Thermoresponsive
microgels with a hollow capsule architecture have
been widely used in drug delivery and molecular encapsulation, and
their efficacy is contingent on the internal structure in the deswelling
dynamics process. Despite a large number of experimental studies on
microgels,
proper theoretical methods based on an individual microgel capsule
are still a few because of the complexity of the microgels. Herein,
we first propose
a novel methodology to investigate the structural properties and deswelling
dynamics of microgel capsules by integrating a temperature-dependent
Morse potential with Langevin dynamics simulation. Different properties,
including volume phase transition temperature, temperature-dependent
diameter, and structural morphologies of individual microgels, are
assessed to rationalize our simulation method, and a good agreement
between simulation predictions and experimental observations has been
obtained. Depending on the system temperature, the morphological transition
of three regimes in the shell structure is identified: scattered nanogels,
progressively porous sponge gels, and dense ribbonlike gels. The temperature-switchable
sensors composed of microgel capsules on the substrates are devised,
which exhibit tunable reflectivity or thickness by simply varying
the system temperature. Our mesoscale results provide helpful insights
into the transient structure within the networked microgels and the
design of smart polymeric nanomaterials, such as biosensors, drug
delivery systems, and actuators.
Control of the microstructure
of microgels adsorbed on solid surfaces plays an essential role in
various fields, including lithography, optical sensing, and biocatalysis.
Here, we adopt an experimentally validated molecular dynamics simulation
approach to investigate the structural properties and deswelling dynamics
of thermoresponsive microgel capsules on solid substrates. Specifically,
by examining the interfacial elastocapillarity of the adsorbed microgel
capsules, we find that the poorly cross-linked microgel capsules (i.e.,
cross-link density ψ ≤ 0.0217) display a crossover adsorption
regime between polymeric wetting and colloidal adhesion, whereas the
highly cross-linked microgel capsules present only colloidal adhesion
adsorption. As the system temperature increases, the microgel capsules
progressively transform from the fully swollen state to the fully
collapsed state on the solid substrates, whereas the capsule architecture
remains. The adsorption regime of the microgel capsule is mutually
determined by the elastic deformation and surface attraction strength.
In addition, the elastic deformation is attributed to the internal
structure of the microgel capsule, which varies with the system temperature
and cross-link density. Aiming to identify the adsorption regime over
wider ranges of the control variables, a machine learning study on
an artificial neural network is further carried out and a three-dimensional
phase diagram of the adsorption regime and multiple control variables
is constructed, unraveling the comprehensive relationship among the
adsorption regime and the operational parameters.
Although ion dehydration in confined water is ubiquitous in many important processes concerning ion adsorption, transport and separation, and so forth, few theoretical models have been developed to unravel the mechanism of dehydration in confined space. Herein, a molecular model is proposed by weighing the molecular ori-
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