Monodisperse Polymer Research Articles

On activated seed swelling technique

AbstractThe activated seed swelling technique is one of the promising methods in synthesis of micron‐sized monodispersed polymer particles. However, there are some parameters (eg the interference of acetone residue on particle swelling) that make this method difficult to carry out and even lead to a broad particle‐size distribution. Here, these parameters are studied and how to control them is discussed. The polydisperse seed swelling appeared at lower concentration of acetone and with incomplete evaporation of acetone from the system. The monodisperse swelling and larger particle sizes were achieved at higher concentration of acetone and longer evaporation time using a vacuum pump. These results suggest that the particle size and particle‐size distribution in the activated seed swelling technique can be controlled by the carrier (acetone) and the hydrophobe concentration in aqueous medium before and after the swelling process. Copyright © 2005 Society of Chemical Industry

Design and Size Control of Uniform Zeolite Nanocrystals Synthesized in Adjustable Confined Voids Formed by Recyclable Monodisperse Polymer Spheres

Design and Size Control of Uniform Zeolite Nanocrystals Synthesized in Adjustable Confined Voids Formed by Recyclable Monodisperse Polymer Spheres

Design and Size Control of Uniform Zeolite Nanocrystals Synthesized in Adjustable Confined Voids Formed by Recyclable Monodisperse Polymer Spheres

Design and Size Control of Uniform Zeolite Nanocrystals Synthesized in Adjustable Confined Voids Formed by Recyclable Monodisperse Polymer Spheres

Lattice Monte Carlo Simulations of Chain Conformations in Polymer Nanocomposites

Lattice Monte Carlo simulations were performed on monodisperse polymer melts, with DP's ranging from 100 to 400, filled with nanoparticles of sizes comparable to the chain Rg. We critically study the role of the mean distance between these nanofillers on the overall conformation of polymer chains and, more importantly, on the statistics of bridges, dangling ends, loops, and trains. We are motivated to study these issues since it has been suggested that the mechanical behavior of nanocomposites result from the formation of a long-lived transient filler network mediated by the chains. Further, the experimentally observed increase in low frequency, low strain amplitude elastic modulus on the addition of filler is attributed to strongly stretched bridge segments. We find that the overall chain statistics remain Gaussian regardless of filler loading (up to 27 vol %). Short bridges, loops, and tails are strongly stretched, but in a manner that is quantitatively equivalent to the statistics of subchains in a mel...

Effects of the Polydispersity on Rheological Properties of Entangled Polystyrene Solutions

Previous studies on extensional properties of entangled solutions have mainly dealt with monodisperse polymers. To investigate the effect of polydispersity on rheological properties of entangled polystyrene solutions, a polydisperse blend with an average molecular weight of 2.65 × 106 was made by mixing 18 components of nearly monodisperse polystyrene. The effect of polydispersity is illustrated by comparing the rheological behavior of this blend with that of a solution of monodisperse polymer with the same average molecular weight and at the same concentration. Shear, small-amplitude sinusoidal flow, step strain in shear, and uniaxial extension are used in this study. The multicomponent system has a much broader relaxation spectrum and a slightly smaller zero-shear-rate viscosity than the solution of monodisperse polymer. The shear thinning behavior of the two solutions are very similar except that the polydisperse system shows an earlier onset of shear thinning. In step strain experiments, the polydispe...

Self-Assembled Colloidal Crystals: Visualizing Atomic Crystal Chemistry Using Microscopic Analogues of Inorganic Solids

Monodisperse spherical colloids spontaneously crystallize into close-packed crystals, in analogy to the simple crystal structures of many of the elements. Since colloids are orders of magnitude larger than atoms, students can directly observe crystal structure and behavior in a microscope using colloidal crystals. This laboratory exercise provides a modular series of materials science experiments appropriate for undergraduate chemistry and engineering majors. The individual modules include aspects of chemical synthesis (monodisperse SiO2 and polymer spheres), self-assembly (colloidal crystallization), and structural characterization through microscopy (optical and scanning electron microscopies) and optical spectroscopy (optical diffraction and UV–visible spectroscopy). Using these experiments, students learn new inorganic and organic synthetic techniques, study crystal behavior (e.g., coordination, defects, close-packing) in model systems, and apply optical characterization techniques to the analysis of their materials. The experiments can easily be tailored to the desired level of complexity and instrumental availability.

