Name: thermal scanning conductometry (tsc) as a general method for studying and controlling the phase behavior of conductive physical gels
Uploaded: 2018-01-23T13:30:00.000+00:00
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Description: Watch this Scientific Journal Video about Thermal Scanning Conductometry TSC as a General Method for Studying and Controlling the Phase Behavior of Conductive Physical Gels at JoVE.com

Financial support for this work was provided by the National Center for Science as grant No. DEC-2013/11/D/ST3/02694.

1. Preparation of the Experimental Site for TSC Measurement
<ol>
	<li>To measure the full characteristics of the TSC method, use the commercially available conductometer equipped with four electrode cells (alternatively, two electrode cells can be used for low conductivities) and a temperature sensor. Connect it to the PC and record the conductivity and temperature of the sample (4% wt% of methyl-4,6-O-(p-nitrobenzylidene)-&#945;-D-glucopyranoside in 1 M molar concentration of tetraethylammonium bromide - TEABr in glycerol - Glyc used in studied case, see paragraph 3 for ionic gel sample preparation) along with computer time.</li>
	<li>For automatic readouts, use the software supplied by the manufacturer along with the conductometer, and set the measuring mode to continuous with interval readings every 1 s.</li>
	<li>Prepare the nitrogen line (fill the high-pressure nitrogen tank with liquid nitrogen and start to evaporate it to get gaseous nitrogen in the nitrogen line), and set the pressure to 2 bars and required flow, then decrease the initial temperature of the nitrogen gas with the aid of a refrigerator.</li>
	<li>Tightly mount the screw cap of the vial on the conductive sensor, and secure it with a piece of teflon tape (crucial with volatile samples) (see Figure 2).</li>
</ol>
2. Preparation of Electrolyte Solution
<ol>
	<li>Prepare the electrolytes by mixing an appropriate amount of glycerol, used as a solvent, and tetraethylammonium bromide (TEABr) (use scale to weigh the required amount of compounds accordingly for the concentration needed for investigation), used as a solute, in a glass vial tightly closed and heated at 100 &#176;C for 15 min.</li>
	<li>Next, stir the mixture for 1 min and heat it again at 100 &#176;C for 5 min to ensure that all the solute is dissolved and the mixture is homogeneous.</li>
	<li>Use these prepared electrolyte solutions for measurements, and afterwards for preparation of ionogels.</li>
</ol>
3. Preparation of Low Molecular Weight Ionic Gels
<ol>
	<li>Prepare the ionogels from the electrolyte solutions (see section 2) by adding 178.6 mg of the low molecular weight gelator to 4 mL of 1 M TEABr/Glyc electrolyte solution to obtain 4% wt% of ionic gel sample. 
	NOTE: The chemical synthesis of the used gelator was described elsewhere11.</li>
	<li>To dissolve the gelator, add it to the glass vial with the electrolyte solution and heat it at 130 &#176;C for 20 min with additional stirring to assist dissolution.</li>
	<li>After completely dissolving the gelator, heat the mixture for an additional 5 min to ensure the sample is homogenous.</li>
	<li>Next, quickly cool down the sample in a dry cooling block at 10 &#176;C to ensure physical gelation. After the procedure, a homogeneous, transparent, or opaque gel phase should be obtained (Figure 3). 
