1
|
Thoen J, Cordoyiannis G, Jiang W, Mehl GH, Glorieux C. Phase transitions study of the liquid crystal DIO with a ferroelectric nematic, a nematic, and an intermediate phase and of mixtures with the ferroelectric nematic compound RM734 by adiabatic scanning calorimetry. Phys Rev E 2023; 107:014701. [PMID: 36797863 DOI: 10.1103/physreve.107.014701] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2022] [Accepted: 12/21/2022] [Indexed: 06/18/2023]
Abstract
High-resolution calorimetry has played a significant role in providing detailed information on phase transitions in liquid crystals. In particular, adiabatic scanning calorimetry (ASC), capable of providing simultaneous information on the temperature dependence of the specific enthalpy h(T) and on the specific heat capacity c_{p}(T), has proven to be an important tool to determine the order of transitions and render high-resolution information on pretransitional thermal behavior. Here we report on ASC results on the compound 2,3',4',5'-tetrafluoro[1,1'-biphenyl]-4-yl 2,6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate (DIO) and on mixtures with 4-[(4-nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). Both compounds exhibit a low-temperature ferroelectric nematic phase (N_{F}) and a high-temperature paraelectric nematic phase (N). However, in DIO these two phases are separated by an intermediate phase (N_{x}). From the detailed data of h(T) and c_{p}(T), we found that the intermediate phase was present in all the mixtures over the complete composition range, albeit with strongly decreasing temperature width for that phase with decreasing mole fraction of DIO (x_{DIO}). The x_{DIO} dependence on the transition temperatures for both transitions could be well described by a quadratic function. Both these transitions were weakly first order. The true latent heat of the N_{x}-N transition of DIO was as low as L=0.0075±0.0005J/g and L=0.23±0.03J/g for the N_{F}-N_{x} transition, which is about twice the previously reported value of 0.115 J/g for the N_{F}-N transition in RM734. In the mixtures both transition latent heats decrease gradually with decreasing x_{DIO}. At all the N_{x}-N transitions pretransition fluctuation effects are absent and these transitions are purely but very weakly first order. As in RM734 the transition from the N_{F} to the higher-temperature phase exhibits substantial pretransitional behavior, in particular, in the high-temperature phase. Power-law analysis of c_{p}(T) resulted in an effective critical exponent α=0.88±0.1 for DIO and this value decreased in the mixtures with decreasing x_{DIO} toward α=0.50±0.05 reported for RM734. Ideal mixture analysis of the phase diagram was consistent with ideal mixture behavior provided the total transition enthalpy change was used in the analysis.
Collapse
Affiliation(s)
- J Thoen
- Laboratory for Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
| | - G Cordoyiannis
- Condensed Matter Physics Department, Jožef Stefan Institute, 1000 Ljubljana, Slovenia
| | - W Jiang
- Department of Chemistry, University of Hull, Hull HU6 7RX, United Kingdom
| | - G H Mehl
- Department of Chemistry, University of Hull, Hull HU6 7RX, United Kingdom
| | - C Glorieux
- Laboratory for Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
| |
Collapse
|
2
|
Thoen J, Cordoyiannis G, Losada-Pérez P, Glorieux C. High-resolution investigation by Peltier-element-based adiabatic scanning calorimetry of binary liquid crystal mixtures with enhanced nematic ranges. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2021.117204] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
|
3
|
Paoloni S, Mercuri F, Zammit U, Leys J, Glorieux C, Thoen J. Analysis of rotator phase transitions in the linear alkanes hexacosane to triacontane by adiabatic scanning calorimetry and by photopyroelectric calorimetry. J Chem Phys 2018. [DOI: 10.1063/1.5020146] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Affiliation(s)
- S. Paoloni
- Dipartimento Ingegneria Industriale, Università di Roma “Tor Vergata,” Rome, Italy
| | - F. Mercuri
- Dipartimento Ingegneria Industriale, Università di Roma “Tor Vergata,” Rome, Italy
| | - U. Zammit
- Dipartimento Ingegneria Industriale, Università di Roma “Tor Vergata,” Rome, Italy
| | - J. Leys
- Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, P.O. Box 2416, B-3001 Leuven, Belgium
| | - C. Glorieux
- Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, P.O. Box 2416, B-3001 Leuven, Belgium
| | - J. Thoen
- Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, P.O. Box 2416, B-3001 Leuven, Belgium
| |
Collapse
|
4
|
Roozen NB, Glorieux C, Liu L, Rychtáriková M, Van der Donck T, Jacobs A. Converting sunlight into audible sound by means of the photoacoustic effect: The Heliophone. J Acoust Soc Am 2016; 140:1697. [PMID: 27914443 DOI: 10.1121/1.4962493] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
One hundred and thirty-five years after Alexander Graham Bell and his assistant Charles Sumner Tainter explored the photoacoustic effect, and about 40 years after Rosencwaig and Gersho modeled the effect in a photoacoustic cell configuration, the phenomenon is revisited in a "Heliophone" device that converts sunlight into sound. The light is focused on a carbon blackened copper coated Kapton foil in an acoustic cell by means of a compound parabolic collimator, and its intensity is modulated by a mechanical chopper. A horn is employed to make the sound audible without electronic amplification. The description of the photoacoustic effect that was introduced by Rosencwaig and Gersho is extended to a cell-horn configuration, in which the periodically heated air above the foil acts as an oscillating piston, driving acoustic waves in the horn. The pressure in the cavity-horn assembly is calculated by considering the air layer piston as an equivalent volume velocity source. The importance of the carbon black (soot) layer to enhance light absorption, but above all to enhance the photothermal excitation efficiency, is elucidated by means of an experimentally supported physical model.
