From Self-Assembled Monolayers to Polymer Brushes. Rainer Jordan

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1 From elf-assembled Monolayers to Polymer Brushes Rainer Jordan Chair of Macromolecular Chemistry Faculty of Chemistry and Food Chemistry chool of cience

2 Ultrathin, Thin, and Thick(er) Films on olid ubstrates Monolayers Multilayers PMs Brushes Polymer Layers elf-assembly / LB-Deposition Grafting-from / Grafting onto Grafting onto Casting or ( ) ( ) x y (selective) physisorption chemisorption Å Å - nm ome nm More nm-µm nm - µm µm nanoscopic RDER PRBLEM: microscopic MBILITY

3 verview: From elf-assembled Monolayers to Polymer Brushes µcp + patterned AMs Chemical Lithography patterned AM-Initiator ystem + n M IP Lithographic techniques + n M A substrate homogeneous AMs homogeneous AM-Initiator ystem + diffusion, irradiation gradient AMs Chemical Lithography gradient AM-Initiator ystem IP + n M IP Gradients R. Jordan in: Polymeric Materials in rganic ynthesis and Catalysis, (M. Buchmeiser, ed.), Wiley-VCH 2003.

4 PART I elf-assembled Monolayers AMs

5 Definition: elf-assembled monolayers (AMs)......are ordered, chemically and thermally stable two-dimensional aggregates that are formed spontaneously by the adsorption of surface active molecules onto a solid. The surface active molecule should feature: 1. a head group, suitable for strong interactions or even chemical bonding with the surface, 2. a mesogenic moiety responsible for the 2D packing and favorable lateral interactions with the next neighbors and 3. a tail or end group determining the properties of the newly formed solid surface. The A of a film is a concerted interplay of various forces. The overall stability of a AM is determined by all inter- and intramolecular forces in the film. tail mesogen head group substrate (a) Cartoon of a AM. haded circle indicates adsorbed or chemisorbed head group and open circle end group, which can be chosen from variety of chemical functionalities. (b) chematic of different energies. ΔE ads stands for adsorption energy, ΔE corr corrugation (rippling) of substrate potential experienced by molecule, ΔE hyd van der Waals interaction of (hydrocarbon) tails, and ΔE g energy of gauche defect (or, generally, deviation from fully stretched backbone).

6 ubstrate Ligand, Precursor Binding Au RH, ArH (thiols) R-Au Au RR' (disulfides) R-Au Au RR' (sulfides) R-Au Au R 2 H R 2 -Au Au R 3 P R 3 P- Au Ag RH, ArH R-Ag Cu RH, ArH R-Cu Pd RH, ArH R-Pd Pt RNC RNC-Pt GaAs RH R-GaAs InP RH R-InP i 2, oxides RiCl 3, Ri(R') 3 siloxane i/i-h (RC) 2 (neat) R-i i/i-h RCH=CH 2 RCH 2 CH 2 i i/i-cl RLi, RMgX R-i metal oxides RCH RC M metal oxides RCNHH RCNHH--- M Zr 2 RP 3 H 2 RP Zr IV In 2 3 /n 2 (IT) RP 3 H 2 RP M n+ G.Whitesides, Y. Xia, Angew. Chem R. Jordan, From self-assembled monolayers to polymer brushes Wiley-VCH 2003

7 Various types of AMs End Group // ubstrate Acids (RCH, R 3 H, RP 3 H 2 ) on oxide surfaces (Ag, Al 2 3, Fe 2 3 ) Trichlorosilanes (RiCl 3 ), Trialkoxysilanes (Ri(Alkyl) 3 on H surfaces (i 2 (i-h), Al 2 3, H-substituted polymers) ulfur compounds on metallic surfaces (Au, Ag, Cu, Pt, Pd) and on GaAs. C 2 H 3 H P 3 H 2 icl 3 i(ch icl 3 3 ) 3 i(c icl 32 H 5 ) 3 H H HN H Ag, Al 2 3, Fe 2 3, Al 2 3,Ti 2,i 2, oxides Au, Ag, Cu, Pt, Pd, coin metals

