Search

Solid polymer electrolytes (SPEs) have the potential to enhance the safety and energy density of lithium batteries. However, poor interfacial contact between the lithium metal anode and SPE leads to high interfacial resistance and low specific capacity of the battery. In this work, we present a novel strategy to improve this solid-solid interface problem and maintain good interfacial contact during battery cycling by introducing an adaptive buffer layer (ABL) between the Li metal anode and SPE. The ABL consists of low molecular-weight polypropylene carbonate , poly(ethylene oxide) (PEO), and lithium salt. Rheological experiments indicate that ABL is viscoelastic and that it flows with a higher viscosity compared to PEO-only SPE. ABL also has higher ionic conductivity than PEO-only SPE. In the presence of ABL, the interface resistance of the Li/ABL/SPE/LiFePO4 battery only increased 20% after 150 cycles, whereas that of the battery without ABL increased by 117%. In addition, because ABL makes a good solid-solid interface contact between the Li metal anode and SPE, the battery with ABL delivered an initial discharge specific capacity of >110 mA·h/g, which is nearly twice that of the battery without ABL, which is 60 mA·h/g. Moreover, ABL is able to maintain electrode-electrolyte interfacial contact during battery cycling, which stabilizes the battery Coulombic efficiency.

As an effective platform to exploit triplet-triplet-annihilation-based photon upconversion (TTA-UC), microcapsules composed of a fluidic UC core and photonic shell are microfluidically prepared using a triple emulsion as the template. The photonic shell consists of cholesteric liquid crystals (CLCs) with a periodic helical structure, exhibiting a photonic band gap. Combined with planar anchoring at the boundaries, the shell serves as a resonance cavity for TTA-UC emission and enables spectral tuning of the UC under low-power-density excitation. The CLC shell can be stabilized by introducing a polymerizable mesogen in the LC host. Because of the microcapsule spherical symmetry, spontaneous emission of the delayed fluorescence is omnidirectionally amplified at the edge of the stop band. These results demonstrate the range of opportunities provided by TTA-UC systems for the future design of low-threshold photonic devices.

Soluble oligonucleotides are typically introduced to bulk solution to promote hybridization activity on DNA-functionalized surfaces. Here, an alternative approach is explored by encapsulating secondary target strands inside semipermeable colloidal satellite assemblies, then triggering their release at 37 °C for subsequent surface hybridization activity. To prepare DNA-loaded satellite assemblies, uniform gelatin microspheres are fabricated using microfluidics, loaded with 15 base-long secondary DNA targets, capped with a polyelectrolyte bilayer, and finally coated with a monolayer of polystyrene microspheres functionalized with duplexes comprised of immobilized probes and soluble, 13 base-long hybridization partner strands. Once warmed to 37 °C, secondary DNA targets are released from the gelatin template and then competitively displace the shorter, original hybridization partners on the polystyrene microspheres.

Tanaka’s approach to swelling kinetics of a solid gel sphere is extended to a spherical microgel shell. The boundary condition at the inner surface is obtained from the minimization of shear elastic energy. Temporal evolution of a shell is represented in a form of expansion over eigenfunctions of the corresponding diffusion equation. The swelling of Tanaka’s solid spherical gel is recovered as a special case of our general solution if the inner radius approaches zero. In another limiting case of a thin (balloon-like) shell, the set of eigenfunctions is reduced to a single exponential term. In the general case, a solid sphere swells slightly faster than the same sphere with an internal cavity. To test our theoretical model, we prepared monodisperse poly-N-isopropylacrylamide (PNIPAM) hydrogel shells using a microfluidic device. The temporal dependence of the inner and outer radii of the shell were measured, and the data were fitted to our theoretical model. As a result, we obtained the collective diffusion...

Mixtures of nonadsorbing polymer and colloidal particles exhibit a range of different morphologies depending on the particle and polymer concentrations and their relative size ratios. These can be very important for technological applications, where gelation can produce a weak solidlike structure that can help reduce phase separation, extending product shelf life. However, industrial products are typically formulated with polydisperse polymers, and the consequences of this on the phase behavior of the mixture are not known. We investigate the role of polymer polydispersity and show that a small amount of larger polymer in a distribution of nominally much smaller polymer can drastically modify the behavior. It can induce formation of a solidlike gel structure, abetted by the small polymer, but still allow further evolution of the phase separation process, as is seen with a monodisperse distribution of larger polymer. This coarsening ultimately leads to gravitational collapse. We describe the full phase behavior for polydisperse polymer mixtures and account for the origin of the behavior through measurements of the structure and dynamics and by comparing to the behavior with monodisperse polymers.

