WO2007008249A2

WO2007008249A2 - Method for making metallic nanostructures

Info

Publication number: WO2007008249A2
Application number: PCT/US2005/042447
Authority: WO
Inventors: Hassan Sahouani
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2004-11-24
Filing date: 2005-11-22
Publication date: 2007-01-18
Anticipated expiration: 2007-05-24
Also published as: JP2008522032A; US7582330B2; US20060110528A1; WO2007008249A3; CN101076417B; EP1819468A2; CN101076417A

Abstract

A method of making metallic nanostructures by mixing (a) an aqueous composition comprising a chromonic material with (b) a metal salt in solution or a suspension of metal particles.

Description

METHOD FOR MAKING METALLIC UANOSTRUCTURES

FIELD

This invention relates to methods for making metaLlic narαo structures using chromonic materd_als and, in another aspect, to articles comprising a chromonic matrix and metal nanostructures .

BACKGROUND

In recent years, there has been increasing research ef fort to develop metal structures in the nanoscale range (ttαat is, in the 0.1 to 100 nm range) for a variety of technological applications such as, ffor example, electronic and optical devices, labeling of biol-ogical material, magnetic recording media, and quantum computing.

Numerous approaches have been developed for synthesizing/fabricating metal nanostructures such as, for example , metal nanowires, nanorods, rαanotubes, and nanoribbons . Current approaches incILude, for example, fabricating metal nanowires by the eILectroless depositLon of metal into the pores of nanoporous membranes by a metaL aπvplif ication process (see, for example, Barbie et al . , J. Appl. Phys., ,91, 9341 (2002)) and fabricating metal nanowires/nanotubes by a vapor- liquid- solid (VLS) process in wh±ch involves the dissolution of gaseous reactants in nanosized liquid droplets of the metal solvent, followed by nucleation and growth of single crystalline wires (see, for example, Ding et al - , J. Phys. Chem. B 108, 12280 (2004 ) ) . A challenge that remains, however, is controlling the size and shape of metallic nanostructures, as well as their or±entation and distribution, particularly on a large scale. SUMMARY

In vd_ew of the foregoing, it has been recognized thsit there is a. need for a method for making nanostructures thiat provides control over the size and shape of metallic nanostructures, as well as their orienta_tion and distribut_Lon, over a relatively large airea.

Briefly, in one aspect, the present invention provic3.es a method of making metallic nanostructures . The method comprises mixing (a) an aqueous composition comprising a chromonic material with (b) a metal salt in solution or ≡L suspension. of metal particles.

As used herein, "chromonic materiaLs" (or "chromonic compounds" ) refers to large, multi-ring molecules typically characteri.zed by the presence of a hydrophobic core surrounded by various hydrophilic groups (see, for example, Attwood, T^*. K., and Lydon, J. E., Molec . Crystals Liq. Crystals, 108, 349 (1984)). The hydrophobic core can contain airomatic and/or non-aromatic rings. When in solution, these chromonic materials tend to aggregate into a nematic or-dering characterized by a long--range order.

The present invention also provides a method of making metallic nanostructures comprising (a) applying an aqueoiαs composition comprising a chromonic mater~ial to the surface of a substrate; and (b) placing the coated surface in contact wiLth a solution comprising a metal salt.

The tnethods of the invention enable the fabrication of metallic rαanostructures with relatively uniform size and shape. Tine methods further enable relatively uniform distribut-Lon and long-range orientation or order of metallic nanostructures over a relatively large a_rea.

Thus, the methods of the invention meet the need in the art for an. improved method for making metallic nanostructures . In another aspect, the present invention provides articles comprising a chiromonic matrix ancfi metal nanostructures. As used herein, "chromon±c matrix" refenrs to chromonic materials trxat are aggregated! into a nematic ordering .

DESCRIPTION OF DRAWINGS

Figuire 1 is a transmission electron micrograph showzLng a top viβΛΛ? of a coating comprising silver nanowires .

Figuitre 2 is a transmission electron micrograph showzLng an edge view of a coating" comprising silver nanowires.

Figuare 3 is a transmission electron micrograph showing gold nanoparticles .

Figuire 4 is an optical micrograph showing silver nanowires .

