Alkyl tail

Figure Bl.19.8. (a) STM image (5.7 mu x 5.7 mu) of 10-alkylcyanobiphenyl on graphite (b) model showing the packing of the molecules. The shaded and unshaded segments represent the alkyl tails and the cyanobiphenyl head groups, respectively. (Taken from [38], figure 2.)...

The compound in Fig. 3b exhibits two smectic phases (Sm and Sm ) in addition to nematic, whereas the compound in Fig. 3a exhibits only a nematic phase. The substitution of an alkoxy for an alkyl tail is known to shift phase transition temperatures considerably. In the cyano-biphenyls (Fig. 4), substitution of an alkoxy tail raises the melting point from 24 to 48 °C and T from 35 to 68 °C [22]. 

Fig. 4a,b. The effect of substitution of an alkoxy tail for an alkyl tail in cyanobiphenyls a transition sequence is K kf N b transition sequence is K N /... 

These compounds present a new class of LC molecules having a perfluoroalkyl tail on one end and an ordinary alkyl tail on the other. Earlier studies of several groups indicated that terminal fluorination considerably extends the temperature range of the smectic phase [81]. Moreover, mesogens incorporating... 

Fig. 2. Schematic representation of the supramolecular cylinders of the dendrimer derived from macromonomer 9 (R=OC12H25,n=3) in the Qh mesophase atop view of a cylinder containing six repeat units in a stratum with the alkyl tails melted to match the average column radius determined by X-ray scattering experiments b side view of a cylinder containing 30 repeat units of the polymer assembled with melted alkyl tails. Reproduced with permission from references 5 a...

Preformed gold nanoparticles have been used as the top electrode for interrogating SAMs of dithiols diluted within an alkylthiol matrix. The alkyl tails of the alkylthiols do not coordinate to the nanoparticles, but a dithiol s second SH group, sticking above the alkyl level, can bond to the nanoparticle, which is then contacted with an Au-coated AFM probe [42]. 

The first process is due to Schottky barriers [30], which are electrical dipole moments that form at the metal I molecule interfaces, as discussed above [34,40]. The second process arises if the electrically-active portion of the molecule is placed asymmetrically within the metal I molecule I metal sandwich. This geometry is common, because a long alkyl tail is often needed to make the molecule amphiphilic so that it will form well-ordered Langmuir-Blodgett monolayers [76-78]. 

Going from la to Ilia, the collapse pressure (prrc) decreases because the increase in dendron generation contributes hydrophobicity to the amphiphile, resulting in a poorer hydrophobic balance. The series having aU three alkyl tails emanating from a single carbon atom (Ib-VIb) exhibits significantly different behavior compared with the other two series in which the alkyl chains emanate from different carbon atoms (la/b-Vla/c). Whereas the a and c series exhibit linear increases in molecular area with more alkyl chains, the b series reveals not only nonlinear increases in area... 

As expected from the relation of HLD with the free energy of transfer from oil to water, the removal of one carbon atom to the alkyl tail of the surfactant would make it easier for the surfactant to be transferred, and would hence tend to reduce the value of HLD, through a reduction of the characteristic parameter a or a. The experience shows in effect that [23] ... 

Figure 12. (a) Macrocyclic resorcinol tetramer 8 has a rigid bowl shaped conformation with the long alkyl tails in an all-axial and all-c/s configuration, (b) Model of K flow in a hypothetical bimolecular ion channel composed of tail-tail dimer of 8. The ion passes through the inner pore of macrocyclic resorcinol unit which acts as a selectivity filter and then to the area formed by the loose assembly of long alkyls. ... 

Figure 8.6 shows some data measured for benzene solubilized in hexadecyl pyridinium chloride. The abscissa in the figure shows the extent of solubilization expressed as moles of solubilizate per mole of surfactant. The ordinate values show shifts in the resonance frequencies from water taken as an internal standard. Shifts of peaks arising from protons in the pyridinium ring, in benzene, and in methylene groups in the alkyl tail are shown versus the extent of solubilization. 

The enhancement of rate qualitatively follows Michaelis-Menton kinetics, with both the initial slope and the final plateau increasing with increasing length of the alkyl tails of the surfactant. 

QAS QAS with ether spacer group between quaternary N atom and long alkyl tail Goldschmidt (Milbum and Sitz, 2002)... 

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