Influence of comb-like copolymer dispersants with different molecular structures on the performance of CaCO3 suspension in organic system

A series of comb-like copolymer poly(styrene-co-maleic anhydride)-graft-poly(ε-caprolactone) (SMA-g-PCL, SP) with variation in PCL side chain length and side chain density were synthesized and employed as an efficient dispersant for CaCO₃ suspension in organic solvent. The effects of molecular structures of comb-like copolymer on adsorption, rheological behavior, and suspension stability were investigated systemically to elucidate the governing dispersing mechanism. The molecular structures of comb-like copolymer not only significantly influenced the adsorption behavior but also the rheological behavior and suspension stability. Calculations based on the scaling law and Flory theory made a profound understanding of the impact of the molecular structure of comb-like copolymer on dispersion property. The results revealed that the steric repulsive force was enhanced by increasing of side chain length or density. However, the surface area for one molecule on CaCO₃ surface was also increased for its larger radius of the hemispheres of comb-like copolymer. This led to the worse activity of adsorption. The dispersion of CaCO₃ was due to the synergistic effects of adsorption and steric hindrance effect, which resulted that the comb-like copolymer with moderate length and density of side chain presented the best dispersability.     

Synthesis of a novel comb-like copolymer used as dispersant in organic solvent and influence of free comb-like copolymer on CaCO3 suspension

A novel comb-like copolymer poly (1e)-graft-poly (ε-caprolactone) (SMA-g-PCL, SP), which can be used as an effective CaCO₃ dispersant in organic solvent, was prepared via the esterification reaction between SMA and PCL. The structures and compositions of the graft copolymer were determined by Fourier transform infrared spectrometry (FTIR), H-nuclear magnetic resonance (¹H NMR), and gel permeation chromatography (GPC), respectively. The influences of free comb-like copolymer on CaCO₃ suspension viscosity and rheological behavior were investigated. It was found that the particle-binding bridge generated among CaCO₃ particles through hydrogen bonding and/or electrostatic interactions increased the suspension viscosity as well as the depletion flocculation. On the other hand, it was noteworthy that the free comb-like copolymer could make the CaCO₃ suspension evolve from shear-thinning fluid or nearly Newtonian fluid into shear-thickening fluid. It was attributed to the formation of a transient network through intermolecular associations between the adsorbed SP and the free polymer chains under the action of shear. Finally, the fitting parameters from the Herschel–Bulkley model were in good agreement with the evolution of the rheological behavior of CaCO₃ suspension.     

Adsorption properties of comb-like polymer on nanotube surface

The adsorption and wrapping process of a single flexible comb-like polymer to a single wall nanotube was studied by Molecular Dynamics simulation of a coarse-grained model. We varied the grafting density and length of the side chains, the radius of the nanotube and strength of interaction between the monomers of nanotube and side chains of polymer brush. We investigated the structural and dynamical characters of interactions of the nanotube-polymer composite, such as the effect of Lennard-Jones energy parameter ɛ_LJ and the nanotube radius on the adsorption behavior and how the wrapping conformation is affected by the structure of the polymer brush. The simulation results indicate that single comb-like polymer with flexible backbone tends to adsorb and wrap around the nanotube, when the interaction energy exceeds a critical value. The monomer adsorption ratio, interaction energy profiles and moment of inertia are obtained. The helical wrapping only occurs when the interaction energy is large enough. Also, the influence of the polymer structure on the conformational behavior is analyzed. This work underscores design elements important for engineering well-defined nanotube-polymer nanocomposite.     

Elastic behavior of comb-like polymer chains

<正>Three-dimensional Monte Carlo simulations of comb-like polymer chains with various backbone lengths N_b,arm lengths N_a and arm densities m are carried out to study the elastic behavior of comb-like polymer chains.The radius of gyration,the shape factors and bond length in different cases during elastic process are calculated,and it is found that the comb-like polymer molecules with longer backbone or shorter arm are more close to linear chains.But the arm density m affects the chain conformation non-monotonously.Some thermodynamic properties are also studied.Average Helmholtz free energy and elastic force f all increase with elongation ratioλfor all chains.     

