1
|
Reddy MK, Shalini PJ, Lobo NP, Roy A, Narasimhaswamy T. Direct method to grasp molecular topology of mesogens through 13C- 1H dipolar couplings. Phys Chem Chem Phys 2023; 25:14158-14169. [PMID: 37162405 DOI: 10.1039/d3cp00291h] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
A prime factor in determining liquid crystalline phase formation is the overall molecular shape since molecules undergo rotational motion about the long axis. Molecular topology deals with the connectivity of atomic centers in a given molecular architecture, ultimately giving rise to the gross molecular shape. 13C NMR has emerged as the most important technique in establishing the molecular topology of mesogens in the liquid crystalline phase. In this work, we demonstrate the utility of 13C-1H dipolar couplings determined from 2D separated local field NMR for finding the topology of three different mesogens in the liquid crystalline phase. The core unit of the investigated mesogens fundamentally differs, which may be categorized as rod-like, laterally substituted, and bent-core shapes. 1D and 2D 13C NMR measurements in the liquid crystalline phase revealed fascinating information. The 13C-1H dipolar couplings extracted from 2D NMR are found to be sensitive to topologically variant core units. This permitted us to establish the molecular topology just by looking at the 13C-1H dipolar couplings of the protonated carbons of the constituent phenyl rings. By considering the dipolar couplings of rod-like mesogens as a reference, the large variation in the magnitude of 13C-1H dipolar couplings of the laterally substituted and bent-core mesogens is attributed to changes in the topology of their core units. The order parameters estimated from 13C-1H dipolar couplings enabled visualization of the ordering array of phenyl rings of the mesogens. Interestingly large 13C-1H dipolar couplings are observed for mesogens in which (a) laterally located phenyl ring and (b) central phenyl ring of bent-core mesogens exhibited different trends as revealed by the orientational order parameters.
Collapse
Affiliation(s)
- M Kesava Reddy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | - P Jaya Shalini
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | - Nitin P Lobo
- Centre for Analysis, Testing, Evaluation & Reporting Services (CATERS), CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh 201002, India.
| | - Arun Roy
- Soft Condensed Matter, Raman Research Institute, Bangalore, 560080, India
| | - T Narasimhaswamy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh 201002, India.
| |
Collapse
|
2
|
Kotni R, Grau-Carbonell A, Chiappini M, Dijkstra M, van Blaaderen A. Splay-bend nematic phases of bent colloidal silica rods induced by polydispersity. Nat Commun 2022; 13:7264. [DOI: 10.1038/s41467-022-34658-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Accepted: 11/01/2022] [Indexed: 12/02/2022] Open
Abstract
AbstractLiquid crystal (LC) phases are in between solids and liquids with properties of both. Nematic LCs composed of rod-like molecules or particles exhibit long-range orientational order, yielding characteristic birefringence, but they lack positional order, allowing them to flow like a liquid. This combination of properties as well as their sensitivity to external fields make nematic LCs fundamental for optical applications e.g. liquid crystal displays (LCDs). When rod-like particles become bent, spontaneous bend deformations arise in the LC, leading to geometric frustration which can be resolved by complementary twist or splay deformations forming intriguing twist-bend (NTB) and splay-bend (NSB) nematic phases. Here, we show experimentally that the elusive NSB phases can be stabilized in systems of polydisperse micron-sized bent silica rods. Our results open avenues for the realization of NTB and NSB phases of colloidal and molecular LCs.
Collapse
|
3
|
Coumarin substituted symmetric diaminopyridine molecules: Synthesis, mesomorphic characterizations and DFT studies. J Mol Liq 2020. [DOI: 10.1016/j.molliq.2020.113782] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
|
4
|
Chiappini M, Drwenski T, van Roij R, Dijkstra M. Biaxial, Twist-bend, and Splay-bend Nematic Phases of Banana-shaped Particles Revealed by Lifting the "Smectic Blanket". PHYSICAL REVIEW LETTERS 2019; 123:068001. [PMID: 31491177 DOI: 10.1103/physrevlett.123.068001] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Revised: 06/20/2019] [Indexed: 06/10/2023]
Abstract
We perform an extensive computational study on the phase behavior of hard banana-shaped particles, and show that biaxial, twist-bend, and splay-bend nematic phases are metastable with respect to a smectic phase for a system of hard bent spherocylinders. However, if the smectic phase is destabilized-either by polydispersity in the particle length or by curvature in the particle shape-stable biaxial, twist-bend, and splay-bend nematic phases are obtained. This provides a unified and consistent picture on the subtle role of particle shape on the phase behavior of bent rods.
