Myelin Figures: Non-equilibrium organization of amphiphiles induced by hydration

Non-Technical Abstract:

Oil and water do not mix. But many ordinary soaps and detergent negate this proverbial expression by allowing the two substances to mix. Called surfactants, these soft and fragile materials interact with water (or oil) in complex, subtle, and nuanced manners.

Their dissolution in water is often accompanied by the formation of unusual structures that extend far beyond the sizes of molecules producing a dynamic mosaic that characterize the surfactant-laden aqueous phase. One such example is the formation of a class of finger-like cylindrical protrusions called myelin figures, tens of micrometers in diameters and hundreds of micrometers in length, which appear when a dry mass of surfactant meets water.

This project involves controlled laboratory experiments to study their formation, direct their growth, and exploit their morphologies to produce novel nanomaterials. The findings of the project should benefit many areas of applications, including food, cosmetics, soap, and dispersion technologies. The project includes the training and participation of a graduate student and a post-doc in the scientific process.

It also engages undergraduate students and underrepresented groups in STEM through the Vertically-Integrated Program, which offers Science & Society credits and opportunities for laboratory research over multiple years on a single, consolidated project. Technical Abstract:

The equilibration of complex fluids is often accompanied by unusual instabilities as they progress toward equilibrium. This is perhaps best exemplified by myelinic instabilities, which emerge when an insoluble surfactant meets water. The individual myelins ¬– cylindrical smectic liquid crystals tens of micrometers in diameter and hundreds of micrometers in length – grow sinuously, by a two-dimensional reptation-like motion, which tightly juxtapose with their neighbors; elongate, cooperatively; and, often fold morphologically, into symmetry-breaking helical shapes.

This project seeks to understand their formation mechanisms, control their spatial organization, investigate their responsiveness to environmental perturbations, and exploit their nanometer scale confinements to template synthesis of nanostructures. It experimentally tests the hypothesis that the intrinsically non-equilibrium process of amphiphilic hydration can be controllably tuned to lift equilibrium constraints, dial-in structural instabilities, and kinetically trap long-lived metastable states within the free energy landscape that characterizes the hydration process.

It also seeks to exploit myelin figures as self-organizing dynamic templates to synthesize nanoscale materials into hierarchical, extended, and complex superlattices. Using a combination of microscopy based quantitative measurements, the planned research activities include(1) develop methods to control the spatial organization of myelin figures (taming the chaos); (2) characterizing phase-separating mixtures of amphiphiles within myelin morphologies (introducing chemical diversity); (3) accessing higher-order, symmetric breaking organization of myelin figures by coupling physical-chemical stress from their local microenvironment (shape-shifting myelins); and (4) templating synthesis of nanomaterials by exploiting myelinic confinement (templated nanosynthesis).

The effort should yield new insights into non-equilibrium routes for controlling supramolecular organization and novel approaches for synthesis-with-design.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.