Low Molecular Liquid Research Articles

Effects of selected solvents on PMMA after prolonged exposure: unilateral NMR and ATR-FTIR investigations

Exposure of heritage plastics to solvents can cause several changes to their surface layers and bulk. The amorphous nature of certain plastics, particularly polymethyl methacrylate (PMMA), allows penetration and diffusion of low-molecular liquids, which can lead to swelling, cracking, plasticisation or stiffening, extraction and dissolution of polymer and additive components. Such phenomena compromise the visual characteristics, chemical and physical structure of heritage collections and remain, for the most part, unexplored. Research studies present contradicting evidence concerning the use of solvents and their safe application on PMMA. The main discrepancy is about PMMA being permeable to water or not. Alcohols have also triggered debates about whether they cause leaching and/or depolymerisation. This paper investigates the potential effects that selected free polar and non-polar solvents—employed in different media as cleaning systems—can have on PMMA after prolonged contact. The Hildebrand solubility theory was used to select solvents based on PMMA’s miscibility. The effects of deionised water, ethanol, isopropanol and petroleum ether are examined through a 30-day immersion study of PMMA via microscopic examination, weight change measurements, ATR-FTIR, peak height ratios, and NMR MOUSE. All four solvents extracted soluble components, i.e. unreacted residual monomer, and increased PMMA’s surface sensitivity to abrasions. Water and petroleum ether did not cause any measurable chemical or physical changes. Alcohols caused surface crystallisation and crazing, with isopropanol leading to stiffening and ethanol to plasticisation of the material. These effects, although extreme and absent in most routine cleaning timeframes, demonstrate the cumulative damage these solvents can potentially induce to PMMA.

Effects of dye doping on electro-optical, thermo-electro-optical and dielectric properties of polymer dispersed liquid crystal films

In this study, polymer dispersed liquid crystal (PDLC) films comprising a phase separated low molecular weight thermotropic liquid crystal (LC) and high molecular weight polymer were, prepared using the polymer–induced phase separation method. In order to enhance the optical efficiency of the PDLC films, LC was doped with dichroic azo dye. Various characterization techniques were employed to determine the properties of the components and, the operating principles of the dye–doped PDLC (DPDLC) films. Morphological studies using polarizing optical microscopy and scanning electron microscopy indicated that the LC droplet configuration changed with various dye concentrations and voltages. Electro-optical analysis showed that the performance of the DPDLC film with a low dye concentration (0.007%) was excellent, with a high contrast ratio (241) and transmittance difference (ΔT = 98.57%), low threshold (VTH = 0.85 V/μm) and saturation voltages (VSAT = 1.45 V/μm), and a minimum hysteresis effect. The effects of temperature on the electro-optical properties of the DPDLC films were studied. Absorbance analyses were conducted using ultraviolet–visible spectrophotometry to complement the transmittance analyses. Dielectric relaxation spectroscopy was employed to measure relaxation frequency/time of DPDLC films. Debye and Cole – Cole modeling were conducted to understand nature of the relaxation process. The zero values of the distribution parameter (α) for all of the DPDLC composite films confirmed their Debye type relaxation process.

Entropy optimization for Darcy–Forchheimer electro-magneto-hydrodynamic slip flow of ferronanofluid due to stretching/shrinking rotating disk

The flow of ferronanofluid due to a rotating disk finds its significant place in biomedical sciences, pharmaceuticals, electronics, aerodynamics etc. Entropy generation appears in the systems/processes where its minimization is needed because it prohibits the decay of available energy which in turn boosts the efficiency of the associated thermal systems where it matters the most. In view of these added advantages, the flow and heat transfer behavior of ferronanofluid subject to slip, suction, electromagnetic field, Darcy–Forchheimer effect, and viscous dissipation, Ohmic heating and thermal radiation has been explored within this research. In addition, the role of entropy minimization associated with the flow concern has been analyzed. The apposite governing equations are numerically treated via shooting method. The important outcome of the study include infusion of more porous matrix develops controlled rotating flow due to both deformed disks. Rise in slip parameter augments flow velocity for stretched RD while that shows the adverse effect for shrunk RD. Controlled rate of heat transportation due to enhanced convective heating is significant for shrunk RD than that of stretched RD. Further, low Prandtl fluids, low molecular heat conduction and liquid friction yield entropy minimization thereby leading to uplift efficiency of thermal systems.

