1
|
Colloidal and fumed particles in nematic liquid crystals: Self-assembly, confinement and implications on rheology. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2021.116241] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
|
2
|
Yamaguchi T, Nut Leelaphattharaphan N, Shin H, Ogawa M. Acceleration of photochromism and negative photochromism by the interactions with mesoporous silicas. Photochem Photobiol Sci 2019; 18:1742-1749. [PMID: 31093626 DOI: 10.1039/c9pp00081j] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The adsorption of merocyanine dye onto mesoporous silicas with varied pore sizes (5.5, 9.4 and 2.2 nm) from the toluene solution of 1,3,3-trimethylindolino-6'-nitrobenzopyrylospiran under UV irradiation was investigated quantitatively. The photoinduced adsorption of merocyanine onto SBA-15 with the pore diameter of 9.4 nm followed the pseudo-second order kinetics and the rate constant was larger than that observed for MCM-41 (pore size of 2.2 nm) owing to the efficient diffusion of merocyanine. The maximum adsorbed amounts of the merocyanine dye was 152 mg g-1 of SBA-15, which corresponded to the sufficiently high concentration of merocyanine in the pores (0.376 mol L-1 of pore). The resulting red-colored hybrids (SBA-15 containing merocyanine) showed decoloration in the solid-state by visible light irradiation (negative photochromism). The conversion was high (about 80% at the photostationary state) under visible light irradiation at room temperature using a solar simulator (100 W). The red color was re-generated by storing the photochemically formed colorless samples in the dark at room temperature. The half-lives of the thermal coloration process were 2.6, 1.9 and 1.3 h for the MCM-41, SBA-15s with the BJH pore sizes of 5.5 and 9.4 nm, respectively. Since the coloration was affected by the diffusion of the molecules in the pores, larger pores provided the efficient molecular diffusion, leading to faster reactions.
Collapse
Affiliation(s)
- Tetsuo Yamaguchi
- School of Energy Science and Engineering, Vidyasirimedhi Institute of Science and Technology (VISTEC), 555 Moo 1 Payupnai, Wangchan, Rayong 21210, Thailand.
| | - Nattapat Nut Leelaphattharaphan
- School of Energy Science and Engineering, Vidyasirimedhi Institute of Science and Technology (VISTEC), 555 Moo 1 Payupnai, Wangchan, Rayong 21210, Thailand.
| | - Hojoon Shin
- School of Energy Science and Engineering, Vidyasirimedhi Institute of Science and Technology (VISTEC), 555 Moo 1 Payupnai, Wangchan, Rayong 21210, Thailand.
| | - Makoto Ogawa
- School of Energy Science and Engineering, Vidyasirimedhi Institute of Science and Technology (VISTEC), 555 Moo 1 Payupnai, Wangchan, Rayong 21210, Thailand.
| |
Collapse
|
3
|
Tallavaara P, Jokisaari J. Behavior of Liquid Crystals Confined to Mesoporous Materials as Studied by 13C NMR Spectroscopy of Methyl Iodide and Methane as Probe Molecules. J Phys Chem B 2008; 112:764-75. [DOI: 10.1021/jp076840i] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Pekka Tallavaara
- Department of Physical Sciences, NMR Research Group, University of Oulu, P. O. Box 3000, FIN-90014 University of Oulu, Finland
| | - Jukka Jokisaari
- Department of Physical Sciences, NMR Research Group, University of Oulu, P. O. Box 3000, FIN-90014 University of Oulu, Finland
| |
Collapse
|
4
|
Kausik R, Fatkullin N, Hüsing N, Kimmich R. Investigations of polymer dynamics in nanoporous media by field cycling NMR relaxometry and the dipolar correlation effect. Magn Reson Imaging 2007; 25:489-92. [PMID: 17466770 DOI: 10.1016/j.mri.2006.11.018] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2006] [Accepted: 11/30/2006] [Indexed: 11/20/2022]
Abstract
The chain dynamics of short-chain perfluoropolyether melts confined in Vycor nanoporous media has been characterized by field cycling nuclear magnetic resonance relaxometry and the dipolar correlation effect. The slowdown of motions under confinement, leading to larger residual dipolar couplings, has been probed by looking at the quotient of stimulated and primary echoes. Using field cycling relaxometry, it has been shown that there is strong evidence of reptation-like motion, even for such short-chain polymers as shown by the frequency and molecular weight dependences of the spin-lattice relaxation time.