DETAILED DESCRIPTION

Any chromonic mater±al can be useful in the methods of the invention. Compounds that form chromonic phases are known in the art, and include, for example, xanthoses (for example, azo dyes and cyanine dyes) and perylenes (see, for example, Kawasaki et al . , Langmuir 16, 54O9 (2000) , or Lydon, J. , Colloid and Interface Science, 8_, 480 (2004) ) . Representative examples of useful chromond-C materials include cl±- and mono-palladium organyls, sulfamoyl- substituted copper phthalocyanines, and hexaarylt iryphenylene .

Preferred chromonic materials include those represented by one of the following general structures :

wherein each R² is independently selected from the group consisting of electron donating groups, electron withdrawing groups, and electron neutral groups, and

R³ is selected from the group consisting of substituted and unsubstituted heteroeiromatic rings and substituted arxd unsubst ituted heterocyclic rings, the rings being linked to the triazine group through a nitrogen atom, within the ring of R³.

As depicted above, the chromonic compound is neutral. , but it can exist in alternative forms such, as a zwitterion or proton tautomer (for example, where a hydrogen atom is dissociated from one of the carboxyl groups and is associated with one of trie nitrogen atoms in the triazine ring) . The chromonic compound can also be a salt such as , for exa.πιple, a carboxylate salt.

Th.e general structures above show orientations in whiich the car\boxyl group is para with respect to the amino linkzage to the triazine backbone of the compound ( formula I) and in which the carboxy group ±s meta with respect to the amino linkages to the triazine backbone (formula II) . The carboxy group can also be a combination of para and meta orientations (not shown) . Preferably, the orientation is para.

P-tref erably, each R² is hydrogen or a substituted or unsubstituted alkyl grou_p. More preferably, R² is independently selected from the group consisting of hydrogen, unsubstituted alkyl groups, alkyl groups substituted with a hydroxy or halide functional group, and alkyl groups comprising an ether, ester, or sulfonyl. Mos ^~fc preferably, R² is hydrogen.

R³ can be, but is not limited to, heteroaroraatic rings derived from pyridine, pyridazine, pyrimidine , pyrazine, imidazole, oxazole, isoxiazole thiazole, oxadiazole, thiadiazole, pyrazole, triazole, triazine, quinoline, and isoquinoline . Pref erablLy, R³ comprises a heteroaromatic rdLng derived! from pyridine or- imidazole. A suϋostituent for the heteroaromatic ring R³ can be selected from, but is not limited! to, the group consisting of substituted and unsubstituted alkyl, carrboxy, amino, alkoεy, thio, cyano, amide, sulfonyl, hydroxy, halide, perf luo-troalkyl, aryl, ether, and ester. Preferably, the substituent for R³ is selected from the group consisting of alkyl, sulfonyl, carboxy, halide, perfluoroalkyl, aryl, ettier, and alkyl substituted with hydroxy, sulfonyl, carbo>cy, halide, perfluoroalkyl, aryl, orr ether. When R³ i_s a substituted pyridine, the substituent is preferably located at the 4- position. When R³ is a substituted imidazole, the substituent is preferably located at the 3 -position.

Representative examples of R³ include 4-

(dimettiylamino) pyridiniu.m-1-yl, 3-methylirnidazolium-l-yl, A- (pyrrolidin- 1 -yl ) pyridinium- 1 -yl , 4 - isopropylpyridinium- 1- yl, 4- [ (2-hydroxyethyl) me thylamino] pyridinium- 1-yl, 4-(3- hydroxypropyl ) pyridinium- 1-yl , 4-methylpy3ridinium-l-yl, quinolinium-1-yl, 4 -ter fc-butylpyridinium.-1-yl , and 4- (2-sulf oethyl) pyridin±um-1-yl, shown below.

R³ can also be represented by the following general structure :

wherein R⁴ is hydrogen or a substituted or unsubstituted alkyl group. More preferably, R⁴ is selected from the group consisting of hydrogen, unsubstituted aILkyl groups, and alkyl groups substitutecl with a hydroxy, ether, ester, sulfonate, or halide functional group. Most preferably R* is selected from the group consisting of prropyl sulfonic acicϋ, methyH , and oleyl . R³ can also be selected from heterocyclic rings such as, for example, morphol±ne, pyrrolidine, piperidine, and piperazine .

