Reversibly Switchable Surfactants and Methods of Use Thereof

Abstract

Reversible switchable surfactants are provided. A surfactant is the salt of an amidine or guanidine having at least one R group that is a hydrophobic moiety selected from the group consisting of higher aliphatic moiety, higher siloxyl moiety, higher aliphatic/siloxyl moiety, aliphatic/aryl moiety, siloxyl/aryl moiety, and aliphatic/siloxyl/aryl moiety. The other R groups are smaller moieties such as H, C 1 to C 4 aliphatic or the like. The surfactant is turned on by a gas that liberates hydrogen ions, such as, for example, carbon dioxide, which liberates hydrogen ions in the presence of water. The surfactant is turned off by exposure to a flushing gas and/or heating. When “on” the surfactants are useful to stabilize emulsions, and when “off” they are useful to separate immiscible liquids or a liquid and a solid. The surfactants find uses in polymerization and in the oil industry.

We claim: 
     
         1 .- 21 . (canceled) 
     
     
         22 . A composition comprising:
 (a) water or an aqueous solution;   (b) a switchable surfactant compound that comprises:
 a hydrophobic portion, and 
 a nitrogen-containing salt portion comprising a protonated amine moiety, wherein said nitrogen-containing salt portion reversibly converts to a non-salt form upon contact with a source of heat and/or a flushing gas, wherein said flushing gas contains substantially no gas that liberates hydrogen ions in the presence of water; 
   (c) a water immiscible liquid that is in a stable emulsion with said water or aqueous solution and forms an unstable emulsion or other two-phase mixture with said water or aqueous solution when the switchable surfactant compound is converted to the non-salt form, or
 a water insoluble solid that is in a stable suspension with said water or aqueous solution and forms an unstable suspension or other two-phase mixture with said water or aqueous solution when the switchable surfactant compound is converted to the non-salt form; and 
   (d) a dissolved gas that liberates hydrogen ions in the presence of water, wherein the gas does not include HCN or HCl.   
     
     
         23 . The composition of  claim 22 , wherein the protonated amine moiety is a protonated primary amine moiety. 
     
     
         24 . The composition of  claim 22 , wherein the protonated amine moiety is a protonated secondary amine moiety. 
     
     
         25 . The composition of  claim 22 , wherein the protonated amine moiety is a protonated tertiary amine moiety. 
     
     
         26 . The composition of  claim 22 , wherein the gas that liberates hydrogen ions in the presence of water is carbon dioxide. 
     
     
         27 . The composition of  claim 26 , wherein the switchable surfactant compound comprises the general formula (VI):
   R 1 —NHR 2 R 3+   (VI)
   wherein   at least one of R 1 , R 2 , and R 3  is selected from the group consisting of higher aliphatic moiety, higher siloxyl moiety, higher aliphatic/siloxyl moiety, aliphatic/aryl moiety, siloxyl/aryl moiety, and aliphatic/siloxyl/aryl moiety; and   the rest of R 1 , R 2 , and R 3  are selected from the group consisting of H, lower aliphatic, lower siloxyl, lower silyl, lower aliphatic/siloxyl, lower aliphatic/silyl, and aryl groups;   where the higher aliphatic and/or siloxyl moiety is a hydrocarbon and/or siloxyl moiety having a straight chain length of linked atoms equivalent to that of a C 5  to C 25  straight chain, which may be substituted or unsubstituted, and may optionally contain one or more SiO unit, an ether or ester linkage or both.   
     
     
         28 . The composition of  claim 27 , wherein the composition comprises a compound of formula (VIa):
   [R 1 —NH 2 R 2 ] + [R 1 R 2 NCO 2 ] −   (VIa)
   wherein   at least one of R 1  and R 2  is selected from the group consisting of higher aliphatic moiety, higher siloxyl moiety, higher aliphatic/siloxyl moiety, aliphatic/aryl moiety, siloxyl/aryl moiety, and aliphatic/siloxyl/aryl moiety; and   where only one of R 1  and R 2  is selected from the group consisting of higher aliphatic moiety, higher siloxyl moiety, higher aliphatic/siloxyl moiety, aliphatic/aryl moiety, siloxyl/aryl moiety, and aliphatic/siloxyl/aryl moiety, the other is selected from the group consisting of H, lower aliphatic, lower siloxyl, lower silyl, lower aliphatic/siloxyl, lower aliphatic/silyl, and aryl groups;   where the higher aliphatic and/or siloxyl moiety is as defined in  claim 27 .   
     
