Figure 6 - uploaded by Susmita Roy
Content may be subject to copyright.
Schematic free energy diagram of the spinodal decomposition. ( a ) Spinodal decomposition is shown on the phase diagram displaying a miscibility gap. Note that the boundary separating the metastable and the unstable region is known as spinodal curve that can be obtained by performing a common tangent construction of the free-energy curve. ( b ) The free energy curve is plotted as a function of composition for the phase separation temperature T 2 . In the spinodal region, the curvature of the free-energy curve is neg-
Source publication
We explore the potential energy landscape of structure breaking binary mixtures (SBBM) where two constituents dislike each other, yet remain macroscopically homogeneous at intermediate to high temperatures. Interestingly, we find that the origin of strong composition dependent non-ideal behaviour lies in its phase separated inherent structure. The...
Similar publications
We introduce a coarse-grained approach for characterizing the long-timescale dynamics of ion diffusion in general polymer electrolytes using input from short molecular dynamics trajectories. The approach includes aspects of the dynamic bond percolation model [ J. Chem. Phys. 1983, 79, 3133-3142 ] by treating ion diffusion in terms of hopping transi...
Citations
... Here, coalescence causes the retention of the concentration gradient until the entire system is in composition χ 1 or χ 2 , as shown in Fig. 2 For the case of spinodal decomposition, illustrated in Fig. 2.3, the Gibbs free energy G is also reduced, however, contrary to nucleation, the composition changes gradually and against the concentration gradient (B in Fig. 2.3). [72] Because the entire system change follows that process simultaneously, no localized jumps occur in the composition. Only in the end, when the entire system is fully divided among these sections of composition χ 1 and χ 2 , does a sharp border appear. ...
The doctoral thesis presented provides a comprehensive view of laser-based ablation techniques promoted to new fields of operation, including, but not limited to, size, composition, and concentration analyses. It covers various applications of laser ablation techniques over a wide range of sizes, from single molecules all the way to aerosol particles. The research for this thesis started with broadening and deepening the field of application and the fundamental understanding of liquid-phase IR-MALDI. Here, the hybridization of ion mobility spectrometry and microfluidics was realized by using IR-MALDI as the coupling technique for the first time. The setup was used for monitoring the photocatalytic performance of the E-Z isomerization of olefins. Using this hybrid, measurement times were so drastically reduced that such photocatalyst screenings became a matter of minutes rather than hours. With this on hand, triple measurements screenings could not only be performed within ten minutes, but also with a minimum amount of resources highlighting its potential as a green chemistry alternative to batch-sized reactions. Along the optimizing process of the IR-MALDI source for microfluidics came its application for another liquid sample supply method, the hanging drop. This demarcated one of the first applications of IR-MALDI for the charging of sub-micron particles directly from suspensions via their gas-phase transfer, followed by their characterization with differential mobility analysis. Given the high spectral quality of the data up to octuply charged particles became experimentally accessible, this laid the foundation for deriving a new charge distribution model for IR-MALDI in that size regime. Moving on to even larger analyte sizes, LIBS and LII were employed as ablation techniques for the solid phase, namely the aerosol particles themselves. Both techniques produce light-emitting events and were used to quantify and classify different aerosols. The unique configuration of stroboscopic imaging, photoacoustics, LII, and LIBS measurements opened new realms for analytical synergies and their potential application in industry. The concept of using low fluences, below 100 J/cm2, and high repetition rates of up to 500 Hz for LIBS makes for an excellent phase-selective LIBS setup. This concept was combined with a new approach to the photoacoustic normalization of LIBS. Also, it was possible to acquire statistically relevant amounts of data in a matter of seconds, showing its potential as a real-time optimization technique. On the same time axis, but at much lower fluences, LII was used with a similar methodology to quickly quantify and classify airborne particles of different compositions. For the first time, aerosol particles were evaluated on their LII susceptibility by using a fluence screening approach.
... Methanol induces microheterogeneity in the aqueous solution even at room temperature, which is akin to other similar aqueous binary mixtures. [188][189][190][191][192][193][194][195][196][197][198][199][200][201] ...
Although water is the most ubiquitous liquid it shows many thermodynamic and dynamic anomalies. Some of the anomalies further intensify in the supercooled regime. While many experimental and theoretical studies have focused on the thermodynamic anomalies of supercooled water, fewer studies explored the dynamical anomalies very extensively. This is due to the intricacy of the experimental measurement of the dynamical properties of supercooled water. Violation of the Stokes-Einstein relation (SER), an important relation connecting the diffusion of particles with the viscosity of the medium, is one of the major dynamical anomalies. In absence of experimentally measured viscosity, researchers used to check the validity of SER indirectly using average translational relaxation time or α-relaxation time. Very recently, the viscosity of supercooled water was accurately measured at a wide range of temperatures and pressures. This allowed direct verification of the SER at different temperature-pressure thermodynamic state points. An increasing breakdown of the SER was observed with decreasing temperature. Increasing pressure reduces the extent of breakdown. Although some well-known theories explained the above breakdown, a detailed molecular mechanism was still elusive. Recently, a translational jump-diffusion (TJD) approach has been able to quantitatively explain the breakdown of the SER in pure supercooled water and an aqueous solution of methanol. The objective of this article is to present a detailed and state-of-the-art analysis of the past and present works on the breakdown of SER in supercooled water with a specific focus on the new TJD approach for explaining the breakdown of the SER.
