Name: application of voltage in dynamic light scattering particle size analysis
Uploaded: 2020-01-24T13:00:00
Description: Watch this Scientific Journal Video about Application of Voltage in Dynamic Light Scattering Particle Size Analysis at JoVE.com

The authors would like to acknowledge the financial support from NSF (CBET 1638893), (CBET 1638896), NIH (P20 GM113131), and the Hamel Center for Undergraduate Research at UNH. Further, the authors would like to recognize the assistance of Darcy Fournier for the assistance in cabling and Scott Greenwood for access to the DLS.

1. Example polymer preparations
<ol>
	<li>pNIPAM polymer synthesis 
	NOTE: This preparation produces 10 mL of 1 g/L solution, which is enough for 3-4 experiments.
	<ol>
		<li>Prepare the Schlenk line apparatus. Ensure the cold trap Dewar flask is filled with a slurry of dry ice and acetone, or if a mechanical refrigeration trap is used, ensure that the trap has reached an appropriate temperature.</li>
		<li>In a 50 mL round-bottom flask, add 0.566 g of N-isopropylacrylamide (NIPAM) monome...

<ol>
	<li>Xu, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Particuology+Light+scattering+:+A+review+of+particle+characterization+applications.">Particuology Light scattering : A review of particle characterization applications.</a> Particuology. 18, 11-21 (2015).</li><li>Szczubia&#322;ka, K., Nowakowska, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Response+of+micelles+formed+by+smart+terpolymers+to+stimuli+studied+by+dynamic+light+scattering.">Response of micelles formed by smart terpolymers to stimuli studied by dynamic light scattering.</a> Polymer. 44 (18), 5269-5274 (2003).</li><li>Kotsuchibashi, Y., Ebara, M., Aoyagi, T., Narain, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+Advances+in+Dual+Temperature+Responsive+Block+Copolymers+and+Their+Potential+as+Biomedical+Applications.">Recent Advances in Dual Temperature Responsive Block Copolymers and Their Potential as Biomedical Applications.</a> Polymers. 8, 380 (2016).</li><li>Lanzalaco, S., Armelin, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Poly(N-isopropylacrylamide)+and+Copolymers:+A+Review+on+Recent+Progresses+in+Biomedical+Applications.">Poly(N-isopropylacrylamide) and Copolymers: A Review on Recent Progresses in Biomedical Applications.</a> Gels. 3, 36 (2017).</li><li>Lessard, D. G., Ousalem, M., Zhu, X. X., Eisenberg, A., Carreau, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Study+of+the+phase+transition+of+poly(N,N-diethylacrylamide)+in+water+by+rheology+and+dynamic+light+scattering.">Study of the phase transition of poly(N,N-diethylacrylamide) in water by rheology and dynamic light scattering.</a> Journal of Polymer Science Part B: Polymer Physics. 41, 1627-1637 (2003).</li><li>Garner, B. W., Cai, T., Hu, Z., Neogi, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electric+field+enhanced+photoluminescence+of+CdTe+quantum+dots+encapsulated+in+poly+(N-isopropylacrylamide)+nano-spheres.">Electric field enhanced photoluminescence of CdTe quantum dots encapsulated in poly (N-isopropylacrylamide) nano-spheres.</a> Optics express. 16, 19410-19418 (2008).</li><li>Gallei, M., Schmidt, B. V. K. J., Klein, R., Rehahn, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Defined+Poly[styrene-+block+-(ferrocenylmethyl+methacrylate)]+Diblock+Copolymers+via+Living+Anionic+Polymerization.">Defined Poly[styrene- block -(ferrocenylmethyl methacrylate)] Diblock Copolymers via Living Anionic Polymerization.</a> Macromolecular Rapid Communications. 30, 1463-1469 (2009).</li><li>Grenier, C., Timberman, A., 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=High+Affinity+Binding+by+a+Fluorescein+Templated+Copolymer+Combining+Covalent,+Hydrophobic,+and+Acid-Base+Noncovalent+Crosslinks.">High Affinity Binding by a Fluorescein Templated Copolymer Combining Covalent, Hydrophobic, and Acid-Base Noncovalent Crosslinks.</a> Sensors. 18, 1330 (2018).</li><li>Chiefari, J., Chong, Y. K. B., 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=Living+Free-Radical+Polymerization+by+Reversible+Addition&#8722;Fragmentation+Chain+Transfer:+The+RAFT+Process.">Living Free-Radical Polymerization by Reversible Addition&#8722;Fragmentation Chain Transfer: The RAFT Process.</a> Macromolecules. 31, 5559-5562 (1998).</li><li>Perrier, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=50th+Anniversary+Perspective+:+RAFT+Polymerization-A+User+Guide.">50th Anniversary Perspective : RAFT Polymerization-A User Guide.</a> Macromolecules. 50, 7433-7447 (2017).</li></ol>

Applying voltage to either pNIPAM or p(NIPAM-b-FMMA) solutions changed the polymer aggregation behavior in response to temperature. With both materials, when an applied voltage was present, the polymers&#39; volume size remained high even when the solutions were cooled below their LCST. This was an unexpected result, as the trials with no voltage showed the polymers returning to their original sizes. These experiments allow us to conclude that for our temperature range, and with an applied voltage, polymer aggre...