Constriction flows of monodisperse linear entangled polymers: Multiscale modeling and flow visualization

We explore both the rheology and complex flow behavior of monodisperse polymer melts. Adequate quantities of monodisperse polymer were synthesized in order that both the materials rheology and microprocessing behavior could be established. In parallel, we employ a molecular theory for the polymer rheology that is suitable for comparison with experimental rheometric data and numerical simulation for microprocessing flows. The model is capable of matching both shearand extensional data with minimal parameter fitting. Experimental data for the processing behavior of monodisperse polymers are presented for the first time as flow birefringence and pressure difference data obtained using a Multipass Rheometer with an 11:1 constriction entry and exit flow. Matching of experimental processing data was obtained using the constitutive equation with the Lagrangian numerical solver, FLOWSOLVE. The results show the direct coupling between molecular constitutive response and macroscopic processing behavior, and differentiate flow effects that arise separately from orientation and stretch.

Effects of colloid polydispersity on the phase behavior of colloid-polymer mixtures

We study theoretically the equilibrium phase behavior of a mixture of polydisperse hard-sphere colloids and monodisperse polymers, modeled using the Asakura-Oosawa model [S. Asakura and F. Oosawa, J. Chem. Phys. 22, 1255 (1954)] within the free volume approximation of H. N. W. Lekkerkerker, W. C. K. Poon, P. N. Pusey, A. Stroobants, and P. B. Warren [Europhys. Lett. 20, 559 (1992)]. We compute full phase diagrams in the plane of colloid and polymer volume fractions, using the moment free energy method. The intricate features of phase separation in pure polydisperse colloids combine with the appearance of polymer-induced gas-liquid coexistence to give a rich variety of phase diagram topologies as the polymer-colloid size ratio xi and the colloid polydispersity delta are varied. Quantitatively, we find that polydispersity disfavors fluid-solid against gas-liquid separation, causing a substantial lowering of the threshold value xi(c) above which stable two-phase gas-liquid coexistence appears. Phase splits involving two or more solids can occur already at low colloid concentration, where they may be kinetically accessible. We also analyze the strength of colloidal size fractionation. When a solid phase separates from a fluid, its polydispersity is reduced most strongly if the phase separation takes place at low colloid concentration and high polymer concentration, in agreement with experimental observations. For fractionation in gas-liquid coexistence we likewise find good agreement with experiment, as well as with perturbative theories for near-monodisperse systems.

Synthesis of micron-sized, monodisperse polymer particles of disc-like and polyhedral shapes by seeded dispersion polymerization

Micron-sized, monodisperse polymer particles having unique “disc-like” and “polyhedral” shapes were produced by seeded dispersion polymerization of various methacrylates with 1.57 μm-sized polystyrene seed particles in the presence of saturated hydrocarbon droplets in methanol/water. Such nonspherical shapes were controllable by the polymerization conditions.

