## 2 Results and Discussion  
### Material Characterisation  
PS-_co_-DVB polyHIPE materials were fabricated in situ within fused silica capillary housings. Scanning electron microscopy (SEM) imaging confirmed attachment of the polyHIPE to the capillary wall, as shown in Figure S1. No contraction or detachment from the capillary wall was observed after flow-through. Figure 1a shows the PS-_co_-DVB polyHIPE within fused silica capillary where no GONPs have been incorporated. However, Figure 1b shows the effect of the 250-nm GONPs on the polyHIPE structure. The GONP-modified polyHIPE appears to have a greater surface roughness compared to the unmodified material. It was expected that the GONP-modified material, upon application of Brauner-Emmet-Teller (BET) theory, would show an increase in surface area. However, the resulting information obtained through nitrogen adsorption/desorption showed that the surface area of the unmodified material was 25 m\({}^{2}\cdot\)g\({}^{-1}\) while the GONP-modified material was found to be only 16 m\({}^{2}\cdot\)g\({}^{-1}\). Upon fabrication of an additional GONP batch, in the repeat BET analysis the resulting surface area was found to be lower at 12 m\({}^{2}\cdot\)g\({}^{-1}\). The Barret-Joyner-Halenda (BJH) method was applied for investigation of pore size distributions, and revealed there was a reduction in mesopore size and volume with the addition of GONP to the material. The average mesopore width was calculated to be \(\sim\)20 nm in PS-_co_-DVB polyHIPEs compared to \(\sim\)16 nm in graphene oxide nanoparticle-modified polystyrene-divinylbenzene polymeric high internal phase emulsion (GONP PS-_co_-DVB polyHIPEs). Pore size distribution curves obtained from the absorption branch of the isotherm are included, with Figure S2 showing the BJH pore size distribution curve for the PS-_co_-DVB polyHIPE, and Figure S3 showing the same for the GONP PS-_co_-DVB polyHIPE. As evident from Figures S2 and S3, there was a broader width distribution in the material prior to addition of GONP. Following addition of GONP there was also a reduction in pore volume from 0.098 cm\({}^{3}\cdot\)g\({}^{-1}\) to 0.035 cm\({}^{3}\cdot\)g\({}^{-1}\). This shows a definite reduction in surface area and pore width and volume with the addition of GONPs, however it is argued that nitrogen adsorption on hydrophobic surfaces is less localised due to weaker adsorbate-surface interactions where there is more freedom for lateral movement. This can result in nitrogen molecules occupying a larger area and thus leads to an underestimation of the surface area of the hydrophobic surface since there are less nitrogen molecules in the adsorbed monolayer [41]. Therefore, the application of these polyHIPE materials in liquid chromatography was explored as a means to further understand their properties through the reversed phase separation of a series of hydrophobic alkylbenzenes. The addition of NPs to polymer monoliths has been shown to negatively impact upon surface area [18; 19; 42], where the decrease is generally attributed to NPs blocking the pores of the monolithic materials. However, in the case of polyHIPEs which possess large macropores, this is an unlikely source of the reduction in surface area. The pore morphology was affected by addition of 250-nm GONPs to the emulsion, as observed by SEM imaging, where a reduction in both void and window size was noted, as shown in Table 1. This change in morphology was expected to impact upon the properties of the polyHIPE when applied as an adsorbent. Figure 2 shows the Fourier transform infrared (FTIR) absorption spectrum of an unmodified polyHIPE. FTIR analysis demonstrated that on an unmodified polyHIPE no OH stretches present in the expected region of 3200-3600 cm\({}^{-1}\) were observed. \begin{table}
\begin{tabular}{l c c} \hline \hline
**PolyHIPE** & **Void Size (\(\upmu\)m)** & **Window Size (\(\upmu\)m)** \\ \hline Unmodified & 15.59 \(\pm\) 13.62 & 4.29 \(\pm\) 1.73 \\ Modified & 10.92 \(\pm\) 5.81 & 2.48 \(\pm\) 0.75 \\ \hline \hline \end{tabular}
\end{table}