Diffusion Of Solvent Molecules Research Articles

Molecular simulations of the effects of substitutions on the dissolution properties of amorphous cellulose acetate

The dissolution behavior of cellulose acetate (CA) is an extremely important property in its extensive applications and preparation of derivatives. In this paper, we proposed a molecular model building strategy to construct amorphous CA with various substituent distributions (different degrees of substitution and substitution positions). A protocol combing molecular dynamics simulation and density functional theory (DFT) was applied to systematically investigate the dissolution behavior of CAs, and the structural properties of CAs. The reduced cohesive energy and polarity of CAs caused by the increase in substituents would enhance its solubility. The interaction of solvent molecules and CAs and the diffusion of solvent molecules in CAs have a synergistic effect on the dissolution of CAs. The diffusion coefficient is the primary factor affecting the solubility. Moreover, substituents at different positions of the anhydroglucose units along the CAs chains would produce different steric hindrance effects, which in turn affect the dissolution behavior.

High-Precision Colorimetric Sensing by Dynamic Tracking of Solvent Diffusion in Hollow-Sphere Photonic Crystals.

Expensive instruments and complicated data processing are often required to discriminate solvents with similar structures and properties. Colorimetric sensors with high selectivity, low cost, and good portability are highly desirable to simplify such detection tasks. Herein, we report the fabrication of a photonic crystal sensor based on the self-assembled resorcinol formaldehyde (RF) hollow spheres to realize colorimetric sensing of polar solvents, including homologs and isomers based on the saturated diffusion time. The diffusion of solvent molecules through the photonic crystal film exhibits a unique three-step diffusion profile accompanied by a dynamic color change, as determined by the physicochemical properties of the solvent molecules and their interactions with the polymer shells, making it possible to accurately identify the solvent type based on the dynamic reflection spectra or visual perception. With its superior selectivity and sensitivity, this single-component colorimetric sensor represents a straightforward tool for convenient solvent detection and identification.

Hydrated Micellar Structure of Ethoxylated Nonyl Phenols from PGSE NMR

Abstract Solvent self-diffusion coefficients $D_{w}^{*}$ and Dw are respectively determined by PGSE NMR in the bulk solvent and in suitably prepared aqueous micellar solutions of a series of commercial ethoxylated nonyl phenols (ENPs) at 298 and 317 K. The capability of ENP micelles for obstructing the free diffusion of solvent molecules is characterized by the obstruction ratio $K = D_{w}/D_{w}^{*}$, which turns out to depend merely on the volume fraction of EO units present—regardless of significant changes in solute concentration, distribution of EO chain length, micellar aggregation number and temperature. The experiments are interpreted in terms of a renewed analytical model of ENP micellar structure, based on Tanford’s concept of hydrodynamic particle. The results from model fitting return the characteristic sizes of ENP monomers, support the ellipsoid shape of the micelles, indicate a stable EO shell, follow the trend in the variation of hydration number vs. the chain length predicted by thermal analysis in PEO solutions.

Adsorption behavior of acetone solvent at the HMX crystal faces: A molecular dynamics study

Molecular dynamics simulations have been performed to understand the adsorption behavior of acetone (AC) solvent at the three surfaces of 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctan (HMX) crystal, i.e. (011), (110), and (020) faces. The simulation results show that the structural features and electrostatic potentials of crystal faces are determined by the HMX molecular packing, inducing distinct mass density distribution, dipole orientation, and diffusion of solvent molecules in the interfacial regions. The solvent adsorption is mainly governed by the van der Waals forces, and the crystal-solvent interaction energies among three systems are ranked as (020)≈(110)>(011). The adsorption sites for solvent incorporation at the crystal surface were found and visualized with the aid of occupancy analysis. A uniform arrangement of adsorption sites is observed at the rough (020) surface as a result of ordered adsorption motif.