Unnatural Proteins for the Control of Surface Forces

We introduce a new method for the stabilization of colloidal particles via the synthesis and adsorption of unnatural proteins. Biosynthesis of protein-based polymers offers the advantages of preparation of complex sequences through control of the primary sequence, monodisperse polymers, ease of combinatorial search for anchor blocks, environmentally friendly synthesis, use of water as the solvent, and incorporation of a palette of known natural proteins. We have synthesized an unnatural protein with the sequence thioredoxin-Pro(39)Glu(10) for modification of the forces between alumina particles. The polyglutamate sequence, Glu(10), is anionic (pH > 3) and is designed to anchor the protein to positively charged solids, e.g. alumina in water (pH < 9). The polyproline sequence, Pro(39), is neutral. The thioredoxin is a recombinant form of the natural globular protein with a histidine patch (His-patch-thioredoxin) and is zwitterionic. The combined thioredoxin-Pro(39) sequence is hydrophilic with pI approximately 6.3. This block is designed to remain in solution, thereby providing a steric barrier to the approach of two particles in a range of salt and pH conditions. Ellipsometry experiments show that thioredoxin-Pro(39)Glu(10) does adsorb to alumina. Force measurements with the atomic force microscopy (AFM) colloid probe technique show that adsorption of thioredoxin-Pro(39)Glu(10) leads to repulsive forces that decay exponentially with the separation between the surfaces and are independent of salt concentration in the range 0.001-0.1 M KNO(3). This demonstrates that the repulsive forces are not electrostatic. We hypothesize that the repulsion is due to confinement and loss of solvent for the adsorbed polymer; the forces are similar to those expected for a polymer brush. Force measurements between thioredoxin-coated alumina surfaces also show a repulsive force, but the force has a decay length that is consistent with electrostatic double-layer forces: the thioredoxin has not neutralized the surface charge of the underlying alumina. Our results point to interesting future experiments where recombinant DNA technology could be used to synthesize fusion proteins containing useful natural proteins and an anchor. This may allow preparation, via single-step aqueous self-assembly, of anchored proteins that maintain their natural structure. Our technique is not limited to homopolymer blocks; more complex primary sequences can be used.

Viscoelastic Properties of Polymer Melts from Equilibrium Molecular Dynamics Simulations

Viscoelastic Properties of Polymer Melts from Equilibrium Molecular Dynamics Simulations

Self-assembly of monodisperse polymer microspheres from PPQ-b-PEG rod-coil block copolymers in selective solvents

Self-assembly of monodisperse polymer microspheres from PPQ-b-PEG rod-coil block copolymers in selective solvents

Self-assembly of monodisperse polymer microspheres from PPQ-b-PEG rod-coil block copolymers in selective solvents

Poly(phenylquinoline)-block-poly(ethylene glycol)(PPQ-b-PEG) rod-coil block copolymers possess the self-assembly behavior in selective solvents. The copolymers in the mixed solvents ofV(trifluoroacetic acid, TFA):V(dichloromethane, DCM) = 1:1 can self-assemble into polymer hollow microspheres with diameters of a few micrometers. The polymer hollow microspheres are monodisperse, and the diameters of them increase with an increased polymerization degree of the PPQ rigid-rod block. The solution concentration has no effect on the microsphere diameter, but spherical surface shows burrs when the solution concentration is too low. It has been found that the obtained dilute solution has the strongest absorption peak at 376 nm and strongest emission peak at 604 nm by the spectroscopy analysis.

Two‐Dimensional, Open‐Pored, Mesoscopic Titania Layers Using Polymeric Nanoparticle Monolayers as a Template

Open-pored mesoscopic 2D titania layers (see Figure) were fabricated by using a nanoparticle layer as a template. Monodisperse polymer particles approximately 60 nm in diameter were spontaneously formed by dissolving polystyrene-b-poly(N-methyl-2-vinylpyridinium iodide) in toluene. These particles self-assembled at the air–water interface to form well-ordered monolayers, which were then used as templates in a sol–gel reaction to form porous 2D titania layers with a pore size of ∼ 55 nm.

Modeling strain hardening of polydisperse polystyrene melts by molecular stress function theory

The strain hardening of blends of polystyrene (PS) and ultra-high molecular weight polystyrene (UHMW-PS) in elongational flow is modeled by the molecular stress function (MSF) theory. Assuming that the ratios of strain energies stored in polydisperse and monodisperse polymers are identical for linear and nonlinear deformations, the value of the only non-linear parameter of the theory in extensional flows, the maximum molecular stress fmax, can be determined and is shown to be related to steady-state compliance Je0. Using only linear-viscoelastic data, the elongational viscosity of PS/UHMW-PS blends is consistently predicted by the MSF theory.

