74 results on '"Qingteng Zhang"'
Search Results
52. Dynamic Scaling of Colloidal Gel Formation at Intermediate Concentrations
- Author
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Alec Sandy, Eric M. Dufresne, Robert L. Leheny, S. Ramakrishnan, Qingteng Zhang, Piotr Maj, Robert Szczygiel, Suresh Narayanan, Pawel Grybos, Divya Bahadur, and Piotr Kmon
- Subjects
Materials science ,Scattering ,General Physics and Astronomy ,Thermodynamics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,Condensed Matter::Soft Condensed Matter ,Dynamic light scattering ,0103 physical sciences ,X-ray crystallography ,Sensitivity (control systems) ,Small-angle scattering ,010306 general physics ,0210 nano-technology ,Structure factor ,Scaling - Abstract
We have examined the formation and dissolution of gels composed of intermediate volume-fraction nanoparticles with temperature-dependent short-range attractions using small-angle x-ray scattering, x-ray photon correlation spectroscopy, and rheology to obtain nanoscale and macroscale sensitivity to structure and dynamics. Gel formation after temperature quenches to the vicinity of the rheologically determined gel temperature, T_{gel}, was characterized via the slowdown of dynamics and changes in microstructure observed in the intensity autocorrelation functions and structure factor, respectively, as a function of quench depth (ΔT=T_{quench}-T_{gel}), wave vector, and formation time t_{f}. We find the wave-vector-dependent dynamics, microstructure, and rheology at a particular ΔT and t_{f} map to those at other ΔTs and t_{f}s via an effective scaling temperature, T_{s}. A single T_{s} applies to a broad range of ΔT and t_{f} but does depend on the particle size. The rate of formation implied by the scaling is a far stronger function of ΔT than expected from the attraction strength between colloids. We interpret this strong temperature dependence in terms of cooperative bonding required to form stable gels via energetically favored, local structures.
- Published
- 2017
53. Thermal Fluctuations of Ferroelectric Nanodomains in a Ferroelectric-Dielectric PbTiO3/SrTiO3 Superlattice
- Author
-
Zhonghou Cai, Pice Chen, Sara J. Callori, Yongqi Dong, Matthew Dawber, Paul G. Evans, Margaret P. Cosgriff, Qingteng Zhang, Alec Sandy, Hua Zhou, Ross Harder, Eric M. Dufresne, Joonkyu Park, Mohammed Humed Yusuf, and Dillon D. Fong
- Subjects
Materials science ,Condensed matter physics ,Scattering ,Superlattice ,General Physics and Astronomy ,Thermal fluctuations ,Energy landscape ,02 engineering and technology ,Dielectric ,021001 nanoscience & nanotechnology ,01 natural sciences ,Ferroelectricity ,Topological defect ,Condensed Matter::Materials Science ,Dynamic light scattering ,0103 physical sciences ,010306 general physics ,0210 nano-technology - Abstract
Ferroelectric-dielectric superlattices consisting of alternating layers of ferroelectric ${\mathrm{PbTiO}}_{3}$ and dielectric ${\mathrm{SrTiO}}_{3}$ exhibit a disordered striped nanodomain pattern, with characteristic length scales of 6 nm for the domain periodicity and 30 nm for the in-plane coherence of the domain pattern. Spatial disorder in the domain pattern gives rise to coherent hard $x$-ray scattering patterns exhibiting intensity speckles. We show here using variable-temperature Bragg-geometry $x$-ray photon correlation spectroscopy that $x$-ray scattering patterns from the disordered domains exhibit a continuous temporal decorrelation due to spontaneous domain fluctuations. The temporal decorrelation can be described using a compressed exponential function, consistent with what has been observed in other systems with arrested dynamics. The fluctuation speeds up at higher temperatures and the thermal activation energy estimated from the Arrhenius model is $0.35\ifmmode\pm\else\textpm\fi{}0.21\text{ }\text{ }\mathrm{eV}$. The magnitude of the energy barrier implies that the complicated energy landscape of the domain structures is induced by pinning mechanisms and domain patterns fluctuate via the generation and annihilation of topological defects similar to soft materials such as block copolymers.
