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Published online: 10 January 2008 | doi:10.1038/nchina.2008.6

Organogels: Set in sound

Felix Cheung

Introduction

© (2007) Wiley Interscience

Over the past decade, scientists have discovered a wide range of gelling agents (gelators) that can turn organic solvents into gel forms (organogels). Some of these organogels have the ability to switch their properties, such as surface wettability, when subjected to light or heat. Tao Yi, Chunhui Huang and co-workers at Fudan University in Shanghai¹ have developed a novel family of asymmetric cholesterol-based fluorescent gelators for making organogels that set and switch wettability in response to ultrasound.

For comparison, the researchers studied three compounds of the gelator family — each with an aromatic group at one end and a steroidal group at the other linked by different alkyl chains, containing zero, one, or two hydrogen-bond sites. They found that the compound without any hydrogen bonds could not form gels in a range of organic solvents. However, compounds with one and two hydrogen-bond sites could form gels in alcohols and in a variety of organic solvents, respectively, when subjected to ultrasound. The organogels could then be restored to the original solution by heating and subsequent cooling.

The researchers hold the opinion that the ultrasound provides heat and pressure for the organogels, which allows the molecules to form hydrogen bonds with each other and aggregate into helical structures.

The researchers also tried coating glass with organogels and tested the surface wettability with a water droplet. They found an organogel that can make glass surfaces water-attracting when subjected to ultrasound, but extremely water-repelling when heated (see image).

The authors of this work are from:
Department of Chemistry and Laboratory of Advanced Materials, Fudan University, Shanghai, China.

Reference

1. Wu, J.et al. Ultrasound switch and thermal self-repair of morphology and surface wettability in a cholesterol-based self-assembly system. Angew. Chem. Int. Edn doi: 10.1002/anie.200703946 (2007). | Article |