When Colloidal Particles Become Polymer Coils

Abstract

This work concerns interfacial adsorption and attachment of swollen microgel with low- to medium-level cross-linking density. Compared to colloids that form a second, dispersed phase, the suspended swollen microgel particles are ultrahigh molecular weight molecules, which are dissolved like a linear polymer, so that solvent and solute constitute only one phase. In contrast to recent literature in which microgels are treated as particles with a distinct surface, we consider solvent-solute interaction as well as interfacial adsorption based on the chain segments that can form trains of adsorbed segments and loops protruding from the surface into the solvent. We point out experimental results that support this discrimination between particles and microgels. The time needed for swollen microgels to adsorb at the air/water interface can be 3 orders of magnitude shorter than that for dispersed particles and decreases with decreasing cross-linking density. Detailed analysis of the microgels deformation, in the dry state, at a solid surface enabled discrimination particle like microgel in which case spreading was controlled predominantly by the elasticity and molecule like adsorption characterized by a significant overstreching, ultimately leading to chain scission of microgel strands. Dissipative particle dynamics simulations confirms the experimental findings on the interfacial activity and spreading of microgel at liquid/air interface.

A comparison of the network structure and inner dynamics of homogeneously and heterogeneously crosslinked PNIPAM microgels with high crosslinker content

“…Due to the high crosslinker content the typical fried egg type structure is not as visible. 63 The lateral dimensions of the microgels in Fig. 6 are similar.…”

Optical Waveguide‐Enhanced Diffraction for Observation of Responsive Hydrogel Nanostructures

“…Interestingly, when the surface was swollen again in water at T = 22 °C and dried at a higher temperature of T = 38 °C after the temperature‐induced volume collapse, the array topography of the nanopillars partially recovered on the surface, see Figure c. Apparently the topographic erasure of the array features upon drying at low temperature is induced by the strong surface tension of the air–water interface as it passes over the surface structure during water evaporation . This process leads to the rearrangement of the swollen polymer chains as the surface tension strongly competes (and apparently exceeds) the elastic restoring force of the swollen polymer network.…”

“…Apparently the topographic erasure of the (5 of 10) 1600400 array features upon drying at low temperature is induced by the strong surface tension of the air-water interface as it passes over the surface structure during water evaporation. [34] This process leads to the rearrangement of the swollen polymer chains as the surface tension strongly competes (and apparently exceeds) the elastic restoring force of the swollen polymer network. This hypothesis is corroborated by the observation of structure recovery when drying is performed at elevated temperatures above the LCST of 32 °C for the used NIPAAm copoly mer.…”

Microgels at fluid-fluid interfaces for food and drinks

“…Increased distortion from spherical increases the interfacial area occupied by the microgel and thus might be expected to increase the desorption energy, by analogy with classic Pickering particles. Thus, more deformable particles might be expected to adsorb more easily and be better stabilizers and this seems to be supported by several experimental Ngai, 2018b, Kwok andNgai, 2018a); (Destribats et al, 2011), (Matsui et al, 2017), (Schmitt and Ravaine, 2013) and modelling studies (Mourran et al, 2016), (Style et al, 2015), (Vilgis and Stapper, 1998). On the other hand, this seems to be contradicted by other findings, i.e., more deformable particles adsorbed less efficiently and are worse stabilizers (Destribats et al, 2014a), (Keal et al, 2017), (Koh and Saunders, 2005).…”

“…There is ample experimental evidence (Geisel et al, 2015), (Minato et al, 2018, Zielinska et al, 2017, Zielinska et al, 2016) that microgels change their shape on adsorption, as well as simulations and theoretical models that describe this (Matsui et al, 2017), (Mourran et al, 2016), (Rumyantsev et al, 2016). Gelissen et al (Gelissen et al, 2016) have recently used in situ electron and super-resolved fluorescence microscopy techniques to visualize microgel internal structure during swelling and shrinkage.…”