Steric Repulsive Forces Research Articles

Pebax/NC-PCL membrane containing well-distributed PCL grafted biodegradable nano-chitosan particles for CO2 separation

This study presents a novel method to improve carbon dioxide (CO2) separation performance in mixed-matrix membranes (MMMs) by incorporating polycaprolactone (PCL) grafted biodegradable nano-chitosan (NC) particles into a Pebax membrane matrix. Adding NC particles strengthens the interaction between the polymer mixed-matrix and CO2 molecules through functional groups on the NC particles via a facilitated transport mechanism. Grafting NC particles with PCL prevents the aggregation of particles by introducing steric repulsive forces between them, ensuring a well-dispersion of NC particles within the polymer matrix. Gas separation tests revealed that the membrane containing NC-PCL particles at a 1:1 ratio achieved a superior CO2 permeability of 99.8 Barrer and a CO2/N2 selectivity of 234.9. This performance marks a moderate increment of 20.7% in CO2 permeability and a substantial 413% increase in CO2/N2 selectivity compared to the neat Pebax membrane. Overall, the membranes managed to exceed the Robeson upper bound line by enhancing both CO2 permeability and CO2/N2 selectivity simultaneously, thereby better balancing the trade-off effect between selectivity and permeability.

Impact of dissolved organic matter characteristics and inorganic species on the stability and removal by coagulation of nanoplastics in aqueous media

The aggregation of rough, raspberry-type polystyrene nanoparticles (PS-NPs) was investigated in the presence of six hydrophobic and hydrophilic dissolved organic matter (DOM) isolates and biopolymers (effluent OM) in NaCl and CaCl2 solutions using time-resolved dynamic light scattering. Results showed that the stability of PS-NPs mainly depends on OM characteristics and ionic composition. Due to cation bridging, the aggregation rate of PS-NPs in Ca2+-containing solutions was significantly higher than at similar Na+-ionic strength. Biopolymers rich in protein and carbohydrate moieties showed higher affinity to the surface of PS-NPs than the other DOM isolates in the absence of both Ca2+ and Na+. Overall, the stability of PS-NPs followed the order of biopolymers > hydrophobic isolates > hydrophilic isolates in the presence of Na+ and biopolymers > hydrophilic isolates > hydrophobic isolates in Ca2+-containing solutions. In the presence of high MW structures (biopolymers), PS-NPs aggregation in both NaCl and CaCl2 solutions was attributed to steric repulsive forces. The impact of hydrophilic and hydrophobic isolates on PS-NPs aggregation highly relied on the ionic composition. Coagulation was an effective pretreatment for PS-NPs removal. Using inductively coupled plasma-mass spectrometry, higher removals were recorded with Al2(SO4)3 in the absence of DOM, while PACl more efficiently coagulated PS-NPs in the presence of DOM isolates.

DFT, Structure Activity Relationship, Fukui, Wave Function, NBO, NLO, Spectral and Hole-Electron Analyses of Dexmethylphenidate

Dexmethylphenidate (DMP) is used to treat attention deficit hyperactivity disorder (ADHD) and belongs to the central nervous system (CNS) stimulant group of medicines. The physical properties of DMP were analyzed under the DFT/B3LYP/6-311++G(d,p) basis set. The ESP study reveals the electrophilic attack is possible, while FMO analysis shows that the molecule is hard, stable and an electron donor. The non-covalent interaction (NCI) study explains that van der Waals and steric repulsion forces are observed. The HEI studies indicated that this molecule has CT excitation in the S0→S5 state. The shaded surface map analysis reveals the presence of electron depletion regions in this molecule. The UV-Vis spectral analysis was carried out in various solvents. The Fukui function analysis conveys that 7C is the best domain for electrophilic attack. Theoretical IR determinations and NLO properties were also performed. The structure-activity relationship findings were performed in order to improve the docking score.

