Adsorption Regimes Research Articles

Molecular Structure and Conformation of Biodegradable Water-Soluble Polymers Control Adsorption and Transport in Model Soil Mineral Systems.

Water-soluble polymers (WSPs) are used in diverse applications, including agricultural formulations, that can result in the release of WSPs to soils. WSP biodegradability in soils is desirable to prevent long-term accumulation and potential associated adverse effects. In this work, we assessed adsorption of five candidate biodegradable WSPs with varying chemistry, charge, and polarity characteristics (i.e., dextran, diethylaminoethyl dextran, carboxymethyl dextran, polyethylene glycol monomethyl ether, and poly-l-lysine) and of one nonbiodegradable WSP (poly(acrylic acid)) to sand and iron oxide-coated sand particles that represent important soil minerals. Combined adsorption studies using solution-depletion measurements, direct surface adsorption techniques, and column transport experiments over varying solution pH and ionic strengths revealed electrostatics dominating interactions of charged WSPs with the sorbents as well as WSP conformations and packing densities in the adsorbed states. Hydrogen bonding controls adsorption of noncharged WSPs. Under transport in columns, WSP adsorption exhibited fast and slow kinetic adsorption regimes with time scales of minutes to hours. Slow adsorption kinetics in soil may lead to enhanced transport but also shorter lifetimes of biodegradable WSPs, assuming more rapid biodegradation when dissolved than adsorbed. This work establishes a basis for understanding the coupled adsorption and biodegradation dynamics of biodegradable WSPs in agricultural soils.

Adsorption and activation of small molecules on boron nitride catalysts.

Hexagonal boron nitride possesses a unique layered structure, high specific surface area and similar electronic properties as graphene, which makes it not only a promising catalyst support, but also a highly effective metal-free catalyst in the booming field of green chemistry. Reactions involving small molecules (e.g., oxygen, low carbon alkanes, nitrogen and carbon dioxide) have always been a hot topic in catalytic research, especially associated with the adsorption and activation regime of different forms of small molecules on catalysts. In this review, we have investigated the adsorption of different small molecules and the relevant activation mechanisms of four typical chemical bonds (OO, C-H, NN, CO) on hexagonal boron nitride. Recent progress on approaches adopted to enhance the activation capacity such as doping, defect engineering and heterostructuring are summarized, highlighting the potential applications of nonmetallic hexagonal boron nitride catalysts in various reactions. This comprehensive investigation offers a reference point for the enhanced mechanistic understanding and future design of effective and sustainable catalytic systems based on boron nitride.

Engineering of Silica Mesoporous Materials for CO2 Adsorption.

Adsorption methods for CO2 capture are characterized by high selectivity and low energy consumption. Therefore, the engineering of solid supports for efficient CO2 adsorption attracts research attention. Modification of mesoporous silica materials with tailor-made organic molecules can greatly improve silica's performance in CO2 capture and separation. In that context, a new derivative of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, possessing an electron-rich condensed aromatic structure and also known for its anti-oxidative properties, was synthesized and applied as a modifying agent of 2D SBA-15, 3D SBA-16, and KIT-6 silicates. The physicochemical properties of the initial and modified materials were studied using nitrogen physisorption and temperature-gravimetric analysis. The adsorption capacity of CO2 was measured in a dynamic CO2 adsorption regime. The three modified materials displayed a higher capacity for CO2 adsorption than the initial ones. Among the studied sorbents, the modified mesoporous SBA-15 silica showed the highest adsorption capacity for CO2 (3.9 mmol/g). In the presence of 1 vol.% water vapor, the adsorption capacities of the modified materials were enhanced. Total CO2 desorption from the modified materials was achieved at 80 °C. The obtained silica materials displayed stable performance in five CO2 adsorption/desorption cycles. The experimental data can be appropriately described by the Yoon-Nelson kinetic model.

