Observations of Changes in Surface Chemistry of Metallic FLSP Surfaces as a Function of Wettability

Graham Kaufman Author

04/01/2021 Added

17 Plays

Description

Poster presentation of surface analysis of superhydrophilic and hydrophobic silver (Ag) FLSP.

Searchable Transcript

Search:

[00:00:00.480]Hello. My name is Graham Kaufman.
[00:00:02.670]I'm a graduate student here at the university of Nebraska in the electrical
[00:00:05.670]engineering department.
[00:00:06.420]And today I'll be presenting my research on observations of changes in surface
[00:00:09.420]chemistry and metallic FLSP surfaces as a function of wettability.
[00:00:19.130]Here's some motivation behind the work: Metal surfaces processed with femtosecond
[00:00:22.970]laser surface processing or FLSP have a wide variety of applications.
[00:00:27.200]One application is the creation of superhydrophilic or hydrophobic surfaces on
[00:00:30.950]metals.
[00:00:31.700]Creating a superhydrophobic surface on an electrical power line can limit the
[00:00:34.820]ice build up during winter storms, preventing the cables from snapping,
[00:00:37.850]potentially saving millions of dollars annually.
[00:00:39.230]Metal FLSP surfaces are intrinsically superhydrophilic. However,
[00:00:44.060]when exposed to air, the wettability of the surfaces transitions from
[00:00:47.060]superhydrophilic to superhydrophobic.
[00:00:49.130]We are interested in investigating what changes in surface chemistry result
[00:00:52.580]in these shifts in wettability over time. Here, we focus on FLSP applied to
[00:00:56.330]aluminum and silver.
[00:00:57.640]Silver is investigated because the wettability properties change within hours of
[00:01:01.100]exposure to air versus more than a month with aluminum.
[00:01:04.340]Our goal is to use surface analysis techniques to study what changes in surface
[00:01:07.490]chemistry of a metal FLSP surface as
[00:01:09.830]the wettability transitions from superhydrophilic to hydrophobic due to
[00:01:13.010]exposure to air.
[00:01:20.270]A little background on what FLSP does and how it works.
[00:01:23.390]FLSP creates dual-hierarchal structuring on the micro- and nano-scale on metals in
[00:01:27.500]particular here,
[00:01:28.730]intense electric fields from a focused ultra short laser pulse ablate
[00:01:31.940]the metallic surface, leading to material removal, surface melts,
[00:01:35.300]and redeposition of material. And this leads to the self-organized structuring.
[00:01:39.080]We can see in figure (a) here. This is on silver. These
[00:01:43.970]micro-scale structures here are about 30 microns across and on the orders of
[00:01:47.840]about 50 microns tall. And the bottom right here,
[00:01:50.750]we can see the nano structuring,
[00:01:52.380]which is a result of the redeposition of material.
[00:01:58.730]Here's the experimental setup we use here. The laser we use in
[00:02:02.390]this work is a 6 mJ
[00:02:03.770]coherent Astrella laser with the center wavelength of 800 nm,
[00:02:07.100]a repetition rate of 1000 Hz and a pulse duration of 35 fs.
[00:02:11.750]In the case of silver [FLSP], we use a technique called dual pulse,
[00:02:15.020]which takes the incident beam and splits it into two different paths based on
[00:02:18.110]horizontal and vertical polarization The two different paths traveled
[00:02:21.830]different path lengths, nd since the speed of light is constant and air,
[00:02:25.700]these two different path links arrive at the sample at a slightly different
[00:02:29.270]time. In this case, we typically use less than a nanosecond of pulse delay.
[00:02:34.520]Dual pulse takes advantage of the time dependent light matter interaction,
[00:02:37.910]processes of FLSP.
[00:02:46.580]The procedure for this experiment is as follows: four samples of both silver and
[00:02:50.270]aluminum are individually cleaned in a 20 minute Sonic bath of acetone, then
[00:02:54.440]ethanol, and finally,
[00:02:55.430]distilled water. FLSP is applied to these samples using the following parameters:
[00:02:59.980]for the silver, Our pulse delay is 120 picoseconds. And for aluminum,
[00:03:03.460]there is no pulse delay since we're just using single pulse FLSP.
[00:03:06.760]The laser spot radius,
[00:03:07.900]the raster offset, the power, and the velocity of the raster all lead to two main
[00:03:11.920]parameters of the laser processing: the peak fluence,
[00:03:14.560]which is the energy per centimeter squared, and then the pulse count,
[00:03:18.520]which is how many times an individual spot on the surface is irradiated with the
[00:03:21.760]laser. Varying peak fluennce and pulse count gives different size and shape
[00:03:25.960]structures. For both the silver and the aluminum immediately after processing.
[00:03:30.100]and before the samples have had a chance to transition,
[00:03:32.590]One sample is placed inside the ultra high vacuum chamber for analysis and the
[00:03:36.880]contact angle is measured on the other sample.
[00:03:39.250]Two additional samples are used for hydrophobic experiments.
[00:03:42.400]These are set under a clean upside down Petri dish in open air,
[00:03:45.310]and we wait for those to transition.
[00:03:47.410]XPS is performed on a first superhydrophilic sample.
[00:03:50.440]And after the exposure to air,
[00:03:51.550]the contact angle is measured on the one of the remaining two samples.
[00:03:55.450]Once the sample's wettability has transitioned to hydrophobic,
[00:03:57.940]The other sample,
[00:03:58.510]which is also hydrophobic, is placed in the ultra high vacuum system
[00:04:01.750]And XPS is performed. Here, we have the results of the contact angle measurements