	NOTE: After the first gelation has been performed, the sample becomes liquid when turning to sol phase at high temperatures, but after returning to room temperature it turns to the gel phase again. The temperature needed for the gel-sol phase transition is lower than the temperature needed for dissolution of the crystalline gelator. By changing the kinetics of the cooling stage, one can influence the physical properties of the obtained ionogel, like microstructure, optical appearance, or the gel-sol phase transition temperature (Tgs).</li>
</ol>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56607/56607fig3.jpg" /> 
Figure 3: The physical appearance of the investigated sample. The 1M TEABr/Glyc electrolyte (a), 4% ionogel with 1M TEABr/Glyc electrolyte in transparent phase (b), 4% ionogel with 1M TEABr/Glyc electrolyte in opaque phase (c). <a href="//cloudfront-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/56607/56607fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
4. In Situ Thermal Scanning Conductometry of Ionogels
<ol>
	<li>To prepare the sample for TSC measurement, heat the ionogel above the Tgs temperature, 94.85 &#176;C in the studied case. Transfer it to the precooled polypropylene vial after it turns to sol phase. Due to the fast cooling down of the sol, the gel phase is created.</li>
	<li>Insert the conductivity sensor (with the screw cap of the vial on it) into the vial by pushing it into the gel, tighten the screw cap, and secure it with Teflon tape.</li>
	<li>Perform the TSC measurement and record conductivity, temperature, and time to prepare conductivity vs temperature, temperature vs time, and conductivity vs time dependencies. Repeat the measurement in the investigated temperature range (9.85 - 99.85 &#176;C) in heating-cooling cycles (at least 2 times). 
	NOTE: Remember the 1st cycle is used to eliminate all discrepancies of the sample caused by the preparation procedure.</li>
	<li>Perform the measurements with different cooling rates (7 &#176;C/min, 4 &#176;C/min, and 1 &#176;C/min in studied case) to explore how it influences the conductive and thermal properties of investigated ionogels. 
	NOTE: To demonstrate how the TSC method can be used as a tool to obtain ionogels with targeted properties, a series of experiments with non-aqueous ionogel based on gelator 1, glycerol, and TEABr was performed and presented in this manuscript.</li>
</ol>
5. Example of TSC Measurement
<ol>
	<li>Insert the investigated ionogel into the vial, and push in the conductivity sensor.</li>
	<li>Perform the 1st heating-cooling cycle to improve the electrode contact, and remove all imperfections of the ionogel microstructure resulting from placing the sample in the vial and seen as scratches, cracks, and air bubbles included in the gel.</li>
	<li>Measure the conductivity and temperature along with time during the 2nd and 3rd heating-cooling cycle to investigate the performance of the ionogel, and the reproducibility of the system. Set the heating rate to 2 &#176;C/min and cooling rate to 7 &#176;C/min, and gelation temperature to 10 &#176;C. As a result, obtain a transparent gel phase.</li>
	<li>Perform the 4th and 5th heating-cooling cycle, with the heating and cooling rates equal to 2 &#176;C/min, and the gelation temperature equal to 10 &#176;C. As a result, obtain a mixture of the transparent and opaque gel phases.</li>
	<li>Perform the 6th and 7th heating-cooling cycle with heating and cooling rates equal to 2 &#176;C/min, and a gelation temperature equal to 60 &#176;C. As a result, obtain an opaque, white gel phase.</li>
	<li>Perform the analysis of the 1st derivatives for recorded data to see differences between samples.</li>
	<li>Keep the sample for 20 min at each of the gelation temperatures to ensure that the gelation process is completed.</li>
</ol>