8 AMs of Thiols Experimental In the preparation of AMs, the substrate is immersed into a dilute (10 mm to 1 mm) solution of the desired thiol. For thiols on gold, initial adsorption is fast (seconds); then an organization phase follows which should be allowed to continue for > 15 h for best results. Au(111) on i(100) thiol solution Adsorption fully assembled AM rganization Au

9 Alkanethiols Film Formation Evolution of structures of decanethiol on Au(111) during growth. (not all are stable equilibrium structures). Preparation method: Adsorption from the gas phase in UHV conditions (A) ``Lattice gas'' at very low coverage. (B) (C) triped phase (for which two slightly different structures were reported). Intermediate structure (D) Intermediate structure (E) tanding-up Phase, which superlattice of hexagonal ( 3x 3)R30 base or rectangular (2 3x3) unit cell.

10 Constant-current TM scans for increasing exposures of mercaptohexanol vapor on Au(111). (A) clean ``herringbone'' reconstructed Au(111) surface; the inset shows three stable islands nucleated between herringbone double rows after first stage of exposition. (B) triped phase island (pointing finger). (C) Continued striped phase growth displacing herringbone elbows. (D) Continued striped phase growth with Au vacancy islands (pointing finger) becoming visible. (E) Nucleation of standing-up phase within striped phase. (F) Growth of standing-up phase at expense of striped phase until saturation. From G.E. Poirier, Langmuir 1999.

11 LB-FILM vs. AMs Langmuir-Blodgett Monolayers elf-assembled Monolayers solid urface Pressure liquid-solid liquid gas Area / Molecule D.K. chwarz, Annu. Rev. 2001

12 Alkanethiols Film Formation elf-assembly The FG signal is a measure for the amount of surface bonded groups in a non-centrosymmetric environment: Different time scales (including long-time effects) in solution-growth of docosanethiol (H (CH 2 ) 21 -CH 3 ) on Au, derived from vibrational mode intensity (detected by FG) as function of immersion time. v as (CH 2 ) 1. First step is the chemisorption of sulfur head group, i.e., signal similar to that of the previous Langmuir isotherm. (strong increase of v as ) - FAT 2. econd phase corresponds to a straightening of chains, represented by decrease of the d - mode (antisymmetric CH 2 becomes invisible). CH 2 group adjacent to end group already exhibits slower ordering (represented by d tch2 + mode; symmetric). v s (CH 3 ) 3-4 TIME LWER 3. End of chain shows slowest ordering, as evidenced by evolution of d + tch2 mode of end groups (increase of symmetric; CH 3 and CH 2 ). v s (CH 2 ) TIME LWER Himmelhaus, Eisert, Buck, Grunze, J. Phys. Chem. B = 17 h

ulfur atom The bonding is NT with a single gold atom, but with multiple gold atoms at

13 AMs from Thiols Chemistry A side-view of the p-bonding orbital between the CH3 adsorbate and the Au(111) surface in the hollow site position. ulfur atom The bonding is NT with a single gold atom, but with multiple gold atoms at the surface. A gold atom in the second layer, directly underneath the hollow site, participates in the bonding. CH3

14 Chemisorption of thiols on Au(111) give Au + thiolate (R - ) species probably by: 0 n AMs from Thiols Chemistry [ - 2+ ] - + R Au H Aun R Au Aun H2 Au + RH + The adsorbing species is the thiolate. The heat of adsorption is ~28 kcal/mol. The homolytic surface- bond strength is ~44 kcal/mol. The proton leaves as H 2 however even in 3D AMs on nanoparticles with high surface area/mass no H 2 could be detected until 2 1

AMs from Thiols Chemistry H 2 found! L. Kankate, A. Turchanin, A. Gölzhäuser, n the release of hydrogen from the -H groups in the formation of self-assembled monolayers of thiols.

15 AMs from Thiols Chemistry H 2 found! L. Kankate, A. Turchanin, A. Gölzhäuser, n the release of hydrogen from the -H groups in the formation of self-assembled monolayers of thiols. Langmuir 2009, 25, As determined by XP, A of thiols lead to a partial reduction of a nitro group to amine, while adsorption of the analogue disulfide compound did not show signs of reduction. The reduction of the nitro headgroups is accounted to the released H *.

