Surface modification of metal and metal oxide substrates by organic monolayers Hubert Mutin ICGM mutin@univ-montp2.fr Surface modification Inorganic surface •metal •oxide •hydroxide •carbonate •phosphate •nitride •sulfide Coupling Agent: R Organic •alkyl •functional group •polymer •metal complex •proteine •enzyme • DNA -R T Coupling agent •thiol •organoalkoxysilane •carboxylic acid •phosphonic acid stable bonds with both organic and inorganic moieties R R R R R R Route to hybrid materials, complementary to Sol-Gel monolayer Surfaces Composition: silicium, metal (Au, Ti...), oxide, hydroxide, carbonate, phosphate, nitrure, sulfure Amorphous, microcrystalline, monocrystalline R R R R Flat (Nano)particles Porous Monolayer or self-assembled monolayer? Monolayer: surface modification (chemical bonds with the surface) no lateral interaction between coupling agent molecules low or medium density, disordered Self-Assembled Monolayer = SAM surface modification + intermolecular interactions Usually : long alkyl chains (10 to 20 CH2 groups): intermolecular van der Waals forces between methylene groups: ordered chains, high grafting density (4-4.5 /nm2) Thiol and disulfide coupling agents Alkylthiols, dialkyl disulfides Organic: stable S-C bonds Surfaces: SAMs on Au(111), Pt, Ag, Cu, Hg, Fe, y-Fe203, GaAs, ZnSe, InP Coupling: M-S-C bonds R-S-H + Au°-> R-SAu+ + V2 H2 R-S-S-R + Au°-> 2 R-SAu+ S-H Deposition of Alkylthiol SAMs on Au •Preferred crystal face for alkanethiolate SAM preparation Au (111) - single crystal substrates: evaporation of thin Au films (200-400 nm) on flat supports (glass or silicon) • Thiol concentrations: 1-2 mM, most common solvent ethanol. • Time: a self-assembled monolayer forms very rapidly on the substrate, but it is necessary to use adsorption times of 15 h or more to obtain well-ordered, defect-free SAMs. Multilayers do not form, and adsorption times of two to three days are optimal in forming highest-quality monolayers. Structure Figure 9. Hexagonal coverage scheme for alkanethiolates substrates (showing tilt angles of 12T and 27°, respectively), on Au(l 11). The open circles are gold atoms and the shaded circles are sulfur atoms. 2-D packing Tilt: •to increase VdW contact alkyl chains of alkanethiol SAMs) surfactants are often tilted •Depends on the metal (distance between M atoms) Caracterization of density / ordering in alkyl SAMs IR :CH stretching vib. very sensitive to packing density and gauche defects as CH2stretching vibration (d) : 2916 or 2917 cm1 for SAMs of exceptional quality or cooled below RT 2918 cm1 : normal value for a high-quality SAM, -2926 cnr1 heavily disordered, "spaghetti-like" SAM. 0.005 0 IRAS spectrum of a hexadecanethiolate SAM. d+ and d- are the s and as CH2 stretches; r+ and r- s and as CH3 stretches 3050 3000 2950 2900 2850 2800 2750 Wavenumber (cm1) Mixed SAMs: two-component molecular gradients Liedberg and Tengvall {LangmuirJlJl (1995), 3821). Cross-diffusion of two different thiols through an ethanol-soaked polysaccharide gel: formation of a continuous gradient of 10-20 mm length may be formed. \ X X X X x X o o oo 0 o o Preparation of two-component alkanethiolate gradients. (a) The two different thiols, represented by X and O, are injected into glass filters. (b) They diffuse slowly through the polysaccharide gel and attach to the gold substrate. (c) Top view showing the placement of the gold substrate between the filters. (d) Schematic illustration of a fully assembled gradient. Post-modification