Microhoneycomb Monoliths Prepared by the Unidirectional Freeze-drying of Cellulose Nanofiber Based Sols: Method and Extensions

Abstract

Monolithic honeycomb structures have been attractive to multidisciplinary fields due to their high strength-to-weight ratio. Particularly, microhoneycomb monoliths (MHMs) with micrometer-scale channels are expected as efficient platforms for reactions and separations because of their large surface areas. Up to now, MHMs have been prepared by a unidirectional freeze-drying (UDF) method only from very limited precursors. Herein, we report a protocol from which a series of MHMs consisting of different components can be obtained. Recently, we found that cellulose nanofibers function as a distinct structure-directing agent towards the formation of MHMs through the UDF process. By mixing the cellulose nanofibers with water soluble substances which do not yield MHMs, a variety of composite MHMs can be prepared. This significantly enriches the chemical constitution of MHMs towards versatile applications.

A Directional Strain Sensor Based on Anisotropic Microhoneycomb Cellulose Nanofiber‐Carbon Nanotube Hybrid Aerogels Prepared by Unidirectional Freeze Drying

“…Note that the formation of the aligned microhoneycomb structure is attributed to the unique structure‐directing function of CellF which we have discussed in detail in another paper . The size of the microhoneycomb cells of MCCA can be easily changed by altering the unidirectional freezing speed (the immersion speed) . Specifically, speeds of 10, 20, and 70 cm h −1 yielded MCCAs with cell sizes of 50, 20, and 5 µm, respectively(Figure c–e).…”

“…Previous studies have shown that CellFs contribute to the formation of a microhoneycomb structure during UDF even with only 20 wt% CellFs in the precursor . In addition, we have recently demonstrated that an aqueous CNT dispersion produces a lamella‐like micromorphology by UDF .…”

“…Preparation of the Two Component Precursors Used in the UDF Experiment : The two component precursor was prepared by mixing 1 wt% CellF sol and a 5 wt% CNT aqueous dispersion. Preparation of the 1 wt% CellF sol used a method that was previously reported . The 5 wt% CNTs aqueous dispersion (NTP 2021) was bought directly from NTP Company, Shenzhen, China and was used without further treatment.…”

“…Scanning electron microscopy (SEM) of the aerogel's cross section shows an ordered microhoneycomb‐like morphology (Figure a and Figure S2, Supporting Information) containing continuous unidirectional penetrating microchannels along its length (Figure b and Figure S3, Supporting Information) with highly intertwined CellF and CNTs forming the channel walls (Figure S4, Supporting Information). Note that the formation of the aligned microhoneycomb structure is attributed to the unique structure‐directing function of CellF which we have discussed in detail in another paper . The size of the microhoneycomb cells of MCCA can be easily changed by altering the unidirectional freezing speed (the immersion speed) .…”

“…However, the hydrophilic nature of cellulose means that the aerogel cannot be wetted by the most of polymers . In addition, the fact that they are electrically insulating limits their applications, especially in the areas of electronics, electric sensors, and energy storage …”