Cellulose-Based Liquid Crystalline Photoresponsive Films with Tunable Surface Wettability

Abstract

We report on a new type of liquid crystalline cellulosic films with light controllable reversible wettability. The films are prepared from a thermotropic cellulose derivative functionalized with azo-containing groups. These groups exhibit dynamic changes in interfacial properties in response to UV irradiation. The UV irradiation induces trans-to-cis isomerization in the azobenzene moiety, which causes a conformational change in the upper molecular layers of the thin films. These changes originate a hydrophobic to comparatively hydrophilic transformation of the surface. The reversible wettability of the surface results from the cis/trans photo and thermal isomerization. The UV-vis absorption spectra, as well as contact angle measurements with UV irradiation, clearly support the understanding of the phenomenon. This type of surface design enables the amplification of molecular level conformational transitions to macroscopic changes in interface properties using the means of isomerism. This opens new opportunities in surface engineering using eco-friendly cellulose manipulation.

Electrospun Azo‐Cellulose Fabric: A Smart Polysaccharidic Photo‐Actuator

“…[38][39] Therefore, the materials having the trans isomer generally show greater Water Contact Angle (WCA) than those having the cis isomer. [40][41] A similar phenomenon was observed for the Azo-Cel fabric. One notes that the photo-isomerization of the azobenzene moiety in Azo-Cel from the trans to the cis isomers under UV irradiation and vice versa under visible light irradiation in the solution state was reported in our previous study.…”

Bio-Based Coatings for Paper Applications

“…Interestingly, these materials can respond to external stimuli such as mechanical stress [164], humidity [165], light [163], and temperature [162], and desired user properties can be achieved on demand. Especially, researchers could reversibly tune the wetting mechanisms (hydrophilic to hydrophobic and vice versa) of a liquid crystalline cellulosic film under UV light exposure, which was attributed to conformational transformation of the photo-sensitive molecules that results from the cis/trans isomerization of functional azo-groups [166]. A new way to make hydrophobic paper has been discussed by combining the layer-by-layer (LbL) technique with the adsorption of a colloidal paraffin wax onto the multilayer structure [167]: thermal curing for 30 min at 160 °C can initiate the cross-linking between the adsorbed layers and cellulose fibers, which further increases the surface roughness followed by an increase in contact angle up to 150°, probably because of intensification of wax hydrophobic properties.…”

Synthesis and photosensitivity of azobenzene functionalized hydroxypropylcellulose

“…Typical photosensitive moieties include spiropyran, azobenzene, triphenylmethane derivatives, and cinnamoyl groups. The use of polymer materials containing photosensitive moieties has promising applications in the fields of optical message storage, 1,2 surface property regulation, [3][4][5][6] and optical driving actuators. [7][8][9][10][11] Among photosensitive moieties, the azobenzene moiety is popular for the regulation of the properties of polymeric materials.…”

“…Cellulosic functional materials are generally prepared via the modification of cellulose through derivation [39][40][41][42][43][44][45] or graft copolymerization. [46][47][48][49][50][51][52][53][54][55] The introduction of azobenzene moieties onto cellulose backbones has been achieved by directly bonding the azobenzene moieties via esterification 3,[56][57][58] or graft polymerization. [59][60][61] However, the liquid crystalline behaviour is mainly focused on in previous work.…”