Marangoni-Induced Honeycomb Structures in Spin-Coated Polymer Nanocomposite Films.

This study investigates Marangoni effect-induced structural changes in spin-coated polymer nanocomposite (PNC) films composed of poly(methyl methacrylate)-grafted silica nanoparticles (NPs) and poly(styrene--acrylonitrile). Films cast from methyl isobutyl ketone (MIBK) solvent exhibit distinct hexagonal honeycomb cells with thickness gradients driven by surface tension variations. Atomic force microscopy reveals protruded ridges and junctions at cell intersections, where NP concentration is the highest.

Size-Dependent Electrostatic Adsorption of Polymer-Grafted Gold Nanoparticles on Polyelectrolyte Brushes.

Designing a functional surface that selectively adsorbs nanoparticles based on their size and shape is essential for developing an advanced adsorption-based, postsynthesis nanoparticle separation device. We demonstrate selective adsorption of larger nanoparticles from solution onto a polyelectrolyte brush by tuning the salt concentration. Specifically, a positively charged polyelectrolyte brush is created by converting pyridine groups of poly(2-vinylpyridine) to -methylpyridinium groups using methyl iodide.

Controlling spatial distribution of functional lipids in a supported lipid bilayer prepared from vesicles.

Conjugating biomolecules, such as antibodies, to bioconjugate moieties on lipid surfaces is a powerful tool for engineering the surface of diverse biomaterials, including cells and nanoparticles. We developed supported lipid bilayers (SLBs) presenting well-defined spatial distributions of functional moieties as models for precisely engineered functional biomolecular-lipid surfaces. We used quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM) to determine how vesicles containing a mixture of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[azido(polyethylene glycol)-2000] (DSPE-PEG-N) form SLBs as a function of the lipid phase transition temperature (T).

Capillary filling dynamics of polymer melts in a bicontinuous nanoporous scaffold.

Polymer infiltrated nanoporous gold is prepared by infiltrating polymer melts into a bicontinuous, nanoporous gold (NPG) scaffold. Polystyrene (PS) films with molecular weights (Mw) from 424 to 1133 kDa are infiltrated into a NPG scaffold (∼120 nm), with a pore radius (Rp) and pore volume fraction of 37.5 nm and 50%, respectively.

Using Focused Ion Beam Time-of-Flight Secondary Ion Mass Spectrometry to Depth Profile Nanoparticles in Polymer Nanocomposites.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a versatile surface-sensitive technique for characterizing both hard and soft matter. Its chemical and molecular specificity, high spatial resolution, and superior sensitivity make it an ideal method for depth profiling polymeric systems, including those comprised of both inorganic and organic constituents (i.e.

pH-Mediated Size-Selective Adsorption of Gold Nanoparticles on Diblock Copolymer Brushes.

Precise control of nanoparticles at interfaces can be achieved by designing stimuli-responsive surfaces that have tunable interactions with nanoparticles. In this study, we demonstrate that a polymer brush can selectively adsorb nanoparticles according to size by tuning the pH of the buffer solution. Specifically, we developed a facile polymer brush preparation method using a symmetric polystyrene--poly(2-vinylpyridine) (PS--P2VP) block copolymer deposited on a grafted polystyrene layer.

Enhancing Nanoparticle Detection in Interferometric Scattering (iSCAT) Microscopy Using a Mask R-CNN.

Interferometric scattering microscopy (iSCAT) is a label-free optical microscopy technique that enables imaging of individual nano-objects such as nanoparticles, viruses, and proteins. Essential to this technique is the suppression of background scattering and identification of signals from nano-objects. In the presence of substrates with high roughness, scattering heterogeneities in the background, when coupled with tiny stage movements, cause features in the background to be manifested in background-suppressed iSCAT images.

Nanoscale Structure-Property Relations in Self-Regulated Polymer-Grafted Nanoparticle Composite Structures.