Influence of dispersion conditions and nature of the emulsifier on the dispersity and stability of artificial polymer suspensions based on polyetherimide

New methods for producing artificial polyetherimide suspensions in the presence of domestic cationic surfactants, their mixtures, and mixtures of cationic and organosilicon surfactants were proposed. The effect of the polymer concentration in the initial solution and conditions of emulsion dispersion on the stability and particle size of the final polymer suspensions is shown. The colloidal chemical properties of the obtained polymer suspensions are considered. Conclusions about the influence of the nature and concentration of surfactants on the stability of the obtained suspensions are drawn. When using a mixture of cationic and organosilicon surfactants, polymer suspensions stable during production and storage are formed, which is explained by the formation of structural mechanical and electrostatic stability barriers in the surface layers of the particles.

     

Impact of in situ polymer coating on particle dispersion into solid laser-generated nanocomposites

The crucial step in the production of solid nanocomposites is the uniform embedding of nanoparticles into the polymer matrix, since the colloidal properties or specific physical properties are very sensitive to particle dispersion within the nanocomposite. Therefore, we studied a laser-based generation method of a nanocomposite which enables us to control the agglomeration of nanoparticles and to increase the single particle dispersion within polyurethane. For this purpose, we ablated targets of silver and copper inside a polymer-doped solution of tetrahydrofuran by a picosecond laser (using a pulse energy of 125 μJ at 33.3 kHz repetition rate) and hardened the resulting colloids into solid polymers. Electron microscopy of these nanocomposites revealed that primary particle size, agglomerate size and particle dispersion strongly depend on concentration of the polyurethane added before laser ablation. 0.3 wt% polyurethane is the optimal polymer concentration to produce nanocomposites with improved particle dispersion and adequate productivity. Lower polyurethane concentration results in agglomeration whereas higher concentration reduces the production rate significantly. The following evaporation step did not change the distribution of the nanocomposite inside the polyurethane matrix. Hence, the in situ coating of nanoparticles with polyurethane during laser ablation enables simple integration into the structural analogue polymer matrix without additives. Furthermore, it was possible to injection mold these in situ-stabilized nanocomposites without affecting particle dispersion. This clarifies that sufficient in situ stabilization during laser ablation in polymer solution is able to prevent agglomeration even in a hot polymer melt.     

Impact of solvent quality on nanoparticle dispersion in semidilute and concentrated polymer solutions

We investigated how solvent quality affects the stability of polymer-grafted nanoparticles in semidilute and concentrated polymer solutions, which extends our previous studies on these types of dispersions in good solvents [Langmuir 2008, 24, 5260-5269]. As discussed in the current article, dynamic light scattering (DLS) was used to quantify the diffusion of polydimethylsiloxane-grafted silica nanoparticles, or PDMS-g-silica, in bromocyclohexane as well as in PDMS/bromocyclohexane solutions. We established that bromocyclohexane is a theta solvent for PDMS by varying the temperature of the solutions with PDMS-g-silica nanoparticles and detecting their aggregation at a theta temperature of T(Θ) = 19.6 °C. Using this temperature as a benchmark for the transition between good and bad solvent conditions, further stability tests were carried out in semidilute and concentrated polymer solutions of PDMS in bromocyclohexane at T = 10-60 °C. Irrespective of temperature, i.e., solvent quality, we found that the nanoparticles dispersed uniformly when molecular weight of the graft polymer was greater than that of the free polymer. However, when the free polymer molecular weight was greater than that of the graft polymer, the nanoparticles aggregated. Visual studies were also used to confirm the correspondence between nanoparticle stability and graft and free polymer molecular weights in a wide range of marginally poor solvents with PDMS. Further, the correspondence between nanoparticle stability and instability with graft and free polymer molecular weight and solvent quality was also supported with self-consistent mean-field calculations. Thus, by relating experiment and theory, our results indicate that nanoparticle stability in semidilute and concentrated polymer solutions is governed by interactions between the graft and free polymers under conditions of variable solvency.     

