Influence of Anions and Alkyl Chain Lengths ofN-Alkyl-n-(R)-12-Hydroxyoctadecyl Ammonium Salts on Their Hydrogels and Organogels

Abstract

The self-assembly and gelating characteristics of a set of N-alkyl-(R)-12-hydroxyoctadecylammonium salts (n-HOA-X, where n = 0-6, 18 is the length of the alkyl chain on nitrogen, X = Cl, n = 3, and X = Br, NO3, and BF4) are described. Solid-solid phase transitions were observed for powders of n-HOA-Cl, and orthorhombic-type crystal packing arrangements and lattice spacings were calculated from X-ray diffractograms at 22 °C. The diffractogram of 3-HOA-Br indicates the presence of more than one morph at room temperature, and that of 3-HOA-I corresponds to a lamellar packing arrangement. Differences in the molecular packing arrangements of 3-HOA-X are reflected in their gelation abilities. The melting temperatures (T(gel)) of the hydrogels of 3-HOA-Br are higher than those of 3-HOA-Cl at the same concentrations, and 3-HOA-I failed to gelate any of the investigated liquids. 3-HOA-NO3 gelated only water and CCl4 and 3-HOA-BF4 formed only hydrogels. Plots of changes in conductivities of the 3-HOA-X salts (where X = Cl, Br, NO3 and BF4) as a function of temperature were used to calculate the critical aggregation concentrations (CGCs). Because the CGCs from the 'falling drop' method are nearly the same as those from the conductivity measurements, aggregation, nucleation, and gelation must occur within a very narrow 3-HOA-X concentration range. T(gel) values of 2 wt % 3-HOA-Cl hydrogels (prepared by fast cooling of the sol phase) increased upon adding KCl up to 0.1 M. The effects can be attributed principally to the chloride anion rather than its cation partners. The properties of the hydrogels of 3-HOA-X do not follow the Hofmeister ranking rule. The variations in the counterions afford detailed insight into the behavior of 3-HOA-X in their neat solids and assemblies in gels as well as the processes accompanying gel formation in water and organic liquids.

How do H-bonding interactions control viscoelasticity and thixotropy of molecular gels? Insights from mono-, di- and tri-hydroxymethylated alkanamide gelators

“…Those prepared by the ice-cooling and fast-cooling protocols showed only fibers with ~8-10 μm and ~3-4 μm diameters, respectively. Similar dependencies of SAFIN structures on the mode of gel preparation from sol phases have been observed in other systems 46,[55][56][57].…”

“…Gel-to-sol transition temperatures (T gel ) were determined by the ‗‗falling ball'' method. 46 A 130 mg steel ball was placed gently at the top of the gel and then the tube containing the gel was flame-sealed. The tube was submerged in a thermostatted water bath starting at room temperature and the temperature was raised slowly (0.…”

Self‐assembled fibrillar networks and molecular gels employing 12‐hydroxystearic acid and its isomers and derivatives

“…Some are 'ambidextrous', gelating both water and organic liquids, such as toluene and carbon tetrachloride. [24] The XRD diffractogram of the neat powder of n-HOA-Cl is consistent with an orthorhombic-type crystal packing arrangement; the diffractogram of 3-HOA-Br indicates the presence of more than one morph at room temperature, and that of 3-HOA-I corresponds to a lamellar packing arrangement. 3-HOA-Cl and 3-HOA-Br are ambidextrous, whereas 3-HOA-I failed to gelate any of the liquids investigated.…”

Dicationic organic salts: gelators for ionic liquids

“…Indeed, data previously collected by us using corresponding m-diimidazolium salts shed light on the lack of gelling ability. 42 Analysis of previous reports in the literature evidences that gelation of organic salts, above all monocationic ones, frequently occurs both in organic solvents and water solution, 3,[57][58][59] only very few examples deal with their gelation in IL solution. Among the latter, to the best of our knowledge, the only case in which gelation of monocationic ILs in IL solution has been observed, was reported a few years ago.…”

“…The study of self-assembly by organic salts has been recently the topic of several papers. [1][2][3][4] The main reason for this growing interest seems to lie in the possibility of obtaining them from easy synthesis procedures and in the wide range of available cations and anions that allows a huge number of different combinations. From an applicative point of view, self-assembly of organic salts gives rise to conductive materials that can nd different applications.…”