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	<li>Bielejewski, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+approach+in+determination+of+ionic+conductivity+and+phase+transition+temperatures+in+gel+electrolytes+based+on+Low+Molecular+Weight+Gelators.">Novel approach in determination of ionic conductivity and phase transition temperatures in gel electrolytes based on Low Molecular Weight Gelators.</a> Electochim. Acta. 174, 1141-1148 (2015).</li><li>Bielejewski, M., &#321;api&#324;ski, A., Luboradzki, R., Tritt-Goc, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+solvent+on+the+thermal+stability+and+organization+of+self-assembling+fibrillar+networks+in+methyl-4,6-O-(p-nitrobenzylidene)-&#945;-D-glucopyranoside+gels.">Influence of solvent on the thermal stability and organization of self-assembling fibrillar networks in methyl-4,6-O-(p-nitrobenzylidene)-&#945;-D-glucopyranoside gels.</a> Tetrahedron. 67, 7222-7230 (2011).</li><li>Atsbeha, T., 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=Photophysical+characterization+of+low-molecular+weight+organogels+for+energy+transfer+and+light+harvesting.">Photophysical characterization of low-molecular weight organogels for energy transfer and light harvesting.</a> J. Mol. Struct. 993, 459-463 (2011).</li><li>Gronwald, O., Snip, E., Shinkai, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gelator+for+organic+liquids+based+on+self-assembly:+a+new+facet+of+supramolecular+and+combinatorial+chemistry.">Gelator for organic liquids based on self-assembly: a new facet of supramolecular and combinatorial chemistry.</a> Curr. Opinion in Coll. Interface Sci. 7, 148-156 (2002).</li><li>Vintiloiu, A., Leroux, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Organogels+and+their+use+in+drug+delivery-a+review.">Organogels and their use in drug delivery-a review.</a> Control. 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Sci. 128, 3982-3992 (2013).</li><li>Tao, L., 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=Stable+quasi-solid-state+dye-sensitized+solar+cell+using+a+diamide+derivative+as+low+molecular+mass+organogelator.">Stable quasi-solid-state dye-sensitized solar cell using a diamide derivative as low molecular mass organogelator.</a> J. Power Sources. 262, 444-450 (2014).</li><li>Kataoka, T., Ishioka, Y., Mizuhata, M., Minami, H., Maruyama, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+Conductive+Ionic-Liquid+Gels+Prepared+with+Orthogonal+Double+Networks+of+a+Low-Molecular-Weight+Gelator+and+Cross-Linked+Polymer.">Highly Conductive Ionic-Liquid Gels Prepared with Orthogonal Double Networks of a Low-Molecular-Weight Gelator and Cross-Linked Polymer.</a> ACS Appl. Mater. Interfaces. 7, 23346-23352 (2015).</li><li>Bielejewski, M., Nowicka, K., Bielejewska, N., Tritt-Goc, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ionic+Conductivity+and+Thermal+Properties+of+a+Supramolecular+Ionogel+Made+from+a+Sugar-Based+Low+MolecularWeight+Gelator+and+a+Quaternary+Ammonium+Salt+Electrolyte+Solution.">Ionic Conductivity and Thermal Properties of a Supramolecular Ionogel Made from a Sugar-Based Low MolecularWeight Gelator and a Quaternary Ammonium Salt Electrolyte Solution.</a> J. Electrochem. Soc. 163, G187-G195 (2016).</li><li>Gronwald, O., Shinkai, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bifunctional'+sugar-integrated+gelators+for+organic+solvents+and+water-on+the+role+of+nitro-substituents+in+1-O-methyl-4,6-O-(nitrobenzylidene)-monosaccharides+for+the+improvement+of+gelation+ability.">Bifunctional' sugar-integrated gelators for organic solvents and water-on the role of nitro-substituents in 1-O-methyl-4,6-O-(nitrobenzylidene)-monosaccharides for the improvement of gelation ability.</a> J. Chem. Soc., Perkin Trans. 2, 1933-1937 (2001).</li><li>Bielejewski, M., Ghorbani, M., Zolfigol, M., Tritt-Goc, J., Noura, S., Narimani, M., Oftadeh, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermally+reversible+solidification+of+novel+ionic+liquid+[im]HSO4+by+self-nucleated+rapid+crystallization:+investigations+of+ionic+conductivity,+thermal+properties,+and+catalytic+activity.">Thermally reversible solidification of novel ionic liquid [im]HSO4 by self-nucleated rapid crystallization: investigations of ionic conductivity, thermal properties, and catalytic activity.</a> RSC Adv. 6, 108896-108907 (2016).</li></ol>