16 Alkanethiols tand-up Phase a) Au (CH 2 ) n-x A schematic model of the ( 3 3)R30 o overlayer structure formed by alkanethiolate AMs on Au(111). This structure places the thiols in distance of 4.99 Å, which results in their tilt to reestablish the vdw interchain interactions. The angle can be deduced using FTIR spectroscopy. b) ca Å X 2-3 nm (CH 2 ) n Au

17 Alkane Mesogen: urface Reconstruction Advancing and receding water contact angles on AMs of HUT [H(CH 2 ) 11 H] AMs on Au(111) time Θ adv Δθ 15 Θ re Highly polar surfaces of AMs of n-alkylthiols undergo surface reconstruction when exposed to air to minimize the surface free energy. Evans, R. harma, A. Ulman Langmuir 1991, 7, 156.

18 Various types of AMs Different Mesogens In e.g. alkane thiols or silanes the ordering ('crystallization') lateral stability is provided by vdw interactions between the methylene groups. Further stability can be introduced by e.g. dipoldipol interactions or ππ-interactions of aromatic mesogenes: (CH 2 ) n : with n> 10 stable AMs are formed (Ø) n : with n 2 stable AMs are formed 2 C F 2 C F 2 C F 3 C F 2 X a.s.f... C F 2 2 H H H H H H H

19 Various types of AMs Different Mesogens δ+ δ- δ- C C 109 in-plane dipole moment of the sulfone group: 1.6 D : 1.79 Å C H: 1.1 Å Introduction of free-volume? Ulman et al. Langmuir 1991

20 elf-assembled Monolayers of RIGID Biphenyl Thiols Why BIPHENYL? Rigid system biphenyl is an effective mesogenic moiety for A conjugated system Ø different reactivity of thiol group Ø different molecular dipole moment X CH 3 DIFFERENT A BEHAVIR X = 23 different functionalities: e.g. H,-CH 3,-CF 3,-H, -H, -CH 3,-F,-Cl,-Br,-I, -N 2,-NH 2,-CCH 3,-CR, -CN H

21 elf-assembled Monolayers Alkanethiols vs. Biphenylthiols 1 cosθ CH 3 H CH 3 H Θ adv Θ red 0.5 3days old H I H II fresh 0 H χ surface hydrophobic hydrophilic H DDT H HUT Ø mall hysteresis uniform layer no surface reorientation Ø Linear relationship ideal mixture at the surface Ø table θ for weeks no surface reconstruction Ø Higher absolute values polarizable system J. F. Kang, A. Ulman,. Liao, R. Jordan, G. Yang, G.-Y. Liu, Langmuir 2001, 17, 95.

22 elf-assembled Monolayers Alkanethiols vs. Biphenylthiols ca. 5 Ψ X Θ ca. 30 X nm 2-3 nm (CH 2 ) n Au J. F. Kang, A. Ulman,. Liao, R. Jordan, G. Yang, and G. Y. Liu, Langmuir, 2001, 17, 95.

23 Various types of AMs Alkylsilanes AM formation of tetradecyltrichlorosilane (TT, C 14 H 29 icl 3 ) on silicon at 20 o C and 30% relative humidity. Contact angle: Water Cosθ Hexadecane i/i 2 / 3 i(ch 2 ) 13 CH 3 θ a AM thickness: The calculated thickness is 21.1 Å based on an alltrans configuration. Alkyl chains are perpendicular to the surface. Length Å L calculated t (min)

24 A schematic description of the polysiloxane formed in situ at the monolayer substrate interface. H 2 i 2 Proposed Model by ilberzan et al. : P. ilberzan, L. Leger, D. Ausserre, J. J. Benattar, Langmuir 1991, 7, The fact that the roughness is lower for silanated wafers is compatiblew ith a vision in which the layer is not linked to the surface by all the individual molecules but, rather, forms a "net" where molecules are linked to each other; this net would be bonded to the surface by only a few bonds. The equatorial i- bonds that can be connected either to another polysiloxane chain or to the surface