OSO3H 0 L*^\ HO- O" \ / Epichlorohydrin (CF3C0)2O CISO3H I OH R 0 II O—P—OH 1 OH POCI3 4 OH (CH2)3 NH o o=C R-N=C=S \ 1.Cg02Clg °~\ O 2. R-NH2 * o Si-O-Si + HX Competition heterocondensation / homocondensation Surface modification by trialkoxysilanes Competition heterocondensation / homocondensation Depends on the amount of water (adsorbed, in the solvent...) R EtO-Si-OEt OEt no H20 R 6 OH OHO7 x0 OH R EtO-Si-OEt M M M M M M only Si-O-M, Partial monolayer OH OH OHOH OH OH n sH20 J_L M M M M M M HoO R R lj? o-Si-0—Si-o-Si 6 oh 6 oh6xo _j_i_i_i i i M M M M M M Si-O-M + Si-O-Si Dense monolayer R ~ ,R xSi- HO-Si-0 °^Si 6 OHOHO7 \) OH J_ _l_ _l__l_ _L_ M M M M M M VI few Si-O-M, multilayer Carboxylic acids •RCOOH saturated fatty acids :CnH2n+1COOH Surfaces: • oxides (Al203, AgO) • oxidized metals(Ag, Au...) • carbonates (CaC03) Coupling: ionic bonds Formation of a « surface salt » RC(0)0" M+ Bonding mode: mono- or bidentate Carboxylic acids AgO CuO; Al203 Carboxylic acids Ex.: PP/ CaC03/ stearic acid system Surface CaC03 not compatible with PP melt of PP + CaC03: extremely high viscosity, extremely difficult mixing, -> poor dispersion of CaC03 filler Surface modification of CaC03 by stearic acid (C17H35COOH): —» alkyl chains at the surface of particles —» hydrophobic particles, good wettability by melt PP, incorporation and dispersion easier Compatibilizer —» Improved mechanical properties (shock resistance) Organotitanates Titanium alcoxides (also Zr, Al), modified by carboxylic acids or chelating groups (p-dicetones, cetoesters, glycols, hydroxyacides, phosphates). o o CH3-(CH2)16-C-Ox /O-C—(CH2)16-CH3 Ti H / V H3C—C-0 0-C-(CH2)16-CH3 O O ?H3 II II I CH3-(CH2)16—C-O^ O-C—C=CH2 Ti H /\ H3C—C—O O—C—C=CHo CH II O CH- Non reactif (dispersant) Reactif • Commercial, goods results with CaC03 or oxide fillers • 1300 patents + 400 technical articles • Mecanism? M-OH + Ti-OR -> M-O-Ti ? source of carboxylic acid? • Real composition and structure ????? Titanium oxoalcoxydes Ti(OR)4 [Ti3O](OR)10 [Ti7O4](OR)20 (a) „ (jta. [Ti10O8](OR)24 [Ti^O^KOR)^ a. Xv,-M > '4?/"is f .... V~~L^ " \ W ,, It?r. ^C2', [Ti16016](OR)32 [Ti^O^KOR)^ [Ti16016](OR)32 '■7h rl V - 1 9 Ti02 Fig. 1. Formulas of structurally -characterized titanium(IV) polyoxo-alkoxides [TixOy](OR)4x_2y arranged in order of their degrees of condensation relative to Ti(OR)4 and TiOo. 6 [Ti30](OMe)(OiPr)9 Sulfonates coupling agents / SiQ2 H-bonding jacs 1999,121,5961 ocn co +Rh Ph2P Ph2Px PPh2 H I o H I o 'Si02: pretreated at 300°C 'Rh complex: dissolved in CH2CI2 •Washing with CH2CI2no loss of Rh • Washing with MeOH: Rh complex dissolved • Catalysis: hydrogenation and hydroformylation of alkenes, recyclable, Rh en solution < 1 ppm Sulfonates / Si02: FTIR I-i-1-r 4000 3900 3800 3700 3600 3500 3400 3300 Conditions: Si02: 370 m2/g Pellets dried at 300°C/105 mm Hg, 16h dried Si0o + sulfonate dried Si02 difference spectrum •decrease of free OH •increase bonded OH => H-bonding Wavenumber (cm"1) c o- ?FS 0 -s—o Sulfonates / SiOo H-bonds + electrostatic bonds Chem. Comm. 2000, 1797 Grafting onto MCM-41 Catalysis: hydrogénation of enamides [ H H H H H I I I I I O O O O O J_I_I_I_L Si Si Si Si 1 R >= R' ,C02R N(H)Ac NaB[C6H3(CF3)2]4 PF3 x e o: m© Na cf3 q -s—o Characterization 31 P. 19F NMR Organophosphorus coupling agents Nucleophilic attack at P: difficult: R QEt 6NHCI R 0H • Hydrolysis of P-OC : harsh conditions r\~L^ 15 hrs _ n=o^ °~^OEt 100oC' O-P^OH • No homocondensation of P-OH: P-OH + P-OH £ P-O-P + H20 Possible coupling agents : organophosphorus acids (or salts) X R-O-P^OH X R OH OH R-0X OH phosphonic phosphinic Mono- or di- esters of acids acids phosphoric acid Phosphonic acids coupling agents P-C^H^P-OH £ P-O-P + H20 =>no homocondensation Heterocondensation P-OhUM-OH P-O-M + HoO Acids stable in water: surface modification in water Great affinity for metal oxides : Ti02, Zr02, Al203, Fe203 etc. Ex.: metal phosphonates R R R \ \ \ Zr; /Zr^ ^Zr ^Zr O P^u O p"u O p"u \ \ \ R R R R R R \ \ \ \ /0/KP /0/KQ /0/KP x Zr; ^Zr' ^Zr ^Zr O P"u O P'u 0>p"u \ \ \ R R R Growth of C18H37P03H2 SAMs on titanium in situ multireflexion ATR FTIR Substrate: 20 nm Ti on a silicon ATR crystal 1 mM C18H37P03H2in CD3CD2OD, 15 °C VasCHs, vsCH2 1 week j 1 day J 1 y\^J 1 min r i i i 3000 2900 2800 Wavenumber (cm1) Water contact angle / 12 24 36 Time / h • No need to control the water content, simple and reproducible! Surface modification of Ti02 particles TiO, + PhPO,H 3' '2 H,0 31PMAS-NMR 120°C / especes greffeejs P-O-P 100°C Tj(PhP03)2 20°C: no P-O-P =^> monolayer 100°C: no P-O-P, but dissolution/precipitation F^h F^h F^h x .cTP9 ^cTP9 /0/PQ ^ Ji ^Ti JTi JTi 0~P'U 0~P'U 0~P'U \ \ \ Ph Ph Ph F^h F^h F^h \ /0"P Q /0"P Q o'pQ T\ ^Ti ^Ti ^Ti 0~p'u 0~p'u 0~p'u \ \ \ Ph Ph Ph 100 50 0 -50 -100 Chem. Mater. 2001, 13,4367-4373 8 (ppm) 170 NMR of phosphonate monolayers collaboration F. Babonneau, C. Gervais (UPMC) Binding of phosphonic acids to oxide surfaces: evidencing P-O-M bonds 170-enriched C12H25P03H2 monolayer on Ti02 • phosphonic acids 17Q MAS-NMR i Chem. Mater. 2008 Surface modification by phosphonate esters o= P^OEt 0-H I H /C0Et T Ti Ti l/OH CHoCIo Ti02 + PhPO(OEt)2 ——^ 40 °C R I^OEt A or o J_L 31P MAS-NMR 100 50 0 -50 -100 8 (ppm) - EtOH Ti Ti J Surface catalyzed condensation Controlled bifunctionalization 1-step: Orthogonal Self-Assembly (Gardner et al, JACS 1995) ITO Au 1 1 I Si3N4 i Fe RP03H2 + RSH -> MeOH/CHCL R R R R R HO 1 R PqOOqOOqQ ^_ __1 1 I Fe V RP03H2/RSH : 0.1 mM in MeOH/CHCI3 (1:3) RCOOH/RSH : 0.1 mM in EtOH/hexane (1:20) in Selectivity >60 Hydrolytic stability of M-O-P Basic conditions : stability of Ti-O-P , Zr-O-P » Ti-O-Si, Si-O-Si but Si-O-P + H20 —> Si-OH + P-OH 31P MAS NMR Si02 + C12H25P03H2 MeOH/H20 1~d " Si02 + C12H25P03H2 Toluene. 1 d _1_i_I_i_I_i_I_i_I_i_I_i_1_ 80 60 40 20 0 -20 -40 5 (ppm) selective surface modification Selective surface modification TiO. C-12H25 Si02 substrate prepared by microlithography Repartition of organic groups controlled by the inorganic support HoO Chem. Mater. 2004, 16, 5670-5675 100 o c o o o E o 5 10 15 Distance (pm) Controlled bifunctionalization 2-step TiO RP03H2 Me,SiCI S\0. H,0 Toluene R R R • a k a i i i Me MeBj p p p MeN| xMeMes| ^.Me • patterning substrates made by microlithography • selective bifunctionalization of mesoporous Si02-Ti02 mixed oxides prepared by sol-gel Chem. Mater. 2004 16, 5670 Grafting oxide NPs in aqueous colloidal solutions collaboration J. Oberdisse, C. Genix L2C Silica colloids: used In ceramics, composite materials, cements, catalysts, polishing pastes, paper, textile... Levasil® 200S/30: "cationic silica sol" = alumina-coated silica NPs oh Modification of the NPs in the aqueous sol : © I Sl° © © © OPA > .o EPA o=p: oh x)h o=p: P R o .oh t>h OPA ; hydrophobic R group DEPA ; hydrophilic R group Tuning interactions between nanoparticles in aqueous solutions Grafting oxide NPs in aqueous colloidal solutions OH u Í^OH 0=P. "OH DEPA OPA Zeta potential Grafting