Aminosilane-co-Graphene Oxide/Epoxy nanocomposite coating: An approach towards toughness and viscoelastic properties enhancement

Graphene oxide (GO) nanoplatelets are synthesized via modified Hummer method. Then, GO is surface functionalized using (3-aminopropyl) triethoxysilane, i.e. APTES, to substitute its functionalities with primary amine groups. Chemical, structural and morphological analyses reveal that APTES molecules have successfully been grafted on the GO flakes, interlayer d-spacing in the stacks has increased, an intercalated/exfoliated morphology with smaller agglomerations has obtained and number of flakes in the stacks has been reduced. Subsequently, various concentrations, i.e. 0.25 %, 0.5 % and 1%, are impregnated into a low molecular weight Bisphenol-A liquid epoxy resin which is then cured by a polyamidoamine hardener. The effects of the nano fillers on mechanical characteristics of the cured epoxy films are investigated by universal tensile test, dynamic mechanical analysis and morphology assessment of the ruptured cross sectional area. The results show significant increases in elastic modulus (24 %), maximum stress (12 %), maximum strain (24 %) and work of fracture (69 %) for the nanocomposite containing 1 wt.% silane-modified GO compared to blank epoxy. DMA outcomes also show that highest Tg and maximized crosslinking density belongs to this sample. Fractured-surface morphology studies describe the mechanical properties enhancement. Such enhancement in mechanical properties empowers the prospective of this coating as a heavy-duty protective coating in various industries.

Temperature‐Responsive Low Molecular Weight Ionic Liquid Based Gelator: An Approach to Fabricate an Anti‐Cancer Drug‐Loaded Hybrid Ionogel

AbstractConceptualising gelators with stimuli responsiveness is advantageous to design smart materials for emerging technologies. These gelators, if are surface active and made up of active pharmaceutical ingredients, can (i) exhibit an interesting pharmaceutical profile, (ii) be useful in drug formulations and (iii) exert direct effects on cell membranes. Herein, cetylpyridinium salicylate (CetPySal) that offers higher surface activity than its precursor surfactant, cetpylpyridinium chloride (CPCl), was synthesised. CetPySal forms a temperature‐responsive ionogel at a critical gelation concentration that changes its physical appearance with temperature, i. e. opaque to transparent, owing to its structural arrangement within its supramolecular framework, that are characterized through spectrometric, calorimetric, scattering and microscopic techniques. The viscoelastic nature of the ionogels was studied through dynamic rheological measurements and the interactions that governs the phase transition were studied through FTIR spectroscopy. The hybrid pharmaceutical ionogels was successfully constructed through encapsulation of the chemotherapeutic drug imatinib mesylate within the ionogel matrix. The sustained release of the drug was investigated from this hybrid ionogel matrix. These results suggest that this new thermo‐responsive ionogel may be used to improve sustained release of drugs and open up new avenues as low‐cost gelators for biomedical applications.

Structurally Related Scaling Behavior in Ionic Systems.

We examine the density scaling properties of two ionic materials, a classic aprotic low molecular weight ionic liquid, 1-butyl-3-methylimidazolium bis(perfluoroethylsulfonyl)imide ([BMIm][BETI]), and a polymeric ionic liquid, poly(3-methyl-1,2,3-triazolium bis(trifluoromethylsulfonyl)imide) (TPIL). Density scaling is known to apply rigorously to simple liquids lacking specific intermolecular associations such as hydrogen bonds. Previous work has found that ionic liquids conform to density scaling over limited ranges of temperature and pressure. In this work, we find that the dc-conductivity of [BMIm][BETI] accurately scales for density changes of 17%; however, there is a departure from scaling for TPIL for even more modest variations of temperature and pressure. The entropy of both ionic samples conforms to density scaling only if the scaling exponent is allowed to vary linearly with the magnitude of the entropy.

