Bulk and shear moduli of compressed microgel suspensions

Lietor‐Santos, Juan Jose; Sierra‐Martin, Benjamin; Fernández‐Nieves, Alberto

doi:10.1103/physreve.84.060402

Cited by 49 publications

(58 citation statements)

References 25 publications

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“…[12][13][14] For disordered suspensions of hard spheres, whose interactions and phase behavior are solely dictated by excluded volume, the elasticity results from changes in the equilibrium configuration of the particles when caged by their neighbors in the glassy phase. 15 Colloidal microgels are different from drops, bubbles, and hard spheres for two main reasons: (i) they are compressible 16,17 and (ii) can potentially interpenetrate to some extent due to the presence of dangling polymer chains at their periphery. 18 They are, however, also potentially able to change shape like drops and bubbles.…”

Section: Introductionmentioning

confidence: 99%

Form factor of pNIPAM microgels in overpacked states

Gasser

Hyatt

Lietor‐Santos

et al. 2014

The Journal of Chemical Physics

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We study the form factor of thermoresponsive microgels based on poly(N-isopropylacrylamide) at high generalized volume fractions, ζ, where the particles must shrink or interpenetrate to fit into the available space. Small-angle neutron scattering with contrast matching techniques is used to determine the particle form factor. We find that the particle size is constant up to a volume fraction roughly between random close packing and space filling. Beyond this point, the particle size decreases with increasing particle concentration; this decrease is found to occur with little interpenetration. Noteworthily, the suspensions remain liquid-like for ζ larger than 1, emphasizing the importance of particle softness in determining suspension behavior.

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Section: Introductionmentioning

confidence: 99%

Form factor of pNIPAM microgels in overpacked states

Gasser

Hyatt

Lietor‐Santos

et al. 2014

The Journal of Chemical Physics

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show abstract

“…2,[16][17][18][19] Microgels are also oen used as additives in personal care products, foods, and in advanced oil recovery, where their tunable material properties are exploited for precisely controlling the macroscopic viscoelastic properties of the material. 5,[20][21][22][23] Despite the widespread use of these materials in these practical applications, as well as in applied and fundamental scientic studies, their macroscopic mechanical properties are still poorly understood. Such understanding must link single particle properties to properties at the macroscopic scale.…”

Section: Introductionmentioning

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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“…However, the measurement of mechanical properties at the microscopic scale is not straightforward [34][35][36] . Atomic Force Microscope (AFM) or Micropipette Aspiration are methods that are often employed for measuring single cell mechanics 37,38 ; they can also be used to characterize the mechanical properties of 55 isotropic soft particles at the microscopic scale [39][40][41]38 .…”

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confidence: 99%

Capillary micromechanics for core–shell particles

et al. 2014

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In this work, we have developed a facile, economical microfluidic approach as well as a simple model 5 description to measure and predict the mechanical properties of composite core-shell microparticles made from materials with dramatically different elastic properties. By forcing the particles through a tapered capillary and analyzing their deformation, the shear and compressive moduli can be measured in one single experiment. We have also formulated theoretical models that accurately capture the moduli of the microparticles in both the elastic and the non-linear deformation regimes. Our results show how the 10 moduli of these core-shell structures depend on the material composition of the core-shell microparticles, as well as on their microstructures. The proposed technique and the understanding enabled by it also provide valuable insights into the mechanical behavior of analogous biomaterials, such as liposomes and cells.

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Bulk and shear moduli of compressed microgel suspensions

Cited by 49 publications

References 25 publications

Form factor of pNIPAM microgels in overpacked states

Form factor of pNIPAM microgels in overpacked states

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

Capillary micromechanics for core–shell particles

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