Electronic supplementary information

X-ray radiography

Figure 1. X-ray radiographs of polyHIPEs revealing a heterogeneous structure throughout the monolith with up to 50% higher polymer density compared to the prepared density as indicated by the color contrast. Images reproduced by permission.[1]

Figure 1 shows the density heterogeneity in polyHIPEs. This level of heterogeneity is not acceptable for high energy laser physics experiments that rely on accurate modeling to obtain experimental validation.

[1] AWE internal report, 2013.

Preparation of HIPEs and polyHIPEs

The polyHIPEs were prepared from the precursor High Internal Phase Emulsion (HIPE) using the two-syringe technique developed at Los Alamos National Laboratory, USA. Formulations were prepared for 100 mg/cm3. Two gas-tight syringes (Hamilton) were used to achieve emulsification. One syringe contained the oil phase, and the other contained the aqueous phase were attached together by a luer connector before being pumped forward and backward from one syringe to the other by hand until the formation of emulsion. This was indicated by a rapid increase in viscosity rendering successive pushes considerably more difficult. The number of pumps required was in the region of 10-20 pumps. Typically, higher number of pumps were required for emulsions containing more DVB 80 or para-DVB. The oil phase contained the monomers and surfactant, and the aqueous phase contained the dissolved initiator in deionized water. Once emulsified, HIPEs were transferred to a plastic vessel, sealed, and put into a 60°C oven to polymerize for 48 hours. The polyHIPE monoliths were washed with water and methanol, and then dried at 30°C.

A brief description of TD-NMR (NMR relaxometry)

TD-NMR measures nuclear spin relaxation times in low magnetic field strengths, this can be described as the time taken for the perturbed spin system to return to an equilibrium state. Unlike regular solution- or solid-state NMR spectroscopy, the end result is a time rather a chemical shift spectrum obtained from the Fourier transformation of this time domain data. NMR relaxation occurs via various mechanisms, but is dominated by homonuclear dipolar coupling, which is modulated by molecular motion. Frequencies of motion in polymers can be readily probed using this technique, allowing a thorough investigation of structure and dynamics in a non-destructive manner. Frequencies of fast motions (e.g., hanging/end rotations of polymers) are in the order of megahertz (MHz) and slower motions (e.g., macromolecular chain rotations) in the order tens of kilohertz (kHz) [13]. Spin-lattice () relaxation probes fast molecular motion regimes, and spin-lattice relaxation in the rotating frame/relaxation under radiofrequency (RF) () probes molecular motion in the range of tens of kHz.

An underlying but key purpose of this work was to demonstrate that TD-NMR was a valid characterization technique for porous polymer materials by showing correlation to DMA data. Porous polymer structure is sensitive to structure and composition which made TD-NMR suitable in this case. In DMA, relaxation times () refer to the molecular chain relaxation in response to an applied stress (equation S.1). In NMR, relaxation times refer to the response of perturbed nuclear spins returning to an equilibrium state, which uses correlation time () to define molecular motion (equation 3.7). They both have frequency () dependency and similar form of expression (derived), which relates them;

(S.1)

(S.2)

An alternative method of relating DMA and TD-NMR can be described by the loss modulus as the energy loss in a material due to internal molecular motions8 and spin-lattice relaxation energy loss occurs by the spin flipping relaxation mechanism throughout the molecular structure (or lattice).12 More detailed information can be found elsewhere and describes the loss modulus, , and relaxation in far more detail than can be put here.9-12

The relaxation data was fitted to a single component using the following equation;

(S.3)

The relaxation data was fitted using equation 1.1 Single component fitted to the data due to spin diffusion being efficient on the timescale of . [14]

(S.4)

The NMR and DMA data was an average of 3 measurements, and the R2 value from fitting was >0.98, indicating that the single component fit was suitable at for the NMR data.

DMA (Youngs modulus) data

The Youngs modulus data is given in figures X-Z. In some cases it was likely that the presence of air bubbles or densification in one or more polyHIPEs despite the care, time and remade cylinders

Figure S1. S-co-DVB 70:30% DMA data.

Figure S2. S-co-DVB 30:70% DMA data.

Figure S3. DVB80 100% DMA data.

Figure S4. Para-DVB 100% DMA data. The standard deviation is heavily influenced by the presence of an abnormal cylinder. The data as a result appears less reliable but highlights the fact that the stability of para-DVB in HIPEs is very random using this emulsion formulation. The high modulus value could be due to polyHIPE densification

Figure S5. S-co-Para-DVB 70:30% DMA data. The unreliable emulsion stability of para-DVB is even apparent at much lower concentrations

1