A preferred chromonic compound for use in the methods of the invention can be represented by one of the following structures :

whexrein X^" is a counterion. Preferabl_y, X^" is selected from the group consisting of HSO₄ ^", Cl^", CH₃COO^", and CF₃COO^".

Formula III depicts the compound in its zwitterioni±c form. The pyridine nitrogen therefore carries a positive cha_trge and one of the carboxy functional groups carries a negative charge (COO^" ) .

The compound can also exist in other tautomeric foxms suctα as where both carboxy functional groups carry a negative charge and where positive charges are carried 3by one of the nitrogens in the triazine groups and the nitrogen on the pyridine group .

As described in U.S. Patent No. 5,948,487 (Sahouani et al . ) triazine derivatives with formuILa I can be prepared as aqueous solutions. A typical synthetic route for the tr±azine molecules shown in formula U above involves a two- step process. Cyaniαric chloride is treated with 4- am±nobenzoic acid to give 4- { [4- (4-ca.rboxyanilino) -6-chloro- 1, 3 , 5-triazin-2-yl] eimino} benzoic aciόl. This intermediate is treated with a substituted or unsubstituted nitrogen- containing heterocycle. The nitrogen, atom of the heterocycle displaces the chlorine atom on the triazine to foitrm the corresponding chloride salt . The zwitterionic derivative, such as that shown in foxmula III above, is prepared by dissolving the chloride salt in ammonium hydroxide and passing it down an anion exchange column to replace the chloride with hydroxide, followed by solvent removal . Alternative structures, such as that shown in foarmula II above, may be obtained by using 3-aminobenzcoic acid instead of 4-aminobenzoic acid.

Chromonic mate-trials are capable of forming a chronαonic phase or assembly when dissolved in an aqueous solution (p-tref erably, an alkaline aqueous solxαtion) . Chromonic phases or assemblies are well known in the art (see, for example, Handbook of: Liquid Crystals , Volume 2B, Chapter XVJCII, Chromonics, John Lydon, pp. 9Sl - 1007, 1998) and consist of stacks of flat, multi-ring- aromatic molecules. The molecules consist of a hydrophobic core surrounded by hyc±rophilic groups . The stacking can take on a number of moαrphologies, but is typically characterized by a tendency to form columns created by a stack o-f layers. Ordered stacks of molecules are formed that grow with increasing concentration . Preferably, the chromonic material is placed in a.queous solut ion in the presence of one or moire pH- adjust ing compounds and a surfactant . The addition of pH- adjust ing compounds allows the chromonic mater ial to become more soluble in aqueous solution . Suitable pH-adj usting compounds include any known base such as , for example, ammonium hydroxide oic various amines . Surfactant can i>e added to the aqueous solution to promote wetting of th_e solut ion onto the surface of a substrate . Suitable surfactants include ionic and non- ionic surfactants (pref erably, non- ionic ) . Optional additives such as viscosity modif iers ( for example , polyethylene glycol) and/or binders ( for example , low molecular weight hydirolyzed starches ) can also be added.

Typically, the chromonic materia ls are dissolved in the aqueous solution at a temperature les s than about 40 ⁰C (more typically, at room temperature) . One skilled in the a_rt will recognize , however, that the geometry and size of the resuIL ting metallic ns.no structures can be controlled to some extent by varying the temperature .

The relative concentrations of each of the components in ttαe aqueous solut ion will vary witHn the desired orientation of the resulting nanostructures and their intended application . Generally, however, the chromon-ic mateirial will be added to the solution to achieve a concentration in the range of about 4 to about 20 (pref erably, about 4 to about 8 ) percent by weight of the solut ion .

The aqueous composition comprising a chromonic material can fc>e mixed with a suspension of metal particles . Typically, the concentration of metal particles in the resuILting mixture wi ll be in the range of about 1 to a.bout 35 percent by weight of the total sol ids . Prreferred metal particles include noble metal particles . More pref erred metal partic les include siWer particl.es , gold particles , platinum parotides , and mixtures and alILoys thereof . ISTon-noble metal particles such as , for example , particles comprising iron can also be used .

