In the presence of HEA, the Pn3m-type cubic phase is formed at higher water content, 45 and 55wt% (lattice constant of 9.9 nm and 11.3 nm), further supporting the smaller effective headgroup areas at the interface in the presence of HEA. Similar effects have been described with glycosides, used for the in-meso protein crystallization, where the Ia3d and lamellar structures were formed at 40 wt% of water content due to the additive molecule partitioning at the interface of the cubic structure. To conduct a more in-depth analysis of this effect, the temperature dependence of the structures was examined. The temperature-dependent phase behavior of the bulk samples is summarized in Figure . With temperature increase from 25 to 40 °C, the lattice parameter of the Ia3d structure decreases from 15.8 to 14.5 nm, respectively. A transition from Ia3d to Pn3m structure with a lattice constant of 8.4 nm occurs when the sample is heated to 50 °C. An intriguing effect of HEA on the bulk phase is the expansion of the temperature range of the Pn3m structure up to 80°C, whereas the GMO/water bulk phase transitioned to the H2 at ~ 70 °C. No H2 phase was observed in the HEA-containing samples. The 2D images in Figure demonstrate that the HEA integration likely leads to microcrystalline domains and grain boundaries in the bulk phase. This is indicated in the SAXS curves by the spot-like patterns instead of rings with relatively homogeneous radial intensities from randomly oriented structures. This effect became more pronounced upon increasing temperature. At 95°C, the Pn3m-cubic phase transitioned to the inverse micellar phase (L2 phase), which shows a broad peak around q ~ 1.5 nm -1 in SAXS. 3.2. Polymerization of HEA in the Inverse Bicontinuous Cubic Bulk Phase. Free radical polymerization of HEA was attempted within the GMO60HEA5 cubic phase using LAP as a photoinitiator at a weight ratio of HEA/LAP = 5/1 and UV irradiation of the sample. The transparent-to-turbid transition observed upon polymerization at 25 °C may result from the formation of micron-sized domains with multiple light scattering from the grain boundaries. Such domain formation was previously discussed as the result of demixing, where the phase rich in surfactant separates from the polymer-rich domain during polymerization. 39,40 1 H NMR of HEA within the inverse bicontinuous cubic phase was obtained before and after polymerization with HEA/LAP to gain insights into the polymerization reaction inside the nanochannels (see Figure in SI). Owing to the high viscosity of the LLC structure and limited mobility of the molecules, peak broadening is observed for HEA inside the structure, as compared to HEA in isotropic (bulk) D2O (see Figure and S3 in SI). A previous NMR study of additive molecules in the bicontinuous cubic phase shed light on the interactions between incorporated molecules and the lipidic bilayer, giving rise to changes in chemical shifts. Here, the difference in HEA chemical shifts in D2O and the cubic phase (see Table in SI) cannot distinguish whether HEA is mainly segregated in the aqueous channels or interacting with GMO headgroups at the lipid-water interface, which was further studied with SAXS. However, the decrease in the signal of the vinylic protons at 6.49, 6.25, and 5.95 ppm after polymerization confirms the HEA double-bond conversion through the reaction. HEA was also polymerized as a control in isotropic D2O solution at 10/1 and 5/1 HEA/LAP weight ratios. The presence of unreacted monomer after polymerization was detected with GPC (see Figure and Table in SI). The number averaged molar mass (Mn) obtained by GPC indicates larger HEA polymer chains formed within the aqueous channels of the GMO-based bicontinuous cubic phase (GPCDMF: Mn = 35000 Da, Ð = 3.1) compared to the polymerization in water (GPCDMF: Mn = 28000 Da, Ð = 5.4) at 5/1 HEA/LAP. A similar trend for polymerization in the cubic phase and water at 10/1 HEA/LAP weight ratio is observed with a somewhat higher molecular weight (GPCDMF: Mn = 44000 Da, Ð = 3.8, see Table ). The higher molecular weight of the polymer and its lower dispersity in the nanoconfined environment indicate a decrease in the termination reaction rate in diffusion-controlled free radical polymerization. This is also in line with the higher molecular weight at the lower initiator concentration, which directly impacts the chain propagation and termination rate during the reaction. Kinetic studies comparing polymerization in liquid crystalline phases to isotropic solution revealed that the confinement increased the polymerization rate, while the propagating chains diffusional limitation decreased the termination reaction rate. In addition, radical polymerization of methyl acrylate monomers among different mesophases increased the polymerization rate and produced polymers with higher molecular weight. The structural effect of HEA integration and polymerization on the Ia3d type cubic structure was investigated with SAXS at different HEA/LAP ratios: 200/1, 10/1, and 5/1, allowing a relative comparison of the effect of monomer conversion on the structure (see scattering curve in Figure and Figure in SI). Upon HEA polymerization at HEA/LAP of 200/1 and 10/1, the Ia3d cubic phase is transformed into coexisting Pn3m/Im3m-type cubic structures (see Figure in SI). The Im3m cubic phase was only observed after polymerization. In contrast, the formation of the Pn3m structure is due to the increased water content in the system with the addition of the LAP to > 40 wt% (see phase diagram in Figure ). The cubic Im3m/Pn3m lattice parameters at HEA/LAP of 200/1 and 10/1 were 12.6 nm / 9.8 nm and 13.1 nm /10.3 nm at 25°C, respectively. The lattice parameter ratio between the Im3m/Pn3m structures, the so-called Bonnet ratio, is in the range of the theoretical value of 1.279, supporting the coexistence of the structures within the polymerized bulk phases. A Bonnet transformation between the cubic phase during the reaction implies that the cubic structures are energetically degenerate and, therefore, can continuously deform to interconvert each other. Alternatively, the interconversion between Pn3m and Im3m cubic phases may be interpreted as forming new water channels created by splitting the water junction in the cubic phases. Further increase of LAP content relative to HEA with HEA/LAP = 5/1 led to a complete transition into an Im3m cubic structure (see Figure ). The lattice parameter of the Im3m cubic phase is 14.6 nm at 25°C, which is higher than the previously discussed Im3m /Pn3m coexisting cubic phases formed at lower LAP concentrations. The complete Pn3m-to-Im3m phase transition at a higher initiator concentration could be linked to higher HEA conversion in the system.