Volume Fraction Of Gel Research Articles

Ion corrosion behavior of tunnel lining concrete in complex underground salt environment

In this study, the ion corrosion behavior of tunnel lining concrete in complex underground salt corrosion environment was investigated using a self-designed corrosion simulation test device in a complex underground environment. The results indicated the following: the corrosion of flowing water leads to the dissolution of lining concrete, and the load promotes the development of cracks in the tensile area of lining concrete and inhibits the development of defects in the compression area, resulting in the transmission speed of chloride and sulfate ions in lining concrete under different corrosion conditions given as follows: concrete in tensile zone under flowing corrosive solution and load > flowing corrosion solution acting alone > static corrosion solution > concrete in compression zone under flowing corrosive solution and load. When the flowing corrosion solution alone and flowing corrosion solution and load act on the concrete in the tensile zone, the pore volume fraction of gel decreases and the macropore volume fraction increases. Under the combined action of static corrosion solution and flowing groundwater and load, the pore volume fraction of gel in the pressurized area increases and the harmless pore volume fraction decreases.

Time gel and origin of matter

Standard model and/or QCD broadly envisage operation of a symmetry breaking in creation of mass [1]. Likewise, any phase transition brought about by a critical transition refer to operation of a symmetry breaking [2,3]. Such aspects of symmetry breaking directly follows from Noether's theorem and further implies that in principle, non-equlibrium self-assembly could emulate under correct electrochemical conditions creation of ‘matter’. In this work, we test this earlier conjecture of ours and show with experimental evidence how space-time symmetry breaking emulated by electrochemical realization of a ‘Time-Gel’ in the lab brought about by a critical phenomenon can be explored to demonstrate, at least in principle, origin of matter. The ‘Time-Gel’ is realized by electrochemical induction of a critical phenomenon of ‘gelation’ of discrete molecular precursors, where upon with temporally controlled charge injection/abstraction Q (as an indicator of temporal information) we evidence direct creation of ‘Time-Gel's (a polymer-colloid mixture) ‘mass’ (volume fraction, Φg) from a mass ‘null’ state. ‘Time-Gel's volume fraction (Φg) acts as a descriptor of spatio-temporal information. We observe further the descriptor of temporal information (Q) varies with volume fraction of gel formed (Φg) manifest as spatio-temporal fluctuation with a relation Q∝ Φgn. The order of n, is 5, and is obtained experimentally. Such an exponent in the power law, implies divergence in creation of matter. The above observation implicit in our finding is consistent to existing knowledge of divergent creation of matter as a direct consequence of breaking of symmetry under conditions following directly from Noether's theorem. In short, the present proposition prompted by experimental findings centers around the idea of symmetry breaking, where an experimental realization of a ‘time-gel’ model shows how space-time and charge might have led to the formation of matter under conditions away from equilibrium. ‘Time-Gel’ may thus act as an alternative model based on Chemical Science to explain and envisage the emergence of matter as a direct consequence of Noether's theorem.

Polyethylene Gel Volume Fraction (Cross-linked Percentage) Measurement Using DSC Technique

In this paper, the measurement of the crosslinking percentage (gel volume fraction) of polyethylene materials by using DSC technique is presented. To obtain the calibration curve, the networked samples of ASTMD 2765-01 corresponding to the curves of pure melt samples at the start of the reaction were used. The resulting calibration curve was used to predict the percentage of polyethylene cross-linked in a continuous process, and these results were compared with those obtained from D 2765-01, which resulted in excellent agreement between the two states. This technique is faster and cheaper and requires less raw material, the product does not release any harmful substances and is ASTM correct.

Multiscale synergistic toughened pluronic/PMEA/ hydroxyapatite hydrogel laminated aramid soft composites: Puncture resistance and self-healing properties

In order to solve the recycling of the puncture-resistant soft composites, this study constructs a multiscale self-healing gel-fabric soft composite synergistically toughened by Pluronic/PMEA hydrogel, hydroxyapatite nanoparticles (HAP NPs) and aramid fabric. Results show that the gel matrix has a self-healing efficiency of 85% after puncture damage, and the stab resistances are highly positively associated with the toughness of the hydrogel matrix. When toughened by 4% HAP NPs, the spike and knife resistances of soft composites are improved by 132% and 130%, respectively. After being laminated, the composite exhibits a self-repairing efficiency of 52% and still has excellent performance after multiple punctures. At lamination angle of 45° and the gel volume fraction of 45%, the composite has the best puncture resistance properties, and the 37 layers can resist against the E1 stab resistance energy. The synergistic toughened mechanism is due to the interfacial shear strength between the fiber and the gel matrix. Overall, this research provides a novel structural design for the recycling of high-performance puncture-resistant composites.

