Fabrication of polyaniline nanofiber dispersions and films

Abstract

A new method for forming stable polyaniline nanofiber colloids uses electrostatic repulsion to maintain dispersion of the nanofibers and prevent aggregation during synthesis of the nanofibers. The colloidal suspensions are formed directly from the reactants in solution maintained at a pH of about 1.0 to about 4.0 and a temperature of about 10° C. to about 100° C. with minimal or no stirring. Also set forth are new methods for forming ultrathin films of polyaniline nanofibers via self-assembly.

1 . An improved method of forming stable colloids of nanofiber polyaniline comprising: 
 mixing the reactants with any mixing or stirring terminated prior to initiation of polymerization while maintaining the pH of the polymerization composition at greater than about 1.5 but less than about 4.0 and the temperature greater than about 25° C. but less than about 60° C. to form a colloidal suspension of nanofibers.    
   
   
       2 . The improved method of  claim 1  wherein the colloidal suspension is purified by washing and centrifugation to remove excess acid and byproducts.  
   
   
       3 . The improved method of  claim 1  wherein the pH of the polymerization composition is maintained at between about 2.3 and about 3.5.  
   
   
       4 . The improved method of  claim 1  wherein the pH of the polymerization composition is maintained at about 2.6.  
   
   
       5 . The improved method of  claim 1  wherein the temperature of the reactants is maintained from about 10 to about 100° C.  
   
   
       6 . The improved method of  claim 1  wherein the temperature of the reactants is maintained at 60° C.±10° C.  
   
   
       7 . A method of preventing or retarding aggregation of polyaniline nanofiber during formation thereof comprising maintaining mechanical stirring to less then about 325 RPM.  
   
   
       8 . The method of  claim 7  comprising conducting polymerization thereof without stirring.  
   
   
       9 . A method of forming a monolayer of polyaniline nanofibers on a negatively charged substrate comprising forming a stable aqueous colloidal suspension of the nanofibers, maintaining the stable colloidal at a pH of 2.6±0.5 and immersing the substrate in the colloidal suspension.  
   
   
       10 . The method of  claim 9  wherein the substrate is a silica wafer or a silica glass substrate and the colloidal suspension is maintained at a temperature of from about 25° C. to about 60° C.  
   
   
       11 . A method of forming a coating of two or more monolayers of polyaniline nanofibers on a substrate comprising forming a stable aqueous colloidal suspension of the nanofibers, maintaining the stable colloidal at a pH of 2.6±0.5 and 
 immersing a negatively charged substrate into the colloidal suspension to form a monolayer of the nanofibers on the substrate, washing the substrate with monolayer of the nanofibers using a polystyrenesulfonic acid solution and immersing the washed substrate with monolayer of the nanofibers in the colloidal solution, subsequent layers being formed by repeating the washing and immersion procedure.    
   
   
       12 . A method of forming an image on a substrate comprising forming a stable aqueous colloidal suspension of the nanofibers, said stable suspension substantially free of stabilizer, maintaining the stable colloidal at a pH of 2.6±0.5 and applying the stable aqueous colloidal suspension of the nanofibers to the surface using standard printing techniques.  
   
   
       13 . The method of  claim 12  wherein the standard printing technique comprises using an ink jet printer.  
   
   
       14 . A stable aqueous colloidal suspension of nanofiber polyaniline comprising: 
 in situ formed polyaniline in an aqueous carrier, the aqueous suspension having a pH from about 1.5 to about 4.0 and being substantially free of stabilizer.    
   
   
       15 . The stable aqueous colloidal suspension of nanofiber polyaniline of  claim 14  wherein said colloidal suspension is stable for at least about one week.  
   
   
       16 . The stable aqueous colloidal suspension of nanofiber polyaniline of  claim 14  wherein said colloidal suspension has a pH of 2.6±0.5 and is stable for at least about two months.  
   
   
       17 . The method of  claim 1  for forming a stable colloid of nanofiber polyaniline further comprising the step of adjusting the pH of the stable colloid to form about 4.0 to about 10.0 to form a stable colloid of dedoped polyaniline nanofibers.  
   
   
       18 . The method of  claim 17  wherein the pH of the colloid is adjusted to about 7.0.  
   
   
       19 . A stable aqueous colloid of dedoped polyaniline nanofibers comprising; 
 in situ formed polyaniline in an aqueous carrier, the aqueous suspension having a pH of from about 4.0 to about 10.0 and being substantially free of stabilizer.    
   
   
       20 . The stable aqueous colloid of dedoped polyaniline nanofibers of  claim 19  having a pH of about 7.0.