Self-Sustainable, self-healable, Load Bearable and Moldable stimuli responsive ionogel for the Selective Removal of Anionic Dyes from aqueous medium

Among the tested strategies to remove the toxic dyes from the aquatic environment, absorption is widely preferred owing to its ease of formation, lower cost and modulating ability of the absorbents used. Designing advance absorbents that offer higher absorptivity, selectivity, reusability, moldability and high pre-concentration factor for the analyst is a challenging task yet to be achieved. Herein, we had designed new age low molecular weight gelator from prototypical molecular gelators, an ionic liquid based gelator; 1-n-hexadecyloxy-carbonylmethylpyridinium bromide (C16EPyrBr) that exhibited unusual, unprecedented stimuli responsive reversible transition from opaque to transparent ionogel due to the change in the gel microstructure from lamellar for the opaque ionogel to cylindrical for the transparent ionogel. Small angle neutron scattering and scanning and scanning electron microscopy measurements characterized the microstructure and morphology of the ionogel respectively. Although having lower molecular weight based, the ionogel show excellent tolerance against the salinity (1500 mM concentration of NaCl), offer good mechanical strength and have self-healing, self-sustaining, and load bearing characteristics. The ionogel could be loaded in apparatus like dialysis membrane and syringe with 99% removal efficiency and can selectively remove the anionic dye, methyl orange from the aqueous medium even after 20 cycles. As a final thought, the low molecular weight ionic liquid based gelator could be a promising alternative to the traditional anionic dye absorbents.

Paintable Encapsulated Body-Temperature-Responsive Photonic Reflectors with Arbitrary Shapes

A temperature-responsive photonic coating on a flexible substrate was prepared by a photoinduced phase-separation process. In this coating a low molecular weight cholesteric liquid crystal (Ch-LC) mixture was encapsulated between the substrate and an in situ formed protective polymer top layer. The photonic coating showed a blue-shift of the photonic reflection band of 100 nm by heating from 22 to 23 °C due to the close proximity to the smectic to cholesteric phase transition and an overall 330 nm blue-shift while heating from 22 to 45 °C. Hence, the red coating turned green upon contact with skin within seconds. Furthermore, the coating structure and composition were investigated in detail, revealing a thick top coat. The adhesion of the coating was improved by providing trays on the substrate (by etching or 3D printing), resulting in a link between arbitrary-shaped substrates and the protective polymer top layer. These bendable coatings could be of interest for sensors, anticounterfeit labels, or custom...

On the similarity of the self-diffusion and shear viscosity coefficients in low-molecular liquids

We discuss the similarity of the self-diffusion and kinematic shear viscosity coefficients for low-molecular liquids. The rotational motion of molecules is the main prerequisite of this similarity. Due to it, the interparticle potentials are selves-averaged and they become argon-like. The applicability of the van der Waals equation of state for low-molecular liquids is one of the important consequences of this fact. Taking into account that as rule the period of rotational motion is essentially smaller in comparison with the characteristic time needed for a change of molecular configuration formed by the nearest neighbors, we conclude that the similarity should also take place for mentioned kinetic coefficients. We illustrate the manifestation of the argon-like similarity for atomic liquids of argon type, dumbbell a disk-like liquid of nitrogen and benzene types, water, and other associated liquids. At that, liquid states of associated liquids are divided into two regions: one of which adjoins to the critical point and corresponds to argon-like translational thermal motion, and the second includes the triple point and the rotational motion of molecules has activation character in it. In this region, the similarity relations also take place although they have another character in comparison with that for argon-like liquids. The inapplicability of standard activation representations for low-molecular liquids is in details discussed. The careful comparison with experimental data is carried out.

A Dielectric and Vibrational Spectroscopy Study of the Confinement Effects on Ion Dynamics in a Methacrylate Based Polymerized Ionic Liquid within Nanoporous Silica Membranes

