Rheological Behavior of Concentrated Hyperbranched Polymer/Silica Nanocomposite Suspensions

Are all poorly soluble drugs dissolved in deep eutectic solvents true solutions?

HYPOTHESIS

The ability of deep eutectic solvents (DES) to enhance solubility of poorly soluble drugs has attracted increasing attention. Researchers have shown that drugs could be dissolved well in DES. In this study, we propose a new existence state of drugs in DES: a quasi-two-phase colloidal system.

EXPERIMENTS

Six poorly soluble drugs were used as the models. The formation of colloidal systems was observed visually by the Tyndall effect and DLS. TEM and SAXS were performed to obtain their structure information. The intermolecular interactions between components were probed via DSC and ¹H¹H-ROESY. In addition, the properties of colloidal systems were further studied.

FINDINGS

Our key finding is that several drugs like lurasidone hydrochloride (LH) could form stable colloids in [Th (thymol)] - [Da (decanoic acid)] DES, resulting from weak interactions between drugs and DES, which is different from the true solution of drugs like ibuprofen where strong interactions were formed. In this LH-DES colloidal system, DES solvation layer was directly observed on the surface of drug particles. In addition, the colloidal system with polydispersity shows superior physical and chemical stability. Different to the prevailing view that substances are fully dissolved in DES, this study discovers another existence state as stable colloidal particles in DES.

Numerical Simulation of the Rheological Behavior of Nanoparticulate Suspensions

Nanoparticles significantly alter the rheological properties of a polymer or monomeric resin with major effect on the further processing of the materials. In this matter, especially the influence of particle material and disperse properties on the viscosity is not yet understood fully, but can only be modelled to some extent empirically after extensive experimental effort. In this paper, a numerical study on an uncured monomeric epoxy resin, which is filled with boehmite nanoparticles, is presented to elucidate the working principles, which govern the rheological behavior of nanoparticulate suspensions and to simulate the suspension viscosity based on assessable material and system properties. To account for the effect of particle surface forces and hydrodynamic interactions on the rheological behavior, a resolved CFD is coupled with DEM. It can be shown that the particle interactions caused by surface forces induce velocity differences between the particles and their surrounding fluid, which result in increased drag forces and cause the additional energy dissipation during shearing. The paper points out the limits of the used simulation method and presents a correction technique with respect to the Péclet number, which broadens the range of applicability. Valuable information is gained for a future mechanistic modelling of nanoparticulate suspension viscosity by elucidating the interdependency between surface forces, shear rate and resulting drag forces on the particles.

A review of polymer nanohybrids for oil recovery

As oil fields go into their final stage of production, new technologies are necessary to sustain production and increase the recovery of the hydrocarbon. Chemical injection is an enhanced recovery technique, which focuses on increasing the effectiveness of waterfloods. However, the use of chemical flooding has been hampered by its relatively high cost and the adsorption of the injected chemicals onto the reservoir rocks. In recent years, nanofluids have been launched as an overall less expensive and more efficient alternative to other chemical agents. Nanoparticle inclusion is also proposed to mitigate polymer flooding performance limitations under harsh reservoir conditions. This review presents a comprehensive discussion of the most recent developments of polymer nanohybrids for oil recovery. First, the preparation methods of polymer nanohybrids are summarized and explained. Then, an explanation of the different mechanisms leading to improved oil recovery are highlighted. Finally, the current challenges and opportunities for future development and application of polymer nanohybrids for chemical flooding are identified.