Evaluating the operational properties of concrete admixtures containing molecularly modified polycarboxylate superplasticizers

The objective of this study focused on the design and preparation of a molecularly modified polycarboxylate superplasticizer to develop concretes with enhanced engineering features. For this purpose, polyethylene glycol was chemically modified with maleic anhydride to give the mono polyethylene glycol maleate (MPEGM). Then, polycarboxylate superplasticizer comprising of isoprenyl oxy polyethylene glycol (TPEG) and acrylic acid (AA, PCE-1), and the synthesized MPEGM with TPEG and AA (PCE-2) were prepared through solution radical polymerization. Subsequently, concrete mixtures with different dosages (0, 0.1, 0.15, 0.2, 0.25, 0.3 wt%) of PCE-1 and PCE-2 were prepared. Chemical structure of the synthesized MPEGM and superplasticizers together with their copolymer composition were identified by FTIR and 1HNMR analyses. The molecular weights (Mw) and molecular weight distributions (PDI) of PCE-1 (8.74 × 104, 1.36) and PCE-2 (8.74 × 104, 2.19) were studied by GPC analysis, respectively. The zeta potential of cement particles (2.8 mV) becomes negative in the presence of 0.6 g/L of PCE-1 (− 7.8) and PCE-2 (− 9.5). This implies that electrostatic and steric hindrance forces of adsorbed superplasticizers synergistically provide a situation for appropriate dispersion of cement particles. The results of water-reducing percentage, fluidity, air content, bleeding water rate, initial and final setting times, wet density, flexural and compressive properties, and ultrasonic pulse velocity analyses exhibit significant enhancement on the features of concrete mixtures made of polycarboxylate superplasticizer. The superiority of PCE-2 to PCE-1 was connected to its adsorption-dispersibility potent induced by stronger electrostatic and steric repulsion forces, which result in quality and continuity enhancement in concretes.

Extensive study of droplet dynamics with end-grafted polymer chains in Pickering emulsions: Molecular Dynamics simulation and a generic model derived from the generalized Langevin equation

This paper investigates Pickering emulsions (PEs), formed by suspending oil droplets as the dispersed phase in water as the continuous phase using uncharged particles at their interface. To prevent coalescence, the particles are grafted with polymer chains, as emulsifier, not only to provide steric repulsion forces through the excluded volume between monomers floating in water, compensating for the absence of Coulombic repulsive forces but also control emulsion stabilization/destabilization. We combined molecular dynamics (MD) simulations and a generalized Langevin equation (GLE) model to study the dynamics of hairy-droplets using two dynamic quantities: mean square displacement (MSD) and velocity autocorrelation function (VACF). The number of grafted-polymer-chains, f, was the main parameter of interest, while the other parameters of the system were kept constant. A statistical approach was used to estimate theoretical GLE-based model parameters along with their uncertainties, providing insight into the diffusion behavior of these hairy-droplets and specifically addressing the transition between different observed regimes. we capture three specific values of grafted-polymer-chains as, fb=47 and ft=185 describe the transitions of mushroom-brush conformation of grafted-polymer-chains and viscous-viscoelastic behavior of hairy-droplets, respectively, and fg=257 representing the gel-like state number.

Polymer-Assisted Graphite Exfoliation: Advancing Nanostructure Preparation and Multifunctional Composites.

Exfoliated graphite (ExG) embedded in a polymeric matrix represents an accessible, cost-effective, and sustainable method for generating nanosized graphite-based polymer composites with multifunctional properties. This review article analyzes diverse methods currently used to exfoliate graphite into graphite nanoplatelets, few-layer graphene, and polymer-assisted graphene. It also explores engineered methods for small-scale pilot production of polymer nanocomposites. It highlights the chemistry involved during the graphite intercalation and exfoliation process, particularly emphasizing the interfacial interactions related to steric repulsion forces, van der Waals forces, hydrogen bonds, π-π stacking, and covalent bonds. These interactions promote the dispersion and stabilization of the graphite derivative structures in polymeric matrices. Finally, it compares the enhanced properties of nanocomposites, such as increased thermal and electrical conductivity and electromagnetic interference (EMI) shielding applications, with those of neat polymer materials.

