Name: fabrication of large-area free-standing ultrathin polymer films
Uploaded: 2015-06-03T14:00:00
Description: Watch this Scientific Journal Video about Fabrication of Large-area Free-standing Ultrathin Polymer Films at JoVE.com

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

1. Solution Preparation
<ol>
	<li>Filter 60 g of ethyl lactate using a syringe and a 0.20 &#181;m syringe filter. Add 0.3 g of polyvinyl formal to the ethyl lactate. Place the solution into the oven at 50&#160;&#176;C for 4 hr. Shake the vial gently to see if the polymer has dissolved completely.
	<ol>
		<li>If the solution is cloudy or still shows optical inhomogeneities, return the vial to the oven for another 2 hr. This recipe is for a 0.5 wt% polymer solution, which is typically used for film thicknesses around 30 ...

<ol>
	<li>Cheng, W., Campolongo, M. J., Tan, S. J., Luo, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Freestanding+ultrathin+nano-membranes+via+self-assembly.">Freestanding ultrathin nano-membranes via self-assembly.</a> Nano Today. 4, 482-493 (2009).</li><li>Greco, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultra-thin+conductive+free-standing+PEDOT/PSS+nanofilms.">Ultra-thin conductive free-standing PEDOT/PSS nanofilms.</a> Soft Matter. 7, 10642-10650 (2011).</li><li>Matsui, J., Mitsuishi, M., Aoki, A., Miyashita, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+Optical+Gating+Devices+Based+on+Polymer+Nanosheets+Assemblies.">Molecular Optical Gating Devices Based on Polymer Nanosheets Assemblies.</a> J. Am. Chem. 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Mater. 19, 2560-2568 (2009).</li><li>Okamura, Y., Kabata, K., Kinoshita, M., Saitoh, D., Takeoka, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Free-Standing+Biodegradable+Poly(lactic+acid)+Nanosheet+for+Sealing+Operations+in+Surgery.">Free-Standing Biodegradable Poly(lactic acid) Nanosheet for Sealing Operations in Surgery.</a> Adv. Mater. 21, 4388-4392 (2009).</li><li>Sreenivasan, R., Bassett, E. K., Hoganson, D. M., Vacanti, J. P., Gleason, K. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultra-thin+gas+permeable+free-standing+and+composite+membranes+for+microfluidic+lung+assist+devices.">Ultra-thin gas permeable free-standing and composite membranes for microfluidic lung assist devices.</a> Biomaterials. 32, 3883-3889 (2011).</li><li>Wan, L. -. S., Liu, Z. -. M., Xu, Z. -. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+engineering+of+macroporous+polypropylene+membranes.">Surface engineering of macroporous polypropylene membranes.</a> Soft Matter. 5, 1775-1785 (2009).</li><li>Alcoutlabi, M., McKenna, G. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+confinement+on+material+behaviour+at+the+nanometre+size+scale.">Effects of confinement on material behaviour at the nanometre size scale.</a> Journal of Physics-Condensed Matter. 17, R461-R524 (2005).</li><li>Ellison, C. J., Torkelson, J. 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L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chain+entanglement+in+thin+freestanding+polymer+films.">Chain entanglement in thin freestanding polymer films.</a> Phys. Rev. Lett. 94, (2005).</li><li>Torres, J. M., Stafford, C. M., Vogt, B. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elastic+Modulus+of+Amorphous+Polymer+Thin+Films:+Relationship+to+the+Glass+Transition+Temperature.">Elastic Modulus of Amorphous Polymer Thin Films: Relationship to the Glass Transition Temperature.