Natural rubber-SiO2 nanohybrids: interface structures and dynamics

Homogeneous dispersion of silica nanoparticles (SiO₂ NPs) in natural rubber (NR) is a key challenge for engineering high-performance nanocomposites and elucidation of their structure on a molecular basis. Towards this, the present work devised a novel route for obtaining 3D self-assembled SiO₂ NP-NR nanocomposites under aqueous conditions and in the presence of Mg²⁺, by establishing a molecular bridge that clamped the negatively charged NR and SiO₂ colloidal particles with a favoured NR-SiO₂ NP hetero-aggregation. The characteristic NR-SiO₂ NP hetero-aggregates displayed a decreased heat capacity with increase in the SiO₂ mass-fraction, implying a restricted NR chain mobility. Such changes in the interfacial layers were tapped by ²⁹Si NMR, DFT calculations and molecular dynamics simulations towards a mechanistic understanding of the structure and dynamics of the NR/SiO₂ NP hybrid. Simple models were used to illustrate basic ideas; specific electrostatic interactions such as ion-dipole and H-bonding interactions proved to be the driving forces for the organized assembly leading to the NR-SiO₂ hetero-aggregate over the NR-NR or SiO₂ NP-SiO₂ NP homo-aggregate. Molecular dynamics simulation of the aqueous canonical ensemble of the hybrid showed the stable molecular conformation to reveal a SiO₂ NP spherical core encapsulated by a hydrophobically interconnected NR polymer layer as the outer shell, as a unique structural model. Specifically, the lipid end of the NR was involved electrostatically while the lysine end (the protein part of NR) H-bonded to the core silica cluster thereby restricting random aggregation. The calculated negative free energy changes for the hetero-aggregate composites via their vibrational and rotational spectra proved the spontaneity of composite formation.

Influence of molecular weight on molecular dynamics and dynamic rheology of polypropylene glycol filled with silica

Molecular weight strongly influences the molecular dynamics and rheological responses of nanocomposites, which is far from being well understood. Herein molecular dynamics and rheological behaviors of hydrophilic fumed silica filled unentangled polypropylene glycol (PPG) were investigated as a function of weight averaged molecular weight (M w) of PPG and volume fraction (∅) of silica. It is shown that M w does not affect the glassy layers surrounding the nanoparticles and the segmental dynamics of the mobile PPG phase. On the other hand, the mobile PPG phase in the highly filled nanocomposites exhibits an abnormal "more fragile" to "stronger" transition with increasing M w. The reinforcement and thinning behaviors are stronger in lower-M w nanocomposites with the "more fragile" mobile PPG phase. The results suggest that reinforcement of nanocomposites affects the dynamic fragility of the mobile phase of the matrix.

Injectable tissue adhesive composite hydrogel with fibroblasts for treating skin defects

In this work, an injectable composite hydrogel was synthesized via a unique way of crosslinking glycol chitosan (GC) with silica nano-particles (SiNP) through non-chemical interactions, and was then applied as a kind of wound dressing. Gelation was achieved through the incorporation of SiNPs with the GC segments in aqueous solution, therefore strictly confining the movement of the solubilized polymer chains. Rheology tests showed that the sol-gel transition and the moduli of the hydrogel were influenced by the composition of the two components, the size of the nano-particles and the conformation of the polymers. Using such a strategy, tissue adhesion properties of GC were well-preserved in the GC/SiNP hydrogel and therefore it gains gluey properties toward biological tissues as demonstrated through the adhesion of two pieces of mouse skin, obtaining a lap-shear stretching force of ca. 90 kPa. This characteristic, together with the injectability, allowed the hydrogel to be administrated directly on the wound site and to fill the wound area. Meanwhile, the hydrogel also works as a carrier of protein and cells. The in situ encapsulation of fibroblasts enabled the promising properties of the GC/SiNP hydrogel to be used for treating full-thickness skin defects in a mouse model, resulting in the favorable growth of hair follicles and microvessels, hence reducing the risk of scar formation.

