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Glassy liquid crystals Observation of a quenched twisted nematic
Volume SOA, number 5
PHYSICS LETTERS
30 December 1974
GLASSY LIQUID CRYSTALS. OBSERVATION OF A QUENCHED TWISTED NEMATIC J.O. KESSLER* and E.P. RAYNES** Received 18 November 1974 A twisted nematic liquid crystalline layer has been rapidly solidified by exposure to liquid nitrogen. The resultant glass retained the macroscopic and microscopic liquid crystalline order.
It is well-known that many nematic liquid crystals supercool quite readily. Certain ones, like MBBA, form a glassy phase when cooled to 80”K, as demonstrated by X-ray diffraction [ 1,2]. It has also been shown [ 1] that within experimental error the anisotropy of at least one transport property, the thermal conductivity, of the glassy liquid crystal is the same as that of the normal nematic. These measurements implied, but did not rigorously prove, that the molecular distribution as well as the main features of the macroscopic alignment produced by an applied magnetic field are retained in the quenching process. Since no measures of the macroscopic alignment other than the thermal conductivity were obtained in the previous work, it remained unknown whether the quenching process resulted in some sort of local realignments which might not have been observed due to the averaging nature of the experiment. The chief purposes of the present experiment were to ascertain, in some way other than by large-scale ’ averaging experiments, (a) the correctness of the claim that both the molecular distribution and the director alignment are maintained during a liquid nitrogen quench, and (b) whether alignment of the liquid crystal by adjacent surfaces is maintained throughout such a process. Experimenrul. Two glass microscopic slides were cleaned and rubbed in the usual manner in order to produce an aligning surface. They were than assembled, using 12 pm spacers, with the rubbed surfaces facing each other, rubbing directions orthogonal. A droplet * Physics Department, University of Arizona, Tucson, Arizona 85721, USA. ** Royal Radar Establishment, England.
of a cyanobiphenyl eutectic mixture E3* was introduc. ed into the room temperature sandwich. Placed between parallel polarizer and analyser on a microscope stage, this sandwich gave complete extinction, demonstrating that a typical twisted nematic preparation has been assembled. The sandwich was then dipped into liquid nitrogen, held there for about half a minute, and then rapidly transferred to the polarizing microscope. It was found that complete extinction was retained in spite of the fact that the “liquid crystal” had solidified. Rapid random searching of the specimen did not uncover any areas with impaired extinction, As the preparation warmed to room temperature on the microscope state several phase changes could be observed, with the sample eventually reverting to the nematic phase. Although no detailed studies of these phase changes were made, the low melting point of E3 (0°C) and the persistance of extinction in the quenched material makes it certain that the rapid quenching produced a glassy rather than a crystalline phase. Conclusions. The transition of a nematic liquid crystal to a glass with nematic order upon quenching has been confirmed. Furthermore, it has been shown that in spite of the thermal shock the macroscopic alignment continues to operate effectively throughout the whole process. Our relatively simple technique should prove a useful method for the study of optical properties of the quenched glassy phase of liquid crystals. Apart from demonstrating the desired objectives of this experiment, this work suggests new and simple methods for constructing solid (i.e. solidified) thin layer optical components and other types of glassy anisotropic structures.
Malvern, Worcs. WR14 3PS, ‘Supplied by BDH Chemicals Ltd, Poole, England.
335
Volume
50A, number
5
PlIYSICS
One of us (JOK) wishes to thank the National Science Foundation for a travel grant, and Dr. J. Kirton for a number of very helpful discussions and for extending the hospitality of RRE.
336
LLITTERS
30 I)cccmbcr
1974
References [l] J.O. Kessler and J.E.. Lydon, Fluids Vol 2, eds. Press, N.Y. 1974) 121 .I. Lydon and J.O. Conf.. Stockholm.
