Experimentalist in soft condensed matter physics interested in order - disorder phenomena. Phone: 508-831-5631 Address: 100 Institute Rd. Department of Physics Worcester, MA 01609
Drying colloidal droplets have a wide range of applications from medical diagnostics to coatings ... more Drying colloidal droplets have a wide range of applications from medical diagnostics to coatings for industries. This paper explores the effects of the substrate temperature (ranging from 25 to 55 °C) and various initial concentrations (∅) of 1 to 20 wt% of lysozyme in an aqueous solution on its drying and final dried film state using bright-field optical microscopy. The ∅ is divided into three regimes, ultraconcentrated (20 < ∅ ≤ 17 wt%), concentrated (17 < ∅ ≤ 9 wt%) and diluted (9 < ∅ ≤ 1 wt%). During the drying process, initially, the fluid front moves slowly and linearly inward followed by a fast, non-linear movement in both dilute and concentrated regimes. Increasing ∅ in these regimes finds that this movement in the later non-linear region slows down as the front carries and deposits protein molecules until the supply in solution is exhausted. In the ultra-concentrated regime, the fluid front moves linearly throughout the drying process. The deposition of protein ont...
We present a high-resolution study of the isotropic to nematic phase transition of a low birefrin... more We present a high-resolution study of the isotropic to nematic phase transition of a low birefringence liquid-crystal compound incorporating an aerosil gel. Calorimetry, light scattering, and microscopy data coherently combine to allow for an accurate determination of the temperature dependence of the onset of the nematic state. The nematic order develops on cooling through two distinct processes while the nematic correlation length mildly decreases. We understand the doubling of the phase transition as due to a crossover from a random-dilution regime, where the silica gel couples to the scalar part of the nematic order parameter, to a low-T random-field regime, where the coupling induces distortions in the director field. DOI: 10.1103/PhysRevLett.93.127801 PACS numbers: 64.70.Md, 61.30.Eb The study of ordering transitions in systems within disordered environments has provided new insights into the physics of phase transitions The three-dimensional nematic orientational order, estab...
High-resolution calorimetry has been performed to study the effect of dilution by a nonmesogenic,... more High-resolution calorimetry has been performed to study the effect of dilution by a nonmesogenic, low-molecular weight solvent ͑linear n-hexane͒ on the isotropic-nematic ͑I-N͒ phase transition in the liquid crystal ͑LC͒ octylcyanobiphenyl ͑8CB͒ as a function of n-hexane concentration. Numerous temperature scans were performed without continuous mixing for pure 8CB and all mixture samples of n-hexane mole fraction ranging from x hex = 0.02 to 0.12. The I-N specific heat peak remains first-order for all samples and shifts toward lower temperature nonlinearly while the two-phase I + N coexistence width broadens linearly with increasing x hex . Multiple heating and cooling scans are reproducible and indicate phase separation, if it occurs, must be on very short length scales and is reversible. These results may be a consequence of a competition between random dilution effects and the tendency to phase separate. It is shown that solvent dilution of a LC, if miscible and depending on solv...
Rapid progress in the synthesis and processing of materials with structure on nanometer length sc... more Rapid progress in the synthesis and processing of materials with structure on nanometer length scales has created a demand for greater scientific understanding of nanoscale thermal transport in individual nanostructures of composite materials. This paper reports the synthesis and sample construction as well as measurements of the specific heat and thermal conductivity of cobalt nanowires (CoNWs). Specific heat (cp) and thermal conductivity (κ) is measured by an AC calorimetric technique from 300 to 400 K parallel and perpendicular to the CoNW long-axis. The specific heat both parallel (c|| p) and perpendicular (c ⊥ p ) to the long-axis deviates strongly from the bulk amorphous powder behavior above room temperature. The perpendicular thermal conductivity (κ⊥) of CoNWs follows a bulk-like behavior revealing a maximum value near 365 K, indicating the onset of boundary-phonon scattering. The parallel thermal conductivity (κ‖) increases smoothly with the increase of temperature from 300...
