Process for forming organic films on electrically conductive or semi-conductive surfaces using aqueous solutions
The present invention concerns the area of surface coatings in the form of organic films, the coatings being in the form of organic films. It most especially relates to a method for forming copolymer organic films by electrochemical grafting on electrically conductive or semi-conductive surfaces using electrolytic aqueous solutions containing at least one protic solvent, at least one radically polymerizable monomer and at least one surfactant. The invention also concerns surfaces obtained with the use of this method, their applications especially for preparation of microelectronic components, biomedical devices or screening kits, as well as the electrolyte solution used in the course of the method.
1. Method for forming a copolymer organic film on an electrically conductive or semi-conductive surface by electrolysis of an electrolyte solution until the said copolymer organic film is grafted on the said surface, the said method being characterized in that:
a) the electrolyte solution contains:
i) at least one protic solvent,
ii) at least one aryl diazonium salt as primer for radical polymerization, the said aryl diazonium salt being soluble in the said protic solvent,
iii) at least one radically polymerizable monomer having a solubility in the protic solvent lower than 0.1 M, and
iv) at least one non-ionic surfactant selected from the group consisting of polyethoxylated surfactants and polyols,
b) the electrolysis of the electrolyte solution is carried out with a reducing potential at least equal to the reducing potential of the said primer, and the working potential being at maximum greater than 5% of the potential value of reduction of the primer and no more cathodic than −0.8 V.
2. Method according to claim 1 , characterized in that the electrically conductive or semi-conductive surface is selected from the group consisting of stainless steel, steel, iron, copper, nickel, cobalt, niobium, aluminum, silver, titanium, silicon with or without its oxide, titanium nitride, tungsten, tungsten nitride, tantalum, tantalum nitride and noble metal surfaces made up of at least one metal selected from the group consisting of gold, platinum, iridium and irradiated platinum.
3. Method according to claim 1 or 2 , characterized in that the protic solvent is selected from the group consisting of water, acetic acid, hydroxylated solvents, liquid glycols with low molecular weight and mixtures thereof.
4. Method according to claim 1 , characterized in that the protic solvent is used in mixture with an aprotic solvent, the resulting mixture being a protic solvent.
5. Method according to claim 1 , characterized in that the protic solvent is distilled or deionized water.
6. Method according to claim 1 , characterized in that the at least one aryl diazonium salt correspond to the following formula (I):
R—N 2 + , A − (I)
in which:
A represents a monovalent anion and
R represents an aryl group.
7. Method according to claim 6 , characterized in that R is a nitrophenyl radical.
8. Method according to claim 1 , characterized in that the radical polymerization primer is selected from the group consisting of phenyl diazonium tetrafluoroborate, 4- nitrophenyl diazonium tetrafluoroborate, 4- bromophenyl diazonium tetrafluoroborate, 2- methyl-4-chlorophenyl diazonium chlorate, 4-benzoylbenzene diazonium tetrafluoroborate, 4-cyanophenyl diazonium tetrafluoroborate, 4-carboxyphenyl diazonium tetrafluoroborate, 4-acetamidophenyl diazonium tetrafluoroborate, 4-phenylacetic acid diazonium tetrafluoroborate, 2-methyl-4-[(2-methylphenyl)diazenyl]benzene diazonium sulfate, 9,10-dioxo-9,10-dihydro-1-anthracene diazonium chloride, 4-nitronaphthalene diazonium tetrafluoroborate and naphthalene diazonium tetrafluoroborate.
9. Method according to claim 1 , characterized in that the concentration of the primer within the electrolyte solution is between 10 −4 and 0.5 M.
10. Method according to claim 1 , characterized in that the radically polymerizable monomers have a solubility in the said protic solvent which is finite.
11. Method according to claim 1 , characterized in that the radically polymerizable monomers are vinyl monomers.
12. Method according to claim 11 , characterized in that the vinyl monomers correspond to the following formula (II):
in which the groups R 1 to R 4 , identical or different, represent a non-metallic monovalent atom selected from the group consisting of an atom of halogen, an atom of hydrogen, a saturated chemical group, and an unsaturated chemical group, said saturated and unsaturated chemical group being selected from an alkyl group, an aryl group, and a —COOR 5 group in which R 5 represents a hydrogen atom or an alkyl group in C 1 —C 6 , nitrile, carbonyl, amine or amide.
13. Method according to claim 12 , characterized in that the monomers of formula (II) are selected from the group consisting of acrylonitrile, methacrylonitrile, methyl methacrylate, ethyl methacrylate, butyl methacrylate, propyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, glycidyl methacrylate;
crotononitrile, pentene nitrile, ethyl crotonate and their derivatives; acrylamides selected from the group consisting of aminoethyl, propyl, butyl, pentyl and hexyl methacrylamides;
cyanoacrylates, di-acrylates and di-methacrylates, tri-acrylates and tri-methacrylates, tetra-acrylates and tetra-methacrylates, styrene and its derivatives, parachioro-styrene, pentafluoro-styrene, N-vinyl pyrrolidone, 4-vinyl pyridine, 2-vinyl pyridine, vinyl, acryloyl and methacryloyl halides, and divinylbenzene (DVB).
14. Method according to claim 1 , characterized in that the quantity of polymerizable monomer present in the electrolyte solution represents 18 to 40 times the solubility of the said monomer in the protic solvent at a given temperature.
15. Method according to claim 1 , characterized in that the quantity of radically polymerizable monomer is between 0.1 M and 5 M.
16. Method according to claim 1 , characterized in that the concentration of the surfactant within the electrolyte solution is between 0.5 mM and 5 M.
17. Method according to claim 1 , characterized in that the pH of the electrolyte solution is between 1.6 and 2.2.