We report on the use of hydrostatic pressure, P, to deswell thermosensitive poly(N-isopropylacrylamide) (pNIPAM) microgels and show that it can affect the polymer−solvent mixing as much as temperature, which is the traditional variable used to deswell pNIPAM particles. Interestingly, the microgel volume changes more gradually with pressure than it does with temperature. By comparing the pressure and temperature induced deswelling, we obtain the pressure dependence of the Flory solvency parameter, χ; it increases with P, indicating that pressure decreases the polymer−solvent miscibility. We interpret this increase in terms of the entropy change, △S, when a polymer−solvent contact is broken to form a solvent−solvent contact and find that |△S| also increases with P, consistent with previous experimental results with polymers and other gels. Hydrostatic pressure thus changes the entropic contribution of mixing, causing χ to increase and ultimately leading to particle deswelling.

We present a robust and straightforward method for fabricating remarkably responsive hydrogel scaffolds consisting of submicron-sized microgel particles. We demonstrate that the microgel particles assemble either through bridging or depletion interactions to yield a structure that swells or deswells at a macroscopic level in much shorter times as compared to a bulk polymer gel of similar characteristics. This approach offers a new way of fabricating functional hydrogel scaffolds with controllable responsiveness to applied stimuli and excellent loading capability for a wide variety of materials, irrespective of chemistry, size, and shape.

Microgel particles based on poly (N-isopropylacrylamide) have been shown to display an initial swelling behavior, followed by a collapse, with increasing concentration of added poly(ethylene oxide), PEO, chains. This paper considers the thermodynamic reasons for the observed expansion and subsequent shrinkage of the particles. At low concentrations of PEO, the free chains permeate into the microgel particles and cause an increase in osmotic pressure, expanding the particles. At higher concentrations of PEO, the particles are saturated and an increase in osmotic pressure in the external phase causes the particles to collapse again. The calculated magnitude of swelling and the effect of PEO molecular weight are, at least qualitatively, in agreement with the experimental observations reported elsewhere.

In this work, the aggregation of microgel particles has been investigated, paying special attention to the structure of the clusters formed in the process. In particular, the aggregates' fractal dimension was determined by static light scattering. The results indicate that the aggregates are more compact than expected for diffusive aggregation. A reversible aggregation mechanism is proposed on the basis of the competition between osmotic and elastic contributions arising from the soft character of the particles. Aggregation proceeds in an energy minimum of restricted depth, giving rise to the formation of more compact clusters than expected. Finally, the process reversibility is tested, confirming the secondary minimum controlled aggregation.

The objective of this work is to test the very recent Levin's theory for charged colloids (Levin, Y.; Barbosa, M. C.; Tamashiro, M. N. Europhys. Lett. 1998, 41 (2), 123). To accomplish this, the fraction of condensed ions has been experimentally obtained from electrophoretic mobility data and surface charge values. Latexes with different functionalities, surface charges, and sizes were selected in order to support the universality of the ion condensation effect. The good agreement between charge and fraction of condensed ions confirms Levin's theory and makes ion condensation a clear candidate for explaining the observed insensitivity of the electrophoretic mobility to surface charge variations, for sufficiently large charge.

The swelling of cationic microgel particles has been studied experimentally, in the weak screening regime. The solution pH was selected as the external variable triggering the swelling, which was followed by dynamic light scattering. The particle charge was determined by conductometric and potentiometric titrations, leading to a good correlation between the charge of the microgel network and its size. This leads to the conclusion that the swelling is mainly charge controlled. The Flory−Huggins thermodynamic theory for gels, including a term accounting for the counterion distribution within the microgel, has been used to interpret the experimental data. The osmotic term associated with the counterions explains fairly well the observed behavior, and additional contributions due to the internal microgel microscopic structure are not necessary, as Pincus et al. have suggested.