Theory of volume transition in polyelectrolyte gels with charge regularization

We present a theory for polyelectrolyte gels that allow the effective charge of the polymer backbone to self-regulate. Using a variational approach, we obtain an expression for the free energy of gels that accounts for the gel elasticity, free energy of mixing, counterion adsorption, local dielectric constant, electrostatic interaction among polymer segments, electrolyte ion correlations, and self-consistent charge regularization on the polymer strands. This free energy is then minimized to predict the behavior of the system as characterized by the gel volume fraction as a function of external variables such as temperature and salt concentration. We present results for the volume transition of polyelectrolyte gels in salt-free solvents, solvents with monovalent salts, and solvents with divalent salts. The results of our theoretical analysis capture the essential features of existing experimental results and also provide predictions for further experimentation. Our analysis highlights the importance of the self-regularization of the effective charge for the volume transition of gels in particular, and for charged polymer systems in general. Our analysis also enables us to identify the dominant free energy contributions for charged polymer networks and provides a framework for further investigation of specific experimental systems.

Self-diffusion of non-interacting hard spheres in particle gels

Different kinds of particle gels were simulated using a process of randomaggregation of hard spheres. The mean square displacement of Brownianspherical tracer particles through these rigid gels was monitored and theaverage diffusion coefficient, normalized with the free diffusion coefficient (D), was obtained. For each gel structure the effect of the gel volume fraction (ϕ) and size ratioof the tracer (d) on the relative diffusion coefficient was investigated systematically.The volume fraction that is accessible to the tracers (ϕa) was determinedin each case. D was found to be approximately the same ifϕa was the same,independent of ϕ, d and the gel structure. However a different behaviour is found if thetracers can penetrate the strands of the gel. A state diagram ofd versusϕ is given that showsthe critical values (dc, ϕc) atwhich all tracers become trapped. Different values are found for different gel structures. The dependenceof D onϕ/ϕc is independentof d, while thedependence of D on d/dc isindependent of ϕ.

Phase Behavior and Shrinking Kinetics of Thermo-Reversible Poly(N-Isopropylacrylamide-2-Hydroxyethyl Methacrylate)

AbstractWe study the thermodynamic properties of solutions of the physically gelling poly(N-isopropylacrylamide-2-hydroxyethyl methacrylate) [poly(NIPPAm-HEMA)]. We construct its phase diagram and characterize its kinetics of phase separation. This material belongs to a class of thermosensitive, “smart” polymers, that exhibit complex phase behavior. The copolymer studied is liquid at low temperatures and undergoes phase separation near 28°C, with negligible dependence on concentration. Above the transition temperature we observe coexistence between a polymer-dilute solution and a gel. We show that, upon quick heating, liquid solutions form a homogeneous gel that phase separates (shrinks) from a dilute polymer solution. We find that the evolution of the gel volume fraction is well described by a double exponential decay, indicating the presence of two shrinking regimes in a close parallel to the behavior of chemically cross-linked gels. The first stage is characterized by quick water ejection. In the second stage, slower shrinking is observed associated with internal reorganization of the polymers that allows the creation of gel-forming contacts.

A Metastable van der Waals Gel: Transitioning from Weak to Strong Attractions

Here we describe a method to create gels where the gel point is decoupled from gel elastic properties. Working with charge stabilized polystyrene latex particles with diameters, D, of 508-625 nm at ionic strengths of 0.1-1 M, the gel volume fraction is varied from 0.10-0.35 through the addition of less than monolayer coverage of hexaethylene glycol monododecyl ether (C6E12). At each surfactant concentration, the gel volume fraction depends on the background ionic strength. The changes in gel point with surfactant concentration suggest the strength of interparticle attraction decreases with increasing surfactant concentration. These changes are not reflected in the gel moduli, which are independent of surfactant concentration and ionic strength. We propose a model to describe this behavior based on gelation due to localization in a shallow truncated van der Waals minimum produced by the surfactant acting as a steric stabilizing layer. The surfactant remains mobile on the surface. Below the gel volume fraction, the time particles spend in the truncated well are not sufficient for the surfactant to be displaced such that the particles can only sample the shallow well. Above the gel volume fraction, particles are localized in the truncated van der Waals minima for sufficient periods of time to displace the surfactant layers with the result being that the particles fall into a primary van der Waals minimum. The result is gel points sensitive to surfactant concentration but moduli that are independent of the gel volume fraction.

