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

Summary

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.

Abstract

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 °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.

Introduction

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, π-π 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 u....

Protocol

1. Preparation of the Experimental Site for TSC Measurement

1. 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)-α-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.
2. For automatic readouts, use the sof....

Results

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.......

Discussion

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. .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
SevenCompact S230 conductometer	Mettler-Toledo		equiped with InLab 710 sensor
home-build VTC
LabX PH 3.2 software	Mettler-Toledo		software used for data aqusition
tetraethylammonium bromide	Sigma-Aldrich	140023
glycerol	Sigma-Aldrich	G5516
methyl-4,6-O-(p-nitrobenzylidene)-a-D-glucopyranose			synthezied according to Gronwald, O., Shinkai, S., J. chem. Soc., Perkin Trans. 2 1933-1937 (2001).
[im]HSO4			synthezeid by group of prof. Mohammad Ali Zolfigol, Faculty of Chemistry Bu-Ali Sina University Hamedan, I.R.Iran  according to Bielejewski, M., Ghorbani, M., Zolfigol, M., Tritt-Goc, J., Noura, S., Narimani, M., Oftadeh, M. RSC Adv. 6, 108896-108907 (2016).
polypropylene vial	Paradox Company, Cracow, Poland	PTC 088	www.insectnet.eu