The authors gratefully acknowledge the National Science Foundation (DMR-1409034) for support of this project. We also acknowledge the support of the National Institute of Standards and Technology, U.S. Department of Commerce, in providing the USANS facilities used in this work, where these facilities are supported in part by the National Science Foundation under Agreement No. DMR-0944772. The SANS experiments of this research were completed at ORNL&#39;s High Flux Isotope Reactor, which was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy.

All handling of chemicals should be carried out with proper personal protective equipment and within a safety hood. All samples exposed to ionizing radiation should be handled under the supervision of the facilities radioactive control technicians. This protocol was performed by individuals who had completed appropriate radiation safety training.
1. Preparation of P3HT in d-ODCB Solutions
<ol>
	<li>Sample Acquisition
	<ol>
		<li>Purchase 1 g of high regioregularity (&#62;90%...

<ol>
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D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Illumination+Alters+the+Structure+of+Gels+Formed+from+the+Optoelectronic+Material+P3HT.">Illumination Alters the Structure of Gels Formed from the Optoelectronic Material P3HT.</a> Polymer. 108, 313-321 (2017).</li><li>Morgan, B., Dadmun, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Illumination+of+Conjugated+Polymer+in+Solution+Alters+Its+Conformation+and+Thermodynamics.">Illumination of Conjugated Polymer in Solution Alters Its Conformation and Thermodynamics.</a> Macromolecules. 49 (9), 3490-3496 (2016).</li><li>Ilavsk, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phase+Transition+in+Swollen+Gels.+2.+Effect+of+Charge+Concentration+on+the+Collapse+and+Mechanical+Behavior+of+Polyacrylamide+Networks.">Phase Transition in Swollen Gels. 2. Effect of Charge Concentration on the Collapse and Mechanical Behavior of Polyacrylamide Networks.</a> Macromolecules. 15, 782-788 (1982).</li><li>Tanaka, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Collapse+of+Gels+and+the+Critical+Endpoint.">Collapse of Gels and the Critical Endpoint.</a> Phys. Rev. Lett. 40 (12), 820-823 (1978).</li><li>. SANS &amp; USANS Data Reduction and Analysis Available from: <a target="_blank" href="https://www.ncnr.nist.gov/programs/sans/data/red_anal.html">https://www.ncnr.nist.gov/programs/sans/data/red_anal.html</a> (2017)</li><li>Feigin, L., Svergun, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Structure Analysis by Small-Angle X-Ray and Neutron Scattering. , (1987).</li><li>Mittelbach, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Zur+Rontgenkleinwinkelstreuung+verdunnter+kolloider+systeme.">Zur Rontgenkleinwinkelstreuung verdunnter kolloider systeme.</a> Acta Phys. Austriaca. 14, 185-211 (1961).</li><li>Schulz, G. Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=&#220;ber+die+Kinetik+der+Kettenpolymerisationen.">&#220;ber die Kinetik der Kettenpolymerisationen.</a> Z. Phys. Chem. 43, 25 (1935).</li><li>. Neutron activation and scattering calculator Available from: <a target="_blank" href="https://www.ncnr.nist.gov/resources/activation">https://www.ncnr.nist.gov/resources/activation</a> (2017)</li><li>Kline, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reduction+and+Analysis+of+SANS+and+USANS+Data+Using+IGOR+Pro.">Reduction and Analysis of SANS and USANS Data Using IGOR Pro.</a> J. Appl. Crystallogr. 39 (6), 895-900 (2006).</li><li>Guinier, A., Fournet, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Small-Angle Scattering of X-Rays. , (1955).</li></ol>

First, looking at the SANS data as a function of temperature, the increase in the Elliptical Cylinder Model scale factor indicates a marked increase in the amount of P3HT present in the nanofibril phase, which isconsistent with the progression of the gelation process. Simultaneously, the decrease in free chain Rg paired with an increase in Porod exponent reveals that the deteriorating thermodynamic conditions associated with temperature decrease are causing a chain collapse in the P3HT chains still present in ...

