Unusual temperature-induced swelling of ionizable poly(N-isopropylacrylamide)-based microgels: experimental and theoretical insights into its molecular origin

Giussi, Juan M.; Velasco, Manuel I.; Longo, Gabriel S.; Acosta, Rodolfo H.; Azzaroni, Omar

doi:10.1039/c5sm01853f

Cited by 29 publications

(23 citation statements)

References 63 publications

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“…Soft materials exhibit a subtle competition between physical interactions, chemical equilibria and entropic forces that enables their self-assembly into organized structures. [1][2][3][4] Block-copolymers, [5][6][7] amphiphilic molecules 3,8 and colloids 9,10 are typical examples of soft materials that exhibit rich selfassembly behaviours. Due to the complexity of their freeenergy landscapes, self-assembled soft materials are, in many cases, in metastable states (i.e.…”

Section: Introductionmentioning

confidence: 99%

Minimum free-energy paths for the self-organization of polymer brushes

2017

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A methodology to calculate minimum free-energy paths based on the combination of a molecular theory and the improved string method is introduced and applied to study the self-organization of polymer brushes under poor solvent conditions. Polymer brushes in a poor solvent cannot undergo macroscopic phase separation due to the physical constraint imposed by the grafting points; therefore, they microphase separate forming aggregates. Under some conditions, the theory predicts that the homogeneous brush and the aggregates can exist as two different minima of the free energy. The theoretical methodology introduced in this work allows us to predict the minimum free-energy path connecting these two minima as well as the morphology of the system along the path. It is shown that the transition between the homogeneous brush and the aggregates may involve a free-energy barrier or be barrierless depending on the relative stability of the two morphologies and the chain length and grafting density of the polymer. In the case where a free-energy barrier exists, one of the morphologies is a metastable structure and, therefore, the properties of the brush as the quality of the solvent is cycled are expected to display hysteresis. The theory is also applied to study the adhesion/deadhesion transition between two opposing surfaces modified by identical polymer brushes and it is shown that this process may also require surpassing a free-energy barrier.

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Section: Introductionmentioning

confidence: 99%

Minimum free-energy paths for the self-organization of polymer brushes

2017

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“…3b). We have previously shown that changes in the matrix structure of the gel leads to variations in the T 2 values35. In this way, the decrease of the relaxation rates can be interpreted as a restriction in the mobility of the water molecules of the different populations due to an increase in the silicate matrix crosslinking.…”

Section: Resultsmentioning

confidence: 96%

“…This behavior is usually related to the existence of distinct phases with independent T 2 values; where the shortest relaxation times (in the order of a few milliseconds) is associated to water molecules in tight contact with the solid polymeric backbone, while bulk water renders longer relaxation times (in the order of seconds)323334. Additionally, it is expected that in gels a pool of water molecules exhibit an intermediate relaxation behavior (in the order of tens or hundreds of miliseconds), that is, water molecules that are trapped within the gel network or pores, with an intermediate mobility35. In the present work T 2 values were determined for protons in the silicate gels employing CPMG pulse sequence36 and subsequently analyzed with an inverse Laplace transformation.…”

Section: Resultsmentioning

confidence: 99%

Environmental Topology and Water Availability Modulates the Catalytic Activity of β-Galactosidase Entrapped in a Nanosporous Silicate Matrix

Burgos

Velasco

Acosta

et al. 2016

Sci Rep

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In the present work we studied the catalytic activity of E. coli β-Gal confined in a nanoporous silicate matrix (Eβ-Gal) at different times after the beginning of the sol-gel polymerization process. Enzyme kinetic experiments with two substrates (ONPG and PNPG) that differed in the rate-limiting steps of the reaction mechanism for their β-Gal-catalyzed hydrolysis, measurements of transverse relaxation times (T2) of water protons through 1H-NMR, and scanning electron microscopy analysis of the gel nanostructure, were performed. In conjunction, results provided evidence that water availability is crucial for the modulation observed in the catalytic activity of β-Gal as long as water participate in the rate limiting step of the reaction (only with ONPG). In this case, a biphasic rate vs. substrate concentration was obtained exhibiting one phase with catalytic rate constant (kcA), similar to that observed in solution, and another phase with a higher and aging-dependent catalytic rate constant (kcB). More structured water populations (lower T2) correlates with higher catalytic rate constants (kcB). The T2-kcB negative correlation observed along the aging of gels within the 15-days period assayed reinforces the coupling between water structure and the hydrolysis catalysis inside gels.

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“…Microgel and ZIF-8@microgel synthesis and characterization By means of free-radical precipitation copolymerization, thermoresponsive poly(N-isopropyl-acrylamide-co-methacrylic acid) or poly(NIPAm-co-MAA) microgels with 81% NIPAm-19% MAA composition were obtained (see ESI † for further details about synthesis procedures and NIPAm : MAA ratio calculation from NMR). 19 Taking advantage of the affinity between carboxylate moieties and Zn 2+ ions, microgels were used as so preconcentration platforms, which then allowed for conned ZIF-8 growth (hereaer referred as ZIF-8@microgel). 47 Reaction time needed for composite synthesis was determined by mixing methanolic solutions of ZIF-8 precursors at 25 C while continuously monitoring hydrodynamic diameter (D h ) via DLS.…”

Section: Resultsmentioning

confidence: 99%