Study Of Intermolecular Interactions In Micelles Under High Pressure

Pressure, temperature, composition are three parameter for substance. The change of temperature and composition is the usual method to study the characters and improve the performance. We can obtain new material, which cannot be prepared atmosphere by studying the state of sample at high pressure. The essential effect of pressure is to reduce interatomic distance, which leads to modification in lattice constants of crystalline material as well as to change in atomic positions within crystallographic cells. In general reductions of lattice spacing and force constants between atoms induce modifications in the band structures of solids and thus in electronic properties and optical properties. Thus the physical and chemical characters of substances at high pressure are quite abundant.According to Jean-Marie Lehn, who is one of the founders of this field of science, supramolecular chemistry is'chemistry beyond the molecule'. Supramolecular chemistry is concerned, in particular, with the following problems: investigations of the nature and detailed characteristics of intermolecular interactions; the design of supramolecular devices and simulation of biochemical processes. High pressure studies can help in solving all these various problems as applied to diverse supramolecular systems. Micelles are prototype of biological molecules, which exhibit a rich structural polymorphism, depending on their molecular structure and environmental conditions. Hydrostatic pressure has been used as a physical parameter for studying the stability of micelles, because high pressure is an important feature of certain natural membrane environments.In this paper, we have carried out a comparative study of the hydrophobic interaction andπ-πinteraction in micelles, the main work is done by Raman spectrum and synchrotron radiation X-ray diffraction and infrared spectrum to achieve the in-situ high pressure experiment, obtaining the results thereinafter:1. We use high-pressure Raman spectroscopy with DAC for the first time to investigate pressure-induced phase transition in typical cationic surfactant CTAB-micellar solution. The coagelization pressure of 0.3 mol/L CTAB is observed at 0.64 GPa on increasing pressure, whereas the micellarization pressure is observed at 0.47 GPa on decreasing pressure. This phase transition has a pressure hysteresis, thus exhibiting first-order phase transition properties. Further experimental results show that, the structure of the coagel is similar to that of the CTAB crystal, however, the interchain distance is slightly larger in the coagel phase.2. The in-situ synchrotron x-ray diffraction and far-IR spectra of DPP-11 and its micelles in aqueous solution have been studied. Although X-ray studies show no indication of structure changes, however, theπ-πinteractions become stronger with increasing pressure which can be deduced from far-IR spectra. A new far-IR absorption peak is found to be related to theπ-conjugated aromatic dyes in DPP-11 micelles. Upon increasing pressure, the peak shifted toward higher wavenumber region due to strongerπ-πinteractions.In summary, pressure is an efficient tool for influencing relatively weak intermolecular interactions and conformations of molecules in supramolecular assemblies. Studies of high pressure on supramolecular assemblies can yield a wealth of enlightening new information on their structure and phase behavior.