In this study, the structures and dynamics of a low molecular weight ionomer confined at length-scales below which solvation layers have been shown to form for ionic liquids within nanoporous silica are investigated using broadband dielectric spectroscopy, Raman spectroscopy and 1H NMR. Silica membranes having 7nm unidirectional pores were prepared using well-defined electrochemical etching procedures in a 1:1 volume fraction ethanol:hydrofluoric acid electrolyte solution. In situ free radical polymerization of the low molecular weight ionic liquid polymer, poly-[(methacryloyloxy)ethyl]dimethylammonium bis[(trifluoromethyl)-sulfonyl]imide, was performed monitored with Raman spectroscopy to observe changes in ion coordination and anion conformational fluctuations with monomer conversion in bulk and within nanoporous silica. The free radical polymerization reaction kinetics were observed to be increased under confinement compared to bulk as previously reported, and resulted in a 5kg/mol polymer with narrow molecular weight distribution. From the dielectric spectra, the dc conductivities of the polymer under confinement were determined to be increased compared to the polymer in the bulk. Using a simple model accounting for porosity within the membranes, a calculated adsorbed layer at the interface of the pore wall with the ionic liquid was determined to decrease with polymerization, effectively counteracting the effects of immobilization of ions within the polymer backbone. Furthermore, the possible changes in free volume under confinement and with polymerization are discussed through detailed observation of the Raman spectra regarding anion conformational changes. These changes in free volume are shown to correlate to increased ion dynamics. The ion dynamics in these materials are further described in terms of the current understanding of interfacial electrostatic interactions of ionic liquids with solid surfaces and in conjunction with the effects of polymer dynamics under confinement.

MODELING OF POLYMER MELT FLOW WITH THE PRESENCE OF A LOW VISCOSITY NEAR-WALL LAYER

Investigation of polymers movement process in the channels of processing equipment showed that the polymer layer near channel walls warms up faster and therefore acquires different properties from the main mass of the material - increased temperature, low molecular weight, and then reduced viscosity. A number of factors determines the nature of the wall layer: the amount of wall friction, the speed of the material, the mode of heating of the raw material. Such near-wall layers differ from those of ordinary low-molecular liquids, since they have a different nature.An analysis of these works showed that with a thin relative to the main flow of the boundary layer, the distribution of velocities in it can be considered close to linear. The purpose of the article is to analyze the results of mathematical modeling of the flow of polymer melts with imitation of the presence of low viscosity wall layer.Of particular interest is the study of the nature of polymer flows with a wall layer in the channel of the head of the device for forming by the method of spatial printing (3D printer). A device based on the method of layer-by-layer surfacing of the shape of the future product is selected as the basis the channel of the working body usually has a diameter of from 0.1 mm to 1.2 mm. For small nozzle diameters, the polymer properties throughout the channel volume correspond to the properties of the near-wall layer. However, as the diameter of the nozzle increases, the polymeric material becomes cooler and more viscous closer to the central axis.A feature of the conducted numerical experiments is that, since the value of the velocity of the polymer at the wall is not known in advance, instead of it, a conditional thin layer of liquid is introduced, with properties different from those of the base material. This simulates the presence of low molecular weight fractions in the surface layer of the polymer, or the use of lubricating impurities during extrusion.It has been established that with an increase in productivity, the pressure increases along a flatter nonlinear curve, in contrast to this dependence in the absence of a near-wall layer. Therefore, the introduction of a lubricating wall layer increases the productivity of processing equipment.The obtained dependences of the distribution of the flow parameters of the polymer in the channel on the presence and properties of the near-wall layer, as well as the dependence of the viscosity of the near-wall layer on the velocity and temperature. The simulation results help to clarify the results of calculations of the parameters of extrusion, 3D printing and other polymer processing processes, as well as recommend the use of lubricant additives to increase productivity and prevent.Prospects for further research may be modeling flow with a wall of melts with highly elastic properties.

(Invited) Elucidating Ion Transport Mechanisms in Polymerized Ionic Liquids

Poor ionic conductivity typically hinders the utilization of ion containing polymers from functioning as a single ion conductor for energy storage or conversion applications. A provocative sub class of these materials are polymerized ionic liquids (polyILs) which have the potential to combine the desirable ion transport of an ionic liquid with the favorable mechanical properties of a polymer. However, the room temperature conductivity of polyILs is usually 2 or 3 orders of magnitude lower than that of low molecular weight ionic liquids, yet a decoupling of conductivity and structural dynamics in polyILs demonstrates the opposite at the normalized glass transition temperature (T g/T). This seemingly conflicting observation can be reconciled by the fact that polyILs have higher T g and lower dielectric permittivity at the same T g/T than their molecular counterparts. Moreover, ionic conductivity of polyILs is found to be significantly slower than ion diffusion. Inverse Haven ratio shows a strong temperature dependence: saturating at 0.2 at higher temperature and decreasing at lower T. Pronounced reduction in conductivity is attributed to the cross correlation between the mobile ions since the ion pair diffusion is infeasible in polyILs. This speculation remains unverified. We have recently undertaken atomistic molecular dynamics (MD) simulations to elucidate transport mechanism in polyILs and demonstrate the dynamical heterogeneity and cooperative motion of ion transport in polyILs establishing for the first time quantitative evidence of mobile ion hopping. The hopping of anions is found to be dominantly interchain in nature and is generally facilitated by five associating cations from two different chains. Intrachain hopping was found to be much less significant being mediating with fewer chains. The mobile anions tend to form string-like structures and move cooperatively; and the string length of concerted motion of mobile anions increases with decreasing temperature. Our results reveal the important role of a distance criterion in defining hopping events to correctly elucidate the components of the ion transport mechanism. This molecular-level information will provide an important step in both rationalizing experimental observations and the design of novel ion-containing polymers with superior transport properties.

