Wever D.A.Z.,Nijenborgh |
Wever D.A.Z.,Dutch Polymer Institute |
Riemsma E.,Nijenborgh |
Picchioni F.,Nijenborgh |
Polymer (United Kingdom) | Year: 2013
A series of comb-like block and random copolymers based on acrylamide (AM) and N-isopropylacrylamide (NIPAM) have been prepared by atom transfer radical polymerization (ATRP). The number of side-arms, the length of the AM and NIPAM blocks as well as the distribution of the two monomers (block or random) were systematically varied. The aqueous solution properties, i.e. the solution viscosity as a function of shear rate and temperature and the critical micelle concentration (CMC) of the different copolymers were evaluated. Particular emphasis is dedicated to the thermo-responsiveness of the aqueous copolymer solutions as measured by the rheological behaviour. The CMC is a function of the molar ratio between the AM and NIPAM, as well as the distribution (block or random). The surface tension of the block copolymers is close to the value for pure poly(NIPAM), while that of the random copolymers is a function of the composition. The block copolymers tend to precipitate from the solution at temperatures above the Lower Critical Solution Temperature (LCST) of poly(NIPAM), indicating the formation of strong aggregates. Random copolymers of AM and NIPAM do not precipitate from the solution (up to 80 C). In addition, depending on the composition, thermothickening behaviour is observed. The thermothickening behaviour is only present at low shear rates (γ ≤ 10 s-1). This, in connection with the ease of the synthesis, makes these copolymers especially interesting for application in Enhanced Oil Recovery (EOR). © 2013 Elsevier Ltd. All rights reserved.
PubMed | Nijenborgh
Type: | Journal: NeuroImage | Year: 2013
In contrast to our increasing knowledge of the role that oscillations in single brain regions play in cognition, very little is known about how coherence between oscillations in distant brain regions is related to information transmission. Here I present a cognitive modeling approach that can address that question. Specifically, I show how a model of the attentional blink implemented in the ACT-R cognitive architecture is related to the amplitude and coherence of EEG oscillations. The dynamics of the models working memory resource is primarily associated with parietal 4-9 Hz theta oscillations, while the dynamics of the models declarative memory, visual perception and procedural resources together are correlated with posterior theta oscillations. I further show that model predictions about inter-module communication during the processes of stimulus identification and target consolidation are associated with selective increases in coherence at the predicted points in time.