{"title":"各向同性相向列液晶的绝热体积模量和声速","authors":"Carlindo Vitoriano","doi":"10.1007/s13538-025-01794-x","DOIUrl":null,"url":null,"abstract":"<div><p>We obtain an expression for the sound velocity <span>\\(\\varvec{v}_{\\varvec{s}}\\)</span> in the isotropic phase of nematic liquid crystals from the nematodynamics that incorporates the energetic coupling between <span>\\(\\varvec{Q}_{\\varvec{\\alpha \\beta }}\\varvec{(} \\textbf{r}\\varvec{)}\\)</span> (the order parameter of the nematic-isotropic transition) and inhomogeneities in the local mass density <span>\\(\\varvec{\\rho }\\varvec{(} \\textbf{r}\\varvec{)}\\)</span>. It differs from the well-known formula <span>\\(\\varvec{v}_{\\varvec{s}}\\varvec{=}\\sqrt{\\varvec{B}_{\\varvec{s}}\\varvec{/}\\varvec{\\rho }_{\\varvec{0}}}\\)</span>, in which <span>\\(\\varvec{B}_{\\varvec{s}}\\)</span> is the adiabatic bulk modulus and <span>\\(\\varvec{\\rho }_{\\varvec{0}}\\)</span> is the average value of <span>\\(\\varvec{\\rho }\\varvec{(} \\textbf{r}\\varvec{)}\\)</span>. Using the measured values of <span>\\(\\varvec{v}_{\\varvec{s}}\\)</span> in the regime of low frequencies, we then calculate <span>\\(\\varvec{B}_{\\varvec{s}}\\)</span> as a function of temperature for three different liquid crystals. The critical form of <span>\\(\\varvec{B}_{\\varvec{s}}\\)</span> that emerges is unexpected, and its physical interpretation is discussed in terms of the Anderson-Grüneisen parameter. An explanation for the critical dip of <span>\\(\\varvec{v}_{\\varvec{s}}\\)</span> near the nematic-isotropic transition is provided.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"55 4","pages":""},"PeriodicalIF":1.5000,"publicationDate":"2025-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Adiabatic Bulk Modulus and Sound Velocity of Nematic Liquid Crystals in the Isotropic Phase\",\"authors\":\"Carlindo Vitoriano\",\"doi\":\"10.1007/s13538-025-01794-x\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>We obtain an expression for the sound velocity <span>\\\\(\\\\varvec{v}_{\\\\varvec{s}}\\\\)</span> in the isotropic phase of nematic liquid crystals from the nematodynamics that incorporates the energetic coupling between <span>\\\\(\\\\varvec{Q}_{\\\\varvec{\\\\alpha \\\\beta }}\\\\varvec{(} \\\\textbf{r}\\\\varvec{)}\\\\)</span> (the order parameter of the nematic-isotropic transition) and inhomogeneities in the local mass density <span>\\\\(\\\\varvec{\\\\rho }\\\\varvec{(} \\\\textbf{r}\\\\varvec{)}\\\\)</span>. It differs from the well-known formula <span>\\\\(\\\\varvec{v}_{\\\\varvec{s}}\\\\varvec{=}\\\\sqrt{\\\\varvec{B}_{\\\\varvec{s}}\\\\varvec{/}\\\\varvec{\\\\rho }_{\\\\varvec{0}}}\\\\)</span>, in which <span>\\\\(\\\\varvec{B}_{\\\\varvec{s}}\\\\)</span> is the adiabatic bulk modulus and <span>\\\\(\\\\varvec{\\\\rho }_{\\\\varvec{0}}\\\\)</span> is the average value of <span>\\\\(\\\\varvec{\\\\rho }\\\\varvec{(} \\\\textbf{r}\\\\varvec{)}\\\\)</span>. Using the measured values of <span>\\\\(\\\\varvec{v}_{\\\\varvec{s}}\\\\)</span> in the regime of low frequencies, we then calculate <span>\\\\(\\\\varvec{B}_{\\\\varvec{s}}\\\\)</span> as a function of temperature for three different liquid crystals. The critical form of <span>\\\\(\\\\varvec{B}_{\\\\varvec{s}}\\\\)</span> that emerges is unexpected, and its physical interpretation is discussed in terms of the Anderson-Grüneisen parameter. An explanation for the critical dip of <span>\\\\(\\\\varvec{v}_{\\\\varvec{s}}\\\\)</span> near the nematic-isotropic transition is provided.</p></div>\",\"PeriodicalId\":499,\"journal\":{\"name\":\"Brazilian Journal of Physics\",\"volume\":\"55 4\",\"pages\":\"\"},\"PeriodicalIF\":1.5000,\"publicationDate\":\"2025-05-13\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Brazilian Journal of Physics\",\"FirstCategoryId\":\"101\",\"ListUrlMain\":\"https://link.springer.com/article/10.1007/s13538-025-01794-x\",\"RegionNum\":4,\"RegionCategory\":\"物理与天体物理\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"PHYSICS, MULTIDISCIPLINARY\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Brazilian Journal of Physics","FirstCategoryId":"101","ListUrlMain":"https://link.springer.com/article/10.1007/s13538-025-01794-x","RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"PHYSICS, MULTIDISCIPLINARY","Score":null,"Total":0}
Adiabatic Bulk Modulus and Sound Velocity of Nematic Liquid Crystals in the Isotropic Phase
We obtain an expression for the sound velocity \(\varvec{v}_{\varvec{s}}\) in the isotropic phase of nematic liquid crystals from the nematodynamics that incorporates the energetic coupling between \(\varvec{Q}_{\varvec{\alpha \beta }}\varvec{(} \textbf{r}\varvec{)}\) (the order parameter of the nematic-isotropic transition) and inhomogeneities in the local mass density \(\varvec{\rho }\varvec{(} \textbf{r}\varvec{)}\). It differs from the well-known formula \(\varvec{v}_{\varvec{s}}\varvec{=}\sqrt{\varvec{B}_{\varvec{s}}\varvec{/}\varvec{\rho }_{\varvec{0}}}\), in which \(\varvec{B}_{\varvec{s}}\) is the adiabatic bulk modulus and \(\varvec{\rho }_{\varvec{0}}\) is the average value of \(\varvec{\rho }\varvec{(} \textbf{r}\varvec{)}\). Using the measured values of \(\varvec{v}_{\varvec{s}}\) in the regime of low frequencies, we then calculate \(\varvec{B}_{\varvec{s}}\) as a function of temperature for three different liquid crystals. The critical form of \(\varvec{B}_{\varvec{s}}\) that emerges is unexpected, and its physical interpretation is discussed in terms of the Anderson-Grüneisen parameter. An explanation for the critical dip of \(\varvec{v}_{\varvec{s}}\) near the nematic-isotropic transition is provided.
期刊介绍:
The Brazilian Journal of Physics is a peer-reviewed international journal published by the Brazilian Physical Society (SBF). The journal publishes new and original research results from all areas of physics, obtained in Brazil and from anywhere else in the world. Contents include theoretical, practical and experimental papers as well as high-quality review papers. Submissions should follow the generally accepted structure for journal articles with basic elements: title, abstract, introduction, results, conclusions, and references.