Dynamic light scattering (DLS) is a technique to determine particle size through the use of random changes in intensity of light scattered through solution1. DLS is capable of measuring aggregation of polymers by determining particle size. For this experiment, DLS was coupled with controlled temperature changes to observe when a polymer aggregates which is indicative of exceeding the lower critical solution temperature (LCST)2,3. Below the LCST, there exists one homogeneous liquid phase; above the LCST, the polymer becomes less soluble, aggregates, and condenses out of solution. An applied voltage (i.e., applied potential or electric field) was introduced across the scattering field to observe the effects of the electric field on aggregation behavior and LCST. The application of voltage in particle sizing measurements allows for new insights into particle behavior and subsequent applications in the fields of sensors, energy storage, drug delivery systems, soft robotics, and others.
In this protocol, two example polymers were used. Poly(N-isopropylacrylamide), or pNIPAM, is a thermal sensitive polymer, which contains both a hydrophilic amide group and a hydrophobic isopropyl group on the macromolecular chain4,5. Thermal-responsive polymer materials like pNIPAM have been widely used in controlled drug release, biochemical separation, and chemical sensors in recent years3,4. The LCST literature value of pNIPAM is around 30-35 &#176;C4. pNIPAM is typically not electrochemically active. Therefore, as a second sample polymer an electrochemically-active block was added to the polymer. Specifically, ferrocenylmethyl methacrylate was used to create a poly(N-isopropylacrylamide)-block-poly(ferrocenylmethyl methacrylate) block-copolymer, or p(NIPAM-b-FMMA)6,7. Both example polymers were synthesized by reversible addition fragmentation chain-transfer polymerization with controlled chain length8,9,10. The non-electrochemically active polymer, pNIPAM, was synthesized as 100 mer pure pNIPAM. The electrochemically active polymer, p(NIPAM-b-FMMA), was also 100 mer chain length, which contains 4% ferrocenylmethyl methacrylate (FMMA) and 96% NIPAM.
In this article, a protocol and methodology to study the effect of applied voltage on polymer aggregation is demonstrated. This method could also be extended to other applications of DLS, such as the analysis of protein folding/unfolding, protein-protein interactions, and agglomeration of electrostatically charged particles to name a few. The sample was heated from 20 &#176;C to 40 &#176;C to identify the LCST in the absence and presence of a 1 V applied field. Then, the sample was cooled from 40 &#176;C to 20 &#176;C without disrupting the applied field to study any hysteretic or equilibrium effects.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>N-Isopropylacrylamide</td>
			<td>Tokyo Chemical Industry CO., LTD</td>
			<td>I0401-500G</td>
			<td></td>
		</tr>
		<tr>
			<td>1,4-Dioxane</td>
			<td>Alfa Aesar</td>
			<td>39118</td>
			<td></td>
		</tr>
		<tr>
			<td>2,2&#34;-Azobis(2-methylpropionitrile)</td>
			<td>SIGMA-ALDRICH</td>
			<td>441090-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>Cuvette</td>
			<td>Malvern</td>
			<td>DTS0012</td>
			<td></td>
		</tr>
		<tr>
			<td>Dynamic Light Scattering</td>
			<td>Malvern</td>
			<td>Zetasizer NanoZS</td>
			<td></td>
		</tr>
		<tr>
			<td>Ferrocenylmethyl methacrylate</td>
			<td>ASTATECH</td>
			<td>FD13136-1G</td>
			<td></td>
		</tr>
		<tr>
			<td>Phthalimidomethyl butyl trithiocarbonate</td>
			<td>SIGMA-ALDRICH</td>
			<td>777072-1G</td>
			<td></td>
		</tr>
		<tr>
			<td>Potentiostat</td>
			<td>Gamry</td>
			<td>Reference 600</td>
			<td></td>
		</tr>
	</tbody>
</table>

application of voltage in dynamic light scattering particle size analysis

Dynamic light scattering (DLS) is a common method for characterizing the size distribution of polymers, proteins, and other nano- and microparticles. Modern instrumentation permits measurement of particle size as a function of time and/or temperature, but currently there is no simple method for performing DLS particle size distribution measurements in the presence of applied voltage. The ability to perform such measurements would be useful in the development of electroactive, stimuli-responsive polymers for applications such as sensing, soft robotics, and energy storage. Here, a technique using applied voltage coupled with DLS and a temperature ramp to observe changes in aggregation and particle size in thermoresponsive polymers with and without electroactive monomers is presented. The changes in aggregation behavior observed in these experiments were only possible through the combined application of voltage and temperature control. To obtain these results, a potentiostat was connected to a modified cuvette in order to apply voltage to a solution. Changes in polymer particle size were monitored using DLS in the presence of constant voltage. Simultaneously, current data were produced, which could be compared with particle size data, to understand the relationship between current and particle behavior. The polymer poly(N-isopropylacrylamide) (pNIPAM) served as a test polymer for this technique, as pNIPAM's response to temperature is well-studied. Changes in the lower-critical solution temperature (LCST) aggregation behavior of pNIPAM and poly(N-isopropylacrylamide)-block-poly(ferrocenylmethyl methacrylate), an electrochemically active block-copolymer, in the presence of applied voltage are observed. Understanding the mechanisms behind such changes will be important when trying to achieve reversible polymer structures in the presence of applied voltage.

The real-time file output of each run in the temperature ramp is presented as a table, as seen in Figure 3. Each record can be chosen independently to see the volume size (Figure 4) and correlation coefficient (Figure 5). Volume particle size distribution (PSD) is the most accurate data to interpret the overall distribution and LCST, but the quality of data should be assessed via correlation graph (<...

Watch this Scientific Journal Video about Application of Voltage in Dynamic Light Scattering Particle Size Analysis at JoVE.com

Application of Voltage in Dynamic Light Scattering Particle Size Analysis

Here, a protocol to apply voltage to solution during dynamic light scattering particle size measurements with the intent to explore the effect of voltage and temperature changes on polymer aggregation is presented.

Dynamic light scattering (DLS) is a common method for characterizing the size distribution of polymers, proteins, and other nano- and microparticles. ...

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