The author has nothing to disclose

The thermal scanning conductometry is a new experimental method which has proven to be an efficient and effective way of investigating dynamically changing systems, like ionogels based on low molecular weight gelators, electrolytes, or ionic liquids. However, its applicability is not restricted only to ionogels. The TSC method can be easily used with other types of conducting soft matter systems like hydrogels, emulsions, creams, or any other charge containing carriers into which the conductivity sensor can be inserted. ...

Thermally Reversible Ionogels 
Physical gelation is a process which allows the construction of structures of self-assembled gelator molecules in presence of the solvent molecules. Due to non-covalent nature of the interactions responsible for this phenomenon (e.g. hydrogen bonding, van der Waals interactions, dispersion forces, electrostatic forces, &#960;-&#960; stacking, etc.), these systems are thermally reversible. This thermal reversibility, together with the very low concentration of the gelator and the wide variety of the systems that can be created, are some of the main advantages of physical gels over chemical ones. Thanks to the unique properties of the physical gel state, the ionogels are characterized with desirable features like easy recycling, long cycle life, enhanced physical properties (e.g. ionic conductivity), ease of production, and lowering of the production costs. Taking into the account the above advantages of physical gels (which already have a wide range of different applications1,2,3,4), these were thought to be used as an alternative way for electrolyte solidification and obtaining of ionogels5,6,7,8. However, the classical conductometry was not sensitive and accurate enough to follow such dynamically changing systems. Therefore,it could not detect the phase transitions and enhanced dynamics of ions in the gel matrix9. The reason for this insensitivity was the time needed for the temperature stabilization, during which dynamic changes of the sample properties were underway before the measurement was started. Furthermore, the number of measured temperatures was limited in order, not to significantly extend the experimental time. Therefore, to fully and accurately characterize the ionogels, a new method was needed, which would be able to follow the dynamic changes of properties as a function of temperature, and record data continuously in real time. The way the gelation process is conducted determines the properties of the created ionogel. The intermolecular non-covalent interactions are defined during the cooling stage; by changing the gelation temperature and cooling rates, one can strongly influence those interactions. Therefore, it was extremely important to measure the system during cooling when the gelation takes place. With the classical approach, this was impossible due to temperature stabilization time for the measurement, and the fast cooling rates required for successful gelation. However, with the thermal scanning conductometry method this task is very simple, delivers accurate and reproducible results, and allows the investigation of the influence of different kinetics of thermal changes applied to the sample on sample properties10. As a result, the ionogels with targeted properties can be studied and manufactured at the same time.
Thermal Scanning Conductometry (TSC) 
The thermal scanning conductometry is supposed to deliver a reproducible, accurate, and fast responding experimental method for the conductivity measurement of dynamically changing and thermally reversible systems, like ionogels based on low molecular weight gelators. However, it can be also used with electrolytes, ionic liquids, and any other conducting sample that can be placed in the measuring cell and has conductivity in the measuring range of the sensor. Additionally, besides the research application, the method was successfully used to manufacture ionogels with targeted properties like microstructure, optical appearance or thermal stability, and phase transition temperature in an accurate and easy way. Depending on the kinetics and history of thermal treating with use of the TSC method, we gain full control over some basic properties of physical gel systems. Additionally the chamber have been equipped in a video camera to inspect the sample state and record the changes of the sample especially during gelation and dissolution processes. An additional advantage of the TSC method is its simplicity, as the system can be built from a standard conductometer, a programmable temperature controller, the gaseous nitrogen line for the heating/cooling medium, the refrigerator, measuring chamber, and a PC, which can be found in most laboratories.
The TSC Experimental Site 
The thermal scanning conductometry experimental setup can be built in almost every laboratory with relatively low costs. In return, one obtains an accurate, reproducible, and fast method for measuring liquid and semisolid conductive samples at different external conditions. A detailed scheme of the TSC experimental setup built in our laboratory is given in Figure 1.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56607/56607fig1v2.jpg" /> 
Figure 1: Block diagram of the measurement site. The components consisting on working experimental setup for thermal scanning conductometry method. <a href="//cloudflare-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/56607/56607fig1v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
For the temperature change, a homemade temperature controller was used, but any kind of programmable temperature controller, which can change the temperature linearly with a defined change rate, can be used. For thermal isolation, a special chamber has been built. The purpose of using an isolation chamber is to minimize temperature horizontal gradients in the sample, and to assure fast cooling rates. The chamber consists of a glass cylinder with a 40-mm inner diameter and 300 mm length. At the bottom side, where the heater with gaseous nitrogen inlets are located, the end of the inlet is equipped with a diffusor to evenly spread the hot or cold gas. This is also the place where the temperature sensor PT100 of the variable temperature controller (VTC) is located. The temperature of the sample is recorded independently by the temperature sensor located in the conductivity sensor. Additionally, the chamber have been equipped in a video camera to inspect the sample state and record the changes of the sample especially during gelation and dissolution processes. The gaseous nitrogen obtained from evaporation of liquid nitrogen in the 250 L high pressure tank is used as a heating and cooling medium. The working pressure in the nitrogen line is set to 6 bars, and reduced to 2 bars at the measuring site. Such settings allow the obtainment of flow rates between 4 and 28 L/min without any disturbances, which allows a cooling rate of 10 &#176;C/min. To lower the initial temperature of the nitrogen gas, the external refrigerator has been used, and the decreased temperature was 10 &#176;C. This allows the obtainment of good linearity of the temperature change, starting from room temperature. During fast cooling, the temperature of the nitrogen gas is decreased to -15 &#176;C to assist high cooling rates. It is necessary to use gaseous nitrogen, and not even dry air, to avoid icing the refrigerator because of low temperatures.
The samples were inserted into a vial of 9 mm inner diameter and length of 58 mm, made of polypropylene, and equipped with a screw cap, which has a rubber ring for tight closing. The vials can be used up to 120 &#176;C. (see Figure 2).
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56607/56607fig2.jpg" /> 
Figure 2: The picture of a polypropylene vial and its mounting on the conductivity sensor. (1) the polypropylene vial, (2) the screw cap with rubber ring, 2a - the screw cap mounted on the conductivity sensor, (3) the vial with mounted conductivity sensor, the screw cap secured with Teflon tape. <a href="//cloudflare-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/56607/56607fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

