Peculiarities in the Director Reorientation and the NMR Spectra Evolution in a Nematic Liquid Crystals under the Effect of Crossed Electric and Magnetic Fields
The illustrative description of the field-induced peculiarities of the director reorientation in the microsized nematic volumes under the effect of crossed magnetic <inline-formula> <math display="inline"> <semantics> <mi mathvariant="bold">B</mi> &l...
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| Format: | Article |
| Language: | English |
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MDPI AG
2019-05-01
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| Series: | Crystals |
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| Online Access: | https://www.mdpi.com/2073-4352/9/5/262 |
| _version_ | 1818033476099637248 |
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| author | Alex V. Zakharov Izabela Sliwa |
| author_facet | Alex V. Zakharov Izabela Sliwa |
| author_sort | Alex V. Zakharov |
| collection | DOAJ |
| description | The illustrative description of the field-induced peculiarities of the director reorientation in the microsized nematic volumes under the effect of crossed magnetic <inline-formula> <math display="inline"> <semantics> <mi mathvariant="bold">B</mi> </semantics> </math> </inline-formula> and electric <inline-formula> <math display="inline"> <semantics> <mi mathvariant="bold">E</mi> </semantics> </math> </inline-formula> fields have been proposed. The most interesting feature of such configuration is that the nematic phase becomes unstable after applying the strong <inline-formula> <math display="inline"> <semantics> <mi mathvariant="bold">E</mi> </semantics> </math> </inline-formula>. The theoretical analysis of the reorientational dynamics of the director field provides an evidence for the appearance of the spatially periodic patterns in response to applied large <inline-formula> <math display="inline"> <semantics> <mi mathvariant="bold">E</mi> </semantics> </math> </inline-formula> directed at an angle <inline-formula> <math display="inline"> <semantics> <mi>α</mi> </semantics> </math> </inline-formula> to <inline-formula> <math display="inline"> <semantics> <mi mathvariant="bold">B</mi> </semantics> </math> </inline-formula>. The feature of this approach is that the periodic distortions arise spontaneously from a homogeneously aligned nematic sample that ultimately induces a faster response than in the uniform mode. The nonuniform rotational modes involve additional internal elastic distortions of the conservative nematic system and, as a result, these deformations decrease of the viscous contribution <inline-formula> <math display="inline"> <semantics> <msub> <mi>U</mi> <mi>vis</mi> </msub> </semantics> </math> </inline-formula> to the total energy <i>U</i> of the nematic phase. In turn, that decreasing of <inline-formula> <math display="inline"> <semantics> <msub> <mi>U</mi> <mi>vis</mi> </msub> </semantics> </math> </inline-formula> leads to decrease of the effective rotational viscosity coefficient <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>γ</mi> <mi>eff</mi> </msub> <mrow> <mo>(</mo> <mi>α</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math> </inline-formula>. That is, a lower value of <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>γ</mi> <mi>eff</mi> </msub> <mrow> <mo>(</mo> <mi>α</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math> </inline-formula>, which is less than one in the bulk nematic phase, gives the less relaxation time <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>τ</mi> <mi>on</mi> </msub> <mrow> <mo>(</mo> <mi>α</mi> <mo>)</mo> </mrow> <mo>∼</mo> <msub> <mi>γ</mi> <mi>eff</mi> </msub> <mrow> <mo>(</mo> <mi>α</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math> </inline-formula>, when <inline-formula> <math display="inline"> <semantics> <mi>α</mi> </semantics> </math> </inline-formula> is bigger than the threshold value <inline-formula> <math display="inline"> <semantics> <msub> <mi>α</mi> <mi>th</mi> </msub> </semantics> </math> </inline-formula>. The results obtained by Deuterium NMR spectroscopy confirm theoretically obtained dependencies of <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>τ</mi> <mi>on</mi> </msub> <mrow> <mo>(</mo> <mi>α</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math> </inline-formula> on <inline-formula> <math display="inline"> <semantics> <mi>α</mi> </semantics> </math> </inline-formula>. |
| first_indexed | 2024-12-10T06:23:52Z |
| format | Article |
| id | doaj.art-f725ba2d00e5437fa90ef446bd0a74d9 |
| institution | Directory Open Access Journal |
| issn | 2073-4352 |
| language | English |
| last_indexed | 2024-12-10T06:23:52Z |
| publishDate | 2019-05-01 |
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| record_format | Article |
| series | Crystals |
