In Situ Examination of the Structure of Model Reversed-Phase Chromatographic Interfaces by Sum-Frequency Generation Spectroscopy

Abstract

Model reversed-phase chromatographic interfacial systems were examined using sum-frequency generation (SFG) spectroscopy to study the effect of solvent on the structure and conformation of the stationary phase. Monolayers formed from mixed C 18 and C 1 alkysilanes (both polymeric octadecyltrichlorosilane-methyl trichlorosilane mixed monolayers and monomeric octadecyldimethylchlorosilane-trimethylchlorosilane mixed monolayers) on fused silica were examined in contact with air, deuterated acetonitrile (CD 3 CN), D 2 O, and mixtures of CD 3 CN and D 2 O. When mixed composition (C 18 and C 1 ) monolayers were examined, significant disorder was observed in the alkyl chains for all solvents examined at intermediate alkyl chain densities for the polymeric materials, and at all chain densities for the monomeric materials. Maximum order for intermediate polymeric chain densities was found to occur in contact with 40-50 vol % D 2 O solutions. These results indicate that solvent microheterogeneity has a large effect on alkyl chain order.

Tuning the Molecular Order of C60 Functionalized Phosphonic Acid Monolayers

“…Interfaces, however, break the prevailing bulk symmetry of these materials and give rise to additional nonzero χ (2) components. Thus, SFG is a powerful technique for studies of interfaces, their molecular composition, and structure. , SFG has been applied extensively to study the structure of SAMs on metal and oxide substrates. − However, all applications of SFG at mixed SAMs on solid substrates were limited to the CH/OH region which impedes spectral discrimination of the two species. − This issue is resolved by using fluorinated alkyl chains which facilitate independent determination of surface coverage and molecular ordering for the two species.…”

Influence of the linkage type between the polymer backbone and side groups on the surface segregation of methyl groups during film formation

“…The strength of the methyl symmetric stretch mode in the ssp spectra increases as the average tilt angle of the methyl groups decreases and also as the number density of the methyl groups in the adsorbed layer increases. [59][60][61] The changes observed in the intensity of this peak can be interpreted in terms of the changes of the segregation amount accompanied by the orientation changes of the side chain methyl groups of the polymers. As seen from Fig.…”

Encapsulation of PEG-modified Myoglobin in Hydrophobic Mesoporous Silica as Studied by Optical Waveguide Spectroscopy

“…In this case, the straight chain conformation would be maintained even if the pores are filled with water, 42,43 and the average thickness of the ODS layer has been reported as about 2 nm. 41 Accordingly, considering the diameter of the silica mesopore (ca.…”

“…On the other hand, for ODS-MS1 with a less densely packed ODS layer, the ODS-chains could be significantly disordered. 42,43 Due to the disordered structure of the octadecyl-chain, it seems that the pores in ODS-MS1 have enough space for the adsorption and diffusion of PEG-Mb into them.…”