Raman Study of the Conformational Characteristics of Chain Molecules under High Pressure
As part of a continuing program to study the properties of lubricants and polymers, we have undertaken an investigation of the conformational properties of linear alkanes and polymers as functions of temperature and pressure. We have successfully obtained the Raman spectra of these materials over a range of 1 to 20 kbar from a gasketed diamond-anvil cell while calibrating the pressure with the ruby fluorescence technique . The conformation of heptane (C7H34) and hexadecane (C16H34) have been monitored by the Observation of conformationally sensitive Raman bands. Our data indicate that heptane becomes more “kinked” (more gauche bonds) as a function of pressure. This result was surprising to us at first, since at sufficiently high pressure heptane freezes in the unkinked, all-trans conformation. We have developed a theory, based on excluded volume considerations, which is consistent with these observations.
KeywordsChain Molecule Linear Alkane Conformational Characteristic Gauche Conformation Room Pressure
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