Conjugated polymers promise functional materials that can be utilized in a broad range of devices, such as organic light emitting diodes, organic semiconductors, chemical sensors, and organic photovoltaics.1,2,3,4,5,6 A crucial aspect of the performance in these devices is the ordering and packing of the conjugated polymer in the solid state in the active layer.7,8,9,10,11,12,13,14 This morphology is&#160;largely&#160;pre-determined by both the conformation of the polymer chain in solution as well as the structures that&#160;evolve as these solutions are cast unto a substrate and the solvent is removed. By studying the structures present throughout a typical sol-gel transition of a model optoelectronic polymer in a suitable solvent, these systems can be effectively modeled and a quantitative glimpse into the self-assembly that occurs during material deposition can be obtained.15,16,17,18,19,20
Specifically, we examine the conjugated polymer benchmark P3HT in the solvent deuterated ortho-dichlorobenzene (ODCB), a polymer-solvent system which has seen extensive use due to its suitability for a variety of organic electronic device fabrication techniques.23,24,25 In this given solvent environment, P3HT chains begin to aggregate upon an appropriate environmental stimuli, such as temperature decrease or loss of solvent quality. The exact mechanism for this assembly process is under investigation, with one of the leading proposed pathways believed to be a gradual process where individual P3HT molecules &#960;-stack to form lamellar nano-aggregates known as nanofibrils, which then themselves agglomerate to form larger micron scale macro-aggregates.24 Understanding these pathways and the resultant structures formed is&#160;key to properly predicting and influencing the formation of optimal device active layer morphologies.
Towards this ultimate goal of more precisely directing the formation of these active layer architectures, there exists a need to develop additional experimental and industrial methods to non-destructively alter conjugated polymer morphology in-situ. One relatively new methodology centers around the use of light exposure as an inexpensive means for altering polymer chain morphology, with both computational and experimental results pointing towards its feasibility.25,26,27 Recent work by our laboratory has indicated the existence of a light induced alteration of the conjugated polymer-solvent interaction in a dilute solution, leading to a notable change in polymer chain size upon illumination.30,31 Here, we present a protocol to continue this work by effectively monitoring the effects of exposing a much more concentrated conjugated polymer solution to direct light&#160;throughout a gelation process that is directed by a thermostat-controlled temperature ramp. We employ neutron scattering as it allows robust analysis of structural parameters of the polymer-solvent sol-gel system on length scales from angstroms to microns, an ability not possible through other more common rheological or spectroscopic instrumental methods.16,17,30,31 Thus, by comparing the properly analyzed small and ultra-small angle neutron data for the assembly of gels formed under illumination to identical data collected in complete darkness, structural differences brought on by illumination-driven effects can be comprehensively identified and quantified.

<table border="0" cellpadding="0" cellspacing="0" width="822">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:353px;">M(106) poly(3-hexylthiophene-2,5-diyl) (P3HT)</td>
			<td style="width:143px;">Ossila</td>
			<td style="width:160px;">104934-50-1</td>
			<td style="width:167px;">Conjugated polymer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;">deuterated 1,2 ortho-dichlorobenzene (ODCB)</td>
			<td style="width:143px;">Sigma Aldrich</td>
			<td>AC321260050</td>
			<td>solvent</td>
		</tr>
	</tbody>
</table>

monitoring the effects of illumination on the structure of conjugated polymer gels using neutron scattering

We demonstrate a protocol to effectively monitor the gelation process of a high concentration solution of conjugated polymer both in the presence and absence of white light exposure. By instituting a controlled temperature ramp, the gelation of these materials can be precisely monitored as they proceed through this structural evolution, which effectively mirrors the conditions experienced during the solution deposition phase of organic electronic device fabrication. Using small angle neutron scattering (SANS) and ultra-small angle neutron scattering (USANS) along with appropriate fitting protocols we quantify the evolution of select structural parameters throughout this process. Thorough analysis indicates that continued light exposure throughout the gelation process significantly alters the structure of the ultimately formed gel. Specifically, the aggregation process of poly(3-hexylthiophene-2,5-diyl) (P3HT) nano-scale aggregates is negatively affected by the presence of illumination, ultimately resulting in the retardation of growth in conjugated polymer microstructures and the formation of smaller scale macro-aggregate clusters.

Through SANS and USANS experiments, the gelation process of P3HT in d-ODCB was effectively monitored from the dispersed solution state at 70 &#176;C to a fully gelled state at 20 &#176;C. These experiments were conducted in both complete darkness and under white light illumination. Figure 1 displays some example SANS reduced data curves from these experiments, with an example curve fit shown in Figure 2. From this data, the struc...

Watch this Scientific Journal Video about Monitoring the Effects of Illumination on the Structure of Conjugated Polymer Gels Using Neutron Scattering at JoVE.com

Monitoring the Effects of Illumination on the Structure of Conjugated Polymer Gels Using Neutron Scattering

A protocol for the analysis of gels formed from the optoelectronic conjugated polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) using small and ultra-small angle neutron scattering in both the presence and absence of illumination is presented.

We demonstrate a protocol to effectively monitor the gelation process of a high concentration solution of conjugated polymer both in the presence and ...