Using high-resolution synchrotron x-ray scattering we have studied the effects of aerosil dispers... more Using high-resolution synchrotron x-ray scattering we have studied the effects of aerosil dispersions on the nematic to smectic A transition in octylcyanobiphenyl (8CB). The aerosil, nanometer-scale silica particles which hydrogen-bond to form a thixotropic gel, creates locally preferred orientations in the liquid crystal. We find that the presence of this weak disorder suppresses the temperature at which smectic ordering forms.
We have performed high-resolution AC calorimetric studies on Aerosil dispersions in the liquid cr... more We have performed high-resolution AC calorimetric studies on Aerosil dispersions in the liquid crystal 8OCB (4&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-octyloxy-4-cyanobiphenyl), as a function of silica concentration and thermal history. Aerosils are 7 nm diameter silica particles that form a fractal gel network of strands by hydrogen bonding. This system provides a good physical model of the effects of quenched random disorder. It is observed
Soft-matter systems when driven out-of-equilibrium often give rise to structures that usually lie... more Soft-matter systems when driven out-of-equilibrium often give rise to structures that usually lie in-between the macroscopic scale of the material and microscopic scale of its constituents. In this paper we review three such systems, the two-dimensional square-lattice Ising model, the Kuramoto model and the Rayeligh-Bénard convection system which when driven out-of-equilibrium give rise to emergent spatio-temporal order through self-organization. A common feature of these systems is that the entities that self-assemble are coupled to one another in some way, either through local interactions or through a continuous media. Therefore, the general nature of non-equilibrium fluctuations of the intrinsic variables in these systems are found to follow similar trends as order emerges. Through this paper, we attempt to look for connections between among these systems and systems in general which give rise to emergent order when driven out-of-equilibrium.
Living systems are open, out-of-equilibrium thermodynamic entities, that maintain order by locall... more Living systems are open, out-of-equilibrium thermodynamic entities, that maintain order by locally reducing their entropy. Aging is a process by which these systems gradually lose their ability to maintain their out-of-equilibrium state, as measured by their free-energy rate density, and hence, their order. Thus, the process of aging reduces the efficiency of those systems, making them fragile and less adaptive to the environmental fluctuations, gradually driving them towards the state of thermodynamic equilibrium. In this paper, we discuss the various metrics that can be used to understand the process of aging from a complexity science perspective. Among all the metrics that we propose, action efficiency, is observed to be of key interest as it can be used to quantify order and self-organization in any physical system. Based upon our arguments, we present the dependency of other metrics on the action efficiency of a system, and also argue as to how each of the metrics, influences a...
High-resolution calorimetry results are presented of carbon nanotubes (CNTs) and the liquid cryst... more High-resolution calorimetry results are presented of carbon nanotubes (CNTs) and the liquid crystal (LC) 9OO4 nano-colloidal dispersions as a function of temperature, scan rate, and CNT concentration ($0$, $0.025$, $0.05$, $0.20$ wt/$\%$). The CNT used have an enantiomeric excess that has been shown to induce chirality into this LC. The pure LC exhibits the phase sequence $I$-$N$-Sm$A$-Sm$C$-Sm$B$-$Cr$ on cooling with the expected heat capacity $C_p$ signatures, except for the Sm$A$-Sm$C$ transition, manifesting a double-$C_p$ peak ...
We review results of a high resolution systematic study of the specific heat for alkyl-cyanobiphe... more We review results of a high resolution systematic study of the specific heat for alkyl-cyanobiphenyl liquid crystals confined to the 0.2µm diameter cylindrical pores Anopore membranes. The nematic director alignment at the pore wall is varied from homeotropic to tangential by pore surface treatment. Several phenomena are uncovered by these studies which probed the weakly first order nematic to isotropic, the continuous smectic-A to nematic and the first order smectic-A to isotropic phase transitions. The specific heat is strongly dependent on the nematic director configuration, and confinement effects are remarkably distinct according to the order of the phase transition. The influence of elastic distortions and surface ordering and disordering effects are evident. Despite considerable departures from bulk behavior with regards to specific heat peaks size, rounding and width, and transition temperature shifts, a bulk-like critical behavior appears to be retained. The formation of smectic translational order within the pores is hindered for those liquid crystals that also possess a nematic phase. The average scalar order parameter temperature dependence is extracted from the specific heat results using a simplified Landau-de Gennes type of model, and is shown to be consistent with nuclear magnetic resonance results.
