Swelling process of thin polymer film studied via in situ spectroscopic ellipsometry

Solvent-assisted self-assembly of block copolymer thin films

Solvent-assisted block copolymer self-assembly is a compelling method for processing and advancing practical applications of these materials due to the exceptional level of the control of BCP morphology and significant acceleration of ordering kinetics. Despite substantial experimental and theoretical efforts devoted to understanding of solvent-assisted BCP film ordering, the development of a universal BCP patterning protocol remains elusive; possibly due to a multitude of factors which dictate the self-assembly scenario. The aim of this review is to aggregate both seminal reports and the latest progress in solvent-assisted directed self-assembly and to provide the reader with theoretical background, including the outline of BCP ordering thermodynamics and kinetics phenomena. We also indicate significant BCP research areas and emerging high-tech applications where solvent-assisted processing might play a dominant role.

Preparation of biological samples for microplastic identification by Nile Red

Many methods have been used to isolate and identify microplastics from biological matrices. In biological samples, Nile Red can stain undigested residues, such as fats, soaps, and gels formed during organic matter removal, hindering the identification of fluorescent microplastics (≥2 μm). Thus, adjustments on sample preparation (e.g., fat removal) are required for the accurate identification of Nile Red stained microplastics. Multiples tests allowed to identify that digestion with 10% KOH at 60 °C for 24 h, followed by treatments with boiling water, acetone, and staining, produced good results in fourteen biological samples, including vertebrates and invertebrates. Digestion efficiencies were 94-100%, except for feces, which were 87%. Recovery rates of spiked microplastics were 97-100%, and few effects were observed in the infrared spectra and carbonyl index of seven polymers, with only the occasional yellowing suggesting surface changes. Filtration rates were improved by reducing the amount of sample. Small fluorescent microplastics could be identified in all samples under the microscope. Overall, the proposed method was efficient in removing natural organic matter from biological samples for Nile Red staining, requiring minimal sample handling, improving sample throughput, and allowing quantification of fluorescent microplastics in biological samples.

Inconsistency of Diffusion and Relaxation of Ring Polymers Adsorbed on Rough Surfaces

We explore the diffusion and relaxation dynamics of a single ring polymer strongly adsorbed on rough surfaces with different roughnesses by means of molecular dynamics simulations. Our simulations demonstrate that on rough surfaces the intrachain topological constraint deriving from the closed architecture induces the inconsistency of diffusion and relaxation of ring polymers. When the lateral chain size is larger than the obstacle distance (2R_g∥,r > d), the ring closure induces the polymers to anchor on a single obstacle and dramatically reduces their diffusivity, where R_g∥,r and d are the lateral components of the mean-square radius of gyration and the obstacle distance, respectively. However, the single obstacle anchoring has no effect on the relaxation of ring polymers, which implies a deviation between the diffusion and the relaxation. With the lateral chain size beyond twice of the obstacle distance (R_g∥,r > d), the ring polymers are totally confined in the array of obstacles and can only diffuse through hopping over the obstacles, resulting in an exponential reduction of their diffusion coefficient. However, the relaxation of ring polymers mainly depends on their rotating reptation and satisfies the reptation-like dynamics, which means that the diffusion and the relaxation are nearly irrelevant. This inconsistency between the diffusion and relaxation is a unique property of adsorbed ring polymers, which would be meaningful to understand the physical nature of polymers with ring closure and significant to develop the corresponding applications.