Nonlinear elasticity and yielding of depletion gels

A microscopic activated barrier hopping theory of the viscoelasticity of colloidal glasses and gels has been generalized to treat the nonlinear rheological behavior of particle-polymer suspensions. The quiescent cage constraints and depletion bond strength are quantified using the polymer reference interaction site model theory of structure. External deformation (strain or stress) distorts the confining nonequilibrium free energy and reduces the barrier. The theory is specialized to study a limiting mechanical description of yielding and modulus softening in the absence of thermally induced barrier hopping. The yield stress and strain show a rich functional dependence on colloid volume fraction, polymer concentration, and polymer-colloid size asymmetry ratio. The yield stress collapses onto a master curve as a function of the polymer concentration scaled by its ideal mode-coupling gel boundary value, and sufficiently deep in the gel is of an effective power-law form with a universal exponent. A similar functional and scaling dependence of the yield stress on the volume fraction is found, but the apparent power-law exponent is nonuniversal and linearly correlated with the critical gel volume fraction. Stronger gels are generally, but not always, predicted to be more brittle in the strain mode of deformation. The theoretical calculations appear to be in accord with a broad range of observations.

Investigation of a whole blood fluidized bed Taylor-Couette flow device for enzymatic heparin neutralization.

The use of clinical bioreactors will increase as more therapeutic proteins are being cloned, expressed, and produced at a reduced cost. The proposed use of an immobilized heparinase I reactor to make heparin anticoagulation a safer therapy is an example of how the specificity and high activity of an enzyme could be incorporated into a system to ultimately benefit a patient. However, the development of a safe and efficient bioreactor is important for the use of immobilized heparinase I and other therapeutic proteins designed for use in medical extracorporeal procedures. This study examined the possibility of using Taylor-Couette flow and "flow-induced" recirculation of the agarose beads as a way to fluidize agarose-bound heparinase in whole blood. Heparinase I was immobilized onto agarose beads via cyanogen bromide activation. A reactor based on Taylor-Couette flow was designed and modified with a tangential recirculation line. The reactor was tested for efficacy and safety in vitro in human blood. Visualization studies in water and 42% glycerol were used to determine the minimum rotation rate for efficient fluidization. The strategic placement of the recirculation line allowed recirculation of the agarose without the use of an external pump. The device removed 90% of the heparin activity within 2 min from 450 cc of human blood at a blood flow rate of 100 mL/min. Furthermore, the device maintained inlet and outlet clotting times of 269 +/- 10 and 235 +/- 6 s, respectively, demonstrating the potential for regional heparinization. Blood damage was a function of gel volume fraction and rotation rate of the inner cylinder. Hemolysis of the red cells is an important issue when Taylor vortices are combined with macroscopic solid particles such as agarose beads. A modified Taylor-Couette flow device was developed to treat whole blood and operational criteria were established to minimize hemolysis.

Simulations of Sol-to-Gel Modeling: Effects of Mobility, Reversibility, and Quality of Solvent

Some of our recent work on computer simulation modeling of the sol-to-gel transition for the polymerization by step reaction are presented. Depending on the variants of the model, a random distribution of bifunctional and tetrafunctional monomers of concentration C2 and C4 respectively, and their chains (bond-fluctuating) are used as primary reacting units on a simple cubic lattice as the initial sol-phase. Effects of solvent, temperature, mobility of monomers, rate of reaction, and reversibility are considered in understanding the evolution of microgels, onset of gelation and the nature of sol-to-gel transition, inhomogeneity, etc. Gel point (pc, gel volume fraction (PG), weight average degree of polymerization (MW), structure factor (S(q, t)) show various interesting variations with the conversion factor (p). For example, sol-to-gel transition seems nonuniversal with respect to quality of the solvent, degree of inhomogeneity depends on the quality of solvent and rate of reaction due to interplay between the phase-separation and cross-linking.