... Several experimental and simulation studies identified and reported composition dependent non-ideality in transport and physicochemical properties of water-DMSO and water-ethanol binary mixtures. [14][15][16][22][23][24][25][26][27][28][29][30][31][32] In the case of water-DMSO mixtures, Luzar and Chandler 15 rendered correct and almost exact predictions based on the simplified mean-field considerations without invoking the concept of significant structures. Later on, many attempts were made to understand the structural origin of the observed anomalies in these mixtures. ...
Aqueous binary mixtures often exhibit dramatic departure from the predicted hydrodynamic behavior when transport properties are plotted against composition. We show by inherent structure (IS) analysis that this sharp composition dependent breakdown of the Stokes–Einstein relation can be attributed to the non-monotonic variation in the average inherent structure energy of these mixtures. Further IS analysis reveals the existence of a unique ground state, stabilized by both the formation of an optimum number of H-bonds and a favorable hydrophobic interaction at this composition. The surprisingly sharp turnaround behavior observed in the effective hydrodynamic radius also owes its origin to the same combination of these two factors. Interestingly, the temperature dependence of isothermal compressibility shows a minimum at the particular composition. Extensive studies on water–dimethyl sulfoxide and water–ethanol mixtures using two different force-fields of water reveal many features that are nearly universal. A justification of this quasi-universal behavior is provided in terms of a mode-coupling theory (MCT) of viscosity, which can serve as the starting point of a remarkable correlation observed with the nearest neighbor structure, as captured by the first peaks of the radial distribution function, and the slowdown in the intermediate scattering function at intermediate wavenumbers. Therefore, the formation of the local structure captured through IS analysis can be correlated with the MCT.
... 7,8 However, the exact status of this microheterogeneity (MH), as well as the consequences of its existence upon thermophysical properties of such systems, is not well understood. 8,9 One point that we have investigated in our previous works 8 is how to distinguish the microheterogeneity (MH) from concentration fluctuations (CF), the latter which are accessible through the Kirkwood-Buff integrals [10][11][12] (KBI). The difference between CF and MH relates, respectively, to the k = 0 part of the structure factors (associated to the KBI) and the k 0 part corresponding to the pre-peak in partial structure factors associated with hydrogen bonding atoms. ...
The evolution of the micro-segregated structure of aqueous methanol mixtures, in the temperature range 300 K-120 K, is studied with computer simulations, from the static structural point of view. The structural heterogeneity of water is reinforced at lower temperatures, as witnessed by a pre-peak in the oxygen-oxygen structure factor. Water tends to form predominantly chain-like clusters at lower temperatures and smaller concentrations. Methanol domains have essentially the same chain-like cluster structure as the pure liquid at high concentrations and becomes monomeric at smaller ones. Concentration fluctuations decrease with temperature, leading to quasi-ideal Kirkwood-Buff integrals, despite the enhanced molecular interactions, which we interpret as the signature of non-interacting segregated water and methanol clusters. This study throws a new light on the nature of the micro-heterogeneous structure of this mixture: the domain segregation is essentially based on the appearance of linear water clusters, unlike other alcohol aqueous mixtures, such as with propanol or butanol, where the water domains are more bulky.
... Until now many attempts have been made to understand the interconnection between the secondary structure, micellization and solvent properties of b-CN (Faizullin et al., 2013;Horne & Davidson, 1987;Horne, 2002;Mikheeva et al., 2003;O'Connell, Kelly, Auty, Fox, & de Kruif, 2001a;O'Connell, Kelly, Fox, & de Kruif, 2001b;O'Connell et al., 2003;Portnaya et al., 2006Portnaya et al., , 2008Stroylova et al., 2013;Trejo & Harte, 2010;Ye & Harte, 2013;Zadow, 1993). There is a strong opinion (Corsaro, Maisano, Mallamace, & Dugo, 2013;D'Angelo, Onori, & Santucci, 1994;Dolenko et al., 2015;Onori, 1988;Sarkar et al., 2015;Sato, Chiba, & Nozaki, 1999;Wakisaka & Ohki, 2005;Wakisaka & Matsuura, 2006) that the peculiarities of various physico-chemical properties of water-alcohol mixtures are governed by their microphase separation. It means that after dissolution of small amphiphilic protic molecules such as alcohols in water the microdomains enriched either by water or by alcohol are formed. ...
