Revisiting Smectic E Structure through Swollen Smectic E Phase in Binary System of 4-Nonyl-4′-isothiocyanatobiphenyl (9TCB) and n-Nonane

Abstract

Thermodynamic and diffraction analyses were performed to establish the phase diagram for a binary system between 4-n-nonyl-4'-isothiocyanatobiphenyl (9TCB) and n-nonane. The swollen SmE structure is identified in the binary system. Upon swelling, a characteristic two-dimensional herringbone array is maintained whereas the layer spacing of SmE structure increases with the content of n-nonane. Considering the difficulties in explaining the experimental findings based on the traditional model of SmE structure, a new model, lamellar with two types of sublayers consisting of aromatic core and alkyl chain moieties, is proposed.

Reassessment of structure of smectic phases: Nano-segregation in smectic E phase in 4-n-alkyl-4′-isothiocyanato-1,1′-biphenyls

“…12,[33][34][35][36][37][38] Indeed, the phase problem for a bicontinuous Gyroid phase was solved while taking into account the systematic variation of reflection intensities with the alkyl chain length. 12,37 In this paper, we attempt to establish the validity of the model proposed in a previous paper 29 for SmE phase through the analysis of systematics against chain-length n in the X-ray diffraction intensity of neat nTCB. Implications of the aggregation struc- ture are discussed in relation to the intrinsic lyotropic nature of thermotropic smectics.…”

“…It contradicts the excellent mobility exhibited by SmE phase. 6 Considering these difficulties, in a previous paper, 29 the present authors proposed a new model involving nano-segregation between aromatic cores and alkyl chains.…”

“…2 for n = 4), on which the largest number of studies has been reported as a representative of SmE mesogens, 3,7,8,[15][16][17][18][19][20][21][22][23][24][25][26][27][28] exhibits a swollen SmE phase in a continuous range of composition. 29 Only the c, the cell constant parallel to the molecular long axis in average, exhibits a notable increase in swelling while retaining the three-dimensional periodicity. If the traditional model of molecular packing (Category II according to Diele et al 30 ) is accepted, two possibilities are raised.…”

“…Both structures are hard to explain the experimental findings. 29 Besides, the uniformly mixed layer of aromatic cores and chains is unfavorable for the electronic/hole conduction within the commonsense of organic conductors 31 that π -electrons (holes) on aromatic parts are responsible for the conduction and that the electronic interaction between aromatic parts, i.e., the overlap of wave functions of π -electrons (π -orbitals) of neighboring molecules, is essential. The situation becomes more serious if the length of the alkyl chain is longer than that of the core part of a mesogen having a core-chain structure.…”

“…Note, however, that the model has a mechanism that naturally explains threedimensional periodicity of the SmE phase. 29 This paper is organized as follows: Sec. II deals with the molecular form factor of a nTCB molecule through quantum chemical calculation.…”