Heterogeneous polyelectrolyte gels as stimuli-responsive membranes

Stimuli-responsive membranes may act as “on–off switches” or “permeability valves”, producing patterns of pulsatile release, where the period and rate of mass transfer can be controlled by external or environmental triggers (e.g. pH, temperature, electric field). In this work, composite-heterogeneous polyelectrolyte gel (composite-HPG) membranes consisting of polymethacrylic acid (PMAA) gel particles dispersed within a polydimethylsiloxane (PDMS) network were developed and evaluated as pH-responsive membranes. The mechanism of permeability control for caffeine and vitamin B 12 through composite-HPG membranes was determined to be a synergistic function of membrane hydration and the percolating volume fraction of PMAA gel. Larger changes in permeation as a function of pH were achieved when both hydration and percolation effects occurred together than when either of these effects occurred on their own. Vitamin B 12 permeation was observed when the hydrated gel volume fraction was above approximately 0.38, but not below. Furthermore, the percolating fraction of composite-HPG membranes containing 28% (dry basis) PMAA gel particles was manipulated via pH to fall above (pH 7) or below (pH 3) this transition in permeability, resulting in membranes that delivered solutes of high molecular weight (vitamin B 12) with large on/off delivery ratios (160).

Viscoelastic properties of colloidal gels

The microstructure and scaling of mechanical properties of dense colloidal gels were investigated as a function of volume fraction and strength of interparticle attraction. Gels were reversibly formed by cooling suspensions of octadecyl silica particles in decalin or tetradecane. Shear history independence of mechanical properties was ensured by preshearing the suspensions in the gelled state. Gelation resulted in suspensions with apparent fractal dimensions of 1.4. Shear densification resulted in an apparent fractal dimension of 2.5 for structures containing many particles. When the gelled suspension was presheared, just after the shear rate was set to zero, elastic moduli were small. Over time, the moduli recovered to a time independent value, G∞′, at a rate α. When measured over a wide range of volume fraction, φ, and strength of interparticle attraction, G∞′, α, and the strain limiting the extent of linear response to oscillatory deformations, γM, fell onto master curves when plotted as a function of φ/φG for 1.1<φ/φG<5. Here φG is the gel volume fraction that varied from 0.11 to 0.59 for temperatures studied.

Influence of Predilution on Cross-Link Density: Consequences for the Front Factor and the Flory-Huggins Relation

Abstract The influence of predilution before formation of a polymer network is considered. From theoretical and experimental considerations it is deduced that γ = γ °V0 and γ = γ g °V0 2 where γ y is the network segment density of the polymer phase, γg is the network segment density of the gel portion, Vo is the volume fraction of gel in the diluted stock, and the superscript zeros refer to the undiluted condition. As a result, it is concluded that the “front factor” for the elastic equation of state cannot vary with dilution of the network before cure as some have proposed. The reasons for the supposed variation are examined and a probable weakness found in the determination of cross-link density by chemical methods. The existence of the front factor is doubted. Use is made of the extended Flory-Huggins relation, whereby during differentiation the polymer-solvent interaction parameter is assumed to vary linearly with concentration, to equate network segment densities of prediluted and undiluted polymers through the relationγ g = γ g °V0. It is found that the slope of the curve X vs V2 calculates to be 0.33 where is the customary polymer-solvent interaction parameter and V2 is the volume fraction of polymer in a solvent swollen gel. A number of actual slopes are computed and found to be in the range 0.26 to 0.43 with some exceptions. In agreement with the work of Koningsveld, Staverman, Flory, and Tatara, it is shown that the first and second partial derivatives of the extended Flory-Huggins equation for soluble polymers may be used to calculate conditions at phase separations, which should be closer to experimental fact than those calculated from the original relation. Derivatives were obtained for cross-linked polymers but are not presented.

Stress‐strain behavior of polychloroprene vulcanizates containing polymer‐gel particles

AbstractThe equations of stress‐strain of gel‐filled polymer under large deformation were derived by using a simple model i.e. a sphere in a cubic matrix. The author finds for no adhesion between the phases: equation image In case of perfect adhesion between the phases: equation image where σ(α) is the stress of a blend at an elongation ratio of α, σR(α) the stress of a rubber matrix at α, σG(αG) the stress of a gel component at αG, σR (αR) the stress of a rubber matrix at αR, ϕ the volume fraction of gel. The validity of Eq 1 was shown for the polychloroprene vulcanizates containing polystyrene‐gel which exhibits no adhesion with the polychloroprene matrix. This result shows the value of the model proposed here. The tensile strength of polychloroprene vulcanizates filled with polychloroprene‐gel at break is discussed by the use of Eqs 2–4.