Poly(ethylenimine) and its role in gene delivery

1. Introduction to colloid science and rheology 2. Hydrodynamic effects 3. Brownian hard spheres 4. Stable colloidal suspensions 5. Non-spherical particles 6. Weakly flocculated suspensions 7. Thixotropy 8. Shear thickening 9. Rheometry of suspensions 10. Suspensions in viscoelastic media 11. Advanced topics.

Colloidal Suspension Rheology

A recurring challenge in the field of nanocomposites is to control the spatial distribution of nanoparticles (NPs) in a polymer matrix. This issue is of critical importance since it is now well-established that a specific NP dispersion state is necessary to optimize a desired property of polymer nanocomposites (PNCs). This Perspective focuses on one particular approach to controlling NP spatial dispersion, and hence the properties of polymer-based nanocomposites: the use of polymer-grafted NPs. Novel developments over the past decade in synthesis techniques allow us to controllably functionalize NPs with polymer chains. This has ignited considerable interest in this field, leading to significant advances in creating nanocomposites with tunable physical properties. We begin by briefly outlining the various synthetic strategies for functionalizing NPs and then discuss various methods for controllably dispersing them in a polymer matrix. The consequences of having states with controlled NP dispersion on nano...

https://www.benicewiczgroup.com/UserFiles/benigroup/Documents/BB91.pdf

Nanocomposites with Polymer Grafted Nanoparticles

The viscoelastic properties of high molecular weight polymeric liquids are dominated by topological constraints on a molecular scale. In a manner similar to that of entangled ropes, polymer chains can slide past but not through each other. Tube models of polymer dynamics and rheology are based on the idea that entanglements confine a chain to small fluctuations around a primitive path that follows the coarse-grained chain contour. Here we provide a microscopic foundation for these highly successful phenomenological models. We analyze the topological state of polymeric liquids in terms of primitive paths and obtain parameter-free, quantitative predictions for the plateau modulus, which agree with experiment for all major classes of synthetic polymers.

https://science.sciencemag.org/content/sci/303/5659/823.full.pdf

Rheology and microscopic topology of entangled polymeric liquids.

In this era of portability and rapid technological advances, polymers are more than ever under pressure to be cheap and offer tailored property profiles. Often, the key lies in designing blends and alloys carefully structured at the appropriate scale (preferably less than a micrometre) from existing polymers. Block copolymers - two or more different polymer chains linked together - have long been thought to offer the solution. Local segregation of the different polymer blocks yields molecular-scale aggregates of nanometre size. Recent progress in synthetic chemistry has unveiled unprecedented opportunities to prepare tailored block copolymers at reasonable cost. Over twenty years of intense academic research and the advent of powerful statistical theories and computational methods should help predict the equilibrium and even non-equilibrium behaviour of copolymers and their blends with other polymers. The gap between block copolymer self-assembly and affordable nanostructured plastics endowed with still-unexplored combinations of properties is getting narrower.

Block copolymers in tomorrow's plastics

We investigate the dispersion of polymer-grafted particles suspended in a polymer matrix by viscoelastic measurements and electron microscopy. We find that, when the graft density is low, the particle dispersion improves with an increase of the graft density, while the particle dispersion becomes worse when the graft density is too high; i.e., there is an optimum graft density for dispersing the particles. We explain the phenomena by showing that the grafted polymers cause attraction for high graft density.

Optimum Graft Density for Dispersing Particles in Polymer Melts

The modelling of molecular entanglement in polymeric materials is an old problem, and has evolved gradually over the last 60 years, with two key approaches: the network model of Green & Tobolsky, and the tube model of Edwards and de Gennes. We will show that these models can be merged together in a straightforward manner. The resulting model, called the dual slip-link model, can be handled by computer simulation, and it can predict the linear and nonlinear rheological behaviours of linear and star polymers with arbitrary molecular weight distribution.

Molecular modelling of entanglement.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/bip.360340410

Direct observation of the coil‐globule transition in dna molecules

To examine the scaling relation proposed for textured materials, viscoelastic properties of binary mixtures of immiscible Newtonian fluids were measured in steady shear flows and in the transient states after step changes of the shear rate. The sample was a mixture of silicone oil and resin oil, which have almost equal density and viscosity. It was observed that (i) the shear stress and the first normal stress difference, under the steady shear flows, are almost proportional to the shear rate, and that (ii) the plots of the scaled transient stresses after a step change of shear rate, against the scaled strain, compose a single curve. These results can be well explained by the scaling relation. However, the shape of the transient stress curves after step changes of shear rate do not agree with that predicted by the constitutive equation proposed by Doi and Ohta.

Masao Doi

Papers

Optimum Graft Density for Dispersing Particles in Polymer Melts

Molecular modelling of entanglement.

Direct observation of the coil‐globule transition in dna molecules

Experimental tests of the scaling relation for textured materials in mixtures of two immiscible fluids

Direct observation of the biphasic conformational change of DNA induced by cationic polymers