Ultrafast laser-oriented crystallization of glass materials is an emerging and promising research field. Glass is an ideal functionalization enabler material, and it permits the study of light-driven crystallization induced by ultrashort pulses. Femtosecond (fs, 1 fs = 10⁻¹⁵ s) laser direct writing (FLDW) is a tool that enables nano-structuring and multi-functionalization for the fabrication of new active photonic devices in 3D. It takes advantage of efficient nonlinear absorption processes triggered by high light power densities (typ. 1-100 TW/cm²).This Ph.D. work principally investigates the effect of laser irradiation conditions, through the control of four tunable laser parameters (pulse energy, repetition rate, polarization and scanning speed), on glass crystallization in 3D. The first part of this work relates on the synthesis of borate glasses by sol-gel technique, and silicate and borosilicate ones by the conventional melt-quenching one. Then, a second part is dedicated to femtosecond laser irradiation of the silicate and borosilicate samples to trigger, and control, localized and oriented crystallization of non-centrosymmetric nanocrystals of LiNbO₃. Patterns including dots and lines were written inside the glass samples, and laser-structural modification threshold energies were identified. A third part is related to the characterization of the laser-induced structures. Second harmonic generation (SHG), originating from LiNbO₃ nanocrystals, was investigated. The effect of laser polarization on the nanocrystal orientation was investigated through its angular dependency of SHG intensity. The study of nanocrystals orientation concerns the effect of SiO₂ substitution with B₂O₃ into the glass matrix. The nanocrystals orientation and laser track microstructure is further investigated through electron backscattering diffraction (EBSD).Through laser writing, nanogratings, i.e., lamellar-like structures growing perpendicular to the laser polarization, were observed in both silicate and borosilicate glasses. These sub-wavelength structures induced a birefringent response taking its root from the local variation of refractive indices between glass and crystal phases. Additionally, it was found that B₂O₃-rich glasses promote fabrication of birefringent structures, precisely a larger and faster birefringent response (>150 nm at λ=550 nm) than B₂O₃-free glass as well as lower glass-making temperatures.The effect of scanning speed on crystallization mechanisms is discussed through from the basis of Time Temperature Transformation (TTT) and Continuous Cooling Transformation (CCT) diagrams. For the ease to nucleate and grow crystals in B₂O₃-rich glasses (21% mol), the crystallization domain is wider relative to B₂O₃-free glasses glass. It is demonstrated that the progressive substitution of SiO₂ with B₂O₃ (from 0% to 21% mol) leads to a progressively fast crystallization of LiNbO₃ nanocrystals induced by fs-laser irradiation.As a final note, a suitable choice of laser parameters is critical to control both size and orientation of photo-precipitated nonlinear nanocrystals. A direct consequence is an enhanced tunability in optical properties essential for photonic applications.
We present a microscopic study of water–dimethyl sulfoxide (DMSO) binary mixtures using optical tweezers and thermal lens techniques. Binary mixtures of DMSO with water show anomalous behavior due to the specific hydrogen bonding ability of DMSO. We use a tightly focused femtosecond laser at a low average power to optically trap microspheres with diameters of 1 micron for use as probes. The binary mixture exhibits various viscosities, depending on its composition ratio, and hence different trapped particle characteristic frequencies (corner frequencies) due to Brownian motion. The power spectrum density method is used to obtain the corner frequency from forward-scattered data. Thus, using low-power optical tweezer experiments, we find that the maximum viscosity occurs at a DMSO mole fraction of 0.276. At higher powers, the propensity for trapping is highly diminished. It may be surprising to note that these viscosity values obtained from the corner frequencies do not exactly match those published in the literature. However, this deviation can be attributed to the thermal behavior of the binary mixture, which affects the Brownian motion and hence the obtained viscosity values. Studies at the microscopic level can thus provide a newer perspective on these already important binary mixtures. Intensity-dependent measurements further confirm the contribution of thermal effects in this study.
The kinetics of phase separation subsequent to a finite temperature quench is assumed to be driven by diffusion on the altered free energy surface and is generally assumed to be slow. The situation can be different in phase separating liquid binary mixtures, especially for systems characterized by the large difference in mutual interactions between solute and solvent molecules. In such cases, the phase separation kinetics could be fast and may get completed within a short time (ns) scale. As a result, in these systems, one may observe diverse dynamical features arising out of local heterogeneity leading to the onset of phase separation through pattern formation, spinodal decomposition, nucleation, and growth. By using a coarse-grained analysis, we examine phase separation kinetics in each spatial grid and indeed observe important effects of initial heterogeneity on the subsequent evolution. Interestingly, we observe slower separation kinetics for those regions that correspond to the composition at the minimum of the high-temperature surface. The heterogeneous dynamics has been captured here through the non-linear susceptibility function, which shows a pattern similar to what is observed in the supercooled liquid. Each grid shows somewhat different dynamics in the three-stage (exponential, power-law, and logarithmic regime) phase separation dynamics. The late stage of phase separation kinetics is usually attributed to the coarsening of the phase-separated domains. However, in a liquid binary mixture, the late-stage power-law decay undergoes a further change. A new dynamical regime arises characterized by a logarithmic time dependence, which is due to the “smoothening” of the rough interface of already well-separated phases. This can also be described as opposite to the roughening transition described by Chui and Weeks [Phys. Rev. Lett. 40, 733 (1978)]. This reverse roughening transition can explain the logarithmic time dependence observed in the simulation.
