title: Formation of hierarchical molecular assemblies from poly(oxypropylene)-segmented amido acids under AFM tapping.
abstract: Molecular self-aligning of amphiphilic molecules into bundles with a constant width of 7-13 nm was observed under tapping-mode atomic force microscopy (TM-AFM). The requisite amphiphile, a poly(oxypropylene)-trimellitic amido acid sodium salt, is constituted of a symmetric amido acid structure with potential noncovalent forces of ionic charges, hydrogen bonds, pi-pi aromatic stacking, and hydrophobic interactions for intermolecular interaction. The amphiphiles are able to self-align into orderly hierarchical assemblies after simply being dissolved in water and dried under spin-coated evaporation. Under the TM-AFM tapping process, the bundles increased their length from an initial 20 to 600 nm. A sequential TM-AFM scanning and interval heating process was designed to probe the morphological transformations from the molecular bundles to lengthy strips (nearly micrometer scale) and to columns (with 5-7 nm spacing between the parallel strips). The formation of hierarchical arrays via molecular stretching, aligning, and connecting to each other was simultaneously observed and accelerated under the TM-AFM vibration energy. The molecular self-alignment caused by vibrations is envisioned to be a potential methodology for manipulating molecules into assembled templates, sensors, and optoelectronic devices.
authors.affiliation: Institute of Polymer Science and Engineering, National Taiwan University, Taipei 10617, Taiwan. jianglin@ntu.edu.tw
authors.forename: Jiang-Jen
authors.initials: JJ
authors.lastname: Lin
authors.forename: Wei-Cheng
authors.initials: WC
authors.lastname: Tsai
authors.forename: Chi-He
authors.initials: CH
authors.lastname: Wang
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D002627:Chemistry, Physical / Q000379:methods; D004581:Electronics; D006860:Hydrogen Bonding; D007477:Ions; D046911:Macromolecular Substances; D018625:Microscopy, Atomic Force / Q000379:methods*; D008956:Models, Chemical; D053758:Nanoparticles / Q000737:chemistry; D036103:Nanotechnology / Q000379:methods*; D011126:Polypropylenes / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D000596:Amino Acids; D007477:Ions; D046911:Macromolecular Substances; D011126:Polypropylenes