| spelling | doaj.art-f725ba2d00e5437fa90ef446bd0a74d92022-12-22T01:59:16ZengMDPI AGCrystals2073-43522019-05-019526210.3390/cryst9050262cryst9050262Peculiarities in the Director Reorientation and the NMR Spectra Evolution in a Nematic Liquid Crystals under the Effect of Crossed Electric and Magnetic FieldsAlex V. Zakharov0Izabela Sliwa1Saint Petersburg Institute for Machine Sciences, The Russian Academy of Sciences, Saint Petersburg 199178, RussiaPoznan University of Economics and Business, Department of Mathematical Economics, Al. Niepodleglosci 10, 61-875 Poznan, PolandThe illustrative description of the field-induced peculiarities of the director reorientation in the microsized nematic volumes under the effect of crossed magnetic <inline-formula> <math display="inline"> <semantics> <mi mathvariant="bold">B</mi> </semantics> </math> </inline-formula> and electric <inline-formula> <math display="inline"> <semantics> <mi mathvariant="bold">E</mi> </semantics> </math> </inline-formula> fields have been proposed. The most interesting feature of such configuration is that the nematic phase becomes unstable after applying the strong <inline-formula> <math display="inline"> <semantics> <mi mathvariant="bold">E</mi> </semantics> </math> </inline-formula>. The theoretical analysis of the reorientational dynamics of the director field provides an evidence for the appearance of the spatially periodic patterns in response to applied large <inline-formula> <math display="inline"> <semantics> <mi mathvariant="bold">E</mi> </semantics> </math> </inline-formula> directed at an angle <inline-formula> <math display="inline"> <semantics> <mi>α</mi> </semantics> </math> </inline-formula> to <inline-formula> <math display="inline"> <semantics> <mi mathvariant="bold">B</mi> </semantics> </math> </inline-formula>. The feature of this approach is that the periodic distortions arise spontaneously from a homogeneously aligned nematic sample that ultimately induces a faster response than in the uniform mode. The nonuniform rotational modes involve additional internal elastic distortions of the conservative nematic system and, as a result, these deformations decrease of the viscous contribution <inline-formula> <math display="inline"> <semantics> <msub> <mi>U</mi> <mi>vis</mi> </msub> </semantics> </math> </inline-formula> to the total energy <i>U</i> of the nematic phase. In turn, that decreasing of <inline-formula> <math display="inline"> <semantics> <msub> <mi>U</mi> <mi>vis</mi> </msub> </semantics> </math> </inline-formula> leads to decrease of the effective rotational viscosity coefficient <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>γ</mi> <mi>eff</mi> </msub> <mrow> <mo>(</mo> <mi>α</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math> </inline-formula>. That is, a lower value of <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>γ</mi> <mi>eff</mi> </msub> <mrow> <mo>(</mo> <mi>α</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math> </inline-formula>, which is less than one in the bulk nematic phase, gives the less relaxation time <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>τ</mi> <mi>on</mi> </msub> <mrow> <mo>(</mo> <mi>α</mi> <mo>)</mo> </mrow> <mo>∼</mo> <msub> <mi>γ</mi> <mi>eff</mi> </msub> <mrow> <mo>(</mo> <mi>α</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math> </inline-formula>, when <inline-formula> <math display="inline"> <semantics> <mi>α</mi> </semantics> </math> </inline-formula> is bigger than the threshold value <inline-formula> <math display="inline"> <semantics> <msub> <mi>α</mi> <mi>th</mi> </msub> </semantics> </math> </inline-formula>. The results obtained by Deuterium NMR spectroscopy confirm theoretically obtained dependencies of <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>τ</mi> <mi>on</mi> </msub> <mrow> <mo>(</mo> <mi>α</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math> </inline-formula> on <inline-formula> <math display="inline"> <semantics> <mi>α</mi> </semantics> </math> </inline-formula>.https://www.mdpi.com/2073-4352/9/5/262liquid crystalsNMRhydrodynamics of liquid crystals |
| spellingShingle | Alex V. Zakharov Izabela Sliwa Peculiarities in the Director Reorientation and the NMR Spectra Evolution in a Nematic Liquid Crystals under the Effect of Crossed Electric and Magnetic Fields Crystals liquid crystals NMR hydrodynamics of liquid crystals |
| title | Peculiarities in the Director Reorientation and the NMR Spectra Evolution in a Nematic Liquid Crystals under the Effect of Crossed Electric and Magnetic Fields |
| title_full | Peculiarities in the Director Reorientation and the NMR Spectra Evolution in a Nematic Liquid Crystals under the Effect of Crossed Electric and Magnetic Fields |
| title_fullStr | Peculiarities in the Director Reorientation and the NMR Spectra Evolution in a Nematic Liquid Crystals under the Effect of Crossed Electric and Magnetic Fields |
| title_full_unstemmed | Peculiarities in the Director Reorientation and the NMR Spectra Evolution in a Nematic Liquid Crystals under the Effect of Crossed Electric and Magnetic Fields |
| title_short | Peculiarities in the Director Reorientation and the NMR Spectra Evolution in a Nematic Liquid Crystals under the Effect of Crossed Electric and Magnetic Fields |
| title_sort | peculiarities in the director reorientation and the nmr spectra evolution in a nematic liquid crystals under the effect of crossed electric and magnetic fields |
| topic | liquid crystals NMR hydrodynamics of liquid crystals |
| url | https://www.mdpi.com/2073-4352/9/5/262 |
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