</a> Acs Nano. 3, 2677-2685 (2009).</li><li>Baxamusa, S. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhanced+Delamination+of+Ultrathin+Free-Standing+Polymer+Films+via+Self-Limiting+Surface+Modification.">Enhanced Delamination of Ultrathin Free-Standing Polymer Films via Self-Limiting Surface Modification.</a> Langmuir. 30, 5126-5132 (2014).</li><li>Buck, M. E., Lynn, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Free-Standing+and+Reactive+Thin+Films+Fabricated+by+Covalent+Layer-by-Layer+Assembly+and+Subsequent+Lift-Off+of+Azlactone-Containing+Polymer+Multilayers.">Free-Standing and Reactive Thin Films Fabricated by Covalent Layer-by-Layer Assembly and Subsequent Lift-Off of Azlactone-Containing Polymer Multilayers.</a> Langmuir. 26, 16134-16140 (2010).</li><li>Freund, L. B., Suresh, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Thin Film Materials: Stress, Defect Formation and Surface Evolution. , (2003).</li><li>Dubas, S. T., Farhat, T. R., Schlenoff, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiple+Membranes+from+&#8220;True&#8221;+Polyelectrolyte+Multilayers.">Multiple Membranes from &#8220;True&#8221; Polyelectrolyte Multilayers.</a> J. Am. Chem. Soc. 123, 5368-5369 (2001).</li><li>Linder, V., Gates, B. D., Ryan, D., Parviz, B. A., Whitesides, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Water-soluble+sacrificial+layers+for+surface+micromachining.">Water-soluble sacrificial layers for surface micromachining.</a> Small. 1, 730-736 (2005).</li><li>Mamedov, A. A., Kotov, N. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Free-Standing+Layer-by-Layer+Assembled+Films+of+Magnetite+Nanoparticles.">Free-Standing Layer-by-Layer Assembled Films of Magnetite Nanoparticles.</a> Langmuir. 16, 5530-5533 (2000).</li><li>Ono, S. S., Decher, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+of+Ultrathin+Self-Standing+Polyelectrolyte+Multilayer+Membranes+at+Physiological+Conditions+Using+pH-Responsive+Film+Segments+as+Sacrificial+Layers.">Preparation of Ultrathin Self-Standing Polyelectrolyte Multilayer Membranes at Physiological Conditions Using pH-Responsive Film Segments as Sacrificial Layers.</a> Nano Lett. 6, 592-598 (2006).</li><li>Stroock, A. D., Kane, R. S., Weck, M., Metallo, S. J., Whitesides, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Synthesis of Free-Standing Quasi-Two-Dimensional Polymers. Langmuir. 19, 2466-2472 (2002).</li><li>Kriz, J., Dybal, J., Kurkova, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cooperativity+in+macromolecular+interactions+as+a+proximity+effect:+NMR+and+theoretical+study+of+electrostatic+coupling+of+weakly+charged+complementary+polyions.">Cooperativity in macromolecular interactions as a proximity effect: NMR and theoretical study of electrostatic coupling of weakly charged complementary polyions.</a> J. Phys. Chem. B. 107, 12165-12174 (2003).</li><li>Krogman, K. C., Zacharia, N. S., Schroeder, S., Hammond, P. 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The PDAC substrate treatment is based on self-limiting electrostatic interactions, meaning substrates of any size can be easily treated provided that they are negatively charged (e.g., silicon or glass). Figures 1-2 shows very large thin films (up to 13 cm in diameter) fabricated using this protocol, with the only change being the volume of reagents used. The ultimate achievable size appears to be limited only by the deposition and delamination equipment or the ultimate strength of the polymer u...