Collapse
Affiliation(s)
- Massimiliano Chiappini
- Soft Condensed Matter, Debye Institute for Nanomaterials Science, Department of Physics, Utrecht University, Princetonplein 1, Utrecht 3584 CC, The Netherlands
| | - Tara Drwenski
- Institute for Theoretical Physics, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands
| | - René van Roij
- Institute for Theoretical Physics, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands
| | - Marjolein Dijkstra
- Soft Condensed Matter, Debye Institute for Nanomaterials Science, Department of Physics, Utrecht University, Princetonplein 1, Utrecht 3584 CC, The Netherlands
| |
Collapse
|
5
|
Pfletscher M, Wysoglad J, Gutmann JS, Giese M. Polymorphism of hydrogen-bonded star mesogens – a combinatorial DFT-D and FT-IR spectroscopy study. RSC Adv 2019; 9:8444-8453. [PMID: 35518674 PMCID: PMC9061708 DOI: 10.1039/c8ra09458f] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Accepted: 03/01/2019] [Indexed: 12/13/2022] Open
Abstract
A comprehensive study combining detailed computational analyses with temperature-variable FT-IR experiments was performed in order to elucidate the structure of the hydrogen-bonded liquid crystals based on phloroglucinol and azopyridine in their mesophase. Conformational analysis revealed three relevant conformers: star, λ- and E-shape. The results demonstrate an entropy-driven unfolding mechanism of the assembly. The stability of the conformers is given by intermolecular π–π and dispersion interactions of the azopyridine side chains. Correlating the calculated vibrational frequency with experimental FT-IR spectra suggests a λ-folded conformation of the assemblies as the predominant species in the mesophase. The structure of hydrogen-bonded star mesogens is investigated using modern quantum chemistry methods in combination with infrared spectroscopy.![]()
Collapse
Affiliation(s)
- Michael Pfletscher
- Institute of Organic Chemistry
- University Duisburg-Essen
- 45141 Essen
- Germany
| | - Janek Wysoglad
- Institute of Physical Chemistry
- University Duisburg-Essen
- 45141 Essen
- Germany
| | - Jochen S. Gutmann
- Institute of Physical Chemistry
- CENIDE
- University Duisburg-Essen
- 45141 Essen
- Germany
| | - Michael Giese
- Institute of Organic Chemistry
- University Duisburg-Essen
- 45141 Essen
- Germany
| |
Collapse
|
6
|
Liu J, Guan R, Dong X, Dong Y. Molecular properties of a bent-core nematic liquid crystal A131 by multi-level theory simulations. MOLECULAR SIMULATION 2018. [DOI: 10.1080/08927022.2018.1517416] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Affiliation(s)
- Jingwei Liu
- Jilin Provincial Key Laboratory for Numerical Simulation, Jilin Normal University, Siping, People’s Republic of China
| | - Rongfeng Guan
- College of Applied Chemistry, Shenyang University of Chemical Technology, Shenyang, People’s Republic of China
| | - Xuanchen Dong
- College of Chemistry, Jilin University, Changchun, People’s Republic of China
| | - Yanhua Dong
- Jilin Provincial Key Laboratory for Numerical Simulation, Jilin Normal University, Siping, People’s Republic of China
| |
Collapse
|
7
|
Ivšić T, Vinković M, Baumeister U, Mikleušević A, Lesac A. Towards understanding the NTB phase: a combined experimental, computational and spectroscopic study. RSC Adv 2016. [DOI: 10.1039/c5ra26078g] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Combined studies support the hierarchical model for the NTB phase that involves formation of embryonic self-assembly of the propeller-shaped dimeric molecules with syn-parallel orientation in the isotropic melt.
