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Jurnal
Teknologi
Jurnal
Teknologi
Preparation of Papers for Jurnal Teknologi

Author1,a,* Author2,a Author3,b Author4c

a Address1 b Address2 c Address3
*Corresponding author: email@utm.my

Article historyReceived XXXXReceived in revised form XXXXAccepted XXXXGraphical abstract | AbstractOver recent years, there has been an explosive growth of interest in the development of novel gel-phase materials based on small molecules. It has been recognised that an effective gelator should possess functional groups that interact with each other via temporal associative forces. This process leads to the formation of supramolecular polymer-like structures, which then aggregate further, hence gelating the solvent. Supramolecular interactions between building blocks that enable gel formation include hydrogen bonds, interactions, solvatophobic effects and van der Waals forces. Keywords: Dendritic gels; tunable materialsAbstrakOver recent years, there has been an explosive growth of interest in the development of novel gel-phase materials based on small molecules. It has been recognised that an effective gelator should possess functional groups that interact with each other via temporal associative forces. This process leads to the formation of supramolecular polymer-like structures, which then aggregate further, hence gelating the solvent. Supramolecular interactions between building blocks that enable gel formation include hydrogen bonds, interactions, solvatophobic effects and van der Waals forces. Kata kunci: Dendritic gels; tunable materials© 2012 Penerbit UTM Press. All rights reserved. | |

1.0 INTRODUCTION

Over recent years, there has been an explosive growth of interest in the development of novel gel-phase materials based on small molecules.1 It has been recognised that an effective gelator should possess functional groups that interact with each other via temporal associative forces. This process leads to the formation of supramolecular polymer-like structures,2 which then aggregate further, hence gelating the solvent. Supramolecular interactions between building blocks that enable gel formation include hydrogen bonds,  interactions, solvatophobic effects and van der Waals forces.3 Recently, great emphasis has been placed on ways in which the structure of the gelator can control gel formation.4 This has led to the investigation of a wide range of structurally diverse gelators, including those with dendritic structures.5 Combinatorial libraries have also been investigated to enable the discovery of gelators with tunable properties.6
In some cases, which are still relatively rare, two component gelators have been reported.7-9 The two components interact with one another to form a complex, which is then capable of further supramolecular self-assembly leading to gelation. In 2001, we made a preliminary report of the first dendritic two component system for the gelation of organic solvents (Fig. 1).10 This two component system has a number of features which are important for effective gel formation: a) acid-base interactions between components, b) dendritic branching, c) aliphatic diamine spacer chain. This communication illustrates how using two components enhances the tunability of gel-phase materials, and indicates three ways in which macroscopic properties and microstructural features of the gel can be controlled.
As might be expected, the concentration of the gelator system controls the structure and properties of the gel. The solvated gelator network was observed using cryo transmission electron microscopy (cryo TEM) at different concentrations, maintaining a 2:1 (dendrimer:diamine) ratio. At low concentration, thin fibres were present (Fig. 2a), which at higher concentration aggregate and assemble into thick fibre bundles (Fig. 2b). The effect of molar concentration on the thermally reversible gel-sol phase transition (Tgel) was monitored using the tube inversion technique.11 The validity of this approach, and the reversibility of the phase transition, was checked with differential scanning calorimetry. As the molar concentration of the dual components

Table 1 Catalytic alkylation of resorcinol to 4-tert-butyl resorcinol and 4,6-di tert-butyl resorcinol a

Entry | Catalysts | Conversion / % | Product yield / mmol | Selectivity / % | Ratio of Lewis acid to Brönsted acid b | | | | | 4-tert butyl resorcinol | 4,6-di tert-butyl resorcinol | | 1 | MA | 0 | 0 | 0 | 0 | 0 | 2 | 3%Ga-BEA | 38.0 | 15.6 | 97.4 | 2.6 | 0.5 | 3 | 8%Ga-BEA | 54.4 | 21.7 | 95.8 | 4.2 | 0.7 | 4 | 10%Ga-BEA | 59.1 | 23.6 | 100 | 0 | 1.0 | 5 | 25%Ga-BEA | 32.2 | 12.9 | 100 | 0 | 1.5 | 6 | H2SO4 c | 6.5 | 2.6 | 96.0 | 4.0 | contain only Brönsted acid | 7 | MA + H2SO4 d | 6.0 | 2.4 | 96.0 | 4.0 | 1.0 |

a All reactions were carried out at 80 °C for 8 h with resorcinol (40 mmol), MTBE (60 mmol) and catalyst (0.2 g) with vigorous stirring. b The ratio of Lewis acid to Brönsted acid is calculated by using the peak area of peaks at wavenumber of 1540 cm-1 and 1450 cm-1 for Brönsted and Lewis acids, respectively (see Fig. 1). c The amount of H2SO4 is 25 mol. d The MA in a solution containing H2SO4. The amount of MA and H2SO4 are similar as entries 1 and 6, respectively.

was increased, Tgel also increased (Fig. 2c).

2.0 EXPERIMENTAL

In a two-component gel, it is easy to modify the molecular structure of either of the two components.

3.0 RESULTS AND DISCUSSION

Most interestingly, the ratio of the two components has a profound effect on the microscopic structure and macroscopic properties of the gel in toluene.

Figure 1 SEM of 2:1 (dendrimer:diamine) gelation system A in toluene [Dendritic Branch] = 9 mM, [Aliphatic Diamine] = 3 mM

4.0 CONCLUSION

The nature of the aggregates present in dilute solution, below the gelation threshold concentration, was investigated using atomic force microscopy (AFM). When the two components were present in a 2:1 (dendrimer:diamine) ratio, rod like aggregates were observed in the AFM images (Fig. 4a – shows aligned rods running from upper left to lower right). The lngth of these rods was approximately 100 nm, and their diameters were ca. 9 nm (depth ca. 1 nm).
Acknowledgement. We are grateful for the UTM scholarship to Author 1.

References

(1) P. B. Moore, J. Louisnathan. 1967. Science. 156: 1361. (2) A. M. Valentine. 2006. Titanium: Inorganic and Coordination Chemistry. Encyclopedia of Inorganic Chemistry. New York: Wiley. (3) B. Notari. 1993. Catalysis Today. 18: 163. (4) H. Nur, S. Ikeda, B. Ohtani. 2001. J. Catal. 204: 402. (5) V. A. Zeitler, C. A. Brown. 1957. J. Phys. Chem. 61: 1174. (6) G. P. Pez, P. Apgar, R. K. Crissey. 1982. J. Am. Chem. Soc. 104: 482. (7) E. Astorino, J. B. Peri, R. J. Willey, G. Busca. 1996. J. Catal. 157: 482. (8) R. H. Glaser, G. L. Wilkes, C. E. Bronnimann. 1989. J. Non-Cryst. Solids. 113: 73.