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. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Automated+Process+for+Improved+Uniformity+and+Versatility+of+Layer-by-Layer+Deposition.">Automated Process for Improved Uniformity and Versatility of Layer-by-Layer Deposition.</a> Langmuir. 23, 3137-3141 (2007).</li><li>Hall, D. B., Underhill, P., Torkelson, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spin+coating+of+thin+and+ultrathin+polymer+films.">Spin coating of thin and ultrathin polymer films.</a> Polymer Engineering &amp; Science. 38, 2039-2045 (1998).</li></ol>

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 ...

fabrication-of-large-area-free-standing-ultrathin-polymer-films

Research

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Chemistry

Towards Biomimicking Wood: Fabricated Free-standing Films of Nanocellulose, Lignin, and a Synthetic Polycation

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and lignin. Layer-by-layer (LbL) assembly process which relies on the assembly of oppositely charged molecules from aqueous solutions was used to build a freestanding composite film of isolated wood polymers of lignin and oxidized nanofibril cellulose (NFC). To facilitate the assembly of these negatively charged polymers, a positively charged polyelectrolyte, poly(diallyldimethylammomium chloride) (PDDA), was used as a linking layer to create this simplified model cell wall. The layered adsorption process was studied quantitatively using quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry. The results showed that layer mass/thickness per adsorbed layer increased as a function of total number of layers. The surface coverage of the adsorbed layers was studied with atomic force microscopy (AFM). Complete coverage of the surface with lignin in all the deposition cycles was found for the system, however, surface coverage by NFC increased with the number of layers. The adsorption process was carried out for 250 cycles (500 bilayers) on a cellulose acetate (CA) substrate. Transparent free-standing LBL assembled nanocomposite films were obtained when the CA substrate was later dissolved in acetone. Scanning electron microscopy (SEM) of the fractured cross-sections showed a lamellar structure, and the thickness per adsorption cycle (PDDA-Lignin-PDDA-NC) was estimated to be 17 nm for two different lignin types used in the study. The data indicates a film with highly controlled architecture where nanocellulose and lignin are spatially deposited on the nanoscale (a polymer-polymer nanocomposites), similar to what is observed in the native cell wall.

The objective of this research was to form synthetic plant cell wall tissue using layer-by-layer assembly of nanocellulose fibrils and isolated lignin assembled from dilute aqueous suspensions.&#160; Surface measurement techniques of quartz crystal microbalance and atomic force microscopy were used to monitor the formation of the polymer-polymer nanocomposite material.

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and ...

Confocal Imaging of Confined Quiescent and Flowing Colloid-polymer Mixtures

The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed assembly1-3, drug delivery4, improved hydrocarbon recovery5-7, and flowable electrodes for energy storage8. Suspensions containing fluorescent colloids and non-adsorbing polymers are appealing model systems, as the ratio of the polymer radius of gyration to the particle radius&#160;and concentration of polymer control the range and strength of the interparticle attraction, respectively. By tuning the polymer properties and the volume fraction of the colloids, colloid fluids, fluids of clusters, gels, crystals, and glasses can be obtained9.&#160;Confocal microscopy, a variant of fluorescence microscopy, allows an optically transparent and fluorescent sample to be imaged with high spatial and temporal resolution in three dimensions. In this technique, a small pinhole or slit blocks the emitted fluorescent light from regions of the sample that are outside the focal volume of the microscope optical system. As a result, only a thin section of the sample in the focal plane is imaged. This technique is particularly well suited to probe the structure and dynamics in dense colloidal suspensions at the single-particle scale: the particles are large enough to be resolved using visible light and diffuse slowly enough to be captured at typical scan speeds of commercial confocal systems10. Improvements in scan speeds and analysis algorithms have also enabled quantitative confocal imaging of flowing suspensions11-16,37.&#160;In this paper, we demonstrate confocal microscopy experiments to probe the confined phase behavior and flow properties of colloid-polymer mixtures. We first prepare colloid-polymer mixtures that are density- and refractive-index matched. Next, we report a standard protocol for imaging quiescent dense colloid-polymer mixtures under varying confinement in thin wedge-shaped cells. Finally, we demonstrate a protocol for imaging colloid-polymer mixtures during microchannel flow.