Collapse
Affiliation(s)
- Trpimir Ivšić
- Division of Organic Chemistry and Biochemistry
- Ruđer Bošković Institute
- 10000 Zagreb
- Croatia
| | | | - Ute Baumeister
- Institute of Chemistry
- Physical Chemistry
- Martin Luther University Halle-Wittenberg
- 06120 Halle
- Germany
| | - Ana Mikleušević
- Division of Organic Chemistry and Biochemistry
- Ruđer Bošković Institute
- 10000 Zagreb
- Croatia
| | - Andreja Lesac
- Division of Organic Chemistry and Biochemistry
- Ruđer Bošković Institute
- 10000 Zagreb
- Croatia
| |
Collapse
|
8
|
Boyd NJ, Wilson MR. Optimization of the GAFF force field to describe liquid crystal molecules: the path to a dramatic improvement in transition temperature predictions. Phys Chem Chem Phys 2015; 17:24851-65. [DOI: 10.1039/c5cp03702f] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Systematic optimization of the General Amber Force Field (GAFF) for mesogenic fragments leads to a dramatic improvement in the modelling of liquid crystal clearing points.
Collapse
|
9
|
Figueirinhas JL, Dong RY. NMR of bent-core nematogens: a mini-review. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2014; 52:614-624. [PMID: 24975632 DOI: 10.1002/mrc.4097] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2014] [Accepted: 05/26/2014] [Indexed: 06/03/2023]
Abstract
This review focuses on two of our studied bent-core liquid crystals 2-methyl-3-[4-(4-octylbenzoyloxy)-benzylidene]-amino-benzoic acid 4-(4-dodecylphenylazo)-phenyl ester A131, and a shape-persistent fluorenone mesogen, F1a by means of temperature-dependent (13)C NMR spectra and deuterium NMR spectra, respectively. Orientational order parameters, molecular packing, and/or conformations in the nematic phases or nematic glass can be extracted from the observed NMR spectra. These will be discussed in terms of certain motional models. In particular, F1a has been found to form a biaxial nematic glass. The derived orientational order parameters would put the biaxial system of phase symmetry lower than orthorhombic.
Collapse
Affiliation(s)
- João L Figueirinhas
- Departamento de Física, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal; CFMC, Universidade de Lisboa, Lisboa, Portugal
| | | |
Collapse
|
10
|
Lobo NP, Phani Kumar BVN, Narasimhaswamy T, Mandal AB. (13)C NMR investigations and the molecular order of 4-(trans-4'-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). Phys Chem Chem Phys 2014; 16:14713-21. [PMID: 24919592 DOI: 10.1039/c4cp01569j] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The static 1D (13)C and 2D Proton Encoded Local Field (PELF) NMR experiments are carried out in the nematic phase of a less viscous liquid crystal 4-(trans-4'-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT) with a view to find orientational order. The PELF spectra provide better resolution which facilitates the assignment of cyclohexyl and phenyl ring carbons relatively easy. For the cyclohexyl unit, four pairs of dipolar splitting are clearly noticed in contrast to earlier reports on structurally similar mesogens where only two pairs of doublets are seen. The linear relationship between anisotropic chemical shifts and orientational order is established and semi-empirical parameters are obtained to aid the study of the order behaviour of 6CHBT over the entire nematic range. The data further fitted to the Haller equation and a reasonably good agreement is observed. The temperature dependence trends of orientational order parameters extracted for various carbons using (13)C-(1)H dipolar couplings with those of (13)C chemical shifts are compared. A gradual decrease in the order parameter is noticed for different molecular segments while traversing from the core to the aliphatic chain via the cyclohexyl ring. The notable decreasing trends of order parameters along the chain are observed similar to those of the corresponding phenyl cyclohexanes reported earlier.
Collapse
Affiliation(s)
- Nitin P Lobo
- Chemical Physics Laboratory, Council of Scientific and Industrial Research (CSIR)-Central Leather Research Institute (CLRI), Adyar, Chennai 600020, India.