Liquid Crystals and Ordered J.F. Johnson and R.S. Porter (Plenum p. 331- 339. Kessler, Vth Intern. Liquid Crystal 1974, and to be published in J.dc Phys
PHYSICS LETTERS
30 December 1974
GLASSY LIQUID CRYSTALS. OBSERVATION OF A QUENCHED TWISTED NEMATIC J.O. KESSLER* and E.P. RAYNES** Received 18 November 1974 A twisted nematic liquid crystalline layer has been rapidly solidified by exposure to liquid nitrogen. The resultant glass retained the macroscopic and microscopic liquid crystalline order.
It is well-known that many nematic liquid crystals supercool quite readily. Certain ones, like MBBA, form a glassy phase when cooled to 80”K, as demonstrated by X-ray diffraction [ 1,2]. It has also been shown [ 1] that within experimental error the anisotropy of at least one transport property, the thermal conductivity, of the glassy liquid crystal is the same as that of the normal nematic. These measurements implied, but did not rigorously prove, that the molecular distribution as well as the main features of the macroscopic alignment produced by an applied magnetic field are retained in the quenching process. Since no measures of the macroscopic alignment other than the thermal conductivity were obtained in the previous work, it remained unknown whether the quenching process resulted in some sort of local realignments which might not have been observed due to the averaging nature of the experiment. The chief purposes of the present experiment were to ascertain, in some way other than by large-scale ’ averaging experiments, (a) the correctness of the claim that both the molecular distribution and the director alignment are maintained during a liquid nitrogen quench, and (b) whether alignment of the liquid crystal by adjacent surfaces is maintained throughout such a process. Experimenrul. Two glass microscopic slides were cleaned and rubbed in the usual manner in order to produce an aligning surface. They were than assembled, using 12 pm spacers, with the rubbed surfaces facing each other, rubbing directions orthogonal. A droplet * Physics Department, University of Arizona, Tucson, Arizona 85721, USA. ** Royal Radar Establishment, England.
of a cyanobiphenyl eutectic mixture E3* was introduc. ed into the room temperature sandwich. Placed between parallel polarizer and analyser on a microscope stage, this sandwich gave complete extinction, demonstrating that a typical twisted nematic preparation has been assembled. The sandwich was then dipped into liquid nitrogen, held there for about half a minute, and then rapidly transferred to the polarizing microscope. It was found that complete extinction was retained in spite of the fact that the “liquid crystal” had solidified. Rapid random searching of the specimen did not uncover any areas with impaired extinction, As the preparation warmed to room temperature on the microscope state several phase changes could be observed, with the sample eventually reverting to the nematic phase. Although no detailed studies of these phase changes were made, the low melting point of E3 (0°C) and the persistance of extinction in the quenched material makes it certain that the rapid quenching produced a glassy rather than a crystalline phase. Conclusions. The transition of a nematic liquid crystal to a glass with nematic order upon quenching has been confirmed. Furthermore, it has been shown that in spite of the thermal shock the macroscopic alignment continues to operate effectively throughout the whole process. Our relatively simple technique should prove a useful method for the study of optical properties of the quenched glassy phase of liquid crystals. Apart from demonstrating the desired objectives of this experiment, this work suggests new and simple methods for constructing solid (i.e. solidified) thin layer optical components and other types of glassy anisotropic structures.
Malvern, Worcs. WR14 3PS, ‘Supplied by BDH Chemicals Ltd, Poole, England.
335
Volume
50A, number
5
PlIYSICS
One of us (JOK) wishes to thank the National Science Foundation for a travel grant, and Dr. J. Kirton for a number of very helpful discussions and for extending the hospitality of RRE.
336
LLITTERS
30 I)cccmbcr
1974
References [l] J.O. Kessler and J.E.. Lydon, Fluids Vol 2, eds. Press, N.Y. 1974) 121 .I. Lydon and J.O. Conf.. Stockholm.
Liquid Crystals and Ordered J.F. Johnson and R.S. Porter (Plenum p. 331- 339. Kessler, Vth Intern. Liquid Crystal 1974, and to be published in J.dc Phys