<table><tbody><tr><td>SevenCompact S230 conductometer</td><td>Mettler-Toledo</td><td></td><td>equiped with InLab 710 sensor</td></tr><tr><td>home-build VTC</td><td></td><td></td><td></td></tr><tr><td>LabX PH 3.2 software</td><td>Mettler-Toledo</td><td></td><td>software used for data aqusition</td></tr><tr><td>tetraethylammonium bromide</td><td>Sigma-Aldrich</td><td>140023</td><td></td></tr><tr><td>glycerol</td><td>Sigma-Aldrich</td><td>G5516</td><td></td></tr><tr><td>methyl-4,6-O-(p-nitrobenzylidene)-a-D-glucopyranose</td><td></td><td></td><td>synthezied according to Gronwald, O., Shinkai, S., J. chem. Soc., Perkin Trans. 2 1933-1937 (2001).</td></tr><tr><td>[im]HSO&lt;sub&gt;4&lt;/sub&gt;</td><td></td><td></td><td>synthezeid by group of prof. Mohammad Ali Zolfigol, Faculty of Chemistry&lt;br/&gt; Bu-Ali Sina University&lt;br/&gt; Hamedan, I.R.Iran&amp;nbsp; according to Bielejewski, M., Ghorbani, M., Zolfigol, M., Tritt-Goc, J., Noura, S., Narimani, M., Oftadeh, M. RSC Adv. 6, 108896-108907 (2016).</td></tr><tr><td>polypropylene vial</td><td>Paradox Company, Cracow, Poland</td><td>PTC 088</td><td>www.insectnet.eu</td></tr></tbody></table>

thermal scanning conductometry (tsc) as a general method for studying and controlling the phase behavior of conductive physical gels

The thermal scanning conductometry protocol is a new approach in studying ionic gels based on low molecular weight gelators. The method is designed to follow the dynamically changing state of the ionogels, and to deliver more information and details about the subtle change of conductive properties with an increase or decrease in the temperature. Moreover, the method allows the performance of long term (i.e. days, weeks) measurements at a constant temperature to investigate the stability and durability of the system and the aging effects. The main advantage of the TSC method over classical conductometry is the ability to perform measurements during the gelation process, which was impossible with the classical method due to temperature stabilization, which usually takes a long time before the individual measurement. It is a well-known fact that to obtain the physical gel phase, the cooling stage must be fast; moreover, depending on the cooling rate, different microstructures can be achieved. The TSC method can be performed with any cooling/heating rate that can be assured by the external temperature system. In our case, we can achieve linear temperature change rates between 0.1 and approximately 10 &#176;C/min. The thermal scanning conductometry is designed to work in cycles, continuously changing between heating and cooling stages. Such an approach allows study of the reproducibility of the thermally reversible gel-sol phase transition. Moreover, it allows the performance of different experimental protocols on the same sample, which can be refreshed to initial state (if necessary) without removal from the measuring cell. Therefore, the measurements can be performed faster, in a more efficient way, and with much higher reproducibility and accuracy. Additionally, the TSC method can be also used as a tool to manufacture the ionogels with targeted properties, like microstructure, with an instant characterization of conductive properties.

The organic ionic gels constitute a new class of functional materials which can become an alternative solution for polymer gel electrolytes. However, to achieve this aim, these gels have to be deeply investigated and understood. The thermally reversible character of the gelation process, and the dynamically changing properties of temperature and phase occurrence, required a new experimental method which will allow the recording of data and detection of subtle changes in temperature change...

Watch this Scientific Journal Video about Thermal Scanning Conductometry TSC as a General Method for Studying and Controlling the Phase Behavior of Conductive Physical Gels at JoVE.com

Thermal Scanning Conductometry TSC as a General Method for Studying and Controlling the Phase Behavior of Conductive Physical Gels

The kinetics of the cooling process defines the properties of ionic gels based on low molecular weight gelators. This manuscript describes the usage of thermal scanning conductometry (TSC), which obtains full control over the gelation process, along with in situ measurements of the samples' temperature and conductivity.

Thermal Scanning Conductometry (TSC) as a General Method for Studying and Controlling the Phase Behavior of Conductive Physical Gels

The thermal scanning conductometry protocol is a new approach in studying ionic gels based on low molecular weight gelators. The method is designed to ...

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7.6K Views.  Institute of Molecular Physics Polish Academy of Sciences. The kinetics of the cooling process defines the properties of ionic gels based on low molecular weight gelators. This manuscript describes the usage of thermal scanning conductometry (TSC), which obtains full control over the gelation process, along with in situ measurements of the samples' temperature and conductivity. 

Video: Thermal Scanning Conductometry TSC as a General Method for Studying and Controlling the Phase Behavior of Conductive Physical Gels

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Scanning-probe single-electron capacitance spectroscopy facilitates the study of single-electron motion in localized subsurface regions. A sensitive charge-detection circuit is incorporated into a cryogenic scanning probe microscope to investigate small systems of dopant atoms beneath the surface of semiconductor samples.

The integration of low-temperature scanning-probe techniques and single-electron capacitance spectroscopy represents a powerful tool to study the ...

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Magnetic beads with ~1.9 &#181;m average diameter were used to transport microliter volumes of liquids between contiguous liquid segments with a tube for ...

Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor performance, which suggest a new direction for the development of next-generation ultrathin and flexible photonic and electronic devices. Enhanced luminescence quantum efficiency has been widely observed in these atomically thin 2D crystals. However, dimension effects beyond quantum confinement thicknesses or even at the micrometer scale are not expected and have rarely been observed. In this study, molybdenum diselenide (MoSe2) layer crystals with a thickness range of 6-2,700 nm were fabricated as two- or four-terminal devices. Ohmic contact formation was successfully achieved by the focused-ion beam (FIB) deposition method using platinum (Pt) as a contact metal. Layer crystals with various thicknesses were prepared through simple mechanical exfoliation by using dicing tape. Current-voltage curve measurements were performed to determine the conductivity value of the layer nanocrystals. In addition, high-resolution transmission electron microscopy, selected-area electron diffractometry, and energy-dispersive X-ray spectroscopy were used to characterize the interface of the metal&#8211;semiconductor contact of the FIB-fabricated MoSe2 devices. After applying the approaches, the substantial thickness-dependent electrical conductivity in a wide thickness range for the MoSe2-layer semiconductor was observed. The conductivity increased by over two orders of magnitude from 4.6 to 1,500 &#937;&#8722;1 cm&#8722;1, with a decrease in the thickness from 2,700 to 6 nm. In addition, the temperature-dependent conductivity indicated that the thin MoSe2 multilayers exhibited considerably weak semiconducting behavior with activation energies of 3.5-8.5 meV, which are considerably smaller than those (36-38 meV) of the bulk. Probable surface-dominant transport properties and the presence of a high surface electron concentration in MoSe2 are proposed. Similar results can be obtained for other layer semiconductor materials such as MoS2 and WS2.

We describe the approaches for the device fabrication and electrical characterization of molybdenum diselenide (MoSe2) layer semiconductor nanostructures with different thicknesses. In addition, the fabrication of ohmic contacts for MoSe2-layer nanocrystals by the focused-ion beam deposition method using platinum (Pt) as a contact metal is described.

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor ...