| | | | | | | |
Collapse
|
11
|
Domenici V, Lelli M, Cifelli M, Hamplova V, Marchetti A, Veracini CA. Conformational Properties and Orientational Order of a de Vries Liquid Crystal Investigated through NMR Spectroscopy. Chemphyschem 2014; 15:1485-95. [DOI: 10.1002/cphc.201301036] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Indexed: 11/05/2022]
|
12
|
Greco C, Marini A, Frezza E, Ferrarini A. From the Molecular Structure to Spectroscopic and Material Properties: Computational Investigation of a Bent-Core Nematic Liquid Crystal. Chemphyschem 2014; 15:1336-44. [DOI: 10.1002/cphc.201301030] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2013] [Indexed: 11/12/2022]
|
13
|
Kim YK, Senyuk B, Shin ST, Kohlmeier A, Mehl GH, Lavrentovich OD. Surface alignment, anchoring transitions, optical properties, and topological defects in the thermotropic nematic phase of organo-siloxane tetrapodes. SOFT MATTER 2014; 10:500-509. [PMID: 24651889 DOI: 10.1039/c3sm52249k] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We perform optical, surface anchoring, and textural studies of an organo-siloxane "tetrapode" material in the broad temperature range of the nematic phase. The optical, structural, and topological features are compatible with the uniaxial nematic order rather than with the biaxial nematic order, in the entire nematic temperature range -25 °C < T < 46 °C studied. For homeotropic alignment, the material experiences surface anchoring transition, but the director can be realigned into an optically uniaxial texture by applying a sufficiently strong electric field. The topological features of textures in cylindrical capillaries, in spherical droplets and around colloidal inclusions are consistent with the uniaxial character of the long-range nematic order. In particular, we observe isolated surface point defects - boojums and bulk point defects - hedgehogs that can exist only in the uniaxial nematic liquid crystal.
Collapse
Affiliation(s)
- Young-Ki Kim
- Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent, OH 44242, USA.
| | | | | | | | | | | |
Collapse
|
14
|
Lobo NP, Das BB, Narasimhaswamy T, Ramanathan KV. Molecular topology of three ring nematogens from 13C–1H dipolar couplings. RSC Adv 2014. [DOI: 10.1039/c4ra03963g] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
A facile way of estimating the order parameter and the molecular orientation from 13C–1H dipolar couplings for three ring based nematogens with a terminal C–H vector.
Collapse
Affiliation(s)
- Nitin P. Lobo
- Department of Physics
- Indian Institute of Science
- Bangalore 560012, India
| | - Bibhuti B. Das
- Department of Physics
- Indian Institute of Science
- Bangalore 560012, India
| | - T. Narasimhaswamy
- Polymer Laboratory
- CSIR-Central Leather Research Institute
- Chennai 600 020, India
| | - K. V. Ramanathan
- NMR Research Centre
- Indian Institute of Science
- Bangalore 560012, India
| |
Collapse
|
15
|
Cifelli M, Domenici V, Veracini CA. Recent advancements in understanding thermotropic liquid crystal structure and dynamics by means of NMR spectroscopy. Curr Opin Colloid Interface Sci 2013. [DOI: 10.1016/j.cocis.2013.03.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
16
|
Kesava Reddy M, Subramanyam Reddy K, Yoga K, Prakash M, Narasimhaswamy T, Mandal AB, Lobo NP, Ramanathan KV, Rao DSS, Krishna Prasad S. Structural Characterization and Molecular Order of Rodlike Mesogens with Three- and Four-Ring Core by XRD and 13C NMR Spectroscopy. J Phys Chem B 2013; 117:5718-29. [DOI: 10.1021/jp4000126] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- M. Kesava Reddy
- Department of Chemistry, S. V. University, Tirupati 517502, India
| | | | - K. Yoga
- Polymer Laboratory and Chemical
Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | - M. Prakash
- Polymer Laboratory and Chemical
Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | - T. Narasimhaswamy
- Polymer Laboratory and Chemical
Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | - A. B. Mandal
- Polymer Laboratory and Chemical
Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | - Nitin P. Lobo
- Department of Physics, Indian Institute of Science, Bangalore, 560012, India
| | - K. V. Ramanathan
- NMR Research Centre, Indian Institute of Science, Bangalore, 560012, India
| | - D. S. Shankar Rao
- Centre for Soft Matter Research, Jalahalli, Bangalore, 560013, India
| | - S. Krishna Prasad
- Centre for Soft Matter Research, Jalahalli, Bangalore, 560013, India
| |
Collapse
|
17
|
