Ionic liquids (ILs) are defined as pure salts with a melting temperature below 100 °C with a subset called room-temperature ILs (RTILs) with melting temperatures at or below room temperature. The sizes of the cation and anion play a critical role in determining the properties, with smaller ions forming stronger ionic forces and packing better, raising viscosity and lowering conductivity of the IL. At the same time, intermolecular forces such as van der Waals and hydrogen bonding can play a role in IL properties as well. Our research described herein is focused on three tetraalkylphosphonium-based cations coupled with three alkylsulfate anions, all containing different alkyl chain lengths. Changes in physicochemical properties as a function of changing alkyl chain length were investigated (i.e. van der Waals forces) across all nine possible IL combinations.
Specifically, studies were focused on conductivities, viscosities, and densities. In general, the purity of the synthesized ILs was estimated to be above 98%. In the case of density, ILs with the smallest cation (tbP+) family had the highest density, while the largest cation family demonstrated the lowest density, with the trend as follows: tbP+ > tbtdP+ > thtdP+. With viscosity, a slightly different trend was observed; the tbtdP+ cation family had the highest viscosity among the three, followed by TdP+ then thtdP+. The change in pattern could be due to the impact of not just size/packing and ionic forces but also van der Waals forces. Conductivity was highest for the smallest ILs (tbP+) while the lowest conductivity was reported for the largest IL (thtdP+). Within the same cation group higher conductivity was measured for the smallest anion size in the order of ds- > dds- > tds-.
Polymerized ionic liquids, or poly ILs, are a special type of polyelectrolyte that contains a monomeric IL species in the repeating unit. Different polymer synthetic methods have been applied to create PILs; however, thiol-ene ‘click’ photopolymerization offers a solventless, rapidly-curing platform for the preparation of homogenous polymer networks. In the second study, a tetrafunctional thiol, pentaerythritol tetrakis (3-mercapto-propionate) (PTMP), was reacted with a bifunctional ionic liquid ene, 1,3-bisallylimidazolium (NTf2) to form polyIL networks. In the particular project described herein, the aforementioned advantages of thiol-ene photopolymerization was utilized in stereolithographic (SLA) 3D printing. However, the initial resolution of the printed pieces was not satisfactory due to light scattering within the neat thiol-ene resin. For this reason, further steps to improve the resolution were taken by adding an absorptive, anti-scattering material (Sudan I) to the thiol-ene resins.
The impact of Sudan I addition at various weight percents on thermal, mechanical, and conductive properties, as well as thiol-ene curing rate, were examined. Thiol-ene photopolymers were prepared in two ratios: 1.0:1.0, and 1.0:2.0 (corresponding to the thiol:ene mol ratio) with different weight percents (0.02%, 0.05%, 0.10%) of Sudan I dye for each ratio. Thermal, mechanical, and conductive properties for both 3D printed, and UV lamp cured parts were tested to measure any differences in properties. In general, the type of curing and addition of Sudan I to the resin did not significantly change the thermal stability of the polymer. The conductivity of the different polymer compositions including UV cured, 3D printed, and the additions of both 0.02% and 0.05% Sudan I were measured, and the results were nearly identical. For evaluating resolution, squares of know dimensions were printed and actual and specified dimensions were computed. A 1:2 thiol-ene containing no Sudan were between 20 - 28% bigger than specified (“overgrowth”), while the same 1:2 polymer containing 0.02% Sudan showed improved resolution with between 12 and 17% overgrowth.
Year manuscript completed
Year degree awarded
Ionic Liquid, Polymer, Conductivity, thiolene, 3D printing
Alhussain, Mustafa Mohammed, "PROPERTIES AND APPLICATIONS OF TETRAALKYLPHOSPHONIUM ALKYLSULFATE IONIC LIQUIDS AND 3D PRINTED POLYMERIZED IONIC LIQUIDS" (2019). Murray State Theses and Dissertations. 158.