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Zeolites are strongly hydrophilic materials that are widely used as water adsorbents. They are also promising candidates for antifogging coatings; however, researchers have yet to devise a suitable method for coating glass substrates with zeolite-based films. Here, we report on a direct wet deposition technique that is capable of casting zeolite films on glass substrates without exposing the glass to highly basic solutions or the vapors used in zeolite synthesis. We began by preparing cast solutions of pure silica zeolite MFI synthesized in hydrothermal reactions of various durations. The solutions were then applied to glass substrates via spin-on deposition to form zeolite films. The resulting zeolite MFI thin films were characterized in terms of transmittance to visible light, surface topography, thin film morphology, and crystallinity. Wetting and antifogging properties were also probed. We found that hydrophilicity and antifogging capability increased with the degree of thin film crystallinity. We also determined that the presence of the amorphous silica in the thin films is critical to transparency. Fabricating high-performance zeolite-based antifogging coatings requires an appropriate composition of zeolite crystals and amorphous silica.

Seeded growth is the most popular approach to the preparation of zeolite thin films and membranes. Herein, we report a simplified method of fabricating zeolite Faujasite (FAU) thin films through the direct wet deposition of zeolite FAU thin films using stabilized colloidal suspensions. Zeolite FAU suspensions are stabilized by adjusting the pH values and the suspensions are spin-coated on a silicon wafer substrate to form dense zeolite FAU thin films. Dynamic light scattering (DLS) was used to investigate the colloidal properties of the zeolite FAU suspensions. The time-dependent hydrodynamic radius Rh was derived from DLS measurements for use as a quantitative measure of colloidal stability. It was found that high pH values destabilize the colloidal suspensions. Thin film samples cast using the relatively stable zeolite FAU suspensions yielded thin films with uniform morphology. In thin films formed from suspensions with a high pH value, the zeolite FAU crystals transformed into a dense phase. We also measured the relative permittivity (er) of the thin film samples cast from various suspensions. At a low frequency (

Producing zeolite films with controlled preferred orientation on an industrial scale is a long-standing challenge. Herein we report on a scalable approach to the direct wet deposition of zeolite thin films and membranes while maintaining a high degree of control over the preferred crystal orientation. As a proof of concept, thin films comprising aluminophosphate zeolite AEI were cast on silicon wafer or porous alumina substrates. Electrical properties and separation performance of the zeolite thin films/membranes were engineered through controlling degree of preferred crystal orientation.

The control of nanostructural dimension by crystallization-induced chain stretching was investigated in a novel double-crystalline block copolymer, syndiotactic poly(4-methyl-1-pentene)-block-poly(l-lactide) (sPMP–PLLA), featuring a lamellar phase. Because of the similar glass transition temperatures of sPMP and PLLA, their blocks could crystallize under soft confinement (i.e., a crystallization temperature higher than the glass transition temperatures of the constituent blocks) in sPMP–PLLA. With the strong segregation of sPMP–PLLA, the first-crystallized sPMP block was templated by microphase separation to form confined crystalline sPMP lamellae within the microphase-separated lamellar texture. Most interestingly, the first-crystallized sPMP block may also induce significant stretching of the PLLA chains from the lamellar interface, resulting in the increase of microdomain thickness of the PLLA block. With the increase of crystallization temperature, this chain stretching may become more significant, re...

The operating condition effects on the cross-flow microfiltration performance of dilute macromolecular suspension were studied. Track-etched membranes of different pore sizes were used to filter blue dextran with a molecular weight of 2000 kDa. Increasing the membrane pore diameter results in higher filtration flux but decreases the dextran rejection coefficient. For filtration using 0.2-μm membrane, an increase in cross-flow velocity or filtration pressure leads to higher filtration flux, but the impact of cross-flow velocity is more significant. A membrane fouling model based on force analysis and membrane pore size reduction caused by dextran adsorption at pseudo-steady state is proposed. The effective membrane pore diameter and pseudo-steady filtration flux under various conditions can then be estimated. On the other hand, the pseudo-steady dextran rejection coefficient increases with increasing cross-flow velocity or decreasing filtration pressure when cross-flow velocity is lower than 0.3 m/s. This can be reasonably explained by the sweeping effect of tangential flow or using the modified gel-polarization model. However, a contrary trend occurs under the conditions with higher cross-flow velocity. This result is attributed to the dextran molecular deformation. The “coil-stretched” deformation of blue dextran molecules can be indicated using the Reynolds number in the permeating flow direction or Deborah number for macromolecular flow through porous media.

We investigate the crystallization behavior of isotactic polypropylene (iPP) under the influence of nanoscale confinement templated by the microphase-separated structure of an iPP-based diblock copolymer system, isotactic polypropylene-block-atactic polystyrene (iPP-b-aPS). Three types of iPP microdomains, i.e., lamellae, cylinder, and sphere, were generated by controlling the composition of the diblock. The effect of microdomain morphology on the nucleation mechanism, crystallization kinetics, self-nucleation behavior, the population of the helical sequence of iPP block in the melt state, and crystal orientation have been systematically studied. It was found that the crystallization rate of iPP was predominantly controlled by homogeneous nucleation when the crystallization process was largely confined within the individual cylindrical and spherical microdomains. Such a nucleation mechanism and the highly frustrated crystal growth in the isolated microdomains led to the absence of Domain II and atypical crystallization kinetics in Domain III in the self-nucleation study. The population of the longer helical sequence of iPP block revealed by infrared spectroscopy was found to be affected by temperature but not by the spatial confinement, chain stretching, and junction point constraint imposed by the microdomains. Finally, the orientation of α-form iPP crystals in the lamellae-forming iPP-b-aPS was identified over a broad range of crystallization temperatures (T(c)). Different from other crystalline-amorphous diblocks, a lamellar branching of α-form iPP was observed in the lamellar microdomains at T(c) lying between 15 and 80 °C, where the daughter lamellae developed from the perpendicularly orientated parent iPP crystals with a specific angle of 80° or 100°. Once the sample was crystallized at T(c) ≤ 10 °C, the iPP crystals became randomly oriented.