Collapse
Affiliation(s)
- N B Roozen
- Laboratory of Acoustics, Division Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
| | - C Glorieux
- Laboratory of Acoustics, Division Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
| | - L Liu
- Laboratory of Acoustics, Division Soft Matter and Biophysics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
| | - M Rychtáriková
- STU Bratislava, Faculty of Civil Engineering, Department of Building Structures, Radlinskeho 11, Bratislava, 810 05, Slovak Republic
| | - T Van der Donck
- Department of Materials Engineering, KU Leuven, Kasteelpark Arenberg 44, 3001 Leuven, Belgium
| | - A Jacobs
- Overtoon, Platform for Sound Art, Luchtvaartsquare 19, 1070, Brussels, Belgium
| |
Collapse
|
5
|
Verstraeten B, Sermeus J, Salenbien R, Fivez J, Shkerdin G, Glorieux C. Determination of thermoelastic material properties by differential heterodyne detection of impulsive stimulated thermal scattering. Photoacoustics 2015; 3:64-77. [PMID: 26236643 PMCID: PMC4519808 DOI: 10.1016/j.pacs.2015.05.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Revised: 05/27/2015] [Accepted: 05/28/2015] [Indexed: 06/04/2023]
Abstract
The underlying working principle of detecting impulsive stimulated scattering signals in a differential configuration of heterodyne diffraction detection is unraveled by involving optical scattering theory. The feasibility of the method for the thermoelastic characterization of coating-substrate systems is demonstrated on the basis of simulated data containing typical levels of noise. Besides the classical analysis of the photoacoustic part of the signals, which involves fitting surface acoustic wave dispersion curves, the photothermal part of the signals is analyzed by introducing thermal wave dispersion curves to represent and interpret their grating wavelength dependence. The intrinsic possibilities and limitations of both inverse problems are quantified by making use of least and most squares analysis.
Collapse
Affiliation(s)
- B Verstraeten
- Laboratory of Acoustics and Thermal Physics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, B-3001 Heverlee, Belgium
| | - J Sermeus
- Laboratory of Acoustics and Thermal Physics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, B-3001 Heverlee, Belgium
| | - R Salenbien
- Laboratory of Acoustics and Thermal Physics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, B-3001 Heverlee, Belgium
| | - J Fivez
- KU Leuven, Campus Brussels, Warmoesberg 26, B-1000 Brussels, Belgium
| | - G Shkerdin
- Institute of Radio Engineering and Electronics of the Russian Academy of Sciences, Vvedensky sq., 1, Fryazino, Moscow Region, Russia
| | - C Glorieux
- Laboratory of Acoustics and Thermal Physics, Department of Physics and Astronomy, KU Leuven, Celestijnenlaan 200D, B-3001 Heverlee, Belgium
| |
Collapse
|
6
|
Contreras-Gallegos E, Domínguez-Pacheco FA, Hernández-Aguilar C, Carballo-Carballo A, Cruz-Orea A, Thoen J, Glorieux C. Study of Thermal and Structural Properties of Starch Granules from Different Maize Genotypes. FOOD BIOPHYS 2014. [DOI: 10.1007/s11483-014-9344-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
|
7
|
Felipe K, Benites J, Glorieux C, Sid B, Valenzuela M, Kviecinski M, Pedrosa R, Valderrama J, Levêque P, Gallez B, Verrax J, Buc Calderon P. Antiproliferative effects of phenylaminonaphthoquinones are increased by ascorbate and associated with the appearance of a senescent phenotype in human bladder cancer cells. Biochem Biophys Res Commun 2013; 433:573-8. [DOI: 10.1016/j.bbrc.2013.03.028] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2013] [Accepted: 03/13/2013] [Indexed: 11/16/2022]
|
8
|
Shkerdin G, Glorieux C. Interaction of Lamb modes with an inclusion. Ultrasonics 2013; 53:130-140. [PMID: 22727491 DOI: 10.1016/j.ultras.2012.04.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Revised: 04/29/2012] [Accepted: 04/30/2012] [Indexed: 06/01/2023]
Abstract
The interaction of Lamb modes propagating in a steel plate containing a thin inclusion is analyzed for cases where the inclusion material has elastic parameters similar to the ones of the plate, and where the inclusion is in perfect mechanical contact with the surrounding plate material. A modal decomposition method is used to calculate the conversion of an incident Lamb mode to other modes. Hence, the influence of the type of incident mode, of the location and geometry of the inclusion, and of the elastic parameters of the inclusion and plate material on the mode conversion coefficients is analyzed. Besides the expected increase of the conversion efficiency with increasing cross section of the inclusion, it is found that due to reasons of symmetry, the presence of an inclusion leads to an efficient conversion of an incident S0 mode into reflected and transmitted A0 modes, unless the inclusion is located very close to the plate center. On the other hand, the conversion efficiency of an incident A0 mode into a reflected A0 mode is found to be strongly dependent on the depth of the inclusion, this conversion even disappearing for some location depths. For the cases studied, the inclusion location dependence of the mode conversion seems to be correlated with the normal profile of the longitudinal normal stress component σ(yy)(y). As intuitively expected, the mode conversion efficiency increases with the mismatch of an acoustic impedance like factor between the uniform plate and the inclusion region.
Collapse
Affiliation(s)
- G Shkerdin
- Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde, K.U. Leuven, Celestijnenlaan 200 D, B-3001 Leuven, Belgium
| | | |
Collapse
|
9
|
Hauptmann M, Struyf H, Mertens P, Heyns M, De Gendt S, Glorieux C, Brems S. Towards an understanding and control of cavitation activity in 1 MHz ultrasound fields. Ultrason Sonochem 2013; 20:77-88. [PMID: 22705075 DOI: 10.1016/j.ultsonch.2012.05.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2012] [Revised: 04/27/2012] [Accepted: 05/06/2012] [Indexed: 05/21/2023]
Abstract
Various industrial processes such as sonochemical processing and ultrasonic cleaning strongly rely on the phenomenon of acoustic cavitation. As the occurrence of acoustic cavitation is incorporating a multitude of interdependent effects, the amount of cavitation activity in a vessel is strongly depending on the ultrasonic process conditions. It is therefore crucial to quantify cavitation activity as a function of the process parameters. At 1 MHz, the active cavitation bubbles are so small that it is becoming difficult to observe them in a direct way. Hence, another metrology based on secondary effects of acoustic cavitation is more suitable to study cavitation activity. In this paper we present a detailed analysis of acoustic cavitation phenomena at 1 MHz ultrasound by means of time-resolved measurements of sonoluminescence, cavitation noise, and synchronized high-speed stroboscopic Schlieren imaging. It is shown that a correlation exists between sonoluminescence, and the ultraharmonic and broadband signals extracted from the cavitation noise spectra. The signals can be utilized to characterize different regimes of cavitation activity at different acoustic power densities. When cavitation activity sets on, the aforementioned signals correlate to fluctuations in the Schlieren contrast as well as the number of nucleated bubbles extracted from the Schlieren Images. This additionally proves that signals extracted from cavitation noise spectra truly represent a measure for cavitation activity. The cyclic behavior of cavitation activity is investigated and related to the evolution of the bubble populations in the ultrasonic tank. It is shown that cavitation activity is strongly linked to the occurrence of fast-moving bubbles. The origin of this "bubble streamers" is investigated and their role in the initialization and propagation of cavitation activity throughout the sonicated liquid is discussed. Finally, it is shown that bubble activity can be stabilized and enhanced by the use of pulsed ultrasound by conserving and recycling active bubbles between subsequent pulsing cycles.
