Preparation And Properties Of Solvent-free Cellulose Thermotropic Liquid Crystal Materials

Solar energy and the accompanying low-temperature heat energy are abundant natural resources.At present,improving theutilization efficiency of these energies is one of the hot topics in the field of energy materials.Since the photon energy can be converted into thermal energy via the reversible photoisomerization of photochromic molecules,the development of photoresponsive phase change materials can realize the storage of low-temperature thermal energy storage and photon energy.The reported azobenzene-containing phase change materials have two working ways.In the first working way,phase change materials realize energy storage via heating treatment.The incorporated azobenzene could regulate the melting and crystallization points via photoisomerization,supporting the relative long term thermal energy storage and photocontrolled heat release.This way encounters a challenge to achieve low-grade heat absorption at room temperature.In the other working method,the phase change materials take advantage of the trans-cis isomerization of azobenzene for photon energy storage and the simultaneous resulted solid-liquid phase change for latent heat storage.However,in the absence of light irradiation,the energy storage density will be greatly reduced.Cellulose is the most abundant natural biomass resources.However,without the photochromic motif in molecular level,cellulose can hardly furnish the phase change under light.Therefore,an introduction of photochromic molecules like azobenzene would be necessary for developing cellulose into photoresponsive phase change materials.Taking advantage of the preparation method for biomacromolecules-based thermotropic liquid crystals,an azobenzene-containing ammonium surfactant would be synthesized for the electrostatic complexation with carboxymethyl cellulose.A new type of photoresponsive phase change material CMC-AZO is obtained after centrifugation,water-washing and lyophilization.By using the same synthetic method and doping gold nanoparticles,CMC-AZO@Au NP could also be prepared.Such cellulose materials can realize the energy storage and controllable release of low-grade thermal energy and photon energy.With nematic ordered structure,CMC-AZO and CMC-AZO@Au NP exhibit good thermal stability up to 200 ?.Importantly,the reported cellulose materials can store energy in two different ways.Under UV light irradiation,thcellulose materials can store photon energy via photoisomerization of azobenzene and low temperature thermal energy via photoinduced phase transition at room temperature.In the absence of UV light,the cellulose materials can store low-temperature thermal energy through gradual phase transitions upon heating.The gravimetric energy densities of these two ways can reach202 J/g and 150 J/g,respectively.The stored energy can be rapidly released in the form of heat under visible light.In addition,the incorporation of gold nanoparticles into cellulose materials was demonstrated to be an efficient method for fast energy storage under UV light irradiation.This work provides a strategy for value-added utilization of cellulose in energy storage field,which also provides a new strategy for the development of energy storage materials with other biomolecules.