Photoresponsive Chiral Dopants: Light‐Driven Helicity Manipulation in Cholesteric Liquid Crystals for Optical and Mechanical Functions

AbstractThis Review focuses on recent advancements regarding the design of photoisomerizable chiral dopants which can switch the helical orientation in cholesteric liquid crystals upon light stimuli. Chiral dopants exhibiting conformational change in response to an external stimulus can provide dynamic control of the cholesteric pitch. Development of such responsive systems has been attempted since the 1970s. However, major advances on efficient chiral dopants exhibiting either high helical twisting power or large photoswitching have been achieved only in recent years. This Review covers photoresponsive low molecular weight cholesteric liquid crystal systems based on chiral dopants capable of photochemically “switching power to twist” surrounding liquid crystalline host molecules, “inverting” their handedness or even “inducing” helical organization from the racemic nematic phase.

Shear flows of low molecular weight nematic liquid crystals between parallel circular plates

Shear flows of low molecular weight nematic liquid crystals between parallel circular plates

Nature of Self-Diffusion in Fluids

The nature of the self-diffusion in low-molecular fluids is discussed. The particular attention is paid to atomic fluids (such as argon), liquid metals, and associated fluids (such as water). The self-diffusion coefficient in the fluids of all indicated types is considered to be the sum of two components: one of them is associated with the transfer of molecules by hydrodynamic vortex modes, and the other is generated by the circulatory motion of local molecular groups. The both components have a collective nature, they are genetically related to each other and differ only by their scales: the former is mesoscopic, the latter is nanoscopic. Manifestations of the collective vortical transport of molecules as specific features in the time dependence of the root-mean-square displacement of molecules are discussed. Sound arguments are proposed concerning the inadequacy of the activation mechanism of thermal molecular motion in low-molecular liquids. The immanent contradiction of exponential temperature dependences for the viscosity and self-diffusion coefficients is proved. In all cases, the preference is given to qualitative arguments.

Qualitative Properties of the Shear Viscosity of Liquids

In this paper, two theses are substantiated. (i) The viscosity of liquids in the larger part of the temperature interval, where this phase state exists, is governed by frictional effects between the molecular layers that move relative to one another. (ii) Argon and water at temperatures TH < T < TC (TH ≈ 315 K and TC is the corresponding critical temperature) have kinetic coefficients belonging to the same class of similarity. This is so because the behavior of the shear viscosity in water is driven by the averaged interaction potential between the molecules. On the basis of the similarity principle applied to the corresponding states of water and argon, the self-diffusion and shear viscosity coefficients of water are calculated. The inadequacy of activation mechanisms responsible for the formation of the viscosity and self-diffusion processes in water and most low-molecular liquids is discussed.

New Possibilities Provided by the Analysis of the Molecular Velocity Autocorrelation Function in Liquids

Long-time tails of the molecular velocity autocorrelation function (VACF) in liquid argon at temperatures higher and lower than the spinodal temperature have been analyzed. By considering the time dependence of the VACF, the self-diffusion and shear viscosity coefficients, and the Maxwell relaxation time are determined, as well as their changes when crossing the spinodal. It is shown that the characteristic changes in the temperature dependences of the indicated kinetic coefficients allow the spinodal position to be determined with a high accuracy. A possibility toapply the proposed method to other low-molecular liquids is considered. As an example, nitrogen and oxygen are used, for which the averaged potential of intermolecular interaction has the Lennard-Jones form.