Pore-scale study of dynamic adsorption of a water-soluble catalyst during drainage displacement in porous media using lattice Boltzmann simulations

This paper presents the first systematic pore-scale study of the dynamic adsorption of a water-soluble catalyst during two-phase flows of immiscible fluids (water and oil) in porous media. The results of this paper are based on mathematical modeling in two-dimensional synthetic porous structures using the lattice Boltzmann simulations for two-phase flow and convective-diffusive transport of catalyst dissolved in a water that cannot penetrate the oil. The results showed that an increase in oil viscosity tends to a decrease in the maximum adsorbed amount of catalyst measured in a quasi-stationary state. An increase in capillary number, on the contrary, promotes an increase in the adsorbed amount. In this paper, for the first time, we have characterized the dynamic adsorption regimes versus the adsorption rate constant and capillary number. At a low adsorption rate, the adsorbed amount is determined by the duration of the reaction between the catalyst and the adsorbent particles, while at a high adsorption rate, the adsorbed amount is controlled by the maximum adsorption value. In addition, it has been established that a prediction accuracy of the adsorbed amount deteriorates significantly with decreasing capillary number.

Transport of double-stranded ribonucleic acids (dsRNA) and deoxyribonucleic acids (DNA) in sand and iron oxide-coated sand columns under varying solution chemistries.

Assessing ecological risks associated with the use of genetically modified RNA interference crops demands an understanding of the fate of crop-released insecticidal double-stranded RNA (dsRNA) molecules in soils. We studied the adsorption of one dsRNA and two double-stranded DNA as model nucleic acids (NAs) during transport through sand- and iron oxide-coated sand (IOCS)-filled columns over a range of solution pH and ionic compositions. Consistent with NA-sand electrostatic repulsion, we observed only slight retention of NAs in sand columns. Conversely, pronounced NA retention in IOCS columns is consistent with strong and irreversible NA adsorption involving electrostatic attraction to and inner-sphere complex formation of NAs with iron oxide coatings. Adsorption of NAs to iron oxides revealed a fast and a slow kinetic adsorption regime, possibly caused by the excluded-area effect. Adsorption of NAs to sand and IOCS increased in the presence of dissolved Mg2+ and with increasing ionic strength, reflecting cation-bridging and screening of repulsive electrostatics, respectively. The co-solute phosphate and a pre-adsorbed dissolved organic matter isolate competitively suppressed dsRNA adsorption to IOCS. Similar adsorption characteristics of dsRNA and similarly sized DNA suggest that existing information on DNA adsorption to soil particles helps in predicting adsorption and fate of dsRNA molecules in soils.

Molecular Engineering of Silicon Phthalocyanine to Improve the Charge Transport and Ammonia Sensing Properties of Organic Heterojunction Gas Sensors

AbstractNovel organic heterostructures fabricated with a bilayer consisting of an axially substituted silicon phthalocyanine (R2‐SiPc) derivative and lutetium bis‐phthalocyanine (LuPc2) are investigated for their ammonia sensing properties. Surface and microstructure characterization of the heterostructure films reveal either compact or highly porous surface topography in (345F)2‐SiPc and Cl2‐SiPc‐based heterostructures, while electrical characterization reveals a strong influence of the axial substituent in R2‐SiPc on NH3 sensing capabilities. Electrical characterization further demonstrates an apparent energy barrier for interfacial charge transport, which is higher in the (345F)2‐SiPc/LuPc2 heterojunction device. In‐depth charge transport studies by impedance spectroscopy further reveal a resistive interface in (345F)2‐SiPc/LuPc2 and faster bulk and interfacial charge transport in Cl2‐SiPc/LuPc2 heterojunction devices. Different interfacial charge transport capabilities and surface topographies affect NH3 sensing properties of the two heterojunction devices, in which (345F)2‐SiPc/LuPc2 reveals a fast and non‐linear response with a limit of detection (LOD) of 310 ppb, while Cl2‐SiPc/LuPc2 exhibits a slow, and linear response to NH3 with LOD of 100 ppb. Finally, different metrological parameters of the two sensors are correlated to the respective gas‐material interactions, in which adsorption and diffusion regimes are modulated by the surface topography and hydrophobicity of the sensing layer.

