Report (First Version)_CHOW JUN KANG

7/27/2019 Report (First Version)_CHOW JUN KANG

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HONG KONG UNIVERISITY OF SCIENCE ANDTECHNOLOGY

UNDERGRADUATE RESEARCH OPPORTUNITY PROGRAM(UROP)

SUMMER 2012/2013

THE EXPLORATORY STUDY OF ON THE

APPLICATIONS OF TRANSPARENT SOILS

By CHOW Jun Kang


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ContentsHONG KONG UNIVERISITY OF SCIENCE AND TECHNOLOGY....................1

UNDERGRADUATE RESEARCH OPPORTUNITY PROGRAM (UROP)...........1SUMMER 2012/2013.................................................................................................1

THE EXPLORATORY STUDY OF ON THE APPLICATIONS OF TRANSPARENT

SOILS..................................................................................................................................1Contents...............................................................................................................................2

Abstract................................................................................................................................2

Literature Review.................................................................................................................3

Fluorinated Ethylene Propylene...........................................................................................4Material Selection............................................................................................................4

Solutions Chosen.............................................................................................................5

Surface Treatment............................................................................................................5Testing Program, Result and Discussion.........................................................................6

Silica Gel .............................................................................................................................6

Material Selection............................................................................................................6

Solution Chosen...............................................................................................................6Testing Program, Result and Discussion.........................................................................7

Improvement........................................................................................................................7

De-airing process.............................................................................................................7Surface treatment.............................................................................................................7

Disturbance on the light energy.......................................................................................8

Conclusion...........................................................................................................................8

AbstractExperimental models to measure spatial deformation patterns within a soil mass are

typically limited by the fact that soil sensors do not provide a continuous image of the

measured continuum. Furthermore, different characteristic of soil sensors in both static

and dynamic with the surrounding soils could alter the response of the measure

continuum. The study of transparent slurry was originally done by Mannheimer (1990). It

was further developed by Iskander (1994) with the creation of three families of

transparent soils, namely amorphous silica powder, silica gels and Aquabeads. Besides,

another type of transparent soil by using Nafion has been developed by a team of

researchers from the James Hutton Institute and the University of Abertay Dundee

(2012). In this UROP, study was done on the characteristics of transparent soils


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developed and test was carried out to find another suitable material in making synthetic

transparent soil that is low cost and easy-to-prepare.

Literature ReviewTransparent materials exhibit the characteristics of little light energy is reflected while

most of them enter through the boundary into the second medium. For the transmitted ray

entering the second medium, its direction depends on the ratio of refractive index of both

materials. In transparent soils, refraction of light is prevented by matching the refractive

indices of the materials and pore fluids used. Next, the clarity of transparent soils also

depends on the existence of entrapped air and impurities, which tend to reflect light

resulting in a translucent or partially transparent medium. Air has to be displaced as it is

the major source of transparency degradation due to the different of its refractive index

(nair 1.003) with that of materials and pore fluid used.

According to Mannheimer (1990), transparent slurries can be made by dispersing solid

particles that have a refractive index close to a typical glass (1.4 1.5) in a liquid with the

same refractive index. However, in practice, solid particles tend to contain flaws or

defects that make it impossible to perfectly match their refractive index.

While there are 2 main criteria mentioned by Iskander (1994) in order to develop

transparent soil. First, the diameter of the microparticles is shorter than the wavelength of

light so that they do not scatter light. Second, the aggregtes (materials) are hygroscopic

have a high tendency in adsorbing pore fluid and displacing entrapped air in the system.

Following these 2 properties, 3 families of transparent materials have been developed by

Iskander for modeling sand and clay. The first family is made of consolidating

suspensions of amorphous silica and liquids to model natural clay. The second family is


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made of silica gels and matched refractive index liquids, which models sand. The third

family is AquaBead, which can be used to model soil with hydraulic conductivity within

the range of 10-2 to 10-5 cm/s. The pore fluids used in these 3 families are the same. The

first is a 50:50 blend by weight of colourless mineral oil and a normal-paraffinic solvent,

to have a refractive index of 1.447 at 25C. The second pore fluid is a brine mixture

blended from calcium bromide and water to have a refractive index of 1.448 at 25C.

Fluorinated Ethylene Propylene

Material Selection

Nafion was first selected to be the material used in modeling transparent soil. Nafion is

the first class of synthetic polymers with ionic properties. Its unique hydrophilic property

(water-loving) is due to the incorporation of perfluorovinyl ether groups terminated with

sulfonate groups onto a tetrafluoroethylene backbone. However, it was given up as the

first choice in the experiment due to its high cost. Fluorinated ethylene propylene (FEP)

was selected as the alternative as suggested by the team doing research on optically

transparent porous medium of microbial film from University of Duisburg-Essen. The

main difference between Nafion and FEP is their interaction towards polar/ionic groups.

As discussed, Nafion consists of a polar sulphonate group that interacts with other polar

groups while only hydrophobic interaction is involved in FEP as it mainly consists of

C-F groups. However, the main concern is whether the material selected is hygroscopic

its tendency to adsorb the pore fluid and displace the entrapped air. The FEP pellets

used is manufactured by Shandong Huaxia Shenzhou New Material Co. Ltd., it is about


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cube in shape, with size approximately 3 mm x 3 mm x 3 mm, with refractive index of

1.344.