Preferably, the metal particles arre surface modif ied, for example , with alkyl thiols , alkyl glycol thiols , aϋkyl amines , or glycol amines .

Thie resulting mixture can be applied to the surface of a substrate . Suitable substrates inclucie any solid materials that wdL ll accept the application of the mixture ( for example , glass or polymeric f ilms ) .

Ttαe mixture can t>e applied by any useful means that provides for the ordenred arrangement off the chromonic materials such as , fortr example , by coating techniques such as wirewound coating πrod or extrusion clie methods . Preferably, shear orientation or magnetic orientation is applied, to the mixture either during orr after applicat ion . The application of shear or magnetic force to the mixt^~ure can help promote alignment of the chrotnonic materials such that, tαpon drying, an oriented structurre or matrix is obtained .

Dirying of the coated layer can be achieved using any means suitable for drying aqueous coatings . Useful drying methods will not damage the coating or significantly disrupt the orientation of the coated layer imparted during coating or appXication .

Aff ter drying, the chromonic material can be removed such trαat only metall ic nanostructures remain on the substrate . The chrotnonic material can be removed using any means such as , for example by heating to decomposition ( for example; , by heating to higher than about 300⁰ C) . Alternatively, if the substrate is glass , the chroraonic material can be removed with a basic soliition.

-Alternatively, the aqueous composit don comprising a_ chromonic material can be mixed with a metal salt in solution. Preferred metal salts include noble metal sal_ts. More preferred metal salts include silver salts (for example, silver nitrate , silver acetate, and the like) , gold salts (for example, gold, sodium thiomalate, gold chloride, and the like) , platinum salts (for example, platinum nitrate, platinum chloiride, and the like ) , and mixtures thereof . Most preferred metal salts include, silver nitrate, silver acetate, gold sodium thiomalate, gold chloride, and mixtures thereof.

Generally, the metal salt will be pxesent in the resulting mixture at a concentration of less than about 50 percent by weight of ttie mixture.

The resulting mixture can be applied to the surface of a substrate (preferably, with the application of shear orientation or magnetic orientation durixig after the application) as described above.

The metal salt can be reduced via reduction methods known in the art either- before or after applying the mixture to the surface of a substrate. For example, the reduction can be accomplished by using a reducing agent (for example, tris ( clime thylamino) borane , sodium borohydride, potassium borotrydride, or ammoniuLin borohydride), electron beam (e — beam) processing, or uILtraviolet (UV) light.

After the metal sa.lt is reduced, tb_e coated layer can be dried and the chromonic material can be removed such that only metallic nano structures remain on the substrate as described above.

The aqueous composition comprising a chromonic material can also be applied to the surface of a substrate (preferably, with the application of shear orientation c»r magnetic orientation during after the application) befoire mixing with a metal salt in solution. T^fter the aqueous composition comprising a chromonic materrial is applied to the surface of a subst-trate, it can be pILaced in contact with (for example, immersed in) a solution comprising a metaL salt. Preferred metal salts are the same as those preferred above . The metal salt can then be reduced, and the chromonic material can optionally be removed as described above .

The methods descr±bed can be used to make nanos tructures such as, for example, nanowires and reguL ar arrays of nanostructures (that is, arrays in which relatively uniformly sized and shaped na.no structures (for example, spherical nanoparticles) are substantially everxly spaced) . The methods of the invention can facilitate tb_e fabrication of nanostrmctures over large areas, which ca.ii be advantageous, for example, for applications such as electromagnetic interference (EMI) filters.

EXAMPLES

Objects and advantages of this invention are further- illustrated by the foil. owing examples, but the particular" mater-ials and amounts thereof recited in these examples, a.s well a.s other conditions and details, should not be const xued to unduly limit this invention.

Unless otherwise .noted, all reagents and compounds were or can be obtained from Aldrich ChemicaIL Co., Milwaukee, WI.

As used herein, "purified water" refers to water available under the trade designation "OMNISOLVE" from EMD Chemicals, Inc., Gibbstown, NJ; "APG 325" refers to a 7O we i grit percent aqueous solution of an alkyl polyglucosicle, a surfactant available fnrom Cognis Corp. USA, Cincinnati, OH; and "ICB 3003" refers to a starch obtained from A. E. Staley Manufacturing Co., Decatur, IL.