Atmospheric microplastics and nanoplastics as vectors of primary air pollutants - A theoretical study on the polyethylene terephthalate (PET) case

Polyethylene terephthalate (PET) microplastics and nanoplastics are ubiquitously present in the atmosphere as atmospheric and airborne forms (PET-aMPs). Using first-principles calculations, we analyze the uptake of primary air pollutants onto PET-aMPs, focusing on their stabilities, adsorption mechanisms, and thermochemistry. The results show that PET-aMPs are selective for the spontaneous adsorption of CO, CO2, NO, N2O, NO2, NH3, and SO2, reaching stable adsorption energies of 6–20 kcal/mol per molecule, with comparable uptake ability than carbon-based materials, metals/metalloids, and metal oxide surfaces. Then, PET-aMPs become a vector for coexisting air pollutants in the atmosphere, which adsorb by inner or outer adsorption depending on the molecular polarity (dipole moment) and atomic constitution (electronegativity) of gaseous molecules. Also, atmospheric H2O and O2 are not competitive molecules, and ozone could enhance adsorption due to surface oxidation and structure breakdown. The interplay of electrostatic (46–61%) and dispersion forces (21–58%) drives the adsorption mechanism, where low-polar pollutants display almost a balanced electrostatic vs. dispersion contribution, while high polar molecules display a higher electrostatic stabilization. The outer adsorption is reached by strong dispersion, hydrogen bonding, and dipole-dipole-induced pairs, while lone-pair-π interactions appear in the inner adsorption regime. These results expand the understanding of the hazards and risks of atmospheric and airborne microplastics/nanoplastics, their impacts, co-transport ability, and interaction with the environment.

Characterization of dynamic adsorption regimes in synthetic and natural porous structures using lattice Boltzmann simulations

This paper presents the first systematic study on the characterization of dynamic adsorption regimes of gas in porous media using the ratio of inter- to intraparticle diffusion coefficients. The effect of the ratio between the two diffusion coefficients on the adsorption dynamics was investigated in combination with the adsorbent particles size and the disorder parameter, which numerically describes pore space heterogeneity, by mathematical modelling using the lattice Boltzmann simulations for fluid flow and the convective-diffusive transport of an adsorbate dissolved in a fluid. To characterize the dynamic adsorption regimes, for the first time, a relationship between the surface and total adsorption amount was used. The obtained results during simulations in two-dimensional synthetic porous structures showed that the size of the adsorbent particle strongly affects the surface and the total adsorption dynamics. An increase in the particle size promotes an increase in the rate of surface adsorption. Depending on the ratio of inter- to intraparticle diffusion coefficients, increasing particle size promotes either an acceleration or slowdown of the total adsorption dynamics. The results revealed in two-dimensional structures were verified by simulations in three-dimensional digital models of natural sandstones, which were obtained using X-ray computed tomography.

Adsorption of the Polymer on a Clay Matrix : Theoretical Study

Adsorption of polymers is a phenomenon of great importance in a number of areas of our daily life. However, understanding this phenomenon is essential. This work focuses on the theoretical study of the polyethylene glycol (PEG) adsorption phenomenon on thenatural clay-layer surface. Clay is considered as a matrix. Different adsorption regimes have been presented. The expressions of the surface coverage ratio as a function of the volume fraction of monomer for each regime were calculated. A strong adsorption was noted for the first two regimes (dilute surface, and bidimensional semi-dilute surface) confirmed by the exponential term. When the surface becomes saturated, we are in the plateau regime for which the adsorption varies logarithmically, due to the occupation of most of the sites available on the clay-layer surface. Finally, we presented the variation of the volume fraction as a function of 𝑧(axis perpendicular to the surface), we have shown that a layer of polyethylene glycol (PEG) adsorbed on a natural clay-layer surface is composed of three zones (proximal, central and distal) with different volume fractions.

