Mimicking Natural Surface Wettability with 3D Carbon Nanoarchitectures
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00:00
Surface scienceCarbon (fiber)Functional groupInorganic chemistryMedicalizationCarbon nanotube
00:13
Functional groupCarbon nanotubeChemical structureInorganic chemistrySurface scienceBiochemistryMeeting/Interview
00:44
Carbon (fiber)Sequence alignmentBiosynthesisCarbon nanotubeMaterials scienceSurface scienceInitiation (chemistry)MicrostructureIngredientLactitolChemical structureBiochemistryFunctional groupGrowth mediumProcess (computing)Meeting/Interview
01:32
Materials scienceCarbon nanotube
01:42
Deep seaCarbon nanotubeAreaFunctional groupBiosynthesisIslandChemical structureChemistryMeeting/Interview
01:52
Precursor (chemistry)Chemical vapor depositionChemical structureCarbon nanotubeBiosynthesis
02:08
Substrat <Chemie>Thin filmSurface scienceDeposition (phase transition)IronHuman body temperatureAluminiumWursthülleCell growthProcess (computing)SubstitutionsreaktionMetalMeeting/Interview
02:26
Carbon (fiber)AluminiumCarbon nanotubePrecursor (chemistry)IronEthyleneNanoparticlePrecipitation (chemistry)Lot <Werkstoff>HydrogenHuman body temperatureLake
02:47
Van-der-Waals-KraftLot <Werkstoff>Chemical experiment
02:55
Substrat <Chemie>OperonProcess (computing)AluminiumAufdampfenVakuumverpackungChemical experiment
03:22
LegierenFiningsThin filmIslandIronDeposition (phase transition)WalkingChemical experimentLecture/Conference
03:34
Substrat <Chemie>WalkingLegierenIronCarbon nanotubeChemical experiment
03:48
NanotubeQuartzCarbon nanotubeBiosynthesisSubstrat <Chemie>Human body temperatureChemical experiment
04:00
HydrogenWaterAgeingController (control theory)Volumetric flow rateChemical experiment
04:09
EthyleneHuman body temperatureWaterChemical experiment
04:22
Chemical reactorCarbon nanotubeProcess (computing)WaterSubstrat <Chemie>Setzen <Verfahrenstechnik>Chemical experiment
04:35
Process (computing)Substrat <Chemie>ZigarettenschachtelWine tasting descriptorsLactitolExplosionChemical experiment
04:47
NanoparticleSubstrat <Chemie>LactitolChemical experimentMeeting/Interview
05:03
Chemical structureCarbon nanotubeSteelQuartzSubstrat <Chemie>Deposition (phase transition)Separation processEmission spectrumNanotubeComputer animation
05:32
AreaChemical propertyMaterials scienceCarbon nanotubeBiosynthesisFunctional groupMeeting/Interview
06:05
SchmierstoffHydro TasmaniaAssembly (demo party)Carbon nanotubeStimulus (physiology)SandMaterials scienceSurface scienceSample (material)KorngrenzeWaterMeeting/Interview
06:43
Materials scienceChemical structureStimulus (physiology)Carbon nanotubeFunctional groupAspirinHydro TasmaniaMeeting/Interview
06:59
Chemical structure
07:12
Sequence alignmentProcess (computing)Functional groupSurface sciencePotenz <Homöopathie>RapidWaterMan pageHydro TasmaniaChemical experiment
07:33
Drop (liquid)Surface scienceMedical historyFunctional groupTransportWasserbeständigkeitHydro TasmaniaSetzen <Verfahrenstechnik>Chemical structureAdhesionChemical experiment
08:00
TransportDrop (liquid)
08:12
Chemical structureSurface roughnessSurface scienceFunctional groupSiloxaneProcess (computing)Drop (liquid)Stream gaugeComputer animation
08:27
Joint (geology)Forensic scienceHighway Addressable Remote Transducer ProtocolMicroarrayCarbon nanotubeAcetazolamideCarbon (fiber)WettingPICTDrop (liquid)Surface scienceComputer animation
Transcript: English(auto-generated)
00:13
Hello, my name is Joerg Schneider, and I'm heading the research group of inorganic chemistry here at the Teschnische Universität Darmstadt.
00:21
And in this upcoming video, we want to show you how we synthesize carbon nanotubes and how we align those carbon nanotubes in certain structures. And these structures are very important for bringing carbon nanotubes into the real world of application. These applications can be plentiful, they can be in microenergy harvesting, but they can also be in biomimicking natural surfaces.
00:48
For these biomimicking natural surfaces, we need to align these carbon nanotubes, which we will show you in the first part of the video, in the synthesis part. And in the second part, we will show you how we align those carbon nanotubes.
01:01
This alignment is very important because it brings together the nanostructure of the initial carbon nanotubes with a microstructure which comes from the aligning of the carbon nanotubes. And both the nanostructure and the microstructure are important ingredients for biomimicking these natural surfaces of the carbon nanotubes,
01:23
which come very close to materials like lotus leaf or rose petals. And these natural materials, rose petals and lotus leaf, have the ability to show strong superhydrophobicity, and that can be mimicked by these carbon nanotube materials.