Using a model system of poly(methyl methacrylate)-grafted silica nanoparticles (PMMA-NP) and poly(styrene--acrylonitrile) (SAN), we generate unique polymer nanocomposite (PNC) morphologies by balancing the degree of surface enrichment, phase separation, and wetting within the films. Depending on the annealing temperature and time, thin films undergo different stages of phase evolution, resulting in homogeneously dispersed systems at low temperatures, enriched PMMA-NP layers at the PNC interfaces at intermediate temperatures, and three-dimensional bicontinuous structures of PMMA-NP pillars sandwiched between two PMMA-NP wetting layers at high temperatures. Using a combination of atomic force microscopy (AFM), AFM nanoindentation, contact angle goniometry, and optical microscopy, we show that these self-regulated structures lead to nanocomposites with increased elastic modulus, hardness, and thermal stability compared to analogous PMMA/SAN blends.

Investigating the Sequence Specific Adsorption Behavior of Polypeptides at the Solid/Liquid Interface.

Polymer adsorption at the solid/liquid interface depends not only on the chemical composition of the polymer but also on the specific placement of the monomers along the polymer sequence. However, challenges in designing polymers with well-controlled sequences have limited explorations into the role of polymer sequence on adsorption behavior to molecular simulations. Here, we demonstrate how the sequence control offered by polypeptide synthesis can be utilized to study the effects small changes in polymer sequence have on polymer adsorption behavior at the solid/liquid interface.

Nanoparticle dynamics in hydrogel networks with controlled defects.

The effect of nanoscale defects on nanoparticle dynamics in defective tetra-poly(ethylene glycol) (tetra-PEG) hydrogels is investigated using single particle tracking. In a swollen nearly homogeneous hydrogel, PEG-functionalized quantum dot (QD) probes with a similar hydrodynamic diameter ( = 15.1 nm) to the mesh size (〈〉 = 16.

Zwitterionic surface chemistry enhances detachment of bacteria under shear.

The ubiquitous nature of microorganisms, especially of biofilm-forming bacteria, makes biofouling a prevalent challenge in many settings, including medical and industrial environments immersed in liquid and subjected to shear forces. Recent studies have shown that zwitterionic groups are effective in suppressing bacteria and protein adhesion as well as biofilm growth. However, the effect of zwitterionic groups on the removal of surface-bound bacteria has not been extensively studied.

Electrochemically deposited molybdenum disulfide surfaces enable polymer adsorption studies using quartz crystal microbalance with dissipation monitoring (QCM-D).

Polymer and small molecules are often used to modify the wettability of mineral surfaces which facilitates the separation of valuable minerals such as molybdenum disulfide (MoS) from gangue material through the process of froth flotation. By design, traditional methods used in the field for evaluating the separation efficacy of these additives fail to give proper access to adsorption kinetics and molecule conformation, crucial aspects of flotation where contact times may not allow for full thermodynamic equilibrium. Thus, there is a need for alternative methods for evaluating additives that accurately capture these features during the adsorption of additives at the solid/liquid interface.

Effect of Nanoscale Confinement on Polymer-Infiltrated Scaffold Metal Composites.

Most research on polymer composites has focused on adding discrete inorganic nanofillers to a polymer matrix to impart properties not found in polymers alone. However, properties such as ion conductivity and mechanical reinforcement would be greatly improved if the composite exhibited an interconnected network of inorganic and polymer phases. Here, we fabricate bicontinuous polymer-infiltrated scaffold metal (PrISM) composites by infiltrating polymer into nanoporous gold (NPG) films.

Grafted Nanoparticle Surface Wetting during Phase Separation in Polymer Nanocomposite Films.

Wetting of polymer-grafted nanoparticles (NPs) in a polymer nanocomposite (PNC) film is driven by a difference in surface energy between components as well as bulk thermodynamics, namely, the value of the interaction parameter, χ. The interplay between these contributions is investigated in a PNC containing 25 wt % polymethyl methacrylate (PMMA)-grafted silica NPs (PMMA-NPs) in poly(styrene--acrylonitrile) (SAN) upon annealing above the lower critical solution temperature (LCST, 160 °C). Atomic force microscopy (AFM) studies show that the areal density of particles increases rapidly and then approaches 80% of that expected for random close-packed hard spheres.

pH-Mediated nanoparticle dynamics in hydrogel nanocomposites.