MIL-100(Fe)@GO composites with superior adsorptive removal of cationic and anionic dyes from aqueous solutions

The separation of synthetic dyes from industrial wastewaters is an important objective in addressing water pollution. The removal of pollutant dyes from industrial wastewater prior to its release into the environment is an essential task; thus, synthesizing new adsorbent materials with superior adsorption efficiency is an important undertaking. Herein, we report the synthesis of MIL-100(Fe)@GO (graphene oxide) composites exhibiting superior adsorption performance toward methyl orange (MO), Congo red (CR), methylene blue (MB), and acid chrome blue K (AC). The room-temperature adsorption capacities of MIL-100(Fe)@GO-1 for these dyes were 533.7 (MB), 760.1 (MO), 1386.3 (AC), and 1786.6 (CR) mg g–1, exceeding those values previously reported for pristine MIL-100(Fe) by 31.1%, 17.8%, 54.8%, and 8.9%, respectively. The adsorption behavior of the composites can be described on the basis of the structural and morphological characteristics and zeta potential of MIL-100(Fe)@GO and the adsorption capacity and structural characteristics of the dyes. The adsorption uptakes of MIL-100(Fe)@GO toward the pollutant dyes was controlled by the synergistic effects of the hydrogen-bonding, hydrophobic interactions, and π–π interactions and agglomeration pores of MIL-100(Fe)@GO. The obtained results revealed that the synergetic interplay of electrostatic, hydrogen-bonding, π–π, and hydrophobic interactions and adsorption space led to two distinct adsorption regimes for MO and AC depending on the adsorbate concentration.

CO2 Adsorption on the N- and P-Modified Mesoporous Silicas.

SBA-15 and MCM-48 mesoporous silicas were modified with functionalized (3-aminopropyl)triethoxysilane (APTES) by using the post-synthesis method, thus introducing N- and P-containing groups to the pore surface. The structure of the newly synthesized modifiers (aldimine and aminophosphonate derivatives of (3-aminopropyl)triethoxysilane and their grafting onto the porous matrix were proved by applying multinuclear NMR and FTIR spectroscopies. The content of the grafted functional groups was determined via thermogravimetric analysis. The physicochemical properties of the adsorbent samples were studied by nitrogen physisorption and UV–Vis spectroscopy. The adsorption capacity of CO2 was measured in a dynamic CO2 adsorption regime. The modified silicas displayed an enhanced adsorption capacity compared to the initial material. The 13C NMR spectra with high-power proton decoupling proved the presence of physically captured CO2. A value of 4.60 mmol/g was achieved for the MCM-48 material grafted with the Schiff base residues. The total CO2 desorption was achieved at 40 °C. A slight decrease of about 5% in CO2 adsorption capacities was registered for the modified silicas in three adsorption/desorption cycles, indicating their performance stability.

Adsorption kinetics, mechanistic, isotherm and thermodynamics study of petroleum produced water coagulation using novel Egeria radiate shell extract (ERSE)