(Invited) Ion Transport in Polymerized Ionic Liquids: Structure-Morphology-Property Relationships

Polymerized ionic liquids (PolyILs) are a novel class of functional polymers that combine the unique physicochemical properties of molecular ionic liquids with the outstanding mechanical characteristics of polymers. This special mix of features might help to circumvent the key limitations of low molecular weight ionic liquids, namely, leakage and poor mechanical properties while utilizing their outstanding characteristics such as low vapor pressures, wide liquidus ranges, high thermal stability, high ionic conductivity, and wide electrochemical windows. PolyILs have shown remarkable advantages when employed in electrochemical devices such as dye-sensitized solar cells, lithium batteries, actuators, field-effect transistors, light emitting electrochemical cells, and electrochromic devices, among others. Despite their promising prospects as ideal polymer electrolytes, the role of molecular structure, morphology, and polymer dynamics on charge transport in PolyILs remains poorly understood. According to classical theories, the self-diffusion and ion transport in electrolytes are controlled by structural relaxation. These approaches predict similar temperature dependence for the dc conductivity and structural dynamics. Although this prediction has been shown to hold reasonably well for low molecular weight aprotic ionic liquids, it fails for PolyILs. In addition, the impact of morphology on charge transport is not considered within the framework of these theories. This talk will focus on new insights obtained from experimental studies employing broadband dielectric spectroscopy, temperature-modulated differential scanning calorimetry, rheology, and scattering techniques to elucidate the impact of morphology on charge transport and structural dynamics in systematic series of polymerized ammonium- and imidazolium- based ionic liquids. Detailed analyses reveal strong decoupling of these processes in the PolyILs, implying the limitation of the classical theories in describing charge transport and molecular dynamics in these materials, in contrast to low molecular weight systems. In addition, the strong correlation observed between ionic conductivity from dielectric experiments and morphologies from scattering and computational studies will be discussed.

Optical reversible behavior of poly(ethylene-b-ethylene oxide) block copolymer dispersed liquid crystal blends

Optical properties of novel polymer dispersed liquid crystal (PDLC) blends based on two different low molecular weight nematic liquid crystals, 4′-(hexyloxy)-4-biphenylcarbonitrile (HOBC) and N-(4-ethoxybenzylidene)-4-butylaniline (EBBA), and poly(ethylene-b-ethylene oxide) block copolymer (PE-b-PEO), were studied to develop optically reversible PDLC blends applying a temperature gradient. Differential scanning calorimetry (DSC) showed that the liquid crystals, HOBC and EBBA, maintain their nematic-isotropic transition in designed PDLC blends, which was visualized by optical microscopy (OM). Results obtained using photoluminescence and UV–vis spectroscopies indicated that HOBC and EBBA liquid crystals maintain their reversible optical behavior passing from opaque to transparent state when temperature gradient was applied. The reversible switching process was proved in four consecutive heating/cooling cycles. Designed thermo-responsive PDLC blends possessed interesting optical properties, which make them potential candidates to be use as temperature sensors or thermo-optical devices.

Optical sensor platform based on cellulose nanocrystals (CNC) – 4′-(hexyloxy)-4-biphenylcarbonitrile (HOBC) bi-phase nematic liquid crystal composite films

The preparation of composite materials has gained tremendous attention due to the potential synergy of the combined materials. Here we fabricate novel thermal/electrical responsive photonic composite films combining cellulose nanocrystals (CNC) with a low molecular weight nematic liquid crystal (NLC), 4′-(hexyloxy)-4-biphenylcarbonitrile (HOBC). The obtained composite material combines both intense structural coloration of photonic cellulose and thermal and conductive properties of NLC. Scanning electron microscopy (SEM) results confirmed that liquid crystals coated CNC films maintain chiral nematic structure characteristic of CNC film and simultaneously, transversal cross-section scanning electron microscopy images indicated penetration of liquid crystals through the CNC layers. Investigated composite film maintain NLC optical properties being switchable as a function of temperature during heating/cooling cycles. The relationship between the morphology and thermoresponsive in the micro/nanostructured materials was investigated by using transmission optical microscopy (TOM). Conductive response of the composite films was proved by Electrostatic force microscopy (EFM) measurement. Designed thermo- and electro-responsive materials open novel simple pathway of fabrication of CNC-based materials with tunable properties.