Dependence of the viscosities of some organic aliphatic acids on temperature and molar volume

Abstract

The viscosities of some aliphatic acids were measured in the vicinity of the melting point with a H6ppler viscosimeter. The dependence of the viscosity on the molar volume permitted calculation of the covolume, which is compared to that obtained from structural data.The thermodynamic properties of fusion of organic aliphatic acids from C10 to Cas were dealt with in two preceding notes [1,2], in which two stages were distinguished in the fusion process: prefusion and actual fusion. The prefusion enthalpy for stearic acid represents a value of about 10 70 of the fusion enthalpy; this value decreases from stearic acid to the acids with lower molecular weights. Such an energetic value, according to Barr et al. [3 ], is involved in the rocking motions of the methylene groups in the chain.The fusion entropies of these acids were related to those of the analogous paraffins; the average fusion entropy is slightly lower in the acids, thus revealing, in comparison with the paraffins, a certain inertia induced by the dicarboxylic ring (of the dimer) on the chain.It was hypothesized that such an entropy was working to increase the width of the twisting motion of the methylene groups on the chain. The present note examines the viscosities of these acids in the vicinity of the melting point in an attempt to elucidate the structure of the melt, the viscosity being dependent on the free volume through Batschinski's formula [4], and thus to ascribe the ASfus at a precise variation of structure. Experimental MethodsThe viscosity measurements were made on a H6ppler viscosimeter manufactured by VEB Freital, DDR.The fall tube was on a 10 ~ slope with respect to the vertical of the base plane and was enclosed in a jacket through which circulated warm water, originating from an ultrathermostat with exterior circulation. The viscometer was thermostated to __+0.05 ~ .

Fusion entropy and melt viscosity in some aliphatic hydrocarbons. Relation between fusion entropy and parameterb of the Batchinski equation

“…The viscometric measurements in this note are given to 2~ [1]; hence, an inaccuracy higher than 5~ is to be expected in ASruj(b -Virltr). This relation was also examined on a wide class of ionic compounds, alkali metal halides and nitrates, via data given in the literature [12].…”

“…The chemicals employed: Fluka purissimum octadecane, nonadecane, eicosane and 1-eicosene, were treated as described previously [1].…”

“…Generally b is higher than the intrinsic volume and lower than the molar volume. For the acids [1, 3] a geometrical form of volume b was found, whose packing gives the molar volume approximatively.The hypothesis was put forward that b is generally not the intrinsic volume, but the volume not utilizable for the flux owing to the motions of the molecules, i.e.Therefore, b -Vintr may be a measure of the disorder caused by the motions of the molecules and introduced at the fusion point.In this note a relation between the fusion entropy and V~is is examined for the studied compounds [1][2][3]; in addition, four hydrocarbons are investigated and the relation is also verified for them. Finally, the relation is extended to a wide class of molten salts (alkali metal halides and nitrates) by employing data from the literature.…”

“…Generally b is higher than the intrinsic volume and lower than the molar volume. For the acids [1,3] a geometrical form of volume b was found, whose packing gives the molar volume approximatively.…”

“…A relation between dSfus and the parameter b of the Batchinski equation is given for these compounds and for others previously studied. By employing the calorimetric and viscometric data found in the literature for ionic melts, a similar relation is found to hold for molten salts.In two previous papers [1,2] and at a recent congress [3] it was pointed out that some organic melts follow the Batchinski equation [4]; in fact the fluidity is a linear function of the molar volume:From the experimental straight line ~ =f(V) the b values were obtained for several acids, two esters and two ethers. Generally b is higher than the intrinsic volume and lower than the molar volume.…”