Co-assembly And Properties Of Cellulose Nanocrystal Composites

Cellulose nanocrystals(CNC)are nanomaterials extracted from bio-based sources with the ability to self-assemble to obtain unique optical properties due to their rigid rodlike structures.CNC self-assembly methods generally include evaporation-induced selfassembly(EISA),vacuum-assisted self-assembly,and uniaxial self-assembly.Under different external forces condition,the CNC presents different assembly structures and shows adjustable structural colors,which can be applied in the fields of anticounterfeiting,information hiding,optical sensing,and so on.However,the insulation and rigidity of CNC limited its applications in antistatic packaging and mechanical sensing.To expand the application field and achieve functional integration of CNC selfassembled materials,this work explored the stability of co-dispersion between CNC and nanoparticles in different dimensions by co-assembly 1D CNC with different dimensions of nanoparticles.Also,the results of different dispersion stability were analyzed by a semi-quantitative calculation from thermodynamics.Besides,the effect of CNC size and concentration on the dispersion stability of 2D nanomaterials was further studied.Finally,to enhance the flexibility and luminous intensity of CNC assembled structural color materials,CNCs were co-assembled with flexible polymers to obtain co-assembled materials with mechanical response characteristics,and the mechanism of response characteristics was also explored.The study found that CNCs could act as a solid emulsifier for hydrophobic carbon nanoparticles(CNP)due to their amphiphilic properties.CNC surface modifications proved that hydrophilic CNC is more favorable for CNP dispersion,but CNC only showed better co-dispersion effect for 0D carbon black and 1D carbon nanotubes,but the poor effect for 2-dimensional graphene,which is due to the difference of phase separation Gibbs free energy caused by different dimensions of CNP.Adjusting the combination and concentration of CNP/CNC could further obtain different surface resistivity by uniaxial co-assembly,and the structure color material with blue light under UV light could be applied in the field of antistatic anti-counterfeiting packaging materials.Besides,as for2 D black phosphorus nanosheet(BPNS)that are prone to phase separation,by adjusting the aspect ratio and concentration of the CNC,BPNS and CNC could complete the assembly before phase separation occurred,and the chemical stability of the BPNS was enhanced by physical coating and the formation of new chemical bonds with the BPNS.The composite material with uniform dispersion and good chemical stability,as well as near-infrared photothermal conversion ability could be obtained by the EISA method and CNC extracted by the tunicate with a higher concentration(1.2 wt%),which had a good application prospect in the field of infrared ignition.In addition,the orientation enhancement of CNC assembly could be achieved by introducing poly(vinyl alcohol)(PVA)and CNCs for uniaxial co-assembly,which in turn greatly improved the luminescence quantum yield of CNC under UV illumination(more than 60%).Meanwhile,PVA brought flexibility to the material,changing the ratio of CNC and PVA could regulate the CNC assembly array structure,and then made the excitation wavelength and luminescence quantum yield of the CNC/PVA material showed responsiveness to the elongation of the material,which had the application prospect of optical coding and sensing.The reason for this responsiveness was that the creation of the vacuum inside the material during the tensile process led to the change of the effective refractive index of the material,while the enhancement of the luminous intensity came from the reduction of the CNC spacing in a parallel arrangement.In summary,this study achieved thermodynamic and kinetic regulation of CNCs and nanoparticles by co-assembly CNCs with nanoparticles and polymers,increases the functionality of CNC assembled structural color materials and expanded the application field.Meanwhile,the adjusting of co-assembly with flexible polymers realized the luminescence enhancement and mechanical response characteristics of CNC uniaxially assembled materials,bringing CNC potential for the application of sensing and coding of assembled structural color materials.