Collapse
Affiliation(s)
- M Hauptmann
- IMEC vzw, Kapeldreef 75, B-3001 Leuven, Belgium.
| | | | | | | | | | | | | |
Collapse
|
10
|
Hauptmann M, Frederickx F, Struyf H, Mertens P, Heyns M, De Gendt S, Glorieux C, Brems S. Enhancement of cavitation activity and particle removal with pulsed high frequency ultrasound and supersaturation. Ultrason Sonochem 2013; 20:69-76. [PMID: 22682476 DOI: 10.1016/j.ultsonch.2012.04.015] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Revised: 04/27/2012] [Accepted: 04/28/2012] [Indexed: 05/21/2023]
Abstract
Megasonic cleaning as applied in leading edge semiconductor device manufacturing strongly relies on the phenomenon of acoustic cavitation. As the occurrence of acoustic cavitation is incorporating a multitude of interdependent effects, the amount of cavitation activity in the cleaning liquid strongly depends on the sonication conditions. It is shown that cavitation activity as measured by means of ultraharmonic cavitation noise can be significantly enhanced when pulsed sonication is applied to a gas supersaturated liquid under traveling wave conditions. It is demonstrated that this enhancement coincides with a dramatic increase in particle removal and is therefore of great interest for megasonic cleaning applications. It is demonstrated that the optimal pulse parameters are determined by the dissolution time of the active bubbles, whereas the amount of cavitation activity depends on the ratio between pulse-off and pulse-on time as well as the applied acoustic power. The optimal pulse-off time is independent of the corresponding pulse-on time but increases significantly with increasing gas concentration. We show that on the other hand, supersaturation is needed to enable acoustic cavitation at aforementioned conditions, but has to be kept below values, for which active bubbles cannot dissolve anymore and are therefore lost during subsequent pulses. For the applicable range of gas contents between 100% and 130% saturation, the optimal pulse-off time reaches values between 150 and 340 ms, respectively. Full particle removal of 78 nm-diameter silica particles at a power density of 0.67 W/cm(2) is obtained for the optimal pulse-off times. The optimal pulse-off time values are derived from the dissolution time of bubbles with a radius of 3.3 μm and verified experimentally. The bubble radius used in the calculations corresponds to the linear resonance size in a 928 kHz sound field, which demonstrates that the recycling of active bubbles is the main enhancement mechanism. The optimal choice of the pulsing conditions however is constrained by the trade-off between the effective sonication time and the desire to have a sufficient amount of active bubbles at lower powers, which might be necessary if very delicate structures have to be cleaned.
Collapse
Affiliation(s)
- M Hauptmann
- Imec vzw, Kapeldreef 75, B-3001 Leuven, Belgium.
| | | | | | | | | | | | | | | |
Collapse
|
11
|
Tripathi CSP, Losada-Pérez P, Leys J, Cordoyiannis G, Glorieux C, Thoen J. Evidence from adiabatic scanning calorimetry for the Halperin-Lubensky-Ma effect at the N-SmA phase transitions in mixtures of 7OCB+heptane with an injected SmA phase. Eur Phys J E Soft Matter 2012; 35:54. [PMID: 22763720 DOI: 10.1140/epje/i2012-12054-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Revised: 06/05/2012] [Accepted: 06/11/2012] [Indexed: 06/01/2023]
Abstract
The high-resolution adiabatic scanning calorimetric technique has been used to investigate the nematic-smectic A transition (N-SmA in binary mixtures of the non-smectogenic liquid crystal heptyloxycyanobiphenyl (7OCB) and heptane, exhibiting a so-called injected smectic A phase. With the exception of a mixture with the lowest heptane mole fraction for which only an upper limit of 0.2 ± 0.2 J kg(-1) for a possible latent heat could be obtained, for all other mixtures finite latent heats were obtained. The mole fraction dependence of the latent heat could be well fitted with a crossover function consistent with a mean-field free energy expression with a non-zero cubic term arising from the Halperin-Lubensky-Ma (HLM) coupling between the SmA order parameter and the orientational director fluctuations. The mole fraction dependence of the heat capacity effective critical exponents is similar to that observed in mixtures of the two liquid crystals octyloxycyanobiphenyl (8OCB) and nonylcyanobiphenyl (9OCB). The thermal behavior observed along the N-SmA phase transition line yields further strong evidence for the HLM coupling effect.
