Glassy Liquid Research Articles

Entropy Scaling of Molecular Dynamics in a Prototypical Anisotropic Model near the Glass Transition.

Dynamics and thermodynamics of molecular systems in the vicinity of the boundary between thermodynamically nonequilibrium glassy and metastable supercooled liquid states are still incompletely explored and their theoretical and simulation models are imperfect despite many previous efforts. Among them, the role of total system entropy, configurational entropy, and excess entropy in the temperature-pressure or temperature-density dependence of global molecular dynamics (MD) timescale relevant to the glass transition is an essential topic intensively studied for over half of a century. By exploiting a well-known simple ellipsoidal model recently successfully applied to simulate the supercooled liquid state and the glass transition, we gain a new insight into the different views on the relationship between entropy and relaxation dynamics of glass formers, showing the molecular grounds for the entropy scaling of global MD timescale. Our simulations in the anisotropic model of supercooled liquid, which involves only translational and rotational degrees of freedom, give evidence that the total system entropy is sufficient to scale global MD timescale. It complies with the scaling effect on relaxation dynamics exerted by the configurational entropy defined as the total entropy diminished by vibrational contributions, which was earlier discovered for measurement data collected near the glass transition. Moreover, we argue that such a scaling behavior is not possible to achieve by using the excess entropy that is in excess of the ideal gas entropy, which is contrary to the results earlier suggested within the framework of simple isotropic models of supercooled liquids. Thus, our findings also warn against an excessive reliance on isotropic models in theoretical interpretations of molecular phenomena, despite their simplicity and popularity, because they may reflect improperly various physicochemical properties of glass formers.

Effects of Smectic Layer Deformation on Mechanical Properties of Glassy Liquid Crystal Polymer Fibers

AbstractIn this work, it is demonstrated that the stress response of glassy smectic liquid crystal (LC) polymer fibers is largely dependent on layer deformations. Fibers with smectic layers stacked along the fiber axis (fiber A), prepared by stretching a molten main‐chain LC polyester, deform the layers by tensile deformation in the LC state, yielding fibers with layers tilted from the fiber axis (fiber B) and those with divided layers (fiber C). These fibers in the glassy LC state differ in Young's modulus (E), yield stress and strain (σy, εσy), and strain at break (εb). Fiber A has εb = 30%; however, fiber B is much more ductile (εb > 290%). Fiber C has higher E = 0.97 GPa and σy = 82 MPa than fiber A (E = 0.33 MPa and σy = 33 MPa). Annealing fiber C in the LC state yields fiber D with large‐area layers, similar to fiber A. Fiber D has E = 0.74 GPa and σy = 25 MPa, comparable to those of fiber A. Thus, dividing layers improves E and σy. This strengthening of glassy smectic LC by dividing layers applies to other polymers with layered structures, including lamellar block copolymers and semi‐crystalline polymers.

Columnar Liquid Crystalline Glasses by Combining Configurational Flexibility with Moderate Deviation from Planarity: Extended Triaryltriazines.

Triply phenanthryl- and tetrahelicenyl-substituted triazine-hexaalkyl esters with short alkyl chains show glass transitions conveniently above room temperature within the hexagonal columnar liquid crystalline state, resulting in a solid columnar order at room temperature. As the hexagonal columnar mesophase is easily aligned with the director perpendicular to a solid substrate, such glassy columnar liquid matrices are aimed at for the orientation of guest emitters, to obtain anisotropic emission. A condition for face-on alignment on substrates are attainable melting and clearing temperatures, which is achieved with the moderately nonplanar tetrahelicenyl derivatives in spite of their short alkyl periphery. An unusual phase transition between two columnar mesophases of same hexagonal symmetry, but very different long-distance regularity of the column lattice, is found in one phenanthryl homolog.

Structure evolution, properties and synthesis mechanism of ultra-lightweight eco-friendly ceramics prepared from kaolin clay and sewage sludge

