PeakForce QNM AFM study of chitin-silica hybrid films

Comparative study of photoinduced surface-relief-gratings on azo polymer and azo molecular glass films

Photoinduced surface-relief-gratings (SRGs) on azo polymer and azo molecular glass films, caused by trans-cis isomerization of azo chromophores, have attracted wide interest for their intriguing nature and many possible applications in recent years. Understanding the mechanical properties of SRGs at the nanoscale is critically important for elucidating their formation mechanism and exploring their applications. In this work, a representative azo polymer (BP-AZ-CA) and a typical azo molecular glass (IAC-4) were comparatively studied for the first time concerning their properties related to SRG formation through a variety of methods. The results indicate that when inscribing SRGs on the films, IAC-4 shows a much higher efficiency for forming SRGs relative to that of BP-AZ-CA. The overall average moduli of SRGs measured by nanomechanical mapping techniques are obviously smaller compared with the moduli of the corresponding films of both materials. The moduli at different regions of SRGs are periodically varied along the grating vector direction for both BP-AZ-CA and IAC-4 gratings. The moduli at the trough regions of SRGs are always larger than those of the crests, while the moduli at the hillsides are the smallest. Distinct from BP-AZ-CA, even the moduli at the trough regions of IAC-4 SRG are smaller compared with that of the original film, and the ratio between the trough and crest moduli is significantly larger for IAC-4. These results provide deep understanding of the SRG formation mechanism and reveal the clear distinction between these two types of glassy materials for their SRG-forming behavior, which are important for future applications.

Mapping the surface potential, charge density and adhesion of cellulose nanocrystals using advanced scanning probe microscopy

Cellulose nanocrystals (CNC) are the focus of significant attention in the broad area of sustainable technologies for possessing many desirable properties such as a large surface area, high strength and stiffness, outstanding colloidal stability, excellent biocompatibility and biodegradability, low weight and abundance in nature. Yet, a fundamental understanding of the micro- and nanoscale electrical charge distribution on nanocellulose still remains elusive. Here we present direct quantification and mapping of surface charges on CNCs at ambient condition using advanced surface probe microscopy techniques such as Kelvin probe force microscopy (KPFM), electrostatic force microscopy (EFM) and force-distance (F-D) curve measurements. We show by EFM measurements that the surface charge in the solid-state (as contrasted with liquid dispersions) present at ambient condition on CNCs provided by Innotech Alberta is intrinsically negative and the charge density is estimated to be 13 μC/cm². These charges also result in CNCs having two times the adhesive force exhibited by SiO₂ substrates in adhesion mapping studies. The origin of negative surface charge is likely due to the formation of CNCs through sulfuric acid hydrolysis where sulfate half esters groups remained on the surface (Johnston et al., 2018).

Structure of Composite Based on Polyheteroarylene Matrix and ZrO₂ Nanostars Investigated by Quantitative Nanomechanical Mapping

It is known that structure of the interface between inorganic nanoparticles and polymers significantly influences properties of a polymer⁻inorganic composite. At the same time, amount of experimental researches on the structure and properties of material near the inorganic-polymer interface is low. In this work, we report for the first time the investigation of nanomechanical properties and maps of adhesion of material near the inorganic-polymer interface for the polyheteroarylene nanocomposites based on semi-crystalline poly[4,4'-bis (4″-aminophenoxy)diphenyl]imide 1,3-bis (3',4-dicarboxyphenoxy) benzene, modified by ZrO₂ nanostars. Experiments were conducted using quantitative nanomechanical mapping (QNM) mode of atomic force microscopy (AFM) at the surface areas where holes were formed after falling out of inorganic particles. It was found that adhesion of AFM cantilever to the polymer surface is higher inside the hole than outside. This can be attributed to the presence of polar groups near ZrO₂ nanoparticle. QNM measurements revealed that polymer matrix has increased rigidity in the vicinity of the nanoparticles. Influence of ZrO₂ nanoparticles on the structure and thermal properties of semi-crystalline polyheteroarylene matrix was studied with wide-angle X-ray scattering, scanning electron microscopy, and differential scanning calorimetry.