Collapse
Affiliation(s)
- C S P Tripathi
- Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde, KU Leuven, Leuven, Belgium.
| | | | | | | | | | | |
Collapse
|
12
|
Kviecinski M, Pedrosa R, Felipe K, Farias M, Glorieux C, Valenzuela M, Sid B, Benites J, Valderrama J, Verrax J, Buc Calderon P. Inhibition of cell proliferation and migration by oxidative stress from ascorbate-driven juglone redox cycling in human bladder-derived T24 cells. Biochem Biophys Res Commun 2012; 421:268-73. [DOI: 10.1016/j.bbrc.2012.03.150] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2012] [Accepted: 03/30/2012] [Indexed: 12/13/2022]
|
13
|
Lagrain B, Wilderjans E, Glorieux C, Delcour JA. Importance of Gluten and Starch for Structural and Textural Properties of Crumb from Fresh and Stored Bread. FOOD BIOPHYS 2012. [DOI: 10.1007/s11483-012-9255-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
14
|
Hauptmann M, Brems S, Struyf H, Mertens P, Heyns M, De Gendt S, Glorieux C. Time-resolved monitoring of cavitation activity in megasonic cleaning systems. Rev Sci Instrum 2012; 83:034904. [PMID: 22462949 DOI: 10.1063/1.3697710] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The occurrence of acoustic cavitation in the cleaning liquid is a crucial precondition for the performance of megasonic cleaning systems. Hence, a fundamental understanding of the impact of different parameters of the megasonic process on cavitation activity is necessary. A setup capable of synchronously measuring sonoluminescence and acoustic emission originating from acoustically active bubbles is presented. The system also includes a high-speed-stroboscopic Schlieren imaging system to directly visualize the influence of cavitation activity on the Schlieren contrast and resolvable bubbles. This allows a thorough characterization of the mutual interaction of cavitation bubbles with the sound field and with each other. Results obtained during continuous sonication of argon-saturated water at various nominal power densities indicate that acoustic cavitation occurs in a cyclic manner, during which periods of stable and inertial cavitation activity alternate. The occurrence of higher and ultraharmonics in the acoustic emission spectra is characteristic for the stable cavitation state. The inertial cavitation state is characterized by a strong attenuation of the sound field, the explosive growth of bubbles and the occurrence of broadband components in the acoustic spectra. Both states can only be sustained at sufficiently high intensities of the sound field. At lower intensities, their occurrences are limited to short, random bursts. Cleaning activity can be linked to the cavitation activity through the measurement of particle removal on standard 200 mm silicon wafers. It is found that the particle removal efficiency is reduced, when a continuous state of cavitation activity ceases to exist.
Collapse
Affiliation(s)
- M Hauptmann
- IMEC vzw, Kapeldreef 75, B-3001 Leuven, Belgium.
| | | | | | | | | | | | | |
Collapse
|
15
|
Fivez J, Longuemart S, Glorieux C. Fragility of supercooled liquids from differential scanning calorimetry traces: theory and experiment. J Chem Phys 2012; 136:044502. [PMID: 22299886 DOI: 10.1063/1.3678313] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Starting from the Debye model for frequency-dependent specific heat and the Vogel-Fulcher-Tammann (VFT) model for its relaxation time, an analytic expression is presented for the heat capacity versus temperature trace for differential scanning calorimetry (DSC) of glass transitions, suggesting a novel definition of the glass transition temperature based on a dimensionless criterion. An explicit expression is presented for the transition temperature as a function of the VFT parameters and the cooling rate, and for the slope as a function of fragility. Also a generalization of the results to non-VFT and non-Debye relaxation is given. Two unique ways are proposed to tackle the inverse problem, i.e., to extract the fragility from an experimental DSC trace. Good agreement is found between theoretically predicted DSC traces and experimental DSC traces for glycerol for different cooling rates.
Collapse
Affiliation(s)
- J Fivez
- HUB, Warmoesberg 26, B-1000 Brussel, Belgium.
| | | | | |
Collapse
|
16
|
Descheemaeker J, Glorieux C, Lauriks W, Groby JP, Leclaire P, Boeckx L. Study of Circumferential Waves on a Poroelastic Cylinder. ACTA ACUST UNITED AC 2011. [DOI: 10.3813/aaa.918453] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The dispersion relations of acoustic modes in poroelastic cylinders with and without elastic shell coating are determined and solved. The influence of elastic frame parameters and the Biot parameters on the dispersion curves is studied in the configuration with and without coating.
The dispersive Rayleigh and whispering gallery waves are highly sensitive to the density and the shear modulus of the skeleton, opening a perspective for the evaluation of the mechanical parameters of poroelastic materials confined in cylindrical tubes during the manufacturing process. The
predicted dispersion curves are validated with experimental results obtained by use of different experimental set-up in the case of a porous circular cylinder.
Collapse
|
17
|
van Dalen KN, Drijkoningen GG, Smeulders DMJ, Heller HKJ, Glorieux C, Sarens B, Verstraeten B. Medium characterization from interface-wave impedance and ellipticity using simultaneous displacement and pressure measurements. J Acoust Soc Am 2011; 130:1299-1312. [PMID: 21895072 DOI: 10.1121/1.3605537] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The interface-wave impedance and ellipticity are wave attributes that interrelate the full waveforms as observed in different components. For each of the fluid/elastic-solid interface waves, i.e., the pseudo-Rayleigh (pR) and Stoneley (St) waves, the impedance and ellipticity are found to have different functional dependencies on Young's modulus and Poisson's ratio. By combining the attributes in a cost function, unique and stable estimates of these parameters can be obtained, particularly when using the St wave. In a validation experiment, the impedance of the laser-excited pR wave is successfully extracted from simultaneous measurements of the normal particle displacement and the fluid pressure at a water/aluminum interface. The displacement is measured using a laser Doppler vibrometer (LDV) and the pressure with a needle hydrophone. Any LDV measurement is perturbed by refractive-index changes along the LDV beam once acoustic waves interfere with the beam. Using a model that accounts for these perturbations, an impedance decrease of 28% with respect to the plane wave impedance of the pR wave is predicted for the water/aluminum configuration. Although this deviation is different for the experimentally extracted impedance, there is excellent agreement between the observed and predicted pR waveforms in both the particle displacement and fluid pressure.
