Transient formation of bcc crystals in suspensions of poly(<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>N</mml:mi></mml:math>-isopropylacrylamide)-based microgels

Gasser, Urs; Lietor‐Santos, Juan Jose; Scotti, Andrea; Bunk, Oliver; Menzel, Andreas; Fernández‐Nieves, Alberto

doi:10.1103/physreve.88.052308

Cited by 30 publications

(31 citation statements)

References 39 publications

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“…In this case, we use the position of the first peak in SðqÞ to obtain the nearest neighbor distance, d nn ; we do the same for all liquid and glassy samples. However, for crystalline samples, we find that SðqÞ is consistent with a random hexagonal close packed structure for both monodisperse and bidisperse samples; this structure is consistent with what has been reported before for similar and other microgel suspensions and is also realized by hard and charged spheres (14)(15)(16)(17)(18). In this case, we obtain the lattice constant and hence d nn from the position of the second ring of Bragg peaks, which can be clearly seen in the detector image, as shown in Fig.…”

Section: Significancesupporting

confidence: 91%

The role of ions in the self-healing behavior of soft particle suspensions

Scotti

Gasser

Herman

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

185

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Impurities in crystals generally cause point defects and can even suppress crystallization. This general rule, however, does not apply to colloidal crystals formed by soft microgel particles [Iyer ASJ, Lyon LA (2009) Angew Chem Int Ed 48:4562-4566], as, in this case, the larger particles are able to shrink and join the crystal formed by a majority of smaller particles. Using small-angle X-ray scattering, we find the limit in large-particle concentration for this spontaneous deswelling to persist. We rationalize our data in the context of those counterions that are bound to the microgel particles as a result of the electrostatic attraction exerted by the fixed charges residing on the particle periphery. These bound counterions do not contribute to the suspension osmotic pressure in dilute conditions, as they can be seen as internal degrees of freedom associated with each microgel particle. In contrast, at sufficiently high particle concentrations, the counterion cloud of each particle overlaps with that of its neighbors, allowing these ions to freely explore the space outside the particles. We confirm this scenario by directly measuring the osmotic pressure of the suspension. Because these counterions are then no longer bound, they create an osmotic pressure difference between the inside and outside of the microgels, which, if larger than the microgel bulk modulus, can cause deswelling, explaining why large, soft microgel particles feel the squeeze when suspended with a majority of smaller particles. We perform small-angle neutron scattering measurements to further confirm this remarkable behavior.oint defects in crystalline materials disrupt the crystal structure and often prevent crystallization. This is the case, for instance, when large particles are introduced in a crystal of smaller particles. Bragg illustrated the consequences of this disruption using soap bubbles (1). In metal melts, a size mismatch of 15% between the atoms suppresses crystallization (2), and, in hard spheres, which constitute an important model system for condensed matter, a polydispersity above 12% also prevents crystallization (3). Furthermore, the polydispersity in hard sphere crystals does not exceed 5.7%, due to local segregation of dissimilar particles during crystallization (4, 5).Remarkably, these restrictions do not necessarily apply to suspensions of soft microgels, which are cross-linked polymer particles immersed in a solvent that can exist in either swollen or deswollen states, depending on external conditions like temperature (6) and pH (7). Indeed, microgel suspensions containing a small fraction of larger particles can crystallize without defects by shrinking the larger particles to a size that is identical to that of the smaller and more abundant microgel particles (8). This deswelling was hypothesized to result either from the direct interaction between large and small particles or from the osmotic pressure exerted by the small microgels on the larger ones (2). Here, we show that none of these effects drive this proces...