- Published
- 2017
54. Photoinduced Domain Pattern Transformation in Ferroelectric/Dielectric Superlattices
- Author
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Mohammed Humed Yusuf, Haidan Wen, Joonkyu Park, Qingteng Zhang, Paul G. Evans, Youngjun Ahn, Matthew B. Rich, Anastasios Pateras, Matthew Dawber, and Pice Chen
- Subjects
Condensed Matter - Materials Science ,Materials science ,Condensed matter physics ,Scattering ,Superlattice ,General Physics and Astronomy ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,Dielectric ,021001 nanoscience & nanotechnology ,Polarization (waves) ,01 natural sciences ,Ferroelectricity ,Condensed Matter::Materials Science ,Lattice constant ,0103 physical sciences ,Charge carrier ,010306 general physics ,0210 nano-technology ,Excitation - Abstract
The nanodomain pattern in ferroelectric-dielectric superlattices transforms to a uniform polarization state under above-band-gap optical excitation. $X$-ray scattering reveals a disappearance of domain diffuse scattering and an expansion of the lattice. The reappearance of the domain pattern occurs over a period of seconds at room temperature, suggesting a transformation mechanism in which charge carriers in long-lived trap states screen the depolarization field. A Landau-Ginzburg-Devonshire model predicts changes in lattice parameter and a critical carrier concentration for the transformation.
- Published
- 2017
- Full Text
- View/download PDF
55. Structural sensitivity of x-ray Bragg projection ptychography to domain patterns in epitaxial thin films
- Author
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Qingteng Zhang, Stephan O. Hruszkewycz, Paul G. Evans, Matthew J. Highland, Paul H. Fuoss, and Martin V. Holt
- Subjects
Physics ,Diffraction ,business.industry ,Bragg's law ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Coherent diffraction imaging ,Ptychography ,Orientation (vector space) ,Condensed Matter::Materials Science ,Projection (relational algebra) ,Optics ,Condensed Matter::Superconductivity ,0103 physical sciences ,X-ray crystallography ,Sensitivity (control systems) ,010306 general physics ,0210 nano-technology ,business - Abstract
Bragg projection ptychography (BPP) is a coherent diffraction imaging technique capable of mapping the spatial distribution of the Bragg structure factor in nanostructured thin films. Here, we show that, because these images are projections, the structural sensitivity of the resulting images depends on the film thickness and the aspect ratio and orientation of the features of interest and that image interpretation depends on these factors. We model changes in contrast in the BPP reconstructions of simulated ${\mathrm{PbTiO}}_{3}$ ferroelectric thin films with meandering ${180}^{\ensuremath{\circ}}$ stripe domains as a function of film thickness, discuss their origin, and comment on the implication of these factors on the design of BPP experiments of general nanostructured films.
- Published
- 2016
56. Thermal Fluctuations of Ferroelectric Nanodomains in a Ferroelectric-Dielectric PbTiO_{3}/SrTiO_{3} Superlattice
- Author
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Qingteng, Zhang, Eric M, Dufresne, Pice, Chen, Joonkyu, Park, Margaret P, Cosgriff, Mohammed, Yusuf, Yongqi, Dong, Dillon D, Fong, Hua, Zhou, Zhonghou, Cai, Ross J, Harder, Sara J, Callori, Matthew, Dawber, Paul G, Evans, and Alec R, Sandy
- Abstract
Ferroelectric-dielectric superlattices consisting of alternating layers of ferroelectric PbTiO_{3} and dielectric SrTiO_{3} exhibit a disordered striped nanodomain pattern, with characteristic length scales of 6 nm for the domain periodicity and 30 nm for the in-plane coherence of the domain pattern. Spatial disorder in the domain pattern gives rise to coherent hard x-ray scattering patterns exhibiting intensity speckles. We show here using variable-temperature Bragg-geometry x-ray photon correlation spectroscopy that x-ray scattering patterns from the disordered domains exhibit a continuous temporal decorrelation due to spontaneous domain fluctuations. The temporal decorrelation can be described using a compressed exponential function, consistent with what has been observed in other systems with arrested dynamics. The fluctuation speeds up at higher temperatures and the thermal activation energy estimated from the Arrhenius model is 0.35±0.21 eV. The magnitude of the energy barrier implies that the complicated energy landscape of the domain structures is induced by pinning mechanisms and domain patterns fluctuate via the generation and annihilation of topological defects similar to soft materials such as block copolymers.