An In Situ Investigation into the Formation of the Solvent‐Induced Crystalline Phase of Poly(9,9‐Dioctylfluorene) in Solvent Vapor Annealing

A new metastable solvent‐induced clathrate liquid crystalline phase of β phase (named β' here) in crystalline poly(9,9‐dioctylfluorene) (PFO) thin film induced by solvent annealing is found by a combination of in situ ultraviolet and visible spectrophotometry (UV‐vis), photoluminescence spectroscopy (PL), and grazing incidence wide‐angle X‐ray scattering (GIWAXS). The solvent annealing process consists of three processes: diffusion of solvent molecules into the film; saturation of solvent in the film; and drying of the film under nitrogen. The formation of β' phase with ordered packing of side chains and disordered packing of backbones occurs during the diffusion process of solvent molecules into the film. When the solvent molecules penetrate the film, the disordered side chains start to align themselves to form an ordered structure, and the ordering would gradually in the saturationprocess. Furthermore, the ordering of side chains drives an ordered rearrangement of the backbones during the drying process; however, the crystallinity of the side chains decreases with the orderly rearrangement of backbones due to the helical conformation of PFO. image

A simplified coupled thermo-mechanical model for the transient analysis of temperature-sensitive hydrogels

The present work investigates the deformation characteristics of a temperature sensitive hydrogel. The state of mechanical and chemical equilibrium is first formulated via a variational approach, upon which a finite element model is developed and implemented through user-defined material subroutine UMAT in the commercial software ABAQUS. We will show that this UMAT implementation allows for more versatility in the imposition of initial conditions over existing models developed using UHYPER subroutine. Furthermore, we propose an approach to simulate the transient swelling process of a temperature sensitive hydrogel. This is achieved through the simultaneous application of three user-defined subroutines, which model the constitutive properties of the gel, as well as the diffusion of solvent molecules within the gel. Several numerical case studies are presented to verify the present model developed with experimental data, as well as to illustrate its capabilities in simulating a wide array of complex gel phenomena, including surface creasing, bifurcation and buckling of gels. Through these numerical examples, we are able to gain deeper insights, and explain some of the new interesting physical phenomena observed in reported experiments.

Investigation of diffusion mechanisms during pervaporation of molecules of organic solvents in polymer membranes

With the help of the original experimental setup using a pervaporation process, parameters which allow to indirectly determine the mechanisms and models of diffusion of solvent molecules in the polymer membrane body were investigated. The time dependencies of these parameters during pervaporation were obtained for both unsaturated and saturated membranes. It was shown that the mechanism of diffusion of the solvent molecules in the polymer membrane for the unsaturated membranes consists of two components: diffusion through thermal activation of the system and diffusion occurring through the free volume. Moreover, the rate of thermally activated diffusion is much higher and is observed in the beginning of the pervaporation process, whereas the diffusion using the free-volume model begins to emerge in the middle of the process and runs more slowly, but it is a source of transfer of the majority of solvent molecules. For saturated membranes, the main transfer mechanism is diffusion through the structural voids of the polymer. These results allow to interpret diffusion models in polymer membranes.

A diffusion-viscous analysis and experimental verification of defect formation in sintered silver bond-line

Abstract

Use of environmentally-responsive smart glasses in controlled release: Diffusion of molecules under applied stimuli

The use of organosilica sol-gels as environmentally-responsive materials for stimuli-controlled release of encapsulated molecules is reported. These sol-gels exhibit bulk volume changes with respect to applied stimuli such as pH, temperature, salt, and solvents. These volume changes result in expulsion/intake of solvent molecules which can be utilized as a means for externally-regulated release and delivery of dopant molecular entities. For these materials, which undergo a volume transition in response to environmental changes, the magnitude and response time of the material is related to diffusion of solvent molecules in and out of the material. The release of encapsulated molecules and diffusion of solvent accompanies the volume transitions, which can be initiated by changes in temperature or ionic concentration. The kinetics and mechanism of volume changes of organosilica network consisting of hydrophilic and hydrophobic segments are investigated which provide critical insights into the nature of underlying factors that influence release of encapsulated entities. The diffusion coefficient of water molecules in these gels is determined to be considerably faster as compared to organic polymer gels and silica gels indicating rapid volume responses which can be utilized as efficient trigger mechanisms for release of molecules. The results validate preliminary feasibility of stimuli-controlled release of molecules with these gels initiated by the diffusional flow of solvent established by the volume changes.

Dynamic phase holograms in anthracene-containing polymer layers under conditions of rapid diffusion

A model of the dynamics of phase holographic gratings in a polymer layer containing monosubstituted anthracene and a solvent-plasticizer is developed for the case when diffusion of all low-molecular components occurs. Good agreement between this model and the experimental data is demonstrated. It is shown that the photoinduced trapping and diffusion of solvent molecules also occur in highly plasticized polymer matrices, affecting significantly the dynamics of holographic gratings. Differences in the dynamics of holograms under conditions of rapid diffusion and thermolysis of the photoproduct (the photodimer) are noted. The trends in variations of the recording parameters as a function of the solvent content are revealed.

