Novel Surfactant Gels
Opportunities for Templated Synthesis of Nanostructured Materials
 :: Background

In recent years, there has been a recognition that self-assembled molecular systems can serve as templates in the synthesis of nanostructured materials. Nature is full of examples (skin, bone, shell, wood, etc.) where such "synthesis with construction" concepts lead to materials with unique functional properties. Our research objective is to understand the self-assembly involved in the transformation of a surfactant-containing inverse micellar solution to a series of organogels and organohydrogels. The rigidity of these gel structures allows us to use them as templates in the synthesis of extended nanostructures of polymers, ceramics, polymer-ceramic composites. We also seek to use these self-assembled rigid structures in the synthesis of functionally gradient materials.



 :: Selected Accomplishments

We have developed two new classes of surfactant containing gel systems.

In the first class of gels (slide 1), we are able to adjust the curvature of inverse micellar AOT systems by the addition of lecithin (phosphatidylcholine) which tends to form flatter bilayer structures. As a consequence, the liquid solution transforms into "organohydrogels", i.e. gels containing a structured aqueous phase and a structured organic phase. Over the past year we have had two significant accomplishments:


  • We had remarkable success in using small angle neutron scattering (SANS) to understand the microstructure of the gel. SANS revealed transitions from hexagonal to lamellar microstructures upon addition of water or by increasing the temperature. SANS was also able to capture the transitions between these microstructures.

  • We have started making materials in these systems and we see clear evidence of templating. For example, we have synthesized silica in these systems (slide 1). We see a macroporous structure to the silica. But when we do cut-section transmission electron microscopy, we find that the walls of these macroporous silica structures are themselves nanostructured with pores of the order of 10-20 nm. And the nanostructure shows evidence of hexagonal symmetry.

Thus, these materials have a dual porosity and have long-range structure. They may have significant uses as catalysts where large molecules can enter the macropores but only the smaller species can enter the nanoporous structures. Or they could be used in making structural materials where the macropores are filled in by polymers. Our continuing work seeks to exploit the properties of these gels through the synthesis of polymer-polymer and polymer-ceramic nanocomposites.

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The second class of gels is a pure organogel, where AOT reverse micelles have been transformed into long entangled chain structures by the addition of phenolic dopants that hydrogen bond to the surfactant (slide 2). Selected accomplishments are the following:


  • We have been able to obtain a full understanding of the formation of these gels using a combination of spectroscopic, scattering and microscopy tools. From a fundamental perspective this effort has been very rewarding. The small angle x-ray scattering shows assembly of strands to fibers and the atomic force microscopy reveals further assembly to fiber bundles.

  • We have been able to incorporate ferrite nanoparticles into these gel strands to make magnetically responsive gels.

  • In continuing work, we will attempt to develop luminescent and magnetically responsive gels by doping these organogels with semiconductor quantum dots and magnetic nanoparticles. We will also use these gels as templates to synthesize structured polymers and polymer-ceramic nanocomposites.





 ::Scientific Uniqueness

A new class of surfactant gels have been realized. The fact that small molecules in relatively low concentrations can mimic long entangled polymer chains is a remarkable aspect of molecular self-assembly. This is especially true when it occurs in nonpolar environments where hydrogen bonding and dispersion forces are the prevalent modes of molecular interaction. Additionally, the aspects of adjusting interfacial curvature to build rigid gel structures by mixing surfactants with varying size and charge parameters may lead to new concepts in surfactant self assembly. The rational design of surfactant gel systems would indicate routes to the rational design of templated nanocomposites. This is really our objective:

to correlate materials morphology and nanostructure evolution with the self-assembly of surfactant systems, and to bring rational design into materials synthesis in such systems.




 :: Impact

Some potential applications of these gel systems and of materials synthesized these systems are enumerated.


  1. Field responsive organogels with very sharp phase transitions may be used in sensor development. For example, if magnetic particles and luminescent particles are incorporated into the chain strands, contraction of the gel upon application of a magnetic field could be translated into a photoluminescent signal. Similarly, temperature induced luminescent signals is another possibility.

  2. The organohydrogel systems have significant applications as hosts for biomolecules, in drug delivery for sustained release of hydrophobic drug molecules, etc.

  3. Most important are materials synthesis aspects in the organohydrogels. If synthesis is done in either the organic or the aqueous microphase, the other phase translates into well-defined pore structures. Or, if synthesis is carried out in both the microphases, we can obtained structured composites (eg. nanostructured polymer-ceramic composites, or composites of hydrophobic and hydrophilic polymers). These materials have significant applications in membrane and seprations technology, in high strength polymer films, in ballistic protection technologies, in microencapsulation technologies, in the fabrication of electrooptical devices, and the fabrication of functionally gradient systems.

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