- Published
- 2016
57. Pushing x-ray photon correlation spectroscopy beyond the continuous frame rate limit
- Author
-
Eric M. Dufresne, Eric C. Landahl, Alec Sandy, Steve Ross, Qingteng Zhang, Suresh Narayanan, and David Kline
- Subjects
Physics ,Millisecond ,business.industry ,Scattering ,Frame (networking) ,Detector ,Frame rate ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,010305 fluids & plasmas ,Speckle pattern ,Microsecond ,Optics ,0103 physical sciences ,010306 general physics ,business ,Visible spectrum - Abstract
We demonstrate delayed-frame X-ray Photon Correlation Spectroscopy with 120 microsecond time resolution, limited only by sample scattering rates, with a prototype Pixel-array detector capable of taking two image frames separated by 153 ns or less. Although the overall frame rate is currently limited to about 4 frame pairs per second, we easily measured millisecond correlation functions. This technology, coupled to the use of brighter synchrotrons such as Petra III or the NSLS-II should enable X-ray Photon Correlation Spectroscopy on microsecond time scales on a wider variety of materials.
- Published
- 2016
58. Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy
- Author
-
Haidan Wen, Donald A. Walko, John W. Freeland, Stuart S. P. Parkin, Il Woong Jung, Matthew J. Highland, Pice Chen, Jaewoo Jeong, Paul G. Evans, Qingteng Zhang, Mahesh G. Samant, Zhonghou Cai, Eric M. Dufresne, and Yi Zhu
- Subjects
Diffraction ,Mesoscopic physics ,Phase transition ,Multidisciplinary ,Materials science ,Condensed Matter - Mesoscale and Nanoscale Physics ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Article ,Photoexcitation ,Chemical physics ,Phase (matter) ,Excited state ,0103 physical sciences ,X-ray crystallography ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,010306 general physics ,0210 nano-technology ,Excitation - Abstract
Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.
- Published
- 2016
59. Structural phase progression in photo-excited VO2
- Author
-
Paul G. Evans, Haidan Wen, Pice Chen, Z. Cai, Donald A. Walko, Stuart S. P. Parkin, Yi Zhu, Qingteng Zhang, John W. Freeland, Mahesh G. Samant, Eric M. Dufresne, Jaewoo Jeong, Il Woong Jung, and Matthew J. Highland
- Subjects
0301 basic medicine ,Diffraction ,Structural phase ,Materials science ,Condensed matter physics ,business.industry ,Wave propagation ,01 natural sciences ,Pulsed laser deposition ,03 medical and health sciences ,030104 developmental biology ,Optics ,Lattice (order) ,Excited state ,0103 physical sciences ,Microscopy ,Thin film ,010306 general physics ,business - Abstract
We reveal inhomogeneous structural phase transformation in photo-excited VO 2 thin films by time-resolved x-ray diffraction microscopy. The in-plane plane phase progression is a result of displacive lattice transformation rather than driven by thermal transport.