Example 1

Prepeiration of Silver Nanoparticles in a Chromonics Assembly

A mixture of purified water (4.Og) , ethylene diamine (0.09g) , the chromonic compound of Formula III (1.Og) , glucose (0.3g) , and AlPG 325 (O.Olg) was magnetically stzLrred in a flask for approximately 15 minutes. A separate mixture of purified water (4. Og) , poly (acrylic acid) (O.lδg of a. 25 weight percent aqueous solution of 90, O00 molecular weight poly (acrylic acid)), ammonium hydroxide (0.42g of a 30 weight percent aqueous solution) , and silver nitrate (0. 03g) was magnetically stirired for approximately 15 minutes. The two mixtures were combined in a flask 3oy stirring them together for 15 minutes to provide a mixture for coating^". This mixture was coated onto a glass microscope slide using a #3 wound wire coating rod. The coating was then exposed to t-tris (dimethyl amino ) borane vapor by ^placing the coatecl glass slide in a sealed glass jar for 2 minutes. After the slide was removed from the jar, the coating was allowed to dry in air at room temperature for at least 5 minutes.

Example 2

Preparation of Silver Nanoparticles in. a Chromonics Assembly

A mixture of purified water (4.Og) , the chromonic compound of Formula IZI (1.Og) , APG 325 (O.lg of a 10 weight percent aqueous solution) , and ammoniuτn hydroxide (0.3g of a 30 weight percent aqueous solution) was magnetically stirred in a flask for approximately 15 minutes. A separate mixture of pmrified water (4. Og) , ammonium hydroxide (l.Og of a 30 weiglit percent aqueous solution) , and silver oxide (0.2g) was magnetically stirred in a flask fox approximately 15 minutes. The two mixtures were combined in a flask by stirr-±ng them together for 15 minutes to provide a mixtixre for coating. This mixture was coated onto a glass microscope slide using^" a #3 wound wire coating rod. The coating was then exposed to tris (dimetlrylamino) borane va_por by placing the coated glass slide in a sealed glass jar for 2 miniates. After the slide was removed from the jar, trxe coating was allowed to dry in air at room temperature for at least 5 minutes .

Example 3

Preparation of Silver Nanowires in a Chromonics Assembly^

A mixture of purified water (8.0g) , ammonium hydroxiide (1.3g- of a 30 weight percent aqueous solution) , the chromonic compound of Formula III (1.Og) , APG 325 (0.0Ig^") , and silver benzoate ( 0.2g) was magnetically stirred for approximately 20 minutes in a flask. This mixture was coated onto a glass microscope slide using a #5 wound wd_re coating rod. The coa.ting was then exposed to tris ( dime thylamino) bo rane vapor by placing the coated gILass slide in a sealed glass jar for 2 minutes. After the sl_ide was r-emoved from the jar, the coating was allowed to dry in air set room temperature for at least 5 minutes . The coa-ting was then examined by transmission electron microscopy us ing a Model H9000 electron microscope (available from Hitaclai High Technologies America, Inc., Pleasanton, CA) operat-Lng at 300 kV. Transmission electron micrographs of the silLver nanowires are shown in Figures 1 and 2 . Figure 1 is a top view of the coating ( showing the lengtϊis of the nanowires) in wriich the silver nanowires are the <dark features. FiLgure 2 is an edge view of the coating (showing the ends of trie nanowires) in which the silver nanowires are the dark f eatu-res . Examjple 4

Preparation of Silver Nanowires in a Chromonics AssemblLy

A mixture of purified water (8.Og) , lithium hydroxide (0.0Sg) , the chromorαic compound of Formula III (1.Og) , APG 325 (0.3g of a 10 weight percent aqueous solution) , M2O 0 hydrolyzed starch (O.03g, available frrom Grain Processi_ng Corp. , Muscatine, I.A.) , silver nitrate (0.2Ig) , and ammonium hydroxide (0.075g of a 30 weight percent aqueous solutzLon) was magnetically st±rred for approximately 30 minutes d_n a flask. This mixture was coated onto a glass microscope slide using a #3 wound wire coating rrod, after which a 10 weight percent solution of potassium borohydride in ethvanol was carefully applied via pipette to the surface of the coat±ng. After approximately 5 minutes, the glass si idle was rinsed with ethanol and was allowed to dry in air at room temperature .