A Facile in Situ and UV Printing Process for Bioinspired Self-Cleaning Surfaces

A facile in situ and UV printing process was demonstrated to create self-cleaning synthetic replica of natural petals and leaves. The process relied on the spontaneous migration of a fluorinated acrylate surfactant (PFUA) within a low-shrinkage acrylated hyperbranched polymer (HBP) and its chemical immobilization at the polymer-air interface. Dilute concentrations of 1 wt. % PFUA saturated the polymer-air interface within 30 min, leading to a ten-fold increase of fluorine concentration at the surface compared with the initial bulk concentration and a water contact angle (WCA) of 108°. A 200 ms flash of UV light was used to chemically crosslink the PFUA at the HBP surface prior to UV printing with a polydimethylsiloxane (PDMS) negative template of red and yellow rose petals and lotus leaves. This flash immobilization hindered the reverse migration of PFUA within the bulk HBP upon contacting the PDMS template, and enabled to produce texturized surfaces with WCA well above 108°. The synthetic red rose petal was hydrophobic (WCA of 125°) and exhibited the adhesive petal effect. It was not superhydrophobic due to insufficient concentration of fluorine at its surface, a result of the very large increase of the surface of the printed texture. The synthetic yellow rose petal was quasi-superhydrophobic (WCA of 143°, roll-off angle of 10°) and its self-cleaning ability was not good also due to lack of fluorine. The synthetic lotus leaf did not accurately replicate the intricate nanotubular crystal structures of the plant. In spite of this, the fluorine concentration at the surface was high enough and the leaf was superhydrophobic (WCA of 151°, roll-off angle below 5°) and also featured self-cleaning properties.

Effect of functionalized graphene oxide with hyperbranched POSS polymer on mechanical and dielectric properties of cyanate ester composites

Functionalized graphene oxide with a hyperbranched POSS polymer was designed and synthesized and then compounded with dicyclopentadiene bisphenol dicyanate ester to prepare nanocomposites.

Direct Evidence for Percolation of Immobilized Polymer Layer around Nanoparticles Accounting for Sol-Gel Transition in Fumed Silica Dispersions

Immobilized polymer fractions have been claimed to be of vital importance for sol-gel transitions generally observed in nanoparticle dispersions but remain a matter of debate regarding mechanism and difficulty for prediction. Here we investigate the immobilized layer structures of trifunctionality polyether polyol (PPG) near the surfaces of hydrophilic and hydrophobic fumed silica (FS) nanoparticles to reveal the role of surface chemistry on the molecular dynamics and sol-gel transitions of the dispersions. Using modulated differential scanning calorimetry, we measure the specific heat capacity during glass transition and the enthalpy during cold-crystallization. Comparing with hydrophobic FS that forms a fully immobilized (glassy) layer, we find that hydrophilic FS immobilizes more PPG, forming a partially immobilized outer layer being unable to crystallize next to the inner glassy layer. By correlating the thickness of the glassy layer with half of the minimum spacing between nanoparticles, we directly evidence the percolation of this layer along the nearest neighbor nanoparticles responsible for the sol-gel transition. Using effective volume fraction including the glassy layer, we successfully construct master curves of relative viscosity of both hydrophilic and hydrophobic FS dispersions, pointing to a common sol-gel transition mechanism mediated by the surface chemistry.

Hyperbranched polymers: advances from synthesis to applications

This review summarizes the advances in hyperbranched polymers from the viewpoint of structure, click synthesis and functionalization towards their applications in the last decade.

Suppression of phase coarsening in immiscible, co-continuous polymer blends under high temperature quiescent annealing

The properties of polymer blends greatly depend on the morphologies formed during processing, and the thermodynamic non-equilibrium nature of most polymer blends makes it important to maintain the morphology stability to ensure the performance stability of structural materials. Herein, the phase coarsening of co-continuous, immiscible polyamide 6 (PA6)-acrylonitrile-butadiene-styrene (ABS) blends in the melt state was studied and the effect of introduction of nano-silica particles on the stability of the phase morphology was examined. It was found that the PA6-ABS (50/50 w) blend maintained the co-continuous morphology but coarsened severely upon annealing at 230 °C. The coarsening process could be divided into two stages: a fast coarsening process at the initial stage of annealing and a second coarsening process with a relatively slow coarsening rate later. The reduction of the coarsening rate can be explained from the reduction of the global curvature of the interface. With the introduction of nano-silica, the composites also showed two stages of coarsening. However, the coarsening rate was significantly decreased and the phase morphology was stabilized. Rheological measurements indicated that a particle network structure was formed when the concentration of nano-silica particles was beyond 2 wt%. The particle network inhibited the movement of molecular chains and thus suppressed the coarsening process.