ABSTRACT One-dimensional materials, such as nanotubes, and their composites attract interest due ... more ABSTRACT One-dimensional materials, such as nanotubes, and their composites attract interest due to their potential use in applications as well as model systems for understanding low-dimensional physics. There is a need for detailed measurements of the specific heat (cp) and thermal conductivity (kappa) in order to guide theoretical efforts. This talk presents cp and kappa using an ac-calorimetric technique for single-wall (SW) and multi-wall (MW) carbon nanotubes (CNT) in a composite sample+cell arrangement. From 300 to 400 K, cp exhibits a linear behavior for both nanotubes. However, kappa for MWCNT and SWCNT with the heat flow perpendicular to the nanotube long-axis is bulk-like in behavior until 370 K, thereafter decreasing with increasing temperature, indicating the onset of phonon-phonon scattering. For samples where the heat flow is parallel to the nanotube long-axis, kappa for the MWCNT sample is consistent with ballistic phonon transport.
ABSTRACT Modulated Differential Scanning Calorimetry (MDSC) is used to investigate the weakly fir... more ABSTRACT Modulated Differential Scanning Calorimetry (MDSC) is used to investigate the weakly first-order isotropic to nematic (I-N) and the continuous nemat to smectic-A (N-SmA) phase transitions of the liquid crystal octylcyanobiphenyl (8CB) doped with well-dispersed quantum dots (QdS) as a function of Qd concentrations. Thermal scans were performed for all samples having Qd (CdS) weight percent from φw = 0.3 to 3 wt% first on cooling and then heating under near-equilibrium conditions. The I-N transitions heat capacity peak first glows then decreases in magnitude with increasing φw leaving a maximum at φw = 0.3% . The N-SmA heat capacity peak remains bulk-like for all samples. Both transitions temperatures shift lower monotonically by 3 K for φw = 0.3% . The enthalpy of both transitions evolve in a nontrival way, generally decreasing with increasing φw. These results are discussed in terms of the predominate disordering effects of the Qds.
Drying colloidal droplets have a wide range of applications from medical diagnostics to coatings ... more Drying colloidal droplets have a wide range of applications from medical diagnostics to coatings for industries. This paper explores the effects of the substrate temperature (ranging from 25 to 55 °C) and various initial concentrations (∅) of 1 to 20 wt% of lysozyme in an aqueous solution on its drying and final dried film state using bright-field optical microscopy. The ∅ is divided into three regimes, ultraconcentrated (20 < ∅ ≤ 17 wt%), concentrated (17 < ∅ ≤ 9 wt%) and diluted (9 < ∅ ≤ 1 wt%). During the drying process, initially, the fluid front moves slowly and linearly inward followed by a fast, non-linear movement in both dilute and concentrated regimes. Increasing ∅ in these regimes finds that this movement in the later non-linear region slows down as the front carries and deposits protein molecules until the supply in solution is exhausted. In the ultra-concentrated regime, the fluid front moves linearly throughout the drying process. The deposition of protein ont...
We present a high-resolution study of the isotropic to nematic phase transition of a low birefrin... more We present a high-resolution study of the isotropic to nematic phase transition of a low birefringence liquid-crystal compound incorporating an aerosil gel. Calorimetry, light scattering, and microscopy data coherently combine to allow for an accurate determination of the temperature dependence of the onset of the nematic state. The nematic order develops on cooling through two distinct processes while the nematic correlation length mildly decreases. We understand the doubling of the phase transition as due to a crossover from a random-dilution regime, where the silica gel couples to the scalar part of the nematic order parameter, to a low-T random-field regime, where the coupling induces distortions in the director field. DOI: 10.1103/PhysRevLett.93.127801 PACS numbers: 64.70.Md, 61.30.Eb The study of ordering transitions in systems within disordered environments has provided new insights into the physics of phase transitions The three-dimensional nematic orientational order, estab...