BackgroundThe mechanistic and adsorptive component of petroleum produced water (PPW) coagulation has been studied, using novel Egeria radiata shell extract (ERSE). MethodsPhysiochemical and instrumental characterization of the precursor (Egeria Radiata Shell, ERS) and bio-coagulant were studied. Effects of process parameters on treatment efficiency and rate-determining step for the particles decontamination were investigated. The coag-flocculation data obtained were analyzed in the light of adsorption kinetics, mechanistic modeling, isotherm and thermodynamics studies. Significant findingsEvidenced results from the characterization showed that extracted coagulant (ERSE) possessed significant properties required to drive surface phenomenon process. Surface morphology and thermo-gram profile revealed significant porosity and thermal stability, respectively for ERSE. The highest adsorption capacity of 2068.132 ​mg/g was obtained at 5 ​g/L, 30 ​min, pH 4 and 45 ​°C. The adsorption regime was spontaneous, physically predominated and best described by the pseudo second order kinetic and Langmuir isotherm models. The thermodynamic analysis confirmed the process to be endothermic and entropy driven. High grade ERSE successfully demonstrated adequate treatment of the PPW at 90.9% efficiency, while maintaining significant influence of adsorption on the coagulation process. Moreover, the total cost of treating 1 ​L of PPW (involving material cost and electricity) was determined to be 3.8 $. Also, the costs of ERSE optimal dosage of 5 ​g/L preparation and energy are 0.3 and 3.5 $, respectively. Summarily, ERSE can be applied in effective decontamination of PWW.

Fracture-Matrix Modeling Technique Unlocks CO2 Enhanced Shale Gas Recovery

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202222, “Fracture-Matrix Modeling of CO2 Enhanced Shale Gas Recovery in Compressible Shale,” by Dhruvit Satishchandra Berawala, SPE, Equinor, and Pål Østebø Andersen, University of Stavanger. The paper has not been peer reviewed. With technology available at the time of writing, only 3–10% of gas from tight shale is recovered economically through natural depletion, demonstrating a significant potential for enhanced shale gas recovery (ESGR). Experimental studies have demonstrated that shale kerogen/organic matter has a higher adsorption affinity for carbon dioxide (CO2) than methane (CH4). CO2 is preferentially adsorbed over CH4 with a ratio of as much as 5:1. The complete paper examines CO2 ESGR in compressible shale during huff ’n’ puff injection to understand better the parameters controlling its feasibility and effectiveness. The authors present a mathematical model in the complete paper in which the CO2/CH4 substitution mechanism is implemented in an injection/production setting representative of field implementation. Introduction Modeling of CO2 injection and the interplay between CO2 and CH4 sorption has been extremely challenging for scientists and engineers. The presence of CO2 with methane during the CO2 ESGR process makes gas-desorption behavior and measurement more difficult. Few researchers have evaluated the efficiency of CO2 ESGR in compressible shale. To improve the understanding of this technique, the authors present a numerical modeling approach using a 1D+1D fracture-matrix model in order to study the feasibility of CO2 injection in shale formations. The model consists of a high-permeability fracture extending from a well perforation, symmetrically surrounded by a shale matrix as shown in Fig. 1 of the complete paper. The fracture is assumed to have fixed width for simplicity. The system is assumed to consist of free gas in the pores as well as adsorbed gas in the matrix. When pressure in the well is reduced, free and adsorbed gas from the matrix flows toward the fracture and then to the well. The pressure-based advective forces, along with concentration-based diffusive forces, are considered the main transport mechanisms in this work. After the CH4 production cycle, CO2 is injected from the same well into the fracture and to the matrix. Injection of CO2 leads to an increase in total gas pressure in the system. CH4/CO2 adsorption kinetics are modeled using a multicomponent adsorption isotherm presented in earlier works by the authors. Apparent permeability is used to account for gas slippage effect, effective stress, adsorption, and other flow regimes relevant to the nanopore structure of the shale formation. The effect that compressible rock has on the porosity and apparent permeability changes with CH4 production. CO2 injection also is considered. The resulting model is composed of nonlinear partial differential equations that are solved numerically using an operator splitting approach. The geometry, mole conservation, pressure-dependent parameters, and initial and boundary conditions of the mathematical model are detailed in the complete paper, including mathematical definitions and solution procedures in its appendix.

RNA Secondary Structures Regulate Adsorption of Fragments onto Flat Substrates.

