1. AFM Studies of High Generation PAMAM Dendrimers at the Liquid/Solid Interface Structural Distortion of Isolated Features and Aggregate Formation

2. Polyamidoamine (PAMAM) Dendrimers # amines # amines 3 o 1 o G21416 G46264 G6254256... G1040944096 pKa 3-67-9 G2 29 Å G4 45 Å G6 67 Å

3. Polyamidoamine (PAMAM) Dendrimers N N O NH H 2 N G=0 O H N H 2 N 1 o O N H N O HN N 3 o 3 o ( CH2 - CH2 - CO - NH - CH2 - CH2 - N ) Repeating (monomer) unit : 3 o O O N H N H NH 2 NH 2 G=1 1 o 1 o 3 o O O NH NH NH 2 NH 2 1 o 1 o pKa = 7-9 pKa = 3-6 N N

4. Structure & Applications G7 PAMAM Dendrimer Ordered Dendrimer Film High density of functional groups, branched structure, spherical shape for gen. ≥ 5, empty “container” space (micelle mimic), size: diameter ~10 nm for G9 Many transport applications, catalysis / reaction vessels, molecular antennae Self-assembly at interface Useful for chemical sensing devices, modifies size & shape of dendrimers

5. Focus: dried adsorbate on hydrophilic surfaces Focus: dried adsorbate on hydrophilic surfaces Amine-terminated dendrimers readily adsorb Amine-terminated dendrimers readily adsorb Observed single/packed dendrimers & smooth films Observed single/packed dendrimers & smooth films Compression along surface normal & lateral spreading Compression along surface normal & lateral spreading (G5: d = 15nm, h = 1nm / G10: d = 25nm, h = 5nm) (G5: d = 15nm, h = 1nm / G10: d = 25nm, h = 5nm) Surface hydrophobicity & neighboring dendrimers Surface hydrophobicity & neighboring dendrimers lessen dendrimer distortion lessen dendrimer distortion Previous Studies Evolution of conditions during drying process ? Evolution of conditions during drying process ? Influence of residual water (& capillary forces) ? Influence of residual water (& capillary forces) ?  Investigate adsorption in situ (in the presence of solvent)

6. G7 PAMAM at H2O/HOPG interface (pH~7): Extensive Aggregation Possible 100  g/ml 10  g/ml 1  g/ml 100 ng/ml 1 ng/ml 0.01 ng/ml (all images 10  m scan size)

7. G9 PAMAM, 1  g/ml, on HOPG pH = 2.2, 10  m scan size Moderate Accumulation at Step Edges Domain Formation pH = 10.7, 10  m scan size Other Characteristics of Dendrimer Aggregation

8. G9 PAMAM Dendrimers in MeOH Section analysis of small features Many features with h < 5 nm, d < 20 nm Single dendrimers, small size Very different than in H 2 O …

9. High Polarity & Autoprotolysis of Water: Highly Charged PAMAM Dendrimers Autoprotolysis Const. Dielectric Const. H 2 O 10 -14 78.5 MeOH 10 -17 32.6 EtOH 10 -19 24.3 BuOH 10 -21 17.1 n-Alkanes << 10 -21 ~ 2 Decreasing polarity & protonation

10. Dendrimer Generation QuartzCrystal Kang, Durning, Rahman PAMAM Dendrimers on Gold Surface Ethanol Water Adsorbed Mass at liquid/solid Interface from QCM Measurements More evidence that water is special as dendrimer solvent …

11. Solvent Influence on Aggregation David Knapp’s Study of PAMAM Dendrimers in BuOH Confirms absence of aggregates in less polar solvents Confirms absence of aggregates in less polar solvents Stronger adsorption on mica than HOPG Stronger adsorption on mica than HOPG [see also Macromol. Symp. 167, 257 (2001)] [see also Macromol. Symp. 167, 257 (2001)] Determination of single dendrimer sizes in situ challenging Determination of single dendrimer sizes in situ challenging (possibly less dendr. distortion in less polar solvents) (possibly less dendr. distortion in less polar solvents) Doubts about aggregation in aqueous solvent … Doubts about aggregation in aqueous solvent …

12. Mica, 5  m, pH~7, 0.05% NaN 3 Less Aggregation on Hydrophilic Substrates Azide (bacteriostatic) & pH made no difference for aggregation More coverage at lower pH Mica, 1.5  m, pH 3.3, no NaN 3 G9 PAMAM on mica: mostly isolated dendrimers

13. HOPG, 10  m, pH~7, no LiCl Web-Formation on Hydrophobic Substrates Web-formation: signature of loose surface bonding ? Consistent with dragging effects in small scale scans & with studies of dried films [Macromol. Symp. 167, 257 (2001)] LiCl (“water structure breaker”) has no effect HOPG, 5  m, pH~7, 0.05M LiCl G9 PAMAM on HOPG without Aggregates

14. Aggregates & Webs Web-formation & aggregates up to d~100nm Acidification may promote aggregation G5 PAMAM on HOPG: More aggregation than G9 HOPG, 5  m, pH~7 HOPG, 1  m, pH~7 HOPG, 2  m, pH 2.0

15. In Situ Isolated Dendrimers In dried films: w~20nm Governed by H 2 O surface tension ? G9 PAMAM on Mica w~11–13nmh~4-5nm

16. In Situ Isolated Dendrimers Acidification may increase dendrimer volume G9 PAMAM on Mica, pH 3.3 w~16-18nmh~6nm