At present, the problem of pollution and re-pollution caused by sewage sludge stacking at random has become increasingly serious in many regions and countries including China, which requires and stimulates researchers to explore more industrially feasible options to reduce environmental and eco-economic problems related to the current sludge management. In this work, an ultra-lightweight and eco-friendly ceramic (UEC) was synthesized from waste sewage sludge (SS) and kaolin clay (KC). By changing proportion of SS to KC, the mineral species, structure evolution, physical-mechanical properties, heavy metal risk assessment and sintering mechanism of UEC specimens were investigated. The results showed that the change of SS content did not vary the mineral species of UEC specimens, which all contained five mineral components: mullite (Al6Si2O13), sillimanite (Al2SiO5), hematite (Fe2O3), cristobalite (tetragonal SiO2) and aluminum iron phosphate (Al0.67Fe0.33(PO4)), but influenced their structure and performance. As the SS content increased from 20 to 50 wt%, the UEC specimen structure became denser and the inner pores grew continuously due to the increase of gas and glassy liquid phase. Meanwhile, the linear shrinkage, mass loss and bulk density also increased continuously, with corresponding maximum values of 18.59%, 30.45% and 1.92 g/cm3, respectively. Whereas the apparent porosity decreased significantly, and its value varied from 39.32% to 17.50%. Among all UEC specimens, the UEC-30 (SS/KC=30/70) and UEC-40 (SS/KC=40/60) had the most promising compressive strength (120 MPa) and bending strength (66 MPa), respectively. Also, the heavy metal leaching results of UEC specimens revealed that the final developed ceramic products were safe and non-toxic.

Effect of repeated sorption–desorption on irreversible and reversible absorption of hydrophobic perfluoroalkyl acids to freshwater sediment

Understanding the factors governing irreversible and reversible sorption is essential to predict the influence of sediment on contaminant fate and transport in surface waters. This study used sediment of an urban water body to demonstrate irreversible accumulation and reversible absorption of perfluoroalkyl acids (perfluorooctane sulfonate (PFOS), perfluorononanoic (PFNA) and perfluorodecanoic acid (PFDA)) during two sorption–desorption (S–D) cycles. Absorption and desorption isotherms were consistent with sorption to irreversibly absorbing glassy sediment organic carbon (SOC) and liquid–liquid like partitioning to rubbery SOC. The observed absorption isotherms and the desorption isotherms were adequately fitted linear models. Irreversible absorption showed signs of saturation and the reversible partitioning diminished during the 2nd S–D cycle causing the composite sorption capacity to decrease. Results suggest that under the conditions tested, surface water sediment can act as sink for the studied PFAAs. Rubbery SOC can potentially release or absorb contaminants, thus acting as a concentration buffer. S–D cycling can cause irreversible absorption concentration to increase even when exposure occurs at lower concentrations (i.e. 5 μ g / L ). log K O C values of sediment that underwent S–D cycling overlaps with the range of field date, suggesting that the sediment of surface water may have experienced some degree of S–D cycling. • History of absorption–desorption affect the fate of PFAAs in aquatic environment. • Sorption of PFAAs is consistent with two-domain absorption assumption. • Surface water sediment can act as sink for PFAAs. • Rubbery sediment organic carbon can act as a concentration buffer.

Glassy cholesteric liquid crystal siloxane photonic coatings in response to temperature and reflection angles

Responsive liquid crystal (LC) photonic coatings demonstrating tunable selective reflection are appealing for various of applications, such as information encryption. However, the fabrication of such LC photonic coatings remains a challenge. In this work, temperature and reflection angle-responsive coatings consisting of glassy cholesteric LC siloxane, applied by a screen printing method. First, a series of cyclic side-chain LC oligosiloxane containing chiral 4-(4-(4-Menthyloxy-4-oxobutanoyloxy)benzoyloxy)phenyl 4-allyloxybenzoate (M1) and chiral 4′-(4-menthyloxy-4-oxobutanoyloxy)biphenyl-4-yl-4-allyloxybenzoate (M2), denoted as P1-P5, were prepared via molecular grafting. Subsequently, the LC coatings were fabricated by coating the cholesteric LC oligomers on substrate, and then quenched with liquid nitrogen. Notably, the glassy cholesteric LC coatings retained temperature and reflection angle responsiveness due to the presence of chiral monomers. Upon increasing the temperature, the LC coatings P2-P5 showed a continuous blue shift and P1 showed a red shift. And all the LC coatings showed a continuous blue shift with increasing reflection angles.

Glassy nematogenic properties induced by six-membered ring’s trimeric fluorinated Schiff base liquid crystals

ABSTRACT New non-conventional Schiff base trimers composed of two fluorinated benzylideneaniline moieties connected to a halogen-substituted benzalideneaniline core at the ortho and para positions via octylene spacers were synthesized and characterized. The halogen X at the 4-position of the benzalideneaniline core includes F, Cl, Br and I. All the members exhibit enantiotropic nematic phase except for the compounds possessing fluorine and iodine substituents, which show only monotropic characteristics. A notable feature is that upon cooling the trimers vitrified to form the glassy state at low temperature. The Schlieren texture remains unchanged even it reaches the room temperature. This phenomenon resembles the one exhibited by glassy nematic liquid crystals and the enthalpy changes associated with the nematic to glass transition are unresolved due to the negligible value of heat change. The effect of different halogens towards the mesomorphic properties of the trimers was also described.