Aluculesei A, Vaca Chávez F, Cruz C, Sebastião PJ, Nagaveni NG, Prasad V, Dong RY. Proton NMR Relaxation Study on the Nematic–Nematic Phase Transition in A131 Liquid Crystal. J Phys Chem B 2012; 116:9556-63. [DOI: 10.1021/jp305064x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- A Aluculesei
- Department of Physics, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
| | | | | | | | | | | | | |
Collapse
|
18
|
Lin SC, Ho RM, Chang CY, Hsu CS. Hierarchical Superstructures with Control of Helicity from the Self-Assembly of Chiral Bent-Core Molecules. Chemistry 2012; 18:9091-8. [DOI: 10.1002/chem.201200057] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2012] [Indexed: 11/11/2022]
|
19
|
Marini A, Dong RY. Density-functional-theory investigation of conformations, 13C shielding, and magnetic field interactions in a V-shaped phenylene bis carboxylate homologous series. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2011; 83:041712. [PMID: 21599191 DOI: 10.1103/physreve.83.041712] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2010] [Indexed: 05/30/2023]
Abstract
Density functional theory (DFT) has been employed in a conformational study of a bent-core PBBC homologous series. IR spectra, GIAO-DFT chemical shielding tensors (CSTs), and molecular susceptibility tensors (MSTs) are theoretically calculated for various optimized conformations established by searching the potential energy surface of each PBBC V-shaped molecule. The IR results could aid the understanding of vibration normal modes, while the MST results can illuminate the alignment properties of the V-shaped molecules in an external magnetic field. CSTs of the aromatic carbons, and those previously measured by the 2D-NMR SUPER technique (with some (13)C NMR peaks reassigned for correctness based on new DFT calculations), were found to be in good agreement. These verified experimental CSTs are then used to revisit the (13)C NMR data to yield structural and local orientational order parameters for two members of the PBBC series. The PBBC series studied using the combined DFT-(13)C NMR approach strongly supports the notion that lesser populated conformational states found by DFT could be reached in the studied mesogens 10DClPBBC and 11ClPBBC upon decreasing temperature, as revealed by the change in the bend angle determined by NMR and identified with those of the DFT molecular structures optimized for various conformers.
Collapse
Affiliation(s)
- Alberto Marini
- Dipartimento di Chimica e Chimica Industriale, Universitá di Pisa, via Risorgimento 35, I-56126 Pisa, Italy
| | | |
Collapse
|
20
|
Abbandonato G, Catalano D, Marini A. Aggregation of perfluoroctanoate salts studied by 19F NMR and DFT calculations: counterion complexation, poly(ethylene glycol) addition, and conformational effects. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:16762-16770. [PMID: 20883045 DOI: 10.1021/la102578k] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
The aggregation of perfluoroctanoate salts in H(2)O is studied by (19)F NMR on solutions of LiPFO, NaPFO, and CsPFO, without and with the addition of two poly(ethylene glycol) (PEG) oligomers of molecular weight 1500 and 3400 Da, respectively, and with the addition of suitable crown ethers. The (19)F chemical shift (cs) trends are monitored, at 25 °C, in a concentration range including the critical micellar concentration (cmc) or, in the presence of PEG, the critical aggregation concentration (cac). The cac values in the samples with PEG are lower than the cmc values of the corresponding samples without PEG; moreover, the (19)F cs trends above the cac and above the polymer saturation concentration reveal and help to explain some peculiarities of the aggregation process of PEG on PFO micelles, which, in the first step, seems to occur while the surfactant concentration in water is still increasing. Also in LiPFO/H(2)O or NaPFO/H(2)O solutions containing 12-crown-4 or 15-crown-5 ethers, suitable to complex Li(+) or Na(+) ions, respectively, the cmc decreases. On the other hand, the micellization process in the presence of crown ethers does not show other peculiarities. The prevailing conformations of the PFO chain are discussed on the basis of quantum-mechanical calculations. The theoretical chemical shifts were computed at the DFT level of theory, taking into account the effects of the environment by means of the IEF-PCM method. The helical structure is the most stable one, but anti conformations are easily accessible, in both the aqueous and fluorinated environment. The comparison between computed and experimental chemical shifts indicates that anti conformations are more important in the micelles than in water and in CsPFO micelles than in LiPFO or NaPFO ones.