Collapse
Affiliation(s)
- K N van Dalen
- Faculty of Civil Engineering and Geosciences, Department of Geotechnology, Delft University of Technology, Stevinweg 1, 2628 CN Delft, The Netherlands.
| | | | | | | | | | | | | |
Collapse
|
18
|
Verrax J, Beck R, Dejeans N, Glorieux C, Sid B, Pedrosa RC, Benites J, Vásquez D, Valderrama JA, Calderon PB. Redox-active quinones and ascorbate: an innovative cancer therapy that exploits the vulnerability of cancer cells to oxidative stress. Anticancer Agents Med Chem 2011; 11:213-21. [PMID: 21395522 DOI: 10.2174/187152011795255902] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2011] [Accepted: 03/08/2011] [Indexed: 11/22/2022]
Abstract
Cancer cells are particularly vulnerable to treatments impairing redox homeostasis. Reactive oxygen species (ROS) can indeed play an important role in the initiation and progression of cancer, and advanced stage tumors frequently exhibit high basal levels of ROS that stimulate cell proliferation and promote genetic instability. In addition, an inverse correlation between histological grade and antioxidant enzyme activities is frequently observed in human tumors, further supporting the existence of a redox dysregulation in cancer cells. This biochemical property can be exploited by using redox-modulating compounds, which represent an interesting approach to induce cancer cell death. Thus, we have developed a new strategy based on the use of pharmacologic concentrations of ascorbate and redox-active quinones. Ascorbate-driven quinone redox cycling leads to ROS formation and provoke an oxidative stress that preferentially kill cancer cells and spare healthy tissues. Cancer cell death occurs through necrosis and the underlying mechanism implies an energetic impairment (ATP depletion) that is likely due to glycolysis inhibition. Additional mechanisms that participate to cell death include calcium equilibrium impairment and oxidative cleavage of protein chaperone Hsp90. Given the low systemic toxicity of ascorbate and the impairment of crucial survival pathways when associated with redox-active quinones, these combinations could represent an original approach that could be combined to standard cancer therapy.
Collapse
Affiliation(s)
- J Verrax
- Toxicology and Cancer Biology Research Group, Louvain Drug Research Institute (LDRI), Université Catholique de Louvain, Brussels, Belgium.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
19
|
Beck R, Dejeans N, Glorieux C, C. Pedrosa R, Vasquez D, A. Valderrama J, B. Calderon P, Verrax J. Molecular Chaperone Hsp90 as a Target for Oxidant-Based Anticancer Therapies. Curr Med Chem 2011; 18:2816-25. [DOI: 10.2174/092986711796011256] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2011] [Accepted: 05/15/2011] [Indexed: 11/22/2022]
|
20
|
Octave JN, Huysseune S, Glorieux C, Tasiaux B, Kienlen-Campard P. C8 Gènes différentiellement exprimés sous l’influence de l’APP. Rev Neurol (Paris) 2009. [DOI: 10.1016/s0035-3787(09)72561-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
|
21
|
Abstract
The nonlinear interaction between a high frequency probing Lamb wave and a bilayer containing a tangential delamination at the interlayer interface, whose contact conditions are dynamically changing due to a high amplitude Lamb wave with a long wavelength, is modeled in a quasistationary approach. The impact of the evolution of the contact condition on the mode conversion coefficients that describe the interaction of the probing wave with the delamination region leads to spectral enrichment due to cross-modulation spectral components between the probing wave and the modulating wave. The dynamical behavior of the normal displacement at the externally accessible surfaces is investigated for two different types of incident probing wave, both for an absorbing and a nonabsorbing bilayer structure, for variations in the contact quality modulation and as a function of defect size. The results can serve as a parametric guide for experimentalists considering the use of nonlinear harmonic generation of Lamb waves as a tool for nondestructive testing of bilayers, such as rubber-steel composites, in storage tanks and pipelines.
Collapse
Affiliation(s)
- G Shkerdin
- Departement Natuurkunde, Laboratorium voor Akoestiek en Thermische Fysica, KU Leuven, Leuven, Belgium
| | | |
Collapse
|
22
|
Pfeiffer H, Klose G, Heremans K, Glorieux C. Thermotropic phase behaviour of the pseudobinary mixtures of DPPC/C12E5 and DMPC/C12E5 determined by differential scanning calorimetry and ultrasonic velocimetry. Chem Phys Lipids 2006; 139:54-67. [PMID: 16293237 DOI: 10.1016/j.chemphyslip.2005.10.001] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2005] [Revised: 09/25/2005] [Accepted: 10/04/2005] [Indexed: 11/22/2022]
Abstract
The present paper reports on the phase behaviour of the pseudobinary aqueous mixtures of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/pentaethylene glycol monododecyl ether (C12E5) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine monohydrate (DMPC)/C12E5. Both systems exhibit a variety of mesophases, such as lamellar gel, liquid crystalline and micellar phases. The phase diagrams show peritectic and eutectic behaviours. The existence of a compound complex is established. From the phase diagrams, the temperature dependence of the solubilisation parameters is obtained. The phase diagrams, especially with respect to the solubilisation process were qualitatively explained assuming that the packing of the constituents plays a dominating role. Finally, differential scanning calorimetry and ultrasonic velocimetry are compared concerning their potentials to determine characteristics of phase transitions in pseudobinary phospholipid/surfactant mixtures.
Collapse
Affiliation(s)
- H Pfeiffer
- Department of Physics and Astronomy, Acoustics and Thermal Physics Section, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium.
| | | | | | | |
Collapse
|
23
|
Sinha G, Leys J, Glorieux C, Thoen J. Dielectric spectroscopy of aerosil-dispersed liquid crystal embedded in Anopore membranes. Phys Rev E Stat Nonlin Soft Matter Phys 2005; 72:051710. [PMID: 16383623 DOI: 10.1103/physreve.72.051710] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2005] [Revised: 09/01/2005] [Indexed: 05/05/2023]
Abstract
The complex dielectric permittivity epsilon* values are presented for aerosil-dispersed 4-pentyl-4-cyanobiphenyl (5CB) confined in Anopore membranes. The dielectric permittivities are measured in the frequency range from 10(-2) Hz to 1 GHz at temperatures ranging from 50 degrees C down to -20 degrees C. In bulk 5CB, which has only a nematic phase, there exist two main relaxation processes: one due to the rotation of molecules around their short axes for parallel orientation of the director to the probing field and another fast relaxation process due to the librational motion of molecules for perpendicular orientation. Inside Anopore membranes both these main relaxation processes can be observed, but with subtle differences. The relaxation process due to the rotation of molecules around the short axis is faster in Anopores at all temperatures in comparison with the bulk process. Hydrophilic aerosil particles, when dispersed in the liquid-crystal (LC) phase, attach to each other via hydrogen bonds and form a three-dimensional interconnecting aerosil network, thus dividing the LC phase into small domains. Dispersing 5CB with different concentrations of hydrophilic aerosils leads to a decrease in relaxation time with aerosil concentration. In these dispersed systems a slow additional relaxation process emerges. This slow process becomes stronger with higher concentrations of aerosil. From our experiments we conclude that this process is the relaxation of 5CB molecules homeotropically aligned to the surface of the aerosil particles. In the case of 5CB-aerosil dispersions enclosed in Anopore membranes this slow process still exists and increases also with aerosil concentration. The relaxation time of the rotation of the 5CB molecules around their short axis systematically increases in these 5CB-aerosil samples in Anopore membranes with aerosil concentration from the 5CB-Anopore behavior towards the behavior observed for 5CB-aerosil dispersions. We explain the evolution as resulting from opposing tendencies from size effects (in the Anopore membranes) and disorder effects (in the aerosil dispersions).