Solutions ChosenThe governed factors that affect the transparency of the transparent soil have been studied

before tests were carried out. Few factors have been listed down the pore fluid selected,

size and shape of the materials, surface treatment of materials, and boundary effect of the

medium carried the transparent soil and etc.

After the material was selected to model soil, the next step was to select suitable pore

fluid to match the refractive index of FEP. Few solutions have been selected but only

liquid ethanol was mainly discussed in this report. A series of ethanol solution consisting

10 sets of solution with different fraction of weight of liquid ethanol at constant

temperature was prepared. Reference of refractive index at different fraction was taken. It

was estimated matched refractive index would achieve at weight fraction of about 0.20.

Result will be discussed in the next section. Besides, experimental values of refractive

index at different mole fraction of mixture of ethanol and methanol were referred. It was

found that approximately mixture of them at mole fraction of 50:50 at temperature 25C

would produce a solution with RI of 1.344.

Surface Treatment

FEP is hydrophobic in nature, but the functional group of pore fluid chosen selected is

polar in nature. Surface treatment was carried out in the aim of modifying the functional

groups on the surface of FEP. Concentrated ethanol solution was prepared by mixing 240

cm3 of liquid ethanol and 60 cm3 of deionized water. FEP pellets were allowed to

immerse in it for two weeks before further test was carried out. The figure shows the


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difference observation made for treated FEP pellets and original FEP pellets in deionized

water.

Testing Program, Result and DiscussionA series of ethanol solution with different weight fraction of liquid ethanol was prepared.

Data of refractive index with different fraction of ethanol was referred from the

experiment done by. It was estimated that a matched refractive index with that of FEP

could be achieved at about 0.20. However, a translucent image was produced for whole

series of ethanol solution rather than transparent image. Next, tests were done on mixing

ethanol and methanol at different mole fraction. It was observed that a better image was

produced at a mole fraction of 50:50 of ethanol to methanol. The result predicted was

similar the refractive index referred. Nevertheless, the image produced was still

translucent and it would be discussed in the next section for improvement.

Silica Gel

Material Selection

Similar to Isknader, silica gel was selected to model transparent soil. There are 2 types of

silica gel - irregular and spherical. Basically, the main reason of silica gel is chosen is its

large surface area which allows it to adsorp the pore fluid and displaces the entrapped air.

The irregular silica gel used in this experiment was bought from Nacalai Tesque, Inc.

while the silica gel used by Iskander was still in the progress of purchasing.

Solution Chosen

Taken reference from Iskander, pore fluid of 50:50 blend by weight of colourless mineral

oil and a normal-paraffinic solvent, to have a refractive index of 1.447 at 25C was used.


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Testing Program, Result and Discussion

Silica gels were poured into the test tube layer by layer to prevent the formation of air

bubbles inside the test tube. The result obtained would be discussed in the next section.

A semi-transparent image was produced. Air bubbles were observed being trapped inside

the pore between the irregular silica gel. The significant amount of air bubbles entrapped

play a crucial role in determining the transparency of the silica gel. Due to different

refractive index (nair = 1.003, nsilica gel = 1.442), light tends to refract inside the second

medium instead of just passing through it.

Improvement

De-airing process

As there is no guarantee that no air bubbles are entrapped when material is put into the

container layer by layer. A connector is made to connect the test tube (container) to the

vacuum pump in order to suck all the air bubbles out to create a medium of matched

refractive index between the materials modeling soil and the corresponding pore fluid.

Surface treatment

The modification of surface of FEP pellets has to be verified and revised. The mechanism

of ethanol solution in attacking studied. It has to be verified that whether there is a

surface modification of FEP or only a thin layer of ethanol solution is adsorbed on the

surface of FEP. Besides, the conversion of Nafion from precursor form to acid form

should be studied and see whether it is applicable to the surface treatment on FEP pellets.

It is acknowledged that the acid form of Nafion is the ready form to be used to model

transparent soil.


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Disturbance on the light energy

The ideal case of the travel path of a beam of light should be directly passing though the

medium of transparent soil without any reflection, bending or change in direction. To

achieve this, reflection, refraction and diffraction of light energy has to be minimized so

that no light is scattered. Therefore, few improvements have to be done. Air bubbles have

to be eliminated as discussed previously to minimize the chances of light refracts inside

the medium of transparent soil. Container with curved surface has to be avoided to

minimize the chances of light undergoes refraction when entering the second medium. A

transparent box with dimension of 6cm x 3cm x 5cm and an outlet for de-airing was

made and to be used in the next experiment. Besides, size and shape of the particles is

one of the concerns too. The particles of FEP and silica gel have to be studied to ensure

no total internal reflection will occur therefore it becomes transparent when light passing

through it rather than visible.

ConclusionThe development of transparent soil is still at a very beginning stage. A lot of problems

and questions should be investigated to fully understand the theory and mechanism work

behind it before it can be fully applied in the field of geotechnical engineering.

Report (First Version)_CHOW JUN KANG

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