Characterizing Electron Transport through Living Biofilms

Here we demonstrate the method of electrochemical gating used to characterize electrical conductivity of electrode-grown microbial biofilms under physiologically relevant conditions.1 These measurements are performed on living biofilms in aqueous medium using source and drain electrodes patterned on a glass surface in a specialized configuration referred to as an interdigitated electrode (IDA) array. A biofilm is grown that extends across the gap connecting the source and drain. Potentials are applied to the electrodes (ES and ED) generating a source-drain current (ISD) through the biofilm between the electrodes. The dependency of electrical conductivity on gate potential (the average of the source and drain potentials, EG = [ED + ES]/2) is determined by systematically changing the gate potential and measuring the resulting source-drain current. The dependency of conductivity on gate potential provides mechanistic information about the extracellular electron transport process underlying the electrical conductivity of the specific biofilm under investigation. The electrochemical gating measurement method described here is based directly on that used by M. S. Wrighton2,3 and colleagues and R. W. Murray4,5,6 and colleagues in the 1980&#39;s to investigate thin film conductive polymers.

A protocol for measuring electrical conductivity of living microbial biofilms under physiologically relevant conditions is presented.

Here we demonstrate the method of electrochemical gating used to characterize electrical conductivity of electrode-grown microbial biofilms under ...

Chemistry

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.

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 ...

Combining Microfluidics and Microrheology to Determine Rheological Properties of Soft Matter during Repeated Phase Transitions

The microstructure of soft matter directly impacts macroscopic rheological properties and can be changed by factors including colloidal rearrangement during previous phase changes and applied shear. To determine the extent of these changes, we have developed a microfluidic device that enables repeated phase transitions induced by exchange of the surrounding fluid and microrheological characterization while limiting shear on the sample. This technique is &#181;2rheology, the combination of microfluidics and microrheology. The microfluidic device is a two-layer design with symmetric inlet streams entering a sample chamber that traps the gel sample in place during fluid exchange. Suction can be applied far away from the sample chamber to pull fluids into the sample chamber. Material rheological properties are characterized using multiple particle tracking microrheology (MPT). In MPT, fluorescent probe particles are embedded into the material and the Brownian motion of the probes is recorded using video microscopy. The movement of the particles is tracked and the mean-squared displacement (MSD) is calculated. The MSD is related to macroscopic rheological properties, using the Generalized Stokes-Einstein Relation. The phase of the material is identified by comparison to the critical relaxation exponent, determined using time-cure superposition. Measurements of a fibrous colloidal gel illustrate the utility of the technique. This gel has a delicate structure that can be irreversibly changed when shear is applied. &#181;2rheology data shows that the material repeatedly equilibrates to the same rheological properties after each phase transition, indicating that phase transitions do not play a role in microstructural changes. To determine the role of shear, samples can be sheared prior to injection into our microfluidic device. &#181;2rheology is a widely applicable technique for the characterization of soft matter enabling the determination of rheological properties of delicate microstructures in a single sample during phase transitions in response to repeated changes in the surrounding environmental conditions.

We demonstrate the fabrication and use of a microfluidic device that enables multiple particle tracking microrheology measurements to study the rheological effects of repeated phase transitions on soft matter.

The microstructure of soft matter directly impacts macroscopic rheological properties and can be changed by factors including colloidal rearrangement ...

A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various precursor noble metal ions with reducing agents in a 1:1 (v/v) ratio results in the formation of metal gels within seconds to minutes compared to much longer synthesis times for other techniques such as sol-gel. Conducting the reduction step in a microcentrifuge tube or small volume conical tube facilitates a proposed nucleation, growth, densification, fusion, equilibration model for gel formation, with final gel geometry smaller than the initial reaction volume. This method takes advantage of the vigorous hydrogen gas evolution as a by-product of the reduction step, and as a consequence of reagent concentrations. The solvent accessible specific surface area is determined with both electrochemical impedance spectroscopy and cyclic voltammetry. After rinsing and freeze drying, the resulting aerogel structure is examined with scanning electron microscopy, X-ray diffractometry, and nitrogen gas adsorption. The synthesis method and characterization techniques result in a close correspondence of aerogel ligament sizes. This synthesis method for noble metal aerogels demonstrates that high specific surface area monoliths may be achieved with a rapid and direct reduction approach.

A rapid, direct solution-based reduction synthesis method to obtain Au, Pd, and Pt aerogels is presented.

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various ...