Impact of decoupling approximation between stretch and orientation in rheometrical and complex flow of entangled linear polymers

We study the rheometrical and complex flow response of the coupled version of the double-convection-reptation model with chain stretch. This model for monodisperse entangled linear polymers has recently been proposed by Marrucci and Ianniruberto [G. Marrucci, G. Ianniruberto, Flow-induced orientation and stretching of entangled polymers, Philos. Trans. R. Soc. A 361 (2003) 677–688] to overcome the anomalous shear thickening that was present in an earlier version of the theory. It avoids the decoupling approximation between orientation and stretch. Except for the shear thickening, both coupled and decoupled models show very similar results that are in qualitative agreement with available rheometrical data for two nearly monodisperse polymer solutions. In contraction/expansion flow simulations, however, higher Weissenberg numbers can be attained with the coupled model. Simulations in the stretch-dominated regime predict a dramatic growth of the upstream vortex activity and an increase of the pressure correction.

An analytic Percus–Yevick approach to the RISM model of monodisperse, homopolymer melts

The reference interaction site model is often used as a nonperturbative description of the equilibrium structure of monodisperse polymer melts on nanoscopical scales. Assuming that the single polymer chains in the melt have ideal (Gaussian) conformations, we derive for the melt a set of generalized Percus–Yevick (PY) equations which can be exactly reduced to a simple algebraic systems of equations. While in the case of the simple atomic sphere systems this involves cubic polynomials, in the analogous hard-sphere polymer system this leads to quintic polynomials. In the limit of infinitely long chains the exact, generalized PY static structure factors, the compressibility and the direct correlation functions are found as functions of the monomer density.

Organic light-emitting materials and devices for optical communication technology

This paper outlines our recent efforts to develop organic infrared (IR) and near-infrared (NIR) light-emitting materials and devices for use in optical communication technology. The IR and NIR light-emitting materials investigated are two organic ionic dyes, (2-[6-(4-dimethylaminophenyl)-2,4-neopentylene-1,3,5-hexatrienyl]-3-methyl-benzothiazonium perchlorate) (LDS821) and [C 41H 33Cl 2N 2] +·BF 4 − (IR1051), and an organic rare-earth complex, erbium (III) tris(8-hydroxyquinoline) (ErQ). These materials exhibit photo- and electro-luminescence in the 0.8-, 1.1- and 1.5-μm wavelength regions, respectively. They were used as optically active species in the following three device forms; vacuum-deposited or doped spin-coated polymer thin-films, doped monodispersed polymer microparticles, and embedded polymeric optical waveguides with a doped core. I propose possible optical communication applications based on their optical properties and luminescent processes.

Universality of linear viscoelasticity of monodisperse linear polymers

AbstractWe suggest a universal plot that superposes linear viscoelastic data of nearly monodisperse polymers on a single curve, regardless of the molecular weight, temperature, and species of polymers. The plotting method is based on the time–temperature superposition and rescaling of viscoelastic functions with terminal behavior. Without any information from molecular theories, the plot supports the fact that the molecular theories of the linear viscoelasticity of monodisperse polymers are independent of the species of polymers. Although an appropriate scaling may show universality by separately extracting the reptational mode and the Rouse mode from the whole set of viscoelastic data, our plotting method shows universality in a unified manner that scales the viscoelastic functions measured over the whole frequency range. We explain the origin of the universality of the plot in terms of molecular theory, the phenomenological spectra of the relaxation time (the BSW and CW spectra), and the principle of time–temperature superposition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2730–2737, 2004

Simple method for determining the critical molecular weight from the loss modulus

AbstractThe normal concept is that the critical molecular weight (MC) is about twice as large as the entanglement molecular weight (Me). However, experimental data have shown considerable deviations from MC ≈ 2Me. Furthermore, a determination of MC requires samples with a wide range of molecular weights, including weights lower than MC and higher than MC. In this article, we suggest a simple method for determining MC from the loss moduli of nearly monodisperse linear polymers with M ≫ MC. We consider two characteristic relaxation times, which correspond to the local maximum and minimum of the loss modulus. MC is determined from the intersection of two phenomenological relaxation times as a function of the molecular weight. The method precisely agrees with MC ≈ 2Me, which is not shown by conventional methods. Moreover, our method provides a determination of relaxation time τe, at which chain segments first feel the constraints imposed by the conceptual tube, without the measurement of the tube diameter and the monomeric friction coefficient, which may be determined by complicated procedures with a lot of data. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2724–2729, 2004