- Published
- 2016
60. Giant optical enhancement of strain gradient in ferroelectric BiFeO3 thin films and its physical origin
- Author
-
Qingteng Zhang, Pice Chen, Haidan Wen, Clare E. Rowland, Paul G. Evans, Darrell G. Schlom, Carolina Adamo, Donald A. Walko, Serge Nakhmanson, Yuelin Li, William Parker, and Richard D. Schaller
- Subjects
Multidisciplinary ,Materials science ,Field (physics) ,Condensed matter physics ,Strain (chemistry) ,Exciton ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Bioinformatics ,7. Clean energy ,01 natural sciences ,Ferroelectricity ,Piezoelectricity ,Article ,0103 physical sciences ,Transient (oscillation) ,Thin film ,010306 general physics ,0210 nano-technology ,Absorption (electromagnetic radiation) - Abstract
Through mapping of the spatiotemporal strain profile in ferroelectric BiFeO3 epitaxial thin films, we report an optically initiated dynamic enhancement of the strain gradient of 105–106 m−1 that lasts up to a few ns depending on the film thickness. Correlating with transient optical absorption measurements, the enhancement of the strain gradient is attributed to a piezoelectric effect driven by a transient screening field mediated by excitons. These findings not only demonstrate a new possible way of controlling the flexoelectric effect, but also reveal the important role of exciton dynamics in photostriction and photovoltaic effects in ferroelectrics.
- Published
- 2015
61. Field-Dependent Domain Distortion and Interlayer Polarization Distribution inPbTiO3/SrTiO3Superlattices
- Author
-
Eric M. Dufresne, Paul G. Evans, Qingteng Zhang, Matthew Dawber, Pice Chen, Bernhard W. Adams, Sara J. Callori, and Margaret P. Cosgriff
- Subjects
Diffraction ,Materials science ,Condensed matter physics ,Superlattice ,General Physics and Astronomy ,Field dependence ,Polarization (waves) ,Piezoelectricity ,Synchrotron ,law.invention ,Condensed Matter::Materials Science ,law ,Electric field ,X-ray crystallography - Abstract
The remnant polarization of weakly coupled ferroelectric-dielectric superlattices is distributed unequally between the component layers, and as a result the components respond differently to applied electric fields. The difference is apparent in both the nanometer-scale structure of striped polarization domains and in the development of piezoelectric strain and field-induced polarization. Both effects are probed with in situ time-resolved synchrotron x-ray diffraction in a PbTiO(3)/SrTiO(3) superlattice in fields up to 2.38 MV/cm. Domains are initially distorted to increase the polarization in the SrTiO(3) layer while retaining the striped motif. The subsequent transformation to a uniform polarization state at a later time leads to piezoelectric expansion dominated by the field-induced polarization of the SrTiO(3) layers. The results are consistent with theoretical predictions of the field dependence of the domain structure and electrical polarization.
- Published
- 2013
62. Ultrafast Photostriction in Thin Film Bismuth Ferrite and its Correlation to Electronic Dynamics
- Author
-
Margaret P. Cosgriff, Pice Chen, Carlos Giles, Paul G. Evans, Yuelin Li, Eric R. Dufresne, Qingteng Zhang, Darrell G. Schlom, Carolina Adamo, Haidan Wen, John W. Freeland, Richard D. Schaller, June Hyuk Lee, Donald A. Walko, Christian Schlepuetz, and Clare E. Rowland
- Subjects
Materials science ,business.industry ,Band gap ,Laser pumping ,Laser ,Ferroelectricity ,law.invention ,Photoexcitation ,chemistry.chemical_compound ,Optics ,chemistry ,law ,Ultrafast laser spectroscopy ,Optoelectronics ,Thin film ,business ,Bismuth ferrite - Abstract
A series of laser pump, x-ray probe experiments show that above band gap photoexcitation can generate a large out-of-plane strain in multiferroic BiFeO3 thin films. The strain decays in a time scale that is the same as the photo-induced carriers measured in an optical transient absorption spectroscopy experiment. We attribute the strain to the piezoelectric effect due to screening of the depolarization field by laser induced carriers. A strong film thickness dependence of strain and carrier relaxation is also observed, revealing the role of the carrier transport in determining the structural and carrier dynamics in complex oxide thin films.