Fabrication and Characterization of a Conformal Skin-like Electronic System for Quantitative, Cutaneous Wound Management

Recent advances in the development of electronic technologies and biomedical devices offer opportunities for non-invasive, quantitative assessment of cutaneous wound healing on the skin. Existing methods, however, still rely on visual inspections through various microscopic tools and devices that normally include high-cost, sophisticated systems and require well trained personnel for operation and data analysis. Here, we describe methods and protocols to fabricate a conformal, skin-like electronics system that enables conformal lamination to the skin surface near the wound tissues, which provides recording of high fidelity electrical signals such as skin temperature and thermal conductivity. The methods of device fabrication provide details of step-by-step preparation of the microelectronic system that is completely enclosed with elastomeric silicone materials to offer electrical isolation. The experimental study presents multifunctional, biocompatible, waterproof, reusable, and flexible/stretchable characteristics of the device for clinical applications. Protocols of clinical testing provide an overview and sequential process of cleaning, testing setup, system operation, and data acquisition with the skin-like electronics, gently mounted on hypersensitive, cutaneous wound and contralateral tissues on patients.

This article presents methods to fabricate and characterize a conformal, skin-like electronic system and protocols for the use in clinical applications, particularly on cutaneous wound management.

Recent advances in the development of electronic technologies and biomedical devices offer opportunities for non-invasive, quantitative assessment of ...

Bioengineering

Viscoelastic Characterization of Soft Tissue-Mimicking Gelatin Phantoms using Indentation and Magnetic Resonance Elastography

Characterization of biomechanical properties of soft biological tissues is important to understand the tissue mechanics and explore the biomechanics-related mechanisms of disease, injury, and development. The mechanical testing method is the most straightforward way for tissue characterization and is considered as verification for in vivo measurement. Among the many ex vivo mechanical testing techniques, the indentation test provides a reliable way, especially for samples that are small, hard to fix, and viscoelastic such as brain tissue. Magnetic resonance elastography (MRE) is a clinically used method to measure the biomechanical properties of soft tissues. Based on shear wave propagation in soft tissues recorded using MRE, viscoelastic properties of soft tissues can be estimated in vivo based on wave equation. Here, the viscoelastic properties of gelatin phantoms with two different concentrations were measured by MRE and indentation. The protocols of phantom fabrication, testing, and modulus estimation have been presented.

This article presents a demonstration and summary of protocols of making gelatin phantoms that mimic soft tissues, and the corresponding viscoelastic characterization using indentation and magnetic resonance elastography.

Characterization of biomechanical properties of soft biological tissues is important to understand the tissue mechanics and explore the ...

Hydrogel Arrays Enable Increased Throughput for Screening Effects of Matrix Components and Therapeutics in 3D Tumor Models

Cell-matrix interactions mediate complex physiological processes through biochemical, mechanical, and geometrical cues, influencing pathological changes and therapeutic responses. Accounting for matrix effects earlier in the drug development pipeline is expected to increase the likelihood of clinical success of novel therapeutics. Biomaterial-based strategies recapitulating specific tissue microenvironments in 3D cell culture exist but integrating these with the 2D culture methods primarily used for drug screening has been challenging. Thus, the protocol presented here details the development of methods for 3D culture within miniaturized biomaterial matrices in a multi-well plate format to facilitate integration with existing drug screening pipelines and conventional assays for cell viability. Since the matrix features critical for preserving clinically relevant phenotypes in cultured cells are expected to be highly tissue- and disease-specific, combinatorial screening of matrix parameters will be necessary to identify appropriate conditions for specific applications. The methods described here use a miniaturized culture format to assess cancer cell responses to orthogonal variation of matrix mechanics and ligand presentation. Specifically, this study demonstrates the use of this platform to investigate the effects of matrix parameters on the responses of patient-derived glioblastoma (GBM) cells to chemotherapy.

The present protocol describes an experimental platform to assess the effects of mechanical and biochemical cues on chemotherapeutic responses of patient-derived glioblastoma cells in 3D matrix-mimetic cultures using a custom-made UV illumination device facilitating high-throughput photocrosslinking of hydrogels with tunable mechanical features.

Cell-matrix interactions mediate complex physiological processes through biochemical, mechanical, and geometrical cues, influencing pathological changes ...