Self-assembly of a dialkylurea gelator in organic solvents in the presence of centrifugal and shearing forces.
A novel dialkylurea gelator, 1-methyl-2,4-bis(N(')-octadecaneureido)benzene (designated as MBOB) was synthesized, which can turn some organic solvents into organogels at extremely low concentrations (<2 wt%). The (1)H NMR spectra of MBOB in solution (110 degrees C) and in the gel state (30 degrees C) indicate that intermolecular hydrogen bonding is the driving force for the self-assembly of MBOB. In the process of the self-assembly of MBOB, orientation of MBOB aggregates occurs under the influence of external fields, such as a centrifugal force and shearing force fields. The minimum gelation concentrations of MBOB in organic solvents under a centrifugal force field were significantly higher than those in the absence of a centrifugal force field, indicating a significant effect of the external field on the self-assembly of MBOB. Field emission scanning electron microscopy (FE-SEM) provided evidence for a significantly phase transition of the MBOB aggregates from an amorphous state in the absence of the external field to an oriented state under conditions of a centrifugal or shearing force during the gelation process. A self-assembled structure of MBOB is proposed based upon an X-ray diffraction (XRD) analysis and a molecular simulation. DSC analysis of the organogels indicates that the phase transition temperature increased from 58.5 degrees C in the absence of the external field to 63.3 degrees C under a centrifugal force field and 62.2 degrees C under a shearing force field. The enthalpy of the phase transition decreased from 3.1 J/g in the absence of an external field to 2.6 J/g under a centrifugal force field and 2.7 J/g under a shearing force field.
Department of Chemistry, Huazhong University of Science and Technology, Wuhan 430074, China.
Yun
Y
Xiong
Qingyao
Q
Liu
Hong
H
Wang
Yajiang
Y
Yang