Functional Nanocomposites Prepared by Self-Assembly and Polymerization of Diacetylene Surfactants and Silicic Acid

Conjugated polymer/silica nanocomposites with hexagonal, cubic, or lamellar mesoscopic order
were synthesized by self-assembly using polymerizable amphiphilic diacetylene molecules as both structure-directing agents and monomers. The self-assembly procedure is rapid and incorporates the organic
monomers uniformly within a highly ordered, inorganic environment. By tailoring the size of the oligo(ethylene glycol) headgroup of the diacetylene-containing surfactant, we varied the resulting self-assembled
mesophases of the composite material. The nanostructured inorganic host altered the diacetylene
polymerization behavior, and the resulting nanocomposites show unique thermo-, mechano-, and solvatochromic properties. Polymerization of the incorporated surfactants resulted in polydiacetylene (PDA)/silica
nanocomposites that were optically transparent and mechanically robust. Molecular modeling and quantum
calculations and 13C spin−lattice relaxation times (T1) of the PDA/silica nanocomposites indicated that the
surfactant monomers can be uniformly organized into precise spatial arrangements prior to polymerization.
Nanoindentation and gas transport experiments showed that these nanocomposite films have increased
hardness and reduced permeability as compared to pure PDA. Our work demonstrates polymerizable
surfactant/silica self-assembly to be an efficient, general approach to the formation of nanostructured
conjugated polymers. The nanostructured inorganic framework serves to protect, stabilize, and orient the
polymer, mediate its performance, and provide sufficient mechanical and chemical stability to enable
integration of conjugated polymers into devices and microsystems.