- Published
- 2013
63. Field-dependent domain distortion and interlayer polarization distribution in PbTiO3/SrTiO3 superlattices
- Author
-
Pice, Chen, Margaret P, Cosgriff, Qingteng, Zhang, Sara J, Callori, Bernhard W, Adams, Eric M, Dufresne, Matthew, Dawber, and Paul G, Evans
- Abstract
The remnant polarization of weakly coupled ferroelectric-dielectric superlattices is distributed unequally between the component layers, and as a result the components respond differently to applied electric fields. The difference is apparent in both the nanometer-scale structure of striped polarization domains and in the development of piezoelectric strain and field-induced polarization. Both effects are probed with in situ time-resolved synchrotron x-ray diffraction in a PbTiO(3)/SrTiO(3) superlattice in fields up to 2.38 MV/cm. Domains are initially distorted to increase the polarization in the SrTiO(3) layer while retaining the striped motif. The subsequent transformation to a uniform polarization state at a later time leads to piezoelectric expansion dominated by the field-induced polarization of the SrTiO(3) layers. The results are consistent with theoretical predictions of the field dependence of the domain structure and electrical polarization.
- Published
- 2012
64. Nanodynamics of Ferroelectric Ultrathin Films
- Author
-
Inna Ponomareva, Qingteng Zhang, and Ryan Herchig
- Subjects
Materials science ,Condensed matter physics ,General theory ,Nanosensor ,Thin wall ,Alloy ,engineering ,General Physics and Astronomy ,Boundary value problem ,engineering.material ,Ground state ,Polarization (waves) ,Ferroelectricity - Abstract
The nanodynamics of ferroelectric ultrathin films made of PbTi(0.6)Zr(0.4)TiO(3) alloy is explored via the use of a first-principles-based technique. Our atomistic simulations predict that the nanostripe domains which constitute the ground state of ferroelectric ultrathin films under most electric boundary conditions oscillate under a driving ac field. Furthermore, we find that the atomically thin wall, or nanowall, that separates the nanodomains with different polarization directions behaves as an elastic object and has a mass associated with it. The nanowall mass is size-dependent and gives rise to a unique size-driven transition from resonance to relaxational dynamics in ultrathin films. A general theory of nanodynamics in such films is developed and used to explain all computational findings. In addition, we find an unusual dynamical coupling between nanodomains and mechanical deformations that could potentially be used in ultrasensitive electromechanical nanosensors.
- Published
- 2011
65. Microscopic insight into temperature-graded ferroelectrics
- Author
-
Qingteng Zhang and Inna Ponomareva
- Subjects
Materials science ,Condensed matter physics ,Alloy ,General Physics and Astronomy ,engineering.material ,Polarization (waves) ,symbols.namesake ,Perpendicular direction ,Temperature gradient ,Nuclear magnetic resonance ,Homogeneous ,symbols ,engineering ,Hamiltonian (quantum mechanics) ,Anisotropy ,Order of magnitude - Abstract
A microscopic approach based on the first-principles effective Hamiltonian is developed to study the polarization response in temperature-graded ferroelectrics. This approach has been applied to the case of (Ba(0.75)Sr(0.25))TiO₃ alloy. A comparison of the computational results with available experimental data attests to the remarkable accuracy of the present approach. Our computations reveal a strong anisotropy in the response of polarization to the temperature gradient (TG). In particular, the polarization offset along the direction of TG is an order of magnitude lower than in the perpendicular direction. The large as well as the small TGs are considered and found to yield qualitatively different polarization field responses. Among other striking findings are (i) the coexistence of different phases in chemically homogeneous regions, (ii) formation of low-symmetry phases, and (iii) thermally controlled polarization rotation.