Collapse
Affiliation(s)
- Gerardo Abbandonato
- Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Risorgimento 35, 56126 Pisa, Italy
| | | | | |
Collapse
|
21
|
Senyuk B, Wonderly H, Mathews M, Li Q, Shiyanovskii SV, Lavrentovich OD. Surface alignment, anchoring transitions, optical properties, and topological defects in the nematic phase of thermotropic bent-core liquid crystal A131. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 82:041711. [PMID: 21230299 DOI: 10.1103/physreve.82.041711] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2010] [Revised: 09/29/2010] [Indexed: 05/30/2023]
Abstract
We study optical, structural, and surface anchoring properties of thermotropic nematic bent-core material A131. The focus is on the features associated with orientational order as the material has been reported to exhibit not only the usual uniaxial nematic but also the biaxial nematic phase. We demonstrate that A131 experiences a surface anchoring transition from a perpendicular to tilted alignment when the temperature decreases. The features of the tilted state are consistent with surface-induced birefringence associated with smectic layering near the surface and a molecular tilt that changes along the normal to the substrates. The surface-induced birefringence is reduced to zero by a modest electric field that establishes a uniform uniaxial nematic state. Both refractive and absorptive optical properties of A131 are consistent with the uniaxial order. We found no evidence of the "polycrystalline" biaxial behavior in the cells placed in crossed electric and magnetic fields. We observe stable topological point defects (boojums and hedgehogs) and nonsingular "escaped" disclinations pertinent only to the uniaxial order. Finally, freely suspended films of A131 show uniaxial nematic and smectic textures; a decrease in the film thickness expands the temperature range of stability of smectic textures, supporting the idea of surface-induced smectic layering. Our conclusion is that A131 features only a uniaxial nematic phase and that the apparent biaxiality is caused by subtle surface effects rather than by the bulk biaxial phase.
Collapse
Affiliation(s)
- B Senyuk
- Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, Ohio 44242, USA
| | | | | | | | | | | |
Collapse
|
22
|
Marini A, Domenici V. Conformational Changes at Mesophase Transitions in a Ferroelectric Liquid Crystal by Comparative DFT Computational and 13C NMR Study. J Phys Chem B 2010; 114:10391-400. [DOI: 10.1021/jp105095m] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Alberto Marini
- Dipartimento di Chimica e Chimica Industriale, Università degli studi di Pisa, Via Risorgimento 35, 56126, Pisa, Italy
| | - Valentina Domenici
- Dipartimento di Chimica e Chimica Industriale, Università degli studi di Pisa, Via Risorgimento 35, 56126, Pisa, Italy
| |
Collapse
|
23
|
Lehmann M, Köhn C, Figueirinhas J, Feio G, Cruz C, Dong R. Biaxial Nematic Mesophases from Shape-Persistent Mesogens with a Fluorenone Bending Unit. Chemistry 2010; 16:8275-9. [DOI: 10.1002/chem.201001214] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
|
24
|
Yoon HG, Kang SW, Dong RY, Marini A, Suresh KA, Srinivasarao M, Kumar S. Nematic biaxiality in a bent-core material. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 81:051706. [PMID: 20866246 DOI: 10.1103/physreve.81.051706] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2009] [Revised: 02/21/2010] [Indexed: 05/29/2023]
Abstract
The results of a recent investigation of the nematic biaxiality in a bent-core mesogen (A131) are in apparent disagreement with earlier claims. Samples of mesogen A131 used in the two studies were investigated with polarized optical microscopy, conoscopy, carbon-13 NMR, and crossover frequency measurements. The results demonstrate that textural changes associated with the growth of biaxial nematic order appear at ∼149 °C. The Maltese cross observed in the conoscopic figure gradually splits into two isogyres at lower temperatures indicating phase biaxiality. Presence of the uniaxial to biaxial nematic phase transition is further confirmed by temperature trends of local order parameters based on 13C chemical shifts in NMR experiments. Frequency switching measurements also clearly reveal a transition at 149 °C. Differences between the two reports appear to be related to the presence of solvent, impurities, and/or adsorbed gases in samples of A131 used in the study of Van Le [Phys. Rev. E 79, 030701 (2009)].
Collapse
Affiliation(s)
- Hyung Guen Yoon
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
| | | | | | | | | | | | | |
Collapse
|
25
|
Marchetti A, Domenici V, Novotna V, Lelli M, Cifelli M, Lesage A, Veracini CA. Direct Measure of the Tilt Angle in de Vries-Type Liquid Crystals through NMR Spectroscopy. Chemphyschem 2010; 11:1641-5. [DOI: 10.1002/cphc.201000116] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
|