The effect of n-, s- and t-butanol on the micellization and gelation of Pluronic P123 in aqueous solution

In dilute aqueous solution unimers of copolymer P123 (E21P67E21) associate to form micelles, and in more concentrated solution micelles pack to form high-modulus gels. We are interested in the use of the system as a templating agent in the synthesis of mesoporous materials, and the possibility of determining gel structure, hence mesoporosity, by use of n-, s- or t-butanol. Dynamic light scattering from clear dilute solutions has been used to confirm micellization, visual observation of mobility (tube inversion) to detect gel formation in concentrated solutions, oscillatory rheometry to confirm gel formation and provide values of elastic moduli over a wide temperature range, and small-angle X-ray scattering to determine gel structure. As expected, clear cubic gels (fcc) formed at moderate concentrations and temperatures, e.g. 30 wt.% P123, 20 °C, and clear hexagonal gels at higher concentrations and temperatures. The transition on heating from cubic to hexagonal gel involved an intermediate turbid phase in which cubic and hex structures coexisted. Considering cubic gels of 35 wt.% P123 in 5 wt.% butanol/water, those in n-butanol/water had the lowest critical temperatures for gel formation and the highest maximum values for the dynamic elastic modulus (G′) of the gels, a result consistent with n-butanol/water being the poorest solvent for P123.

The maximum storage modulus measured for the gel of 35 wt.% P123 in 5 wt.% n-butanol/water has a high value compared to the values obtained for corresponding gels in 5 wt.% s- and t-butanol/water. This higher value can be related to the smaller hard-sphere micelle radius in the n-butanol/water gel, as measured using SAXS.Figure optionsDownload high-quality image (89 K)Download as PowerPoint slideResearch highlights
► P123/butanol/water as a structure directing agent for mesoporous materials.
► Cubic gels of 35% P123 in 5% BuOH, cgc is in order n < s < t.
► Maximum values of G′ are in order n > s > t.
► Values of hard sphere micelle radii for the gels are in order n < s < t.