Collapse
Affiliation(s)
- G Sinha
- Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium.
| | | | | | | |
Collapse
|
24
|
Van Roie B, Leys J, Denolf K, Glorieux C, Pitsi G, Thoen J. Weakly first-order character of the nematic-isotropic phase transition in liquid crystals. Phys Rev E Stat Nonlin Soft Matter Phys 2005; 72:041702. [PMID: 16383397 DOI: 10.1103/physreve.72.041702] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2005] [Indexed: 05/05/2023]
Abstract
The classification of phase transitions in first-order and second-order (or continuous) ones is widely used. The nematic-to-isotropic (NI) transition in liquid crystals is a weakly first-order transition, with only small discontinuities in enthalpy and specific volume at the transition which are not always easy to measure. On the other hand, fluctuation effects near the transition, typical for a continuous transition, are present because of the only weakly first-order character. In a recent paper [Phys. Rev. E 69, 022701 (2004)], it was concluded from the static dielectric permittivity in the isotropic phase near the NI transition that less polar mesogens (with little or no pretransitional effects) are characteristic for a first-order NI phase transition, whereas in the case of strongly polar ones (with large pretransitional effects) the NI transition is close to second order. In this paper, we address the question whether it is, indeed, possible to use these fluctuation effects in the isotropic phase to quantify the "strength" of a weakly first-order transition, i.e., how far it is from second order. Therefore, we measured the temperature dependence of the enthalpy near the NI transition of seven liquid crystals with adiabatic scanning calorimetry and compared the measured values of the latent heat with pretransitional effects in the dielectric constant and the specific heat capacity. The compounds used in the comparison are MBBA, 5CB, 8CB, 5NCS, 5CN, 8CHBT, and D7AB. From our analysis we find, contrary to the assertion in the above reference, no correlation between the strength of the NI transition of a given compound and the pretransitional effects observed, neither dielectrically, nor thermally.
Collapse
Affiliation(s)
- B Van Roie
- Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium.
| | | | | | | | | | | |
Collapse
|
25
|
Leys J, Sinha G, Glorieux C, Thoen J. Influence of nanosized confinements on 4-n-decyl-4'-cyanobiphenyl (10CB): a broadband dielectric study. Phys Rev E Stat Nonlin Soft Matter Phys 2005; 71:051709. [PMID: 16089553 DOI: 10.1103/physreve.71.051709] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2004] [Indexed: 05/03/2023]
Abstract
Real (epsilon') and imaginary (epsilon") parts of the complex dielectric permittivity (epsilon*) of the liquid crystal (LC) 4-n-decyl-4'-cyanobiphenyl (10CB) embedded in Anopore membranes and Vycor porous glass, as well as dispersed with hydrophilic aerosils, have been studied by means of broadband dielectric spectroscopy in the frequency range from 10(-2) Hz to 1 GHz . In bulk 10CB, which has a direct transition from an isotropic to a smectic- A phase, there exists one main relaxation process for the parallel orientation of the director with respect to the probing field and a faster one for the perpendicular orientation. All molecular relaxation processes in 10CB are of Debye type and have Arrhenius like temperature dependence. For 10CB embedded in untreated and surface treated cylindrical pores of Anopore membranes the dielectric spectra are similar to the bulk with the exception that both the rotation around the short axis and the libration motion are faster in the pores. In the case of 10CB dispersed with two different concentrations of hydrophilic aerosils an emergence of a slow relaxation process, which is stronger for the higher concentration, is additionally observed along with the bulklike processes. The slow process in the LC-hydrophilic aerosil system is attributed to the relaxation of the molecules that are homeotropically aligned close to the surfaces of the aerosil particles. This process also has an Arrhenius type of temperature dependence. For 10CB embedded in narrow channels of Vycor porous glass three relaxation processes are observed. Two of these processes are bulklike and are due to the librational motion of molecules and the rotation of molecules around their short axes. The slowest process seems to be a surface process, similar in origin to that observed for 10CB dispersed with hydrophilic aerosils, and is prominent amongst all. The material in the Vycor porous glass could be supercooled by at least 185 degrees below bulk crystallization temperature. The slow process has a Vogel-Fulcher-Tamman (VFT) type of temperature dependence typical for glass formers in this wide temperature range. In addition, the bulklike processes are found to be strongly modified and also have a VFT like temperature dependence from measurements done in a wide temperature range. This behavior is in contrast to other reports of glassy behavior in confined LC, where the glassy behavior as concluded from a slow relaxation process observed in a narrow temperature range.