- Published
- 2010
66. Spatially confined low-power optically pumped ultrafast synchrotron x-ray nanodiffraction
- Author
-
Darrell G. Schlom, Carolina Adamo, Jack A. Tilka, Qingteng Zhang, Pice Chen, Yi Zhu, Joonkyu Park, Margaret P. Cosgriff, Paul G. Evans, and Haidan Wen
- Subjects
Physics ,business.industry ,Orders of magnitude (temperature) ,Physics::Optics ,Optical power ,Fluence ,Synchrotron ,law.invention ,Optical pumping ,Optics ,law ,Thin film ,business ,Instrumentation ,Ultrashort pulse ,Excitation - Abstract
The combination of ultrafast optical excitation and time-resolved synchrotron x-ray nanodiffraction provides unique insight into the photoinduced dynamics of materials, with the spatial resolution required to probe individual nanostructures or small volumes within heterogeneous materials. Optically excited x-ray nanobeam experiments are challenging because the high total optical power required for experimentally relevant optical fluences leads to mechanical instability due to heating. For a given fluence, tightly focusing the optical excitation reduces the average optical power by more than three orders of magnitude and thus ensures sufficient thermal stability for x-ray nanobeam studies. Delivering optical pulses via a scannable fiber-coupled optical objective provides a well-defined excitation geometry during rotation and translation of the sample and allows the selective excitation of isolated areas within the sample. Experimental studies of the photoinduced lattice dynamics of a 35 nm BiFeO3 thin film on a SrTiO3 substrate demonstrate the potential to excite and probe nanoscale volumes.
- Published
- 2015
67. Invariance properties and correlation functions in liquid-state theory: Connection with the Ward-Takahashi identities
- Author
-
Qingteng Zhang, Jean-Pierre Badiali, Dung Di Caprio, Institut de Recherche de Chimie Paris (IRCP), Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Ministère de la Culture (MC), and Argonne National Laboratory [Lemont] (ANL)
- Subjects
010304 chemical physics ,Mathematical analysis ,01 natural sciences ,Connection (mathematics) ,[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry ,Liquid state ,Correlation function ,0103 physical sciences ,Field theory (psychology) ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,010306 general physics ,ComputingMilieux_MISCELLANEOUS ,Mathematical physics ,Mathematics - Abstract
International audience
- Published
- 1996
68. Nanodynamics of Ferroelectric Ultrathin Films.
- Author
-
Qingteng Zhang, Herchig, R., and Ponomareva, I.
- Subjects
- *
FERROELECTRIC thin films , *POLARIZATION (Nuclear physics) , *DEFORMATIONS (Mechanics) , *MOLECULAR dynamics - Abstract
The nanodynamics of ferroelectric ultrathin films made of PbTi0.6Zr0.4TiO3 alloy is explored via the use of a first-principles-based technique. Our atomistic simulations predict that the nanostripe domains which constitute the ground state of ferroelectric ultrathin films under most electric boundary conditions oscillate under a driving ac field. Furthermore, we find that the atomically thin wall, or nanowall, that separates the nanodomains with different polarization directions behaves as an elastic object and has a mass associated with it. The nanowall mass is size-dependent and gives rise to a unique size-driven transition from resonance to relaxational dynamics in ultrathin films. A general theory of nanodynamics in such films is developed and used to explain all computational findings. In addition, we find an unusual dynamical coupling between nanodomains and mechanical deformations that could potentially be used in ultrasen- sitive electromechanical nanosensors. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