Natural Surfactant Stabilized Aqueous MoS2 Nano-Lubricants for Reducing Friction and Wear

From the outlook of energy saving and environmental protection, the development of eco-friendly and green lubricants without compromising their lubrication performance has become a global agenda. Nevertheless, water-based lubricants suffer from low lubricity and weak load-bearing capacity, making them unsuitable for various industrial applications. Herein, using liquid-phase exfoliation, bulk MoS2 layers are delaminated into atomically thin nanosheets and stabilized in a water medium by a natural surfactant, Sapindius Mukrossi (SM). A natural SM surfactant consisting of 10 % –12 % saponin molecules has a hydrophobic tail aglycone and hydrophilic head glycone molecules that provide steric repulsive forces against the aggregation of exfoliated MoS2 nanosheets. Optimization of the surfactant concentration in water led to highly concentrated MoS2 nanosheets (∼1.23 mg/ml in a single step) with an average lateral length (<L>) and number of layers (<N>) of ∼ 150 nm and ∼ 8 layers, respectively. Owing to its high concentration and few-layers, MoS2 nanosheets based aqueous dispersion was directly tested for aqueous lubricant applications. Compared to pure water, MoS2 nanosheets (0.1 wt%) in water led to effective reductions in the coefficient of friction and wear scar diameter of ∼ 75 % and ∼ 65 %, respectively. Wear depth ∼ 15 µm on SS ball is reduced to ∼ 1 µm when 0.1 wt% of MoS2 nanosheets-SM surfactant dispersion under similar testing conditions. Post-mortem analysis suggested that the stable formation of protective tribo-film on the worn surfaces of steel surface that were tested at different intervals (1-210-400 Days) leads to an effective sliding under load. To demonstrate the practicality of this dispersion, SM surfactant stabilized MoS2 nanosheets was used as a dielectric lubricant fluid in a wire EDM for advanced metal-cutting fluid applications.

Impact of the reductive deiodination on the sorption of iodinated X-ray contrast media to filter sand and activated carbon

Iodinated X-ray contrast media (ICM) and their aerobic transformation products (TPs) are widespread in the aquatic environment due to their persistent and mobile character. In a previous lab study, we have shown that the reductive (partial) deiodination of selected triiodobenzene derivatives increases the sorption to aquifer sand and loam soil, since iodine affects the compounds by steric hindrance, repulsive forces, resonance and inductive effects. These results suggest that the (partial) deiodination generally occurring to ICM and aerobic ICM TPs during anoxic/anaerobic bank filtration has a potential to increase their removal by sorption to natural sorbents. To basically assess the sorption potential to technically applied materials for drinking water treatment subsequent to bank filtration, we investigated the sorption of iopromide, diatrizoate and 5-amino-2,4,6-triiodoisophtalic acid and their di, mono and deiodinated structures to used filter sand from a waterworks and different fresh powdered activated carbons in batch tests using Berlin drinking water. The filter material, coated by iron and manganese oxides as well as organic material (including biofilm), preferentially removed monoiodinated derivatives, but diffusion through the organic layer heavily slowed the sorption. Therefore, the removal potential by sorption in rapid sand filters of waterworks for (partially) deiodinated benzene derivatives is suggested to be low. The deiodination of iopromide and diatrizoate significantly increased the sorption affinity to activated carbon and the competitiveness with regard to drinking water DOC. Despite the large atom radius of iodine, no clear correlation was found between the pore characteristics of the activated carbons and the molecular size of the compounds. This study emphasises the importance of anoxic/anaerobic conditions for the removal of persistent and mobile ICM and ICM TPs during drinking water treatment.

Enhancing proton transport in polyvinylidenedifluoride membranes and reducing biofouling for improved hydrogen production in microbial electrolysis cells

Hydrophilic porous membranes, exemplified by polyvinylidene fluoride (PVDF) membranes, have demonstrated significant potential for replacing ion exchange membranes in microbial electrolysis cells (MECs). Membrane fouling remains a major challenge in MECs, impeding proton transport and consequently limiting hydrogen production. This study aims to investigate a synergistic antifouling strategy for PVDF membrane through the incorporation of a coating composed of polydopamine (PDA), polyethyleneimine (PEI), and silver nanoparticles (AgNPs). The PDA-PEI-Ag@PVDF membrane not only effectively mitigates fouling through steric and electrostatic repulsion forces, but also amplifies ion transport by facilitating water diffusion and electromigration. The PDA-PEI-Ag@PVDF membrane exhibited a reduced membrane resistance of 1.01 mΩ m2 and PDA-PEI-Ag modifying PVDF membrane was found to be effective in enhancing the proton transportation of PVDF membrane. Therefore, the enhanced hydrogen production rate of 2.65 ± 0.02 m3/m3/d was achieved in PDA-PEI-Ag@PVDF-MECs.

