THERMAL-EXPANSION TENSORS OF PENTAERYTHRITOL (PE) AND PENTAGLYCERIN (PG) AND COMPOSITIONAL DEFORMATION TENSOR OF PG1-XPEX MOLECULAR ALLOYS

The anisotropy of the molecular interactions in the low-temperature phase (body-centered tetragonal) of pentaerythritol [PE, 2,2-bis(hydroxymethyl)-1,3-propanediol, C(CH2OH)4] and pentaglycerin [PG, 2-hydroxymethyl-2-methyl-1,3-propanediol, (CH3)C(CH2OH)3] has been made evident by means of the thermal-expansion tensor calculated from room temperature to 433 K for PE and from room temperature to 353 K for PG. The weakest expansion has been found in the (00l) planes, where the molecules are linked by hydrogen bonds; the strongest has been found in the [001] direction, where van der Waals interactions play a dominant part. In addition, the compositional deformation tensor as a function of the composition in PG(1-x)PE(x), molecular alloys has been calculated at two temperatures (293 and 348 K). On the basis of the structural characteristics of the constituent pure substances, the directions of the strongest and weakest deformations - compression in the [001] direction and expansion in the (00l) planes, respectively - have been explained in terms of the substitution of PE guest molecules in the PG host structure.