Determination of the bulk modulus of microgel particles

Sierra‐Martin, Benjamin; Frederick, Justin A.; Laporte, Yesenia; Markou, George; Lietor‐Santos, Juan Jose; Fernández‐Nieves, Alberto

doi:10.1007/s00396-010-2346-z

Cited by 40 publications

(53 citation statements)

References 36 publications

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“…7,9,37 According to Flory-Rehner theory the swelling equilibrium at each temperature corresponds to the conditions where the total osmotic pressure acting on the gel, P total , is zero. In this context, the osmotic pressure arises from two main contributions.…”

Section: Particle Size As a Function Of Temperaturementioning

confidence: 99%

Micromechanics of temperature sensitive microgels: dip in the Poisson ratio near the LCST

et al. 2013

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Microgels of poly-N-isopropylacrylamide (pNIPAM) exhibit a remarkable sensitivity to environmental conditions, most strikingly a pronounced deswelling that occurs close to the lower critical solution temperature (LCST) of the polymer at z32C. This transition has been widely studied and exploited in a range of applications. Along with changes in size, significant changes are also expected for the mechanical response of the particles. However, the full elastic properties of these particles as a function of temperature, T, have not yet been assessed at the single-particle level. Here we present measurements of the elastic properties of pNIPAM particles as a function of both temperature and cross-linking density using capillary micromechanics, a technique based on the pressure-dependent deformation of particles trapped in a tapered glass capillary. The shear elastic modulus G increased monotonously upon increasing temperature. In contrast, but in qualitative agreement with previous experiments on macroscopic pNIPAM hydrogels, we found that the compressive elastic modulus K of our microgels exhibits a dip close to the LCST. Remarkably, this dip is less sharp and deep than that observed in macroscopic hydrogels. The Poisson ratio of the particles also exhibits a pronounced dip close to the LCST, reaching unusually low minimum values of s z 0.15. To rationalize this behavior, we compared our experimental data to Flory-Rehner theory; the theory is able to qualitatively predict the general mechanical behavior observed, thus indicating that the observed dip in the Poisson ratio can be accounted for by simple thermodynamic arguments.

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Section: Particle Size As a Function Of Temperaturementioning

confidence: 99%

Micromechanics of temperature sensitive microgels: dip in the Poisson ratio near the LCST

et al. 2013

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“…To test this hypothesis, we mix a dilute suspension of microgel particles with a dextran solution of known osmotic pressure d and quantify how the microgels deswell with increasing osmotic pressure using dynamic light scattering [18]. This allows the determination of the bulk modulus of individual microgels K p .…”

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confidence: 99%

Bulk and shear moduli of compressed microgel suspensions

2011

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We independently determine the bulk and shear moduli of compressed microgel suspensions and the bulk modulus of individual microgel particles and find that the elastic behavior of the suspension reflects the degree of compression of the particles. This feature, which is distinct from other soft materials such as emulsions or foams, can give rise to an unusually large difference between the bulk and shear moduli of the suspension. Our results extend our understanding of soft materials to systems based on compressible objects, opening up possibilities for engineering materials with drastically different responses to shear and compression.

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“…To evaluate the critical osmotic pressure, the extrapolation to higher dextran concentrations was conducted based on the deformation data (Figure f). According to the dextran concentration obtained at the transition point from the deformation‐concentration curve, corresponding osmotic pressure can be calculated by using a polynomial expression suggested from analysis of experimental results:

P = 286 c + 87 c^{2} + 5 c^{3}

where c is dextran concentration in weight percentage. The transition point for reinforced (SF‐PL/GO) 4.5 microcapsules was estimated from this analysis to be 33%, which is several‐folds higher than the value of pure silk ionomers based microcapsules.…”

Section: Resultsmentioning

confidence: 99%

“…To evaluate the critical osmotic pressure, the extrapolation to higher dextran concentrations was conducted based on the deformation data (Figure 8 f). According to the dextran concentration obtained at the transition point from the deformation-concentration curve, corresponding osmotic pressure can be calculated by using a polynomial expression suggested from analysis of experimental results: [ 68,72,73 ] P c c c = + + 286 87 5 2 3 (1)…”

Section: Mechanical Stability Of the Hollow Microcapsulesmentioning

confidence: 99%

Robust Microcapsules with Controlled Permeability from Silk Fibroin Reinforced with Graphene Oxide

Combs

Calabrese

et al. 2014

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Robust and stable microcapsules are assembled from poly-amino acid-modified silk fibroin reinforced with graphene oxide flakes using layer-by-layer (LbL) assembly, based on biocompatible natural protein and carbon nanosheets. The composite microcapsules are extremely stable in acidic (pH 2.0) and basic (pH 11.5) conditions, accompanied with pH-triggered permeability, which facilitates the controllable encapsulation and release of macromolecules. Furthermore, the graphene oxide incorporated into ultrathin LbL shells induces greatly reinforced mechanical properties, with an elastic modulus which is two orders of magnitude higher than the typical values of original silk LbL shells and shows a significant, three-fold reduction in pore size. Such strong nanocomposite microcapsules can provide solid protection of encapsulated cargo under harsh conditions, indicating a promising candidate with controllable loading/unloading for drug delivery, reinforcement, and bioengineering applications.

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Determination of the bulk modulus of microgel particles

Cited by 40 publications

References 36 publications

Micromechanics of temperature sensitive microgels: dip in the Poisson ratio near the LCST

Micromechanics of temperature sensitive microgels: dip in the Poisson ratio near the LCST

Bulk and shear moduli of compressed microgel suspensions

Robust Microcapsules with Controlled Permeability from Silk Fibroin Reinforced with Graphene Oxide

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