Collapse
Affiliation(s)
- Ravinath Kausik
- Sektion Kernresonanzspektroskopie, Universität Ulm, 89069 Ulm, Germany.
| | | | | | | |
Collapse
|
5
|
Grinberg F. Surface effects on liquid crystals constrained in nanoscaled pores investigated by field cycling NMR relaxometry and Monte Carlo simulations. Magn Reson Imaging 2007; 25:485-8. [PMID: 17466769 DOI: 10.1016/j.mri.2006.11.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2006] [Accepted: 11/30/2006] [Indexed: 11/18/2022]
Abstract
Proton relaxation rates of nematic liquid crystals confined in nanoporous cavities were measured in a broad frequency range with the help of field cycling nuclear magnetic resonance relaxometry. The shape of relaxation dispersion curves in confined materials strongly deviates from the behavior in bulk, both above and below the bulk isotropization temperature. A strong increase in relaxation rates, exceeding by two orders of magnitude that of the bulk sample, is observed in the range of a few kilohertz. Relaxation rates in bigger pores decreased. Experimental findings are interpreted in terms of surface-induced orientational order and diffusion between sites with different orientations of local directors. With the aid of Monte Carlo simulations, two processes affecting low-frequency relaxation could be identified: (a) exchange losses of molecules from the surface-ordered phase to the bulk-like phase, and (b) Reorientations Mediated by Translational Displacements, which dominate the long-time scale and account for the recovery of correlation in molecular orientations as molecules probe different surface sites. It is shown that the width of the oriented layer may strongly affect the slope of dispersion curves and that cross-over between plateau and power law dispersion regimes shifts towards lower frequencies for bigger pores.
Collapse
Affiliation(s)
- Farida Grinberg
- Department of Physics, University of Leipzig, Linnéstrasse 5, 04103 Leipzig, Germany.
| |
Collapse
|
6
|
Valiullin R, Khokhlov A. Orientational ordering of linear n-alkanes in silicon nanotubes. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2006; 73:051605. [PMID: 16802944 DOI: 10.1103/physreve.73.051605] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2005] [Revised: 01/06/2006] [Indexed: 05/10/2023]
Abstract
Orientational ordering of short and intermediate -alkanes confined to silicon nanotubes has been studied using 1H NMR. The measured residual nuclear dipolar couplings characterizing the degree of molecular ordering were found to depend on the pore size and the molecular length in a complex way. It is inferred from the experimental results that the observed behavior is governed by concomitance of surface and intermolecular interactions as well as the effect of confinement.
Collapse
Affiliation(s)
- Rustem Valiullin
- Fakultät für Physik und Geowissenschaften, Universität Leipzig, 04103 Leipzig, Germany.
| | | |
Collapse
|
7
|
Wasyluk L, Peplińska B, Jurga S. Molecular dynamics of tert-butyl chloride confined in CPG studied by NMR. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2004; 25:177-184. [PMID: 14698407 DOI: 10.1016/j.ssnmr.2003.03.028] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The molecular dynamics of tert-butyl chloride (TBC) confined to Controlled Pore Glass matrices of 25 and 7.5 nm were investigated by measuring NMR linewidths, lineshapes, and 1H and 2H spin--lattice relaxation times. The behaviour of confined TBC can be explained assuming that the guest molecules form two distinct phases; the surface-affected phase, composed of molecules located at the pore surface, and the bulk-like phase located at the centre of the pores. The bulk-like component of confined TBC, at the temperatures corresponding to the phase III, is characterized by two dynamically different subphases.