Free-standing thin polymer films are used in a variety of applications including sensors, 1-3 MEMs, catalysis or filtration, 4 and tissue engineering. 5-8 They are also used for fundamental studies exploring the behavior of polymers under confinement. 9-13 A free-standing film is one that is supported on a non-continuous substrate such as an annular ring or hoop as opposed to a silicon wafer or glass slide. This work describes a simple, repeatable fabrication procedure for ultrathin free-standing polymer films that is suitable for large-area films or high-throughput production. It is compatible with a variety of different polymers, including poly(vinyl formal), polystyrene, and poly(methyl methacrylate). It can be used to fabricate free-standing films that are as large as 13-cm diameter or as thin as 10 nm.
The fabrication of free-standing polymers consists of three basic steps: 1) deposition of polymer film onto a traditional substrate such as a wafer or slide, 2) release or liftoff of the film from the substrate, and 3) capture of the resultant film onto a support. This paper details a procedure that we reported in an earlier study on various release methods. 14
Deposition can be achieved by any number of basic polymer thin film technologies such as spin-coating, vapor deposition, or dip-coating. In this work, we utilize standard spin-coating techniques.
The &#8220;lift off-float on&#8221; technique is the most common method for releasing an ultrathin film from its substrate. 15 In this technique, the film and substrate are immersed in a suitable solvent bath. The solvent swells the film and induces spontaneous delamination, releasing the film and allowing it to float to the top of the bath. The minimum film thickness that can be released using lift off-float on is determined by balancing the interfacial peeling energy with the swelling-induced strain energy: 16
<img alt="Equation 1" src="/files/ftp_upload/52832/52832eq1.jpg" width="200" />&#160;&#160;&#160;&#160;&#160;(1)
Where L is the film thickness, &#957;f is the Poisson&#8217;s ratio of the film, E is the Young&#8217;s modulus of the film, &#958; is the swelling ratio of the film, and &#947; is the interfacial energy of peeling. The typical way to bypass the limitation imposed by Equation (1) is to deposit a sacrificial interlayer between the film and the deposition substrate. 17-20 When this interlayer dissolves in a solvent bath, the film is released and can be captured on a support. A related method is the sacrificial overlayer method, which utilizes mechanical peeling of the film onto a sacrificial layer prior to dissolution. 21
The use of sacrificial materials has several chief drawbacks. First, the addition of an extra process material and step may require a compromise between optimal film fabrication conditions and sacrificial material processing conditions. Second, sacrificial materials may be difficult to deposit without affecting the mechanical properties or purity of the final free-standing film. Third, the process for depositing the sacrificial material must be optimized and monitored for quality as an operation in the overall free-standing film fabrication. 14
In this work, we describe a surface modification technique that decreases the interfacial peeling energy, enabling the lift off-float on technique to be used for ultrathin films. The deposition substrate is modified by assembling a self-limited, self-optimizing near-monolayer of the polycation polydiallyldiammonium chloride (PDAC). Because of the strength of the binding between the polycation and the substrate, this surface modification is robust to subsequent process steps. The self-limiting and self-optimizing nature of the near-monolayer formation requires practically zero optimization and is easily scalable to large areas.
Following removal, the film floats to the top of the solvent bath where it is captured on a hoop-like support. While not given much attention in the extant literature, in this work we will describe techniques for capturing large-area films on supports that reduce the probability of tearing or otherwise damaging the film.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Vinylec E</td>
			<td>SPI</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>ethyl lactate, &#62;98%, FCC, FG,</td>
			<td>Sigma-Aldrich</td>
			<td>W244007-1KG-K</td>
			<td></td>
		</tr>
		<tr>
			<td>4&#34; silicon wafers &#60;100&#62;, Single side polished</td>
			<td>International Wafer Service</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>sulfuric acid, 98%, ACS reagent grade</td>
			<td>Sigma-Aldrich</td>
			<td>320501-6X500ML</td>
			<td></td>
		</tr>
		<tr>
			<td>hydrogen peroxide, 30%, semiconductor grade</td>
			<td>Sigma-Aldrich</td>
			<td>316989-3.7L</td>
			<td></td>
		</tr>
		<tr>
			<td>isopropanol, ACS grade, 4 L</td>
			<td>Fisher Scientific</td>
			<td>A464-4</td>
			<td></td>
		</tr>
		<tr>
			<td>dichloromethane, ACS grade</td>
			<td>Alfa-Aesar</td>
			<td>22917</td>
			<td></td>
		</tr>
		<tr>
			<td>deionized water , distilled</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>PDAC reagent (Sigma-Aldrich 409014)</td>
			<td>Sigma-Aldrich</td>
			<td>409014</td>
			<td></td>
		</tr>
		<tr>
			<td>Spin Coater</td>
			<td>Laurell Technologies&#160;</td>
			<td>WS-650-23</td>
			<td></td>
		</tr>
		<tr>
			<td>Barnstead/Thermolyne Super Nuova explosion-proof hot plate&#160;</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>explosion-proof forced air oven</td>
			<td>VWR&#160;</td>
			<td>1330 FMS&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>balance with a range of 1 mg to 1020 g</td>
			<td>Mettler Toledo</td>
			<td>MS1003S</td>
			<td></td>
		</tr>
		<tr>
			<td>reflectance spectrometer</td>
			<td>Filmetrics</td>
			<td>F20-UV</td>
			<td></td>
		</tr>
		<tr>
			<td>manipulator consisting of a Klinger tilt stage, a Brinkman rack-and-pinion and a lab jack&#160;</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cutting tool/template, LLNL-built, no drawings</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>straight edge, LLNL, no drawings</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Tent hoop, LLNL</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>culture dish 190 mm x 100 mm, Pyrex</td>
			<td>VWR</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>20 ml beaker, Pyrex</td>
			<td>VWR</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>250 ml beaker, Pyrex</td>
			<td>VWR</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>1000 ml beaker, Pyrex</td>
			<td>VWR</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>60 ml glass vial with plastic stopper&#160;</td>
			<td>VWR</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>petri dish, 150 mm diameter x2, Pyrex</td>
			<td>VWR</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>600 ml beaker x2, Pyrex</td>
			<td>VWR</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>tweezers, stainless steel</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>cutting blade</td>
			<td>Exacto</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>clean room wipes</td>
			<td>Contec&#160;</td>
			<td>PNHS-99</td>
			<td></td>
		</tr>
		<tr>
			<td>polyester knit 9/91 IPA/DI water wipes</td>
			<td>Contec&#160;</td>
			<td>Prosat&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluoroware wafer trays</td>
			<td>Ted Pella</td>
			<td>1395-40</td>
			<td></td>
		</tr>
		<tr>
			<td>Nylon Micro fiber (camel hair)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Disposable BD 3-mL plastic syringe</td>
			<td>VWR</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>0.2 um&#160; Luer-lock PTFE filters</td>
			<td>Acrodisc&#160;</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>0.45 um&#160; Luer-lock PTFE filters</td>
			<td>Acrodisc&#160;</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