High-resolution calorimetry has been performed to study the effect of dilution by a nonmesogenic,... more High-resolution calorimetry has been performed to study the effect of dilution by a nonmesogenic, low-molecular weight solvent ͑linear n-hexane͒ on the isotropic-nematic ͑I-N͒ phase transition in the liquid crystal ͑LC͒ octylcyanobiphenyl ͑8CB͒ as a function of n-hexane concentration. Numerous temperature scans were performed without continuous mixing for pure 8CB and all mixture samples of n-hexane mole fraction ranging from x hex = 0.02 to 0.12. The I-N specific heat peak remains first-order for all samples and shifts toward lower temperature nonlinearly while the two-phase I + N coexistence width broadens linearly with increasing x hex . Multiple heating and cooling scans are reproducible and indicate phase separation, if it occurs, must be on very short length scales and is reversible. These results may be a consequence of a competition between random dilution effects and the tendency to phase separate. It is shown that solvent dilution of a LC, if miscible and depending on solv...
Rapid progress in the synthesis and processing of materials with structure on nanometer length sc... more Rapid progress in the synthesis and processing of materials with structure on nanometer length scales has created a demand for greater scientific understanding of nanoscale thermal transport in individual nanostructures of composite materials. This paper reports the synthesis and sample construction as well as measurements of the specific heat and thermal conductivity of cobalt nanowires (CoNWs). Specific heat (cp) and thermal conductivity (κ) is measured by an AC calorimetric technique from 300 to 400 K parallel and perpendicular to the CoNW long-axis. The specific heat both parallel (c|| p) and perpendicular (c ⊥ p ) to the long-axis deviates strongly from the bulk amorphous powder behavior above room temperature. The perpendicular thermal conductivity (κ⊥) of CoNWs follows a bulk-like behavior revealing a maximum value near 365 K, indicating the onset of boundary-phonon scattering. The parallel thermal conductivity (κ‖) increases smoothly with the increase of temperature from 300...
Using high-resolution synchrotron x-ray scattering we have studied the effects of aerosil dispers... more Using high-resolution synchrotron x-ray scattering we have studied the effects of aerosil dispersions on the nematic to smectic A transition in octylcyanobiphenyl (8CB). The aerosil, nanometer-scale silica particles which hydrogen-bond to form a thixotropic gel, creates locally preferred orientations in the liquid crystal. We find that the presence of this weak disorder suppresses the temperature at which smectic ordering forms.
We have performed high-resolution AC calorimetric studies on Aerosil dispersions in the liquid cr... more We have performed high-resolution AC calorimetric studies on Aerosil dispersions in the liquid crystal 8OCB (4&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-octyloxy-4-cyanobiphenyl), as a function of silica concentration and thermal history. Aerosils are 7 nm diameter silica particles that form a fractal gel network of strands by hydrogen bonding. This system provides a good physical model of the effects of quenched random disorder. It is observed
Soft-matter systems when driven out-of-equilibrium often give rise to structures that usually lie... more Soft-matter systems when driven out-of-equilibrium often give rise to structures that usually lie in-between the macroscopic scale of the material and microscopic scale of its constituents. In this paper we review three such systems, the two-dimensional square-lattice Ising model, the Kuramoto model and the Rayeligh-Bénard convection system which when driven out-of-equilibrium give rise to emergent spatio-temporal order through self-organization. A common feature of these systems is that the entities that self-assemble are coupled to one another in some way, either through local interactions or through a continuous media. Therefore, the general nature of non-equilibrium fluctuations of the intrinsic variables in these systems are found to follow similar trends as order emerges. Through this paper, we attempt to look for connections between among these systems and systems in general which give rise to emergent order when driven out-of-equilibrium.
Living systems are open, out-of-equilibrium thermodynamic entities, that maintain order by locall... more Living systems are open, out-of-equilibrium thermodynamic entities, that maintain order by locally reducing their entropy. Aging is a process by which these systems gradually lose their ability to maintain their out-of-equilibrium state, as measured by their free-energy rate density, and hence, their order. Thus, the process of aging reduces the efficiency of those systems, making them fragile and less adaptive to the environmental fluctuations, gradually driving them towards the state of thermodynamic equilibrium. In this paper, we discuss the various metrics that can be used to understand the process of aging from a complexity science perspective. Among all the metrics that we propose, action efficiency, is observed to be of key interest as it can be used to quantify order and self-organization in any physical system. Based upon our arguments, we present the dependency of other metrics on the action efficiency of a system, and also argue as to how each of the metrics, influences a...