Example 5

Preparation of Gold Nanoparticles in a Chromonics Assembly

A mixture of purified water (9.Og) , ammonium hydroxide (0.25g of a 30 weight percent aqueous solution) , APG 325 (3 drops of a 10 weight percent aqueous solution) and the chromonic compound of Formula III (1. Og) was magnetically stirared in a flask if or approximately 15 minutes. To thxis mixture there was added gold sodium thiomalate (O.lg) . The mixture was stirred for an additional. 15 minutes and wa.s then coated onto a cjlass microscope slide using a #5 wound wire coating rod. The coating was then exposed to tris (dimethylamino) borane vapor by pl_acing the coated g-lass slide in a sealed glass jar for 2 minutes . After the slide was ^removed from the jar, the coating was allowed to drry in air SLt room temperature for at least 5 minutes. The coating was dissolved by immenrsing and then agitating the coated glass slide in purified water. A small sample of the resultant suspension of gold nanoparti cles was analyzed by dynamic light scattering using a Model ZEN3600 particle size analyzer (available fnrom Malvern Instruments, Southboroταgh, MA) and was found to liave a mean particle size of approximately 5 nanometers . The small sample was further analyzed by transmission electron microscopy using a Mo<del H9000 electron microscope (available f xom Hitachi High Technologies America, Inc., Pleasanton , CA) operating at 300 kV, wrαich showed gold nanoparticles (as dark features) ^"that were substantially spϊierical. The tra.nsmission electrom micrograph is shown in Figure 3.

Example 6

Preparation of Silver^* Nanowires

Z\ mixture of purified water (9.0 g) , ammonium hydroxide (0.25 g of a 30 weight percent aqueous solution) , APG 325 (0.01 g) , ICB 3003 (0.3 g) , and the ckroraonic compound of Formula III (1.0 g) was magnetically stirred for approximately 15 minutes . The mixture was coated onto a. glass microscope slide using a #3 wound wire coating rod. The coating was allowed to dry for approximately 30 min.^~u.tes in ai-tr at room temperature and then th.e coated glass si ide was immersed in a 40 -weight percent aopαeous solution of silve-tr perchlorate fox approximately 2 minutes. The coated glass slide was then .rinsed with ethaaol and was then immersed in a 3 weiglαt percent solution of potassium borohydride in ethanol for approximately 1 minute. The coatecϋ glass slide was then rinsed segruentially with etlianol and IO weight percent aqueous ammonium, hydroxide solution. Rinsing with the aqueous ammonium hydr-oxide solution removed the ctαromonics assembly. The glass slide was then allo"wed to cbry in air at room temperature for approximately 5 minutes , after which time it was exami ned by optical microscopy using a Model DM4000 M micαroscope ( availabL e from Leica Microsystems , Inc . , Bannockburn, IL) at 1000 power . An optical micrograph, of the silver nanowires is shown, in Figure 4 . In Figure 4 , the silver narxowires are visib> le as the l ight features .

Various modifications and alterat ions to this invention will -become apparent to those skilled in the art without departing from the sc ope and spirit of this invention. It should be understood that this inventi on is not intended to be uncluly limited by the illustrative embodiments and examples set forth he rein and that such examples and embodiments are presented by way of exiample only with the scope of the invention intended to be limited only by the claims set forth here in as follows .

Claims

We claim:

1. A method of making metallic nanostructures comprising mixing (a) an aqueous composition comprising a cϊiromonic material with (b) a metal salt in solution or a suspension of metal particles.

2. The method of claim 1 wherein said chromonic material is selected from the group consisting of compounds .represented by one of the following- general structures :

wϊierein each R² is independently selected from the group consisting of electron donating groups, electron withdrawing cjroups, and electron neutral groups, and

R³ is selected, from the group consisting of substituted and unsubstituted tαeteroaromatic rd_ngs and substitixted and tinsubstituted heterocyclic rings, said rings being linked to the triazine group through a nitrogen atom within the ring of R³, and zwitterions, proton tautomers , and salts thereof.

