The membrane thicknesses shown in Figure have a broad distribution for 50 and 75 mol% PBd22-PEO14 vesicles. When explored more closely, two groups of vesicles within these compositions begin to emerge: population 1 with a membrane thickness < 60 Å and population 2 with a membrane thickness > 70 Å, as shown in Figure . The presence of two populations within each sample is significant to within a 95% confidence using a Tukey and Bonferroni ANOVA analysis. When compared with the pure systems, population 1 in both 50 and 75 mol% PBd22-PEO14 compositions has similar membrane thicknesses as 0% PBd22-PEO14, suggesting a thinner lipid-bilayer-like membrane structure, while measurement of population 2 vesicles infer a thicker polymersome-like membrane.