Collapse
Affiliation(s)
- Lidia Wasyluk
- Department of Macromolecular Physics, Adam Mickiewicz University, ul. Umultowska 85, 61-614 Poznań, Poland.
| | | | | |
Collapse
|
8
|
Grinberg F, Kimmich R. Surface effects and dipolar correlations of confined and constrained liquids investigated by NMR relaxation experiments and computer simulations. Magn Reson Imaging 2001; 19:401-4. [PMID: 11445319 DOI: 10.1016/s0730-725x(01)00256-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Local order and molecular dynamics of liquids near surfaces strongly deviate from the behavior in the bulk. This in particular refers to liquid crystals above the bulk isotropization temperature. Transverse relaxation data of 5CB examined in porous glasses with different pore sizes are reported. A strong pore size effect was found. For the interpretation, a simple diffusion-adsorption computer simulation was carried out. Molecules can diffuse from the isotropic bulk part of the pore fluid to the ordered surface layer and vice versa. The residual dipolar correlation function is characterized by a slowly decaying tail owing to repeated returns of molecules to the surface. At each return the molecular orientation correlation is recovered as far as the surface sites visited have orientations correlated to the initial site. That is, molecular orientation is controlled by the "reorientation mediated by translational displacement" process considered in previous papers.
Collapse
Affiliation(s)
- F Grinberg
- Sektion Kernresonanzspektroskopie, Universität Ulm, 89069, Ulm, Germany.
| | | |
Collapse
|
9
|
Grinberg F, Garbarczyk M, Kuhn W. Influence of the cross-link density and the filler content on segment dynamics in dry and swollen natural rubber studied by the NMR dipolar-correlation effect. J Chem Phys 1999. [DOI: 10.1063/1.480478] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
|
10
|
Grinberg F, Kimmich R, Seitter R, Pusiol D. A new formalism for the evaluation of order-fluctuation modes in liquid crystals from field-cycling NMR-relaxometry data. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 1998; 135:54-60. [PMID: 9799675 DOI: 10.1006/jmre.1998.1530] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
A numerical procedure is presented which permits one to derive a formal distribution of collective fluctuation modes from experimental field-cycling NMR-relaxometry data of an ordered system. The purpose is to distinguish true order-fluctuation modes from local reorientation mechanisms. The evaluation scheme is demonstrated using simulated as well as experimental data. Applications serving the elucidation and characterization of modified or limited director fluctuation modes as they occur with liquid crystals in pores or with lyotropic systems are discussed. Test experiments have been carried out with a potassium laurate system.
Collapse
Affiliation(s)
- F Grinberg
- Sektion Kernresonanzspektroskopie, Universität Ulm, Ulm, 89069, Germany.
| | | | | | | |
Collapse
|
11
|
Fischer E, Grinberg F, Kimmich R, Hafner S. Characterization of polymer networks using the dipolar correlation effect on the stimulated echo and field-cycling nuclear-magnetic resonance relaxometry. J Chem Phys 1998. [DOI: 10.1063/1.476624] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
12
|
Abstract
A new technique based on the dipolar-correlation effect was applied in combination with field-cycling-relaxometry to study ordering effects and slow director fluctuations in a nematic liquid crystal confined in porous glasses. Both methods demonstrate a strong influence of geometrical confinements on the distribution of director fluctuation modes. The mean-squared fluctuation estimated from the dipolar-correlation effect decreases exponentially with decreasing pore diameter. The critical mean pore size for the onset of bulk behaviour was found to be of the order of 120 nm. Frequency dependences of spin-lattice relaxation times exhibit sudden sharp deviations from the square root law at frequencies below the MHz-range. These changes are assumed to reflect the lack of long wavelength fluctuations in the spectrum of director fluctuation modes due to finite pore sizes.
Collapse
Affiliation(s)
- F Grinberg
- Universität Ulm, Sektion Kernresonanzspektroskopie, Germany.
| | | | | |
Collapse
|
13
|
Affiliation(s)
- Y. Shao
- Physics Department, TCU Box 298840, Fort Worth, Texas 76129
| | - T. W. Zerda
- Physics Department, TCU Box 298840, Fort Worth, Texas 76129
| |
Collapse
|
14
|
Grinberg F, Kimmich R, Möller M, Molenberg A. Order fluctuations in the mesophase of polydiethylsiloxane as studied by the dipolar‐correlation effect on the stimulated echo. J Chem Phys 1996. [DOI: 10.1063/1.472774] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|