Heterogeneous Dynamics and Microdomain Structure of High-Performance Chitosan Film as Revealed by Solid-State NMR

Abstract

Understanding the structure–property relationship of biopolymers is crucial for revealing the superior properties of advanced materials in nature, and thus facilitating material innovation. In this work, it was found that the chitosan film cast from acid solution represented a tremendous change of mechanical property, from brittle to tough when neutralized in a strong alkaline solution. The molecular mechanism of the enhancement in mechanical property was systematically investigated by multiscale solid-state NMR coupling with other techniques.1H and 13C NMR experiments revealed that the alkaline treatment leads to a distinct difference in structure and dynamics for the chitosan samples. X-ray experiments and polarized optical microscopic results demonstrated that the crystallinity of alkaline-treated chitosan film was remarkably enhanced due to the removal of acid counterions, resulting in the enhanced interchain hydrogen-bonding interaction. For chitosan films cast from acidic solution, the acid counterions act as a defect and impair the interchain hydrogen-bonding interaction as well as long-range organization, resulting in brittle films with amorphous structure. 1H double quantum filter spin diffusion experiments indicated the enhanced nanoscale phase separation and heterogeneous dynamics in the alkaline-treated chitosan films. Therefore, hydrogen-bonding plays a crucial role in affording high mechanical strength to the neutralized chitosan films with well-defined long-range structure. A deep understanding on the heterogeneous dynamics and nanostructure of the neutralized chitosan films with enhanced mechanical properties at the atomic level could guide the regeneration of high-performance natural polymer materials.

Affinity of Ligands Co-Ordinated on Gold Nanoparticles

“…For the ligands co-ordinated on AuNPs, the chemical bonding of the ligands on the highly faceted Au nanoparticle surface causes heterogeneous broadening, while the interaction between ligands causes homogeneous broadening. To suppress line broadening caused by strong 1 H– 1 H dipolar couplings and chemical shift anisotropy, , we utilized fast MAS ( v R = 25 kHz) to record 1 H high-resolution SSNMR spectra of the ligands on AuNPs. The SSNMR spectra for AuNPs ( d = 2 nm) co-adsorbed with p -MBA and C 18 NH 2 are shown in Figure d.…”

Materials informatics approach using domain modelling for exploring structure–property relationships of polymers

“…In our method using STFT, by simulating the signal for both the frequency and time domain, it was possible to separate the signal related to the motility characteristics of the domain structure based on the indicators of chemical shift and T 2 relaxation time. The NMR signal can be calculated by functions such as Lorentzian 35 , Gaussian 36 , and Voigt 37 in the frequency domain, and by the T 2 relaxation equation 38 in the time domain. In addition, the difference in T 2 relaxation times can be adjusted by the Weibull coefficient 39 .…”

Parameter Visualization of Benchtop Nuclear Magnetic Resonance Spectra toward Food Process Monitoring

“…The analysis of the FID relaxation time of a sample can provide important insights into the sample's chemical composition, structure, and mobility [37,38]. The FID relaxation times can be calculated using Lorentzian, Gaussian, Voigt, and other functions in the frequency domain and the T 2 * relaxation time equation in the time domain during the simulation and fitting of NMR signals [39,40]. The differences in T 2 * relaxation times can be adjusted using the Weibull coefficient [37].…”