25 Lateral Patterning of AMs material deposition "printing" 1 mm 500 nm (50nm) material modification "lithography" exposure through masks: photons, electrons, ions 100 µm direct writing: 10 nm e-beam proximal probe (TM / AFM) 100 nm 0.1 nm

26 Mixed AMs Patterned AMs : µcp Ag i/i 2 EM images of test patterns on layers of silver (A, B, C: 50 nm thick; D: 200 nm thick) that were fabricated by µcp with HDT followed by chemical etching in an aqueous solution of ferricyanide (Whitesides et al. 1998).

The surface was printed in HDT; the remaining regions were then derivatized with H(CH 2 ) 15 CH by immersing the patterned sample in a solution containing the second thiol.

27 µcp C12-H Adsorption Comparison of TM images of AMs of dodecanethiol (DDT) on Au(111) formed by µcp and by adsorption from solution. µcp: a solution of DDT in ethanol as the "ink" ; t = 10 s Adsorption: equilibrated with a solution of DDT in ethanol for about 18 h. LFM. The surface was printed in HDT; the remaining regions were then derivatized with H(CH 2 ) 15 CH by immersing the patterned sample in a solution containing the second thiol. Relatively high frictional forces between the probe and the surface were detected in regions covered with a CH- terminated AM (light), and relatively low frictional forces were measured over regions covered with a CH 3 - terminated AM (dark).

Patterned AMs : canning Probe Lithography Nanoshaving

Electron-induced evaporation Dip-pen 160 nm 2

shaved away from a 50nm 2 square G.Y. Liu et al. Acc.

2000 C 18 nanoislands (3x5 and 50x50 nm 2 ) in the

28 Patterned AMs : canning Probe Lithography Nanoshaving Nanografting Electron-induced diffusion Electron-induced evaporation Dip-pen 160 nm 2 topographic images of C 18 / Au(111) with thiols shaved away from a 50nm 2 square G.Y. Liu et al. Acc. Chem. Res C 18 nanoislands (3x5 and 50x50 nm 2 ) in the matrix of a C 10 monolayer using nanografting. (B), the C 18 islands are 8.8 Å higher than the surrounding C 10 monolayer Consecutive position of C 16 dots (15 nm)on Au(111) LFM-image. C.A. Mirkin et al. Chem. Phys. Chem. 2001

a-c) 100 nm lines after electon exposure (a) and immobilization of TFAA (b) and PFBA (c).

29 Mixed AMs Patterned AMs : Chemical Lithography N 2 N 2 N 2 NH 2 NH 2 NH 2 e -trahl Au Au AFM Images and averaged height profiles of lines that were written with a focused electron beam into a nitrobiphenylthiol monolayer. a-c) 100 nm lines after electon exposure (a) and immobilization of TFAA (b) and PFBA (c). d-f) 20 nm lines after electon exposure (d) and immobilization of TFAA (e) and PFBA (f). Lateral force AFM image of a NBT AM/Au after e -beam exposure (10000 µc/cm 2 at 300 ev) through a 150 nm stencil mask. M. Grunze et al. urf. ci M. Grunze et al. Adv. Mat. 2001

30 AMs: Tailored urfaces as Initiator ystems for urface-initiated Polymerization (IP) I I I I I I I I I I I I I I I I homogeneous AMs I I I I I I I I I I substrate I Adsorption I / µcp/ CL mixed AMs I I I I I I I I I I patterned AMs IP I I I I I I I I 2D/3D gradients I I I I I I I I I I patterned AMs Control of: Chemistry Reaction sites Grafting density Heterogeniety

31 Thank you! to be continued with... PART II Polymer Brushes

Lecture 3. Self-assembled Monolayers (SAM)

10.524 Lecture 3. Self-assembled Monolayers (SAM) Instructor: Prof. Zhiyong Gu (Chemical Engineering & UML CHN/NCOE Nanomanufacturing Center) Lecture 3: Self-assembled Monolayers (SAMs) Table of Contents