     
         29 . The composition of  claim 28 , wherein at least one of R 1  and R 2  is an aliphatic and/or siloxyl moiety having a straight chain length of linked atoms equivalent to that of a C 8  to C 25  straight chain, which aliphatic and/or siloxyl moiety may be substituted or unsubstituted, and may optionally contain one or more SiO unit, an ether or ester linkage or both. 
     
     
         30 . The composition of  claim 29 , wherein at least one of R 1  and R 2  is an aliphatic and/or siloxyl moiety having a straight chain length of linked atoms equivalent to that of a C 11  to C 25  straight chain, which aliphatic and/or siloxyl moiety may be substituted or unsubstituted, and may optionally contain one or more SiO unit, an ether or ester linkage or both. 
     
     
         31 . The composition of  claim 30 , wherein:
 one of R 1  and R 2  is selected from the group consisting of H, C 1 -C 4  alkyl, Si(CH 3 ) 3 , and phenyl.   
     
     
         32 . The composition of  claim 27 , wherein the composition comprises a compound of formula (VIb):
   [R 1 —NHR 2 R 3 ] + [O 2 COH] −   (VIb)
   wherein   at least one of R 1  and R 2  is selected from the group consisting of higher aliphatic moiety, higher siloxyl moiety, higher aliphatic/siloxyl moiety, aliphatic/aryl moiety, siloxyl/aryl moiety, and aliphatic/siloxyl/aryl moiety; and   where only one of R 1  and R 2  is selected from the group consisting of higher aliphatic moiety, higher siloxyl moiety, higher aliphatic/siloxyl moiety, aliphatic/aryl moiety, siloxyl/aryl moiety, and aliphatic/siloxyl/aryl moiety, the other is selected from the group consisting of lower aliphatic, lower siloxyl, lower silyl, lower aliphatic/siloxyl, lower aliphatic/silyl, and aryl groups;   where the higher aliphatic and/or siloxyl moiety is as defined in  claim 27 .   
     
     
         33 . The composition of  claim 32 , wherein the composition is maintained under an atmosphere of CO 2  at a pressure of greater than 1 atm. 
     
     
         34 . The composition of  claim 33 , wherein the switchable surfactant compound reversibly converts to its non-salt form upon exposure to a pressure of carbon dioxide of 1 atm or less. 
     
     
         35 . The composition of  claim 32 , wherein at least one of R 1  and R 2  is an aliphatic and/or siloxyl moiety having a straight chain length of linked atoms equivalent to that of a C 8  to C 25  straight chain, which aliphatic and/or siloxyl moiety may be substituted or unsubstituted, and may optionally contain one or more SiO unit, an ether or ester linkage or both. 
     
     
         36 . The composition of  claim 35 , wherein at least one of R 1  and R 2  is an aliphatic and/or siloxyl moiety having a straight chain length of linked atoms equivalent to that of a C 11  to C 25  straight chain, which aliphatic and/or siloxyl moiety may be substituted or unsubstituted, and may optionally contain one or more SiO unit, an ether or ester linkage or both. 
     
     
         37 . The composition of  claim 36 , wherein:
 one of R 1  and R 2  is selected from the group consisting of C 1 -C 4  alkyl, Si(CH 3 ) 3 , and phenyl.   
     
     
         38 . The composition of  claim 27 , wherein the flushing gas is nitrogen, argon, or air that has insufficient carbon dioxide to maintain said switchable surfactant compound in its salt form. 
     
     
         39 . The composition of  claim 27 , wherein the composition is maintained under an atmosphere of CO 2  at a pressure of 1 atm or less. 
     
     
         40 . The composition of  claim 27 , wherein the composition is maintained under an atmosphere of CO 2  at a pressure of greater than 1 atm.