Smart and Sustainable Hair Products Based on Chitin-Derived Compounds

According to previous research studies, consumers worldwide are searching for new natural-oriented hair products that are both skin and environmentally friendly. Worldwide waste and air pollution, with the consequent environmental disasters, represent the greatest risk to human health and economy, further increased by the COVID-19 pandemic. Among others, non-biodegradable molecules are present in hair products (fossil-based additives, surfactants, etc.) and macromolecules (plastics). Plastics waste is considered the most serious problem, representing a forecast amount of 460 million tons per year by 2030, 12% of which is reused or recycled. Most plastics consumed, therefore, go to landfills and incineration, also if their recycling is considered an important driver of industrial profitability. Thus, the use of biopolymers represents an interesting alternative to produce biodegradable goods and tissues. After an introduction to the worldwide waste problem and the hair structure, the present review proposes the possibility to make biodegradable tissues that, realized by chitin nanofibrils and nano-lignin as natural polymers, may be used to produce an innovative and smart cosmetic hairline. Chitin-derived compounds are considered interesting polymers to produce non-woven tissues able to repair the hair damages provoked by the aggressiveness of both the environment and some aggressive cosmetic treatments, such as setting, bleaching, permanent waving, and oxidative coloring. The possible activity, that positively charged polymers such as chitin could have, has been speculated, interfering with the constitution and organization of the hair fibrils’ structure, which is negatively charged. The possibility of selecting biopolymers for their packaging is also discussed. Moreover, the use of these biopolymers, obtained from forestry-agro-food waste, may be of help to safeguard the further consumption of natural raw materials, necessary for future generations, also maintaining the earth’s biodiversity.

Dissecting Dynamics near the Glass Transition

Though the strong transformation in mechanical properties of glass-forming materials near the glass transition, Tg, has been recognized and exploited for millenia, efforts to understand and predict this phenomenon at a molecular level continue to this day. Close to Tg, where relaxation is considerably slower than predicted by the well-known Arrhenius equation, one of the most versatile and widely-used expressions to describe the dynamics or relaxation of glass formers is that of Vogel, Fulcher and Tammann (VFT). The VFT equation, introduced nearly 100 years ago, contains three adjustable fit parameters. In this work the dynamics of the polymer repeat units are related to macroscopic dynamics in polyelectrolyte complexes, which are hydrated amorphous blends of charged polymers. A simple expression, containing no freely adjustable fit parameters, is derived to quantitatively model relaxation from Tg to temperatures well into the Arrhenius region. The new expression, which also fits a selection of three common neutral polymers, will advance the understanding and use of the glass-forming phenomenon.

Experimental review of PEI electrodeposition onto copper substrates for insulation of complex geometries

Electrophoretic deposition relying on electrodeposition of charged polymers via modulated electrical fields is reported. Superior surface finishes that could pass a dielectric withstand test at 10 kV mm−1 were obtained for pulsed potentials at 20 V.

Interaction of Different Charged Polymers with Potassium Ions and Their Effect on the Yield Stress of Highly Concentrated Glass Bead Suspensions

The interaction of different charged polymers, namely anionic polycarboxylate superplasticizer (PCE) and neutral polyethylene glycol (PEG) with potassium ions, and their effect on the yield stress of highly concentrated glass bead suspension (GBS), were studied under different concentrations of potassium ions ([K+]). It was found that, compared to the neutral PEG, the negatively charged PCE can be adsorbed on glass beads (GB), and then decreases the yield stress of GBS. The increasing concentration of free polymer in the interstitial liquid phase with the increased polymer dosage leads to the higher yield stress of GBS, which may be caused by the higher depletion force. In addition, this effect is also related to the charge density of the polymer and the [K+] in the solution. Along with the increase in [K+], the yield stress of GBS increases significantly with the addition of PCE, but this cannot be observed with PEG, which indicates that potassium ions can interact with negatively charged PCE instead of the neutral PEG. At last, the interparticle forces between two single GB with adsorbed PCE in solutions containing [K+] and PCE were measured by colloidal probe atomic force microscopy to better understand the interaction of the charged polymer with counterions.

Kinetics of charged polymer collapse: effects of additional salt

Extensive molecular dynamics simulations, using simple charged polymer models, have been employed to probe the kinetics and dynamics of early-stage collapse of charged polymers and the effect of additional monovalent salt on such kinetics. The exponents characterizing the coarsening dynamics during such early-collapse stage via finite size scaling for the case of charged polymers are found to be different from the neutral polymers, suggesting that the collapse kinetics of charged polymers are inherently different from that neutral polymers. The kinetics of coarsening of the clusters along the collapsed trajectory also depends significantly on the counterion valency and for higher valency counterions, multiple regimes are observed and unlike the neutral polymer case, the collapse kinetics are a function of charge density along the charged polymer. Inclusion of additional salt affects the kinetics and conformational landscape along the collapse trajectory. Addition of salt increases the value of critical charge density required to initiate collapse for all the counterion valencies, though the effect is more pronounced for monovalent counterion systems. The addition of salt significantly affects the collapse trajectory in the presence of trivalent counterions via promotion of transient long-distance loop structures inducing a parallel and hierarchical local collapsed conformation leading to faster global collapsed states. This may play a role in understanding the fast folding rates of biopolymers such as proteins and RNA from extended state to a collapsed state in the presence of multivalent counterions before reorganizing into a native fold.

Structure–function–dynamics of α-chymotrypsin based conjugates as a function of polymer charge

Atomistic molecular dynamics simulations improve our understanding of protein–polymer conjugates, and can predict how charged polymers affect the native dynamics of the protein.