[00:04:05.800]The unprocessed silver has a contact angle of 80 degrees,
[00:04:08.650]and the unprocessed aluminum has a contact angle of 71 degrees.
[00:04:12.100]The super hydrophilic samples,
[00:04:13.300]which we can see in the left image are completely a wetting.
[00:04:16.330]So you almost can't see the water at all on the surface. We haven't had
[00:04:21.190]chance for the aluminum to fully transition from superhydrophilic,
[00:04:24.370]the hydrophobic,
[00:04:25.000]So we don't have contact angle measurements for hydrophobic aluminum,
[00:04:29.050]but we do for hydrophobic silver that can be seen on the right image there where
[00:04:32.020]the contact angle was 141.1 degrees.
[00:04:38.130]Here's the XPS data for the aluminum FLSP.
[00:04:42.120]I won't spend too much time talking about this because we have nothing to
[00:04:44.670]compare it against because the sample hasn't fully transitioned to hydrophobic
[00:04:47.370]So this is the superhydrophilic aluminum XPS data.
[00:04:53.130]Here,
[00:04:53.280]We have XPS data for the superhydrophilic and hydrophobic silver FLSP samples.
[00:04:57.300]The superhydrophilic
[00:04:59.040]data will be in the left column and a hydrophobic data will be in the right.
[00:05:02.070]Images (a) and (b) are the survey scans for both these samples and atomic percent
[00:05:05.670]compositions are calculated from the area underneath the peaks.
[00:05:10.080]Comparing the superhydrophilic's carbon concentration to the hydrophobic,
[00:05:12.810]We can see that they're both about 34%.
[00:05:15.600]both oxygen concentrations are about 28 or 29%.
[00:05:19.050]And these silver concentration makes up the rest,
[00:05:20.730]So it's about 37% on both of these.
[00:05:23.370]We initially thought that the transition of wettability may have been due to
[00:05:26.730]hydrocarbon attachment from hydrocarbons in the atmosphere.
[00:05:29.850]But if that were the case,
[00:05:30.660]we'd expect to see a higher percent composition of carbon in the hydrophobic
[00:05:34.260]surface compared to the hydrophilic surface. This is not what we see.
[00:05:40.230]Next, we look at the carbon 1S
[00:05:42.300]transition for the superhydrophilic and superhydrophobic. In the
[00:05:46.230]superhydrophilic image, (c),
[00:05:48.180]we see that we have a curve that's relatively consistent with what we'd expect
[00:05:51.240]for adventitious carbon. Adventitious
[00:05:54.330]Carbon is just a layer of carbon that settles from the atmosphere on most samples.
[00:05:58.510]On the right,
[00:05:58.970]we see that we kind of have that same shape over on the right
[00:06:01.910]side from the 285 to the 287 region.
[00:06:04.400]But we also have this new component at 288.8.
[00:06:07.280]We believe that this new component can be attributed to the fact that the
[00:06:10.010]surface chemistry changes as you transition from superhydrophilic to
[00:06:13.040]superhydrophobic or to hydrophobic. If we look at the O 1s transitions, again,
[00:06:17.600]we can see that we have a larger difference in the shapes of the curves.
[00:06:21.080]So we have the same three components fitting, both the image (e),
[00:06:24.410]which is the super hydrophilic and image and (f), which is the hydrophobic samples.
[00:06:28.160]However, the ratio of intensity for these peaks is substantially different.
[00:06:31.850]On the left. We have the peak
[00:06:33.710]at about 533 and the peak at about 530
[00:06:36.860]making a majority of the sample.
[00:06:38.540]But as we transition from superhydrophilic to hydrophobic over in image (f), we
[00:06:42.590]can see that the peak at 531.3 eV dominates the spectrum.
[00:06:46.580]We believe that this also has to do with the fact that
[00:06:49.610]the carbon in image (d) - so the addition of carbon from super hydrophilic to
[00:06:54.200]hydrophobic - most likely contains oxygen as well.
[00:06:59.390]The conclusions from this work: as metallic FLSP surfaces are left in an open
[00:07:03.650]lab environment,
[00:07:04.340]there wettability transitions from superhydrophilic to hydrophobic,
[00:07:07.070]and eventually superhydrophobic. XPS survey scans show little change in the
[00:07:11.060]atomic percent composition of the carbon and oxygen on the surface of the silver
[00:07:14.120]FLSP as the wettability transitions, however,
[00:07:17.120]high resolution scans of the carbon 1s and oxygen, 1S transitions
[00:07:21.170]for the silver FLSP show significant changes in the species present as the
[00:07:24.470]samples wettability transitions.
[00:07:24.830]The hydrophobic silver FLSP sample contains a new carbon
[00:07:29.720]species at a binding energy of 288.8 eV,
[00:07:32.330]often associated with a carbon-oxygen double bond.
[00:07:35.960]And the hydrophobic FLSP surface
[00:07:38.660]oxygen content is dominated by the species found at 531.3 eV.
[00:07:43.820]I'd like to thank the Nebraska center for energy science research (NCESR) for funding
[00:07:46.820]this work. The laser processing and surface characterization was performed in
[00:07:50.390]the center for electro-optics and functionalized surfaces (CEFS),
[00:07:53.270]And the SEM imaging was performed in the Nebraska nanoscale facility,
[00:07:57.380]the nano engineering research core facility, or the NERcF facility.
[00:08:01.520]My name is Graham Kaufman,
[00:08:02.540]and I'd like to thank you for watching my presentation.

The screen size you are trying to search captions on is too small!

You can always jump over to MediaHub and check it out there.

Comments

0 Comments

Observations of Changes in Surface Chemistry of Metallic FLSP Surfaces as a Function of Wettability

Description

Searchable Transcript

Comments icon comment

Related Channels

Comments