Surface-gauche defects

Au surfaces yielded analogous results. Here the authors foimd gauche defects only in the second layer, while the first represented a flat lying chain [133]. 

Fig. 12.4. Order-disorder transition in Cd arachidate multilayers (A) 20°C - chains are normal to the surface (B) 70°C - chains are tilted randomly (C) 95°C - chains acquired gauche defects and distances between head groups increased (D) 110°C - chains are completely disordered and distances between head groups increased further.

For all the temperatures studied, the simulations lead to crystalline monolayers with strong orientational ordering of the chains in a distorted hexagonal structure even in the absence of an applied pressure. The chains are tilted at an angle of 30° to the surface normal. Most of the gauche defects are found near the ends of the chains, as observed in crystals of n-alkanes, but even at 400 K the average number of gauche conformations per chain is only about one. 

Furthermore, the orientation of the alkyl chain (i.e. hexyl, octyl or decyl chain) on the imidazolium cation was pointing in a nearly perpendicular orientation away from the silica surface with a high degree of conformational order and few gauche defects. In Table 5.6-1 some of the structural parameters determined for the examined ionic liquids are summarized. 

Abstract Vibrational sum-frequency spectroscopy in conjunction with interfacial pressure measurements are used to provide the first direct spectroscopic information about the structure of amphiphillic molecules adsorbed to the interface between two immiscible liquids by total internal reflection sum-frequency vibrational spectroscopy (TIR SFVS). The effect of the ionic head group on the conformational order of sodium dodecyl sulfate (SDS), sodium dodecylsulfonate (DDS), dodecyltrimethylammonium chloride (DTAC), and dodecylamine hydrochloride (DAC) adsorbed at the D2O/CCI4 interface has been examined. In addition, the effect of the length of the alkyl chain on the conformation and orientation of sodium hexylsulfonate (HS), sodium undecylsulfonate (UDS), and sodium dodecylsulfonate (DDS) is also presented. SF vibrational spectra indicate the presence of gauche conformations in the hydrocarbon chains of all the surfactants examined. An increase in the surface coverage results in the reduction of gauche defects in the hydrocarbon chains as determined from the intensity ratio of the methyl to methylene symmetric... 

---