High-resolution calorimetry results are presented of carbon nanotubes (CNTs) and the liquid cryst... more High-resolution calorimetry results are presented of carbon nanotubes (CNTs) and the liquid crystal (LC) 9OO4 nano-colloidal dispersions as a function of temperature, scan rate, and CNT concentration ($0$, $0.025$, $0.05$, $0.20$ wt/$\%$). The CNT used have an enantiomeric excess that has been shown to induce chirality into this LC. The pure LC exhibits the phase sequence $I$-$N$-Sm$A$-Sm$C$-Sm$B$-$Cr$ on cooling with the expected heat capacity $C_p$ signatures, except for the Sm$A$-Sm$C$ transition, manifesting a double-$C_p$ peak ...
We review results of a high resolution systematic study of the specific heat for alkyl-cyanobiphe... more We review results of a high resolution systematic study of the specific heat for alkyl-cyanobiphenyl liquid crystals confined to the 0.2µm diameter cylindrical pores Anopore membranes. The nematic director alignment at the pore wall is varied from homeotropic to tangential by pore surface treatment. Several phenomena are uncovered by these studies which probed the weakly first order nematic to isotropic, the continuous smectic-A to nematic and the first order smectic-A to isotropic phase transitions. The specific heat is strongly dependent on the nematic director configuration, and confinement effects are remarkably distinct according to the order of the phase transition. The influence of elastic distortions and surface ordering and disordering effects are evident. Despite considerable departures from bulk behavior with regards to specific heat peaks size, rounding and width, and transition temperature shifts, a bulk-like critical behavior appears to be retained. The formation of smectic translational order within the pores is hindered for those liquid crystals that also possess a nematic phase. The average scalar order parameter temperature dependence is extracted from the specific heat results using a simplified Landau-de Gennes type of model, and is shown to be consistent with nuclear magnetic resonance results.
ABSTRACT One-dimensional materials, such as nanotubes, and their composites attract interest due ... more ABSTRACT One-dimensional materials, such as nanotubes, and their composites attract interest due to their potential use in applications as well as model systems for understanding low-dimensional physics. There is a need for detailed measurements of the specific heat (cp) and thermal conductivity (kappa) in order to guide theoretical efforts. This talk presents cp and kappa using an ac-calorimetric technique for single-wall (SW) and multi-wall (MW) carbon nanotubes (CNT) in a composite sample+cell arrangement. From 300 to 400 K, cp exhibits a linear behavior for both nanotubes. However, kappa for MWCNT and SWCNT with the heat flow perpendicular to the nanotube long-axis is bulk-like in behavior until 370 K, thereafter decreasing with increasing temperature, indicating the onset of phonon-phonon scattering. For samples where the heat flow is parallel to the nanotube long-axis, kappa for the MWCNT sample is consistent with ballistic phonon transport.
ABSTRACT Modulated Differential Scanning Calorimetry (MDSC) is used to investigate the weakly fir... more ABSTRACT Modulated Differential Scanning Calorimetry (MDSC) is used to investigate the weakly first-order isotropic to nematic (I-N) and the continuous nemat to smectic-A (N-SmA) phase transitions of the liquid crystal octylcyanobiphenyl (8CB) doped with well-dispersed quantum dots (QdS) as a function of Qd concentrations. Thermal scans were performed for all samples having Qd (CdS) weight percent from φw = 0.3 to 3 wt% first on cooling and then heating under near-equilibrium conditions. The I-N transitions heat capacity peak first glows then decreases in magnitude with increasing φw leaving a maximum at φw = 0.3% . The N-SmA heat capacity peak remains bulk-like for all samples. Both transitions temperatures shift lower monotonically by 3 K for φw = 0.3% . The enthalpy of both transitions evolve in a nontrival way, generally decreasing with increasing φw. These results are discussed in terms of the predominate disordering effects of the Qds.
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Papers by Germano Iannacchione