Tuning the colour of glassy cholesteric liquid crystals using copolymerization of two left-handed menthyl- and cholesteryl-based mesogenic monomers

ABSTRACT A new series of polysiloxane glassy cholesteric liquid crystal copolymers with menthyl- and cholesteryl-based mesogenic units in the side chains, denoted as P-MtxChy (x, y expresses the molar ratio of monomers Mt and Ch in copolymeric synthesis, and x + y = 7.) were successfully synthesised by hydrosilylation reaction. The mesomorphic properties and phase behaviours were studied by differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X-ray diffraction. Optical properties were investigated by the UV-VIS spectrum. Using the volume-excluding action of mesogenic units in side chains, we obtained glassy cholesteric liquid crystal copolymers. By varying molar ratio of Mt and Ch in copolymers, the helical pitch was adjusted into visible light region. With the increase of Mt, the maximum reflection wavelength off normal 8 ° shifted from 548 nm of P-Mt3Ch4 to 650 nm of P-Mt4Ch3 to 872 nm of P-Mt5Ch2 , and the reflected colours changed from green to red. These well-oriented glassy films have shown good morphological stability below the glass-transition temperature (Tg ) for more than a year.

Quantitative analysis of stereoscopic molecular orientations in thermally reactive and heterogeneous noncrystalline thin films via variable-temperature infrared pMAIRS and GI-XRD

The quantitative estimation of stereoscopic molecular orientations in semicrystalline polymer thin films with characteristic heterogeneous structures is essential for the development of advanced film materials. Grazing-incidence X-ray diffraction (GI-XRD) is a powerful technique used to evaluate the orientational order of crystalline lattices; however, it provides the orientational order of only ordered regions (crystal and glassy liquid crystal regions). In contrast, infrared (IR) p-polarized multiple-angle incidence resolution spectrometry (pMAIRS) can provide the averaged orientational order of overall regions in a film regardless of sample crystallinity. This paper combines variable-temperature (VT) pMAIRS, static GI-XRD and spectroscopic ellipsometry and reports general insight into the molecular orientation mechanism occurring in polymer films revealed through the precise analysis of the structural evolution of linear poly(amic n-alkyl ester), PAE, with different lengths of n-alkyl chains during thermal curing, which involves solvent evaporation and dehydration imidization reactions to form the corresponding polyimide (PI). This combined method clarified that the PAE and PI thin films had a heterogeneous structure consisting of a glassy liquid-crystalline (ordered) region and a nonoriented amorphous region. Furthermore, imidization proceeded faster in the amorphous region than in the ordered (oriented) region. In addition, anomalies of refractive index and birefringence were found by comparing pMAIRS and spectroscopic ellipsometry, although the effect of the side chain length on the molecular orientation of PI was insignificant. The anomalies indicate that an isotropic void structures were generated by the elimination reaction of the side chains and that the volume fraction of voids increased with increasing side chain length. These results demonstrated that the combination of VT-pMAIRS and GI-XRD is a very powerful tool for the in situ structural analyses of noncrystalline (disordered crystal, glassy liquid crystal, and oriented amorphous) thin-film materials ongoing chemical reactions in their components and is inherently applicable to all kinds of interesting polymeric thin-film materials. Thin film aromatic polyimides were quantitatively analyzed by grazing-incidence X-ray diffraction (GI-XRD), variable-temperature infrared p-polarized multiple-angle resolution spectroscopy (VT-pMAIRS), and spectroscopic ellipsometry (SE) methods. Combining VT-pMAIRS and GI-XRD revealed characteristic heterogeneous structures comprising non-oriented amorphous and oriented liquid-crystalline glass regions. Additionally, SE indicated that the film involved anisotropic-shaped void inducing form-birefringence. Such an excess of birefringence can make it difficult to estimate orientational order using birefringence measurement. This methodology presented here will remarkably contribute to general structural analyses of all intriguing thin-film polymers with characteristic heterogeneity.

Numerical analysis and design of a light-driven liquid crystal polymer-based motorless miniature cart.

