Paving the way for molecular design

SMART POLYMER hydrogels are exciting novel materials, which show the capacity to respond to external stimuli. A soft hydro-gel is a lightly cross linked 3-D polymeric network which can swell by absorbing between 10 - 1000 g of water per gramme of dry get. In response to an external stimulus, certain gels can transform from a fully swollen state to a collapsed state by expelling the absorbed water.

The `intelligent' response of such gels can be utilized in novel applications in diverse areas such as sensors, actuators, chemical and biological separations, membranes, controlled drug delivery as well as some consumer products.

Research at National Chemical Laboratory (NCL), Pune, has been directed towards developing new temperature sensitive hydrogels and novel gel-based products and applications. Developments of new thermo-reversible gels is movitated by the fact that currently there is only one gel, poly (N-isopropyl acrylamide) (PNI-PAM), which is used in most of the applications.

Development of new gels requires thorough understanding of why volume transitions occur. Research carried out by the NCL group has demonstrated for the first time that a fine balance between hydrogen bonding and hydrophobic interactions is responsible for such transitions.

LCST-type volume transitions in smart gels can not be predicted by conventional thermodynamic theories such as the Flory-Huggins theory but by a theory such as LFHB theory, which can account for specific interactions like hydrogen bonding apart from the dispersion interactions.

Smart gels find novel applications in chemical and biological separations. One of the applications that has been identified by NCL deals with separation of the aqueous phase from oil-water dispersions and emulsions. o-Toludine (OTD), which is an important organic intermediate when manufactured, contains 30 per cent by weight of water in it.

Although water is insoluble in OTD, the dispersion is difficult to separate because of almost identical specific gravity of the liquids. Currently, separation is done by the highly energy intensive distillation process.

NCL has developed an alternate, highly efficient, gel-based process, in which majority of the water is absorbed by a fine gel powder dispersed with the liquid in a CSTR. The swollen gel is first filtered and then slightly heated, whereby it regenerates by collapsing.

Another interesting gel-based product developed at NCL is the patented Gelofuel, which retains large quantities of a clean fuel such as methanol or ethanol and releases it slowly for burning.

Teh Gelofuel has been developed for the catering industry as a canned fuel used for keeping food items warm.

A variation of this product is also used for slow release of fragrance in automobile or office interior.

- CSIR NEWS

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