Gels birefringence

Figure 11.5 Hot stage microscopy of a crosslinked gel in a crystalline monolayer film a) below the melting temperature, b) optical melting point at 128 °C, c) appearance of birefringence after stressing at 135 °C, and d) intact crosslinked gel after cooling to 30 °C. Photographs were provided by E. Garcia-Meitin of The Dow Chemical Company...

At c > 4 mM, the birefringent solution of Pn-2 becomes a self-supporting birefringent gel (Figure 4g). Gelation is associated with onset of fiber... 

Mishima, K. Satoh, K. Ogihara, T. Optical birefringence of phosphatidylcholine liposomes in gel phases. Biochim. Biophys. Acta 1977, 898, 231-238. 

Cohen s studies of electrophoretic mobility of samples of desoxy-ribosenucleic acid isolated in different ways, indicate that the acid may possess either four or five acidic groups per tetranucleotide unit, depending upon the previous treatment. Indeed, according to Bredereck, depolymerization to the pentabasic tetranucleotide state can be induced by treatment of the polymer with dilute sodium hydroxide at 60 , followed by neutralization with acetic acid and two precipitations with alcoholic hydrochloric acid at 10 . This supposed tetranucleotide did not form a gel or exhibit streaming birefringence it had a molecular weight of 1,196 to 1,274. 

The birefringence patterns seen under crossed polars as a gel resin swells are easily denrtonstratcd using a polarizing microscope and ordinary transmitted light. 

---