density / P nm 0,3 P/nm2 0,5 P/nm2 3,2 P/nm2 Rapp (DLS) Grafting density / P nm • OPA, DEPA: slight decrease of ZP • OPA: aggregation increases with grafting density ^hydrophobic interactions Phase transfer of Ti02 particles • Oxide nanoparticles: cheap, "green" syntheses in aqueous media, sols stabilized by electrostatic repulsion • Inks, paints, nanocomposites: need for organosoluble nanoparticles • Simultaneous grafting / phase transfer (FTIR, NMR) Langmuir 2015, 31,10966-10974 Phase transfer of Ti02 particles Parameters influencing the transfer • Alkylphosphonic acids with chain > 5 Carbons • ca 4-5 P/nm2 • Works even for high sol concentration Langmuir 2015, 31,10966-10974 Phase transfer of Ti02 particles Transfer of aggregated nanoparticles Deaggregation during phase transfer / surface modification R(DLS) organic phase R(DLS) aq 600 - 400 - 200 - 0 pH 2 pH 4 pH 5 600 400 Ol P 200 0 R(DLS) organic phase R(DLS) aq 0 Na#4content (wt%) 6 Applications Photovoltaic cells l~° TiO I \ Complex absorbs visible light. Injection of 2 -o-p é" in the conduction band of the metal hO / •Heterogeneous catalysis Reduction of aromatic ketones Me^O H2 40 bars H20 21h OMe rdt: 99% Me. .OH OMe 0 0-P-(CH2)3< O / 0 TiO r° K)-P-(CH2)3^ Ir-Cl ■O' O Immobilization of Catalyts on Metal Oxides OEt Ph2R /\ Si-OEt \A/ ř OEt ©Si02 ©Ti02 í trans-PdCI2L2.CH2Cl2 40°C // \ °'OEt Ph2P—< V— PN OEt = L 31P MAS-NMR 22 i PPh2 12 33 i 80 40 0 -40 S (ppm) -80 Modification of Si02 fillers in Water No change in morphology, 1-4 P/nm2, hydrophobic Fr. Patent 2005 Rhodia-CNRS C18H37P03H2 SAMs as boundary layer lubricants Long alkyl chains : intermolecular forces between methylene groups formation of Self-Assembled Monolayers Application: lubrication Substrates: 20 nm Ti on Si grafting with C18H37P03H2 in EtOH, 2d. Friction: stainless steel ball D = 2 mm, 260 HV, normal force up to 60 N MRS Symp. Proc. 2004 p p p p p p p'ob o'ob o'&o o'6xo o'ob o'&o Ti' ti Ti Ti Ti TiTi' Ti TiTi Ti TiTi ti TiTi Ti Ti 1 m ; I' rim 30 N Ti/Si untreated Contact angle 11° Friction coeff. 0.6 ODPA/Ti/Si Contact angle 102° Friction coeff. 0.1 Antibacterial Monolayers for Biomaterials Prevention of orthopedic implant infections: Current approach: hinder bacterial adhesion and biofilm formation using "thick" antibacterial coatings : cationic polymers, polyelectrolyte multilayers, silver-releasing sol-gel coatings... Interest of phosphonates: • high affinity for all these materials • good thermal and hydrolytic stability Inorganic implant materials: • metals, metal oxides, phosphates... Monolayers ? steel, Cr/Co or zirconia Hip prosthesis Antibacterial monolayers Proof of principle: silver release SH SH SH AgS AgS OH OH OH OH l' 1 ^ HO 0 0 0 0 0 OH 1 j_i_i _ AgNO, 0 0 O 0 0 OH j_i_i_i _ Biofilm assay: samples immersed 3d at 37 °C in a culture of E. Coll GFP -j ■ => growth of the biofilm at the air- of liquid interface. Decrease of ca 97 % of biofilm density 6000 4000- 2000- C12SH C12S-Ag Fluorescence microscopy (E. coli gfp) Immersion 3 days at 37 C Decrease of 95 % of biofilm density Bis-phosphonate multilayers o o 0H bis-phosphonic acids (BPA) nfL JpC HO' ^(ch2)n OH Controlled deposition of multilayers • Ex.: BPA/Zr Mallouket al., JACS 1993 o o ;P-(CH2)n-P-OH O 0NOH ^P-(CH2)n-P-OH \ o oh ;p-(ch2)n»p-oh oh 1)ZrOCI2 -* 2) BPA ;p-(ch2)r ;p-(ch2)r ;p-(ch2)r ■p complementary >Modification/functionalization of inorganic surfaces ^Interface modification / assemblies • organic-inorganic • inorganic-inorganic