Collapse
Affiliation(s)
- J Leys
- Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
| | | | | | | |
Collapse
|
26
|
Boeckx L, Leclaire P, Khurana P, Glorieux C, Lauriks W, Allard JF. Investigation of the phase velocities of guided acoustic waves in soft porous layers. J Acoust Soc Am 2005; 117:545-554. [PMID: 15759676 DOI: 10.1121/1.1847848] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
A new experimental method for measuring the phase velocities of guided acoustic waves in soft poroelastic or poroviscoelastic plates is proposed. The method is based on the generation of standing waves in the material and on the spatial Fourier transform of the displacement profile of the upper surface. The plate is glued on a rigid substrate so that it has a free upper surface and a nonmoving lower surface. The displacement is measured with a laser Doppler vibrometer along a line corresponding to the direction of propagation of plane surface waves. A continuous sine with varying frequencies was chosen as excitation signal to maximize the precision of the measurements. The spatial Fourier transform provides the wave numbers, and the phase velocities are obtained from the relationship between wave number and frequency. The phase velocities of several guided modes could be measured in a highly porous foam saturated by air. The modes were also studied theoretically and, from the theoretical results, the experimental results, and a fitting procedure, it was possible to determine the frequency behavior of the complex shear modulus and of the complex Poisson ratio from 200 Hz to 1.4 kHz, in a frequency range higher than the traditional methods.
Collapse
Affiliation(s)
- L Boeckx
- Laboratorium voor Akoestiek en Thermische Fysica, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Heverlee, Belgium
| | | | | | | | | | | |
Collapse
|
27
|
Pittois S, Van Roie B, Glorieux C, Thoen J. Static and dynamic thermal quantities near the consolute point of the binary liquid mixture aniline–cyclohexane studied with a photopyroelectric technique and adiabatic scanning calorimetry. J Chem Phys 2005; 122:024504. [PMID: 15638595 DOI: 10.1063/1.1829256] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We studied the thermal conductivity, thermal effusivity, and specific heat capacity at constant pressure of the critical binary liquid mixture aniline-cyclohexane near the consolute point, using a photopyroelectric (PPE) technique and adiabatic scanning calorimetry (ASC). According to recent theoretical predictions based on renormalization group theory calculations, a substantial (but not diverging) enhancement in the thermal conductivity in the homogeneous phase near the critical temperature was expected for this binary system near the consolute point. However, within an experimental precision of 0.05%, we found no deviation from linear behavior in the range of 5 K above Tc down to Tc. The specific heat capacity calculated from the results for the thermal conductivity and effusivity is in good agreement with that measured by ASC. For the ASC results, the theoretical power law expression with the Ising critical exponent was fitted to the specific heat capacity both above and below the transition temperature. Good agreement with theory was found both for the amplitude ratio and the two-scale universality.
Collapse
Affiliation(s)
- S Pittois
- Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, B-3001 Leuven, Belgium
| | | | | | | |
Collapse
|
28
|
Pittois S, Van Roie B, Glorieux C, Thoen J. Thermal conductivity, thermal effusivity, and specific heat capacity near the lower critical point of the binary liquid mixturen-butoxyethanol–water. J Chem Phys 2004; 121:1866-72. [PMID: 15260737 DOI: 10.1063/1.1765652] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Experimental investigations on binary liquid mixtures near the critical mixing point are presently leading to a controversy about the anomaly in the thermal conductivity. A photopyroelectric technique is used to determine the thermal conductivity and the effusivity of the binary liquid mixture n-butoxyethanol-water at its critical concentration near the critical mixing point. It is proven that, contrary to previous reports, there is no critical enhancement in the thermal conductivity. The specific heat capacity is calculated from these results and compared with the results from measurements performed by adiabatic scanning calorimetry.
Collapse
Affiliation(s)
- S Pittois
- Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, B-3001 Leuven, Belgium
| | | | | | | |
Collapse
|
29
|
Sinha G, Glorieux C, Thoen J. Broadband dielectric spectroscopy study of molecular dynamics in the glass-forming liquid crystal isopentylcyanobiphenyl dispersed with aerosils. Phys Rev E Stat Nonlin Soft Matter Phys 2004; 69:031707. [PMID: 15089310 DOI: 10.1103/physreve.69.031707] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2003] [Indexed: 05/24/2023]
Abstract
The glass-forming liquid crystal isopentylcyanobiphenyl (CB15) filled with different concentrations of hydrophilic and hydrophobic aerosils has been investigated by broadband dielectric spectroscopy in the frequency range from 10(-2) Hz to 10(7) Hz over a temperature range of 173 K-300 K. CB15 that consists of chiral molecules has a monotropic system of phases nematic (N*) and smectic-A upon supercooling and forms a glass further on. In the isotropic phase a single Davidson-Cole process exists in the substance, which is due to the rotation of the molecules around their short axes. In the supercooled N* phase a Cole-Cole process that is an order of magnitude faster is additionally present and is due to the rotation in a cone around the local director. The relaxation times of the process due to rotation around short axes obey the empirical Vogel-Fulcher-Tamman behavior typical for glass-forming systems. Filling of the liquid crystal (LC) with different concentrations of hydrophilic aerosils leads to the emergence of a slow relaxation process that grows with the increasing concentration of the aerosils. The aerosil particles, which form a three-dimensional network dividing the LC phase into domains, have little effect on the relaxation times of the bulk processes. As a consequence the glass transition temperature is merely affected. On the other hand, in LCs dispersed with hydrophobic aerosils the slow process is quite weak. The slow process is attributed to the relaxation of the molecules that are homeotropically attached at the surfaces of the aerosil particles. The LC-aerosil surface interaction leads to a considerable slowing down of the molecular rotation around their short axis. The process has an Arrhenius-like temperature dependence of the relaxation times with an activated type of dynamics, which can be explained by considering a nonincreasing rearranging region of cooperativity in surface layers.
Collapse
Affiliation(s)
- G Sinha
- Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
| | | | | |
Collapse
|
30
|
Bentefour EH, Glorieux C, Chirtoc M, Thoen J. Thermal relaxation of glycerol and propylene glycol studied by photothermal spectroscopy. J Chem Phys 2004; 120:3726-31. [PMID: 15268535 DOI: 10.1063/1.1642613] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In this paper we report on experimental data for the frequency and temperature dependence of the thermal properties of supercooled glycerol and propylene glycol. By using a photopyroelectric method the specific heat capacity and thermal conductivity were separately determined in a bandwidth of several decades. We have recently shown that the thermal conductivity has no relaxation behavior, which simplifies the analysis of our results. The relaxation behavior of the specific heat capacity is compared with literature results for other physical quantities and a detailed analysis of the temperature dependence of the relaxation parameters is presented.