Attractive and repulsive forces in a crystal of [Rb(18-crown-6)][SbCl6] under high pressure.

The compression behavior of [Rb(18-crown-6)][SbCl6] crystal under pressure up to 2.16 (3) GPa was investigated in a diamond anvil cell (DAC) using a mixture of pentane-isopentane (1:4) as the pressure-transmitting fluid. The compound crystallizes in trigonal space group R3 and no phase transition was observed in the indicated pressure range. The low value of pressure bulk modulus [9.1 (5) GPa] found in this crystal is a characteristic of soft materials with predominant dispersive and electrostatic interaction forces. The nonlinear relationship between unit-cell parameters under high pressure is attributed to the influence of reduced intermolecular H...Cl contacts under pressure over 0.73 GPa. It also explains the high compression efficiency of [Rb(18-crown-6)][SbCl6] crystals at relatively low pressures, resulting in a significant shift of the Rb atom to the center of the crown ether cavity. At pressures above 0.9 GPa, steric repulsion forces begin to play a remarkable role, since an increasing number of interatomic H...Cl and H...H contacts become shorter than the sum of their van der Waals (vdW) radii. Below 0.9 GPa, both unit-cell parameter dependences (P-a and P-c) exhibit hysteresis upon pressure release, demonstrating their influence on the disordered model of Rb atoms. The void reduction under pressure also demonstrates two linear sections with the inflection point at 0.9 GPa. Compression of the crystal is accompanied by a significant decrease in the volume of the voids, leading to the rapid approach of Rb atoms to the center of the crown ether cavity. For the Rb atom to penetrate into the center of the crown ether cavity in [Rb(18-crown-6)][SbCl6], it is necessary to apply a pressure of about 2.5 GPa to disrupt the balance of atomic forces in the crystal. This sample serves as a compression model demonstrating the influence of both attractive and repulsive forces on the change in unit-cell parameters under pressure.

Dispersing boron nitride nanosheets with carboxymethylated cellulose nanofibrils for strong and thermally conductive nanocomposite films with improved water-resistance

BNNS (boron nitride nanosheets)-CNF (cellulose nanofibrils) nanocomposite films have attracted increasing attention for advanced thermal management applications. However, the nanocomposite films reported so far generally suffer from unsatisfactory overall performance, especially for thermal conductivity and tensile strength. In this work, a nanocomposite film with excellent overall performance was prepared by using CCNF1.2 (carboxymethylated CNF with 1.2 mmol·g−1 carboxyl content) simultaneously as effective dispersant and reinforcement matrix for BNNS. The high aspect ratio of CCNF1.2 is primarily responsible for its excellent dispersion capability for BNNS, which provides strong steric hindrance repulsion force. Meanwhile, CCNF1.2 manifests the strongest hydrophobic-hydrophobic interactions with BNNS, and its carboxyl groups completely interact with the -OH of BNNS by hydrogen bonding. As a result, the BNNS-CCNF1.2 film (50 wt% BNNS) exhibits compacted aligned structure and superior comprehensive performance (125.0 MPa tensile strength, 17.3 W·m−1·K−1 in-plane thermal conductivity, and improved water resistance). This work demonstrates the effectiveness of CCNF in improving the overall performance of BNNS-CNF films and paves the way for their practical application in the advanced thermal management of next-generation electronic devices.

