Volume changes of mixing for the system p,p'-di-n-hexyloxyazoxybenzene + xylene

Orwoll, Robert A.; Rhyne, R. H.; Christesen, Steven D.; Young, S. N.

doi:10.1021/j100517a017

Cited by 7 publications

(8 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The variation of density with temperature was also measured in the vicinity of the A−N‘ transition for pure 8CB and mixtures of each of the above-mentioned quasispherical solutes in 8CB. As the results for the pure 8CB and the Et 4 C/8CB systems (Figures ) show and in agreement with earlier studies, ,, the addition of a solute impurity also broadened the A−N‘ transition region and depressed the temperature of the transition. From best fits of the data in the neighborhood of the onset and completion of the transition, T A and T N ‘ were respectively obtained.…”

Section: Experiments and Resultssupporting

confidence: 92%

“…The variation of density with temperature was measured in the vicinity of the N-I transition for dilute mixtures of each of the quasispherical solute impurities (Et 4 C, Et 4 Sn, Pr 4 Sn, and Bu 4 Sn) in 6CB and 8CB. As expected from earlier studies [3][4][5][6][7][8][9][10][11][12][13][14][15]17 and 4, respectively, the addition of a solute impurity broadened the N-I transition region and depressed the temperature of the transition. From best fits of the data in the neighborhood of the onset and completion of the transition, T N and T I were respectively obtained.…”

Section: Experiments and Resultssupporting

confidence: 71%

“…With few exceptions, 1,2 nonrodlike solute impurities depress the N-I transition temperature, T NI , of nematogenic liquid crystals and, as expected from the first-order nature of the transition, lead to the appearance of a N-I two-phase region [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] bounded by T N , the temperature at which the isotropic phase first appears, and T I , the temperature at which the nematic phase just disappears. Such solute impurities also depress the A-N′ transition temperature, T AN′ , of liquid crystals that exhibit smectic-A and nematic phases and bring about an A-N′ twophase region 11,17,18 bounded by T A , the temperature at which the nematic phase first appears, and T N′ , the temperature at which the smectic-A phase just disappears. Note the use of N′ for a nematic phase bordering the smectic-A-to-nematic transition.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The Effect of Quasispherical Solutes on the Smectic-A−Nematic and Nematic−Isotropic Phase Equilibria in p-n-Alkyl-p‘-Cyanobiphenyl Liquid Crystals

Oweimreen

2001

J. Phys. Chem. B

View full text Add to dashboard Cite

Density as a function of temperature was measured in the nematic and isotropic phases in the immediate vicinity of the nematic-to-isotropic transition temperature (T NI) of p-n-hexyl-p‘-cyanobiphenyl (6CB) and p-n-octyl-p‘-cyanobiphenyl (8CB) and in the smectic-A and nematic phases in the immediate vicinity of the smectic-A-to-nematic transition temperature (T AN ‘) of 8CB. Similar measurements were made on dilute solutions of the quasispherical solutes Et4C (tetraethylmethane) and R4Sn (R = C2H5, n-C3H7, and n-C4H9) in 6CB and 8CB. Addition of these solutes led, as is expected for first-order phase transitions, to a nematic−isotropic two-phase region bounded by temperatures T N and T I, which are lower than T NI, and in the case of the 8CB systems to a smectic-A−nematic two-phase region bounded by temperatures T A and T N ‘, which are lower than T AN ‘. Volume changes at the transitions of the liquid crystals confirm that they are weakly first-order. βN and βI, the moduli of the slopes of the nematic and isotropic boundary lines, respectively, of the nematic−isotropic two-phase regions in the 6CB and 8CB systems were obtained assuming that the respective reduced temperatures T N* (= T N/T NI) and T I* (= T I/T NI) versus solute mole fraction (x 2) diagrams are linear. βA and βN ‘, similarly defined for the smectic-A−nematic two-phase regions in the 8CB systems, were obtained from the respective linear T A* (= T A/T AN ‘) and T N ‘* (= T N ‘ / T AN ‘) versus x 2 diagrams. The dependencies of βN and βA on solute and solvent sizes and the nature of the liquid crystalline phase are discussed.

show abstract

Section: Experiments and Resultssupporting

confidence: 92%

Section: Experiments and Resultssupporting

confidence: 71%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Effect of Quasispherical Solutes on the Smectic-A−Nematic and Nematic−Isotropic Phase Equilibria in p-n-Alkyl-p‘-Cyanobiphenyl Liquid Crystals

Oweimreen

2001

J. Phys. Chem. B

View full text Add to dashboard Cite

show abstract

“…Though several reports of volume-temperature studies on various single component mesogenic materials have appeared in the literature, none have described such studies for a binary system of mesogens.1"5 One study does report, however, excess volumes for binary mixtures of a mesogen with nonmesogenic solvents. 6 Mixtures of 4,4'-diheptyloxyazoxybenzene with m-xylene and p-xylene exhibited considerable width to the observed two phase regions as well as positive and negative excess volumes of mixing which were on the same order of magnitude as those we report here (vide infra). We report here the results of our dilatometric studies on the binary system of the nematogenic azobenzenes: 4-ethoxy-4/-pentanoyland 4-ethoxy-4'-nonanoylazobenzene.…”

Section: Introductionsupporting

confidence: 73%

Dilatometry of binary nematogenic mixtures. 4-Ethoxy-4'-pentanoyl- and 4-ethoxy-4'-nonanoyloxyazobenzene

