The Kinetics of Penetration of Grafted Polymers into a Network

Geoghegan, Mark; Clarke, C. J. S.; Boué, François; Menelle, A.; Russ, Thomas; Bucknall, David G.

doi:10.1021/ma982020f

Cited by 37 publications

(54 citation statements)

References 33 publications

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“…As the brush is entangled between fixed cross-links, the only way for the brush and the network to come apart and disentangle is for the brush to diffuse along its own contour. [1][2][3][4] This is prohibited, all the more so given that all of the other grafted polymers would have to perform the same disentanglement at the same time. The only way to remove the adhesion is therefore to break bonds, leaving the system unusable.…”

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Controlling Network–Brush Interactions to Achieve Switchable Adhesion

et al. 2007

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Polyelectrolytes are remarkable molecules because of their smart behavior. By altering the environmental pH value, polyelectrolytes can undergo conformational transitions, which, if controlled, enable a wide range of applications. Herein, we describe experiments whereby a polyacid gel and a polybase grafted to a silicon substrate can be used as a means of demonstrating reversible switching adhesion in aqueous solution. By changing the environmental pH value, we can control in situ whether the gel adheres to the grafted layer or whether it dissociates. Such control over adhesion may have applications in actuators, microfluidics, drug delivery, personal-care products, or even in the understanding of biological materials.If we consider nonpolyelectrolytic polymers, the adhesion between a grafted polymer layer (polymer brush) and a polymer network in the molten state is due to enthalpic interactions that force the brush into the gel as well as the entropy of the brush as it maximizes its conformations by forming a random or self-avoiding walk structure. As the brush is entangled between fixed cross-links, the only way for the brush and the network to come apart and disentangle is for the brush to diffuse along its own contour. [1][2][3][4] This is prohibited, all the more so given that all of the other grafted polymers would have to perform the same disentanglement at the same time. The only way to remove the adhesion is therefore to break bonds, leaving the system unusable.Polyelectrolytes in aqueous solution, however, often undergo a transition from a hydrophobic state, where they can collapse and fall out of solution, to an extended hydrophilic state. This property makes them useful as nanoactuators when they are attached to a surface. [5,6] The properties of hydrogels in good solvent conditions are perhaps even more dramatic, with swellings greater than an order of magnitude than in their dry state routinely observed. [7] We present herein a means of using the responsiveness to the pH value of polyelectrolytes to create reversible adhesion of two surfaces by studying the interaction of a poly[2-(dimethyl amino)ethyl methacrylate] (PDMAEMA, a polybase) brush-modified surface with a poly(methacrylic acid) (PMAA) gel. The brush and gel were equilibrated in water (initially at pH 7), then brought into contact, where it was found that there was good adhesion between the brush and the gel, a result previously obtained for two oppositely charged polyelectrolyte gels.[8] (The gel will not adhere to a silicon substrate without the brush at any pH value.) At equilibrium, the PMAA gel is partially charged and swollen to 112 % of its collapsed mass at pH 2 (approximately 300 % of its dry mass). There is also expected to be some charge on the PDMAEMA [9] brush, the free polymer of which has a pK a value of approximately 7. The two components of the system should be oppositely charged at the pH value at which equilibrium was achieved (pH 5.8). However, even at pH values of between 3 and 7, there is good adhesion between the br...

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Controlling Network–Brush Interactions to Achieve Switchable Adhesion

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“…In many cases, the relaxation is logarithmic. This behavior is paralleled in a broad range of disordered systems: compaction of granular materials [2,3], crumpling of thin sheets [4,5], aging of contact area in dry friction [6], aging of conductivity in electron glasses [7,8] and mechanical relaxation of star polymers in gels [9,10]. This apparently wide-spread behavior might suggest a generic origin of slow glassy relaxations (aging).…”

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Simple nonlinear equation for structural relaxation in glasses

Kolvin

Bouchbinder

2012

Phys. Rev. E

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A wide range of glassy and disordered materials exhibit complex, non-exponential, structural relaxation (aging). We propose a simple nonlinear rate equation δ = a [1−exp (b δ)], where δ is the normalized deviation of a macroscopic variable from its equilibrium value, to describe glassy relaxation. Analysis of extensive experimental data shows that this equation quantitatively captures structural relaxation, where a and b are both temperature-, and more importantly, history-dependent parameters. This analysis explicitly demonstrates that structural relaxation cannot be accurately described by a single non-equilibrium variable. Relaxation rates extracted from the data imply the existence of cooperative rearrangements on a super-molecular scale.

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“…Ici, on considère le suivi en temps de la pénétration des chaînes greffées de polystyrène deutéré dans un réseau de polystyrène [11]. Par rapport à l'interdiffusion entre chaînes libres, deux contraintes stériques sont à considérer.…”

Section: Pénétration Des Chaînes Greffées De Polymères Dans Un Réseauunclassified

Avantages de la réflectométrie des neutrons pour l'étude des polymères en couches minces

Reiter

Geoghegan

2007

Journées de la Neutronique

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Résumé. Nous présentons quelques exemples qui démontrent l'utilité et la puissance de la réflectométrie de neutrons pour l'étude des surfaces et des interfaces de polymères. Ces exemples concernent l'interdiffusion entre deux polymères miscibles, la pénétration d'une chaîne greffée dans un réseau du même polymère, la cinétique de la formation d'une « brosse » de polymère et l'enrichissement d'un polymère à la surface d'un mélange homogène de deux polymères.

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The Kinetics of Penetration of Grafted Polymers into a Network

Cited by 37 publications

References 33 publications

Controlling Network–Brush Interactions to Achieve Switchable Adhesion

Controlling Network–Brush Interactions to Achieve Switchable Adhesion

Simple nonlinear equation for structural relaxation in glasses

Avantages de la réflectométrie des neutrons pour l'étude des polymères en couches minces

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