The Chiroptical Activity Of Cellulose Nanocrystals And Its Applications

Structural colors which are produced by photonic crystals structure play an important role in nature.In biological world,one kind of the brilliant colors is arise of the helicoidal arrangement of chitin or cellulose microfibrils,as exemplified in jeweled beetles,mantis shrimps,marble berries and tropic leaves.The helicoidal arrangement is capable of selective reflection circularly polarized light(CPL)and the CPL can be used as a secret signal to communicate.Inspired from nature,this thesis is devoted to the researches of chiroptical activities of cellulose nanocrystals based chiral photonic materials and its applications.Cellulose nanocrystals(CNCs)are earth-abundant,cheap,degradable,and have excellent physical and chemical properties.CNCs suspension can self-assemble into chiral nematic phase above a critical concentration and the structure which is responsible for the iridescent colors can be preserved upon drying.Chiral nematic CNCs film can selectively reflect left-handed CPL and the reflection wavelength can be tuned in broad-wavelength-range.CNCs have attracted increasing attention for their wide applications in chiral catalysis,reinforced materials,responsive materials and biomimetic materials.This thesis focuses on the scientific resareches that have not been reported in the field.We develop the chiral photonic crystals materials based on cellulose nanocrystals and focuses on the chiral optical activity and the promising applications.Detail researches are summarized as followings:(1)The modulation effect of spontaneous emission by chiral photonic structure.Chiral photonic CNC/AuNC composite film was prepared by evaporation induced corporative assembly with CNCs and AuNCs.The CNC/AuNC composite film is one dimension photonic crystal and the spontaneous emission of AuNC can be regulated due to the stopband-and band edge-coupling effect between the photonic crystal structure and the emission of AuNC.The CNC/AuNC film shows the promising application in visual fluorescence sensor.(2)The ability of chiral photonic cellulose film to generate multi-color circularly polarized luminescence(CPL).Composite chiral photonic CNC/PDots films with luminescence from blue to red coving the entire visible range were successfully fabricated by evaporaional induced corporatively assembly process.Strong multi-color right-handed circularly polarization luminescence(R-CPL)with tunable chiroptical activity can be realized by three ways:(1)by photonic bandgap effect and emission intensity effect;(2)by varying the emission wavelength of polymer dots;(3)by multi-layer ensembles of chiral photonic CNC/PDots films.The multi-layer ensemble enables left-handed circularly polarized light in sync with the right-handed circularly polarized luminescence,which appears different on the front and back side.(3)Organizaition of flexible chiral phoronic films with responsive circularly polarized light to mechical and chemistry.The poor mechanical property of chial photonic CNCs film limits the practical application and the fabrication of flexible CNCs film is in demand.Inspired from the chameleon and responsive photonic gels,we demonstrated the fabrication of chiral photonic gels by evaporation-induced corporative assembly of CNC and gluocose(GLU).The chiral photonic gels of CNC/GLU are highly stretchable with the maximum strain-at-break of 40.8%,which is about three times of the highest reported value for CNCs-based chiral photonic materials.The photonic gels exhibit real-time tuning of left-handed circularly polarized light in a broad visible region to mechanical tensioning and bending.It also allows reversible tunability of left-handed circularly polarized light in response to 10-100% relative humidity at room temperature from the visible to the near-infrared region,manifesting a promising soft material platform for broad-wavelength-range real-time tunable left-handed circularly polarized light for security applications.