A new family of urea-based low molecular-weight organogelators for environmental remediation: the influence of structure

Six analogous low molecular weight organogelators are comprehensively characterised to investigate the role of small structural modifications on performance.


Figure 6 Gels
To form the gels shown in the manuscript Figure 6 (a), (b) and (c) -5 wt% of the gelator was added to 1-2 mL of pump oil on the surface of 5 mL of either de-ionised or sea water. The oil layer was heated briefly with a heat gun to cause complete dissolution of the gelator, and then allowed to cool to form a solid gel, before inversion. For (d) 120 mL of water was coloured (for contrast) with a few mg of CuSO4 in a 100 mL, B24 neck, round-bottom flask. Next 3 mL of pump oil was added to the surface, followed by 150 mg of gelator 6, and the mixture heated briefly with a heat gun at the next of the flask to cause dissolution. The same procedure and result were possible with 150 mg of gelator 5. After a few minutes of cooling, the gel formed, and the flask was inverted. For (e)/(f) 2 mL of engine oil, recovered used from a 2-stroke engine and filtered, was placed in a vial with 100 mg of gelator 5 and heated briefly with a heat gun. The solution and set gel were photographed.

SXD Measurements and Analysis
Single crystals of o-, m-, and p-C17H28N2O were selected and measured with Cu Kα radiation on a SuperNova, dual source diffractometer equipped with an Atlas CCD detector. The crystals were kept at 150 K during data collection. For o-C17H28N2O, further measurements were made at both 200 K and 295 K. Using Olex2 3 , the structures was solved with the ShelXT structure solution program using intrinsic phasing and refined with the ShelXL 4 refinement package using least-squares minimization. Hydrogen atoms were constrained with the AFIX command with the exception of H(15) for m-and p-C17H28N2O. Further details on all three structures are provided in the summary tables below (Tables S1a-f to S3a-f). For o-C17H28N2O, only an approximate structure is presented as the structure is incommensurate at all of the temperatures measured ( Figure S1). The labelling of the atoms is similar for all three molecules as shown in Figure S2.

Atom -Atom Length / Å Atom -Atom Length / Å
If the lattice parameter a is doubled as shown in (d), the position of the satellite peaks will lie close to the lattice points of the reciprocal space cell (e). A wave with amplitude along a* can be used to describe the off-centre position of the spots. Alternatively, the data can be integrated using a large integration sphere to yield an approximate structure.

S-35
Rheology of gels of 4, 5 and 6 at 2% w/v in pump oil An AR-G2 controlled stress rheometer from TA Instruments fitted with a Peltier plate was used. Initially, the sample was melted and approximately 1 mL was placed on the rheometer, which was closed to a gap of 300 μm with a 60 mm flat plate geometry. The sample was then heated to 70 °C and sheared at 1 Pa for 2 minutes in order to break down any SAFIN structures, minimizing the effects of sample history. The sample was then cooled down to 25 °C at a rate of 5 °C min −1 followed by a hold at 25 o C for 10 minutes. During the cooling ramp the plate geometry was oscillated at 2π rad s −1 , 0.3 Pa. A time sweep was then conducted for 10 minutes using 0.3 Pa at 2π rad s −1 . This time sweep captured the network formation processes and we observed that all samples had stopped evolving before any other measurements were taken.
Each sample was then subjected to a frequency sweep or stress sweep. These experiments measured the shear storage and loss moduli, G′ and G′′ respectively, which describe the solidand liquid-like nature of the samples. The frequency sweep was used to ensure we were working in a region where the materials showed a strong gel structure (ie. G′>G′′ and G′ was frequency independent). The frequency sweep was performed using a stress of 0.3 Pa (10 Pa for 5) between 0.1 and 100 Hz. We used oscillatory stress sweep experiments to identify the linear viscoelastic region and then to measure the samples to breakdown, with oscillatory stress amplitudes started from 0.1 Pa and increased up to 1000 Pa, with a frequency of 2π rad s −1 .

DSC of gels of 4, 5 and 6 at 2% w/v in pump oil
We used a Q20 heat flux DSC from TA Instruments which was calibrated with an indium sample at 10 °C min −1 . Approximately 25 mg of sample was placed into stainless steel pans, which were subsequently hermitically sealed and placed into the furnace of the DSC. At the beginning of the experiment, the sample was heated at 100 °C for 1 minute in order to destroy any crystal memory. Next, the sample was cooled at 5 °C min −1 to 25 °C followed by a heating ramp back at 5 °C min −1 to bring the sample to 100 °C. Gelator Recovery Figure S8. 1 H NMR demonstrating recovery of gelator and organic liquid by shearing and centrifugation of the gel. A 5 wt% gel of 6 in ODE was vigorously sheared and then centrifuged, resulting in pure ODE in the top layer and a crude gelator mixture at the bottom. Some liquid phase remained in the sample due to sampling methods. The inset photo shows the centrifuged sample with the boxes illustrating the sampling regions for the relevant spectra.