The overall goal of this experiment is to quantify the structural evolution of conjugated polymers throughout the gelation process as a function of both temperature change and in situ light exposure. This method can help provide answers to key questions in the behavior of conjugated polymers. It provides insight into the importance of the presence of an exeton on their structure and assembly.The main advantage of this technique is that it allows unobtrusive and nondestructive analysis of the polymer length scales relevant to the structure's form during the conjugated polymer gelation process. To begin the procedure, filter five grams of high purity d4-ODCB through a 0.45 micrometer sieve. Then, place 0.34 grams of P3HT and 1.66 grams of filtered d4-ODCB in five gram glass vial containing a stir bar.Cap the vial with a foil-lined cap and seal the vial with plastic paraffin film. Wrap the vial in aluminum foil to completely exclude light. It is critical to minimize the light exposure that the sample receives from ambient lighting, such as fluorescent room lights.Samples should not be left on bench tops or in staging areas without sufficient shielding from illumination. Stir the solution at 70 degrees Celsius for a minimum of one to three hours. If the solution is not yet homogeneous, leave the solution stirring at 70 degrees Celsius.Once the solution is homogeneous, heat a glass pipette to 70 degrees Celsius in an oven. Use the heated pipette to quickly transfer the viscous solution to a clean, dry, one to two millimeter thick quartz banjo cell. Cap the banjo cell and seal the cell with plastic paraffin film.Wrap the cell in aluminum foil or store the cell in a light excluding container. Prepare a banjo cell containing only filtered d4-ODCB and an empty banjo cell as backgrounds. To begin the experiment, verify that the instrument sample stage is equipped with temperature controls capable of ranging from 70 to 20 degrees Celsius.Place the sample and background banjo cells in an appropriately sized holding block and label the holders. Wrap the block in 0.1 millimeter thick aluminum foil to exclude light while transferring the samples to the sample stage. Unwrap the samples, load the samples into the stage, and apply aluminum foil to the sample stage.Align and calibrate the SANS instrument. Set the detector distance close to its maximum setting. Based on count rates for the P3HT sample and the solvent blank, determine the appropriate scattering time for the experiment.Configure the sample heating scripts to ramp from 70 to 20 degrees Celsius, holding for 15 minutes at each ramp point within the scattering time. Heat the sample stage to 70 degrees Celsius and hold that temperature for 15 minutes to equilibrate the sample. Acquire SANS data, transmission data, and a blocked bean measurement for the sample.Acquire SANS data at room temperature for both the solvent blank and the empty cell. Upon completing the dark experiment, remove the aluminum foil from the sample stage. Position an optical illuminator with a halogen white light source so that the sample slot at the scattering collection position is fully illuminated.Measure and record the maximum light intensity at the sample position. Adjust the illuminator, if necessary, to achieve an intensity of at least 5, 000 lux. Equilibrate the sample at 70 degrees Celsius and collect sample and background data with the exact procedure used for the dark experiment.Process and analyze the data to determine key structural parameters. The reduced SANS data was fit to a linear combination of fitting equations representing nanofibril aggregates through the elliptical cylinder model and the free chains in solution through the polymer excluded volume model. Absolute intensity was observed to increase as temperature decreased for both the dark and light experiments.The distinct difference between the dark and light experiments for each temperature indicates that light exposure significantly affected the P3HT aggregation. Individual structural parameters were extracted from the combined model fit. The nanofibril surface area was consistently greater for samples studied in the dark.The elliptical cylinder model scale factor, which describes the amount of P3HT in the aggregate phase, was also greater for dark samples. The free chain radius of gyration was consistently smaller and the Porod exponent was higher for dark samples. Using ultra-small angled neutron scattering, the aggregate radius of gyration was found to be larger for dark samples at lower temperatures.Overall, the data indicates that exposure to light hindered P3HT aggregation. Once mastered, this technique should take about three to four hours for each sample. While attempting this procedure, remember to choose an appropriate fitting model that spans the entire length scale of interest.Literature, research, and trial and error customization will help find the most robust fitting model that fits your system with minimal residual discrepancy.

monitoring-effects-illumination-on-structure-conjugated-polymer-gels

Research

JoVE Journal

Chemistry

5.6K vistas.  University of Tennessee, Knoxville. The overall goal of this experiment is to quantify the structural evolution of conjugated polymers throughout the gelation process as a function of both temperature change and in situ light exposure. This method can help provide answers to key questions in the behavior of conjugated polymers. It provides insight into the importance of the presence of an exeton on their structure and assembly.The main advantage of this technique is that it allows unobtrusive and nondestructive analysis ...