Super-swelling behavior of stacked lipid bilayer systems

Bilayer systems comprising lipid mixtures are the most well-studied model of biological membranes. While the plasma membrane of the cell is a single bilayer, many intra- and extra-cellular biomembranes comprise stacks of bilayers. Most bilayer stacks in nature are periodic, maintaining a precise water layer separation between bilayers. That equilibrium water separation is governed by multiple inter-bilayer forces and is highly responsive. Biomembranes re-configure inter-bilayer spacing in response to temperature, composition, or mass transport cues. In synthetic bilayer systems for applications in cosmetics or topical treatments, control of the hydration level is a critical design handle. Herein we investigate a binary lipid system that leverages key inter-bilayer forces leading to unprecedented levels of aqueous swelling while maintaining a coherent multilamellar form. We found that combining cationic lipids with bicontinuous cubic phase-forming lipids (lipids with positive Gaussian modulus), results in the stabilization of multilamellar phases against repulsive steric forces that typically lead to bilayer delamination at high degrees of swelling. Using ultra-small-angle X-ray scattering alongside confocal laser scanning microscopy, we characterized various super-swelled states of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and glycerol monooleate (GMO) lipids, as well as other analogous systems, at varied concentration and molar ratios. Through these experiments we established swelling profiles of various binary lipid systems that were near-linear with decreasing lipid volume fraction, showing maximum swelling with periodicity well above 200 nanometers.Graphical abstractConfocal fluorescence micrograph of super-swelled multilamellar structures in 90GMOD sample at 25 mM concentration. Inset plot shows intensity profile of orange line, with pink triangles indicating maxima.

Hard-Needle Elastomer in One Spatial Dimension

We perform exact statistical mechanics calculations for a system of elongated objects (hard needles) that are restricted to translate along a line and rotate within a plane, and that interact via both excluded-volume steric repulsion and harmonic elastic forces between neighbors. This system represents a one-dimensional model of a liquid crystal elastomer, and has a zero-tension critical point that we describe using the transfer-matrix method. In the absence of elastic interactions, we build on previous results by Kantor and Kardar, and find that the nematic order parameter Q decays linearly with tension $$\boldsymbol{\sigma}$$ . In the presence of elastic interactions, the system exhibits a standard universal scaling form, with $$\boldsymbol{Q / \vert \sigma \vert}$$ being a function of the rescaled elastic energy constant $$\boldsymbol{k / \vert \sigma \vert ^\Delta}$$ , where $$\boldsymbol \Delta$$ is a critical exponent equal to 2 for this model. At zero tension, simple scaling arguments lead to the asymptotic behavior $$\boldsymbol{Q \sim k^{1/\Delta }}$$ , which does not depend on the equilibrium distance of the springs in this model.

Elucidating the particle concentration-dependent flow behavior of aqueous TiO2 suspensions based on polymer dispersant structures and interparticle surface distances

Flowing behavior of concentrated aqueous TiO2 suspensions was evaluated in relation to the structure of polymeric dispersants, their adlayer thickness on particle surface, and particle concentrations. Comb-type polymeric dispersants comprising polyethylene glycol-based side chains with different combinations of unit number and side chain length were investigated. Based on particle concentration–apparent viscosity curves of the suspensions with TiO2 nanoparticles saturated with dispersants, maximum packing fraction and polymer adlayer thickness were estimated through the Krieger–Dougherty model. When the steric repulsive force of polymer dispersant dominated van der Waals attractive forces, the flow curves of the suspension exhibited hysteresis characteristics as the average particle surface distance approached the adlayer thickness of polymer dispersants. Additionally, by introducing the concept of relative surface distance, which is the average particle surface distance divided by the adlayer thickness, the particle concentration dependency of the suspension viscosities with different dispersants followed a unified trend.

Comparative study on effects of pH, electrolytes, and humic acid on the stability of acetic and polyacrylic acid coated magnetite nanoparticles