Confocal microscopy is used to image quiescent and flowing colloid-polymer mixtures, which are studied as model systems for attractive suspensions. Image analysis algorithms are used to calculate structural and dynamic metrics for the colloidal particles that measure changes due to geometric confinement.

The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed ...

Preparation of Highly Porous Coordination Polymer Coatings on Macroporous Polymer Monoliths for Enhanced Enrichment of Phosphopeptides

We describe a protocol for the preparation of hybrid materials based on highly porous coordination polymer coatings on the internal surface of macroporous polymer monoliths. The developed approach is based on the preparation of a macroporous polymer containing carboxylic acid functional groups and the subsequent step-by-step solution-based controlled growth of a layer of a porous coordination polymer on the surface of the pores of the polymer monolith. The prepared metal-organic polymer hybrid has a high specific micropore surface area. The amount of iron(III) sites is enhanced through metal-organic coordination on the surface of the pores of the functional polymer support. The increase of metal sites is related to the number of iterations of the coating process.
The developed preparation scheme is easily adapted to a capillary column format. The functional porous polymer is prepared as a self-contained single-block porous monolith within the capillary, yielding a flow-through separation device with excellent flow permeability and modest back-pressure. The metal-organic polymer hybrid column showed excellent performance for the enrichment of phosphopeptides from digested proteins and their subsequent detection using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The presented experimental protocol is highly versatile, and can be easily implemented to different organic polymer supports and coatings with a plethora of porous coordination polymers and metal-organic frameworks for multiple purification and/or separation applications.

A procedure for the preparation of porous hybrid separation media composed of a macroporous polymer monolith internally coated by a high surface area microporous coordination polymer is presented.

We describe a protocol for the preparation of hybrid materials based on highly porous coordination polymer coatings on the internal surface of macroporous ...

Photodynamic Therapy with Blended Conducting Polymer/Fullerene Nanoparticle Photosensitizers

In this article a method for the fabrication and reproducible in-vitro evaluation of conducting polymer nanoparticles blended with fullerene as the next generation photosensitizers for Photodynamic Therapy (PDT) is reported. The nanoparticles are formed by hydrophobic interaction of the semiconducting polymer MEH-PPV (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]) with the fullerene PCBM (phenyl-C61-butyric acid methyl ester) in the presence of a non-compatible solvent. MEH-PPV has a high extinction coefficient that leads to high rates of triplet formation, and efficient charge and energy transfer to the fullerene PCBM. The latter processes enhance the efficiency of the PDT system through fullerene assisted triplet and radical formation, and ultrafast deactivation of MEH-PPV excited stated. The results reported here show that this nanoparticle PDT sensitizing system is highly effective and shows unexpected specificity to cancer cell lines.

This protocol describes a method for the fabrication of conducting polymer nanoparticles blended with fullerene. These nanoparticles were investigated for their potential use as a next generation photosensitizers for Photodynamic Therapy (PDT).

In this article a method for the fabrication and reproducible in-vitro evaluation of conducting polymer nanoparticles blended with fullerene as the next ...

Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films

This report aims to fully describe the experimental technique of using ellipsometry for cooling rate dependent Tg (CR-Tg) experiments. These measurements are simple high-throughput characterization experiments, which can determine the glass transition temperature (Tg), average dynamics, fragility and the expansion coefficient of the super-cooled liquid and glassy states for a variety of glassy materials. This technique allows for these parameters to be measured in a single experiment, while other methods must combine a variety of different techniques to investigate all of these properties. Measurements of dynamics close to Tg are particularly challenging. The advantage of cooling rate dependent Tg measurements over other methods which directly probe bulk and surface relaxation dynamics is that they are relatively quick and simple experiments, which do not utilize fluorophores or other complicated experimental techniques. Furthermore, this technique probes the average dynamics of technologically relevant thin films in temperature and relaxation time (&#964;&#945;) regimes relevant to the glass transition (&#964;&#945; &#62; 100 sec). The limitation to using ellipsometry for cooling rate dependent Tg experiments is that it cannot probe relaxation times relevant to measurements of viscosity (&#964;&#945; &#60;&#60; 1 sec). Other cooling rate dependent Tg measurement techniques, however, can extend the CR-Tg method to faster relaxation times. Furthermore, this technique can be used for any glassy system so long as the integrity of the film remains throughout the experiment.