3. The method of claim 2 wtierein each said R² is independently selected the group consisting of hydrrogen, unsubstituted alJcyl groups, alkyl groups substituted with a hydroxyor halide functional group, and alkyl groups comprising an etrαer, ester, or sυZLfonyl.

4. The method of claim 2 wlnerein said R³ coinprises a heteroaromatic r±ng derived from the group consisting of pyridine, pyridazine, pyrimidine, pyrazine, imidazole, oxazole, isoxazoILe, thiazole, oxadliazole, thiadiazole, pyrazole, triazoILe, triazine, quinoline, and isoquinoline .

5. The method of claim 4 wherein said R³ coinprises a heteroaromatic ring derived from ^pyridine or imidazole .

6. The method of claim 5 wherein said R³ is selected from the group consisting of pyricϋinium-l-yl, 4- (dimethylamino)pyridinium-l-yl, 3— methylimidazolium-1-yl, 4- (pyrrolidin-1-yl) pyridinium-1-yl, 4-isopropylpyridinium-l- yl, 4- [ (2 - hydroxy ethyl)methylamino] pyridinium-1-yl,. 4- (3- hydroxypropyl ) pyiridinium- 1 -yl , 4 -me thylpyr idinium- 1 -yl , quinolinium-1-yl , 4- tert-butylpyridinium-1-yl, and 3- (2-sulf oethyl) jpyridinium-1-yl .

7. The method of claim 2 wherein said chromonic material is represented by the following general structure:

and zwitterions, proton tautomers , and salts thereof

8. The method of claim 7 wherein said chromonic material i s represented by one of the following structures

wherein X^~ is a counterion.

9. The method of claim 8 wherein said X^" is selected from the cjroup of counterions consisting of ΗSO₄ ^", Cl^", CH₃COO^', and CF₃COO^".

10. The method of cla.im 1 wherein said, aqueous composition comprising a crαromonic material is mixed with a metal salt in solution.

11. The method of claim 10 further corcvprising reducing said metal salt .

12 . The metlxod of claim 11 f uitrther comprising applying ttie mixture to the surface of a substrate .

13 . The mettαod of claim 12 f uztrther comprising applying s-hear orientation or magnetic orientation during or sifter application of sa±-d mixture .

14 . The metrαod of claim 12 f uirther comprising itremoving said chromonic material .

15 . The metrαod of claim 10 wherein said metal salt is a. noble metal salt .

16 . The mettiod of claim 15 wherein said metal salt is s elected from the group consisting of silver salts , gold s alts , platinum salts , and mixtures thereof .

17 . The raettαod of claim 16 wherein said metal salt is s elected from the group consisting of silver nitrate , silver acetate , gold sod±um thiomalate , go ld chloride , and mixtures and alloys thereof .

18 . The mettiod of claim 1 whe rein said aqueous composition comprising a chromonic "material is mixed, with a suspension of metal particles .

19 . The metliod of claim 18 farther comprising applying the mixture to the surface a substirate .

20 . The metliod of claim 19 fuirther comprising applying shear orientation, or magnetic orientation during or after application of said mixture .

21. The method of claim 19 further comprising removing said chroτnonic material.

22. The method of claim 18 wherein sarLd metal particles are surface modi±ied metal particHes.

23. The method of claim 18 wherein said metal particles are noble metal particles .

24. The method of claim 23 wherein said metal particles are selected from the group consisting of silver particles, gold particles, platinum particles, and mixtures thereof .

25. The method of claim 18 wherein said metal particles comprise iron.

26. A method of making metallic nanos tructures comprising (a) applying an aqueous composit ion comprising a chromonic material to the surface of a substrate; and (b) placing the coated surface in contact with a solution comprising a metal salt.

27. The method of cILaim 26 further comprising applying- shear orientation or magnetic orientation during or after application of said aqueoiαs composition comprising a chromonic material.

28. The method of cILaim 26 further comprising reducing- said meta.1 salt.

29. The mettiod of claim 28 f-urther comprising removing said chromonic material.

30. An article comprising a chromonic matrix a_nd metal rxa.no structure s .