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Section: Significancesupporting

confidence: 91%

The role of ions in the self-healing behavior of soft particle suspensions

Scotti

Gasser

Herman

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

185

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“…50 Moreover, diverse methodologies have been used for characterization of the thermoresponsive polymeric NPs such as cryogenic transmission electron microscopy (cryo-TEM), 51 atomic force microscopy (AFM), 52 nuclear magnetic resonance (NMR) spectroscopy, 53,54 small-angle X-ray scattering (SAXS), 51,55,56 Fourier-transform infrared spectroscopy (FT-IR), 10 UV–vis, 46 and static and/or dynamic light scattering (SLS/DLS). 46,57 …”

Section: Introductionmentioning

confidence: 99%

Temperature-Responsive Smart Nanocarriers for Delivery Of Therapeutic Agents: Applications and Recent Advances

Karimi

Zangabad

Ghasemi

et al. 2016

ACS Appl. Mater. Interfaces

359

212

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Smart drug delivery systems (DDSs) have attracted the attention of many scientists, as carriers that can be stimulated by changes in environmental parameters such as temperature, pH, light, electromagnetic fields, mechanical forces, etc. These smart nanocarriers can release their cargo on demand when their target is reached and the stimulus is applied. Using the techniques of nanotechnology, these nanocarriers can be tailored to be target-specific, and exhibit delayed or controlled release of drugs. Temperature-responsive nanocarriers are one of most important groups of smart nanoparticles (NPs) that have been investigated during the past decades. Temperature can either act as an external stimulus when heat is applied from the outside, or can be internal when pathological lesions have a naturally elevated termperature. A low critical solution temperature (LCST) is a special feature of some polymeric materials, and most of the temperature-responsive nanocarriers have been designed based on this feature. In this review, we attempt to summarize recent efforts to prepare innovative temperature-responsive nanocarriers and discuss their novel applications.

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“…The observed structure factor is best described with that of a face-centered cubic (fcc) phase, which is common for colloidal crystals. 2,4,34 Here, the first peak and the shoulder arise from the (1,1,1) and (2,0,0) reflections, respectively, the second from the (2,2,0) reflection, and the third one and the corresponding shoulder from the (1,3,1) and (2,2,2) reflections, respectively. Similar reflections are present for sample B.…”

Section: Resultsmentioning

confidence: 98%

“…Their structural properties are frequently studied by scattering techniques. [1][2][3][4][5] In particular, large efforts have been undertaken to investigate in detail the effect of external perturbations such as temperature, 4 electrolyte concentration, 3,6 shear, 7,8 electric, 9,10 and magnetic fields 11,12 on the phase diagram and phase transitions of concentrated colloidal suspensions. The influence of high hydrostatic pressure on these systems is, however, largely unexplored, mainly due to the involved experimental requirements needed for high pressure studies.…”

Section: Introductionmentioning

confidence: 99%

Colloidal crystallite suspensions studied by high pressure small angle x-ray scattering

Schroer

Westermeier

Lehmkühler

et al. 2016

The Journal of Chemical Physics

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We report on high pressure small angle x-ray scattering on suspensions of colloidal crystallites in water. The crystallites made out of charge-stabilized poly-acrylate particles exhibit a complex pressure dependence which is based on the specific pressure properties of the suspending medium water. The dominant effect is a compression of the crystallites caused by the compression of the water. In addition, we find indications that also the electrostatic properties of the system, i.e. the particle charge and the dissociation of ions, might play a role for the pressure dependence of the samples. The data further suggest that crystallites in a metastable state induced by shear-induced melting can relax to a similar structural state upon the application of pressure and dilution with water. X-ray cross correlation analysis of the two-dimensional scattering patterns indicates a pressure-dependent increase of the orientational order of the crystallites correlated with growth of these in the suspension. This study underlines the potential of pressure as a very relevant parameter to understand colloidal crystallite systems in aqueous suspension.

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Transient formation of bcc crystals in suspensions of poly(N-isopropylacrylamide)-based microgels

Cited by 30 publications

References 39 publications

The role of ions in the self-healing behavior of soft particle suspensions

The role of ions in the self-healing behavior of soft particle suspensions

Temperature-Responsive Smart Nanocarriers for Delivery Of Therapeutic Agents: Applications and Recent Advances

Colloidal crystallite suspensions studied by high pressure small angle x-ray scattering

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