Here, we present a protocol for cooling rate dependent ellipsometry experiments, which can determine the glass transition temperature (Tg), average dynamics, fragility and the expansion coefficient of the super-cooled liquid and glass for a variety of glassy materials.

This report aims to fully describe the experimental technique of using ellipsometry for cooling rate dependent Tg (CR-Tg) experiments. These measurements ...

The Preparation and Properties of Thermo-reversibly Cross-linked Rubber Via Diels-Alder Chemistry

A method for using Diels Alder thermo-reversible chemistry as cross-linking tool for rubber products is demonstrated. In this work, a commercial ethylene-propylene rubber, grafted with maleic anhydride, is thermo-reversibly cross-linked in two steps. The pending anhydride moieties are first modified with furfurylamine to graft furan groups to the rubber backbone. These pendant furan groups are then cross-linked with a bis-maleimide via a Diels-Alder coupling reaction. Both reactions can be performed under a broad range of experimental conditions and can easily be applied on a large scale. The material properties of the resulting Diels-Alder cross-linked rubbers are similar to a peroxide-cured ethylene/propylene/diene rubber (EPDM) reference. The cross-links break at elevated temperatures (&#62; 150 &#176;C) via the retro-Diels-Alder reaction and can be reformed by thermal annealing at lower temperatures (50-70 &#176;C). Reversibility of the system was proven with infrared spectroscopy, solubility tests and mechanical properties. Recyclability of the material was also shown in a practical way, i.e., by cutting a cross-linked sample into small parts and compression molding them into new samples displaying comparable mechanical properties, which is not possible for conventionally cross-linked rubbers.

A simple two-step approach involving rubber modification and cross-linking yields fully reworkable, elastic rubber products.

A method for using Diels Alder thermo-reversible chemistry as cross-linking tool for rubber products is demonstrated. In this work, a commercial ...

Capillary Electrophoresis to Monitor Peptide Grafting onto Chitosan Films in Real Time

Free-solution capillary electrophoresis (CE) separates analytes, generally charged compounds in solution through the application of an electric field. Compared to other analytical separation techniques, such as chromatography, CE is cheap, robust and effectively requires no sample preparation (for a number of complex natural matrices or polymeric samples). CE is fast and can be used to follow the evolution of mixtures in real time (e.g., chemical reaction kinetics), as the signals observed for the separated compounds are directly proportional to their quantity in solution.
Here, the efficiency of CE is demonstrated for monitoring the covalent grafting of peptides onto chitosan films for subsequent biomedical applications. Chitosan&#39;s antimicrobial and biocompatible properties make it an attractive material for biomedical applications such as cell growth substrates. Covalently grafting the peptide RGDS (arginine - glycine - aspartic acid - serine) onto the surface of chitosan films aims at improving cell attachment. Historically, chromatography and amino acid analysis have been used to provide a direct measurement of the amount of grafted peptide. However, the fast separation and absence of sample preparation provided by CE enables equally accurate yet real-time monitoring of the peptide grafting process. CE is able to separate and quantify the different components of the reaction mixture: the (non-grafted) peptide and the chemical coupling agents. In this way the use of CE results in improved films for downstream applications.
The chitosan films were characterized through solid-state NMR (nuclear magnetic resonance) spectroscopy. This technique is more time-consuming and cannot be applied in real time, but yields a direct measurement of the peptide and thus validates the CE technique.

Free solution capillary electrophoresis is a fast, cheap and robust analytical method that enables the quantitative monitoring of chemical reactions in real time. Its utility for rapid, convenient and precise analysis is demonstrated here through analysis of covalent peptide grafting onto chitosan films for improved cell adhesion.

Free-solution capillary electrophoresis (CE) separates analytes, generally charged compounds in solution through the application of an electric field. ...