The poor colloidal stability of magnetite nanoparticles (MNPs) limits their mobility and application, so various organic coatings (OCs) were applied to MNPs. Here, a comparative study on the colloidal stability of MNPs coated with acetic (HAc) and polyacrylic acids (PAA) was conducted under varied pH (5.0–9.0) in the presence of different concentrations of cations and anions, as well as humic acid (HA). Comparing the effects of various cations and anions, the stability of both HAc/PAA-MNPs followed the order: Na+ > Ca2+and PO43− > SO42− > Cl−, which could be explained by their adsorption behaviors onto HAc/PAA-MNPs and the resulting surface charge changes. Under all conditions even with more anion adsorption onto HAc-MNPs (0.14–22.56 mg/g) than onto PAA-MNPs (0.04–18.34 mg/g), PAA-MNPs were more negatively charged than HAc-MNPs, as PAA has a lower pHIEP (2.6 ± 0.1) than that of HAc (3.7 ± 0.1). Neither the HAc nor PAA coatings were displaced by phosphate even at considerably high phosphate concentration. Compared with HAc-MNPs, the stability of PAA-MNPs was greatly improved under all studied conditions, which could be due to both stronger electrostatic and additional steric repulsion forces among PAA-MNPs. Besides, under all conditions, Derjaguin-Landau-Verwey-Overbeek (DLVO) explained well the aggregation kinetic of HAc-MNPs; while extended DLVO (EDLVO) successfully predict that of PAA-MNPs, indicating steric forces among PAA-MNPs. The aggregation of HAc/PAA-MNPs was all inhibited in varied electrolyte solutions by HA (2 mg C/L) addition. This study suggested that carboxyl coatings with higher molecular weights and pKa values could stabilize MNPs better due to stronger electrostatic and additional steric repulsion. However, in the presence of HA, these two forces were mainly controlled by adsorbed HA instead of the organic pre-coatings on MNPs.

Nanoengineering the Redispersibility of Cellulose Nanocrystals.

Enhancing the redispersibility of dried colloidal particles to yield stable dispersions after rehydration is a persistent challenge in the sustainable processing of nanocelluloses due to hydrogen bonding-induced irreversible aggregation. Programming nanocelluloses, such as cellulose nanocrystals (CNC), with moieties that enable colloidal repulsion after rehydration may address this challenge and contribute to the United Nation (UN)'s sustainable development goals (SDGs) of urban development and sustainable living (SDGs 9 and 11) and cradle-to-cradle processing (SDG 12). We hypothesize that imparting electrosteric repulsion to CNC via polyanionic disordered cellulose chains (hairs) protruding from each end may render the dried nanocrystals highly redispersible in aqueous media. Anionic hairy CNC (AHCNC), that is, CNC decorated with dicarboxylated cellulose (DCC) chains, were synthesized by the preferential, successive periodate/chlorite oxidation of the disordered regions of cellulose fibrils, bearing >5 mmol of carboxylate groups per gram. The colloidal properties of AHCNC were compared with those of sulfate half-ester group-functionalized CNC and TEMPO-oxidized CNC (TOCNC) after redispersion in aqueous media, followed by comparing the redispersibility of AHCNC and CNC in aqueous solutions containing monovalent or divalent cations and at varying pH. The AHCNC had remarkable aqueous redispersibility even at high ionic strengths and extreme pH. The unique redispersibility mechanism of dried AHCNC relies on the synergistic steric and electrostatic repulsion forces, recuperated upon the rehydration of DCC. This work may open new opportunities for more sustainable and cost-effective handling and processing of nanocelluloses.

Investigation of the Effect of Molecular Weight, Density, and Initiator Structure Size on the Repulsive Force between a PNIPAM Polymer Brush and Protein

This paper focuses on the effect of degree of polymerization (N), density ( σ ), and pattern size ( x ) on the interaction force between a periodically patterned Poly(N-isopropylacrylamide) (PNIPAM) brush and protein. The hydrophobic interaction, the Van der Waals attractive force, and the steric repulsive force were expressed in terms of N , σ , and x . The osmotic constant (k1) and the entropic constant (k2) were determined from the fit of the steric repulsive force to an experimentally obtained force distance curve. The osmotic constant was 0.105, and the entropic constant was 0.255. Using these constants, the steric repulsive force was plotted as a function of the separation distance(s) between the substrate and the protein. The forces were determined at a separation distance equal to 0.3 nm, where L0 is the equilibrium thickness of the PNIPAM brush. At this separation distance, the value of the steric repulsive force was much higher than the value of the sum of the hydrophobic interaction and the Van der Waals attractive force for large degree of polymerization ( N &gt; 100 ) and density ( σ &gt; 0.2 chains/nm2). However, the repulsive force was comparable to the sum of the hydrophobic interaction and the Van der Waals attractive force for a small degree of polymerization ( N &lt; 100 ) and density ( σ = 0.2 ). Furthermore, the steric repulsive force was plotted as a function of pattern size x . The plot indicated that the steric repulsive force becomes nearly zero for all degrees of polymerization and density when the value of the initiator structure size was less than 200 nm. In addition to the steric repulsive force, the lateral extension of the chains in the periodically patterned PNIPAM brush was calculated by scaling low and compared with the experimental data taken from previously published literatures. The polymer brush structure was modelled as if the immediate bare substrate is so wide that even a stretched polymer segment cannot reach to the next polymer brush structure. In such models, the value of the lateral extension was equal to the thickness of the homogenous brush. It was independent of the pattern size. However, when the polymer brush structure was modelled as if there is another polymer brush structure at a distance half of the size of the period, the lateral extension was found to be dependent on the size of the initiator structure size due to chain bridging. This was witnessed by the patterning of polymer brushes using the interferometric patterning of PNIPAM brushes and an atomic force microscopy imaging of the polymer brush structures both in air and in water. The polymer brush structure resolution in water was much lower than the resolution in air, which indicates the lateral extension of the polymer chains in water. For such kind of periodic polymer brush structures, the gap between them was calculated, and it was found dependent on the degree of polymerization, density, and initiator structure size.

