Title: The interplay between spatial and heliconical orientational order in twist-bend nematic materials

Abstract

The helical pitch formed by organic molecules, such as the α-helix of proteins, usually requires hydrogen bonding between chiral units and long-range positional order. It was recently found that certain liquid crystal oligomers can have a twist-bend nematic (NTB) phase with nanoscale heliconical structure without hydrogen bonding, molecular chirality or positional order. To understand the nature of this unique structure, here we present hard and resonant tender X-ray scattering studies of two novel sulfur containing dimer materials. We simultaneously measure the temperature dependences of the helical pitch and the correlation length of both the helical and positional order. In addition to an unexpected strong variation of the pitch with the length of the spacer connecting the monomer units, we find that at the transition to the NTB phase the positional correlation length drops. Additionally, the helical structure was found not only in the NTB phase but observed even in the upper range of a smectic phase that forms just below the NTB state. The coexistence of smectic layering and the heliconical order indicates a layered (SmATB) phase wherein the rigid units of the dimers are tilted with respect to the smectic layer normal in order to accommodate the bent conformationmore » of the dimers and the tilt direction rotates along the heliconical axis.« less

Authors:

Saha, R.  ^[1];

• Search DOE PAGES for author "Saha, R."
• Search DOE PAGES for ORCID "0000-0002-4096-6307"

Feng, C. ^[2]; Welch, C.  ^[3];

• Search DOE PAGES for author "Welch, C."
• Search DOE PAGES for ORCID "0000-0003-1157-6155"

Mehl, G. H.  ^[3];

• Search DOE PAGES for author "Mehl, G. H."
• Search DOE PAGES for ORCID "0000-0002-2421-4869"

Feng, J. ^[4]; Zhu, C.  ^[4];

• Search DOE PAGES for author "Zhu, C."
• Search DOE PAGES for ORCID "0000-0003-1263-5065"

Gleeson, J. ^[1]; Sprunt, S.  ^[5];

• Search DOE PAGES for author "Sprunt, S."
• Search DOE PAGES for ORCID "0000-0001-8386-2228"

Jákli, A.  ^[6]

• Search DOE PAGES for author "Jákli, A."
• Search DOE PAGES for ORCID "0000-0001-8627-7606"

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+ Show Author Affiliations

1. Kent State Univ., Kent, OH (United States)
2. Kent State Univ., Kent, OH (United States). Advanced Materials and Liquid Crystal Institute; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source
3. Univ. of Hull (United Kingdom)
4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
5. Kent State Univ., Kent, OH (United States); Kent State Univ., Kent, OH (United States). Advanced Materials and Liquid Crystal Institute
6. Kent State Univ., Kent, OH (United States). Advanced Materials and Liquid Crystal Institute; Kent State Univ., Kent, OH (United States)

Publication Date:

Wed Feb 03 00:00:00 EST 2021

Research Org.:

Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF); Engineering and Physical Sciences Research Council (EPSRC)

OSTI Identifier:

1838634

Alternate Identifier(s):

OSTI ID: 1765918

Grant/Contract Number:  

AC02-05CH11231; DMR-1904167; EP/M015726/1

Resource Type:

Accepted Manuscript

Journal Name:

Physical Chemistry Chemical Physics. PCCP

Additional Journal Information:

Journal Volume: 23; Journal Issue: 7; Journal ID: ISSN 1463-9076

Publisher:

Royal Society of Chemistry

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY