Modification Of Surface Properties Research Articles

An innovative process chain for the production of antibiofouling polymer parts using ultrafast laser texturing

Polymers are versatile materials widely used in various industries, with significant applications in biomedicine where biofouling on polymer surfaces presents major health and economic challenges. Biofouling, initiated by bacterial adhesion, can be mitigated by modifying surface properties through laser micro- and nano-texturing, an approach that offers advantages over chemical treatments. This study introduces an economical mass production process for textured polymeric components using injection molding to replicate hierarchical textures. Testing revealed that all textured samples significantly reduced bacterial adhesion compared to untextured surfaces across different designs and bacteria types after 24 h of culture. The study examined factors like wettability, nanoscale roughness, and pattern dimensions to explain these outcomes, comparing them with existing studies. Despite all textured samples showing decreased wettability and roughness, these factors alone did not ensure reduced bacterial adhesion. The most effective anti-adhesive performance was observed in surfaces with parallel ridge patterns, which segmented the surface into isolated areas that limited bacterial interaction and hindered micro-colony formation, highlighting the importance of specific surface patterning in combating biofouling.

Inhaled Nanoparticulate Systems: Composition, Manufacture and Aerosol Delivery.

An increasing growth in nanotechnology is evident from the growing number of products approved in the past decade. Nanotechnology can be used in the effective treatment of several pulmonary diseases by developing therapies that are delivered in a targeted manner to select lung regions based on the disease state. Acute or chronic pulmonary disorders can benefit from this type of therapy, including respiratory distress syndrome (RDS), chronic obstructive pulmonary disease (COPD), asthma, pulmonary infections (e.g. tuberculosis, Yersinia pestis infection, fungal infections, bacterial infections, and viral infections), lung cancer, cystic fibrosis (CF), pulmonary fibrosis, and pulmonary arterial hypertension. Modification of size and surface property renders nanoparticles to be targeted to specific sites, which can serve a vital role in innovative pulmonary drug delivery. The nanocarrier type chosen depends on the intended purpose of the formulation and intended physiological target. Liquid nanocarriers and solid-state nanocarriers can carry hydrophilic and hydrophobic drugs (e.g. small molecular weight drug molecules, large molecular weight drugs, peptide drugs, and macromolecular biological drugs), while surface modification with polymer can provide cellular targeting, controlled drug release, and/or evasion of phagocytosis by immune cells, depending on the polymer type. Polymeric nanocarriers have versatile architectures, such as linear, branched, and dendritic forms. In addition to the colloidal dispersion liquid state, the various types of nanoparticles can be formulated into the solid state, offering important unique advantages in formulation versatility and enhanced stability of the final product. This chapter describes the different types of nanocarriers, types of inhalation aerosol device platforms, liquid aerosols, respirable powders, and particle engineering design technologies for inhalation aerosols.

Efficient removal of plasticiser dibutyl phthalate on CoP cluster anchored MXene via boosting peroxymonosulfate activation: Catalytic performance and decomposition mechanism

A novel Ti3C2 synthesis method via strong alkaline etching (MXeneba) was developed to degrade dibutyl phthalate (DBP) using a CoP/MXeneba + peroxymonosulfate (PMS) system. The MXeneba's modified surface properties enabled stable Co2+ adsorption and homogeneous loading of ultrasmall CoP clusters post-phosphatisation. Complete DBP degradation was achieved within 30 min, facilitated by reactive oxygen species (ROS: SO4·-, ·OH, O2·-, and 1O2) and the highly reduced titanium atoms promoting Co3+ to Co2+ conversion. Density functional theory (DFT) calculations elucidated PMS adsorption sites and active species for DBP degradation. This study clarifies the activation mechanism, linking catalyst structure to performance, and provides insights for future advanced oxidation processes in environmental remediation. The findings emphasize the practical application and significance of the CoP/MXeneba catalyst in treating harmful plasticisers in water, contributing to efficient and sustainable water purification methods. The research also highlights this novel catalyst system's robustness and versatility in tackling diverse pollutants.

Durable and dense zwitterionic polymer brushes initiated from surface-segregated cyclic initiator via atom transfer radical polymerization

Immobilization of initiators on a polymer surface for surface-initiated polymerization has primarily been achieved via covalent bonds. However, this approach is subject to limitations, such as the requirement for additional processing steps and different customized methods tailored to the specific characteristics of each polymer. In this study, initiator immobilization was achieved by surface segregation, a phenomenon observed in polymer blends wherein one component spontaneously enriches the surface, thereby enabling the modification of surface properties. Specifically, we designed cyclic oligomers containing an atom transfer radical polymerization (ATRP) initiator. The enhanced performance of surface segregation mediated by the cyclic topology was evaluated, along with the surface-initiated polymerization initiated by the surface-segregated oligomer. The kinetics of the ATRP reaction for the cyclic initiators were investigated, and the zwitterion polymer brush density was also calculated. The robustness of the brushes was evaluated through leaching tests, which revealed no notable alterations before and after the assessments. The antifouling effect of the brushes was confirmed through protein adsorption, platelet adhesion, bacterial attachment, and whole-blood circulation experiments. These antifouling examinations demonstrated reduced substance attachment of zwitterionic polymer brushes. Lastly, experiments on optimizing the ATRP catalyst loading during the surface-initiated ATRP were conducted. The excellent performance of the cyclic initiators is expected to provide new insights and opportunities in the field of surface-initiated polymerization. Moreover, the formation of zwitterion brushes via cyclic initiators holds promise for versatile applications in the field of long-term utilization in biointerfaces, offering a wide range of potential uses.

Boosting catalytic performance of Amberlyst‐15 by modulating surface properties for synthesis of 5-hydroxymethylfurfural from high-concentration fructose

The large-scale production of 5-hydroxymethylfurfural (HMF), a “sleeping giant” in sustainable chemistry, is frequently hampered by the severe formation of humins during the acid-catalyzed dehydration of high-concentration fructose. In this work, we demonstrate that the HMF yield could be remarkably enhanced by boosting the catalytic performance of a commercially used Amberlyst-15 solid acid organocatalyst, wherein the formation of humins could be effectively inhibited. We show that the modification of Amberlyst-15 with a typical cationic surfactant (i.e., cetyltrimethylammonium bromide (CTAB)) via charge interaction between sulfonic acid groups and quaternary ammonium cations led to an improved surface hydrophobicity and a reduced Brønsted acid density on the modified catalyst, thereby contributing to a complete suppression of HMF rehydration and remarkable suppression of humin formation via paths of both etherification-dehydration-condensation and degradative-condensation of fructose and/or HMF. As a result, the catalytic conversion of fructose over the CTAB-modified Amberlyst-15 catalyst in a low-boiling mixed solvent composed of 1,4-dioxane and H2O at 140 °C within 2 h led to high HMF yields in range of 53.3 ∼ 63.1 mol% in converting high-concentration fructose (10.0 ∼ 50.0 wt%), wherein an average enhancement of 20 mol% in product yield was achieved when compared with that over un-modified Amberlyst-15. Moreover, the adsorption of humins on solid catalyst was significantly reduced due to the enhanced surface hydrophobicity and alleviated formation of humins, which accounted for a stable catalytic performance of the modified Amberlyst-15 catalyst for at least five runs. This work highlights the rational adjustment of the surface wettability of a commercial solid acid catalyst to suppress the undesired humin formation for future HMF biorefinery.

Development of a molecularly imprinted polymer-based electrochemical sensor with metal-organic frameworks for monitoring the antineoplastic drug vismodegib

A novel and robust electrochemical sensing tool for the determination of vismodegib (VIS), an anticancer drug, has been developed by integrating the selective recognition capabilities of molecularly imprinted polymer (MIP) and the sensitivity enhancement capability of metal-organic framework (MOF). Prior to this step, the electrochemical behavior of VIS was investigated using a bare glassy carbon electrode (GCE). It was observed that in 0.5 M H2SO4 solution as electrolyte, VIS has an oxidation peak around 1.3 V and the oxidation mechanism is diffusion controlled. The determination of VIS in a standard solution using a bare GCE showed a linear response in the concentration range from 2.5 μM to 100 μM, with a limit of detection (LOD) of 0.75 μM. Since sufficient sensitivity and selectivity could not be achieved with bare GCE, a MIP sensor was developed in the next step of the study. For this purpose, the GCE surface was first modified by drop casting with as-synthesized Co-MOF. Subsequently, a MIP network was synthesized via a thermal polymerization approach using 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as monomer and VIS as template. MOFs are ideal electrode materials due to their controllable and diverse morphologies and modifiable surface properties. These characteristics enable the development of MIPs with more homogeneous binding sites and high affinity for target molecules. Integrating MOFs could help the performance of sensors with the desired stability and reproducibility. Electrochemical analysis revealed an observable enhancement of the output signal by the incorporation of MOF molecules, which is consistent with the sensitivity-enhancing role of MOF by providing more anchoring sites for the attachment of the polymer texture to the electrode surface. This MOF-MIP sensor exhibited impressive linear dynamic ranges ranging from 0.1 to 1.0 pM for VIS, with detection limits in the low picomolar range. In addition, the MOF-MIP sensor offers high accuracy, selectivity and precision for the determination of VIS, with no interference observed from complex media of serum samples. Additionally, in this study, Analytical GREEnness metric (AGREE), Analytical GREEnness preparation (AGREEprep) and Blue Applicability Grade Index (BAGI) were used to calculate the green profile score.

Improving laser powder bed fusion processability of pure Cu through powder functionalization with Ag

The Laser Powder Bed Fusion (LPBF) manufacturing of dense Cu parts with near infrared conventional systems is still challenging due to the high reflectivity and thermal conductivity of the powder. In this paper, we investigate a novel approach to improve LPBF processability of Cu through the modification of particle surface properties. Pure Cu powders were coated with a thin layer of high-conductivity Ag by electrodeposition. The coated powder was also heat-treated at 500 °C and 600 °C to promote diffusion at the coating interface, producing different powder particle configurations. LPBF equipped with 200 W laser was used to produce bulk samples using pure Cu and Cu/Ag powder, which were comprehensively characterized by electron microscopy and X-ray diffraction. The Ag coating improved the material processability and density, forming a eutectic phase mixture able to heal pores and defects at the end of the solidification process.

Modification in electrical conductivity correlated with surface, structural & optical characteristics of graphite ions implanted CR-39

Ion implantation of laser induced graphite plasma has been performed for modifications in surface, optical, electrical and structural properties of CR-39. KrF Excimer laser (248 nm, 18 ns, 120 mJ), at an irradiance of 2.5 × 108 W cm−2 is utilized for the production of graphite plasma. The energy and fluence of graphite ions are estimated by Thomson parabola technique. The targets are implanted with energy of 710 KeV graphite ions for four fluences ranging from 26 × 1012 to 92 × 1015 ions/cm2, in presence of magnetic field of strength 90 mT. The digital optical analysis reveals well-arranged dendritic and island like structure formation on irradiated polymer surface. Confocal microscopic investigation illustrates the growth of nano/micro sized craters and hillocks for various ion fluences. Dissociation of bonds along with formation of new bonds is confirmed from Raman analysis. UV–Vis spectral analysis reveals that the optical transmittance values for visible regions of CR-39 are drastically reduced from 90 % to 68 % for maximum laser fluence of 92 × 1015 ions.cm−2. Significant improvement in electrical conductivity is achieved from 10−9 to 10−7 Scm−1 for lowest fluence value of graphite ions. SRIM software is utilized for the measurement of stopping power or Linear Energy Transfer (LTE) of 710 Kev graphite ions, is about, 55.53 eV/Ǻ, in the CR-39 targets.

Green Synthesis of ZnO Nanostructures and Their Antibacterial Activity Against Catfish Pathogen

Due to its antibacterial activity against clinical bacterial pathogens at the time of tissue development, zinc oxide (ZnO) is considered one of the most important metal oxide nanostructured materials. In this study, ZnO nanostructures were prepared using Aloe vera gel juice, which is easy, inexpensive, and ecofriendly. The nanostructures of ZnO were characterized using a variety of analytical techniques, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and dynamic light scattering (DLS). As a result of the XRD study, the hexagonal phase of ZnO with the structure of wurtzite has been identified. ZnO material with high heterogeneity morphology has been observed by SEM analysis. As-prepared ZnO nanostructures were tested for their antibacterial activity against the newly discovered pathogen of catfish. A ZnO sample prepared with a high concentration of Aloe vera gel possessed an inhibition zone of 13.21±0.04 mm, whereas a ZnO sample prepared with a low concentration of Aloe vera juice had an inhibition zone of 6.23±0.02 mm and a pure ZnO sample had an inhibition zone of 3.31±0.03 mm. Furthermore, we examined the effectiveness of the ZnO nanostructures on bacterial strains based on the type of nanoparticles applied to the commercial strains. In addition to their modified surface properties, small particle size, and highly toxic effects for the killingof bacterial cell growth, the Aloe vera juice assisted ZnO nanostructures demonstrated excellent antibacterial activity against the catfish pathogens.

Synthesis of high-performance antibacterial agent based on incorporated vancomycin into MOF-modified lignin nanocomposites

The alarming rise in antibiotic resistance necessitates urgent action, particularly against the backdrop of resistant bacteria evolving to render conventional antibiotics less effective, leading to an increase in morbidity, mortality, and healthcare costs. Vancomycin-loaded Metal-Organic Framework (MOF) nanocomposites have emerged as a promising strategy in enhancing the eradication of pathogenic bacteria. This study introduces lignin as a novel synergistic agent in Vancomycin-loaded MOF (Lig-Van-MOF), which substantially enhances the antibacterial activity against drug-resistant bacteria. Lig-Van-MOF exhibits six-fold lower minimum inhibitory concentration (MICs) than free vancomycin and Van-MOF with a much higher antibacterial potential against sensitive and resistant strains of Staphylococcus aureus and Escherichia coli. Remarkably, it reduces biofilms of these strains by over 85 % in minimal biofilm inhibitory concentration (MBIC). Utilization of lignin to modify surface properties of MOFs improves their adhesion to bacterial membranes and boosts the local concentration of Reactive Oxygen Species (ROS) via unique synergistic mechanism. Additionally, lignin induces substantial cell deformation in treated bacterial cells. It confirms the superior bactericidal properties of Lig-Van-MOF against Staphylococcus species, underlining its significant potential as a bionanomaterial designed to combat antibiotic resistance effectively. This research paves the way for novel antibacterial platforms that optimize cost-efficiency and broaden microbial resistance management applications.

Controlling Spatial Morphology of Microparticle Deposits via Thermocapillary Flows: Effect of Boundary Geometry.

The production of particle deposits with a desired distribution geometry has significant potential for materials science, printing, and coating technologies. Most methods for achieving well-defined assemblies rely on the spontaneous evaporation of colloidal solutions on substrates with predetermined properties, or on precise control of particle arrangement by external stimuli. Here, we present a combined method that enables the production of centimeter-scale microparticle deposits with a desired geometric shape. The method is based on controlling the massive transport of microparticles by thermocapillary flow in a layer of volatile liquid in a cell with borders of the desired geometry. Capillary forces cause the liquid to be distributed in the cell, forming corner wetting menisci and the flat layer in the central area. The formation of particle deposits occurs in two stages, determined by the flow regime. At the initial stage, the axisymmetric thermocapillary flow occurs in the flat part of the layer, resulting in the circular shape of the particle deposit. During the transition to the second stage of assembling thermocapillary flow is localized in the corner wetting menisci that results in reshaping the current particle deposit to match the geometry of the cell borders. Here, we demonstrated the creation of circular, square, and triangular shapes of the patterns of polystyrene microparticles using a point heater located at the geometric center of the cell. The proposed method is reliable, easy to implement, and potentially capable of producing a wide variety of deposit geometries, making it an attractive technique for patterning and modifying surface properties with particles of any type.

Electrospun poly(ɛ‐caprolactone) membranes modified with heparin and essential fatty acids for biomedical applications

AbstractThis study aimed to modify poly(ε‐caprolactone) (PCL) membranes with sodium heparin (SH) and essential fatty acids (EFA) for later application in wound healing. The electrospinning technique was used to prepare the membranes containing the maximum concentration of SH and EFA, which were then sterilized with ozone. Microbiological tests confirmed effective sterilization. The membrane characterization included scanning electron microscopy for morphological analysis, contact angle determination for wettability studies, Fourier‐transform infrared spectroscopy (FT‐IR) analysis, and thermogravimetry for thermal analysis. Results indicated that the average diameter membrane of PCL, PCL + SH, and PCL + EFA nanofibers was 1.16 ± 0.99 μm, 0.98 ± 0.66 μm and 1.53 ± 0.92 μm, respectively. Adding SH and EFA affected the fiber diameter, with PCL + SH fibers having a smaller diameter than pure PCL and PCL + EFA fibers. The contact angle of the membrane is 123° (PCL), 102° (PCL + SH), and 95° (PCL + EFA). Wettability analysis demonstrated modified surface properties with reduced contact angles. Sterilization of PCL membranes modified with SH and EFA has shown effectiveness in eliminating bacteria and other microorganisms, increasing the permeability of the membranes. Morphological analysis showed well‐formed and randomly distributed fibers, although the PCL + SH membrane exhibited beads on its fibers. FT‐IR analysis showed slight contributions of SH and EFA in the modified PCL membranes, while thermal analysis revealed no substantial changes in thermal stability. In conclusion, PCL membranes modified with SH and EFA can potentially accelerate wound healing, presenting an innovative and cost‐effective approach to treating skin injuries.

Templated silver nanoparticle deposition on laser-induced periodic surface structures for SERS sensing

Organized assemblies of metal nanoparticles exhibit unique optical properties and can be used as platforms for surface-enhanced Raman scattering (SERS) to detect small amounts of analyte molecules. In this work, we demonstrate that using Yb:KGW femtosecond laser structuring of silicon wafer we can modify surface properties by creating laser-induced quasi periodic surface structures (LIPSS) of 850 ± 43 nm periodicity. We show that silicon with LIPSS is a suitable surface for direct nanoparticle deposition because of its superhydrophilic properties and the nanoparticle density affects the density of the hot spots contributing in the Raman enhancement. We have analyzed the influence of the silver nanoparticle deposition on the structured silicon surface conditions on their density and coverage. 101±8 nm size silver nanoparticles were deposited by two methods, namely drop casting colloidal solution at three different temperatures (4 °C, 21 °C, 35 °C) and their SERS enhancements were compared with the monolayers deposited by liquid-liquid interface. It was found that monolayer deposition on a structured surface was the best approach in the sense of even silver nanoparticles coverage which exhibited best SERS performance reaching a limit of detection of 10−7 M for 2-naphthalenethiol. The obtained LoD is comparable with that of commercial substrates available in the market.

Exploring In Vivo Pulmonary and Splenic Toxicity Profiles of Silicon Quantum Dots in Mice.

Silicon-based quantum dots (SiQDs) represent a special class of nanoparticles due to their low toxicity and easily modifiable surface properties. For this reason, they are used in applications such as bioimaging, fluorescent labeling, drug delivery, protein detection techniques, and tissue engineering despite a serious lack of information on possible in vivo effects. The present study aimed to characterize and evaluate the in vivo toxicity of SiQDs obtained by laser ablation in the lung and spleen of mice. The particles were administered in three different doses (1, 10, and 100 mg QDs/kg of body weight) by intravenous injection into the caudal vein of Swiss mice. After 1, 6, 24, and 72 h, the animals were euthanized, and the lung and spleen tissues were harvested for the evaluation of antioxidant enzyme activity, lipid peroxidation, protein expression, and epigenetic and morphological changes. The obtained results highlighted a low toxicity in pulmonary and splenic tissues for concentrations up to 10 mg SiQDs/kg body, demonstrated by biochemical and histopathological analysis. Therefore, our study brings new experimental evidence on the biocompatibility of this type of QD, suggesting the possibility of expanding research on the biomedical applications of SiQDs.

A healable amino silane self-assembled monolayer incorporating polymer capped palladium nanoclusters and its application as the copper diffusion barrier layer on silicon wafer

Self-assembled monolayers (SAMs) with short organic chains terminated with specific functional groups are attractive for modifying surface properties for a variety of applications, including being a copper diffusion barrier layer on Si wafer. However, SAM formation is process-sensitive and ideal SAM is difficult to obtain, both of which need to carefully deal with before practical use. Herein we developed a system to achieve seamless electroless deposited copper (ELD Cu) film on an amino-terminated silane SAM modified Si wafer with the help of a bifunctional polyvinyl alcohol-capped Pd nanocluster (PVA-Pd) catalyst. The PVA-Pd acts as a catalyst for ELD Cu as well as a healing agent to fix defects of the amino silane SAM. The sheet resistance, cross-sectional morphology analysis and adhesion of ELD Cu on the Si wafer are extensively studied. By controlling the abundancy of PVA in PVA-Pd, the diffusion barrier property of a flawed amino-terminated silane SAM remains reliably effective even after a 500 °C rapid thermal annealing (RTA), evidencing the superior healing function of PVA. The whole thickness of the PVA-Pd/amino-terminated silane SAM before and after RTA is 〜6 nm and 〜2 nm, respectively, which is applicable for advanced microelectronic manufacturing.

Effect of TiO2 Drying Conditions on the Catalytic Activity of Pt for Ammonia Synthesis from NO−H2

AbstractThe effect of drying conditions on the physicochemical and catalytic properties of TiO2 were examined for NO to ammonia reaction. TiO2 prepared by different drying conditions such as evaporation (EP), evaporation under reduced pressure (ER) and evaporation under freeze drying conditions (EF) was used for support for Pt loading. At low temperature (below 175 °C), the order for ammonia formation was Pt/TiO2(ER)>Pt/TiO2(EP)>Pt/TiO2(EF). Notably, Pt/TiO2(ER) catalyst was more effective than Pt/TiO2 prepared from commercially available TiO2. The characterization of these catalysts revealed that rutile‐rich phase TiO2, high Pt dispersion and moderate acidic sites were influential factors for ammonia formation. TiO2 drying conditions modified surface properties of TiO2 and consequently, catalytic activity for ammonia formation.

Roles of the A-Site Ca Dopant in Modifying Surface Properties of a Co-Based Perovskite Catalyst for Selective Oxidation of Cyclohexane

Roles of the A-Site Ca Dopant in Modifying Surface Properties of a Co-Based Perovskite Catalyst for Selective Oxidation of Cyclohexane

Surface-engineered Multimodal Magnetic Nanoparticles: Scope and Applications

Abstract: Magnetic nanoparticles (MNPs) are one of the classes of nanoparticles that produce magnetic properties by manipulation using a magnetic field. These MNPs are currently used in the theranostics disease modification of surface properties of MNPs, achieved by surface engineering, which provides different applications, such as enhancing thermal and optical properties, biocompatibility, conductivity and also mechanical and chemical properties. Advancement in the technology leads to the development of MNPs. For this instance, surface coating is used at molecular and cellular levels. The uses of coating material are based on organic and inorganic molecules, including polymer, liposomes, micelles, metal oxide, gold-NPs etc. Using different coatings exhibits multifunction properties, and this helps reduce toxicity, helps in biomedical applications, maintains stability, restricts surface fouling, etc. This review provides an in-depth knowledge of surface-engineered magnetic nanoparticles (MNPs) according to recent developments.

Concentration and reaction duration effects on synthesizing ZIF67 derivatives with NH4BF4 and NH4HF2 as efficient active material of energy storage device

Zeolitic imidazolate framework-67 (ZIF67) with large surface area and tunable pore structure is intensively applied as a tailoring target for design active materials. An in-situ tailoring technique is proposed to design ZIF67 derivatives by using structure directing agents (SDA) to induce favorable morphology and composition. Ammonium fluoride is a common SDA for modifying surface properties of active materials. With the same ammonium and similar fluorine-based groups, NH4BF4 and NH4HF2 are priming to play as SDA for synthesizing ZIF67 derivatives. In this study, the synthetic process of ZIF67 derivatives is tailored by varying the precursor concentration and reaction time in systems with NH4BF4 and NH4HF2 as SDA. The precursor concentration plays significant roles in the composition of ZIF67 derivatives. The reaction duration has higher influences on the morphology. The highest specific capacitance (CF) of 1347.0 F/g at 20 mV/s is achieved for the ZIF67 derivative synthesized using low concentration and 18 h, owing to favorable cobalt and nickel hydroxide compositions and two-dimensional sheet-like structure. An energy storage device composed of the optimal ZIF67 derivative and carbon electrodes shows a maximum energy density of 11.96 Wh/kg at 650 W/kg. The excellent cycling stability with CF retention of 83.6% and Coulombic efficiency of 92.0% is obtained after 10000 cycles.

Synthesis of Raspberry-like Nanoparticles via Surface Grafting of Positively Charged Polyelectrolyte Brushes: Colloidal Stability and Surface Properties.

A method to synthesize stable, raspberry-like nanoparticles (NPs), using surface grafting of poly(glycidyl methacrylate) (PGMA) brushes on a polystyrene (PS) core with varying grafting densities, is reported. A two-step functionalization reaction of PGMA epoxide groups comprising an amination step first using ethylene diamine and then followed by a quaternization using glycidyltrimethylammonium chloride generates permanently and positively charged polyelectrolyte brushes, which result in both steric and electrostatic stabilization. The dispersion stability of the brush-bearing NPs is dramatically improved compared to that of the pristine PS core in salt solutions at ambient (25 °C) and elevated temperatures (60 °C). Additionally, the grafted polyelectrolyte chains undergo a reversible swelling in the presence of different ionic strength (IS) salts, which modulate the surface properties, including roughness, stiffness, and adhesion. An atomic force microscope under both dry and wet conditions was used to image conformational changes of the polyelectrolyte chains during the swelling and deswelling transitions as well as to probe the nanomechanical properties by analyzing the corresponding force-sample separation curves. The quaternized polyelectrolyte brushes undergo a conformational transition from a collapsed state to a swelled state in the osmotic brush (OB) regime triggered by the osmotic gradient of mobile ions to the interior of the polymer chain. At IS ∼ 1 M, the brushes contract and the globules reform (salted brush state) as evidenced by an increase in the surface roughness and a reduction in the adhesion of the brushes. Beyond IS ∼ 1 M, quartz crystal microbalance with dissipation monitoring measurements show that salt uptake continues to take place predominantly on the exterior surface of the brush since salt adsorption is not accompanied by a size increase as measured by dynamic light scattering. The study adds new insights into our understanding of the behavior of NPs bearing salt-responsive polyelectrolyte brushes with adaptive swelling thresholds that can ultimately modulate surface properties.