON PRINTER TONER

Average Contact Angle(°) Standard Deviation(°)130.7° 2.20°

TABLE IIIFEPA SANDPAPER GRADE TO MICRON CONVERSION

Sandpaper Grade (FEPA Scale) Particle Size (µm)P80 201.0

P100 141.0P120 125.0P150 100.0P180 82.0P220 68.0P320 46.2P400 35.0P1000 18.3P2000 10.3P3000 7.0

Fig. 11. The figure shows 5 water droplets on the silicone mold of the Post-itnote.

Fig. 12. The figure shows 5 water droplets on the 201.0µm silicone mold.










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Fig. 22. The figure shows 2 water droplets on a glass surface with tonerparticles on it, which is estimated to be sized 2-7µm.

Fig. 23. The figure shows 4 water droplets on a talcum surface, which hasan estimated particle size of 25.0µm.

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at-home measurement for hydrophobicity in surfaces · fig. 1. real galapagos shark skin (left),...

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