Influence of the molecular architecture on the adsorption onto solid surfaces: comb-like polymers

The processes of adsorption of grafted copolymers onto negatively charged surfaces were studied using a dissipative quartz crystal microbalance (D-QCM) and ellipsometry. The control parameters in the study of the adsorption are the existence or absence on the molecular architecture of grafted polyethyleneglycol (PEG) chains with different lengths and the chemical nature of the main chain, poly(allylamine) (PAH) or poly(L-lysine) (PLL). It was found out that the adsorption kinetics of the polymers showed a complex behavior. The total adsorbed amount depends on the architecture of the polymer chains (length of the PEG chains), on the polymer concentration and on the chemical nature of the main chain. The comparison of the thicknesses of the adsorbed layers obtained from D-QCM and from ellipsometry allowed calculation of the water content of the layers that is intimately related to the grafting length. The analysis of D-QCM results also provides information about the shear modulus of the layers, whose values have been found to be typical of a rubber-like polymer system. It is shown that the adsorption of polymers with a charged backbone is not driven exclusively by the electrostatic interactions, but the entropic contributions as a result of the trapping of water in the layer structure are of fundamental importance.     

Influence of molecular weight on selective oligomer-assisted dispersion of single-walled carbon nanotubes and subsequent polymer exchange

A series of oligofluorenes was synthesized and used as a SWNT selecting template to study the chain length effect on SWNTs dispersions in toluene. The octamer exhibits the same selectivity as the corresponding polymer. Nevertheless, SWNT/oligomer complexes are unstable, which allows fast exchange of the oligomer with a coating polymer.     

Nanoparticle dispersion and aggregation in polymer nanocomposites: insights from molecular dynamics simulation

It is a great challenge to fully understand the microscopic dispersion and aggregation of nanoparticles (NPs) in polymer nanocomposites (PNCs) through experimental techniques. Here, coarse-grained molecular dynamics is adopted to study the dispersion and aggregation mechanisms of spherical NPs in polymer melts. By tuning the polymer-filler interaction in a wide range at both low and high filler loadings, we qualitatively sketch the phase behavior of the PNCs and structural spatial organization of the fillers mediated by the polymers, which emphasize that a homogeneous filler dispersion exists just at the intermediate interfacial interaction, in contrast with traditional viewpoints. The conclusion is in good agreement with the theoretically predicted results from Schweizer et al. Besides, to mimick the experimental coarsening process of NPs in polymer matrixes (ACS Nano 2008, 2, 1305), by grafting polymer chains on the filler surface, we obtain a good filler dispersion with a large interparticle distance. Considering the PNC system without the presence of chemical bonding between the NPs and the grafted polymer chains, the resulting good dispersion state is further used to investigate the effects of the temperature, polymer-filler interaction, and filler size on the filler aggregation process. It is found that the coarsening or aggregation process of the NPs is sensitive to the temperature, and the aggregation extent reaches the minimum in the case of moderate polymer-filler interaction, because in this case a good dispersion is obtained. That is to say, once the filler achieves a good dispersion in a polymer matrix, the properties of the PNCs will be improved significantly, because the coarsening process of the NPs will be delayed and the aging of the PNCs will be slowed.     

The effect of gamma irradiation and particle size of CaCO3 on the properties of HDPE/EPDM blends

Mechanical blends formed of 50 wt% of high-density polyethylene (HDPE) and 50 wt% of ethylene–propylene–diene-monomer (EPDM) elastomer have been loaded with 50 wt% of three different particle size of CaCO₃, namely CaCO₃ 300, CaCO₃ 700, and CaCO₃ 2000 whereby the latter has the smallest particle size of ～311, 82 μm. Mechanical, physico-chemical and thermal properties were followed up as a function of irradiation dose for loaded and unloaded blends. The results obtained indicated that the values of tensile strength, tensile modulus at 50% elongation, gel fraction and decomposition temperature increase with increasing irradiation dose. On the other hand elongation at break, permanent set and swelling number were found to decrease with increasing irradiation dose. Moreover, the effect of particle size of CaCO₃ was observed in a limited but apparent upgrading of mechanical, physico-chemical, and thermal properties. The order of semi-reinforcing capacity of three different types of CaCO₃ is as follow: CaCO₃ 2000 > CaCO₃ 700 > CaCO₃ 300 > unloaded blend. Whereby CaCO₃ 2000 has the smallest particle size.     