Liquid crystal polymers are a special class of soft materials that can change their shape in response to numerous stimuli such as light, heat, electric field, and chemicals. The ability to tailor the deformed shape by tuning the alignment of mesogens across the film has enabled the researchers to generate unique motions from these liquid crystal polymer thin films. Simulating such motions might allow us to understand the underlying mechanisms better and could lead to novel designs. In this paper, we analyze the kinematics of the light-driven rolling motion of wheels fabricated with azobenzene-doped glassy liquid crystal networks through a one-way coupled transient photo-mechanical model. The influence of the isomerization parameters and the alignment of mesogens through the thickness on the kinematics of the wheel is presented. The developed model is further used to assess the feasibility of a light-actuated four-wheeled cart with wheels made of azobenzene-doped liquid crystal network thin films.

Highly Saturated Glassy Liquid Crystal Films Having Nano- and Microscale Thicknesses for High-Power Laser Applications

The optical properties of glassy liquid crystals (GLC’s) designed to provide high resistance to laser-induced damage are explored. GLC’s readily enable freezing of the anisotropic ordering of liqui...

Preparation and optical properties of linear polysiloxane-based glassy cholesteric liquid crystals with green reflected colour

ABSTRACT A new series of glassy chiral-nematic liquid crystals P-ChxNy , were synthesised by hydrosilylation reaction of chiral mesogenic monomer Ch and nematic monomer N grafted onto polymethylhydrosiloxane. The mesomorphic properties, phase behaviour and selective reflection were studied by differential scanning calorimetry (DSC), polarising optical microscopy (POM), and UV-VIS spectrum. Both the Tg and Tc gradually increased as the amount of unit Ch in the copolymer increased. A series of morphologically stable, glassy chiral-nematic liquid crystals were obtained. Among these copolymers, the well-oriented glassy film of the polymer P-Ch4N3 exhibited a selective reflection band centred at approximately 532 nm with green reflected colour below Tg .

Straight-chain alkanediol derivatives leading to glassy cholesteric liquid crystals with visible reflection

ABSTRACT Straight-chain alkanediols such as ethylene glycol are commonly found in our daily life as they are used to produce cosmetics, antifreezes, polyesters and polyurethanes. In this article, we report on the promising potential use of straight-chain alkanediols for rewritable full-colour imaging applications by the preparation of glassy cholesteric liquid crystals (G-CLCs). A series of straight-chain alkanediol derivatives possessing two cholesteryl groups through carbonate ester linkages (Cn-DiCh) showed thermotropic cholesteric liquid crystal phase with visible reflection. The thermally induced shifting ranges of reflection peaks were dependent on the central carbon chain length (n) of Cn-DiCh. Although the pristine Cn-DiCh showed narrow wavelength ranges of the reflection peaks by changing the temperature, we successfully prepared a mixture of two different kinds of Cn-DiCh at their equivalent weight ratio, which exhibited the reflection peak shift throughout a wide visible-wavelength range between 400 nm and 850 nm. Moreover, the binary mixtures of Cn-DiCh were rapidly cooled from the CLC temperatures to 0°C, whereupon the reflection colours could be preserved even at room temperature over 2 months. Such rapid cooling treatment enabled the straightforward preparation of solid-state G-CLCs with visible reflection characteristics, thereby leading to the applications of rewritable full-colour imaging media.

Development of Abuse-Deterrent Formulations Using Sucrose Acetate Isobutyrate.

The objective of the present investigation was to understand the effect of sucrose acetate isobutyrate (SAIB) on abuse-deterrent properties (ADPs) of abuse-deterrent formulations (ADFs) based on Polyox™. SAIB would enhance ADPs of Polyox™-based formulations due to its glassy liquid and hydrophobic properties. Formulations were prepared by granulation followed by compression and heat curing at 90°C. The formulations were evaluated for surface morphology, hardness, manipulation in coffee grinder, particle size distribution, drug (pseudoephedrine hydrochloride) extraction in water, alcohol, 0.1N HCl, 0.1N NaOH at room temperature and elevated temperature using microwave and oven, syringeability and injectability, and dissolution. The heat curing of formulations significantly increased the hardness (> 490N). Addition of SAIB imparted elasticity to formulations and decreased brittleness as indicated by lower values of work done and gradient compared to control formulations. After grinding, about 7.7-25.6% of the powder remained on the sieve (1mm pore opening), D90 was 53.1-136.7μm more, and Q (fraction < 500μm) was 17.8-40.7% less in SAIB-based formulations compared to control formulations. Drug extraction between control and test intact formulations was similar. However, drug extraction was 23.9-42.5% (water), 20.6-26.1% (0.1N HCl), and 37.4-50.6% (0.1N NaOH) less in SAIB-based powder cured and uncured formulations compared to control formulations. Dissolution varied from 65.6 ± 4.2 to 97.6 ± 4.0% in 9h from the formulations. In conclusion, addition of SAIB to Polyox™-based ADFs has synergistic effect on ADPs. This would further decrease potential of drug abuse/misuse by various routes.