01:42
Hi, I'm Deepu, and I'm a PhD student in the group of Professor Schneider. As already described, synthesis and application of carbon nanotubes are one of the major research areas in our group. Rather than unordered CNTs, we specialize in the synthesis of aligned carbon nanotubes.
02:00
These aligned structures are synthesized by a modified chemical vapor deposition method. As you might know, in a CVD process, a precursor gas is flown over a heated substrate, leading to the deposition of a thin film on the substrate surface. In the present case, a silicon wafer coated with a thin layer of aluminum and iron act as the substrate for the CVD process.
02:22
When heated to high temperatures in a reducing atmosphere, a bimetallic catalyst of aluminum and iron is formed, which serves as the catalyst for the CNT growth. When a suitable precursor like ethylene is introduced at such high temperatures, it decomposes, producing carbon or carbon-hydrogen fragments, which diffuses into these catalyst globules and precipitates out as carbon nanotubes.
02:46
Since these catalyst particles are densely packed, the CNTs grow in a vertical direction due to the Van der Waals interaction between the neighboring CNTs.
03:02
Well, that's the description of the whole process. Now let me show you how we realize these in practice. Silicon wafer cut into the required dimension is kept in the thermal evaporator. Once a proper vacuum is achieved, a thin layer of about 10 to 15 nanometer aluminum is deposited on the substrate.
03:31
Next step involves the deposition of a thin layer of iron by sputtering. This step is crucial as variation in the thickness of the iron layer leads to changes in the diameter as well as number of walls of the CNTs.
03:44
The substrate is now ready for CVD. This is our CVD setup for the synthesis of carbon nanotubes. The prepared substrate is introduced into the quartz tube at 450 degrees Celsius and is then heated to the synthesis temperature of 850 degrees Celsius.
04:06
Mass flow controllers are used for delivering predetermined quantities of argon and hydrogen during the ramping stage. Once the set temperature of 850 degrees Celsius is achieved, ethylene supply is
04:20
switched on and at the same time a small quantity of water is introduced. PPM quantities of water keep the catalyst particles alive for longer times leading to the formation of ultra long carbon nanotubes. Once the reactor cools below 500 degrees Celsius, the substrate with the CNTs are pulled out.
04:40
Depending on the process parameters, the CNTs can be made to stick to the substrate or can be peeled off. Since the catalyst particles remain anchored to the substrate after peeling the CNTs off, these substrates can be used for a second cycle of CNT growth. This regrowth assumes greater importance for certain applications and will be discussed shortly.
05:03
Densely packed aligned nature of the as prepared carbon nanotubes are evident from the SCM images. Several T-M measurements confirmed a double walled CNT structure with an average inner diameter of about 8 nanometers. During the catalyst deposition stage, different masks can be used to produce patterned CNTs.
05:22
Here are some of the examples of such patterned structures produced by my colleagues. CNTs can also be grown on different substrates like quartz or steel. So in the first part of the video you have seen how we synthesize and align carbon nanotube structures. And this is always the first part, the synthesis of the material and the manufacturing of the material.
05:43
And now in the second part you will see what are the properties of these materials. And the properties we will study are the superhydrophilicity and the superhydrophobicity of these 3D range carbon nanotube materials. You will see different experiments where the superhydrophilicity and the superhydrophilicity will show up for these artificial nanostructures.
06:09
Water wets the napkin but not the leaf. Why is it so? Wetability studies are important both from a fundamental and application point of view. It plays a crucial role in printing, catalysis, lubrication, etc.
06:24
Wetting behavior of a surface is commonly characterized by its water contact angle. Contact angle is defined as the angle at which a liquid vapor interface meets a solid surface. A sample is said to be wetting or hydrophilic when the contact angle is less than 90 degrees. A sample is said to be non-wetting or hydrophobic when the contact angle is greater than 90 degrees.
06:45
Carbon nanotubes are interesting materials for wetability studies because of the micro-nano structure and the ability to tune the wetability over the entire range from superhydrophobicity to superhydrophilicity by applying an external stimuli. As seen here, the contact angle on an as-prepared CND structure is about 120 degrees, making them hydrophobic.
07:06
An easy way to make these structures water-lowering or superhydrophilic is by plasma treatment. Plasma treatment is an effective method for functionalizing the CNDs because of the rapidity of the process and range of functional moieties that could be grafted to the CND surface.
07:22
Moreover, the vertical alignment remains intact even after plasma treatment. This is a low-pressure radiofrequency plasma with a maximum power output of 300 W. Even a few seconds of exposure to plasma turns the surface completely superhydrophilic. In nature, there exist two types of hydrophobic surfaces.
07:44
Low-adhesive surfaces like in lotus leaves where the water droplet easily rolls off the surface. High-adhesive surfaces like in rose petals where the water droplet pins to the surface. The as-prepared CNDs, similar to a rose petal, have a high adhesion. The droplet sticks to the surface even when the surface is inverted and shaken.
08:06
But applications like self-cleaning or droplet transport requires the hysteresis to be as minimum as possible. This is achieved by engineering the surface structure and removing the hydrophilic groups present on the surface. The roughness is increased by almost three times by a regrowth process mentioned earlier.
08:24
And the hydrophilic groups still present on the surface are subjected to a siloxane functionalization, rendering the surface superhydrophobic. Water droplet easily rolls off the surface thus obtained.