Hecke¹,

Theodore²

1978

J. Phys. Chem.

View full text Add to dashboard Cite

Publication costs assisted by Harvey Mudd College Binary mixtures of the nematogenic homologues 4-ethoxy-4'-pentanoyloxyazobenzene and 4-ethoxy-4'-nonanoyloxyazobenzene exhibit excess molar volumes that can be positive or negative depending on temperature and composition. Negative excess volumes are observed in mixtures of pentanoate mole fraction x5, 0 < x5 < 0.3, and positive excess volumes observed in mixtures of pentanoate mole fraction 0.7 < x5 < 1.

show abstract

“…Evidence that density measurements using a vibrating densitometer exaggerate the ∆V AN value does not, by itself, automatically mean that ∆V AN ) 0 for 8CB. Even if, for the sake of argument, the finite ∆H AN values obtained in many DSC studies [15][16][17][18][19][20][21][22] and the finite ∆V AN values obtained from measurements using a vibrating densitometer 2,21 are put aside, the ∆V AN value of 0.00048 ( 0.00014 cm 3 mol -1 obtained by Leadbetter et al, 22 the results from high pressure 23,24 and diamagnetic susceptibility 25 measurements on 8CB, and the observation 9,17,20,26 of a SmA-N two-phase region for impure 8CB samples together point to a very weak first-order SmA-N transition for 8CB. In addition, dilatometric measurements by Torza and Cladis 27 on p-cyanobenzylidene (CBOOA), a bilayer smectic like 8CB, yielded a ∆V AN value of (5.0 ( 2) × 10 -5 cm 3 g -1 .…”

Section: V(t)mentioning

confidence: 99%

Nature of the Smectic A-to-Nematic Phase Transition of 8CB Revisited

Oweimreen

2002

J. Phys. Chem. B

View full text Add to dashboard Cite

Not including the references 1-6 mentioned in the preceding comment 7 is regrettable. Nonetheless, those references do not necessarily support the view 7 that the SmA-N transition in 8CB and other liquid crystals 5,6 is, "without doubt", second order.In Table 1 of ref 8, the density at 33.56°C was incorrectly reported and should be 0.98916 g cm -3 , and least-squares fits of the density F(θ) versus θ in the smectic A "intermediate" and nematic phase regions, where θ ) t -t′, t is the temperature at which the density is measured, and t′ is a temperature at the center of each region, gave the best correlation coefficients (in excess of 0.997) for equations of the form Such correlation, even if for "apparent" densities, points to the likely existence of a third intermediate phase in the region where the viscosity variation with temperature is different from that in both the smectic A and nematic phases. The comment also refers to Figure 6 in ref 4, which shows that the densities for the smectic A phase of 8OCB obtained using an Anton Paar density meter are higher than those from more accurate density measurements. This does not rule out the possible existence of an intermediate phase extending over about 0.07 K 8 within the 1 K temperature range between the datum at the highest temperature in the smectic A phase and the datum at the lowest temperature in the nematic phase, where no data were collected.Impurities intentionally added or intrinsic to the synthesis or purification procedure affect the density of a liquid crystal, lower or raise the transition temperature, and bring about a two-phase region in the vicinity of a first-order transition. 9 Whereas a sharp "best" value of 307.0942 K is calculated by Ż ywociński and Wieczorek 6 for the SmA-N transition temperature T AN for 8CB, Oweimreen 9 obtained broad and sharp SmA-N and N-I transitions, respectively, from a heating cycle on an 8CB sample. The broadness of the SmA-N transition is attributable to the coexistence of smectic A and nematic phases or the existence of an intermediate phase in the immediate vicinity of the SmA-N transition. The densities in this region are neither for the smectic A phase nor for the nematic phase. The inclusion of data from such a region by Ż ywociński et al. 5 and Ż ywociński and Wieczorek 6 in their V(t) versus t fits, where t ) |(T -T AN )/ T AN |, to the equation in the nematic phase region (T > T AN ) and the equation in the smectic A phase region (T < T AN ) casts doubt on their conclusion that the SmA-N transition is second order on the basis of the smallness of the C -C′ values. A single fit using eq 2 (or eq 3) for all the data above and below T AN is possible if t is defined as T/T AN . If such a fit turns out to be statistically significantly inferior to the fits in the separate regions, such doubt would be confirmed. In the absence of published 5,6 numbers, only the following qualitative analysis is possible.The constructions added to Figure 1 of ref 6 for 8CB and shown in Figure 1 in this comment allow the reader to ...

show abstract

Volume changes of mixing for the system p,p'-di-n-hexyloxyazoxybenzene + xylene

Cited by 7 publications

References 0 publications

The Effect of Quasispherical Solutes on the Smectic-A−Nematic and Nematic−Isotropic Phase Equilibria in p-n-Alkyl-p‘-Cyanobiphenyl Liquid Crystals

The Effect of Quasispherical Solutes on the Smectic-A−Nematic and Nematic−Isotropic Phase Equilibria in p-n-Alkyl-p‘-Cyanobiphenyl Liquid Crystals

Dilatometry of binary nematogenic mixtures. 4-Ethoxy-4'-pentanoyl- and 4-ethoxy-4'-nonanoyloxyazobenzene

Nature of the Smectic A-to-Nematic Phase Transition of 8CB Revisited

Contact Info

Product

Resources

About