Simulation of Circular Dichroism by Chromophores Coupled with Selective Reflection by Cholesteric Stacks.

The Good-Karali theory is extended to simulate composite circular dichroism (CD) through a cholesteric stack by incorporating chromophore's selective absorption (SA) and cholesteric stack's selective reflection (SR). Based on the independently evaluated anisotropic refractive indices and absorption coefficients, helical sense and pitch length, and film thickness, the theory is capable of describing transmission, reflection, and absorption through spin-cast cholesteric glassy liquid crystal films of nonafluorene. The resulting composite CD spectra agree quite well with experimental observations. The theory informs that SA plays a dominant role over SR in the composite CD. Specifically, the right-handed stack of the chromophore with its absorption dipole aligned with the local director in the cholesteric stack preferentially absorbs the left-handed over the right-handed circularly polarized light. The algebraic sign of the predicted composite CD flips by reversing the cholesteric host film's handedness without altering other parameter values. The established theory and computation constitute a solid foundation for optimizing circular polarizers by exploring the readily accessible parameter space targeting various potential applications.

Spontaneous Chain Orientation of Aromatic Polyimides Evolved during Thermal Imidization from Shear-Oriented Glassy Liquid Crystalline Precursors

A series of poly(amic ester)s, PMm, based on pyromellitic acid derivatives with long n-alkylene side chains [−(CH2)mH], were synthesized to prepare low-temperature lyotropic liquid crystalline (LC)...

Synthesis and Mesocrystalline Properties of Glassy Liquid Crystal Compounds Based on Tetrathiofuvalene and Cyanobenzene

Synthesis and Mesocrystalline Properties of Glassy Liquid Crystal Compounds Based on Tetrathiofuvalene and Cyanobenzene

Tracer Transport Probes Relaxation and Structure of Attractive and Repulsive Glassy Liquids.

Dynamic coupling of small penetrants to slow, cooperative relaxations within crowded cells, supercooled liquids, and polymer matrices has broad consequences for applications ranging from drug delivery to nanocomposite processing. Interactions between the constituents of these and other disordered media alter the cooperative relaxations, but their effect on penetrant dynamics remains incompletely understood. We use molecular dynamics simulations to show that the motions of hard-sphere tracer particles probe differences in local structure and cooperative relaxation processes in attractive and repulsive glassy liquid matrices with equal bulk packing fractions and long-time diffusivities. Coupling of the tracer dynamics to collective relaxations in each matrix affects the shape of tracer trajectories, which are fractal within the repulsive matrix and more compact in the attractive. These results reveal that the structure of relaxations controls penetrant transport and dispersion in cooperatively relaxing systems and provide insight into dynamical heterogeneity within glassy liquids.

Scalable Synthesis of Cholesteric Glassy Liquid Crystals

Capable of nonabsorbing circular polarization of unpolarized incident light, cholesteric glassy liquid crystals consisting of hybrid chiral-nematic pendants to volume-excluding cores are potentially useful for the fabrication of various robust optical devices. As illustrated in this study, the well-oriented glassy film of enantiomeric Bz3ChN, with a glass transition at 73 °C and a cholesteric-to-isotropic transition at 295 °C, exhibits a selective reflection band centered at approximately 410 nm, an exceptional set of properties well suited for optical device exploration. To enable sustainable large-scale synthesis of this material class for widespread applications, a productive strategy has been established, requiring a mere three-step scheme with an overall yield, atom economy, and reaction mass efficiency at 34%, 33%, and 12%, respectively. While amenable to improvement, the resulting green chemistry metrics are encouraging as the first attempt.

The curious effect of potassium fluoride on glycerol carbonate. How salts can influence the structuredness of organic solvents

Glycerol carbonate (4-hydroxymethyl-1,3-dioxolan-2-one, shortly GC) is a dense, viscous, water soluble solvent. The high dielectric constant and dipole moment make it a suitable non-aqueous green solvent for several salts in different applications. GC dissolves significant amounts of inorganic salts such as KF. The saturation of GC with KF leads to the formation of a viscous liquid at room temperature. In this paper, we report on conductivity, rheology, differential scanning calorimetry and infrared spectroscopy experiments that indicate the formation of a glassy liquid where GC molecules and KF ion pairs are intercalated in a firm and ordered tridimensional structure, stabilized by hydrogen bonding and strong ion-dipole interactions.