fabrication of large-area free-standing ultrathin polymer films

This procedure describes a method for the fabrication of large-area and ultrathin free-standing polymer films. Typically, ultrathin films are prepared using either sacrificial layers, which may damage the film or affect its mechanical properties, or they are made on freshly cleaved mica, a substrate that is difficult to scale. Further, the size of ultrathin film is typically limited to a few square millimeters. In this method, we modify a surface with a polyelectrolyte that alters the strength of adhesion between polymer and deposition substrate. The polyelectrolyte can be shown to remain on the wafer using spectroscopy, and a treated wafer can be used to produce multiple films, indicating that at best minimal amounts of the polyelectrolyte are added to the film. The process has thus far been shown to be limited in scalability only by the size of the coating equipment, and is expected to be readily scalable to industrial processes. In this study, the protocol for making the solutions, preparing the deposition surface, and producing the films is described.

Figure 1 shows an example of a free-standing thin polymer film over a large area. This 55 nm thick polyvinyl formal film was fabricated using the procedure described here and is mounted on a 13-cm diameter steel hoop. The delamination occurs over large areas without introducing defects that lead to tearing of the film. Thus, the intrinsic strength of polyvinylformal can be exploited even for very thin films. Figure 2 shows a 22 nm thick free-standing film that is strong enough to be load...

Watch this Scientific Journal Video about Fabrication of Large-area Free-standing Ultrathin Polymer Films at JoVE.com

Fabrication of Large-area Free-standing Ultrathin Polymer Films

We describe a method for the fabrication of large-area (up to 13 cm diameter) and ultrathin (as thin as 8 nm) polymer films. Instead of using a sacrificial interlayer to delaminate the film from its substrate, we use a self-limiting surface treatment suitable for arbitrarily large areas.

This procedure describes a method for the fabrication of large-area and ultrathin free-standing polymer films.  Typically, ultrathin films are prepared ...

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