Aspect Ratio Of Nanoplatelets Research Articles

Self-growing nano-liquid-crystal film from dynamic swollen hydrogel substrates.

A hydrogel which spontaneously swells in an aqueous polymer solution was observed to produce a new hydrogel film coated on its swollen surface. Here, inspired by this phenomenon, we theoretically formulate the dynamics of isotropic-to-nematic (I-N) phase transition caused by swelling a hydrogel substrate (HS) in a dilute nanoplatelet suspension, and quantitatively characterize a self-growing nano-liquid-crystal (NLC) film coated on the swollen HS surface. We show that as the HS gets softer, the resulting NLC film can form earlier and achieve greater thickness (up to hundreds of micrometers). Our results and the existing experiments confirm that the growth dynamics of the NLC film or hydrogel film is exclusively regulated by the swelling behaviors of the HS instead of suspension configurations, e.g., I-N phase transition or sol-gel transition, suggesting a universal signature for the solutes ranging from molecules to colloids. However, both the maximum thickness of the NLC film and the corresponding characteristic time rely highly on the inherent elasticity of the HS and nanoplatelet aspect ratio. We demonstrate that the swelling quasiequilibrium state rather than the equilibrium state of the HS is more qualified to formulate a condition which is practically significant in preestimating the moment when the maximum thickness of the NLC film appears. Our theoretical framework serves as a robust paradigm to extensively rationalize (bio)film coatings which self-integrate with diverse nanostructural configurations via swelling-induced phase transition.

Growth dynamics of nanoplatelet liquid crystals by directionally drying colloidal suspensions in a confined channel

Unidirectional solvent evaporation has been increasingly concerned as a versatile microfluidic agent in manipulating the self-assembly dynamics of shape anisotropic colloids by precisely governing a confined nanofluid flow in a microcell. Here we develop a theoretical framework upon unidirectional drying-induced growth of nematic liquid crystals (LC) in nanoplatelet suspension confined to a Hele–Shaw (H–S) channel. The nematic order-dependent permeability assembled in modified Darcy's law and the interactions between nanoplatelets for nematic LC are both explicitly incorporated in a confined nanofluid flow. The growth dynamics of nematic LC that is highly correlated with drying rate (drying Peclet number), nanoplatelet aspect ratio, and geometric confinement have been rationalized by our numerical measurements. Unlike the spherical colloids, the nematic LC grows nonlinearly over time indicating a time-dependent instantaneous growth velocity. The final length of LC, when subjected to an enhanced drying rate, is seen to be compressed toward the drying end, but its time-averaged growth velocity increases significantly. Besides, the LC formed by the thicker nanoplatelets gets the shorter final length, while whether its average growth velocity is affected by nanoplatelet types depends on the drying rate. Importantly, we confirm a noticeable promotion in the growth of LC as the enhanced geometric confinement is imposed. A state diagram we produce suggests a universal signature of enhancement in solvent drying flux with enhanced confinement. However, our results highlight the favorable water retention in nanoplatelet nematic LC with compacted layered architecture prevailing over the spherical colloids deposits with the porous percolation architecture.

Preparation and Barrier Properties of Chitosan‐Layered Silicate Nanocomposite Films

AbstractSummary: In this study, chitosan nanocomposite films were prepared using a solvent‐casting method by incorporation of an organically modified montmorillonite (Cloisite 10A). The effect of filler concentration on the water vapor permeability, oxygen permeability, mechanical and thermal properties of the composite films was evaluated. The structure of nanocomposites and the state of intercalation of the clay were characterized by XRD. The water vapor permeability of pure chitosan films was measured as a function of relative humidity (RH). It was found that the permeability value increased with an increase in RH. The water vapor and gas permeability values of the composite films decreased significantly with increasing filler concentration. Permeation data was fitted to various phenomenological models predicting the permeability of polymer systems filled with nanoclays as a function of clay concentration and aspect ratio of nanoplatelets. According to the XRD results, an increase in basal spacing was obtained with respect to pure clay for chitosan/clay nanocomposites. This demonstrated the formation of intercalated structure of clay in the polymer matrix. Tensile strength and elongation at break of the composites increased significantly with the addition of clay, however the thermal and color properties of the films were not much affected by the intercalation of clay into polymer matrix.

Barrier properties of model epoxy nanocomposites

The barrier properties of two sets of model epoxy nanocomposites with variations in nanoplatelet exfoliation level and aspect ratio have been investigated. The results show that both the exfoliation level and aspect ratio of nanoplatelets have a significant effect on the nanocomposite barrier properties. The results have also been correlated with a number of semi-empirical and physical models. It is found that both Gusev–Lusti's 3D model and Nielsen's 2D model give good correlation with experimental findings. Implication of the present study for barrier properties improvement of polymer nanocomposites is discussed.

Effect of nanoplatelet aspect ratio on mechanical properties of epoxy nanocomposites

To study the effect of the aspect ratio of nanoplatelets on the mechanical properties of polymer nanocomposites, epoxy/α-zirconium phosphate nanocomposites with two distinctive aspect ratios at ca. 100 and 1000 have been prepared and characterized. Scanning electron microscopy and transmission electron microscopy were utilized to confirm the two different sizes and aspect ratios of nanoplatelets in epoxy. As expected, it is found that mechanical properties of the nanocomposite are affected by the aspect ratio of nanoplatelets in epoxy. That is, a higher aspect ratio renders a better improvement in modulus. It is also found that the interfacial characteristics between the nanoplatelets and polymer matrix are most critical in affecting the strength and ductility of the polymer. The operative fracture mechanisms depend strongly on the aspect ratio of the nanoplatelets incorporated. The crack deflection mechanism, which leads to a tortuous path crack growth, is only observed for the high aspect ratio system. The implication of the present findings for structural applications of polymer nanocomposites is discussed.