Revisiting the dispersion mechanism of grafted nanoparticles in polymer matrix: a detailed molecular dynamics simulation

By focusing on the grafted nanoparticles (NPs) embedded in polymer melts, a detailed coarse-grained molecular dynamics simulation is adopted to investigate the effects of the grafting density, the length of the matrix and grafted chains on the dispersion of the NPs. We have employed visualization snapshots, radial distribution functions (RDFs), the interaction energy between NPs, the number of neighbor NPs, and the conformation of the brush chains to clearly analyze the dispersion state of the grafted NPs. Our simulated results generally indicate that the dispersion of the NPs is controlled by both the excluded volume of the grafted NPs and the interface between the brushes and the matrix. It is found that increasing grafting density or grafted chain length leads to better dispersion, owing to larger excluded volume; however, increasing the length of the matrix chains leads to aggregation of NPs, attributed to both a progressive loss of the interface between the brushes and the matrix and the overlap between brushes of different NPs, intrinsically driven by entropy. Meanwhile, it is found that there exists an optimum grafting density (σ(c)) for the dispersion of the NPs, which roughly obeys the following mathematical relation: σ(c) is proportional to N(m)(K)/N(g)(L), where K, L > 0 and N(m) and N(g) represent the length of the matrix and grafted chain length, respectively. Considering the practical situation that the grafted brushes and the matrix polymer are mostly not chemically identical, we also studied the effect of the compatibility between the brushes and the matrix polymer by taking into account the attraction between the grafted chains and the matrix chains. In general, our comprehensive simulation results are believed to guide the design and preparation of high-performance polymer nanocomposites with good or even tailored dispersion of NPs.     

Synthesis and characterization of PEGylated comb-like cationic polymer by polycondensation and ATRP

PEGylated poly(2-(dimethylamino)ethyl methacrylate) with comb-like architecture was synthesized by two-step polymerization. First,poly(oligo(ethylene glycol) malicate)(POEGMA) bearing pendant hydroxyl groups was prepared by direct polycondensation of oligo(ethylene glycol) and malic acid in the presence of scandium triflate as chemoselective catalyst.Then the poly(2- (dimethylamino)ethyl methacrylate) side chains were grafted from the POEGMA backbone by atom transfer radical polymerization (ATRP) after the hydroxyl groups were modified into bromo-ester form,resulting in a PEGylated cationic copolymer with branched architecture.     

An investigation on the high-frequency dielectric dispersion of concentrated ion-exchange resin beads suspensions

In this paper, dielectric measurements were carried out on concentrated suspensions of D₃₅₄ ion-exchange resin (IER) beads dispersed in electrolyte solutions. The distinct high-frequency dielectric behavior occurring in the megahertz frequency range was interpreted based on the understanding of the interparticle interaction and the properties of the constitute phases. The results indicated that the dominant parameter of continuous phase influencing HFDD is the solution concentration after full Donnan equilibrium, while the dominant parameter of dispersed phase influencing HFDD is the fixed charge density. In addition, properties of the dispersed IER beads including electric conductivity and permittivity were obtained in terms of the Hanai’s method.     

Effect of polymer molecular weight on the polymer/surfactant interaction

A thermodynamic analysis of the interaction between fourteen different molar mass poly(ethylene oxide)s (PEO) and sodium dodecyl sulfate (SDS) based on the measured surfactant-binding isotherms is given. The surfactant-binding isotherms were determined by the potentiometric method in the presence of 0.1 M inert electrolyte (NaBr). It was found that there is no PEO/SDS complex formation if M(PEO) < 1000. In the molecular weight range 1000 < M(PEO) < 8000, the critical aggregation concentration (cac) and the surfactant aggregation number are decreasing as the polymer molecular weight increases. The saturated bound surfactant amount is proportional to the number concentration of the polymer in this molecular weight range. If M(PEO) exceeds approximately 8000, the cac does not depend on the polymer molar mass, and the saturated bound amount of the surfactant becomes proportional to the mass concentration of the polymer. It was also observed that independently of the polymer molecular weight the surfactant aggregation number increases as the equilibrium surfactant monomer concentration increases from the cac to the critical micellar concentration (cmc). Finally, it was demonstrated that only one polymer molecule is involved in the complex formation independently of the polymer molecular weight.     