69. Dynamic Scaling of Colloidal Gel Formation at Intermediate Concentrations.
- Author
-
Qingteng Zhang, Bahadur, Divya, Dufresne, Eric M., Grybos, Pawel, Kmon, Piotr, Leheny, Robert L., Maj, Piotr, Narayanan, Suresh, Szczygiel, Robert, Ramakrishnan, Subramanian, and Sandy, Alec
- Subjects
- *
COLLOIDAL gels , *DYNAMICS , *X-ray scattering - Abstract
We have examined the formation and dissolution of gels composed of intermediate volume-fraction nanoparticles with temperature-dependent short-range attractions using small-angle x-ray scattering, x-ray photon correlation spectroscopy, and rheology to obtain nanoscale and macroscale sensitivity to structure and dynamics. Gel formation after temperature quenches to the vicinity of the rheologically determined gel temperature, Tgel, was characterized via the slowdown of dynamics and changes in microstructure observed in the intensity autocorrelation functions and structure factor, respectively, as a function of quench depth (ΔT=Tquench-Tgel), wave vector, and formation time tf. We find the wave-vector-dependent dynamics, microstructure, and rheology at a particular ΔT and tf map to those at other ΔTs and tfs via an effective scaling temperature, Ts. A single Ts applies to a broad range of ΔT and tf but does depend on the particle size. The rate of formation implied by the scaling is a far stronger function of ΔT than expected from the attraction strength between colloids. We interpret this strong temperature dependence in terms of cooperative bonding required to form stable gels via energetically favored, local structures. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
70. Thermal Fluctuations of Ferroelectric Nanodomains in a Ferroelectric-Dielectric PbTiO3/SrTiO3 Superlattice.
- Author
-
Qingteng Zhang, Dufresne, Eric M., Pice Chen, Joonkyu Park, Cosgriff, Margaret P., Yusuf, Mohammed, Yongqi Dong, Fong, Dillon D., Hua Zhou, Zhonghou Cai, Harder, Ross J., Callori, Sara J., Dawber, Matthew, Evans, Paul G., and Sandy, Alec R.
- Subjects
- *
FLUCTUATIONS (Physics) , *SUPERLATTICES , *FERROELECTRIC materials - Abstract
Ferroelectric-dielectric superlattices consisting of alternating layers of ferroelectric PbTiO3 and dielectric SrTiO3 exhibit a disordered striped nanodomain pattern, with characteristic length scales of 6 nm for the domain periodicity and 30 nm for the in-plane coherence of the domain pattern. Spatial disorder in the domain pattern gives rise to coherent hard x-ray scattering patterns exhibiting intensity speckles. We show here using variable-temperature Bragg-geometry x-ray photon correlation spectroscopy that x-ray scattering patterns from the disordered domains exhibit a continuous temporal decorrelation due to spontaneous domain fluctuations. The temporal decorrelation can be described using a compressed exponential function, consistent with what has been observed in other systems with arrested dynamics. The fluctuation speeds up at higher temperatures and the thermal activation energy estimated from the Arrhenius model is 0.35±0.21 eV. The magnitude of the energy barrier implies that the complicated energy landscape of the domain structures is induced by pinning mechanisms and domain patterns fluctuate via the generation and annihilation of topological defects similar to soft materials such as block copolymers. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
71. Field-Dependent Domain Distortion and Interlayer Polarization Distribution in PbTiO3/SrTiO3 Superlattices.
- Author
-
Chen, Pice, Cosgriff, Margaret P., Qingteng Zhang, Callori, Sara J., Adams, Bernhard W., Dufresne, Eric M., Dawber, Matthew, and Evans, Paul G.
- Subjects
- *
POLARIZATION (Electricity) , *DIELECTRIC relaxation , *FIELD theory (Physics) , *INDUCED polarization , *FERROELECTRICITY - Abstract
The remnant polarization of weakly coupled ferroelectric-dielectric superlattices is distributed unequally between the component layers, and as a result the components respond differently to applied electric fields. The difference is apparent in both the nanometer-scale structure of striped polarization domains and in the development of piezoelectric strain and field-induced polarization. Both effects are probed with in situ time-resolved synchrotron x-ray diffraction in a PbTiO3/SrTiO3 superlattice in fields up to 2.38 MV/cm. Domains are initially distorted to increase the polarization in the SrTiO3 layer while retaining the striped motif. The subsequent transformation to a uniform polarization state at a later time leads to piezoelectric expansion dominated by the field-induced polarization of the SrTiO3 layers. The results are consistent with theoretical predictions of the field dependence of the domain structure and electrical polarization. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