Collapse
Affiliation(s)
- E H Bentefour
- Laboratorium voor Akoestiek en Thermische Fysica, Departement Natuurkunde en Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001, Belgium
| | | | | | | |
Collapse
|
31
|
Caerels J, Glorieux C, Thoen J. Photopyroelectric ac calorimetric study of the nematic-smectic-A phase-transition line in binary liquid crystal mixtures with injected smectic-A phases. Phys Rev E Stat Nonlin Soft Matter Phys 2002; 65:031704. [PMID: 11909078 DOI: 10.1103/physreve.65.031704] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2001] [Indexed: 05/23/2023]
Abstract
Using a recently developed photopyroelectric ac calorimetric technique we investigate two binary liquid crystal mixtures with so-called injected smectic-A phases. Characteristic of these systems is the occurrence of nematic-to-smectic-A transition lines in the phase diagram of mixtures of pure compounds having only a nematic phase. The two binary systems are pentylcyanobiphenyl with either 4-n-propylcyclohexyl-carboxylate or 4-n-pentylphenyl 4(')-n-pentyloxybenzoate. Both these systems have domelike smectic-A ranges with narrow nematic ranges at the top. Near the top the N-SmA transitions are of first order and are crossing over to second order at a tricritical point on either side of the top with the increasing width of the nematic range. The obtained critical exponents are almost completely Fisher renormalized because of the strong concentration dependence of the nematic-to-smectic-A transition temperatures.
Collapse
Affiliation(s)
- J Caerels
- Laboratorium voor Akoestiek en Thermische Fysica, Department Natuurkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, 3001 Leuven, Belgium
| | | | | |
Collapse
|
32
|
Glorieux C, Nelson KA, Hinze G, Fayer MD. Thermal, structural, and orientational relaxation of supercooled salol studied by polarization-dependent impulsive stimulated scattering. J Chem Phys 2002. [DOI: 10.1063/1.1445749] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
|
33
|
Glorieux C, Van de Rostyne K, Nelson K, Gao W, Lauriks W, Thoen J. On the character of acoustic waves at the interface between hard and soft solids and liquids. J Acoust Soc Am 2001; 110:1299-1306. [PMID: 11572340 DOI: 10.1121/1.1396333] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Laser ultrasonics is used to optically excite and detect acoustic waves at the interface between a liquid and a solid or coated solid. Several case studies show that this technique is feasible to investigate experimentally the theoretically predicted fundamental properties of different aspects of interface waves at liquid-solid interfaces and to characterize the elastic properties of soft solids. The theoretical prediction that the leaky Rayleigh (LR)-type root of the characteristic determinant becomes forbidden when the shear velocity of the solid lies below the bulk velocity of the liquid was experimentally confirmed. The depth profiling and nondestructive testing potential of Scholte waves was experimentally illustrated and explained by the properties of the wave displacement profile.
Collapse
Affiliation(s)
- C Glorieux
- Departement Natuurkunde, Katholieke Universiteit Leuven, Belgium
| | | | | | | | | | | |
Collapse
|
34
|
|
35
|
Desmet C, Gusev V, Lauriks W, Glorieux C, Thoen J. All-optical excitation and detection of leaky Rayleigh waves. Opt Lett 1997; 22:69-71. [PMID: 18183105 DOI: 10.1364/ol.22.000069] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
The results of experiments on all-optical monitoring of leaky Rayleigh waves are reported. Leaky Rayleigh waves were excited by pulsed laser action on a liquid-solid interface and were detected by the light-beam-deflection technique. Both the measured velocity of their propagation and the attenuation are in good agreement with theoretical predictions. Possible applications include acoustic spectroscopy of materials, depth profiling of layered structures, and tabletop modeling of seismic phenomena.
Collapse
|
36
|
Leclaire P, Kelders L, Lauriks W, Glorieux C, Thoen J. Ultrasonic wave propagation in porous media: determination of acoustic parameters and high frequency limit of the classical models. Stud Health Technol Inform 1996; 40:139-55. [PMID: 10168875] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Abstract
Results on the ultrasonic wave propagation in porous materials are presented with emphasis on the measurement of acoustic parameters and on the discrepancy between experimental results and theoretical predictions for the attenuation at high frequencies. This discrepancy can be observed in Biomedical Engineering where the propagation in different sorts of bones is studied as well as in the fields of Geophysics and Material Science. In the present study, the slow wave propagation in polyurethane foams saturated by different gases is investigated in a frequency range of [70-800 kHz]. Methods are presented to determine the tortuosity and the viscous and thermal characteristic lengths. The experimental results, obtained using standard ultrasonic and vacuum equipments, show that an excess attenuation occurs when the wavelength is not sufficiently large compared to the lateral dimensions of the fibers. This effect constitutes a limit of the classical models of equivalent phases. It is evaluated with the help of a model of ultrasonic scattering. A numerical simulation of osteoporosis using Biot's model is also presented.
Collapse
Affiliation(s)
- P Leclaire
- Departement Natuurkunde, Katholieke Universiteit Leuven, Belgium
| | | | | | | | | |
Collapse
|
37
|
Glorieux C, Thoen J, Bednarz G, White MA, Geldart DJ. Photoacoustic investigation of the temperature and magnetic-field dependence of the specific-heat capacity and thermal conductivity near the Curie point of gadolinium. Phys Rev B Condens Matter 1995; 52:12770-12778. [PMID: 9980443 DOI: 10.1103/physrevb.52.12770] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
|
38
|
Glorieux C, Thoen J. Thermal and magnetic properties of gadolinium by acoustic detection of optically and magnetically induced temperature oscillations. ACTA ACUST UNITED AC 1994. [DOI: 10.1051/jp4:1994764] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
|
39
|
Glorieux C, Caerels J, Thoen J. Photoacoustic and photopyroelectric investigation of the antiferromagnets CoO and Cr2O3 in the neighbourhood of the Neel Temperature. ACTA ACUST UNITED AC 1994. [DOI: 10.1051/jp4:1994763] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
|