Impact of ambient and vacuum pressure on the physico mechanical properties of flexible polyurethane foam reinforced with CaCO3

This study investigates the effects of variable pressure conditions (550 and 1013 mbar) on the physico-mechanical and structural properties of flexible polyurethane foam, incorporating different compositions of calcium carbonate (CaCO₃) filler. The objective is to achieve sustained mechanical and structural properties of flexible polyurethane foam while reducing costs through variable pressure foaming technology. With CaCO₃ filler concentrations ranging from 20 to 100 parts per hundred (pphp) of polyol, it was found that foam produced at low pressure (550 mbar) demonstrated improved resilience and durability, particularly with CaCO₃ compositions up to 100 pphp. Conversely, foam produced at standard atmospheric pressure (1013 mbar) using compositions up to 100 pphp did not exhibit significant enhancements in physico-mechanical properties. The study employs various characterization techniques, including mechanical testing, scanning electron microscopy, differential scanning calorimetry, thermal gravimetric analysis, and Fourier transform infrared spectroscopic analysis, to assess the flexible polyurethane foam. It provides a detailed examination of the effects of variable pressure on cellular structure, cell size, filler distributions, mechanical properties, and thermal stability of flexible polyurethane foam using CaCO₃ filler.     

Bioinspired crystallization of CaCO3 coatings on electrospun cellulose acetate fiber scaffolds and corresponding CaCO3 microtube networks

This article describes the mineralization behavior of CaCO(3) crystals on electrospun cellulose acetate (CA) fibers by using poly(acrylic acid) (PAA) as a crystal growth modifier and further templating synthesis of CaCO(3) microtubes. Calcite film coatings composed of nanoneedles can form on the surfaces of CA fibers while maintaining the fibrous and macroporous structures if the concentration of PAA is in a suitable range. In the presence of a suitable concentration of PAA, the acidic PAA molecules will first adsorb onto the surface of CA fibers by the interaction between the OH moieties of CA and the carboxylic groups of PAA, and then the redundant carboxylic groups of PAA can ionically bind Ca(2+) ions on the surfaces of CA fibers, resulting in the local supersaturation of Ca(2+) ions on and near the fiber surface, which can induce the nucleation of CaCO(3) on the CA fibers instead of in bulk solution. Calcite microtube networks on the macroscale can be prepared by the removal of CA fibers after the CA@CaCO(3) composite is treated with acetone. When the CA fiber scaffold is immersed in CaCl(2) solution with an extended incubation time, the first deposited calcite coatings can act as secondary substrate, leading to the formation of smaller calcite mesocrystal fibers. The present work proves that inorganic crystal growth can occur even at an organic interface without the need for commensurability between the lattices of the organic and inorganic counterparts.     

Theory of broadband dispersion of permittivity of biological cell suspensions

The classical Pauly-Schwan electrical model of the biological cell is generalized by considering the diffusion processes that occur due to the selective (with respect to ions of different signes of charges) conductivity of surface cell structures (cytoplasmic membrane and electrical double layer). The analytical theory of the dispersion of the permittivity of biological cell suspensions that cover a broad frequency band that includes three typical (for these systems) dispersion regions α, β, and γ is constructed using the generalized model, whereas the classical model describes only β and γ regions. Very large values of permittivity and their complete stipulation by the ionic selectivity of surface structures, which are characteristic for the region of α dispersion, predetermine the unique sensitivity of low-frequency dielectric spectrum to the effective conductivity of the membrane of a living cell, which can find important applications in biology and medicine.