The conformations of polymers adsorbed onto a substrate is controlled by changes in interaction energies and entropy upon adsorption.

1. CONFIGURATIONAL MODEL OF POLYMER ADSORPTION AND ADSORPTION OF THIOL DERIVATIVES ON GOLD Maxwell ’ s demon

2. Configurations of tetramer and dimer adsorbed at interface. The solvent is a monomer. All segments are assigned positions in a close-packed hexagonal lattice. 1 2 3 4 5 54 36 48 36 24 6 7 8 9 10 11 24 36 24 36 27 36 12 13 14 15 16 17 48 36 36 24 36 27 1 2 3 5 3 3 config ω config ω config ω J. Bladon, et al, J. Colloid & InterfaceSci., 52 , 14 (1975)

3. Statistical Thermodynamics Used to Calculate Equilibrium Adsorption State equations for free energy, Chemical potential of polymer in bulk solution and at or near surface,

4. XA = - 4 kcal/mol XB = XC = 0 EAA = EBB = ECC = EAB = EBC = EAC = 0 CASE 1 A B B B C

5. J. Bladon, et al, J. Colloid & InterfaceSci., 52 , 14 (1975) Initial Slope = is the ratio of all possible configurations with the end group at the interface to all the configurations in the bulk. Adsorption curve dimer tetramer Adsorption curve for each configuration of the tetramer -XA / kNT

6. CASE 1, con ’t… XA = - 4 kcal/mol All other interactions are zero ADSORBATE MOLECULES IN THE INITIAL SLOPE WILL CONSIST OF ALL NINE CONFIGURATIONS WITH THE END GROUP IN CONTACT WITH THE SURFACE

7. # SEGMENTS IN POLYMER is the ratio of all possible configurations at the interface to the configurations in the bulk and R is the number of segments in the polymer J. Bladon, et al, J. Colloid & InterfaceSci., 52 , 14 (1975)

9. CASE 1, con ’t… XA = - 4 kcal/mol All other interactions are zero THE “WEAK” PLATEAU WILL BE A MIXTURE OF THE FOLLOWING CONFIGURATIONS:

10. XA = - 4 kcal/mol EBC = +1 kcal/mol (POOR SOLVENT) CASE 2 A B B B C

11. THE INITIAL SLOPE: THE PLATEAU: HALF WAY UP THE SLOPE:

14. physisorbed thiol group chemisorbed sulfur Temperature Programmed Desorption (TPD) S.M.Wetterer, Thesis, Princeton Univ., (1998)

15. 10 min 15 min 60 min 0 min physisorbed thiol group chemisorbed sulfur Time held at 208 o K

16. TYPICAL TIME FOR MONOLAYER COVERAGE IS ~1 MIN. DURING THIS TIME, 45-65% OF THE ADSORBATE IS SKATING AROUND THE SURFACE IN THE PHYSISORBED STATE

17. SULFUR-GOLD SUBSTRATE INTERACTION ENERGIES (XA) S.M.Wetterer, Thesis, Princeton Univ., (1998) n-ALKYLTHIOLS DIETHYLSULFIDE DIBUTYLSULFIDE THIOPHENE XA PHYS = 126 kcal/mol XA CHEM = 33 kcal/mol XA PHYS = 24 XACHEM = NONE steric hindrance

18. DIALKYLDISULFIDE XA CHEM = 124 XA PHYS = NONE DIMERIZE ON CONTACT TO PHYSISORBED n-ALKYLSULFIDES Steric hindrance decreases chemisorption strength 2-PROPANETHIOL T-BUTANETHIOL NEOPENTANETHIOL XA CHEM = 107 XA PHYS = 33 XA CHEM = 107 XA PHYS = 33 XA CHEM = 126 XA PHYS = 33

19. CHELATING DITHIOL SHOULD ADSORB BETTER FOR TWO REASONS: GOOD AROMATIC INTERACTIONS AND ENTROPY LOSS IS LESS. N.Garg, T.Lee, Langmuir, 14 , 3815 (1998) ASYMMETRIC FUNCTIONALIZATION WITHOUT FEAR OF “ISLANDS”

20. SPIROALKANEDITHIOL SHOULD ADSORB BETTER THAN TWO n-ALKYLTHIOLS BECAUSE ENTROPY LOSS IS LESS Y. Shon, S. Lee, S. Perry, T. Lee, J. Amer. Chem. Soc., 122 , 1278, (2000) ASYMMETRIC FUNCTIONALIZATION WITHOUT FEAR OF “ISLANDS”

21. THE SECRET TO SELF ASSEMBLED MONOLAYERS

22. Maxwell ’ s demon I know you guys are only physisorbed, but you ’ll like it better standing up!