Effects of soil colloids on the aggregation and degradation of engineered nanoparticles (Ti3C2Tx MXene)

Soil colloid is a nonnegligible factor when evaluating the environmental risk of engineered nanoparticles (ENPs) in the groundwater. In this study, the environmental fate of an emerging ENP (Ti3C2Tx MXene) in the groundwater was investigated for the first time, which currently poses a severe environmental risk due to its cytotoxicity but has received little attention. The colloidal dispersion stability and degradation kinetics of Ti3C2Tx MXene in the groundwater were evaluated by considering the effects of soil colloids prepared from sodium humate (SH), montmorillonite (MT), and a natural soil (NS) under variable solution chemistry. The results showed that the affinity of soil colloids with Ti3C2Tx followed an SH > MT > NS sequence. Increasing SH concentration led to Ti3C2Tx disaggregation by enhancing the electrical and steric repulsive forces, while MT and NS resulted in hetero-aggregation because of the elevated collision frequency. SH and MT enhanced the critical coagulation concentrations of Ti3C2Tx by 100 and 10 folders, respectively, via surface coating process, while NS slightly reduced due to the bridging effects induced by the soluble cations. The soil colloids promoted Ti3C2Tx degradation compared with their absence and in an SH > MT ≫ NS sequence. SH and MT were through forming Ti–O–C and Si–O–Ti bonds with Ti3C2Tx via their carboxyl and hydroxyl groups, respectively, rendering the Ti3C2Tx surface more reactive and faster degradation. NS showed a weak promotion effect because of its less affinity with Ti3C2Tx and limited organic matter and clay contents with hydroxyl and carboxyl groups. This study demonstrated the unstable environmental behaviors of Ti3C2Tx in the groundwater and mitigated its environmental risk concerns.