Measurement of the Rates of Diffusion of Halomethanes into Polymer Films Using ATR-FTIR Spectroscopy

Polymer-modified attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and FEWS (fibre-optic evanescent wave) spectroscopy have been very successful to date for sensitive detection of organic pollutants in water utilising the mid-infrared (MIR) region of the electromagnetic spectrum (4000-400 cm−1). This sensing approach involves the use of different polymer films for preconcentration with optimisation of the sensor related to the rate of diffusion of solvent molecules into these polymer films. Compounds such as chloroform, bromoform, bromodichloromethane and dibromochloromethane which are collectively referred to as trihalomethanes (THMs) were analysed in this work. A gaseous phase experimental design was used and from experimental data the rate of diffusion of each of the halomethanes was quantified based on a Fickian type diffusion model. Individual diffusion coefficient values were found to be in the range 3.38 E-10 ± 0.01 E-10 to 4.72 E-08 ± 0.42 E-08 cm2 s−1. Multicomponent effects were observed for mixtures of compounds diffusing into polyisobutylene and ethylene-propylene copolymer.

UV-visible technique for studying powder coatings and their dissolution

UV-Visible (UVV) technique used to monitor powder coating and its dissolution processes from hard latex particles. Three sets of latex coatings were prepared from poly(methyl methacrylate) (PMMA) particles. The first set of coatings was annealed at elevated temperatures in various time intervals during which reflected photon intensity, Irf, was measured. The second set of coatings was annealed at various temperatures in 10 min time intervals during which transmitted intensity, Itr, was measured. Irf first decreased and then increased as the annealing temperature was increased. Decrease in Irf was explained with the void closure mechanism due to viscous flow. Increase in Itr and Irf against time and temperature were attributed to an increase in crossing density at the junction surface. The activation energy of viscous flow, ΔH, was measured and found to be around 8 kcal/mol and the back and forth activation energies (ΔErf and ΔEtr) were measured and found to be around 49 and 53 kcal/mol for a reptating polymer chain across the junction surface. Diffusion of solvent molecules (chloroform) into the annealed latex coatings was followed by desorption of PMMA chains for the third set of films. Desorption of pyrene, P, labeled PMMA chains was monitored in real-time by the absorbance change of pyrene in the polymer-solvent mixture. A diffusion model with a moving boundary was employed to quantify real-time UVV data. Diffusion coefficients of desorbed PMMA chains were measured and found to be between 2 and 0.6 × 10−11 cm2 s−1 in the 100 and 275°C temperature range.

Real time monitoring of latex film dissolution by UVV technique

UV–visible (UVV) technique is used for monitoring of polymer film dissolution. These films are formed from pyrene (P)-labeled poly(methyl methacrylate) (PMMA) latex particles, sterically stabilized by poly isobutylene (PIB, Annealing of films was performed above Tg at various temperatures for 30-min time intervals. Diffusion of solvent molecules (chloroform) into the annealed latex film was followed by desorption of PMMA chains. Desorption of P-labeled PMMA chains was monitored in real time by the absorbance change of P in the polymer–solvent mixture. A diffusion model with a moving boundary was used to quantify real time UVV data. Diffusion coefficients of desorbed PMMA chains were measured and found to be between 2 and 0.6 × 10−11 cm2 s−1 in the 100 and 275°C temperature range. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1075–1082, 2000

Real time monitoring of latex film dissolution by UVV technique

UV–visible (UVV) technique is used for monitoring of polymer film dissolution. These films are formed from pyrene (P)-labeled poly(methyl methacrylate) (PMMA) latex particles, sterically stabilized by poly isobutylene (PIB, Annealing of films was performed above Tg at various temperatures for 30-min time intervals. Diffusion of solvent molecules (chloroform) into the annealed latex film was followed by desorption of PMMA chains. Desorption of P-labeled PMMA chains was monitored in real time by the absorbance change of P in the polymer–solvent mixture. A diffusion model with a moving boundary was used to quantify real time UVV data. Diffusion coefficients of desorbed PMMA chains were measured and found to be between 2 and 0.6 × 10−11 cm2 s−1 in the 100 and 275°C temperature range. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1075–1082, 2000

NMR measurements of ionic mobility in model polymer electrolyte solutions

19F and 7Li pulsed field gradient (PFG) NMR measurements have been undertaken to determine anion and cation diffusion coefficients of tetraethylene glycol dimethyl ether/LiCF 3SO 3 and N,N dimethyl formamide/LiCF 3SO 3 solutions over a range of temperatures and concentration. The diffusion of the solvent molecules has also been determined by 1H PFG NMR measurements. In addition, viscosity and ionic conductivity measurements have been undertaken. The ionic diffusion and ionic conductivity data are discussed in terms of the Nernst-Einstein equation and the relationship between ionic diffusion and viscosity are considered in terms of the Stokes-Einstein equation. Finally, NMR T 1 data are considered in terms of diffusion and rotation of solvent molecules.