The effect of static silica particles on the dynamics of quantum dot (QD) nanoparticles grafted with a poly(ethylene glycol) (PEG) brush in hydrogel nanocomposites is investigated using single particle tracking (SPT). At a low volume fraction of homogeneously dispersed silica (Φ = 0.005), two distinct populations of PEG-QDs are observed, localized and mobile, whereas almost all PEG-QDs are mobile in neat hydrogel (Φ = 0.

Kinetic Monitoring of Block Copolymer Self-Assembly Using In Situ Spectroscopic Ellipsometry.

Understanding the kinetic pathways of self-assembly in block copolymers (BCPs) has been a long-standing challenge, mostly due to limitations of in situ monitoring techniques. Here, we demonstrate an approach that uses optical birefringence, determined by spectroscopic ellipsometry (SE), as a measure of domain formation in cylinder- and lamellae-forming BCP films. The rapid experimental acquisition time in SE (ca.

Nanorod position and orientation in vertical cylinder block copolymer films.

The self-assembly of gold nanorods (AuNRs) of different sizes with a block copolymer (BCP) is studied. Polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) films containing P2VP functionalized AuNRs are solvent annealed resulting in a BCP morphology of vertical P2VP cylinders in a PS matrix. At the surface of the PS-b-P2VP films long AuNRs are found in the bridging and vertical states.

Nanoparticle diffusion during gelation of tetra poly(ethylene glycol) provides insight into nanoscale structural evolution.

Single particle tracking (SPT) of PEG grafted nanoparticles (NPs) was used to examine the gelation of tetra poly(ethylene glycol) (TPEG) succinimidyl glutarate (TPEG-SG) and amine (TPEG-A) terminated 4-armed stars. As concentration was decreased from 40 to 20 mg mL-1, the onset of network formation, tgel, determined from rheometry increased from less than 2 to 44 minutes. NP mobility increased as polymer concentration decreased in the sol state, but remained diffusive at times past the tgel determined from rheometry.

Dendrimer Ligand Directed Nanoplate Assembly.

Many studies on nanocrystal (NC) self-assembly into ordered superlattices have focused mainly on attractive forces between the NCs, whereas the role of organic ligands on anisotropic NCs is only in its infancy. Herein, we report the use of a series of dendrimer ligands to direct the assembly of nanoplates into 2D and 3D geometries. It was found that the dendrimer-nanoplates consistently form a directionally offset architecture in 3D films.

Cross-linker-Modulated Nanogel Flexibility Correlates with Tunable Targeting to a Sterically Impeded Endothelial Marker.

Deformability of injectable nanocarriers impacts rheological behavior, drug loading, and affinity target adhesion. Here, we present atomic force microscopy (AFM) and spectroscopy measurements of nanocarrier Young's moduli, tune the moduli of deformable nanocarriers with cross-linkers, and demonstrate vascular targeting behavior that correlates with Young's modulus. Homobifunctional cross-linkers were introduced into lysozyme-dextran nanogels (NGs).

Equilibrium Field Theoretic Study of Nanoparticle Interactions in Diblock Copolymer Melts.

Block copolymer matrices are often used to control nanoparticle (NP) dispersion behavior, but the effects of diblock domain interfaces on particle-particle interactions have not been well characterized. In this paper, polymer field theoretic simulations are used to quantify interactions between both bare and grafted spherical NPs in microphase-separated A-B diblock copolymers. It is shown that for bare NPs that have an athermal interaction with and a diameter similar to the B domain, the presence of an A-B interface leads to an effective interaction between the particles with multiple minima separated by a free energy barrier.

Modeling of Entangled Polymer Diffusion in Melts and Nanocomposites: A Review.

This review concerns modeling studies of the fundamental problem of entangled (reptational) homopolymer diffusion in melts and nanocomposite materials in comparison to experiments. In polymer melts, the developed united atom and multibead spring models predict an exponent of the molecular weight dependence to the polymer diffusion very similar to experiments and the tube reptation model. There are rather unexplored parameters that can influence polymer diffusion such as polymer semiflexibility or polydispersity, leading to a different exponent.