In this work we provide a systematic scanning tunneling microscopy (STM) study on the self-assembling and mixing behavior of Arylene Ethynylene Macrocycles (AEMs) containing 1,4-phenylene, 1,4-naphthylene or 9,10-anthrylene substituents at the solid/liquid interface. The effect of bulky substituents on the self-assembly structure was investigated and we found that 1,4-phenylene ethynylene macrocycle (AEM-B) and 1,4-naphthylene ethynylene macrocycle (AEM-N) form four and three different patterns at the 1,2,4-trichloride benzene (TCB)/graphite interface, respectively, and a significant concentration effect was observed for both molecules. 9,10-anthrylene ethynylene macrocycle (AEM-A) only forms a filled honeycomb structure at relatively high concentrations. The effect of bulky substituents was attributed to the steric hindrance, which hinders full interdigitation of alkoxy chains. The mixing behavior of binary mixtures of arylene ethynylene macrocycles was also investigated at the TCB/HOPG interface. The results demonstrate that the steric hindrance brought by the bulky groups does not enable sufficient recognition between identical molecules at the interface and random mixing was observed for binary mixtures of AEM-B and AEM-N. The mixing behavior of AEMs could also be predicted by the parameter called the 2D isomorphism coefficient.
This study investigated the influence of carbon nanotubes (CNTs) on the transport and retention behaviors of bacteria (E. coli) in packed porous media at both low and high ionic strength in NaCl and CaCl2 solutions. At low ionic strengths (5 mM NaCl and 0.3 mM CaCl2), both breakthrough curves and retained profiles of bacteria with CNTs (both 5 and 10 mg L-1) were equivalent to those without CNTs, indicating the presence of CNTs did not affect the transport and retention of E. coli at low ionic strengths. The results were supported by those from cell characterization tests (i.e., viability, surface properties, sizes), which showed no significant difference between with and without CNTs. In contrast, breakthrough curves of bacteria with CNTs were lower than those without CNTs at high ionic strengths (25 mM NaCl and 1.2 mM CaCl2), suggesting that the presence of CNTs decreased cell transport at high ionic strengths. The enhanced bacterial deposition in the presence of CNTs was mainly observed at segments near the column inlet, leading to much steeper retained profiles relative to those without CNTs. Additional transport experiments conducted with sand columns predeposited with CNTs revealed that the codeposition of bacteria with CNTs, as well as the deposition of the cell-CNTs cluster formed in cell suspension due to cell bridging effect, largely contributed to the increased deposition of bacteria at high ionic strengths in porous media.