Fibrillar Structure and its Relevance to Diffusion, Shrinkage, and Relaxation Processes in Nylon Fibers

Quantitative prediction of the properties in fibers of semicrystalline polymers requires a detailed description of the fibrillar structure. Use of small-angle x-ray and neutron scattering (saxs and sans) and wide-angle x-ray diffraction (waxd) to obtain such information is illustrated with data from drawn and annealed nylon 6 fibers. The length, diameter, and orientation of the fibrils and the lamellae, and the spacing between the fibrils and the lamellae, are determined using saxs. Diffusion characteristics of the interlamellar and the interfibrillar regions are studied by following the diffusion of solvent molecules (D2O) using sans. Changes in the amorphous orientation are studied by analytically separating the amorphous scattering in waxd patterns into isotropic and anisotropic components. Our data suggest that the glass transition temperature is due to the superposition of relaxations of unoriented and oriented amorphous components. Diffusion is interpreted as occurring through a network of interconnected interfibrillar (voids and mostly oriented amorphous or noncrystalline chain segments) and interlamellar (primarily unoriented amorphous or noncrystalline chain segments) channels. These channels respond differently to drawing and heat setting. The influence of the crystallization of oriented components of the amorphous phase on shrinkage behavior is discussed.

Effects of translational diffusion on dielectric friction in a dipolar liquid

A microscopic theory of the effects of dipolar solvents dynamics on the dielectric friction of a rotating dipolar solute is presented. We predict that translational diffusion of solvent molecules can significantly reduce the value of the zero-frequency dielectric friction. We find that the orientational correlation function of the solute is non-exponential in general, but can be profoundly influenced by the translational diffusion.

Time-resolved luminescence spectra of dipolar excited molecules in liquid and solid mixtures. Dynamics of dielectric enrichment and microscopic motions

In a liquid mixture the solvation shell of a dipolar molecule is enriched in the solvent of greater polarity (dielectric enrichment); this process requires the diffusion of solvent molecules near the solute dipole and its dynamics is related to the viscosity of the medium. Time-resolved luminescence spectra of dipolar excited states created by short laser pulses have been measured in the nanosecond to microsecond timescale in liquid mixtures and the dynamics of dielectric enrichment is described. The role of the solvent's viscosity is emphasised and the relationship between microscopic and macroscopic viscosities is clarified in a few instances. In mixed rigid matrices the time-resolved phosphorescence spectra of long-lived dipolar triplet states have been measured over times of several seconds in an effort to find evidence for slow microscopic motions of matrix molecules in the neighbourhood of dipolar solutes. Calculations based on the macroscopic viscosities of glassy solvents suggest that diffusion over approximately one solvent shell cannot be neglected over a time of ca. 1 s; the experimental results of time-resolved phosphorescence are considered from the point of view of the microscopic viscosity, and their relevance to the distance dependence of electron-transfer reactions is discussed.

Thermodynamic Properties of Drawn Linear Polyethylene

Measurements of melting curves, density, and long period of undrawn and drawn PE as a function of the draw ratio and the annealing temperature between 118° and 129.8°C for different annealing times were performed. Melting experiments show a linear increase of melting point and a reduction of heat content of the noncrystalline component with increasing draw ratio. As a consequence of plastic deformation during drawing, the tied macromolecules partly incorporated in more than one crystal are under high strain. This reduces not only the entropy but also the intra- (trans instead of gauche conformation) and interchain (aligned extended chains are more closely packed) energy of the amorphous regions. Annealing nearly instantaneously removes the strain on tied chains, restores the enthalpy and entropy to the values in a nearly completely relaxed supercooled melt, and increases crystallinity and long period. Subsequent prolonged annealing produces only slight additional changes. The variation of enthalpy and entropy rather well explains the observed drastic changes in sorption and diffusion of solvent molecules as a consequence of drawing and annealing.