72. Fast nanoparticle rotational and translational diffusion in synovial fluid and hyaluronic acid solutions.
- Author
-
Unni, Mythreyi, Savliwala, Shehaab, Partain, Brittany D., Maldonado-Camargo, Lorena, Qingteng Zhang, Narayanan, Suresh, Dufresne, Eric M., Ilavsky, Jan, Grybos, Pawel, Koziol, Anna, Maj, Piotr, Szczygiel, Robert, Allen, Kyle D., and Rinaldi-Ramos, Carlos M.
- Subjects
- *
SYNOVIAL fluid , *ROTATIONAL diffusion , *HYALURONIC acid , *ACID solutions , *NANOPARTICLES - Abstract
Nanoparticles are under investigation as diagnostic and therapeutic agents for joint diseases, such as osteoarthritis. However, there is incomplete understanding of nanoparticle diffusion in synovial fluid, the fluid inside the joint, which consists of a mixture of the polyelectrolyte hyaluronic acid, proteins, and other components. Here, we show that rotational and translational diffusion of polymer-coated nanoparticles in quiescent synovial fluid and in hyaluronic acid solutions is well described by the Stokes-Einstein relationship, albeit with an effective medium viscosity that is much smaller than the macroscopic low shear viscosity of the fluid. This effective medium viscosity is well described by an equation for the viscosity of dilute polymer chains, where the additional viscous dissipation arises because of the presence of the polymer segments. These results shed light on the diffusive behavior of polymer-coated inorganic nanoparticles in complex and crowded biological environments, such as in the joint. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
73. Hard-sphere-like dynamics in highly concentrated alpha-crystallin suspensions.
- Author
-
Vodnala, Preeti, Karunaratne, Nuwan, Lurio, Laurence, Thurston, George M., Vega, Michael, Gaillard, Elizabeth, Narayanan, Suresh, Sandy, Alec, Qingteng Zhang, Dufresne, Eric M., Foffi, Giuseppe, Grybos, Pawel, Kmon, Piotr, Maj, Piotr, and Szczygiel, Robert
- Subjects
- *
CRYSTALLINE lens , *X-ray spectroscopy , *LIGHT beating spectroscopy - Abstract
The dynamics of concentrated suspensions of the eye-lens protein alpha crystallin have been measured using x-ray photon correlation spectroscopy. Measurements were made at wave vectors corresponding to the first peak in the hard-sphere structure factor and volume fractions close to the critical volume fraction for the glass transition. Langevin dynamics simulations were also performed in parallel to the experiments. The intermediate scattering function f(q,τ) could be fit using a stretched exponential decay for both experiments and numerical simulations. The measured relaxation times show good agreement with simulations for polydisperse hard-sphere colloids. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
74. Photoinduced Domain Pattern Transformation in Ferroelectric-Dielectric Superlattices.
- Author
-
Youngjun Ahn, Joonkyu Park, Pateras, Anastasios, Rich, Matthew B., Qingteng Zhang, Chen, Pice, Yusuf, Mohammed H., Wen, Haidan, Dawber, Matthew, and Evans, Paul G.
- Subjects
- *
FERROELECTRIC materials , *DIELECTRIC devices , *ELECTROMAGNETIC radiation - Abstract
The nanodomain pattern in ferroelectric-dielectric superlattices transforms to a uniform polarization state under above-band-gap optical excitation. X-ray scattering reveals a disappearance of domain diffuse scattering and an expansion of the lattice. The reappearance of the domain pattern occurs over a period of seconds at room temperature, suggesting a transformation mechanism in which charge carriers in long-lived trap states screen the depolarization field. A Landau-Ginzburg-Devonshire model predicts changes in lattice parameter and a critical carrier concentration for the transformation. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
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