RNA is a functionally rich molecule with multilevel, hierarchical structures whose role in the adsorption to molecular substrates is only beginning to be elucidated. Here, we introduce a multiscale simulation approach that combines a tractable coarse-grained RNA structural model with an interaction potential of a structureless flat adsorbing substrate. Within this approach, we study the specific role of stem-hairpin and multibranch RNA secondary structure motifs on its adsorption phenomenology. Our findings identify a dual regime of adsorption for short RNA fragments with and without the secondary structure and underline the adsorption efficiency in both cases as a function of the surface interaction strength. The observed behavior results from an interplay between the number of contacts formed at the surface and the conformational entropy of the RNA molecule. The adsorption phenomenology of RNA seems to persist also for much longer RNAs as qualitatively observed by comparing the trends of our simulations with a theoretical approach based on an ideal semiflexible polymer chain.

Kinetics of transfer of volatile amphiphiles (fragrances) from vapors to aqueous drops and vice versa: Interplay of diffusion and barrier mechanisms

Subject of this work is to investigate the kinetics of mass transfer of volatile amphiphiles from their vapors to aqueous drops, and from the saturated aqueous drop solutions to air. The used amphiphiles are benzyl acetate, linalool, and citronellol, all of which have low saturated vapor pressures, appreciable solubility in water, and well pronounced surface activity. The adequate theoretical processing of the equilibrium surface tension, σ, isotherms is applied to construct the two-dimensional equation of state, which relates σ to the adsorption, Γ, at the interface. The measured surface tension relaxations with time t in the regimes of adsorption from vapor and evaporation from drop combined with the equations of state provide quantitative information on the change of adsorption because of the volatile amphiphile mass transfer across the surface. The theoretical analysis of the diffusion and barrier mechanisms in the case of adsorption from vapor to the aqueous drop shows that the mixed barrier-diffusion control in the vapor and diffusion control in the drop describe experimental data. The obtained values of the adsorption rate constants are six orders of magnitude larger than those for hexane and cyclohexane reported in the literature. The regime of evaporation from aqueous amphiphile solution drop follows the convection-enhanced adsorption mechanism with desorption rate constant in the vapor affected by the simultaneous water evaporation and amphiphile desorption. The water evaporation suppresses the evaporation of linalool and accelerates desorption of benzyl acetate and citronellol. From viewpoint of applications, the obtained physicochemical parameters of the studied three fragrances can help for better understanding of their performance in shampoo systems and perfumes. From theoretical viewpoint, the result show that by introducing an effective amphiphile desorption rate constant it is possible to quantify the complex volatile amphiphile desorption accompanied with the water evaporation.

Theoretical study of small aromatic molecules adsorbed in pristine and functionalised graphene

Small aromatic molecules are precursors for several biological systems such as DNA, proteins, drugs, and are also present in several pollutants. The understanding of the interaction of these small aromatic molecules with pristine and functionalised graphene (fGr) can generate different applications. We performed ab initio simulations based on the density functional theory to evaluate the interaction between the aromatic compounds, benzene, benzoic acid, aniline and phenol, with pristine and fGr. The results show that the binding energy for all cases is less than 103.24kJ/mol (1.07eV) without substantial modification of the electronic properties, indicating that the interaction occurs through a physical adsorption regime. The results are promising because they suggest that pristine graphene and functionalised graphene are suitable for removing these pollutants, or for carrying molecules for biological applications influenced by π-π and H-bonds interaction.