Regulation of nano-biological interface adhesion through grafted polymers

<p indent="0mm">The employment of grafted polymers to modulate the adhesion behavior of nano-biological interfaces has a wide range of applications in the field of biomedicine, and related research has important theoretical significance, thus gaining continuous attention. In this paper, the physicochemical mechanisms involved in the regulation of the adhesion behaviors of the nano-biological interface by grafted polymers are reviewed. There are two key challenges in the field of nanomedicine: Suppressing of immune responses and enhancing the drug retention at disease sites. In the both aspects, grafted polymers play an increasingly important role. By grafting polymers on the surface of nano-drugs, the random adhesion of small biomolecules can be suppressed, thereby decreasing the thickness of protein coronas, reducing the immune response, and prolonging the <italic>in vivo</italic> circulation time. Reduced adhesion also alleviates the dissipation of nano-drugs. In addition, grafted polymers can alter the surface mechanical property, endowing a moderate stiffness and altering collision behaviors, thus enhancing the transport efficiency and nano-drugs in physiological tissues and nano-drug retention at disease sites. The involved mechanisms in this paper are divided into two categories: Interfacial physics and interfacial chemistry. The former group mainly focuses on the microstructure and morphology, which can be adjusted through grafting density, grafting length, chain topology, etc. This paper focuses on two physical mechanisms closely related to the high entropy properties of grafted polymers: Entropic steric hindrance and chain segment dynamics. With increasing grafting density, the repulsive interactions between grafted chains increase, and the chains are stretched further resulting in a thicker grafting layer. Meanwhile, the conformation of grafting polymers experiences a mushroom-to-brush transition. In addition to less free volume, a higher grafting density also enhances chain stiffness, making biomolecules encounter a higher steric repulsive force when colliding with grafting polymer chains and thus less biomolecule adhesion. A high mobility of segmental chains also suppresses adhesion. According to this mechanism, increasing grafting density decreases segmental chain dynamics and promotes adhesion. The two mechanisms compete with increasing grafting density. Entropic steric hindrance dominates in low grafting density regime, while chain segment dynamic plays a larger role in high grafting density regime. A moderate high grafting density has maximal inhibiting ability on adhesion. The regulation of biomolecule adhesion based on interfacial physics combines structural and dynamical factors, and is usually nonspecific, although specific regulation is also possible. This group of mechanisms is independent of specific chemical groups, thus having a certain degree of universality. The mechanisms based on interfacial chemistry depend on special chemical groups, especially the hydrophilicity of functional groups. Most grafted polymers having good anti-fouling properties are hydrophilic, for example, polyethylene glycol (PEG). Hydrophilic functional groups promote the formation of hydrated surface layers, which inhibit biomolecule adhesion. PEG is the most widely used by now. However, its stability and anti-fouling ability are limited. By finding and modifying with appropriate chemical groups on the grafted chains, a better stability and stronger inhabitation of biomolecule adhesion can be achieved. On the other hand, through adjusting the temperature, light or pH dependence of chemical groups, the bio-adhesion of the grafting polymer layer can be dynamically tuned, realizing intelligent response to external stimuli and thus smart coating surfaces. This paper is expected to provide a reference for future fundamental theoretical research and advanced material development in this field.

Nano-SiO2 transport and retention in saturated porous medium: Influence of pH, ionic strength, and natural organics

Nano silica (nSiO2), induces potential harmful effects on the living environment and human health. It is well established that SiO2 facilitates the co-transport of a variety of other contaminants, including heavy metals and pesticides. The current study focused on the systematic evaluation of the effects of multiple physicochemical parameters such as pH (5, 7, and 9), ionic strength (10, 50, and 100 mM), and humic acid (0.1, 1, and 10 mg/L) on the transport and retention of nSiO2 in saturated porous medium. Additionally, the influent concentration of nSiO2 (10, 50, and 100 mg/L) was also varied. Our experimental findings indicate that the size of nSiO2 aggregates was directly related to the pH, ionic strength, HA, and particle concentration had a significant impact on the breakthrough curves (BTCs). The stability provided by the varying concentrations of pH and humic acid had a significant effect on the size of nSiO2 aggregates and transport (C/C0 > 0.7). The presence of a greater magnitude of negative charge on the surface of both nSiO2 and quartz sand resulted in less aggregation and enhanced flow of nSiO2 through the sand column. The Electrostatic and steric repulsion forces were the primary governing mechanisms in relation to the size of nSiO2 aggregates, affecting the single-collector efficiency and attachment efficiency, which determined the maximal transport of nSiO2. Conversely, a probable increase in Van der Waals force of attraction exacerbated the particle deposition and reduced their mobility for high ionic strength, and particle concentrations (C/C0 < 0.1). The formation of large nSiO2 aggregates, in particular, was principally responsible for the enhancement of nSiO2 retention in sand columns over a broad range of IS and particle concentration. The interaction energy profiles based on the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory were determined to understand the mechanism of nSiO2 deposition. Aditionally, all the experimental BTCs were mathematically simulated and justified by the colloidal filtration theory (CFT). Considering the environmental ramifications, the transport behavior of nSiO2 was further evaluated in various natural matrices such as river, lake, ground, and tap water. The nSiO2 suspended in the river, lake, and tap water had significantly higher mobility (C/C0 > 0.7), whereas groundwater indicated higher retention (C/C0 < 0.3). The study advances our collective knowledge of physicochemical and environmental parameters that can affect particle mobility.