Fabrication and Testing of Photonic Thermometers

In recent years, a push for developing novel silicon photonic devices for telecommunications has generated a vast knowledge base that is now being leveraged for developing sophisticated photonic sensors. Silicon photonic sensors seek to exploit the strong confinement of light in nano-waveguides to transduce changes in physical state to changes in resonance frequency. In the case of thermometry, the thermo-optic coefficient, i.e., changes in refractive index due to temperature, causes the resonant frequency of the photonic device such as a Bragg grating to drift with temperature. We are developing a suite of photonic devices that leverage recent advances in telecom compatible light sources to fabricate cost-effective photonic temperature sensors, which can be deployed in a wide variety of settings ranging from controlled laboratory conditions, to the noisy environment of a factory floor or a residence. In this manuscript, we detail our protocol for the fabrication and testing of photonic thermometers.

We describe the process of fabrication and testing of photonic thermometers.

In recent years, a push for developing novel silicon photonic devices for telecommunications has generated a vast knowledge base that is now being ...

Microfluidic Dry-spinning and Characterization of Regenerated Silk Fibroin Fibers

The protocol demonstrates a method for mimicking the spinning process of silkworm. In the native spinning process, the contracting spinning duct enables the silk proteins to be compact and ordered by shearing and elongation forces. Here, a biomimetic microfluidic channel was designed to mimic the specific geometry of the spinning duct of the silkworm. Regenerated silk fibroin (RSF) spinning doped with high concentration, was extruded through the microchannel to dry-spin fibers at ambient temperature and pressure. In the post-treated process, the as-spun fibers were drawn and stored in ethanol aqueous solution. Synchrotron radiation wide-angle X-ray diffraction (SR-WAXD) technology was used to investigate the microstructure of single RSF fibers, which were fixed to a sample holder with the RSF fiber axis normal to the microbeam of the X-ray. The crystallinity, crystallite size, and crystalline orientation of the fiber were calculated from the WAXD data. The diffraction arcs near the equator of the two-dimensional WAXD pattern indicate that the post-treated RSF fiber has a high orientation degree.

A protocol for the microfluidic spinning and microstructure characterization of regenerated silk fibroin monofilament is presented.

The protocol demonstrates a method for mimicking the spinning process of silkworm. In the native spinning process, the contracting spinning duct enables ...

Time-resolved Photophysical Characterization of Triplet-harvesting Organic Compounds at an Oxygen-free Environment Using an iCCD Camera

Here, we present a sensible method of the acquisition and analysis of time-resolved photoluminescence using an ultrafast iCCD camera. This system enables the acquisition of photoluminescence spectra covering the time regime from nanoseconds up to 0.1 s. This enables us to follow the changes in the intensity (decay) and emission of the spectra over time. Using this method, it is possible to study diverse photophysical phenomena, such as the emission of phosphorescence, and the contributions of prompt and delayed fluorescence in molecules showing thermally activated delayed fluorescence (TADF). Remarkably, all spectra and decays are obtained in a single experiment. This can be done for solids (thin film, powder, crystal) and liquid samples, where the only limitations are the spectral sensitivity of the camera and the excitation wavelength (532 nm, 355 nm, 337 nm, and 266 nm). This technique is, thus, very important when investigating the excited state dynamics in organic emitters for their application in organic light-emitting diodes and other areas where triplet harvesting is of paramount importance. Since triplet states are strongly quenched by oxygen, emitters with efficient TADF luminescence, or those showing room temperature phosphorescence (RTP), must be correctly prepared in order to remove any dissolved oxygen from solutions and films. Otherwise, no long-lived emission will be observed. The method of degassing solid samples as presented in this work is basic and simple, but the degassing of liquid samples creates additional difficulties and is particularly interesting. A method of minimizing solvent loss and changing the sample concentration, while still enabling to remove oxygen in a very efficient and a repeatable manner, is presented in this work.

Here, we present a method of the spectroscopic characterization of organic molecules by means of time-resolved photoluminescence spectroscopy on the nanosecond-to-millisecond timescale in oxygen-free conditions. Methods to efficiently remove oxygen from the samples and, thus, limit luminescence quenching are also described.

Here, we present a sensible method of the acquisition and analysis of time-resolved photoluminescence using an ultrafast iCCD camera. This system enables ...