Adsorption and desorption of Thallium(I) in soils: The predominant contribution by clay minerals

Thallium (Tl) is a highly toxic environmental contaminant. To understand the mechanism controlling the mobility and availability of Tl in soil, the adsorption and desorption of Tl(I) were evaluated for six soils. The maximum Tl adsorption capacities of the soils ranged from 6.9 to 244.5 mmol kg−1. The corresponding Tl LIII-edge X-ray absorption near-edge structure (XANES) data revealed that illite, vermiculite, and smectite are the preferential soil constituents for adsorbing Tl(I). Tl(I) adsorption by the soils was reversible in the low Tl adsorption regime and exhibited various degrees of hysteresis as the amount of absorbed Tl increased. The Tl(I) adsorption and extent of adsorption reversibility were mainly dependent on the type and content of clay minerals and exchangeable cations in different soils. Despite high Tl(I) adsorption by the soils, the reversibility of Tl(I) adsorption may result in relatively high mobility and availability of Tl(I) in soils, leading to high environmental risk. Ignoring the reversibility of Tl adsorption could lead to an erroneous prediction of the mobility and availability of Tl in soils and a significant underestimation of the environmental risk posed by Tl in the environment.

Low-fouling properties in serum of carboxylic-oligo(ethylene glycol)-based interfaces

In the present work we evaluated the low-fouling feature of a carboxylic-oligo(ethylene glycol) self-assembled monolayer (carboxylic-OEG-SAM) interface using a quartz crystal microbalance with dissipation monitoring (QCM-D). QCM-D measurements allowed us to estimate the amount of protein loading in two different serum dilutions at two different interfaces: bare gold and carboxylic-OEG. The observed amount of protein adsorbed onto bare gold is about twice higher that of carboxylic OEG interface, confirming the low-fouling characteristics of OEG-modified surfaces. Additionally, QCM-D results demonstrated the existence of two protein adsorption regimes, a faster and a slower, with distinct dissipation energies which was modelled by a two-step kinetic model. The faster regime was attributed to the adsorption of proteins into free sites of the carboxylic-OEG-SAM in a rigid binding process, followed by a slower and more viscoelastic adsorption process ascribed to structural conformational changes; this slower step conforms with the filling of remaining free sites associated with the steric hindrance in which protein-protein interactions defines the slower rate constant for the adsorption.

Swelling pressure of compacted expansive soil over a wide suction range

A series of wetting experiments was performed on a compacted expansive clay to evaluate the swelling pressure generated over a wide suction range. Both osmotic and vapor equilibrium techniques were introduced and implemented to apply the suction required in the swelling pressure measurements. It is shown that, associated with the evolution of the microstructure of soil during wetting, the development of swelling pressure with decreasing suction is nonmonotonic. The soil water retention characteristics were independent of dry density at high suction in the adsorption regime, and a threshold suction was identified to distinguish adsorbed and capillary waters. The development of swelling pressure was closely related to the water retention characteristics. At high suction, the swelling pressure stems mainly from interlayer hydration; at low suction, however, the swelling pressure was controlled by the development of double layers, accompanied by the collapse of some macropores. The nuclear magnetic resonance (NMR) technique was introduced to determine the specific amount of adsorbed and capillary water contents, shedding new insights into the swelling behavior of compacted expansive soil during the wetting process under confined conditions.

Brush Conformation of Polyethylene Glycol Determines the Stealth Effect of Nanocarriers in the Low Protein Adsorption Regime

For nanocarriers with low protein affinity, we show that the interaction of nanocarriers with cells is mainly affected by the density, the molecular weight, and the conformation of polyethylene glycol (PEG) chains bound to the nanocarrier surface. We achieve a reduction of nonspecific uptake of ovalbumin nanocarriers by dendritic cells using densely packed PEG chains with a “brush” conformation instead of the collapsed “mushroom” conformation. We also control to a minor extent the dysopsonin adsorption by tailoring the conformation of attached PEG on the nanocarriers. The brush conformation of PEG leads to a stealth behavior of the nanocarriers with inhibited uptake by phagocytic cells, which is a prerequisite for successful in vivo translation of nanomedicine to achieve long blood circulation and targeted delivery. We can clearly correlate the brush conformation of PEG with inhibited phagocytic uptake of the nanocarriers. This study shows that, in addition to the surface’s chemistry, the conformation of polymers controls cellular interactions of the nanocarriers.